Bob Turner

I am looking at options to run a new exhaust system and wanted to see if anyone had installed 3" pipes all the way back......

Is anyone running an "X" crossover?

Thanks,

Bob :cheers:

twan

i have 2.5' full exhaust from hooker super comp headers back (3' to 2.5' dumps) with my zz4 motor
i remmeber the guy mandrel bending my exhaust saying that the 3inch might rub and make a noise if it hits the holes in the crossmember under torque.

i think 2.5 is fine unless your goin FI (turbo/super charger)

427Hotrod

I have 3" on my C-2. It works fine if you have a good muffler man. Mine installed support straps (using existing crossmember holes) just to the rear of trans crossmember, and I have no trouble with rattles. They are fine.

Just gotta find a guy willing to spend the time and not flat rate it.


JIM

Stewart's74

I know there is a member from Nevada that runs the 3" exhaust in his C3... I cant remember his name though.

isosceles

I hope Ganey gets in on this one and corrects me if I am wrong, but:
Isn't there a disadvantage with too large of a diameter because it allows the exhaust gases to cool too much, making them denser and harder to move out of the exhaust system? I don't dispute that 3" is too big for a big block or high compression, high revving small block. I was thinking that whenever I get new exhaust that I would want 3" if it would fit. But based on the gas cooling issue, I know 3" would not work well on my car. Is this true?

427Hotrod

It all depends on cubic inches and rpm. Total airflow....

Think of the exhaust system as sort of an intake in reverse. You have much more pressure "pushing" it out than you have atmosheric on the other side, but it's the same principle. The pipes are a runner/plenum of sorts. The muffler and crossover (whether X or straight) is another plenum. There are even guys who install Flowmaster 1 chamber mufflers somewhere around the trans crossmember to give it a plenum to allow it to expand. It also helps with reversion (just like stepped headers). This keeps it from flowing back into the smaller pipe.

There are also cases (OEM often) where smaller tailpipes are used to help speed up the cooled gasses out of the muffler. It is usually done for sound though. Look at the old late 70's Z-28's. But some folks have had great success experimenting with 2.5" pipes coming out of a 3" muffler with a 3.5" pipe feeding into it. But is usually a relatively large/low RPM engine (think Buick/Pontiac 455's)

Same as with intakes, smaller runners make for higher velocity. Always will. But there is a point where you need volume, just depends on what you have for an engine. Obviously what works on a 283 will also work on a 383, but it will peak much earlier on the 383. It will make greater low speed TQ numbers with the 283 stuff for sure, but will starve the other end. I think many folks get hung up on all the reading they've done that has touted low speed TQ for the street at the expense of everything else. This produces some oddball power curves that peak very early and fall off rapidly. You need to make sure you have "enough" low speed TQ and then allow it to build as RPM climbs. What is often mistook for good low end numbers is really a poor TQ curve. I think SWCDuke calls it TQ bandwidth. You really do want a wide spread between peak TQ and Peak HP. Don't lop off too much at the top end. A diesel makes fantastic low speed TQ...we'd all love it...but it falls off very rapidly and makes no HP. Many folks mistakenly design their engine combinations around a diesel concept.

All that said, if you have a mild 350 with a mild Hyd cam and stock heads, sure a 2.5" system will likely serve it well. But just installing a 100 hp nitrous kit on it can change the whole picture. Or later adding better heads etc. Or a 383......


Just about anything capped up is going to have backpressure. And contrary to some thoughts, there is no such thing as good backpressure! ANY is keeping air from flowing into the cylinder. The trick is to balance the exhaust flow against cam design to create the scavenging effect needed. Bigger is not always better, but smaller isn't always better for low end power either. If you got a muffler, you will have some backpressure to deal with.

Kind of interesting how for years every header mfg. has sold us 1 5/8" street headers telling everyone they are the best for low speed response up to the 400" range. But it's also interesting to note that almost EVERY LS1 header for C-5's is at least 1 3/4". Now why does the same basic cubes/rpm range all of a sudden need biggger headers? And try to find something smaller than a 1-3/4" tube for a 396 bigblock.

