What is the consenus on how well stock BB exhaust manifolds work? I have been considering installing supercomp headers, but...

I just had a chat with a long-time chevy mechanic/rodder and he said that bigblock, corvette-specific manifolds work very well, and that headers would not make any worthwhile performance gains, especialy with stock-style pipes that are squashed at the rear. He said that headers are not worth the expense, hassle, leaks, or the risk of bottoming them on the ground.

Now this is just his opinion, but he seemed to know Corvettes (better than I...) and I have heard similar statements from other people. But I have also heard the complete opposite in that headers can make a huge difference. I have seen a dynograph of zwede's 454, and he got something like 60 rwhp! Don't recall what other factors may have contributed to this.

What do the other guys with BB's and headers think? Please tell me what other mods your setup had at the time.

Does the story change if I add a better camshaft to the plot?




[Modified by Turbo-Jet, 8:56 PM 8/16/2001]

 

i have a 71 BB vert and yes headers make a diff. they are hooker 4 to 1 and side pipes. the inside stays cooler, the floor does not get anywhere near as hot. i bought a set of spiral inserts from a forum member and the fit and finish was great. you can feel the diff in the seat of the pants. a lot of times you can make a mod like a k&n air filter that makes more hp but you can't feel it with headers and the right inserts you can deff tell. robert

 

Cast iron exaust manifolds can be routed out and polished. Much room for improvement. If the BB manifold flows good to begin with, just imagine......

 

Well since I just got done with this swap, I guess I'm in a good position to comment. The car deffinitly runs better with the headers then it did with the manifolds, it's not a night and day difference but deffinitly a difference in the mid to high rpm's, none of my exhaust is however stock to go along with this so I can't comment on how much of a difference they would make the stock exhaust. One thing is for sure though, those stock air injection tubes have got to be quite the turbulance creater in the exhaust ports, I didn't expect them to be that projected into the ports. I'm sure you read my threads on the header leaks, I fought them for a while, eventually ended up doubling up a set of paper gaskets and pretty much took care of that problem, I do have a new set of the Earl's new header gaskets which look top notch with a large graphite sealing surface on them which is plenty thick which I'll probably end up installing if the paper starts to leak. as far as ground clearance, I ended up with about 4.5"s of clearance and haven't scraped anything yet, and I've been over a few speedbumps and some pretty tall curves, albeit I do take them very slowly, but I don't see my ground clearance as being a major issue. My mods are the same as in my sig. I haven't added a cam yet either, but headers normally help out even more as the more breathing the rest of the engine can do.

:cheers:

Pat Kunz

 

The stock exhaust manifolds are good but... The more powerful the engine, the bigger the difference headers will make.

Chuck

 

QUOTE]What is the consenus on how well stock BB exhaust manifolds work? I have been considering installing supercomp headers, but...

I just had a chat with a long-time chevy mechanic/rodder and he said that bigblock, corvette-specific manifolds work very well, and that headers would not make any worthwhile performance gains, especialy with stock-style pipes that are squashed at the rear. He said that headers are not worth the expense, hassle, leaks, or the risk of bottoming them on the ground.

Now this is just his opinion, but he seemed to know Corvettes (better than I...) and I have heard similar statements from other people. But I have also heard the complete opposite in that headers can make a huge difference. I have seen a dynograph of zwede's 454, and he got something like 60 rwhp! Don't recall what other factors may have contributed to this.

What do the other guys with BB's and headers think? Please tell me what other mods your setup had at the time.

Does the story change if I add a better camshaft to the plot?




[Modified by Turbo-Jet, 8:56 PM 8/16/2001][/QUOTE]


That's a new one on me!? :confused: :bs :confused:

 

I've never tried the stock manifolds but from what I read in the chevy manual they said " Headers really wakes a bigblock up to the tune of about 30 HP over the best cast manifolds." I have never had a problem with ground clearance or leakage. I use the cheap gaskets, cut the flanges almost through between the pipes and use silicon. Never had a problem over the years but I do remove my headers every winter for some reason or other.
Norval

 

BB corvette manifolds are very good for manifolds. LS-5 needs cam then headers. The more power you have the more headers help.

