porting injector housings to 36MM

[wfot]

Ok, I have heard that 36MM is "the" number to get to when going all out.

My questions is that 36MM throughout the entire injector housing?

For example, if you drop a 36MM ball down the top, would it drop out the bottom? I am aware the injector bosses get in the way on the secondaries.... I am working on a solution to that....

When is 35MM good enough?

Can the housings take 36.5MM?? or 37MM?

When do the welded housings need to be done? 750HP??

Inquiring minds need to know.

any thoughts or findings or pics would be appreciated

[Paul Workman]

No, nothing sacred about 36mm. But, it does depend on what you are trying to accomplish - specifically - before porting anything.

That said, there are many successful runner examples of builds that are far larger. But!! Runner dimensions are but ONE part of an overall LT5 performance build, AND there are some quirks with regard to the castings of LT5s to be aware of and avoid - or else you may breach the coolant jacket.

For example, many have "siamesed" the intake plenum AND the input to the injector housing. And, the gen-III LT5 did away with the dual runners entirely - secondaries non-existent, i.e, the septum between runners completely gone, thus leaving a wide oval runner, divided just at the dual intake valves.

If you're not a mechanical injuneer, then I would suggest researching extensively what others have done and what the results have been before (and I mean no offense here) "willy-nilly" opening up this and modifying that.

All that said, there is a TON of performance left on the table when the LT5 left MerCruiser!!!

[wfot]

thank you paul,

this is exactly why I am asking this here. I would like real world examples of what people have done/used and what the results were. and please I would appreciate to hear what a dyno shows vs what does it feel like driving vs actual track numbers.

I am looking for real world HP numbers vs actual runner size...
IE can a 35mm runner support 450 hp?
can a 36mm runner support 550 hp?
I think a 36mm can got a 415 CID motor 600 HP on a dyno

What HP level does it become necessary for the siamesed runners or welded runners?

I think I saw on post somewhere by Pete and he stated that he can actually get the runners to 36.5mm, can the 36.5mm get 650HP?

any input or experience, good or bad, is appreciated.

thank you all again

John

I am also working out a way to be able to port the secondary injector boss just like the primary boss on the 90 housings. I am hoping if I an get the secondaries to flow as much as a fully ported primary, that this would get a full 36mm port on all 16 runners to go over 600hp..

I made a oring bung that is welded on top of the secondary port that lifts the oring point higher just like the primary port. this allows primary orings to be used on all runners and hopefully an excellent balance of flow for over 600 hp and be able to keep the low end torque.

[Pete]

John
Drop a 35mm gauge ball straight thru the port they call this 36mm dropping a 36mm gauge ball straight thru they call this 37mm.
I also have a 36.5mm gauge ball.

Your question about the power level.
You can't get the intake big enough for it to hurt driveability of course alot is also in the tuning.
My lil 350 intake was more or less what they would call 38mm no divider in the plenum with no secondaries made 330 rwtq @ 3k rpm 410 peak car would run 11.0's @128-129 mph ran 154mph 1/2 mile.
Car drove like a stocker would drive it to BG,car shows etc,
My ports are 38mm+- but went into oil same port on 1 on each IH i do not reccommend this for the faint lol

Like i mention its also in the tune.
Hope this helps you with your venture.
Pete

[Corvette95]

So ....I know there are a few Gen3 plenums out there...cannot they be reproduced in a limited run? I wonder the costs of something like that....would a group pre-purchase make it happen? Thinking out loud.

[Pete]

There are a few 350 ZR-1's running around with ported top ends to 37mm some with stock cams some with performance cams
That make good HP/TQ #'s they might come on here and reply on the driveabilty.

I have done hours and hours and lots of $$$$ research on cams on the LT5.
If going with performance cams gotta pick the right set of cams price is irrelevent in this case you get what you pay for.

Pete



John
Drop a 35mm gauge ball straight thru the port they call this 36mm dropping a 36mm gauge ball straight thru they call this 37mm.
I also have a 36.5mm gauge ball.

Your question about the power level.
You can't get the intake big enough for it to hurt driveability of course alot is also in the tuning.
My lil 350 intake was more or less what they would call 38mm no divider in the plenum with no secondaries made 330 rwtq @ 3k rpm 410 peak car would run 11.0's @128-129 mph ran 154mph 1/2 mile.
Car drove like a stocker would drive it to BG,car shows etc,
My ports are 38mm+- but went into oil same port on 1 on each IH i do not reccommend this for the faint lol

Like i mention its also in the tune.
Hope this helps you with your venture.
Pete

[Pete]

So ....I know there are a few Gen3 plenums out there...cannot they be reproduced in a limited run? I wonder the costs of something like that....would a group pre-purchase make it happen? Thinking out loud.


