formularpm

I am currently buying parts for my new combo and Im to the point where I need to choose headers (shorties). I know this has been discussed over a million times, but I cant seem to find this in the archives; Ive heard conflicting ideas on this subject, so Im just trying to clear some things up. It is a widely accepted idea that 1 5/8 headers will increase low end, but it is equally accepted that any increase in exhaust potential can allow enough extra flow (exhaust) to make a higher-duration cam come on earlier and make more power below peak. I want top-end for this combo, but I would like to try to retain as much low end as possible, Ive only got 3.45 gears and an automatic. My combo is 200cc aluminum ProToplines, HSR, 224/230 112* Comp, (or possibly 230/240 110*, havent decided) stock 9.XX:1 compression, and stock bottom end. I dont plan on revving past 6K. Ive already got Hooker 1 5/8 SuperComp shorties, my question is, would purchasing a set of SLP 1 3/4 shorties net enough extra power in this combo to justify the hefty price tag? Would the low end be better in this combo with the 1 5/8s or the 1 3/4s? Opinions are welcome, but if anyone has any experience with this type of combo and shorties, Id appreciate the input. Thanks.

92 zzz28

Have you tried posting/searching in the exhaust forum?

I don't think you would notice much of a difference with the SLP headers. As it is, the Hookers you have now should be suitable for what you are trying to reach. You didn't mention engine size, or I missed it, so I assume a 350. I think you will be okay with the ones you have...

formularpm

Yeah, Ive done quite a bit of searching on the subject, but most of the threads Ive read usually either relate to near-stock engines or end up degrading into discussions about why longtubes are better. Im kinda hesitant to post in the exhaust section, I figured maybe Id get better responses here than 'SLP says to use 1 3/4 on 350s'.

92 zzz28

Sorry I can't be more help. I am running Long Tubes. I considered the SLPs but for the price and performance, the LTs just made more sense to me. More work and expense to install though...

AJ_92RS

David Vizard says to use the following formula.

You have to know the exhaust port flow @ 28"/H2O

92 zzz28

What is that going to tell you?

AJ_92RS

What did he ask?

What size headers to use.

cp87GTA

I know you didn't ask about the cam selection, BUT, you do know the larger duration cam and 345s are going to make it LAZY on the bottom end. 1 3/4 tubes will let it breathe on top, but if it were me I'd use the 1 5/8 you already have. Only way I'd go to the 1 3/4s would be long tubes. With the little xe268 I'm running, and 342s, my car was a little lazy on the bottom. NOW the 4.10s is another story. My combo runs out about 5300/5500, sure the engine will wind up to 6000 but does NOT pull there. Are you burning your own chips? I hope so. I still don't have mine right.

F-BIRD'88

You can make 600 horsepower through 1-5/8" headers.
So your 1-5/8" headers are not holding you back.
They are the right size for your combination.
Improve every point beyond the primary exhaust tubes
to maximize performace before you worry about needing bigger primary tube headers. this includes the header to downpipe transition (collector), the Y pipe, mufflers(s) cats(s) etc.
Getting the exhaust system right is probabily the hardest part of
a winning combination.
You need about 2.2cfm of exhaust system flow per horsepower
for a non restritive system.
Most aftermarket stuff falls far short.
Plan on custom building parts of it.

www.flowmastermufflers.com
www.drgas.com

formularpm

I appreciate the input guys. I wish I could run duals FBIRD88, but sadly I have ZERO ground clearance since I lowered my car I had considered a Mufflex 4in, but thats a bit pricey as well.


Yeah I know itll be lazy on the low end, thats why I was leaning towards the 1 5/8s to retain a little low end. I havent chosen the cam yet, but Ill probably run the 224/230 if I stick with the 700R4, and the 230/240 if I swap to a 5spd. I think the HSR and ProToplines would be a good match for either one. My current PROM is from PCM for less, it costed $150 and works flawlessly.

