header/hipe install...loss of low end torque

FiveO said:

i figured the car would feel more powerful with the header hpipe install (bbk shorties, off road h) but it feels like i loss torque.

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Yes you are correct. Actually if you put the stock headers back on you will pick up more power, but leave the H-pipe on. The H-pipe will be fine.

Yep.

In, fall 2003 I ran a best of 1.78, 13.11 @ 102.74 MPH back when my engine was stock, but had 3.73s, ud pulleys, Bored stock maf, K&N, 65mm T body, slicks, Mac equal lengths, stock H pipe [cats were not gutted] and straight pipes w/ stainless tails plus all the tweaks like timing, weight removal.. Could leave the line @ 4500 and it'd spin the slicks a bit and PULL. Car averaged high 102 MPHs all day.

This spring just passed, I went back.. added an off road X pipe, Magnaflow cat back [basically same as what I had - straight thru muff], and a ton of rear suspension work, and MSD 6AL. Ran....???? 1.77 60' 13.14 @ 102.95 MPH. Had to leave at 5200 this year to get the 1.77 60', and suspension work did its job, motor bogged so hard the car would nose over... leaving at 4500 resulted in high 1.80s for 60s.. averaged 102.0s with the off road X pipe.

I wanted to get into the 12s on the stock motor, and I think if i'd had my ported stock headers, and stock h pipe WITH the suspension work done, it would have did it.

Others will disagree, but I think that if you have a stock engine with just bolt ons, and the stock H and cats are in good shape, then leave it, and as far as headers, I feel its worth it to remove them and hog out the messy welds inside each header primary right where they bolt up to the heads. Port them out till they are the same size as the exhaust ports on your stock heads..

For a 302 c.i. motor, These cars come with pretty decent exhaust from the factory when you stop and think [275 HP LT1s, 325 HP LS1s, 245 HP L98s etc all around 350 c.i., all had single 2 1/2" or 3" ex..]. We have a H pipe w/ balancer tube, and true 2 1/4" stainless mandrel bent dual exhaust header to tail..

I was reading in the Summit Catalogue [old one I had here] a while ago, about exhuast sizing. If I remember correct on a motor with 302 cubes 2 1/2" wasn't even needed until like, the 300 HP mark or something.

I'm just biased towards stock motor = stock H pipe and headers, [always noticed a gain with a good cat back or stock H run open at track] because I have lost too much TQ every time I went to 2 1/2" off road.. [had a 91 Calypso LX that lost a ton of TQ and had 3.08 gears too.. sold the off road stuff went back to stock..].

To quote Thumper "Just me..........".

Are they 1 5/8ths headers or larger? It seems that most headers are too much for stock heads. The port in the heads is the worse restriction in the exaust system. Larger header runners causes you to loose velosity and not gain much top end. I have scene test where they found that 1 1/2" headers make more power with stock engine's. I would either a. re-install the stock headers b. buy smaller headers c. Get some better heads.

89sleeper - checked out your page... nice clean car! love the white Ponies!

Clutches do ease up as they break in, just give it a proper break in. I guess your best option is option C, which was better heads, you'll see gains all over the place.

I was thinking of getting MAC headers... bad idea?

So whats the best Headers to go with?

Header primary size MUST be matched to the power output you are making and the point in the rev range that you aim to maximize torque. Otherwise, you either have a restriction at high RPM or lack of exhaust velocity (which makes headers work) at low RPM.

Generally, for low to midrange torque... 1-1/2" primaries up to maybe 275hp (flywheel), 1-5/8" up to maybe 400hp, 1-3/4 up to maybe 550hp...

smaller primaries to shift torque peak down, larger to shift up.

If you want to make a real gain on the stock engine with headers, get long tubes. 1-5/8" longtubes will make a noticeable improvement right away but allow room for improvement, or get 1-1/2" longtubes for the biggest punch with a near stock motor.

But 1-5/8" short headers... you don't increase the length of the header tubes but you decrease the exhaust velocity, so you lose power unless you have considerably hopped up the engine already.

Yup,I did the same thing.FMS headers and a BBK off rd h-pipe.I put the stock h-pipe back on,and it feels a little better,and it shifts better,I guess the added back pressure helps.

You don't want backpressure... you want high exhaust velocity... whose momentum works to draw out exhaust gases from the cylinders upon opening of exhaust valves.

Making pipes smaller, and pushing the same volume through, makes higher velocity.

Too high velocity, or forcing air around weird shapes (mufflers), causes drag and backpressure.

Ray III said:

You don't want backpressure... you want high exhaust velocity... whose momentum works to draw out exhaust gases from the cylinders upon opening of exhaust valves.

Making pipes smaller, and pushing the same volume through, makes higher velocity.

Too high velocity, or forcing air around weird shapes (mufflers), causes drag and backpressure.

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cool,,got it

Hey Fiveo,

I just happen to have a set of AFR 165's for sale. PM me if interested.