skinny z

Question:
Who runs open headers at the track?

Pocket

iTrader: (24)

Unless there is a specific rule against it, why not

five7kid

iTrader: (14)

Because you'll be slower.

camshaftxe

skinny z

Not necessarily so.
If you just uncork the pipes and have no plans for the additional tuning then you probably would be slower. That's providing your exhaust pipes and mufflers weren't restricting performance too much.
However if you've calculated the proper header secondary lengths and make the required jet/fuel map changes, then you'll be faster.

five7kid

iTrader: (14)

Since you weren't specific about the type or length of headers or any pipes after them, and did say "open headers" rather than "open exhaust", my statement stands.

skinny z

And you would be right.

five7kid

iTrader: (14)

You are correct when you say proper length tubing will produce the best results. However, in our cars, that isn't easy and approaches impossible, especially for street-driven cars.

Assumption #1: Forget open exhaust if you run shorties. There is a slim possibility that you will be a little quicker with cut-outs in place of dual cats, but in that case the "secondary" length, as you called it, won't be the same for each bank, and won't be optimum for either bank. If you are faster with the cut-outs open, it just means the rest of your exhaust is restrictive.

If you have long tubes, you might be able to get proper length after the collector, but making it quick/easy to uncork at the track isn't going to be easy, and cut-outs are going to make the exhaust turn a corner. It's much easier and makes more sense to make the rest of the exhaust free flowing enough so you don't bother uncorking at the track.

A little qualitative data from my experience/efforts/foibles:

Back in the 2002-2003 timeframe, I had 3" Warlocks on the '57. I ran in two classes that allowed open exhaust, and one that didn't. They actually worked pretty well when open, but the data from those races didn't help me when mufflers were required, and the Warlocks flow horrible when corked. Toward the end of the 2003 season, I put Bullets in place of the Warlocks, and it ran as well as the Warlocks did uncorked - but it was really, really loud.

In 2006, I had put in a bigger cam, and was trying to achieve 100 MPH in the quarter at our 5800' elevation. I went out to a test and tune, and tried all sorts of combinations to get there, including open and muffled exhaust (I had 3" Summit welded mufflers on by that time). Regardless of what else I did, such as tire or air cleaner changes, it was always slowest when I uncorked the exhaust at the collectors (didn't have it set up to unhook at the mufflers). If I had about 18" of pipe after the collectors, it probably would have been quickest that way. FWIW, I never got over 100 MPH that day, but with other tuning tweaks, achieved it through the mufflers wind-assisted later in the season. From that day on and through last season, I never opened up the exhaust.

skinny z

I'm not too keen on running open headers because I'm still only 13.4 @ 102 (250' elevation) and I'd feel a little foolish. However for the purposes of testing and tuning, I'll try this season. I think my current exhaust is so poor that I have a few tenths and a couple mph available just by switching to LT headers with collector extentions. Still looking for 12's with a 218* cam.

1989GTATransAm

iTrader: (3)

With a tubular K-Member it might be possible to get an 18" collector on both sides and into a terminator box using shorty headers. I'm still looking into it. Any information appreciated. Not sure if the power gains would justify the money spent though.

Edit. With a tubular K-member it might be possible to redesign the headers into something better than shorties. Looking into that also.

skinny z

It seems that primary pipe length has less effect on performance than secondary length does (with respect to our v8 application, quoting Vizard and McFarland) and with that being said it would be reasonable to assume that terminator boxes onto suitable sized collectors with shorty headers would still be effective. Longer primaries do tend to favour low end just for the record. Generally 18-24 inches of collector length seems to be the norm with longer secondaries helpful with heavier vehicles and tight convertors. The longer secondary moves the torque peak lower in the rpm range.
As far as money spent vs power gains. There's a lot a data to support 10-20% improvements between a well tuned exhaust and the run of the mill set up. Probably something like going from manifolds to headers in the first place. You've just got to take it a step further.
It's finding the optimum length before terminator boxes are built that is the challenge.

1989GTATransAm

iTrader: (3)

I'm at the 440hp level so a 5% increase would be 22 horsepower and a 10% increase would be 44hp. Something in that horsepower range would make it well worth the effort.

PipeMax says my best collector length is 18.3 inches long. For the primary tubing it says my pipe diameter should be 1.576". That would be a 1 5/8" header. I currently have 1 3/4" headers. Maybe to big?

For the header primary tube length it says 21.0" ( 21-24.1") is the shortest recommended. 30.2" (30.2-33.2") is highly recommended. Next is 54.8" and longest recommended.

The 21.0" is the one that got me going as I might be able to make up a set of 1 5/8" headers with that length of a primary tube. The 30.2" is right around the length that the current long tube headers are made at.

Still researching as this won't happen until late in the year. Maybe one of you will have some results by then.

Orr89RocZ

iTrader: (20)

I think that gives up more torque than hp but both will suffer if you go too big. I still think your combo could use the larger and it wont hurt that much if at all over the smaller tubes

My car should be ready to start up by the end of april if the parts get here in time I dont know if i'll drive straight to the track with open heads to do some collector length tuning or just wait to do full exhaust with cutouts just to keep it quiet

i can imagine a big cammed 11 to 1 383 with open headers will be god awful loud thank god i dont have to drive to far to the track

1989GTATransAm

iTrader: (3)

Hopefully you will have some results by this Summer. That will give me a big clue as to which direction I should go.

Orr89RocZ

iTrader: (20)

i'll do what i can with what i got, to help show some light on this subject and get some hardcore data/facts. i'm as interested in the results as much as anyone

skinny z

[QUOTE=Orr89RocZ;3714668] or just wait to do full exhaust with cutouts just to keep it quiet

Probably makes sense to do it that way. It still gives the option of tuning.

unionfootball06

yea i just put headers on with a new y-pipe and im running open y-pipe... i cant tell that much of a difference

camshaftxe

On stock lo3 heads and cam you wont notice much difference, maybe 5 or 10 rwhp but nothing radical. Also injecting more fuel will not compensate for having no back pressure.

5678TA

someone call me???? 11:1, 385, 306S cam, long tubes and turn downs?? did it once and damn..

Orr89RocZ

iTrader: (20)

sounds like my motor man how loud is it? lol

5678TA

just like every other drag car.. yelling at your passenger loud..

Orr89RocZ

iTrader: (20)

thats exactly what i'm trying to avoid right now i dont mind trying to break the motor in with open headers on the back roads during the day. BUT i can not have that on the busy streets for long

ninetyone

iTrader: (2)

open headers made my car very slow on the street.

skinny z

Open headers require collector extensions to be effective. Just leaving them open at the flange will kill all your low end torque.