3D printing.
What would be the purpose for this Gen 3?
More volume?

Pete

[grahambehan]

So ....I know there are a few Gen3 plenums out there...cannot they be reproduced in a limited run? I wonder the costs of something like that....would a group pre-purchase make it happen? Thinking out loud.

Gen 3 plenum, really?

Graham

[Corvette95]

3D printing.
What would be the purpose for this Gen 3?
More volume?

Pete

My thinking was that the higher CU builds all have the Siamese plenums and as I understand was going to the the stock plenum had the LT5 not been discontinued (OBD2). Does the Siamese plenums not provide more clean flow and volume? Again, thinking out loud. From the appearance and appearance alone perspective , I think the standard plenum provides more of a visual impact than the Siamese plenums, but we are talking HP and flow, right? BTW, Pete, I am more than completely happy with the top end work you did on my car. Thanks again!

[A26B]

So ....I know there are a few Gen3 plenums out there...cannot they be reproduced in a limited run? I wonder the costs of something like that....would a group pre-purchase make it happen? Thinking out loud.

Really?? Where are they at? I only know of 1.

[wfot]

Pete, Excellent feedback and I appreciate all of the R & D you have done ,really spectacular stuff.

this is exactly what I was hoping for, real world results.

Graham, in your vast experience, will a port that a 36mm ball will drop thru support a motor in the 650 hp range?

I have a siamised plenum and think this is the path I want to stay on. when is the point where a dropped base would be desired?

John

[Corvette95]

Really?? Where are they at? I only know of 1.
They are right beside those DIS modules you found! :)

[A26B]

They are right beside those DIS modules you found! :)

I wish!!

[grahambehan]

They are right beside those DIS modules you found! :)

Huh, i I didn't find any DIS modules, so that must be why I didn't see any intakes. Still interesting tho since I was asked about the intake yesterday.

Graham

[wfot]

Hey Graham,

when would you need to have a dropped plenum?

would that hurt drivability?

John

[grahambehan]

Hey Graham,

when would you need to have a dropped plenum?

would that hurt drivability?

John

The reason we did a dropped floor on the plenum was to get closer to the engine displacement wrt plenum volume, thereby, in theory, minimizing cylinder robbing as the individual cylinders demand air on opening and revert air on overlap. Really trying to minimize the effect on the standing plenum pressure from the pulses from the ports.
Did it affect driveability, no.

Graham

[wfot]

The reason we did a dropped floor on the plenum was to get closer to the engine displacement wrt plenum volume, thereby, in theory, minimizing cylinder robbing as the individual cylinders demand air on opening and revert air on overlap. Really trying to minimize the effect on the standing plenum pressure from the pulses from the ports.
Did it affect driveability, no.

Graham


I have heard that the best ratio is the plenum center should equal the volume of one cylinder. Correct?

What effect did it have on power output?

John

[wfot]

I was just staring down the mouth of a stock plenum and think that the total volume in that plenum is larger than 1.0 liters. this means that the plenum volume is larger than one cylinder already.

what I noticed was that the front cylinders saw the first 1/4 to a 1/3 draw from a larger/deeper part of the plenum than the back part does....

could this mean that dropping the plenum has a bigger effect on balancing what each cylinder "sees" vs having a larger space to pull from???

it looks like if you drop the floor an inch, all of the cylinders would "see" a much more even area to draw from, not just bigger...

John

[LGAFF]

Motor Trend/Hot Rod Magazine ran a plenum volume test for an LS motor on the show Engine Masters ......episode is called "You're going to need a bigger plenum" They ran an LS Holley high rise intake and then a massive intake probably twice the volume, at the end of the day no difference.

The guy at Westech Performance Group(They do nothing but test engines) said he has never seen EFI intake spacers etc ever make a difference. I conducted a test were I removed the top of a plenum and added a larger lid increasing the plenum volume significantly and also moving the ceiling of the plenum away from the runner entry... at the end of the day it made a few hundred more RPM at peak but there was no change on power, in fact it was down some. This was on a 350 motor with cams.... I am guessing you need a pretty big cube motor to see any difference.

Maybe Graham knows the outcome of this Lingenfelter test.. https://www.youtube.com/watch?v=UjrdqHU4JCA

[wfot]

OMG you did frankenplenum correct?

I saw that and did have hopes for a performance gain....

