Looking forward in my project I am trying to come up with the "optimal" exhaust situation. Here's what I need to know. How much back pressure is needed to make the most hp and torque. I was planning on useing the Clifford street rod headers or the one from SpitFire if they look like they will work, then into a y-pipe then back to a Barracuda S resonator, do you suggest a muffler or should this be enough (might be loud for the street but loud pipes save lives). The engine will be modified, head work, bored +60 etc. etc. etc. allmost forgot, what size pipe is best? And is all the way back too far? Thanks for the help.

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go fast, turn left, don't screw up.
WWW.Mopardropheadcoupe.com

Well, if you run dual outlet headers like you say...you could probably go 2.25" true dual with a balance pipe and mufflers. Or if you want single exhaust go from 2.25" from the headers then "y" it to a 2.5" with no muffler or a 3" with a flowmaster muffler. This is going to move the "power-band" of the engine to a slightly higher rpm. This kind of exhaust should be good for the mods you intend on doing. To answer your question...taking the exhaust all the way back is not too far. Doing so won't really change the sound or performance(if it's mandrel bent) but it will help to keep the interior resonance lower, keeping your car from becoming a mobile perscription for Advil. Well good luck with it.

-Don

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Forget the flowmasters...here come the good ol' GLASSPACKS!!!

Ideally you do not want any back pressure in your exhaust. It just restricts the exhaust getting out. Normally when people report that they have lost low end by going to a less restrictive exhuast it's because they have changed a scavenging effect that actually created an improved flow of exhaust at the lower rpm compared to the new exhaust.

That being said, I have dual outlet Hooker headers on my Barracuda with a full dual exhust system out to the rear bumper. The tubing is 2.25" and I have 18" long glass paks.

This made for a nice deep rumbling exhaust from idle up to about 2500 rpm. From 2500 up the exhaust progressively morphed into an obnoxious loud BLAH that was not at all impressive sounding. Last spring I added a balance pipe (H-pipe) between the two sides just aft of the end of the tranny. This completely transformed the exhaust note from 2500 rpm up while making for a slightly quiter rumble below 2500 rpm. The note at 5000 rpm WOT is hard to describe, it's still quite loud but not at all obnoxious. The best way I can put it is the number of people at cruise nights that look me up the following week after hearing me leave is amazing. They keep telling me they can't believe it's a slant 6.

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Dave Clement
68 Barracuda (Hot-Rod \6)
http://mysite.verizon.net/vze4pgxf/

The best amount of backpressure for maximum horsepower is zero. It is possible that for some engines the best amount of backpressure for maximum low end torque is not zero. I've seen dyno graphs where low end torque was reduced by reducing backpressure, I've seen dyno graphs where low end torque was increaded by doing the same thing. I've even seen one exhaust test of several systems where the first one improved both high and low RPM power, then a second less restrictive exhaust improved high end power but the low end dropped to a point in between the first two graphs.

David Vizard claims that beyond 2.2 cfm of muffler flow per horsepower, you hit a definite point of diminishing returns. The Thrust Magnum Glasspack my turbo Dart will use flows about 500 cfm as tested by Car Craft, so it should be good for a mild turbo build. Perversely, it appears that the effects of exhaust pulses can occasionally cause more back pressure once pipe diameter is increased beyond a certain point (probably 2" to 2.5" for most slants). I've heard reports (but never seen the charts) where increasing pipes too much cost horsepower. However, most of the explanations for why this was so tended to defy several laws of physics and fluid dynamics, sometimes blatantly and sometimes subtly. Turbo motors are less likel to be affected by too large an exhaust pipe diameter, although I'd hate to try snaking a 3" exhaust pipe around my Dart's suspension and shift linkage.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

Is True Dual 2.5" pipes too much for a slant?? this will be flowing from the Hooker Dual Outlet Headers to a set of Cherry Bomb glass-paks.

Also is a Cross over really worth it?? does it improve performance any or is it just a "sound" thing, i'll also have Exhaust dumps for the track

Justin

When I added the cross over to my dual exhaust I didn't get any seat of the pants noticable improvement. However, most articles I have read say that if positioned correctly they will increase low end torque. I added the cross over for noise control.

Matt, I can tell you for sure that mopar 2.2l turbo motors definately like 3" exhaust. My turbo Daytona came stock from the factory with 2.5" pipe from the turbo to the cat and 2.25" back to the muffler (which is at the back of the car.)

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Dave Clement
68 Barracuda (Hot-Rod \6)
http://mysite.verizon.net/vze4pgxf/

I notice Hooker has a muffler they call Maximum flow muffler, its on page 57 of the latest catalog. They claim 595 cfm. Has anyone on the list tried these or know someone who has? Mad Scientist, got any computer models on these?

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go fast, turn left, don't screw up.
WWW.Mopardropheadcoupe.com

The reason too large of an exhaust pipe causes hp/tq losses does NOT defy physics or fluid dynamics. The reason too large of an exhaust pipe can cause power losses is because the exhaust gasses cool more quickly, causing exhaust gas velocity to slow down greatly. This can cause what's know as "reversion" where the spent exhaust gasses try to flow back towards the head along the sides of the pipe. Turbo motors are different though...seems that the bigger the pipe the better the turbo responds. If you want to use a 4" downpipe from a 2.2l turbo, that's fine, just wrap at least 24"-36" of the downpipe in "header wrap". Just my two cents.

-Don

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Forget the flowmasters...here come the good ol' GLASSPACKS!!!