Header size

[Iowan]

What size of header is right for me, I might be using a new cam shaft too but that's another post, I need something that will not be super pricey but works well, I do know that I want Headmans, I really just want better power,flow,gas milage,and sound but the latter is not priority just me being youthful. I cannot do hacking, just simple reliable and requires basic skills (not because I'm lazy just because I'm not overflowing with knowledge or resources. But I will give more info on what driving I do. Hauling and towing,everyday driver,Mernards,dating(someday.)and going to church. Thank you.

 

[1987 GMC Jimmy]

http://www.gmsquarebody.com/forum/showthread.php?t=16911&highlight=Header

 

[Iowan]

except 15/8 kill hp. engine masters.

 

[Camar068]

yup engine masters.

https://www.youtube.com/watch?v=rTlHEOE2Zp4

1 5/8" in their video doesn't kill horsepower. Look at the graph....all three are pretty darn close. Unless 3-5 hp is a lot to you. [edit] there was a 10 hp improvement with 1 3/4' on that engine)

The dent test they did also was very cool and educational.

 

[1987 GMC Jimmy]

I don't know. What's the magic number for you as far as HP goes? I don't think an eighth or two of an inch will fruit that much more if any horsepower less than or equal to 400. Maybe even 450. Plus the fitment is clearly excellent. He didn't have to hammer on those headers and make them ugly at all.

 

[Camar068]

nah I posted because he said 1 5/8" kills HP. It's all dependent on the engine. Which made me think of the video I'd watched earlier this week, lol which is what he mentioned as well.....engine masters.

 

[1987 GMC Jimmy]

nah I posted because he said 1 5/8" kills HP. It's all dependent on the engine. Which made me think of the video I'd watched earlier this week, lol which is what he mentioned as well.....engine masters.

Oh, I didn't see your comment till after I posted mine, bud.

 

[74 Shortbed]

Full dyno high rpm pulls is a far cry from "Hauling and towing,everyday driver" duty, 1 5/8" is plenty adequate and will work just fine for his intent..

 

[Iowan]

Ok sorry,1987 GMC Jimmy.

 

[1987 GMC Jimmy]

You're fine, dude. They're right, though. Practical power on a practical vehicle is different then power made on a screaming engine on a dynamometer.

 

[Iowan]

So time for some more dumb questions, do I have to weld? Can I use 1 pipe instead of 2? Can I use the stock exhaust pipe? Thank you.

 

[1987 GMC Jimmy]

It'll likely end up depending on the dimensions of your Y pipe so maybe or maybe not. Yes. And yes. Let's just assume that the collector on your new set of headers is three inches in diameter and your pipes are 2.5 inches in diameter. Behind your headers you'll need an aftermarket Y pipe that's three inches on the collector side and 2.5 inches on the exit side, and that'll bolt up to your pipe. You need a Y pipe that's pretty horizontal, not hooked upward like the stock one, because you'll be running long tubes that go down way farther than the manifolds. I just made those numbers up. You'll know the collector diameter when you buy the headers, and it'll probably be best to get a tape or a ruler and measure the exhaust pipe diameter where it bolts onto the Y pipe once you remove it so you know what sized aftermarket Y pipe to look for. If the exit on the new Y pipe is bigger than the stock exhaust pipe, you can get a reducer to adapt the two together.

 

[1987 GMC Jimmy]

A simple, supposedly direct fit, performance Y pipe like this, minus the O2 sensor bung, but you could get some type of threaded plug from the hardware store to plug that up if you really had to.
Edit: Well, I can't actually tell if that's curved or not. It probably actually is since one guy said he bolted it up to the manifold. Disregard the picture, but not the info. The correct Y pipe is the key to mating your headers to your single exit exhaust plumbing.

 

[Rusty Nail]

I use 1.5 primaries with 2.5 collectors. I use 2.5 inch pipe.
I think that size offers more useble power in more useable places more of the time for a typical street rod. That is a true statement and you don't have to agree OR like it, but it's still true.

 

[Iowan]

Ok so can you explain the y-pipe a little better.