I hear what you are saying, and it does make sense, however, I am pretty sure that the dropped plenum does actually make an improvement in track times and HP numbers.. please advise if this is not true..... or true...:)

Does anyone have a before and after story of a dropped plenum?
John

[grahambehan]

Maybe Graham knows the outcome of this Lingenfelter test.. https://www.youtube.com/watch?v=UjrdqHU4JCA

Yes, infinite plenum volume worked. That was a 568CID viper engine tested with a hogan intake with a relatively small plenum. With the same runners and a correctly sized plenum the engine made 920 hp.

Graham

[LGAFF]

OMG you did frankenplenum correct?

I saw that and did have hopes for a performance gain....

I hear what you are saying, and it does make sense, however, I am pretty sure that the dropped plenum does actually make an improvement in track times and HP numbers.. please advise if this is not true..... or true...:)

Does anyone have a before and after story of a dropped plenum?
John

It?s often misleading when you see dyno tests due to variances in heat soak or weather. I tested 3 air intakes on an SLK55 AMG and it looked like one produced 12 more hp than the others but in reality it was just the manifold and engine temps that made the difference. So many tests you see could just be variances in condition

[wfot]

Yes, infinite plenum volume worked. That was a 568CID viper engine tested with a hogan intake with a relatively small plenum. With the same runners and a correctly sized plenum the engine made 920 hp.

Graham


Mr Graham

How would I correctly calculate the plenum volume needed for a 402, 650 HPish LT5?

John

[rkreigh]

moving the coils and vacuum stuff out might allow a "bigger" dropped floor plenum. As I remember some of the frankenstein floor drop gained just a modest amount (10 or 15) on a max effort engine


I'd like to see what a fairly inexpensive individual runner ITB style intake could do.


it would remove the inlet restriction , allow running a single injector with an aftermarket Megasquirt or something similar, and should work if the linkage is progressive and doesn't snap stuff open too quick.


these are a cast iron beeotch to tune as the runners have to equalize and any slop in the linkages or blade stops will make for a bad idle.


Not sure how feasible this would be, so perhaps Graham can indulge my wild fantasy of the ITB


some of his finest work is in my bifurcation manifold, and we opened up the runners on the heads to 36.5 so we'll see what the old gal will pull soon.


I also am trying some very nice summit 24 lb injectors for just a bit more headroom as the engine should push around 650 or so if all goes well.


Needs more cam timing, but that will be another day.

[wfot]

moving the coils and vacuum stuff out might allow a "bigger" dropped floor plenum. As I remember some of the frankenstein floor drop gained just a modest amount (10 or 15) on a max effort engine


I'd like to see what a fairly inexpensive individual runner ITB style intake could do.


it would remove the inlet restriction , allow running a single injector with an aftermarket Megasquirt or something similar, and should work if the linkage is progressive and doesn't snap stuff open too quick.


these are a cast iron beeotch to tune as the runners have to equalize and any slop in the linkages or blade stops will make for a bad idle.


Not sure how feasible this would be, so perhaps Graham can indulge my wild fantasy of the ITB


some of his finest work is in my bifurcation manifold, and we opened up the runners on the heads to 36.5 so we'll see what the old gal will pull soon.


I also am trying some very nice summit 24 lb injectors for just a bit more headroom as the engine should push around 650 or so if all goes well.


Needs more cam timing, but that will be another day.

I thought you sold the 390 LPE??

So the 36.5mm porting? is that on the housings only? does that mean a 36.5mm ball will drop thru?

the plenum? mono runners or biforcated?

[rkreigh]

I thought you sold the 390 LPE??

So the 36.5mm porting? is that on the housings only? does that mean a 36.5mm ball will drop thru?

the plenum? mono runners or biforcated?


no didn't sell it. we used the checker balls on each port in the head and were able to get 36.5


port matched the intake, I don't think demps revised the intake manifold porting, but we did do the "pho mono runner mod" with epoxy to get the mono runner look which I like


I hope to get it finished up and back on the road this month.


Meantime, I bought a procharged c5 to play with. Need something nice for spring!!

[wfot]

ok, Ron, I thought I read somewhere that the 390 was sold and went oversea to make room for the C5, my bad. sucks it has been down for so long.