:cool:

 

Anything that can be done to ease the flow and increase scavenging up near the engine will help. The issue is less pronounce towards the rear of the car. As the exhaust moves downstream it expands, cools, and slows. This is why the bends rear of the axle and the 2" outlets on the mufflers don't hurt all that much compared to similar 'defects' upsteam.

The BBC manifolds are certainly some of the better designs compared to the standard GM log-type, but they're not up to performing like a header. Headers are almost always a great addition. Of course you open yourself up to potential customization on the exhaust, collector leaks, ground clearance problems, and steering/frame interference; but a good designed header won't have too many of these problems and will give you a decent performance gain.

 

I can't really comment on headers on a Vette but I can say this. I had a GTO with headers when I was a kid. EVERYTHING about them is a PIA. They make a lot of noise, they leak if not tightened all the time. Forget doing any work under the car. Starter removal is impossible. I know that depends on the brand of header and the application but generally speaking Vettes don't have a lot of room and a Big Block only makes it worse. Now add headers ....not this guy. Also they have more surface area by far than the stock manifolds. This only serves to allow more heat to disipate everywhere, gotta warm up the cockpit. Not that the engine creates more heat but there sure is more surface area to spread the heat around. Oh yeah routing wires to the starter that can be more fun also.

As to perf improvement. Some improvement , certainly so on the track but on the street when closed up? I don't think so. Likely a slight improvement in gas consumption but given the BB what is going from 8 to 9 mpg or 10 to 11 worth as a trade against the annoyances? Zero to me.

For my money unless your racing on the track where every tenth counts forget it.... Kid Stuff.

 

Hooker supercomps work well on a BB vette.

Plug changes are no harder than stock manifolds. Starter comes off. Oil pan comes off. I use mid-price gaskets (mr gasket ultra seals) with silicone around the ports and they do not leak. It is important to retighten once after the gasket compresses, but after that I have not had to retighten at all.

The perf difference is very real, as can be seen on my webpage. The test on the webpage was done when the engine was stock except a mild cam (219/229 flat tappet), torker II and holley 750.

 

zwede: what did you have for pipes? 2-1/2" crushed/mandrel bends? were the pipes flattened at the rear?

is there any way do get away from flatten pipes without major clearance issures? what vendors make a system like this?

thanks :cheers:

 

2 1/2" pipes with normal bends (non mendrel). Dynomax turbos, 2" tips. Not flattened.

 

Headers will not help you as long as you are running an unmodified intake manifold. That is were the biggest restriction is. It is possible to modify the stock intake manifold to work very well. The process is described in David Vizards "How to build horsepower, Vol.2". The TorkerII is a POS that you really don't want to mess with. A high rise manifold means no more stock LS-5 look. With a modified stock intake manifold you can pick up about 30 horsepower and still look stock. Then you can port out thew AIR bosses in the stock exhaust manifolds to pick up another 20hp. A 270 duration cam will then round off the package well. You will see about 75hp over stock for about 350rwhp from this set-up. And the best part is it will look bone stock.

If you want more power than that you will neeed a high rise intake, L-88 hood, headers and headwork. Definitely not stock looking anymore.

 

If you plan on having less than 400 horsepower, stick with the factory exhaust. If you want more than 400hp, even with low rise intake, get a good set of headers. I saw a dyno sheet some time ago, maybe it was even on this forum, that showed a ZL1 Camaro producing 270 hp with factory exhaust system and approximately 550hp with open headers. Yes, the exhaust manifold is not as good as the Vettes; but, the Vette's is not that much better. As I said earlier and was restated by others, the more powerful the engine, the greater the difference headers will make!

Chuck

 

good stuff. thanks guys!