Here ya go jim, I fab'd up a custom header for you. Might need some tweaks for your LT1, but I can make it work!

http://www.fastblackcar.com/temp/kustomhedder.jpg


hehe.

 

Nice. Thanks Jordon.

 

jim

i grabbed these pics, but not with the intention of getting pics of the headers

i was hoping to have the head and headers out but i was plauged with a spiderbite that was makin me nausious (sp?)

had to call it quits early...

heres a sneak preview. more to come this weekend. the fuel lines are out of the way now so i should get some really nice pics

ignore pics of my intresting lifestyle and you can see my finger from the spiderbite that landed me in ER

http://www.worldisround.com/articles/17903/index.html

 

Jordan, those gotta be for a LS1 or a Ford. Still I bet they were cheap.

 

OK, let's assume that you need an exhaust system that will flow well enough for 650-675 horsepower, and that you're limited to a single exhaust path and a maximum diameter in the center section of 3.5"-4.0", and must have dual tips at the rear. What do you do?

I've got a Racing Beat twin tip cat-back at the moment with 3" inlet and dual outlet. I haven't measured the outlest, but I have a feeling that they're under 2" ID, and even at 2" ID, the combined area is 6.3 sq. in. compared to the inlet pipe's area of 7.1.

Assume that I can get 1 3/4 to 1 7/8" stepped (or otherwise) long-tube headers. I have dual bolt patterns on my heads, so I can use either a standard LT1/SBC flange, or a spread-port flange to get the clearance I need on the header fasteners with a bigger primary tube.

After the headers, I'm assuming 3.5" collectors at a minimum, to a single 4.0" "midpipe"? Neck the 4.0" pipe down to 3.5" heading into a single muffler at the rear of the car, and dual 2.25-2.5" outlets. How does that sound?

I'm considering running a Borla XR-1 oval in the mid-section, since that's where the catalytic converter would have been, and I'll have room. It shouldn't restrict flow significantly, and should knock down the sound somewhat. A single electric cut-out would be run in front of this muffler, if I decide to use one.

At the back of the car, Flowmaster makes a single 3.0" inlet, dual 2.25" and 2.5" outlet muffler, but I haven't found anyone with a single 3.5" inlet and dual 2.25-2.5" outlet configuration yet. If the center section were 3.5" (instead of 4.0") and necked down to 3" at the very rear of the car before entering the muffler, would that be an issue?

The Dynomax piping sizing chart that someone linked to in another post wasn't very helpful. The only 600 horsepower listing showed 4.5" single and 3.5" dual diameters. A 4.5" single is probably too large for the center section, and then there's the problem with the muffler at the back of the car. The 700+ horsepower row also lists 4.5" single and 3.5" dual.

One option is to run a cut-out for situations where I need maximum flow and simply build a pretty good exhaust system for the rest of the time, but I'd like to be able to use all my power with the cut-out closed or not cut-out at all, if at all possible. It'd be kind of cool to be semi-stealthy with exhaust note but still have the flow to keep from choking off the engine.

Any advice? Links to sites with more information?

Thanks!

 

According to the Dynomax site, you take the horsepower and multiply by 2.2 to calculate the flow required in SCFM. 650-675 horsepower would be 1430-1485 SCFM.

Dynomax listed their welded Ultra-Flo muffler (straight through design) at 1133 SCFM @ 20.3" of H20, but that's for a 2.5" inlet/outlet side/center configuration. They have a 3" center, dual 2.5" outlet version available that should have even greater flow, I'd assume.

Assuming that I ran 3.5" back to the rear of the car and necked down to 3" before heading into the muffler, any thoughts on whether or not that would be adequate, or am I going to have to have 4" or possibly even a dual path with oval tubing to get the volume I need in the center section?

I'm also assuming that such a huge pipe will kill low end power somewhat, correct?

 

Jim,

In your situation, I'd go with oval tubing and try to get a cross section area equivalent to that of a 4" pipe. You'll get alot more ground clearance with oval.... and I can only imagine that that's a real issue with your setup.
Dr Gas makes ovalized y-pipes that "transition" and Flowmaster, Spin tech and Borla make the low profile mufflers so there should be some worthwhile options.