It is amazing how long it takes to get these things lined out the way you want. I am almost there with collecting parts. Got the cams over the weekend and they look bada$$. I need to start test fitting everything together and makes sure everything plays nice. I think I will need to have the pistons fly cut and I need to finish the housing/plenum porting... then she can start to go together..

the 36.5 must be a scary thing to do, the 36mm takes 50mm brass balls to hog out a port that big without breaking something...lol

[tpepmeie]

I realize I am in the vast minority, but I want to give my opinion on the subject. It is incorrect for one to try to correlate a certain port diameter to a "supported" horsepower for these engines. It's a fallacy that the port diameter is the limiting factor for ultimate power output. There is no equation to be had there.

Lot of people go very big. Big doesn't equal power, necessarily. Ultimate airflow is important, but not the only, constraint on horsepower output. 99% of folks limit the engines potential by camshaft choices, before the size of the ports ever become a constraint.

Couple of examples. GM Indycar engine, 3.5-4.0L, upwards of 750 bhp in those days (1997-2000). I have a few parts and pieces from said engine. The inlet ports were well under 35mm each (Yet the heads flowed over 100 CFM per sq. in. of valve area--generally 39mm valves).

427 cu. in. LT5. "Well" north of 700 crank hp. inlet ports in the head averaged 35.2mm primary / 35.8mm secondary. 390 cfm. Port was already bigger in some areas or would have been even smaller. Injector housings averaged ~38mm because the top 1" was siamesed. The critical areas were quite a bit smaller. Total average diameter of the head+housing inlet tract was 37mm. Shape and airspeed matter more than total diameter. Some areas are not perfectly round in this inlet tract. So the old drop a ball bearing test would never work in this case.

Todd

[wfot]

I realize I am in the vast minority, but I want to give my opinion on the subject. It is incorrect for one to try to correlate a certain port diameter to a "supported" horsepower for these engines. It's a fallacy that the port diameter is the limiting factor for ultimate power output. There is no equation to be had there.

Lot of people go very big. Big doesn't equal power, necessarily. Ultimate airflow is important, but not the only, constraint on horsepower output. 99% of folks limit the engines potential by camshaft choices, before the size of the ports ever become a constraint.

Couple of examples. GM Indycar engine, 3.5-4.0L, upwards of 750 bhp in those days (1997-2000). I have a few parts and pieces from said engine. The inlet ports were well under 35mm each (Yet the heads flowed over 100 CFM per sq. in. of valve area--generally 39mm valves).

427 cu. in. LT5. "Well" north of 700 crank hp. inlet ports in the head averaged 35.2mm primary / 35.8mm secondary. 390 cfm. Port was already bigger in some areas or would have been even smaller. Injector housings averaged ~38mm because the top 1" was siamesed. The critical areas were quite a bit smaller. Total average diameter of the head+housing inlet tract was 37mm. Shape and airspeed matter more than total diameter. Some areas are not perfectly round in this inlet tract. So the old drop a ball bearing test would never work in this case.

Todd

well I think it has become a standard for a reason, it does seem to work. a 35mm hole will flow enough air for x HP and a 36mm hole will flow y amount of HP. there does seem to be a correlation to what size people port a housing to to how much HP they can get out of it.

If you do not measure your housings by a specific size in a specific area< how do you determine where and how much to port? Is it all do this and flow test and do that and then flow test?

John

[tpepmeie]

well I think it has become a standard for a reason, it does seem to work. a 35mm hole will flow enough air for x HP and a 36mm hole will flow y amount of HP. there does seem to be a correlation to what size people port a housing to to how much HP they can get out of it.
John

Ok, that's your theory, not my experience.
Good luck.

[wfot]

Ok, that's your theory, not my experience.
Good luck.


I am not giving you grief, I am legitimately asking what is your reasoning and how are you determining where/how to port your housings?

I am asking about real world experience and what people have actually found that works. most people port to 36mm for what is considered a 650 HP motor regardless of CID. 650 HP needs x amount of air and fuel.

What do your ports look like? Are they like a funnel? are the the same diameter throughout? how are deciding where to port bigger vs smaller?

Have you thought about moving the secondary Oring higher like the primary Oring so the secondary injector hump can be removed completely?

John

[Paul Workman]

In all of the discussion(s) so far, the subject of resonance has been given pretty short shrift, with regard to how runner length too as well as volume affects end result performance.

An example worth considering is the the torque curves comparisons between the stock L98s and the LT1 and LT4 or the curves of the stock L98 vs. the "Mini-Ram" (i.e., how shortening the intake runner length affects how the engine performs over the rpm range!) Among the torque and HP graphs in the public record, it doesn't take a lot of looking to see the effect runner length has torque peak and where it occurs, separate from runner volume, by the way!!

