[Stikman33]

Hey guys, trying to decide on exhaust systems. I made some calls locally and its way to much money to have it done, so i'm buying a kit and doing it myself.

Steering at the moment towards one of the Pypes kits with the race-pro mufflers, but can't decide on the 2.5 or 3 inch systems. Here are some motor specs to give you an idea.

427 .030 over BBC, Solid FT 272/282 , 238/248 @ .050 .550/.570 lift, dual plane intake, holley 3310 vac sec, running through a th350 with 12 bolt 3.55 gears.

Now this is a mostly street car with monthly or so trips to the track during the summer time. it will be taken on 1-2 hour trips occasionally.

which pipe size would offer me the best performance and fit, what do you guys use on these cars? Thanks for the help!

-Daniel

 

[mr 4 speed]

Daniel,I use Pypes 3" headpipes (no H or X) and 2.5" mandrel bent tailpipes (older Flowmaster one piece)
Fit is excellent and tucks up nicely. I went with the 2.5" tails to keep it somewhat quiet.

 

[GRUMPYVETTE]

Ive got a 383 in my corvette, that's vaguely similar in cam duration etc,and swapping from a stock 2.25" to a 3" dual exhaust with an (X)provided a noticeable improvement in the range of 2 tenths in the 1/4 mile with no other changes and I already had headers and a (Y) pipe blending the two sides in the stock configuration, the lower the back pressure the better

http://forum.grumpysperformance.com/viewtopic.php?f=56&t=495

http://forum.grumpysperformance.com/viewtopic.php?f=56&t=1730

 

[fridgeguy]

I run 3" pipes in my Beaumont and 2.5's with 3" tail pipes in my Camaro. I'd go 3" end to end.

 

[cwilks]

running a 3" Flowmaster system (Dynamax Super Turbo muffs) out the back.....no X or H.....on my '70 (468).....perfect fit :thumbsup:

 

[Pman44]

I run 3" to dumps before the rear axle. I think your motor would like 3" better than 2.5".

 

[BillsCamino]

For a mild, mostly street 427 I think a 2.5" exhaust system is just fine on your car. I think a 3" system is overkill...I ran 3" on my 540 with way more compression and cam than you've got.
I've got a 2.5" front pipes, mufflers, and full tails on my '67 w/460 and a hyd roller cam very close to your solid, flat one.

 

[mr 4 speed]

running a 3" Flowmaster system (Dynamax Super Turbo muffs) out the back.....no X or H.....on my '70 (468).....perfect fit :thumbsup:

doesn't the Flowmaster kit come with a built in H pipe?

 

[Stikman33]

Gotcha, so a few say 3 inch, and a few say 2.5 inch Any more takers? I really think this is a thing that could go either way.

Oddly enough when looking at the pypes kits, the SGA10R which is the 2.5 inch version, is $33 more than the SGA13R 3 inch version. Strange, but that alone makes me more inclined to the 3 inch system, always out to save a dime!

-Daniel

 

[FRYNTYR]

I run 3" on my 69 chevellle with a 427, flat out rips

 

[fridgeguy]

Gotcha, so a few say 3 inch, and a few say 2.5 inch Any more takers? I really think this is a thing that could go either way.

Oddly enough when looking at the pypes kits, the SGA10R which is the 2.5 inch version, is $33 more than the SGA13R 3 inch version. Strange, but that alone makes me more inclined to the 3 inch system, always out to save a dime!

-Daniel

Go 3 ". You won't regret it and it'll work just fine.

 

[427L88]

With that setup 3" most defintely. 2.5" WILL hold it back at RPM. I run a 3.5" off the collectors down to 3" out the X, and finally 2.5" tails out the back. A 118.5 mph/ 1/4 mi is proof the exhaust does NOT hold the mill back one iota.

Cam WAS sft 243/251 shifting at 6800.

The only thing you lose with 3" is quiet.

Remember the "smaller is better" theory only holds with the primary tubes, less for the collectors ( actually the math is different for collectors), and is NOT the ryule for the back half of the system. Bigger is better, albeit louder.

Even with a shorter duration cam ( 233/236 HR), I would never go to 2.5" headpipes, although my primaries (2") and collectors( 3.5") are a freckle big for a sub 6800 rpm setup.

Even a much lower rpm setup like Chris's benefited from 3" headpipes.

Size of the tails is mathematically academic, so I chose the more oem/sleeper looking 2.5".

Exhaust heat and velocity are so low by then , size does not matter.

 

[Jeff65SS]

I am currently running the following:
1-3/4" x 3" Hedmans
3" headpipes to a 3" Pypes X
3 x 2-1/2 long flowmater reducers
2-1/2" Gorlich Xcelerator Mufflers (straight through design much like the Race Pros I believe)
2-1/2" Pypes tail pipes.

The car is a pleasure to drive, not loud at all but really barks when you up on it. I also really like the sound the large x pipe gives the exhaust. I wish I had tried the flowmaster tails as Mr. 4-Speed suggested, like the look better. Performance wise I have not been able to tell any difference ET or MPH with the exhaust open vs closed but haven't tried since 2 years ago. Would be interesting to try again.

 

[Calculated Risk]

9.81 sq inch total vs 14.13 sq inch total. That 1/2 inch increase in diameter makes a big jump in surface area of the pipe. If you can fit the 3 inch then do it. it allows alot more room to grow later on down the road.

 

[andrew T]

3 inch allows more growing room and sounds better to boot:thumbsup:

 

[Stikman33]

Alright, well then that probably settles it. The 3 inch kit is the way I'm going to go. Had an exhaust shop guy the other day tell me all the horrors of 3 inch and that "oh you'll almost never need a 3 inch."

Meh, its cheaper anyway to go 3 inch oddly enough.

-Daniel

 

[the heckler]

my 67ss > running a 600hp 496 now. I installed a summit 2.5 header back system (hedman headers). so far I have been pleased. the price was right. came with thier house brand turbo mufflers. the rear tail pipes from the rear of the axle back need to be re-worked for the correct look though....

 

[fenns70]

I using flowmaster's 3" kit #17200 on my bbc and it was a very simple install, I also have a '70 and i found out that "PYPES" makes the stock "SS" tips in 3", just put'em on the other day ------looks awesome, and Hooker comp headers up front.

 

[Malibu ss 64]

doesn't the Flowmaster kit come with a built in H pipe?

If you buy just the pipe kit with no muffler you have to weld in the H have this kit with Pypes race pros on my 64 pretty nice fit with some minor mods.
http://www.summitracing.com/parts/FLO-1041/

Think this kit is for 68-72 http://www.summitracing.com/parts/FLO-1040/?image=large

 

[onovakind67]

Remember the "smaller is better" theory only holds with the primary tubes, less for the collectors ( actually the math is different for collectors), and is NOT the ryule for the back half of the system. Bigger is better, albeit louder.

What's the difference in math? If you've studied guys like Ed Henniman and Jack Burns you learn that the collector follows the same basic rules as the primary tubes. According to Burns, "One of the largest errors street enthusiasts make is in running too large of a primary pipe, and too large of a collector." Henniman has a formula that compares the area of the collector to the combined area of the primary tubes, called the in/out ratio. He specified about 1.6:1 for street cars, 1.3:1 for race applications.
One of the biggest mistakes street setups have is the improper termination of the collector using a reducer, rather than maintaining the collector diameter all the way to the secondary junction.