Another 2.5 inch vs 3.0 inch?

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Kent mosby

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I am prepping the final installs and have a question on exhaust.
My 73 scamp will get its 512 RB installed in the coming weeks. The headers are TTI 440-200 with 2 inch primary tubes with 3.5 collector to 3 inch flange. Trans is 727 and 3.91 gears in an 8 3/4 rearend. Cam grind specs are 244/252 @ .050”, 282/290 adv, .516”/.537” lift(1.5:1 rocker), 112 sep, .016”/.018” lash. Future nitrous is an option but not certain. Holley Super sniper EFI will be installed with the motor.

The question I am debating is do I use 3 inch or 2.5 inch exhaust? I have read a bunch and am still confused.

Then I read this thread New 3" exhaust with 2.5" Tailpipes and yet I did not see any performance evaluation.

I have the 2.5 inch adapters on order but can change them if need be. Thanks for the wisdom.
 
I'm confused. You say a 3.5" collector. The collector is where the exhaust bolts up. Then you say a 3" flange. Do you mean a 3" reducer? I say if you have 3.5" collectors, then run a full 3.5" exhaust. I cannot STAND stepping exhaust down at the collector. That 512 will need every bit of it, IMO.
 
FEATURES of the 440-200 TTI header

Designed for: 67-76 A-body, 62-74 B-body and 70-74 E-body chassis.

Primary tube size: 2" O.D.

Collector size: 3-1/2" with 3" 3-bolt flange.

Flanges: 3/8" thick, laser-cut, contoured for a leak free fit.

Material: Constructed of 16 gauge mild steel tubing. Mandrel bent on sophisticated computer controlled bending machines for precise fit and uninterrupted exhaust flow. The mandrel bending process maintains a constant inside diameter of the tube for a smoother finish with no restriction of flow and no crimping of the tubes.

One piece design: One piece header tubes / No slip tubes.

Under chassis design: Above the steering center link design offers maximum header to ground clearance.

Full length header design: Proven power gain vs. shorty design.

Recommended for: 500-750 horsepower.

Torsion bar removal: Not required on B & E-body applications.

Header set includes: Header gaskets, 12 header bolts, header reducer adapters with 3-bolt gaskets & hardware.
 
HEADER REDUCER ADAPTERS to transition headers to an exhaust system.

Made of 16 gauge aluminized tubing, 3/8" thick flanges, includes 3-bolt gaskets & hardware.

Note: (1 set) Supplied with header purchase. Size required when ordering.

For 67-76 A-body, 66-74 B-body & 70-74 E-body applications....



3.5" x 2.5" x 6" long reducers

# RED35X25X6

$ 56.70 /set

So I have 3 inch to 2.5 inch on order. You are saying just stay 3 inch all the way and no reducer. Correct?



3.5" x 3.0" x 6" long reducers

# RED35X30X6

$ 56.70 /set


3.5" x 3.5" x 6" long adapters

# RED35X35X6

$ 56.70 /set
 
512ci engine... although 3.5" is ideal, 3" will suffice and is easier to come by if you don't want to fab up your own.
 
If your spraying it, biggest thing that will fit practically under the car.
 
You definitely don't want to go from 3.5" to 2.5" with your collectors. Here are high quality 304 stainless 3.5" to 3" collectors. Pypes Stainless Steel Collector Reducers PVR13S

You've chosen some really nice high flowing headers. The 3" X is rated to 550hp and by the time the exhaust is through the mufflers, you've taken most of the back pressure away from the heads for maximum hp. In theory, if you could figure out a way to get 3" tailpipes to fit in there, you'd probably get another 10 hp? With mandrel bends, it's not about the size as much as it is about the smooth and perfectly round tubing.

The 3" to 2.5" hybrid system is perfect for your application unless you want to run dumps and don't mind the dust kicking up and the very loud sound.
 
Kent mosby said:
I am prepping the final installs and have a question on exhaust.
My 73 scamp will get its 512 RB installed in the coming weeks. The headers are TTI 440-200 with 2 inch primary tubes with 3.5 collector to 3 inch flange. Trans is 727 and 3.91 gears in an 8 3/4 rearend. Cam grind specs are 244/252 @ .050”, 282/290 adv, .516”/.537” lift(1.5:1 rocker), 112 sep, .016”/.018” lash. Future nitrous is an option but not certain. Holley Super sniper EFI will be installed with the motor.

The question I am debating is do I use 3 inch or 2.5 inch exhaust? I have read a bunch and am still confused.

Then I read this thread New 3" exhaust with 2.5" Tailpipes and yet I did not see any performance evaluation.

I have the 2.5 inch adapters on order but can change them if need be. Thanks for the wisdom.
Click to expand...

Your build is very very close to mine , I ran full 3 1/2'' dumped in front of the axle , w/ turn downs . Home brewed 12'' bullit (roundy round) mufflers w/ 3 1/2'' spiral inserts slid inside, and tack welded , A little loud on the gas , but doesnt bother me inside.
I f u look up engine size versus exhaust size , a 500'' engine should have 3 1/2'' . Dont remeber where I found that tho , already had it built before hand. Had some used old exhaust wrap and wrapped them completly/nasty stuff !
Had to pie cut a couple of pieces to twist around under the drivers side cross member , into the straight pipes leading to the muffs.
You pobly wouldnt need to do the pie cuts , I have raised port heads , that raise the whole mess up some . Easy to do w/ a mig welder .
DEFINITLY DONT USE 2 1/2 !! Unless u just gotta go over the rear end -------
 
I stand by my full 3.5" recommendation. Anything less won't be optimal.
 
3" goes over the axle easy enough. TTI makes a bolt on system and you can modify their system to go to the bumper with a relocation kit.

20150430_150928.jpg
 
Kent mosby said:
I am prepping the final installs and have a question on exhaust.
My 73 scamp will get its 512 RB installed in the coming weeks. The headers are TTI 440-200 with 2 inch primary tubes with 3.5 collector to 3 inch flange. Trans is 727 and 3.91 gears in an 8 3/4 rearend. Cam grind specs are 244/252 @ .050”, 282/290 adv, .516”/.537” lift(1.5:1 rocker), 112 sep, .016”/.018” lash. Future nitrous is an option but not certain. Holley Super sniper EFI will be installed with the motor.

The question I am debating is do I use 3 inch or 2.5 inch exhaust? I have read a bunch and am still confused.

Then I read this thread New 3" exhaust with 2.5" Tailpipes and yet I did not see any performance evaluation.

I have the 2.5 inch adapters on order but can change them if need be. Thanks for the wisdom.
Click to expand...
with a engine like that I would definitely install the 3” . 2.5 would choke that big engine. Engine masters did a comparison on the dyno with a BBC with basic bolt ons and full 3” with tail pipes and 2.5 and lost quite a bit of HP the 3” was almost as good as open headers I believe it was a magnaflow system. Check it on YouTube. Those engines need to breath!
 
Last edited:
smokindust said:
with a engine like that I would definitely install the 3” . 2.5 would choke that big engine. Engine masters did a comparison on the dyno with a BBC with basic bolt ons and full 3” with tail pipes and 2.5 and lost quite a bit of HP like 40 or 50. I believe it was a magnaflow system. Check it on YouTube. Those engines need to breath!
Click to expand...
 
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