Just sayin...runner volume is but ONE aspect of naturally aspirated performance, e.g., cam lift/duration/timing, bore, stroke. And, let's not forget the exhaust runners!

Exhaust runners too are just as important to consider as part of the equation as the tube dimensions will have a direct effect on harmonics and ultimately scavenging and avoiding reversion and back pressure

The degree of engineering involved in optimizing an engines' performance is beyond the mathematical agility of most car nuts, myself included. So, what to do?

Well, the quality of the pudding is in the tasting! Deep and extensive engineering foundation is essential to efficient theory development. But, in the end the theory doesn't become fact until successful experimentation is accomplished.

I guess my point is, what all goes into engine performance, intake runner or plenum volume is but ONE of several factors that combine to produce the end result. And, in the case of this particular thread, a major factor - resonance fundamentals (specifically - seems to me) is getting omitted. So, in the quest for performance, should not this thread benefit to from some consideration on runner length? Me thinks so...

[tpepmeie]

Right on, Paul. Runner length is the primary factor, by far, in the rpm of peak torque and hp. In the case of the LT5, unlike the other engines you mentioned, there are not practical options available to change the runner length. I know of a couple fabricated short runner manifolds, but 99.9% of folks won't (and shouldn't) pursue that option.

[wfot]

This is exactly what I am asking. real world experience, good or bad.

So far this is what I understand about the LT5 as far as the intake;

1)the plenum is a fixed size, this will lend itself to perform best at a specific CID. I have not figured out the specific volume of the plenum, but am working on it and will post that info once I have it.
2) the runners are a fixed length, this cannot be easily altered, so runner diameter and shape is where changes can be made
3) it seems specific diameters are used on specific CID size and or specific HP levels. there is port matching, then oversizing/altering the runners
4) altering the runners to 36mm, which seems to be the standard by which this forum agrees is used from anything from 510 packages to 625 HP engines. after 625, then I see housings being welded to allow more HP.

here is what I understand about plenum volume vs HP/engine design:
1) the plenum should be as large as the total displacement of the engine it is on.
there are many opinions/variations on this idea but this seems to be the basic concept outside of this forum.

My question from the beginning was what has been real world experience for these various runners sizes/configurations.

I am considering having a port too big for the engine it is on and then causing low speed turbulence and ultimately not have as much power at 3000 vs another engine with smaller volume runners. this is exactly what I am asking.

If 36MM runners are the mark that everyone shoots for and there is a drawback, then why are they shooting for this benchmark.

I am also considering the volume of the runner in the plenum above each port. to that end I read that the volume of the plenum needs to be equal to the engine total displacement because on the shift, the plenum will starve some cylinders because this is the point of max volume used by the engine. with that in mind, when does one consider the area of volume above the housing but not part of the main plenum? at some point the mini plenum will starve the housing in the same manner as the main plenum will starve the mini plenum.. if everything is not matched accordingly.
it would make sense to me to make the volume of the housings equal to the volume of one cylinder, make the mini plenum above the housing equal to the housing/one cylinder (and this can be altered by opening the divider in the housing, effectively moving shared volume from the housings to the mini plenum) and then matching the main plenum to the total CID of the motor it is going on.....

yes I am trying to figure out the best why to get the most out of what I am putting together and have been thinking about it for a long time..

thoughts welcome.
experience in the real world.. I tried this and then that and the result was... appreciated.

[Pete]

Here's a thought.
37mm (36mm drop thru) on a stock 350ci picks up close to 50hp this tells me stock LT5 is over camed and under intake.
So the question is if a 350 picks up that much HP with 37mm port is this still sufficient for a 400+ cubic inch motor.

Things that make u go hmmmmmm.😁
Pete

[wfot]

Here's a thought.
37mm (36mm drop thru) on a stock 350ci picks up close to 50hp this tells me stock LT5 is over camed and under intake.
So the question is if a 350 picks up that much HP with 37mm port is this still sufficient for a 400+ cubic inch motor.

Things that make u go hmmmmmm.😁
Pete

Very interesting observation, Pete.

All of this is very interesting, the theory vs what actually happens.
For instance, everyone agrees that a back cut intake valve shows CFM flow improvement AND actually works in practice. however, everyone agrees that a backcut exhaust valve also shows CFM flow improvement BUT losses HP in practice!!! No one knows why.. just do it. I figured out that all flow testing is done with the flow being pulled from the chamber side of the head, so the intake flow path matches the actual engine flow BUT the exhaust side is pulled the same way, thru the exhaust port into the chamber EXACTLY OPPOSITE of how the flow moves thru the engine.. that back cut on the exhaust valve will have different flow dynamics depending on which way one is doing the testing. I have yet to see someone flow test an exhaust valve with the flow being pulled thru the chamber side then out of the exhaust port. i feel this would show very different flow dynamics...