Later,
-Mg

 

Jim,

Magnaflow makes a few mufflers that might work. They list a 3.5" inlet / 2.5" dual outlet unit as well as a 4"/3" version. They're a "straight through" design like the Dynomax so they should flow pretty well.

http://www.magnaflow.com/02product/universal/oval.htm

However it appears they are designed for RV's and larger vehicles so fitment may be an issue. Also the larger diameter versions are not available in stainless...

 

jim, I would use merge collectors.


www.burnstainless.com

 

My immediate train of thought goes somewhat like this:
- 650+ hp- you’ll pretty much need a 4” single pipe
- there’s very few mufflers that flow that well that a single will work, and none of them will be quiet and few will be small
- Dynomax’s flow #’s make me somewhat wary. The thing is that it is fairly apparent that some of their larger mufflers stretch the capability of their flow bench, since they don’t flow anything over 2200cfm and even mufflers flowing half of that appear to flow more then a straight tube of the same size. OTOH, if they were just BSing then there would be no reason for them to rate their smaller mufflers as low as they do, so generally I trust them (I haven’t found anything that seems to work better)
- The farther back you mount the muffler the less it effects flow. The farther up you mount the muffler the more it quiets the exhaust.
- You’ll be hard pressed to find a twin outlet muffler that really flows as well as a single, why not use a 3.5” or 4” in and out Dynomax ultraflow welded and then just weld a y and even the two tips off of your current exhaust (without the insides)? It would quiet things a little without significantly hurting flow.
- What about splitting the 4” into 2 3” pipes and then running 2 3” bullets? It would be loud but would work well. Actually, I bet it would be quieter and lighter then a single 4” muffler…

 

First off how did you get 1 7/8th SLP's? aren't they 1 3/4? second of all, DAMB THATS NICE !

 

They were 1 3/4" SLPs, not 1 7/8".

Quick question... why can a turbocharged rotary engine produce 500+ RWHP through a single 3" exhaust path and an LT1 apparently requires either dual exhaust or a larger 4" path? Granted, that's with a single 3" inlet/outlet straight through low restriction canister muffler, but still... shouldn't exhaust flow requirements be somewhat relative to the power level?

The BSFC of the rotary is actually lower (0.45) so it's consuming more fuel, but shouldn't the air being ingested by two 600 horsepower engines be comparable, even if one is forced induction? How about the exhaust volume?

One has two exhaust ports (the rotary) and one has eight. One displaces 5 times the volume of the other (6.5 liter vs 1.3 liter, assuming you stick with Mazda's ratings and don't consider that the engine displaces 2.6 liters if you compare it using 2 full rotations of the eccentric shaft in order to be equivalent to the displacement rating method of the V8). However the rotary is forced induction and the V8 is naturally aspirated. If we consider the rotary at 22-25 psi (the boost level required to make roughly equivalent peak horsepower) and 2.6 liters, we're talking about an engine that is ingesting almost twice its "real" displacement, exiting through two big exhaust ports.

If a 500+ RWHP turbo rotary can breath through a 3" pipe to the back of the car, why can't the LT1, assuming that a 3" inlet/outlet canister is also used in that configuration?

Just curious, and I don't remember anyone discussing exhaust volume in depth in the past, especially in this context.

 

Here's 1,125HP flowing through a Mufflex 4" catback...... note large rust cloud, since car hadn't been run in several months...



He claims when he pulled the complete catback off, and was just running collector mufflers, he gained more from the 50# weight reduction than he gained from removing the catback.

 

The turbocharger extracts heat energy from the exhaust in order to drive it, so the turbo-out exhaust stream is much cooler, by 100s of deg. F maybe. That makes the cfm lots lower, so smaller pipes are not as much a problem.

My $.02

 

True, when comparing turbocharged to NA when both engines are piston engines, but a rotary engine's exhaust gas temperatures are significantly higher than either. A modified turbocharged rotary can reach EGTs in the 900+ °C (1,650+ °F) range. In theory at least, my EGTs should be lower than a rotary engine making equivalent power.