DOes porting the plenum and IH make low end torque suffer?

[Nacho_ZR1]

I am contemplating getting my plenum/IH ported this winter but not sure how much my low end torque will suffer? According to my latest dyno shet, peark torque is in the 4100 RPM range. What do ya'll think?

[XfireZ51]

To quote Nike, "Just Do It". With ported top end and headers,
my motor did ~400rwhp and 358rwtq. Show me a stock motor that does that.

[rhipsher]

Your torque will improve. Not suffer.

[GOLDCYLON]

I forsee a port in your future. Do it.... is smart mod.

[mike100]

it just gains over 5k rpms-I noticed no change below 4000 rpm seat of the pants-wise. I think headers are the biggest single gain, but both together would likely be worth a little more than the sum of their parts.

[rhipsher]

it just gains over 5k rpms-I noticed no change below 4000 rpm seat of the pants-wise. I think headers are the biggest single gain, but both together would likely be worth a little more than the sum of their parts. I couldn't agree more. Top end porting along with headers/High flow cats/X pipe and an unrestrictive exhaust system plus a good tune is the ticket. I saw an immediate gain with porting alone. At the time I just didn't have the extra cash to do headers/Exhaust/tune. So I did what I could do on my own. Porting my own top end cost me almost nothing. And it doesn't take a rocket scientist to do it either. If you've got more time than money its the way to go. This winter its getting dropped off at Coreys for an entire Exhaust overhaul and tune. Im thinking 400rwhp baby.:cheers:

[Nacho_ZR1]

I couldn't agree more. Top end porting along with headers/High flow cats/X pipe and an unrestrictive exhaust system plus a good tune is the ticket. I saw an immediate gain with porting alone. At the time I just didn't have the extra cash to do headers/Exhaust/tune. So I did what I could do on my own. Porting my own top end cost me almost nothing. And it doesn't take a rocket scientist to do it either. If you've got more time than money its the way to go. This winter its getting dropped off at Coreys for an entire Exhaust overhaul and tune. Im thinking 400rwhp baby.:cheers:

Lol i think Corey will be very busy this winter :-) i recently went to see him last month to purchase an NOS fogger system he had laying around. That babY is going on my Nova. Anyway, i have jeal headers, no cats, xpipe, Dynomax superflow mufflers and Corey tune and am making 375hp and 356tq to the rears. Maybe i will pickup a 160 degree thermostat so that Corey can reprogram my fans to come on earlier. Also, after reading Goldcylons thread, I will be removing the secondaries as well. Better safe than sorry ya know? Does removing the secondaries yield any extra horsepower????

[LGAFF]

I have a ported 90 plenum that just needs to be painted or powsdercoated, $700 with exchange of your stockers.

http://i134.photobucket.com/albums/q115/lgaff/DSCN4013.jpg

35mm fooseball inside

[Paul Workman]

See 4 yerseff....

This was my stock 90 LT5

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/Basecase-DynoZR-19-20-08Large.jpg

I don't have an intermediate graph showing results with just P&P/headers, but this is after it was fully ported and tuned (see my signature). It appears from the graphs that stock my torque peaked out at 336 @ 4900 whereas it peaked at 377 @ 5100 with full porting. As Pete and Bob G have often proved, the rules for a 4-valve, dual runner heads are different from a 2-valve, single runner setup. (Dual runners changes the whole geometry...the LT5 lives by its own rules, it would seem!) The numbers don't lie, but it has also been said that the LT5, as it came from the factory, was highly under developed. The bottom graph is of a stock bottom 350 LT5 with stock cams and SW headers...and it seem to support that notion, IMO. See what you think.

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/DynoLT510-19-10.jpg

The top end porting is really a not difficult at all for a DIY job. Graduating to heads...is also possible, IF (as I say) you know where the "quicksand" is (aka places to be wary of) and you have a good aluminum welder backing you up! But the plenum and IHs are not difficult at all. I wish I had dyno'ed mine before moving onto the heads, but I can tell you it really woke her up!! (In my case, I did more than just port match the heads. I coned the heads in place down to the valve guides. No one will convince the seat of my pants that as result I didn't pick up at least 60+ RWHP...It transformed the car!)