Another question; Is a manifold vacuum present in either/both situations indicating that the throttle body is a restriction/limiting factor?? like there is more vacuum present AFTER the larger housing are installed? it would make sense that if more air is moving thru the plenum, a more vacuum would be present if the throttle body was a restriction. and then what would be the vacuum difference between a 58MM TB and 63MM TB??

Hummm indeed
John

[spork2367]

I realize I am in the vast minority, but I want to give my opinion on the subject. It is incorrect for one to try to correlate a certain port diameter to a "supported" horsepower for these engines. It's a fallacy that the port diameter is the limiting factor for ultimate power output. There is no equation to be had there.

Lot of people go very big. Big doesn't equal power, necessarily. Ultimate airflow is important, but not the only, constraint on horsepower output. 99% of folks limit the engines potential by camshaft choices, before the size of the ports ever become a constraint.

Couple of examples. GM Indycar engine, 3.5-4.0L, upwards of 750 bhp in those days (1997-2000). I have a few parts and pieces from said engine. The inlet ports were well under 35mm each (Yet the heads flowed over 100 CFM per sq. in. of valve area--generally 39mm valves).

427 cu. in. LT5. "Well" north of 700 crank hp. inlet ports in the head averaged 35.2mm primary / 35.8mm secondary. 390 cfm. Port was already bigger in some areas or would have been even smaller. Injector housings averaged ~38mm because the top 1" was siamesed. The critical areas were quite a bit smaller. Total average diameter of the head+housing inlet tract was 37mm. Shape and airspeed matter more than total diameter. Some areas are not perfectly round in this inlet tract. So the old drop a ball bearing test would never work in this case.

Todd

Totally agree. I think that opening the intakes and runners on the LT5 probably gains as much or more from the change in geometry as the change in cross sectional area. These intakes were built for hood clearance, not power.

While you may unlock 25-35 hp by porting, there is no way to tell if that's from cross sectional area increase, better flow path, etc. To believe that opening them up more magically unlocks more horsepower or somehow raises the hp ceiling is grossly over simplifying things.


Here's a thought.
37mm (36mm drop thru) on a stock 350ci picks up close to 50hp this tells me stock LT5 is over camed and under intake.
So the question is if a 350 picks up that much HP with 37mm port is this still sufficient for a 400+ cubic inch motor.

Things that make u go hmmmmmm.😁
Pete

Where is that 50 hp number from? I've typically seen 35 hp on a 90-92, 20 on the 93+.

[wfot]

Where is that 50 hp number from? I've typically seen 35 hp on a 90-92, 20 on the 93+.

What size port are you making/using? whom is doing it?
35mm, 36mm I think there is a very big difference what people consider porting. I have found it is easy to make the top part of the port very large..36mm or bigger and it does look impressive. however, the difference between 35 and 50 HP is how much porting is done throughout the entire housing and plenum. that is why the drop the ball test was used. if you can get a particular size ball thru the port, then it indicates that port has been enlarged to a certain degree and not just the top or bottom. But I do agree that just being able to shove a ball thru does not mean it is "shaped" well. gouges and inconsistencies in the port wall as well as smoothness of the walls will effect ultimate airflow potential. I do think port matching is overlooked often with the LT5, it is easy to get a plenum from here and a set of housings from there, but how well are they port matched to each other and the head is very important to flow transitions from plenum to housing to heads...
my .02
John

[spork2367]

What size port are you making/using? whom is doing it?
35mm, 36mm I think there is a very big difference what people consider porting. I have found it is easy to make the top part of the port very large..36mm or bigger and it does look impressive. however, the difference between 35 and 50 HP is how much porting is done throughout the entire housing and plenum. that is why the drop the ball test was used. if you can get a particular size ball thru the port, then it indicates that port has been enlarged to a certain degree and not just the top or bottom. But I do agree that just being able to shove a ball thru does not mean it is "shaped" well. gouges and inconsistencies in the port wall as well as smoothness of the walls will effect ultimate airflow potential. I do think port matching is overlooked often with the LT5, it is easy to get a plenum from here and a set of housings from there, but how well are they port matched to each other and the head is very important to flow transitions from plenum to housing to heads...
my .02
John

I'm using Mark Haibeck's numbers.