The Merge collector idea is gaining favor and it does seem to work. Basically it's a carb venturi in reverse...speeds up exhaust as it exits headers and now we're back to the fact that the exhaust is basically an intake in reverse.


JIM

Rumpity Rump

2.5 " pipes with Headers are good for approx. 500 h.p. from articles ive read.

I have Hooker Super Comp. Headers, 2.5 " pipes , 2.5" X , and exiting thru 2.5" exhaust tips (had them punched out from 2" to 2.5"). The 'X' made the exhaust sound a deeper resonant pitch...and it made it much quieter at speeds over 55 mph which i now like on long trips.

Dave

The Money Pit

I just put 3" duals on mine,but with a converter in the middle.The midas shop insisted,and after checking the new emissions testing requirements,I found he was right.So I have a front and rear Y pipe connecting the 3" high flow converter(kind of like an X pipe),dumping into 3" Edelbrock RPM mufflers.
They are a bit load below 2000 rpms,but smooth out nicely around 2500,when you stand on it they sound like side pipes.

The too big theory I agree with if you're talking primary header tubes.This is where the port scavanging happens.Once the exhaust is past the collector,the sooner you dump to the atmosphere,the better.Bigger pipes are not going to hurt your performance.

Wrencher

Most exhaust guys don't have dies for their tubing benders that big and the 3" pipe crushes too much anyway. Sooo, you have to pop for the various mandrel bent parts and then find a patient, competent welder to cut and paste it together. It's gonna cost 'ya, oh yea'! :yesnod:

Hans

shawn_cake

Yes - my 1980 BBC 532 has 3" with Magnaflows - also 3".
Works well. :cheers: :cool: :cheers:

Maurice

I have 3" with an H pipe on my 502. I love the rumble and it runs MUCH better than with the 2" that it came with.

69Rat

I'm running 3" exhaust right now with a BBC.... I'm currently trying to decide between some form of side pipes, or new mufflers... maybe Flowmaster 40's, or similar. I've used the flows before on a sbc... but not on a bbc. The 3" works fine.. but like others have said.. make sure you use extra strong clamps, ot it will rattle either at idle, or under power. :seeya

JoeC427

3" straight back to the rear with a blance tube, and Dr. Gas 3" oval tubes under the rear. Flowmaster 50's. I simply made new holes with 4 1/2 holes that allow the exhaust to go sraight back. It fits nice and tight under the car. I also used DEI heat wrap on the rear section of the system to help keep the fuel pumps cool do to the hot weather here in Florida.

norvalwilhelm

I am running a 3 inch stainless exhaust with 3 inch Dynomax turbo mufflers. I did modify my crossmember to allow the exhaust to pass under it instead of through it.

aharte

I've heard that also, but its not true. Its always easier to push a steady flow of air through a bigger pipe. An engine spits out pulses of air though, not a constant stream, so that's not all there is to it. Each exhaust pulse creates a high pressure region which travels down the pipe. Part of that gets reflected back to the engine, and if the reflections are timed just right, power can be improved in part of the rpm range. The timing is effected by the pipe diameter (and many other things). Optimizing everything could mean that a smaller pipe may give a small advantage over a somewhat larger one, but its not practical to figure that out yourself. Only OEM's or professional race teams have the resources to care. That's the complete (and useless) answer :)

gkull

I have 3 inch through a custom crossmember. To quiet it down I added an H pipe clear back near the rear diff. I used a 3 inch pipe about 4 inches long and i ovaled it to ease welding it up. It right where the pipes are closest together.

I have 3 inch in and out stainless packed race mufflers with 3 1/2 inch tips straight out the rear.

Twin_Turbo

I ran double 3" and will again.

HERE is the sound of the NA engine w/ 3" exh. and no balance pipe (intentionally left out)

I will run 3" again since I love the sound and my downpipes are 3" too


I say, go for it :)




[Modified by Twin_Turbo, 11:15 AM 7/26/2003]