Modifying 360 Degree Headers - What Next?



Modifying 360 Degree Headers - What Next?

Postby phantomjock » July 15th, 2014, 12:46 pm

Grumpy -
I am back to working on my beast, a 383, Weber-ized '78 Corvette Track-Car. As background - probably looking at 450 HP/420 QT, and will run a redline of 6500 RPM. The Torque curve runs fairly flat from 3000 to 5500 (390 and above) - again, that is all on paper and the curves and desktop dyno are posted elsewhere here..

I've read and re-read many of the postings here and elsewhere - a particurally good one :
viewtopic.php?f=56&t=185

And, I note with some interest you had recognized Jere Stahl's 360 degree headers. That is what I have started with:

Stahl 360 cross over headers pairings.jpg


Fortunately, I've set my engine back over a foot so I now clear the rack and pinion I've installed. The road race Canton oil pan I've installed also ensures under engine clearance for the header joins.The pic below, not my Corvette - but similar brings the questions forward.

Setup question.jpg


I've significantly modified the headers. Now, all the primary's are now very close to the same length, and now exit as in the image above, that is to say, as side pipes and not under the car.

My Pics
Revised Left side Stahl Headers.jpg
Revised Right Side looking to engine.jpg


The Stahl's are not a 4-2-1 configuration, that many of he online calculators use, but here is a snapshot of some of the results (using Desktop Dyno inputs from my engine):

pic - calculator
EXHAUST SIZING CALCULATOR.jpg
Header Primary Length Calculations.jpg
My primary tubess are 1.625, so that checks prety close and the lengths are now all "relatively" close to 39-40 inches from cylinder head mount to first 2-1 merge collectors. But, These are not you "average 4-2-1 setup so that is why the questions...

The page I found the calculator on had the following pic for reference,
pic 4-2-1
421 exhaust system.jpg


and I've made some notes you'll see mine is not your average 4-2-1 setup, but maybe a 4-2-2:

My 4 into 2 into 2 xhaust system.jpg


I've checked Victory and other pages you've recommended in the past - but still come up needing some advice regarding what I should do for exhaust. I know we can "tune performance up/down" based on length of tail pipe - but I need a good starting point.

Should I keep the Stahl's flowing into 2 separate (duals) on each side - kind of like the Blue car above -
or merge them as they exit the frame into 2 singles (on each side)?

pic - CAD
ExhaustTail Pipe from 360 headers.jpg


Any recommendations on what diameter and length I might use for the tailpipe section? If I can get to 2 1/4 ID there are spiral/auger traps available - as I'll need to meet track side dB levels. And, naturally larger is possible too.

The calculators seem to suggest 2 1/4" - 2 1/2" for diameter might be close, and maybe 36 inches or so for length, but I need some advice and experience here. Should I join each side - or keep separate (duals)? In other words, should I try and do a 4-2-1 "like" setup - or make as a 4-2-2, and use a cone like "silencer" as you suggested in another thread?

Your thoughts, recommendations, suggestions are much appreciated.

Cheers - Jim
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Re: Modifying 360 Degree Headers - What Next?

Postby grumpyvette » July 15th, 2014, 2:31 pm

you ideally want to have a 4-2-1 config with each step up in diam.as two smaller tubes join a larger remain as small as practical while still allowing the twin feed pipes to fit into the larger pipe they feed into,thus the internal area of a 1.625" primary pipe is about 2.01 sq inches, so at least in theory a 2.25 inch diam could be swaged to fit and allow the twin 1.625' primary to feed, but in reality the 2.5" is going to be more practical taking the tubing wall thickness into account, Id then feed both those into a single pipe of the smallest practical size that will physically fit

http://www.summitracing.com/parts/FLO-C134218234/
Image

I generally just buy the set of these and weld them on,to the primaries cut to 36"-38" as it saves a great deal of work and the results have proven to be similar, ideally the two collectors feed into an (X) pipe with fairly long tail pipes as this seems to help the torque curve be a bit broader , even if it does cost a few peak ft lbs
Image


Image
Image
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: Modifying 360 Degree Headers - What Next?

Postby phantomjock » July 15th, 2014, 5:34 pm

Grumpy -
Good info and ideas all at once!

Where do you source these:
xpipe setup.jpg


The idea of 36 - 38 inches sounds about right too. Those look pretty sharp and a very narrow footprint - for being an X-Pipe.
Do you get locally - or have an address? (I found theothers and some similar to the Summit brand - but not these.)

Thanks - and Cheers - Jim
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Re: Modifying 360 Degree Headers - What Next?

Postby grumpyvette » July 15th, 2014, 5:38 pm

http://www.summitracing.com/parts/sum-642135-ss

I grabbed the picture off summit racing, but I generally have a local muffler shop bend pipe,to match my measurements, I then carefully cut and weld it to fit the application

don,t forget to duct tape all 4 open tube ends with duct tape and flush the air out when welding
viewtopic.php?f=56&t=961&p=15359&hilit=weld+stainless#p15359
IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
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Re: Modifying 360 Degree Headers - What Next?

Postby phantomjock » July 16th, 2014, 3:27 pm

Grumpy - Thanks for that link - I looked all over Summit and could only find Narrow X-pipe! DOOH. Like the idea of using a local shop to fab though. Much appreciated.

BTW - if anybody is interested in any STAHL Headers, components, header parts, or other bits, Jerre and Judy are Retiring after 50 years. Lots of bargains were probably had at their parking lot sale last weekend - and some stuff may remain in the shop too.

Cheers - Jim
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