porting injector housings to 36MM

[wfot]

Originally Posted by tpepmeie

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]

Originally Posted by 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

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]

Originally Posted by 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

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.

Originally Posted by 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

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

[wfot]

Originally Posted by spork2367

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]

Originally Posted by wfot

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