When do headers start limiting power?
 

I am going to be running a 3" exhaust. When would header size start to limit my power gains? What would a 5/8, 3/4, and 7/8 diameter be good to, power wise?

Cam

Re: When do headers start limiting power?
 

Depends on what's inside the engine, how many cubes, and a few other things...

Re: When do headers start limiting power?
 

Well the motor is a 305. I am going to be upgrading some parts of the motor: LT1 cam, 305 vortec heads, and a few other things. The next thing after that will be nitrous...starting with a small shot, 50 or so, but may end up being a large shot, 250+. I know that this doesn't warrant a set of big headers, but I don't want to buy another set when I go to a large shot of nitrous or change to a bigger motor and nitrous. Is there a certain horsepower number that the headers start limiting at?

Cam

Re: When do headers start limiting power?
 

Not real sure I'd go a 250 shot on a stock bottom end 305, those cast pistons are a bit fragile for nitrous.... General rule on headers is the same size, or just a bit larger then the diameter of the exhaust valves.... Doubt even with the Vortec heads you would need anything bigger then 1 5/8" tubes.... Or, if you're so inclined, a set of step headers seem to work quite well with nitrous... Guess I don't have a set of dyno numbers to back it up, but I have seen a number of cars take half a tenth or so off their times with step headers.... I'm really wanting to try the step headers and merge collectors on a nitrous engine......

Re: When do headers start limiting power?
 

1 5/8 primary with a 2.5 inch y pipe to a 3 inch catback will be fine for your application. As for a 250 shot good luck, can't see you engine lasting to long. Limit it to a 100-125 shot.

Re: When do headers start limiting power?
 

That may be what i will wanna do so after the cat you would use a 2.5 to 3" adapter to go to the 3" intermidiate pipe and your cat back system right? I just wanna make sure because the only choices I have found is the 2.5 to 3' cat back systems from the Y pipe would that be ok? because I wanted to go with a set that had a 3" collector to a 3" y pipe I thought that may be better but you have way more knowledge on it then i do

Re: When do headers start limiting power?
 

I think you would be fine with the 1 5/8 headers.


Mark.

Re: When do headers start limiting power?
 

It won't be 250 out of the hole or anything. I am planning on using a nitrous controller, Jacobs mastermind or something similar, and probably doing a two stage setup. I am going to start at as low a shot as whatever kit I get comes with...probably 50hp jet or so. I am planning on eventually doing a 100-125 shot first stage, and then a 100-125 shot on the second stage + the first stage...or shut off the first stage, and do a 200-250 shot second stage. I am going to set it up as best I can to make it last as long as possible...but if it blows, it blows. And if it blows, I will either do a 305 built for nitrous...or a bigger v8.

I am not too concerned with a half a tenth. I just don't want to spend several hundred dollars on headers, and then have to upgrade them again.

Cam

Re: When do headers start limiting power?
 

There will be no y-pipe...maybe an h-pipe, but I doubt it. It will be headers, to mufflers, to exit in front of rear wheels. The exhaust piping will definitely 3". I was just trying to get a primary size that I wouldn't have to change. I may end up going with some used 1 5/8, since I can find them at a pretty good price...but I was looking for some 1 3/4.

I don't really care if the engine pops, to be honest. It is a toy...that is all.

Cam