Ok, I'm not exactly sure where to post this so my apologies if you think it belongs somewhere else.

Anyway, here's my dilemma. The car in question is a 1991 Formula, which is a 3rdgen obviously. The engine is a 350 with Trick Flow 23° heads, a Holley Stealthram, and a Procharger. There aren't many header choices that I feel will support this engine, my power goal is around 500rwhp, and this is a car that is driven on the street.

I actually have three new sets of headers in my posession that I can use. SLP 1 3/4" shorties, Hedman 1 5/8" long tubes, and Hooker 1 3/4" Super Comp long tubes.

First off, I think SLP would be the worst choice of the three, as far as power goes. The collector is 2.5" and then the cat pipes neck down close to 2" ID(!), I guess they would be considered 2.25". Another problem is that for some reason the SLP's for L98 cars have a 1.25"x1.25" opening in the header flange, which is smaller than the D-ports in my heads (around 1.35x1.45") Otherwise, these are nice headers and would offer the best ground clearance.

So, that brought me to the Hookers, which seem to be the obvious choice. However, if you've ever seen these headers on a 3rdgen.. they hang VERY low. I don't know if it would be a great idea to drive the car on the street (the car does have aftermarket springs).

Which brings me to the Hedmans, which I bought because they were inexpensive and I thought I would at least check fitment with them. Believe it or not, they actually tuck up better than the Hookers a bit. Still, long tubes on a 3rdgen are horrible just because of the design of the car.. 4thgens are a lot better off. I think with some creative exhaust work and a custom transmission crossmember I could make them work.

Ok, so cliff notes. If you had to choose between 1.75" primaries with a 2.25" cat pipe or 1 5/8" primaries with a 3" pipe, which would work better in this application? And, when comparing the long tubes to each other, is going with a 1.75" primary at this power level worth losing even more ground clearance? How much power am I leaving on the table if I go with smaller headers?

 

Between the rock and the hard place, huh?

IMO, 1.75 and 3 inch would be great, but that's not the option.

I'd go with the 3 inch collectors even though the 1-5/8 primaries might be a tad small. At the upper power range there's going to be lots of exhaust gas, so putting a 2.25 collector on it is like putting in a cork. Make sure that everything back of the headers is free flowing, especially the mufflers. Putting on a great -flowing header/cat/pipe system and then stuffing in into a "no-flow" muffler will cost you maybe 10-15% of your 500 rw.

The high-end answer is a set of custom built 4-2-1's designed for your car and application. They would be almost invisible and tune and flow like crazy. You are talking probably $2500 minimum, but "speed costs money, etc."

Cliff notes: Smaller primaries and 3 inch collectors and pipes and free-flow muffler(s) would be my choice.

 

Same subject:

http://web.camaross.com/forums/showt...hlight=headers


The long-tubes scavenge exhaust (pull) out of the cylinder. In some well-tuned NA applications, the long-tubes can pull a vacuum on the cylinder during overlap, which sucks intake air in. This can be bad on a supercharged engine because the intake positive pressure can push air and fuel through the cylinder and out the exhaust. A vacuum in the chamber will only make this worse.

So, with a LT header, you have to reduce cam overlap even more to prevent this.

A LT header is more restrictive on top-end than a shorty, so a 1 5/8 LT is far more restrictive than a 1 3/4 shorty. I wouldn't even consider the Hedman's. Also, the port opening on the Hedman is very small and the tubes will interfere with your frame. I spent some time cutting the frame of a friend's '87 T/A to fit the cheapo Hedman's.

If I were you, I'd use the SLP's if you want peak hp or the Hooker Super Comps if you want a good curve and alot of torque.

Another data point is that I ran 11.09 at 122.6 mph with the SLP shorties / 2.25" y-pipe in a 383, AFR210, hyd. cam, carb'd '89 Firebird no nitrous or supercharger. The SLP's aren't bad, even with the small Y-pipe.

Mike

 

With the question's emphasis on "forced induction"..... moving to the "Forced Induction" forum....

 

Only two replies and we already have some conflicting opinions. This is good.

This is pretty much what I was thinking as well. I plan on running Dynomax mufflers, possibly in a dual system with an X-pipe or in a large single configuration. Whatever exhaust I end up with will be custom built.. custom built headers are just about out of the question, though.

Very interesting. The cam does not have a lot of overlap as it is, it was chosen with the blower in mind. So, I wonder if that is something I'll need to worry about.



Is the 1 5/8" LT really more restrictive than the 1 3/4" shorty considering the smaller collector? I understand the part about primary length affecting powerband but I wasn't sure which would be the lesser of the two evils there.

Another note -- believe it or not, the Hedmans have a 1.5" round opening in the flange, which matches my D-ports better than the SLP 1.25" square openings. These could be opened up and rewelded, I suppose..
I think a good torque curve would probably ultimately make the car faster, but I don't want to hurt top end power too much of course.

11.09 @ 122.6 is very impressive. Do you think the car would have been faster with a larger exhaust than dual 2.25"?

 

I've often wondered that myself. . .

The AS&M's shorties I just removed from my '95 have a 2 1/2" y-pipe.

George Baxter made some pretty stupendous supercharged hp (900 hp) with AS&M 1 3/4" shorties, but with a 3" y-pipe.

Mike

 

What you might be able to do is cut off the collector flanges on the SLP's, and cut the collectors to where they get wider near the 4-1 merge. Then when the diameter is big enough, weld on a 3" collector flange. Essentially you'd be converting the headers to 3" collectors. I used to have some AS&M's on my car with a custom 3" collector using this method and they worked great on my supercharged car.