70mm Plenum & Throddle Body Q&A

[1987BuickGrandN]

I have a Hemco 70mm upper Plenum and accufab 70mm throddle body. I had the upper Plenum and throddle body on my last grand national. The car had 80k miles, PTE51 turbo, 42.5 lb injectors, MAF pipe, CHIP, pump, regulator, valve springs, no converter, stock trans, no head work, 3" downpipe & dual 3" exhaust, basic bolt ons. I've herd of people using this throddle body and plenum with stock heads and intercooler. Is it unresonable to use this big of a throddle body and plenum with stock heads? It seems like my last car didnt perform correctly with the throddle body and plenum. Can someone tell me where I went wrong? Im guessing its in the heads. I have another car, (stock heads), all that ive modified so far is MAF Pipe and K&N Filter. I plan on using a 12 sec recipie, TA-49 or TE-44 turbo, injectors, TH Downpipe, valve springs, without any head work, or an intercooler, can I use this throddle body and plenum? Id like to hear some opinions. Perhaps someone who has done it before with similar or dissimilar results.

 

[TurboDave]

Originally posted by 1987BuickGrandN
I have a Hemco 70mm upper Plenum and accufab 70mm throddle body. I had the upper Plenum and throddle body on my last grand national. The car had 80k miles, PTE51 turbo, 42.5 lb injectors, MAF pipe, CHIP, pump, regulator, valve springs, no converter, stock trans, no head work, 3" downpipe & dual 3" exhaust, basic bolt ons. I've herd of people using this throddle body and plenum with stock heads and intercooler. Is it unresonable to use this big of a throddle body and plenum with stock heads? It seems like my last car didnt perform correctly with the throddle body and plenum. Can someone tell me where I went wrong? Im guessing its in the heads. I have another car, (stock heads), all that ive modified so far is MAF Pipe and K&N Filter. I plan on using a 12 sec recipie, TA-49 or TE-44 turbo, injectors, TH Downpipe, valve springs, without any head work, or an intercooler, can I use this throddle body and plenum? Id like to hear some opinions. Perhaps someone who has done it before with similar or dissimilar results.

Where you went wrong was, using that big of a THROTTLE body and plenum on an otherwise internally stock motor. It's way overkill and probably did more to hurt performance than it did to enhance it.
I wouldn't even consider the 70mm stuff unless there was a stage II motor and heads under it. Or at least a REAL GOOD set of heads and cam to match.

Stick with stock size for your goals, it'll work and be easier to tune.

 

[bruce]

Originally posted by 1987BuickGrandN
Is it unresonable to use this big of a throddle body and plenum with stock heads?

It depends.
Are you going to get serious with reengineering things to use it, or not?.
You probably won't see any gain, and probably a lose putting that TB on a relatively stock motor.

There are numerous ways to design an intake tract. You can go hemholtz, non hemholtz, and ram to name a few. To successfully use a large TB like that on a stockish motor, would mean going to an antihemholtz set, and that would be a redesign of the intake manifold.

 

[Chris McDade]

Been there done that before. I slowed down when i put one of these on my car. It's not required until you start running 10.30's or quicker. Bore your stock TB out and go from there. Im running 10.60's with a stock bored TB.

Good luck.

 

[strikeeagle]

I think I read that Red Armstrong was using stock, cleaned up TBs on his and Jane's cars...

 

[1987BuickGrandN]

thanks for the info. the throddle body definately hurt performance in my first car. i wish i kept that sucker off. i'm also thinking about doing a 4.1 with a set of alum champion heads, roller cam, etc. the throddle body just may have to wait for that.

thanks for all the info

 

[rking]

A 70mm TB will work great IF you have the supporting parts. I have the KB on my car, and I love it. I have oversized valves, P and P heads and intake, FMIC with 3 inch in and out, 224/224 cam, 3.5 THDP, and a 3500 stall, and only a PT51. The thing will absolutely fly. With everything opened up, it will MPH good enough for some high 10s - very low 11s. Torque wasnt hurt too bad either. It will smoke them from a dead stop. I love the 70mm TB, but I would only recommend it if your motor will support it.

 

[blackbuick87]

You need more converter. Stock D5 with a PT51 is going to be slightly sluggish. A 2800 stall would have woke the car right up.

 

[Go For 1]

I agree with blackbuick87. You definitely need at least a 2800 stall with a PT-51. This is especially true since you have reduced the velocity of air going through the intake, by using the larger TB. Larger TB's mean more volume of air, but at a lesser velocity. You might want to try a converter stalled anywhere from 2800-3000. HTH

 

[Go For 1]

Forgot to mention. With the added volume of air, you may also need to increase the fuel pressure, by retuning.

 

[Donald McMullin]

Bruce:

There are numerous ways to design an intake tract. You can go hemholtz, non hemholtz, and ram to name a few. To successfully use a large TB like that on a stockish motor, would mean going to an antihemholtz set, and that would be a redesign of the intake manifold.

Could you elaborate on what hemholtz, non hemholtz, etc is about. You left me on First Base.

Deep Enough
Donald McMullin

 

[johnz]

Is this the same for a 62 mm throttle body.Is it going to hurt performance on my mild recipe car

 

[TurboDave]

Originally posted by johnz
Is this the same for a 62 mm throttle body.Is it going to hurt performance on my mild recipe car

Probably not. I put a 62 on both of my GN's.
86 is equiped per my sig. and it really woke it up as far as throttle response.

Same is true with my 87, and it's almost bone stock with the exception of the TA49 and blue tops.

 

[Go For 1]

Originally posted by johnz
Is this the same for a 62 mm throttle body.Is it going to hurt performance on my mild recipe car

No, sorry I didn't clearly explain what I meant by larger TB. IMO, a mildly larger TB such as the 62mm's, are normally good upgrades to help with higher than stock boost pressures.

A 70mm without the associated hardware (mainly converter and ported heads), would most likely hurt performance. I have a PT-51 with a 2800 stall, ported heads and mild cam, and the stall speed that I have is the minimum that I could go.

That's why I would recommend upgrading the converter and doing some retuning. HTH

 

[matt87]

i agree with above. i too thougt a 70mm t-body and plenum was a cheap ticket to better performance but in reality it made the car feel slower and throttle response wasnt better but mushy feeling. its one of those parts you want not need.

 

[BoostedBug]

I think I would go with the Jay Jackson setup....