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/IH7Large.jpg

The "coning" in progress...

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/IH8Large.jpg
http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/IH9Large.jpg

And a shot of the heads in progress...

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/Headporting002Large.jpg

BTW, tapering from 36mm to the stock ID at the guides, if done in a straight line, will be worry free. It isn't until you push the envelope i.e., full head porting, where wandering off the path can get you into trouble; a topic for another day.

I (and others too) have tooling recommendations, if you want to give it a shot. If you're the least bit mechanically inclined, and I believe you are, then you should dig into this one with relesh! Nuttin but good will come of letting her breathe a bit more!!

P.

[FU]

See the above graph's from Mr. Workman ? IMO go for it and do the injector housing's while you in there. Nothing will be lost , just gain's will be found by porting.
When the top end of a LT5 is ported to the max. The only down side is the huge smile on your face. And the loss of a few buck's .

[Paul Workman]

Does removing the secondaries yield any extra horsepower????

I asked Marc Haibeck about that, and he said he hadn't seen much difference in his experience - "maybe 5 hp" (as I recall). Marc still has his in place and last time out he made one pass at 12.1 and 120 mph, if I recall correctly. He has often said he recommends they be left in place to optimize low speed (emissions) performance, among others. (But, Marc knows someone with parts and expertise that is handy and can work on the vac secondaries, BTW;))

On the other hand, studying laminar flow characteristics as applied to intake runners, the highest velocity occurs in the center of the column...And, where is the throttle plate and actuator rod located??

Not disputing Marc's empirical data - it is what it is. But, the study of the physics involving the characteristics of fluid dynamics (in a column) is well established, and obstructions - especially near the center of the column - are not a good thing. With all due respect to Marc's expertise and experience, I believe it is possible that experimentation under scientific conditions might yield higher numbers (than 5 hp) without the obstructing throttle plates.

It would be interesting to conduct a controlled test, "fer sher"! I will say that if data showed a loss of hp as result of removing the plates/rods, I would have chosen to suffer with the BS of maintaining the secondary system, or at least just wire the plates open (as some do). However, in lieu of data from such a trial, I'm guided by the notion that less obstruction (i.e., throttle plates in the air column) the better. If that isn't enough reason to eliminate the plates, maintenance of the system (for me)...IS! And, if I couldn't pass emissions with the secondaries eliminated, I could always whip up a gasket for the IHs that blocked the secondaries, switch the power key to "NORMAL" (or change the cal if NORMAL has been programmed out) and insure the stock calibration (chip) was working properly...Just a thought.;)

P.

[XfireZ51]

Paul,

The alternative I used was to remove the throttle plates then tie wrap the secondaries open(minimizing the x-section of the shaft). That's the config I had when running the car last year. I originally was going to re-install the blades but then found out what a PITA it was to re-center them without a special tool so I said F* it! Besides those tiny screws were concerning as as GC has illustrated.

[rhipsher]

I asked Marc Haibeck about that, and he said he hadn't seen much difference in his experience - "maybe 5 hp" (as I recall). Marc still has his in place and last time out he made one pass at 12.1 and 120 mph, if I recall correctly. He has often said he recommends they be left in place to optimize low speed (emissions) performance, among others. (But, Marc knows someone with parts and expertise that is handy and can work on the vac secondaries, BTW;))

On the other hand, studying laminar flow characteristics as applied to intake runners, the highest velocity occurs in the center of the column...And, where is the throttle plate and actuator rod located??

Not disputing Marc's empirical data - it is what it is. But, the study of the physics involving the characteristics of fluid dynamics (in a column) is well established, and obstructions - especially near the center of the column - are not a good thing. With all due respect to Marc's expertise and experience, I believe it is possible that experimentation under scientific conditions might yield higher numbers (than 5 hp) without the obstructing throttle plates.

