Thread: exhaust size

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working on bored out 235(so its about 242) on a 58 chevy )and i am getting alot of conflicting info about exhaust size. we talked to clifford performance and obviously they recommend their headers which are 2 1/4 in. as opposed to what we had originally designed -- using fentons, which was 2 1/2 in. THe guy we talked to was saying that if too much back pressure is eliminated the torque will suffer because quote" backpressure is good for low end torque but is bad for high end horsepower"??????? just dont get this. why would more force working against the piston on the exhaust stroke creat more torque? What am i to do? Is clifford just trying to get me to buy their headers, which i might add are total:$414.00 with the coating, whereas say hot rods of norco can gove me ceramic coated pair for $219.00. And what size exhaust do i go with? not to mention the problem of fitting on intake and exhaust maifolds ---clifford said that basically their exhaust headers are the only ones that wold fit with their manifold---is this true? cause it sure is expensive.
thanks

I know what the guy's trying to say, but he might want to word it a little differently. Exhaust scavenging plays a large part in the shape of the power curve. While back pressure is never a *good* thing, exhaust system diameters that are larger than neccessary for an engine's particular state of tune can create exhaust gas velocity so low that they affect scavenging, and cylinder filling. Obviously, engines tuned to develop their power in the upper part of the band can utilize larger diameter tubes without severely reducing gas velocity. Milder engine with broader torque bands probably would do better wiith smaller diameters. Hopefully, I've said it a little better than the Clifford Performance guy.

Bob

hey thanks for the response, you did clear it up nicely

appreciate it

will write if more question (which there will no doubt be

As I remember, some of the same bolts secure both the intake and exhaust manifolds on a 235 Chevy 6. It's very likely that one manufacturer's exhaust won't fit with another's intake.

I am just surprised that a 235 will move a 58 barge down the road with anything resembling speed. When we built a 58 Impala kustom leadslead we yanked the 348 in favor of a 396. It moves well but would be a better mover with a 502.

your just as suprised as me. but all the more reason to squeeze as many horses out of my little 242 as i can.

Since you're on a budget, why not use the stocker intake and adapt a Rochester 2bbl to it? Then, shave the head a bit to up the compression to about 9:1.

Both header tube sizes seem a bit large.... 2 1/4 inches is a huge tube to a small block Chevy....are two cylinders feeding a single tube?

Tried to find the Clifford web site...it looks like it is a combo of porn links and car parts.....Jack would roll in his grave if he saw this.

mike in tucson

the clifford site is cliffordperformance.net, and yes two pipes feed into a collector -- thats the reason for the largish tubes. And my pops is not ever too happy about shaving heads so well see. will talk later. thanks for all the help

>Tried to find the Clifford web site...it looks like it is a combo of porn links and >car parts.....Jack would roll in his grave if he saw this.

Try this: http://www.cliffordperformance.net/

Bob

Thanks for the info...if you go to cliffordperformance.com, the site is strange. It does refer to cars and to porn.... maybe not a bad combo in some occasions.

Nothing wrong with shaving the head.... think of it as "trueing the head surface" only the machinist takes a little more metal off. I have had a 235 shaved 0.100" before..... with a '54 Corvette cam, it ran really well.....
well for a 235 that is.

hey hey dont be bangin on my engine....haha

I ran a 235 with a '54 corvette cam, two one-bbl carbs and Fenton splits. With the stock 4.10 gears, it was a pretty good stoplight bandit in a relatively light-weight '52 2-door post. The 390 4-bbl should work OK also. if you get it jetted correctly.

The reason the 6 can move that barge so well is due to it's torque down low. As for the pipe diameter, 2.25" is plenty from the head to the exit.

the reason that it can move is because it has 4.10 gears in the rear, yes the torque helps, but that gearing only mutiplys it