Exhaust sizing race car

[skinny z]

Hello,
I own a 70 Camaro road race car. Its running a 572cu BBC, made 700 RWHP on dyno
(afr 357 cnc, 278/282 @50, 110, .0720 lift, 11.5.1 compression, pro systems 1180cfm carb)
Currently it has 2 1/8 primary tubes into a 3.5 inch collectors. Then 3.5 inch mandrel bent tube to a Flowmaster dual inlet 3.5 inch race muffler.
It feels like it may be restricted at its top end ( 6400rpm)
4 inch would be better, but more difficult to keep under noise limits and we have restricted space
do I need 4 inch system ??

Cheers Richie

Not to discount the impact that suspension has on the overall package but I'm curious as to whether the exhaust is still on the radar as being restrictive or maybe out of spec for the engine output.

[richiev8]

Maybe borescope the muffler to see if it is buggered up inside or a baffle has come apart.
I'm with Tom68 on the pinion angle. With multi-leafs and cal-tracs on an f-body set up for road racing, there isn't much droop when jacked up or much jounce when on its tires. Here's a quick measurement using Solidworks on the pic - the perspective may be making look worse but it shouldn't be off much. A quick check wouldn't hurt.

[richiev88]

Hello,
I own a 70 Camaro road race car. Its running a 572cu BBC, made 700 RWHP on dyno
(afr 357 cnc, 278/282 @50, 110, .0720 lift, 11.5.1 compression, pro systems 1180cfm carb)
Currently it has 2 1/8 primary tubes into a 3.5 inch collectors. Then 3.5 inch mandrel bent tube to a Flowmaster dual inlet 3.5 inch race muffler.
It feels like it may be restricted at its top end ( 6400rpm)
4 inch would be better, but more difficult to keep under noise limits and we have restricted space
do I need 4 inch system ??

Cheers Richie

Not to discount the impact that suspension has on the overall package but I'm curious as to whether the exhaust is still on the radar as being restrictive or maybe out of spec for the engine output.

Hi,
Going to drop exhaust off on dyno, been too busy to get it to the dyno, but is on my list. Couldn't find any flow data on the muffler and flow master have discontinued that muffler now.
Ill keep you posted

Cheers

[skinny z]

Hello,
I own a 70 Camaro road race car. Its running a 572cu BBC, made 700 RWHP on dyno
(afr 357 cnc, 278/282 @50, 110, .0720 lift, 11.5.1 compression, pro systems 1180cfm carb)
Currently it has 2 1/8 primary tubes into a 3.5 inch collectors. Then 3.5 inch mandrel bent tube to a Flowmaster dual inlet 3.5 inch race muffler.
It feels like it may be restricted at its top end ( 6400rpm)
4 inch would be better, but more difficult to keep under noise limits and we have restricted space
do I need 4 inch system ??

Cheers Richie

Not to discount the impact that suspension has on the overall package but I'm curious as to whether the exhaust is still on the radar as being restrictive or maybe out of spec for the engine output.

Hi,
Going to drop exhaust off on dyno, been too busy to get it to the dyno, but is on my list. Couldn't find any flow data on the muffler and flow master have discontinued that muffler now.
Ill keep you posted

Cheers

Don't forget the collector extensions!
I'll make a WAG and say 700 RWHP and a single muffler don't mix well. Even without extensions, I can see the upper RPM benefiting from the exhaust being dropped. I've found that additional tuning is needed after such a change.
I did a simple experiment with my single mufflered drag racer (about half your output) and placed a cutout just before the transversely mounted muffler (behind the rear axle). No science to it other than removing what was an obvious restriction. There were observable improvements in both 1/8 mile ET and MPH. My bet is that PipeMax calculated collector lengths will add even greater performance.
Good luck!

[malibuguy79]

Totally forgot about that muffler. I have never personally handled any oval Flowmasters. Id imagine its like with any of their other race type offerings it essentially terminates the end of the exhaust length at the inlet of the muffler. So this may be a length game play.

However...after some more thought; that is not alot of case volume for the given power let alone dealing with both banks feeding it so it may very well be a restriction at your given power.

[richiev88]

Hey,
Well I've built a new exhaust, lost a bit of ground clearance but gained 65 ish RWHP over the Flowmaster muffler
Pretty happy with the results, guess big blocks need to breath

IMG_6824.PNG

IMG_6866.JPG

[skinny z]

Hey,
Well I've built a new exhaust, lost a bit of ground clearance but gained 65 ish RWHP over the Flowmaster muffler
Pretty happy with the results, guess big blocks need to breath
IMG_6824.PNGIMG_6866.JPG

There looks to be plenty of capacity there! Nice.

I'd like to be able to do something similar but under a 3rd gen Camaro, and a lowered one at that, there's not a lot of real estate. There are a few examples of full length 3" duals going over the axle with mufflers at the back but it's a tight fit. Hooker/Holley do make a 2 -1/2" kit though.

It's your improvement from one muffler to the other that's the eye opener.

[richiev88]

Engine builder recommended 4 inch, but ist just not practical in round tube
We cant buy oval tube locally in 4 inch, and it get pretty pricy importing it, not to mention its very hard to meet track noise limits with tube that big.

[skinny z]

Any details on that muffler? CFM?