Has anyone come across a formula or discussion on approximating what the hp limitation is of the stock exhaust manifold? I am curious how much I can do to improve the power of my engine without changing the exhaust system. I other words, if I change the heads, cam, and fuel delivery, would I be wasting my time because it would choke on the exhaust restrictions? Everything I am reading tells me to avoid modifying the exhaust system in case they should start performing emissions testing in Michigan.

 

I can't believe that none of you have an opinion on this. Come on! Just give me your opinion from when you changed your vehicle from stock exhaust manifold to headers. If I know that it was only an improvement in top end, I would not be too concerned about changing the exhaust.

 

The whole idea of a preforming engine, is to get the fuel in and the exhaust gasses out.
I'm sure that someone has developed a formula for determining a ratio for intake and exhaust applications. The better the flow, the better the preformance. I have heard that headers can add as much as 35 hp, but personally, I have no proof. Not having access to a dyno, I really can't give you any numbers.

On another note though, headers do look cool.

 

Hi Batmobile, I haven't come across and formula to figure that out but you will not get the full potential out of your engine without headers.
Lets say you get a 600 to 700 cfm carb and put it on a high performance intake manifold, change to a streetable cam with a max valve lift of .500 and up to 290 degrees duration, get heads with 2.02 / 1.60 valve combo and then block it off with your stock exhaust. See the problem?
Choice # 2 Get a stock or aftermarket intake manifold and carb and get a free flow cat. You'll geta little moreHP and you'll be legal.
Just my 2 cents worth, PG

 

The Corvette "rams horn" manifolds are one of the more efficient cast iron manifold out there. Chevy used them for years. That being said, if you change (improve) intake, carb, & cam, then headers will probably improve things. Be careful not to get ones with too big of tubes. Also if you go headers, strongly recommend getting them coated with Jet Hot or equiv. It really cools down the engine compartment. Works well on cast iron manifolds also.

 

I'd like to point out, "Rams Horn" exhaust manifolds were only available on small blocks. I don't know if GM still uses them, and if not, what year they stopped.

 

I think '82s were the last year for the cast iron version. Also seem to remember that the '84 had a stainless tubular version. Don't know how long that lasted.

 

Hey Guy's just had to chime in on this as I am in WI and live around alot of circle track racers , they have been using bezinski manifolds for years , they cast ther own ram horns and 2-barrel cast iron mainfolds and get them to flow just as good as headers , cause we all run stock o.e.m pieces in the stock calsses wink wink sniker snicker Later Big Jon

 

Sorry bout that www.castheads.com

 

Yes, even with just a carb, manifold and some ignition work you want headers. 1 5/8" tubes are what you'd want with a small block for the street. You can run a cross pipe ( "H" -one side to the other) about 18 inches back from the collectors to give youthelow end torque with the headers. To a point, the better quality headers, the more hp you'll get from them. The prior posts are right, you want the engine to breathe. When it inhales hard, you want it to exhale equally. Let us know what you do.