I've been playing around with exhaust header calculation programs and one of the inputs is the length of the exhaust port. Does anyone have the specs for the LS1 head or where I can find it?

Thanks.
:cheers:

 

:lurk:

 

On a LS1 head, short side scales about 2-1/4 inches, and long side about 4 inches. 3 inches looks like a good average approximately centerline length.

What program?

 

Thanks friend. The program is on this site: http://www.headerdesign.com/index.asp

you have to register, but it has interesting results. I was using @ 2.2, so my header results should be close. The program on the site allows you to choose where you want the power band to increase, giving up power on the top end. The scale ranges from 1 to 10, with 4 being the RPM range typically used on the street, e.g. rice rocket is messing with me on the interstate at @ 55 MPH and I want to punch it. My A4 will drop into 2nd at @ 3500-4500 (haven't looked at it, exactly :) ) and pull from there. So, my thinking is I want midrange to upper midrange power. Looks like all the LT's available right now, according to this program, are closer to 10 on the scale and actually have primaries larger than that, for a lightly modded 346 ci like mine. Even shooting for 405 to 485 HP at the crank, the program is telling me that I need 1-5/8" primaries with @ 34" length. The closest high-quality LT made is the LGM, but it's got 1-3/4" primaries @ 32" long. The one neat trick LGM did was effectively increase the length of their 3" collector (I need a 2.5" for what I want) by using 3" pipes downstream to the x-pipe junction. The collector length effectively extends from the primaries all the way to the x-pipe, which is quite a distance.

When I e-mail the header mfgs. asking for the details on their headers, they conveniently leave out the primary lengths (or have to 'guess') and I've never gotten info on the collector length :(

I'm going to continue studying the subject, especially as I get closer to purchasing and installing a set. High RPM RWHP doesn't help me since I'm not looking for a land speed record or hitting the drag strip competitively, and I definitely don't want to sacrifice my low end for high end horsepower.

 

Thanks for the site info. I'm still digesting the Terms of Use legal document before I register.

If you want to use headers to maximize midrange torque or more correctly boost torque at peak, there is a formula for primary diameter that does a pretty good job.

The current Car Craft (12/03) has a good header article (the one by Jim McFarland on pg. 62) that explains the formula.

Basically, a 1-5/8 primary helps peak torque around 4000 (346-350 engine), a 1-3/4 around 4400 and a 1-7/8 around 5000.

Had to laugh about manufacturers not knowing primary lengths. Many of them vary a couple of inches from pipe to pipe and they don't really want to admit that. IMO, trying to hold a primary to a fraction of an inch is not necessarily helpful: you may have a perfect header tuned to the wrong rpm.
One view says that varying length primaries tune different cylinders to slightly different rpms around a point and fatten up the torque curve.

IMO, adding 2 or 3 extra 90 degree bends to a primary just to get a length may hurt the flow more than help the tuning. Every 90 degree bend has the extra flow restriction of feet (not inches) of additional length.

My $.02

 

TopCat,

I'm glad you find the program interesting! I just wanted to make sure you realize that most headers come with just a collector stub. You are responsible for making the entire collector length correct to the expansion in the x-pipe. If the header you use has oversize primaries or collector, the program instructions tell you how to adjust the lengths to correct the wave timing.

Also, since the correct headers will pull up the entire midrange, the peak HP RPM might actually decrease while the HP magnitude increases. So be careful if you are using stock RPM specs.

And those LGM longtube headers with collector and x-pipe are an excellent example of how your finished customized headers should look. It looks like I might have designed those header/collector lengths, but I did not.

Let me know if you have any questions.

 

OldSStroker,

Membership and program use is free to individuals. You should read the Terms of Use, but it basically tells you:

1. That you are responsible for your engine project
2. If you are making money with the programs, you probably owe fees.

Individuals pay fees for custom engine designs only. Matching custom cam and header designs are the favorite. The cam and headers are the two engine components that you can truly customize to your exact requirements.

I don't agree with the idea that header pipe lengths should vary to help broaden the torque curve. If you are using the correct header design, the header will work over a broad RPM range (or a narrow one if that is how you designed the header). If you get the primaries within a couple of inches in length, and the collectors equal length into the x-pipe, you will get excellent wave cancellation in the tailpipes. More importantly, you will kill the residual tune in the collectors. This allows each primary to use the collector as an expansion chamber essentially without interference from other cylinders.

 

Nope, didn't realize that. Semantics can get in the way sometimes :D

Didn't know that, either. Time to do more studying :cool:

[EDIT: (Now I get it!!! Duh. Was re-reading your reply and it dawned on me) So, it sounds like a little hit and miss without quantitative data to use for interpolation....and since I don't own a dyno, there's little chance of data collection on my car alone. There's got to be a way to closely estimate this, though. Especially if I can dig up dyno numbers on enough Vettes on this site, know their mods, and know which headers they're using....but that's almost too much work for a armchair/shadetree mechanic like myself :jester ]

Yeah, they're a great looking system. Guess I need to study more, as mentioned earlier, and maybe I'll be able to make minor modifications to the LGM setup to fit my requirements. Don't know if I can compensate for those large 1-3/4 inch diameter primaries, though. Guess I'll head back to the design site and see if I can figure it out. If not, you'll be hearing from me in the future :D

Thanks for the response!!! :party:


[Modified by TopCat, 2:06 PM 10/29/2003]

 

What I meant was that when switching from exhaust manifolds to headers, the upper midrange torque frequently increases enough to actually lower the peak HP RPM from the stock peak. This is a good thing. The most extreme cases I see are with I-4 engines. Stock with the manifolds the factory specs might say peak torque at 2800RPM and peak HP at 6000RPM. Add the headers and the torque curve pulls up at all RPM. The new torque peak goes to like 3500RPM, and the peak HP goes to like 5500RPM. The correct input value for the Header Design Program was 5500RPM not 6000RPM. So just look at Forum member's dyno plots with headers and your basic engine configuration.

 

Yep, like I mentioned, I finally figured out what you were saying and you verified it.

Don't think my employer will appreciate me looking for all those dyno charts :lolg:

Maybe I'll just post a request on the boards to have people post their charts!

BTW, what do YOU think the primary/collector sizes should be for a stock or slightly modded 346ci engine with no. 4 performance results????

:cheers:

 

In the neighborhood of 400HP you would use 1 5/8" into 2 1/2" collector if you insist I guess. Dyno results with a 1 3/4" into 3" header might not differ too much from the correct size header, but driveability and throttle response will change noticeably. Watch your tach and throttle foot, then let your driving habits dominate your header design (cam, too).

 

Thanks for your help. Those are pretty much the numbers I arrived at, too, but now I have to find a manufacturer that makes something like that :D Wish me luck!