Sizing an exhaust system?

[nancejd]

So how do you pick the best exhaust system for a particular application?

Say I have a 350, that I'm looking to get around 450 horse (550 to 600 on the bottle) out of, at say 6500 rpm. It will be in a car that is primarily for the street, so I'm willing to sacrifice some performance for things like ground clearance.

How do you pick headers, exhaust pipe size, and mufflers?

What I'm thinking right now is;
Hooker shorty headers, 1 5/8 primaries with a three inch collector
3" pipe including the x-pipe
2.5" pipe from there
Dynomax Ultra Flo mufflers 2.5 inlet and outlet, round, 12 inches long, and two on each side (four total). I'm thinking they will tuck up where the crossflow muffler would have been located in my '69 Camaro.
2.5 pipes to the end.

Any thoughts or suggestions?

[ProdigyCustoms]

I would not shorty header anything I did not absolutly have to. Primary lentgh is important. Somewhere in the 30 to 36" range (which 90% of all long tube headers are) are what you want. You have a bit of a compromise to consider if you are going to juice it. 1 5/8 primaries will work good on motor, but will stiffle it badly on a 150 shot. if you were racing it and running it only on the giggle, I would suggest 1 3/4 primaries. Problem with running 1 3/4 primaries on the motor NA is they will kill the bottom end torque. And at 350CI, you do not have any torque to give up.

At 450HP, 3" is a bit of over kill, but won't hurt anything. On the hit, you will possitivly need the 3". And tailpipe size has very little to do with anything, so you 2 1/2 idea is good.

Taking all things into account, I would sacrifice a bit on the nitrous performance. I would go with a Hooker 1 5/8 Competition header. You might consider the Flowmaster American Thunder system which is a great budget system.

[nancejd]

Thanks Frank.

Performance on motor only is definately more important than on the bottle. The car is most likely only going to see maybe 50 passes a year, and that will be bracket racing, so I probably won't even use the nitrous on most of those passes (more of an occaisional fun at the track thing).

My only concern with the long tubes is ground clearance. I'm using half height solid body bushings, and the Hotchkis front springs (rears as well). Let's just say Washington is not known for it's well built roads, and the local jurisdictions love to put speed bumps in the roads. Would the long tubes tuck up iside the subframe rails?

[ProTouring442]

Look at Sanderson, they have some nice 3/4 length headders. I used the big block ones on my 442, not as good as long tube, but not as bad as shorties. You can see a bit of them in this pic.

Shiny Side Up!
Bill
'72 442 "Inamorata"

[parsonsj]

James,

Shorty headers are usually no better than exhaust manifolds.

I'm skeptical of 3/4 headers too, but have no data. I'd recommend real headers if you want performance benefits, and for a 350, I'd use 1.75 primaries, though 1.625 is fine too. I'm with Frank on length: 30-36" in length is about right.

Do you have a copy of David Vizard's awesome exhaust article from PHR (about a year ago)? He's got some real tech in it that will help you a lot.

jp

[USAZR1]

Look at Sanderson, they have some nice 3/4 length headers. I used the big block ones on my 442, not as good as long tube, but not as bad as shorties. You can see a bit of them in this pic.

Those are excellent headers and work very well on lowered cars. I've seen dyno testing on the 3/4 intermediates vs over the counter full-length headers and the power difference was minimal.
If you have to have full length tubes,Stainless Works can sell you some that really tuck up tight.

[nancejd]

John, I remember the article, but I don't have a copy of it. I didn't see it at popularhotroding.com either.

The intermediate headers sound like they may be what I'm looking for. I'll have to look at them in relation to the long tubes. I looked at Sanderson's site and didn't see them listed, does anyone have a part number for the Camaro application?

Looking at the Hookers (down Allen), it seems like the 2451s would be the route to go. Going from 1 5/8 to 1 3/4 primaries changes the tube guage from 16 ga. to 18 ga. It seems like the heavier guage tubing would be better, in terms of longevity, and the ability of the header to retain the heat inside the pipe. Also, going to the larger primary changes the primary length from 30 inches to 29 inches. Does any of that make a difference?

[ProdigyCustoms]

I run 1 3/4 Hookers on my street racer. It is pretty slamed in the front, motor is lowered in the frame more then 1 inch (to help prevent wheelies). Even so, I still can go through parking lots, tall speed bumps may scuff a bit, but it is OK. Shorties will hurt you more then you can imagine. One thing to do with long tubes, and I need to do it myself, is get ride of the header flange and band clamp it, that will give you a extra 1/2 to 3/4 inch clearance.

[nancejd]

Thanks Frank, that's probably the way to go. I'm planning on buying a painted set, mocking them up, and then getting them coated locally, so making modifications should be doable. Would I be giving up any bottom end going with the 1 3/4 primaries vs the 1 5/8 primaries? Also, how important is primary tube guage? The 1 3/4" are only 29" long, is that 1" short of 30 critical, in other words, is primary diameter more important thatn primary length?

I'm also curious how you know which primary size and length to select? Is there a formula you use base on CID, RPM, etc.?

