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Discussion Starter #1
i got to reviewing some pictures, it looks possible to run dual 3inch piping through the tank area. could this be done? would it need to be peiced in? is the mark 8 93- 95 tank the same deisgn as our fuel tank or is the exhaust routing alittle better?
 

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the motor that i'm building right now for this is a 5.1 stroker, with a tork tech on top of it, thinking bout runing 10 -12 lbs of boost.
 

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Discussion Starter #5
i'm just trying to come up with the exhaust side what would yeild the best performance level for this set up. and least restriction. i was also going across the idea of kooks 1 3/4 primarys with 3'' collectors dual to a single 3 1/2'' threw the tank area back to dual 3''. i know some stepped headers will yield the best gain.
 

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Discussion Starter #6
my power level i'm looking for is around 500 hp. would 2 1/2'' duals be pushing it?
 

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That chart is not even close to accurate.
 

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That chart is not even close to accurate.
That's what I was thinking. Where did that graph come from?

Even the chart on the linked Magnaflow page doesn't agree with that graph.
 

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Let's end this BS

That chart is not even close to accurate.
Thank you! The basis to those charts is very old. The only time a freer exhaust hurts a cars performance is when the restriction (restrictive exhaust, intake, throttle body, etc.) is covering up another problem (usually cam, head, fuel, etc shortfalls). I know racers that do run different custom cams when the "have" to run racing mufflers (5") because of track rules. I also understand they are racing classes won/lost by .01's. In the early 70's I used to add extensions ranging from 6" to 16" to my Super Comps on my Duster because I was getting too deep in the rounds or the weather was changing to fast (Michigan) to change jets between rounds (hence adding restriction to cover another issue).

This same thought process (adding to old "carb" philosophy) is what makes these boards covered with advice about "throttle body size being to big". All funny. Our cars add fuel at the port and the computer couldn't care two cents about the size of the throttle body until it is TOO small.

Again David, thanks for saying it.

Brad
 

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The source for the graph was http://www.koracing.net/ (I simply googled images for an exhaust size graph and didn't do a lot of digging.)

However, if you are going to disagree with something, please post definitive evidence/proof. I listed two quick sources both indicating the same thing.

And here are a couple other ones:
http://www.autolounge.net/calculators/exhaust/exhaustsizing.html
http://www.mk5cortinaestate.co.uk/calculator5.php

If someone will post some sources backing up their statements, I'll more than gladly agree and change my stance.

I hear all the time statements made about exhaust sizing. It ranks up there with carburetor sizing. You know, "an 850 double pumper on that thar stock small block chebby will give more power that a 650 vac secondary… I know that for a fact cuz Joe Billy Bob did that and he swore his 75 Camaro was faster!!!"

I will still stand by my statement that dual 3" exhaust is too big for his application, based on the limited information provided.

according to that chart the 2.25" true dual on my LSC is too big?
Considering the stock LSC dual exhaust is 2" (behind the third cat), I wouldn't say "too big", but rather say: dual 2.25" is larger than needed and bottom end torque might suffer suffer (assuming bone stock engine). But it all depends on where you want power; bottom end, top end, or the whole power band.

Exhaust sizing is defined by engine volume/displacement, engine rpm, camshaft design, expected power band, and the intended application (to name just a few). A boosted 5.1 cu in modular engine that is a street beast will have a different exhaust requirement than a boosted 5.1 cu in modular engine that is strictly a drag race vehicle. And even with all the information, it still often requires trial and error for a perfectly tuned exhaust sytem.

But just my .02. :thumbsup:
 

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The source for the graph was http://www.koracing.net/

"(I simply googled images for an exhaust size graph and didn't do a lot of digging.)" This is a the most important part of your statements here. Technology is changing dramatically. The internet is an excellent source for all "old and new".

However, if you are going to disagree with something, please post definitive evidence/proof. I listed two quick sources both indicating the same thing.

