I'm looking for some real world examples on whether my hoagie would pick up with bigger headers. Current combo in a 3500lb E-body...
528ci Low deck, 12:1 on E85, Indy SR heads Max Wedge ported by Modern. 1050 Dominator. The car is setup for a decent amount of spray with a fogger. 3.73 gear, 28" tire, 2.28 first gear 727. Cam specs: .816"/.799", 284/300 @.050, 114LSA. Current headers are 2" primary 3.5" collector Super Comps that were probably bought during the Reagan Administration. I plan to run mufflers.

I would use 4" mufflers and dumpers for the track.

I have 3.5" exhaust and mufflers on the car now. I guess my main question is would it pick up power with larger than 2" primaries? If I do something, I'll probably step up to 4" exhaust too.

Not much to add,but my experience was with 2 1/8 primary's and 3" exhaust with 2 chamber mufflers it went 9.4's by surprise. wasn't expecting that.

Most likely the collector is too small and way too short. The 2 inch primary isn't so bad, but the collector is small and too short which is typical.

Bigger primary - if you can do it without a tight bend at the port to make the turn.

By too short do you mean the merge section of the collector or the overall length? Does the exhaust add to the effective length of the collector?

Kinda what I'm thinking too. I still have The bars and a factory steering box to work around too.

i have wondered about the collector/exhaust relationship before as well.
if running same size tubing as the collector to an x or h pipe, does that effectively lengthen the collector ?
or am i not taking something else into account ?

does that effectively lengthen the collector
Yes

I mean the overall length of a straight collector. And as poly says, exhaust length counts. You can also get too long on collector length too. If you are running full exhaust you live with the extra long collector.


I first learned there was an issue with collectors that were too short in the late 70's. My local track started requiring mufflers on everything. And the great majority of guys kept saying their cars went faster with mufflers, which to me was (and still is) counterintuitive.

The case was in fact collectors that were too short to begin with and the extra length of "collector" the muffler gave was why they were going quicker with mufflers. Had they started with the correct length and diameter of collector in the first place, the muffler would have always slowed the car down.


Of course, dealing with bracket racers who didn't really care if their car was .4-.5 tenths slower was also an issue. I still have not reconciled my mind to the mind that willingly thinks it's ok to go slower. But that's me.

Every car I've tested at the race track, both stick shift and automatic picked up ET and a tiny bit of MPH with longer collectors
On a low compression pump gas street motor, 426 Max wedge, it picked up HP and Torque on the DTS engine dyno by going from a set of Hooker BB A body 1 7/8 (42 inch long) with a 3.5 inch collector to a set of 2 1/4 primary 25 inches long with 4.0 inch collector
On your deal I would look at a set of 2/18 to 2 1/4 primary with 4.0 inch merged collectors or 2 1/4 to 4.0 inch collectors

The exhaust gas is looking for a change in area, in either direction: a step, collector, X pipe, even a really bad weld bead, whatever (but not a curve). Any of these cause a reflected pulse. If you're smart or lucky (I'll have to rely on lucky) the extra pulse "lines up" with an existing pulse (called superposition) at a useful RPM and enhances it. If not, it (partially) dampens it or does other evil things.
That's why the old advice "built some length adjustment into it" is still valuable.

Yep. Most guys would look at you like they swallowed a canary if you told them they need an "adjustable" header!!!!

Thanks for the replies everyone.
I was figuring 2 1/4 primaries with a 4" collector would have to pick up some power. If I lose some grunt down low, I can always lean on it to make up the difference.
How do you practically build in adjustment? Just move the collector position? Seems like a bit of a PIA to lengthen primaries. I guess the other question is how much to change the length?

I'd have to look at the current headers to tell if they are in the way of more N/A HP but, I feel it's unlikely. Conversely, if you are spraying a good amount there will be a gain in performance with the correct header. I agree that a nice 2.25x4 is about right based on what you describe.

I definitely feel like a bigger header will be worth power on the spray.

WOW, gave up all the info here !!

I can tell you from my real world experience. I went from Pro parts 2" to a set I made 2 1/4 with 4" collector. Really didn't pick up.
Now after getting my engine Dyno'd at BES, he says whats holding it back is the LENGTH more than the diam. He told me 25" long primaries. (my current headers have 35 - 40" primaries, but its hard in an A body without going fender exits) And we have pretty similar combinations.
Also I cant believe you have so much starting line ratio...?

I also think a lot of guys here are missing the point...this car has nitrous on it, and im sure plenty of it. I cant see collectors helping low end on this car..LOL

Haha! Well, I figured the only way to get good answers was with good info. Besides, the my junk is waaaay to heavy and down a few hundred HP to hang with you guys!
When you're talking collector length, is that the length before a muffler or including a muffler? I'm on the fence for fender exits. Half my buddies are twisting my arm to do it and the other half have threatened to beat my @ss if I cut the car that much. I'm surprised to hear yours didn't gain with bigger primaries. I know you're throwing some spray at it.
I had 4.10 gear with a stock 1st gear. That was plenty of SLR! Not sure if it could pull a Glide at 3500lbs???