305sbc

iTrader: (3)

If you want 1.75" primaries just go with some longtubes then.

formularpm

I cant, Ive already got ZERO ground clearance. I didnt exactly want 1 3/4s, I was just wondering how much they would hurt the already-lacking low end in my combo.

AJ_92RS

IMHO, you're talking about using mismatching parts.

You want to use a big heads, and a big induction system for high RPM operation, yet choke it with small primaries and a mid RPM cam???

Continuing the route you're on may leave you frustrated and upset. You're going to wonder why you don't have any low RPM grunt nor upper RPM HP.

As F-Bird said, 1-1/5" are fine for your application. But IMO, you're gonna be holding back the potential of the heads with that cam. I have a similar cam (230*/.480" I&E) under a pair of Vortecs.

My tires can tell you all about the low RPM grunt. Yet the car still pulls strong to ~5500 RPM. I'm running 1-5/8" long tubes with true duals and a 2500 stall converter.

If you give the Protoplines the cam they need, you're going to have to step up to a loose converter as well as a low rear gear (high numerically) like cp87GTA said in order to get the off-idle pull you're looking for.

Smaller primaries, long tubes, and a balance pipe will help, but it seems they're only going to mask the problem.

formularpm

AJ_92RS, I am going to be using the stock bottom end, so I wont be too comfortable revving it past 6000rpm. I realize this is kind of defeats some of the parts, but bottom end work simply isnt in the budget. If you think those cams are small, you shouldve seen the cam Comp recommended. (212/224, .487"/.489") Ive chosen 276 and 282 cams for the sake of not putting any power above where I can safely rev the engine. In hindsight I probably should have bought 180cc heads, but whats done is done. I will be buying a stall, but my 3.45s are brand new and will have to do.

Nixon1

Comp recommended a cam that small? Christ...what are they thinking... I imagine that cam would give you back some low end grunt though, being so slim on the intake duration and being a pretty low-lift cam... My 302 is running a mild as hell cam and it's beefier than that... (220/220, .498/.498, 110 degrees, EMISSIONS LEGAL. Boatloads of torque around 2 grand, horsepower from 3500-5000 or so)

I wouldn't exactly say you're already LACKING low end though.. If you're only able to yank a 2.4 60', that sounds like you've got plenty of low end....too much for your tires anyways! Your trap could net you at least low 14's.

formularpm

My current setup (using stock heads as of now) has plenty of low end, Im worried about the low end once I install the ProToplines. Using the cam Comp recommended for my heads would be a SERIOUS mismatch in my opinion.

88TPI406GTA

Remember that power is made with your heads, from the airflow through your heads...and the cam simply controls the powerband...if your redline is about 6000 rpm...then keep the 224 intake duration cam (at .500)

and the 1 5/8" headers will make at least 450 HP....

formularpm

406GTA, have you had your car on the dyno?

88TPI406GTA

No, I haven't had it on a dyno...

My info on the headers comes from a few different CHP buildups of a 406 including one with Vortec heads and another with the Trick Flow heads...each used the 274XE cam and made over 500 ft/lbs of torque...with 1 5/8" headers and a 2.5" dual exhaust system....

HTH,

formularpm

Just out of curiosity, wouldnt a larger primary create more of a 'step' down from the bottom of the port to the primary? Wouldnt this prevent some of the slower moving gasses on the bottom of the port/primary from flowing back into the chamber at low engine speeds?

88TPI406GTA

No...because the piston acts as a pump, forcing the gases out of the combustion chamber...no matter what the engine speed is...besides, what do you mean, slower moving gasses? There isn't enough of a difference to measure in reality...

formularpm

I mean the slower moving (in comparison to the top) gasses at the bottom of the port. I was under the impression that the faster moving gasses hug the top of the port, much like the long side radius on an intake port, while the gasses at the port floor can actually reverse-flow back into the chamber. This is part of what causes an engine to act 'cammie' and lack scavenging in the low revs. I dont see why the exhaust gasses would act much different than the intake gasses, and intake gasses do flow more at the top, as evidenced by GMs persistance at making ports taller and taller. Im probably wrong and just wasting bandwidth.