Header Tuning

[JeffYoung]

One of the biggest places for gains on my car is in the header design. I've got a standard Tri-7 4-2-1 design now on both banks (car is a TR8, 3.5 liter V8), but have a 4 into 1 on teh way with LONG pipes back to the collector.

The fabricator (who used to race a TR8 very successfully in the Playboy Endurance series in the late 80s) says he lengthened them to gain back a little torque at teh expense of top end since he was running long races.

I run sprints (45 minutes tops) and want to use the headers to move the torque curve up a bit (peak right now is at 3500 rpm) and trade a little torque (which I have a lot of) for hp (which I am a bit down on).

I understand shorten the header pipes and the pipes behind the collector will do this. However, can somone point me to a web or book resource on how to calculate the correct length of the pipes for proper tuning?

I've done some internet searching with not a whole lot of success. I want to do this right and not screw it up because these headers were not cheap.

Thanks guys.

[Despr8dave]

I don't know how accurate we were, but when I ran stock cars, we put on long painted pipes, where the paint stopped burning is where we cut the pipe. Of course this was on a car that ran 1/3 to 1/2 mile ovals. Cheaper than a dino, and it seemed to work better than anything else we tried and it came from some very experienced and knowledgable techs. It was on an unmuffled system also, no noise meters to worry about. I don't know if it is usable or reliable for road racing, but just a thought...........

David

[Ron Earp]

I've heard David's method cited before and folks saying that it worked well. On the other hand, once you get the specs for the cam/port sizes/RPM range/Primary and collector diameter Adam said he would use his Ford simulation stuff on it to calculate it for you. He knows his stuff.

Ron

------------------
Ron
http://www.gt40s.com
Lotus Turbo Esprit
Ford Lightning
RF GT40 Replica
Jensen-Healey ITS
My electrons don't care if they flow through OEM wires, do yours?

[Tom Donnelly]

Jeff,

Look at Jere Stahl's website. It has some tuning info. http://www.stahlheaders.com/.

And Carroll Smith's books are great.

Tom

[JeffYoung]

Thank you gentlemen.

Jeff

[ShelbyRacer]

Originally posted by rlearp:
I've heard David's method cited before and folks saying that it worked well.


Also works well for locating the correct spot for a balance pipe on dual exhaust systems...



------------------
Matt Green
"Ain't nothin' improved about Improved Touring..."

[trd77]

Jeff, just a side note, my dad raced with T.S. in the playboy series. It was a blast to go to those. They even won the longest day at Nelson twice in their class

[chuck baader]

Jeff, because there is such a giant pool of knowledge in the nastycar community, I would suggest you calling someone like Bassanti or Dr. Gas and weigh your options.

------------------
Chuck Baader
#36 ITA E30 BMW
Alabama Region Divisional Registrar

[Quickshoe]

**** Ideal exhaust length: (measured from valve to collector)

L=(xc)/n

L=length in inches

x=crankshaft degrees from exhaust valve opening to center of overlap.

c=velocity of wave in ft/sec

n=rpm of peak HP

Take all your knowns and solve for your velocity (something around 1700 ft/second is pretty darn close to optimum)

Now take whatever velocity you have now and plug it back into the formula with the RPM where you want the peak to be and it will give you a new length.

Longer is lower peak/shorter is higher peak

**** Ideal Diameter

V=(P/60)*(D^2/d^2)

V= gas velocity
P= piston speed
D= piston bore in inches
d= exhaust pipe inside diameter

Piston speed= (stroke in inches*rpm/360)

Do the same--figure out your exhaust gas velocity now and work it backwards for the new desired rpm and you'll come up with a new inner diameter.

Bigger = higher rpm, Smaller = lower rpm

Something around 300ft/sec for your gas velocity is pretty close to optimum

sorry rotary and 2-stroke guys--not sure what a good range is for wave and gas speeds.

Now get figuring on how to incorporate a non-fixed length exhaust like the 2-stroke single speed road race karts use, known in the old days as a "slippy"



[This message has been edited by Quickshoe (edited December 28, 2004).]

[JeffYoung]

Quickshoe: AWESOME. Thanks a bunch. That is exactly what I needed.

I owe you one.

Jeff

[Boswoj]

Valves?.....We don' need no stinkin' valves gringo!

Boswoj (who's car goes hmmmmmmmmmmmmmmmm - well, kind of like a chainsaw goes hmmm.)

(EDIT: I re-read thr last post then figured I should add. A "slippy"? The Mazda rotary that was at Le Mans had an intake "trombone". The intake tract changed length with RPMS so it could make best torque down low and best HP up high. Do some karts do something like that with the exhaust?)

[This message has been edited by Boswoj (edited December 29, 2004).]

[Quickshoe]

Some karting organizations still allow the use of a slippy pipe in certain classes.

This link describes its' use:

http://www.tsracing.com/Techtips/TSslippy.html

This link has a photo of one...couldn't find a better picture that would explain it better:

http://www.tsracing.com/store/showdetl.cfm...D=1819&CATID=19 (http://www.tsracing.com/store/showdetl.cfm?&DID=7&Product_ID=1819&CATID=19)

How feasible would it be on a rotary? Hadn't done the math to see how long the range would need to be. Not sure how hard it would be to pull against the exhaust pressure either...

[gsbaker]

Nice work 'Shoe, as usual.

Slightly OT, but folks may be interested in a very good source of technical info in the form of an ad hoc link list on an F1 BB:

http://forums.atlasf1.com/showthread.php?s...&threadid=64787 (http://forums.atlasf1.com/showthread.php?s=&threadid=64787)

------------------
Gregg Baker, P.E.
Isaac, LLC
http://www.isaacdirect.com