Bought some reds full length headers for my 64 with a 292. Going to run them into an x pipe then into some glass packs. I was leaning towards the cherry bomb 3inch inlet and outlet and the unit is 18 inches long. I think it will sound badass what's everyone think?

 

Is 3in the optimal pipe size for a 292?


I would think 2 1/4 or 2 1/2.

 

I like glass packs. I prefer Thrush though because they are perforated instead of louvered (I think CB's are louvered - not sure though). The louvered packs are actually quite restrictive from what I have read.

 

Depends on how fast you're going to spin it.

 

I just to my exhaust guy who said 3 is to big so I will go with 2.5. I want perforated if it gets better performance. Next will be 4 barrel carb and intake and maybe a cam. So what glass pack is perforated?

 

Thrush glass packs are the only ones that I found - but I quit looking as soon as I found them.

The real question is though, do you want glass packs for the way they sound when new or when they are blown out?

 

2.5 is too big still 2 1/4 would be optimum for anything below an all out build. the problem is most headers have 3 inch outlets which is way to big for most things and kills torque. if you have to run 2.5, run it to the muffler then neck it down to 2.25 after the glass packs to keep the velocity and back pressure up. this will help with torque production.

 

I'm calling BS. Back pressure doesn't help power - period.

 

I'll second that. Velocity and scavenging is what you want. Lose velocity with a big pipe and you lose scavenging.

 

I wish I could find a convincing explanation of how "scavenging" works, there's lots of theories and speculation on exhaust size but can't find documented evidence for bigger or smaller being better other than sound.
My only real experience was my friends 94 460 that had no exhaust just running out the manifolds and his 97 firebird 350 with headers (two 3" dumping under your seat) and no exhaust, we put completely factory exhaust systems on both (minus cats) and didn't see any change in 0/60 or to torque on either vehicle. Maybe a bigger exhaust system would've made a difference one way or the other but not having one vs having one didn't make a difference other than sound in this case.

 

Here's a link to a good write up on exhaust size and scavenging from a different forum. Exhaust: The straight scoop on backpressure

Running 0-60 at full throttle you want the biggest exhaust pipe size you could get, but the engine can only produce so much exhaust gas, so too big is a waste of money and unnecessary. I would imagine the factory exhaust on the 94 was probably 2.5" which should be sufficiently large to not choke up a stock engine. The headers on the Firebird provided the scavenging effect at WOT. That's why headers are give more power. If you were to dyno them you would see a difference with open exhaust vs. a full system.

 

I agree with keeping velocity up for the scavenging affect. To increase velocity, back pressure must also be increased - but it is a very fine line. If you start increasing back pressure over a certain point, performance drops.

If you have a single one inch pipe on a 460, the velocity will be through the roof. Performance? Not so much.

 

Right, but the focus should not be on back pressure. A great demonstration on back pressure is to get a drinking straw and a coffee stirrer. Blow through both of them. Which is easier? The smaller pipe/straw cannot allow enough gas to escape so pressure builds up behind the restriction (small pipe).

 

Bookmarked couple articles on topic but it appears my Classic Truck, CarCraft, articles are now linked to the "New Hot Rod" network; needless to say I aint going to be renewing. I was able to salvage 1 article that briefly discusses the subject. If able to find the magazine website use to be able to search the magazine 'tech' forum and pull up articles, now not sure?? Not an authority by no means but if I understand the jest of the article a factor factor in determining size, diameter, and length of the exhaust system; exhaust manifold/headers, exhaust pipe, and muffler, would be RPM??? If having it done in shop, which I highly suggest, they should be able to provide the spec's.???

Header Basics - How Headers Contribute to Horsepower - Car Craft Magazine

 

I have dual exhaust with glass packs on. Sounds great. It was the system on my truck when I bought it. 292 with left hand manifold just going toward the ground and back, with crossover eliminated. Truck runs great, sounds great. I think the pipes coming out back are only 2in.