[wfot]

I have spoken to Marc about this personally, a very nicely detailed runner will be about 45 HP over the 35HP posted on his site and yes, 10 less for the 93 - 95 versions.

I have been looking at the differences between the 375 vs 405 housings and finds that the secondary runners are very similar, however the primary runners on the 405hp have much more volume..measured in ML. secondaries are both 80 ML and the 375HP primary about 70ML and the 405HP primary is about 80ML. the 405HP runners seem to be much more equal in volume as far as primary vs secondary.

Pete seems to do more extensive work with a 37mm port and I would doubt that there is an honest 50HP hiding in those housings.... hence this tread... ;)

John

[tpepmeie]

You are tirelessly focusing on size with the assumption that mm=hp. The critical issue in the inlet tract is getting the air to turn (with minimum pressure drop) at the junction between the head port and housing port. Yes, you can use sheer size to overcome that drop, but doesn?t mean the whole port has to be uniformly large. The factory as-cast injector bosses are the other obstacle.

Marc does great work. And he has refined it over the years. There are others too, but don?t get hung up on size...

Maybe tell us more about your build and goals for it?


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[wfot]

Marc does excellent work and a very generous man with his time and knowledge.

I do understand that the turn from the housing to the head is important and I am looking at it like the turn at the short side radius at the valve.. it needs to be done right or the flow will cause turbulence. I feel that port matching the gaskets is an often overlooked basic necessity.

I am developing a way of raising the secondary Oring to mimic the primary Oring location, thus allowing the Oring boss to be removed completely from both ports. so far a 36mm drop thru port like that has about 100ML of volume vs 80ML for stock 405 hp prim/secd ports.

as far as the build
-402 CID/12 to 1 compression
-thinking 36mm ported housings raised Orings on the secondaries
-siamised runner plenum, considering a dropped plenum, but am not sure if a 402 needs this OR ti is just something that no one has wanted to invest in a 402 build ( I have only seen them on 415+ CID motors)
-ported air horn with large throttle body
-stage III cams
- large valve/ported heads
-Jeal headers

I am shooting for crank 630HP or 550 RWHP, hopefully more. I am aware of 2 402/408 builds that have seen between 500 and 550 rwhp with similar parts as I have outlined above.

Again I am basing my posts on what seems to be the accepted things that have worked for people. I have had a lot of positive and negative input from many forum members that I appreciate greatly. There is a lot of good information out there and I am piecing together the parts that I think will work best for my goal.

John

[tpepmeie]

Who?s doing the heads and what size valves?

What rpm do you expect peak power?

Last time I measured the injector housings, they were about 4" long centerline (101.6mm). From that you can work out either diameter or volume, if the other is known.

[wfot]

I got the heads already ported, I believe they were actually done by bill krichoffner for kurt white's old 415 from way back, the valves are 41.5mm and 35.5mm stainless. the chambers have had some smoothing/unshrouding done, but I think they could use a little more. Ti retainers/secondaries removed.

I understand that the stage III's have a pretty high peak RPM, so I am expecting peak between 6900 and 7350 or so..

[tpepmeie]

I got the heads already ported, I believe they were actually done by bill krichoffner for kurt white's old 415 from way back, the valves are 41.5mm and 35.5mm stainless. the chambers have had some smoothing/unshrouding done, but I think they could use a little more. Ti retainers/secondaries removed.

I understand that the stage III's have a pretty high peak RPM, so I am expecting peak between 6900 and 7350 or so..

The oversize inlet valves back then were typically 1.600" inches / 40.6mm.
Bill is a great guy, I just talked to him a few weeks ago.

This is a 402" engine? 4.00" stroke?

compression? << nevermind, I see 12:1>>>

[wfot]

caliper says 41.5mm across the thickest part of the head

I also have one of bill's 12mm studded blocks, 12mm studs on all mains very nice work indeed. The thing is a tank. I hear good things about him as well. I think that was kurt's actual 415 block as well. From what I read, Kurt was going all out with that build and Bill did the work. It does look good. the heads are very nicely done. But I do not have any other LT5 heads to compare them to. Might do some bowl work and match the ports a little, but they are pretty much ready to go

and yes 4.00 x 4.00 motor, bryant crank.. work of art

I am planning on 12 to 1, but if head gasket selection can get me to 12.25:1 or 12.5:1 I would do that a well

[tpepmeie]

The oversize inlet valves back then were typically 1.600" inches / 40.6mm.

I have to correct my post above after talking to Bill. The correct measurements for the valves he installed are: intake 1.580" or 40.132mm and exhaust are 1.445" or 36.703mm.