[zbugger]

Oh man... Someone's gonna shoot me. Ok, here's my suggestion. What transmission are you going to run? I don't know of any intermediates that allow a z-bar to pass through. Only full length headers for that. Otherwise, I also don't know of any intermediates that are larger than 1 5/8", but I haven't recently looked at any. My recommendation for your exhaust would be to run some intermediates that are 1 5/8" going into a 3" dual exhaust. Run a Spintech x-pipe into your muffler of choice. After the mufflers, go 2 1/2" to the back. The smaller pipes actually make the exhaust a touch quieter, while, to my knowledge, helping a little with torque. Not a big change, but big enough. Being that you won't be drag racing, you're under slightly different rules on headers. Equal length full race headers would be best, but for what you're doing they won't be necessary. What I suggested would be pretty good for the street, and would not be visible below the frame, with the exception of the x-pipe and the mufflers. If you don't run the nitruos, 2 1/2" all the way back would be plenty for your motor.

[ProdigyCustoms]

I only run 1 3/4 on a 600HP NA, 900HP Giggle motor in JustBringIt, and found the car quicker then 1 7/8 headers because of the added torque from the smaller tubes. When I first built JBI for the kids, it had a smaller motor much like yours. I ran 1 5/8 headers when it had a 450HP 350, never tried bigger tubes, but it still ran 10.99 on 210 shot with that little motor
.29" is fine, there is no magic formula, that is why high end header companies like Stahl offer different collectors to tune primary lentgh.

[ProTouring442]

Oh man... Someone's gonna shoot me. Ok, here's my suggestion. What transmission are you going to run? I don't know of any intermediates that allow a z-bar to pass through. Only full length headers for that. Otherwise, I also don't know of any intermediates that are larger than 1 5/8", but I haven't recently looked at any. My recommendation for your exhaust would be to run some intermediates that are 1 5/8" going into a 3" dual exhaust. Run a Spintech x-pipe into your muffler of choice. After the mufflers, go 2 1/2" to the back. The smaller pipes actually make the exhaust a touch quieter, while, to my knowledge, helping a little with torque. Not a big change, but big enough. Being that you won't be drag racing, you're under slightly different rules on headers. Equal length full race headers would be best, but for what you're doing they won't be necessary. What I suggested would be pretty good for the street, and would not be visible below the frame, with the exception of the x-pipe and the mufflers. If you don't run the nitruos, 2 1/2" all the way back would be plenty for your motor.

Well, I don't know about for a Camaro, but on mine there is no problem with the Z-bar. There were a few minor tube to frame problems, but I notched the fram for those, didn't want to ding the pipes!

Shiny Side Up!
Bill
'72 442 "Inamorata"

[ProTouring442]

Yeah, I don't see the small block 3/4s listed for the Camaro... it's the CC10 listed under Chevelle, but I don't know if they would fit a Camaro, or how much modification would be needed. I do know that Sanderson will send them out uncoated so you can fit them, then coat them for you.

Street & Performance also makes a 3/4, and they list one for the 67-69 Camaro.

Shiny Side Up!
Bill
'72 442 "Inamorata"

[72.RS/SS]

Just food for thought. You can get any header from Jet Hot and it is way cheaper then buying some and sending them to them.

[Z-man]

This site seems to have quite a bit of good info...

Exhaust Science Link

[nancejd]

Thanks for the link, that's the article I remember reading but didn't have a copy of.

[nancejd]

OK, so I read the article, and what I'm wondering is where you find the flow rating of a muffler?

[Z-man]

I think you have to check with each manufacturer. Here's a list compiled from the Vette site...
The numbers are CFM.


OEM..................................... ........................................ ...225
Gibson SuperFlow 788200.................................. ............311
TTS Bullet Cat Converter............................... ..................324
Flowmaster 40 series 42540................................... .......352
Flowmaster 50 Series.................................. ...................362
Flowmaster 40 series 43040................................... .......392
Dynomax Super Turbo................................... .................410
Flowmaster 62631................................... .......................435
Carsound Cat Converter............................... ..................436
FLP Cat Converter............................... ............................440
Edelbrock Victor 5535.................................... ..................562
Flowmaster 40 series 435409.................................. ........576
Edelbrock RPM series 5511.................................... ..........579
Flowmaster Delta Force Racing 54040-10........................634
Edelbrock 304 series 5560.................................... ...........640
Edelbrock Gen App 5505.................................... ..............708
Dynomax Race Magnum Welded 17216...........................711
Borla XR-1 40600................................... ..........................836
Borla XR-1 40615................................... ..........................854
Dynomax UltraFlow SS 17263................................... .......1000
Dynomax Race Magnum Welded 17218...........................1000
Borla XR-1 40575................................... ..........................1100
Dynomax UltraFlow............................... ...........................1133
Edelbrock Victor 5537.................................... ..................1400
Borla XR-1 40450................................... ..........................1400
Borla XR-1 40741................................... ..........................1450
Dynomax UltraFlow SS 17296, 17268..............................2200
Dynomax Race Magnum Welded 17220, 17224...............2200
Dynomax Race Magnum Welded 17225...........................2600

[USAZR1]

Sanderson intermediates will work with a manual trans. Patriots won't. I'm not sure about Hedmans.