Exhaust sizing race car
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Exhaust sizing race car
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
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
Re: Exhaust sizing race car
Well the new 632ci crate engine made 840hp at the rears with a 3 inch exhaust, maybe look at some better mufflers.richiev88 wrote: ↑Tue Oct 31, 2023 3:13 pm 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
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Re: Exhaust sizing race car
What model flowmaster? I do not recall any dual 3.5 inlet Flowmaster mufflers.
Re: Exhaust sizing race car
Somewhere it was suggested that about 2.2 CFM per HP is required before the exhaust starts to diminish output. The gains are marginal at the top end of the scale.richiev88 wrote: ↑Tue Oct 31, 2023 3:13 pm 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
Although 700 rear wheel might be be difficult to reconcile to engine HP, call it a 20% drivetrain loss. Based on that, engine output could be 840. So, following that guideline, 1680 CFM is required.
As mentioned, gains are small at the top end (as in percentage lost) but even at 1500 CFM, there are only a few mufflers that could flow that much. And I would think that the Db's are through the roof.
Is there room for two?
Combine that with Moparboy440's post regarding pipe diameter and potential CFM...
The rest is math. And packaging.
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Kevin
Re: Exhaust sizing race car
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Re: Exhaust sizing race car
Thanks for the reply’s,
Muffler is as the picture posted
I’ll drop the exhaust at the header flanges, see what changes next time on the dyno
From the tables supplied the muffler could be choke point
Muffler is as the picture posted
I’ll drop the exhaust at the header flanges, see what changes next time on the dyno
From the tables supplied the muffler could be choke point
Re: Exhaust sizing race car
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Re: Exhaust sizing race car
Good luck keeping the flat muffler together.
Twin 3.5" should be enough, chassis dyno with some turn downs on the collectors and see.
So much going on, pinion angle, fuel line heat shield, traction bars, rear antiroll bar with leaf springs, is power the only problem ?
Twin 3.5" should be enough, chassis dyno with some turn downs on the collectors and see.
So much going on, pinion angle, fuel line heat shield, traction bars, rear antiroll bar with leaf springs, is power the only problem ?
Ignorance leads to confidence more often than knowledge does.
Nah, I'm not leaving myself out of the ignorant brigade....at times.
Nah, I'm not leaving myself out of the ignorant brigade....at times.
Re: Exhaust sizing race car
Why would the flat muffler be a problem? I’ve run one for 5 seasons no issue , just not with this motor.
Everything else works fine,all necessary for turning corners
I see u are AU, sometimes we run with your Tourning car masters series
Everything else works fine,all necessary for turning corners
I see u are AU, sometimes we run with your Tourning car masters series
Re: Exhaust sizing race car
Don't forget that by opening the exhaust at the collectors, you'll change the tuned length.
That in itself would affect the dyno results.
Have you determined what the optimum collector length should be for a mufflerless system and your application? Or what the overall length should be including the mufflers for best torque or HP?
Kevin
Re: Exhaust sizing race car
Normally hard to keep flat mufflers from cracking, but if they're working for you that's good.
Ignorance leads to confidence more often than knowledge does.
Nah, I'm not leaving myself out of the ignorant brigade....at times.
Nah, I'm not leaving myself out of the ignorant brigade....at times.
Re: Exhaust sizing race car
No issue with the mild steel ones as long as you mount them correctly, seen stainless ones split the seems
Re: Exhaust sizing race car
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.
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.
Re: Exhaust sizing race car
It’s ok inside.Rick! wrote: ↑Sat Nov 18, 2023 10:07 am 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.
Pinion is 2.5 down . Car was originally built for a historic class which limited suspension mods. Springs used to wrap up under hard braking to the point of nearly binding the uj
Running in a different class with a lot more freedoms now, so slowly working through new mods
Under rider bars are solid fabricated ones , think cal tracks slide ?
I’ve attached a pic of the set up some of our cars run, it’s a F body too.
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