It would be interesting to conduct a controlled test, "fer sher"! I will say that if data showed a loss of hp as result of removing the plates/rods, I would have chosen to suffer with the BS of maintaining the secondary system, or at least just wire the plates open (as some do). However, in lieu of data from such a trial, I'm guided by the notion that less obstruction (i.e., throttle plates in the air column) the better. If that isn't enough reason to eliminate the plates, maintenance of the system (for me)...IS! And, if I couldn't pass emissions with the secondaries eliminated, I could always whip up a gasket for the IHs that blocked the secondaries, switch the power key to "NORMAL" (or change the cal if NORMAL has been programmed out) and insure the stock calibration (chip) was working properly...Just a thought.;)

P.
Excellent observation Dr Paul.:-D That would seem to make common sense that anything obstructing flow would be a hindrance. That's exactly why we grind down the injector bosses in the 375 hp cars. And I think that alone makes the single biggest improvement in flow over anything else in the porting process. The 405 cars need very little ground off on the bosses.

[Paul Workman]

Excellent observation Dr Paul.:-D That would seem to make common sense that anything obstructing flow would be a hindrance. That's exactly why we grind down the injector bosses in the 375 hp cars. And I think that alone makes the single biggest improvement in flow over anything else in the porting process. The 405 cars need very little ground off on the bosses.

And, on the 90s, the primary boss goes entirely away!

The primary (left) has no boss, and the secondary boss top edge has been reduced to a razor thin "lip", and the shoulders reduced in kind and shaped (front and back) to minimize impedance...

http://i185.photobucket.com/albums/x220/6PPC_bucket/tech%20files/ZR-1008.jpg

[rhipsher]

Yep! Bye bye injector bosses on primary and secondary ports.
http://i301.photobucket.com/albums/nn63/keeno1970/16.jpg
http://i301.photobucket.com/albums/nn63/keeno1970/4.jpg
http://i301.photobucket.com/albums/nn63/keeno1970/8.jpg
http://i301.photobucket.com/albums/nn63/keeno1970/7.jpg
http://i301.photobucket.com/albums/nn63/keeno1970/5.jpg
Just like a Mickeys big mouth. Gulp gulp gulp.:cheers:

[Blue Flame Restorations]

Good to hear that most people think P/P helps overall. Pete's talked me into doing mine this Winter. :)

[Locobob]

With an appropriate porting job there will be no ill effects on low/mid range torque. Here is a before and after dyno of my old 91 with just a cat back and a DRM chip - no custom tuning was done to optimize the porting work. The porting work in question is a relatively mild job by todays standards. It's somewhat different than what I normally do for people now - its basically a small port (35mm-ish) partial siamese funneling down to stock size at the top of the heads.

http://i418.photobucket.com/albums/pp270/locobob68/dynos/Be-Afporting.jpg

[Locobob]

Here is a more extreme example - partial siamese "B" port on my LPE 368 cid. As you can see at this level of porting we are trading some low end for top end. It's a net win for area under the useful max acceleration powerband.... but probably not ideal for the cruisers and torque fans.

http://i418.photobucket.com/albums/pp270/locobob68/dynos/368dyno2-06vs4-05aftertune.jpg

[A26B]

Robert,

Very good answer with graphic data, answering the OP's question. Useful & exactly to the point.

[Nacho_ZR1]

Robert,

Very good answer with graphic data, answering the OP's question. Useful & exactly to the point.

Agreed :handshak:

[Paul Workman]

http://i301.photobucket.com/albums/nn63/keeno1970/5.jpg
Just like a Mickeys big mouth. Gulp gulp gulp.:cheers:

Rick: A point of curiosity, regarding the effect the difference in the "siamesing" between your porting and mine has on torque curves:

In my case, I reduced the partition between the runners in proportion to the amount of rpm shift I desired for my torque curve, specifically wanting to push the curve up, without sacrificing mid range torque, if possible. I wound up ending the siamese (knife-edged) about and inch before the plenum outlet. (My resulting torque curves are perhaps(?) compromised by also changing cam timing (via "Pete the Greek"); i.e., not a pure experiment, but I digress...).

By comparison, I see you ended your siamese just below the plenum outlet. Doing the math, it would appear your torque curve might be 5-10% higher than where mine peaked, and I wonder if you have any "before and after" curves to post? If I like what I see, I can always increase my siamese a bit more, is my point.;)

P.