Exhaust idea... will it work???
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From: Blairsville, GA
Exhaust idea... will it work??? I'm looking at making my own dual setup pretty soon, and had an idea pop in my head.
My idea stems from looking at how stepped headers work. The smaller tube sends exhaust into the larger tube at a higher velocity to increase scavenging of the chamber. I'm wondering if running 2 1/2" pipe to the H, X, or whatever letter you choose, and then stepping up to another size pipe would have a similar effect. Would the smaller upstream section offer enough velocity to keep more low-end power while the bigger downstream pipes would wake the engine up more at high rpm???
Here's what I'm looking at using.
Hedman stepped headers
2 1/2" pipe from collectors to H-pipe, catted
2 1/2" stepped to 2 3/4" H-pipe
2 3/4" duals over the axle(two modified OEM catbacks)
Will this make for a best-of-both-worlds exhaust system?
My idea stems from looking at how stepped headers work. The smaller tube sends exhaust into the larger tube at a higher velocity to increase scavenging of the chamber. I'm wondering if running 2 1/2" pipe to the H, X, or whatever letter you choose, and then stepping up to another size pipe would have a similar effect. Would the smaller upstream section offer enough velocity to keep more low-end power while the bigger downstream pipes would wake the engine up more at high rpm???
Here's what I'm looking at using.
Hedman stepped headers
2 1/2" pipe from collectors to H-pipe, catted
2 1/2" stepped to 2 3/4" H-pipe
2 3/4" duals over the axle(two modified OEM catbacks)
Will this make for a best-of-both-worlds exhaust system?
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From: Blairsville, GA
Kind of a trade-off between low-end kick and high-rpm power.
Not looking to go stupid crazy with the car(my wife drives it to work), probably gonna stop at all the bolt-ons, maybe a cam and, WAY down the road, maybe some 243 heads. I know huge exhaust pipes reduce velocity and cut down on low-end torque, while smaller pipes are good for down low, but choke the engine up high.
Make sense at all?
Not looking to go stupid crazy with the car(my wife drives it to work), probably gonna stop at all the bolt-ons, maybe a cam and, WAY down the road, maybe some 243 heads. I know huge exhaust pipes reduce velocity and cut down on low-end torque, while smaller pipes are good for down low, but choke the engine up high.
Make sense at all?
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Joined: Jun 2005
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From: England
Ok I hear what you're saying. However I think you're making it hard for yourself 
Essentially any good cat back with a 3" Y pipe will be great on a bolt on, bolt on cammed car. Any more and you really ought to be looking at 3.5-4" Y or 2.5" duals. These will offer better flow and performance at that level.
The exhaust will only be as efficent as it's most restrictive part.
ALL collectors on LT's are 3", these have to be this size for a V8 engine. If you run cats you will need them to have a 3" inlet/outlet or else they won't flow well enough.
After that it's upto you. You could neck them down to 2.5" for the X or H pipe and then 2.5" all the way out the back. Or you could stick with a 3" X or H pipe then neck it down to 2.5".
If you've already necked them down to 2.5" there's no point making them any bigger later on as there will already be a restriction, so they would be no gain.
If your planning on more than 500rwhp then IMO 3" duals would be worth it.
If your aiming more at 370-420rwhp then 2.5" is plenty (in theory anyhow).
Personally I'd probably go for a 2.5" X/H pipe as it will be easier to locate and have better clearance, if you go with CATS then there may not be enough room to neck down from 3" to 2.5" before the mid pipe, in this case I would run a 3" mid pipe then neck down to 2.5" to go over the axle.
Hope this helps.
Essentially any good cat back with a 3" Y pipe will be great on a bolt on, bolt on cammed car. Any more and you really ought to be looking at 3.5-4" Y or 2.5" duals. These will offer better flow and performance at that level.
The exhaust will only be as efficent as it's most restrictive part.
ALL collectors on LT's are 3", these have to be this size for a V8 engine. If you run cats you will need them to have a 3" inlet/outlet or else they won't flow well enough.
After that it's upto you. You could neck them down to 2.5" for the X or H pipe and then 2.5" all the way out the back. Or you could stick with a 3" X or H pipe then neck it down to 2.5".
If you've already necked them down to 2.5" there's no point making them any bigger later on as there will already be a restriction, so they would be no gain.
If your planning on more than 500rwhp then IMO 3" duals would be worth it.
If your aiming more at 370-420rwhp then 2.5" is plenty (in theory anyhow
).Personally I'd probably go for a 2.5" X/H pipe as it will be easier to locate and have better clearance, if you go with CATS then there may not be enough room to neck down from 3" to 2.5" before the mid pipe, in this case I would run a 3" mid pipe then neck down to 2.5" to go over the axle.
Hope this helps.
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The way stepped header primaries work is to return a small negative pressure wave from each step (much smaller than that from the size change into the collector), as the high pressure pulse passes, thus spreading the scavenging effect over a wider RPM range. Essentially the same thing happens in a merge/megaphone type collector, but the dimensions are very critical and are unlikely to be arrived at by guesswork.
An H pipe is a little different, but with an X pipe, the header/collector pressure tuning effectively ends at the 'knothole' in the X. As mentioned by 300BHP, a 3" collector is about right for the tuned portion, but behind the X, it's just a matter of sufficient flow to minimize backpressure and often a 2.5" will be sufficient. (On the other hand, but for the weight, larger can't hurt..)
An H pipe is a little different, but with an X pipe, the header/collector pressure tuning effectively ends at the 'knothole' in the X. As mentioned by 300BHP, a 3" collector is about right for the tuned portion, but behind the X, it's just a matter of sufficient flow to minimize backpressure and often a 2.5" will be sufficient. (On the other hand, but for the weight, larger can't hurt..)
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From: Blairsville, GA
So I'm worrying about small details here, eh? Aiight.
I've already got the H made(pipes will be about 1/4" apart from each other), so I can't stop now... unless I want to scrounge up more tubing and work late again.
Another reason for the 2 3/4" duals from the H back? That's OEM size, and it's already bent, so I won't have welds all over the place. Just re-work the tail end and crack on.
I've already got the H made(pipes will be about 1/4" apart from each other), so I can't stop now... unless I want to scrounge up more tubing and work late again.
Another reason for the 2 3/4" duals from the H back? That's OEM size, and it's already bent, so I won't have welds all over the place. Just re-work the tail end and crack on.