And here are a couple other ones:
http://www.autolounge.net/calculators/exhaust/exhaustsizing.html
http://www.mk5cortinaestate.co.uk/calculator5.php

If someone will post some sources backing up their statements, I'll more than gladly agree and change my stance.

I hear all the time statements made about exhaust sizing. It ranks up there with carburetor sizing. You know, "an 850 double pumper on that thar stock small block chebby will give more power that a 650 vac secondary… I know that for a fact cuz Joe Billy Bob did that and he swore his 75 Camaro was faster!!!"

I will still stand by my statement that dual 3" exhaust is too big for his application, based on the limited information provided.

Considering the stock LSC dual exhaust is 2" (behind the third cat), I wouldn't say "too big", but rather say: dual 2.25" is larger than needed and bottom end torque might suffer suffer (assuming bone stock engine). But it all depends on where you want power; bottom end, top end, or the whole power band.

I did not think this discussion was about a "bone stock engine". Stock exhaust systems are intended to work in a wide range of driving conditions and generally are not very efficient. Car manufacturers compromise performance for other considerations, such as ease of production and cost.


Exhaust sizing is defined by engine volume/displacement, engine rpm, camshaft design, expected power band, and the intended application (to name just a few). A boosted 5.1 cu in modular engine that is a street beast will have a different exhaust requirement than a boosted 5.1 cu in modular engine that is strictly a drag race vehicle. And even with all the information, it still often requires trial and error for a perfectly tuned exhaust sytem.

I agree (perfectly tuned not possible on a TBird anyways). All charts I have found have refered to minimum sizing required and there are a large number of variances in these charts and graphs. One can find sources to support just about any opinion. Your sourced graph disagrees with the chart from the very same manufacturer.

But just my .02. :thumbsup:
(no comment)

Most charts agree that up to 400hp (flywheel) 2.5" is sufficient. Any good exhaust designer will also tell you though that every bend in that pipe is restrictive (physics) effectively reducing the flow and therefore the effective size of that pipe. Our cars have "many" bends unless you remove the belly tank and go to a tank in the trunk. With that in mind if he is looking at 400hp + installing a 3" exhaust would be prudent, even according to the one site you sourced. Here is another site that quotes Flowmaster:

http://www.sandersonheaders.com/tech_complete_performance_exhaust.php


Since "pulse tuning" through a TBird exhaust system is out of the question allowing the least restrictive is our only option. Scavenging by other than the header design is a moot point. I totally agree with header pipe size being important for scavenging but through a closed system with 10 bends in it the "scavenging" ends at the collector. All in exhaust work is a compromise.
 

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i got to reviewing some pictures, it looks possible to run dual 3inch piping through the tank area. could this be done? would it need to be peiced in? is the mark 8 93- 95 tank the same deisgn as our fuel tank or is the exhaust routing alittle better?
To answer this question, the exhaust man that did mine (2.5") has done at least one in my area with 3" pipes. He said he spot welded the pipes together, used a break right after the 90* turn into the area from the muffler (did mine that way also, works great, you can drop the system in sections). I believe him as my pipes run perfectly along side each other with no rattles so he is an artist with a pipe bender. He did say he used foil backed insulation pads in key places. Looking at mine I can see it being possible. Make sure you get references to any exhaust guru you are going to use. Have seen some real horror stories on here.
 

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The stock Z06 runs dual 3" pipes all the way through and has 505hp. That graph says to use ~1.75" pipes...

If the 3" pipes wont fit in there, though it sounds like it can be done, a 3.5-4" single might fit in there better.
 

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Dual 3" Exhaust fits. There are members on this board that have this size of exhaust. I am not mentioning names, search is your friend. The one thing I will say, you better have a damn good exhaust shop in mind to be able to bend it though.
 

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Discussion Starter #16
what i'm going to do. is have my exhaust man peice it together in the fuel tank section and tig weld those peices. thats way it's really smooth bends, i know mandrel bending is the best but. can be a pain to get a really smoothe bend.
 
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