Perhaps Kurt had additional machining done and new valves after Bill did the initial work?

[wfot]

I bought a 402 "Project" package a few years back. I am almost positive the block is kurt's and was done by bills. the heads I cannot be so sure of. so anything is possible, especially given the many years that have pasted.

for instance;The manifold is a true siamised manifold, the outside it beautiful but the inside is a mess. have no idea who did those but they were done for ecstatic purposes I am sure. The housings are a mess and have various port sizes and there is some serious weld overlap on the plenum. it is taking a long time to figure all of this out and actually get things into shape but it is coming along well.

If this was a typical small block build in the end, no way I would put this much time into it... lol

[tpepmeie]

Hmmmm. I think I recognize that description. Many years back there was a gentleman on this forum (Kevin P.) who spent a ton of money building a 402 using parts sourced from Bill. This would have been 2009-10 time frame. I forgot his screen name, but he and I chatted several times about that build. At the time I was building my first 427 and we would friendly jab each other about which had the nicer parts!

PM me if you want to discuss.

[Polo-1]

I bought a 402 "Project" package a few years back.l

Hello
I tried to send you a pm on this 402. It might be my old 402. I have lost track of who owns it now. It went through a few hands.

Kevin

[HAWAIIZR-1]

Hello

I tried to send you a pm on this 402. It might be my old 402. I have lost track of who owns it now. It went through a few hands.



Kevin



Wow! Talk about a blast from the past. It?s good to see you are still around Kevin!! [emoji1303]🤙🏼


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[wfot]

I cleaned out some old messages, please try again.
I got it from, Kris out of texas about 5 years ago..

[Polo-1]

Not sure who Kris is.

My story as I know it or remember it:

I built the 402 back in 2008-10. Heads were brand new, and porting by GVD. Cams from Pete, they are stage II Not Petes grind the old school stage II's.Had new GM lifters.The intake was built from Bill K. GVD had to fix the mess Bill made. Block was a 91 used has Ron Woods HD liners @ 4inch bore. JE pistons coated, top and sides plus other features. Rods are Crower. Crank is Moldex, nothing fancy will look like a factory crank with mallory in the rear ( I think). Bottom end is still on factory bolts ( 2-bolt main block .) Few other stuff.

I ran it for 20-40 miles. I screwed the drivers side intake cam timing. Nothing hurt just pissed me off. Then had to get a C6 Z06....

I sold it to Jim Donahue back in 2010-11? Jim had it till he died in 2016. Never installed it. David ( in MD) forgot his last name...
He called me and asked about it. I think he somehow got it from the Jims family. David sold it to someone and they were going to have a handbuilt sheet metal intake made for it? Something like that. I never heard anymore about it. Lost track of it.

All that I know for sure is it would kick the S#*@ out of Todd's motor 😝

I wish😀

[Polo-1]

Wow! Talk about a blast from the past. It?s good to see you are still around Kevin!! [emoji1303]🤙🏼


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Yeah still peek in once in a while. Can't get the old LT5 out of my blood. It's a bad boy for sure.

[tpepmeie]

.



My story as I know it

I ran it for 20-40 miles..



All that I know for sure is it would kick the S#*@ out of Todd's motor [emoji13]



I wish[emoji3]


No way man. I went hundreds of miles, an dozens of dyno laps! Lol. Always good to hear from old timers, in forum years anyway!





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[Polo-1]

Good to hear you can still take a ribbing.

The 427 is a monster. You cracked 700 right? It's been a few years for me. Lost track on yours. I know it was out of my builds league!

[Paul Workman]

I have spoken to Marc about this personally, a very nicely detailed runner will be about 45 HP over the 35HP posted on his site and yes, 10 less for the 93 - 95 versions.

I have been looking at the differences between the 375 vs 405 housings and finds that the secondary runners are very similar, however the primary runners on the 405hp have much more volume..measured in ML. secondaries are both 80 ML and the 375HP primary about 70ML and the 405HP primary is about 80ML. the 405HP runners seem to be much more equal in volume as far as primary vs secondary.

Pete seems to do more extensive work with a 37mm port and I would doubt that there is an honest 50HP hiding in those housings.... hence this tread... ;)

John

In addition my using Pete's model runner size as my guide, and Pete later phased my cams slightly as well, the whp was 432.

I'll let you do the math, but the porting and headers and (stock cams) phasing resulted in a HUGE improvement in performance - significantly greater than a paltry 50 hp. So, what am I missing here???

My stock bottom, stock cammed LT5 before and after.