Are exhaust manifolds really that bad?

Having a bit of an issue with my truck build. I was going to build a set of headers but am finding out space is very limited between the heads and upper control arms (maybe three inches max.). My only other option is to run a set of manifolds. I read on another topic that between the carb., intake and manifolds, the net loss was approx. 120 hp. Now, I'm not going to get that wild with this engine, as it's just going to be a driver. How much of a benefit would I see running headers and would it be worth it fighting to get some to fit? What about doing some port work to the manifolds, worth it? I'm at wits end here and it's really bothering me.

A little info: '81 F-100
Front frame stub off a '73 T-Bird (had to get rid of the twin I-beam)
460 was moved back in frame four inches
Right now the engine is a stock '71 with D3 heads but and going to build another with C8ve's (if that matters) Would like to see close to 500 hp out of the new engine.

Thanks in advance

I think you'll lose at least 50hp with stock exhaust manifolds on a 500hp engine. The more power you make ,the more I think they will hold you back.If I was going to drive it alot ,I wouldn't worry about the power loss.On my 66 Comet with a 390, it would lose over a half second in the 1/8 with manifolds on it.

For power production ... YES.

How tight of a bend does it start to hinder performance? The reason for asking is I think I found a bend that will work in the tightest spot (#1 cyl).
2 inch centerline radius, 1-7/8" tube
http://www.jegs.com/i/JEGS-Performance-Products/555/319220/10002/-1?parentProductId=1447417
That would leave it 3" out from the head, very tight yet. May be able to get a little closer by putting the bend into the flange a little.

Another question - When you insert the tube in the flange, do you just flush it up in the inside?

I'm thinking I really want to try to fab these up as I would like to see that 500 hp mark. Hopefully there isn't a tube stuck in the wall when I attempt this.

Hangman wrote:How tight of a bend does it start to hinder performance? The reason for asking is I think I found a bend that will work in the tightest spot (#1 cyl).
2 inch centerline radius, 1-7/8" tube
http://www.jegs.com/i/JEGS-Performance-Products/555/319220/10002/-1?parentProductId=1447417
That would leave it 3" out from the head, very tight yet. May be able to get a little closer by putting the bend into the flange a little.

Another question - When you insert the tube in the flange, do you just flush it up in the inside?

I'm thinking I really want to try to fab these up as I would like to see that 500 hp mark. Hopefully there isn't a tube stuck in the wall when I attempt this.

if it hangs into the flange, just use a grinder to smooth it back out.

On a mild build my buddy and I were almost identical with him having headers and me with manifolds. Our engines were almost identical with mine having better porting done to heads. He had 84gt I had an 86gt and he had a little better street tire than I had but his would go 12.80@118 spinning and mine went 13.10@124 also spinning. We had same lower end same compression, same stall same trans.... Both engines built to make 550hp on 93 octane. My manifolds were port-matched with casting flash removed so not just stock manifolds.

Take that as you will but that has been my experience.

bigblok2000ranger wrote:On a mild build my buddy and I were almost identical with him having headers and me with manifolds. Our engines were almost identical with mine having better porting done to heads. He had 84gt I had an 86gt and he had a little better street tire than I had but his would go 12.80@118 spinning and mine went 13.10@124 also spinning. We had same lower end same compression, same stall same trans.... Both engines built to make 550hp on 93 octane. My manifolds were port-matched with casting flash removed so not just stock manifolds.

Take that as you will but that has been my experience.

You have me thinking again...
Do you remember what heads and manifolds you were running?


I guess for some reason I have it stuck in my mind I have to have headers. I just need to realize that this isn't a full out drag car, just a cruiser. Maybe it'll go to the track just to see what it can do, but other than that...

This project would be soo much easier if manifolds were used, BUT I'm not sure that's the right way to go yet. Somebody convince me.

How many of you are running manifolds and are happy with the performance?

These mite work.

http://www.429-460.com/t11122-cobra-jet-exhaust-manifolds

Manifolds suck, but you can help tham a little by not using an off the shelf cam, give randy Malik a call about a custom cam to use with manifolds.

The guys in F.A.S.T run in the 9's with manifolds..... Heavily modified, but stock appearing......

Hangman wrote:

.....How many of you are running manifolds and are happy with the performance?

I run the D5 car manifolds on my gray T-Bird bracket racer.
From what I have read, you would probably be fine with manifolds in your F-100.
As posted above, once you get into the 500 hp range, then manifolds are real chokers.

I have a set of truck D5 manifolds and they are much more impressive looking than the passenger car manifolds.

I guess now I'm kind of convinced to just run manifolds. Can always do some port work to them. Port match and a good clean up inside. That will make this a whole lot easier. Since it's just going to be run on the street, I'll change a little and go for a smooth curve up to about 5-5500 rpm's as long as I can keep the torque up a little. D5 truck manifolds? Hmmm, I think I know where a set of those are, have to go look Friday.

res0rli9 wrote:These mite work.

http://www.429-460.com/t11122-cobra-jet-exhaust-manifolds

Wow, I didn't realize CJ stuff was going for that now!


Thanks for all the input everybody, appreciate it!

For a really tight turn you can make it with these. http://www.pro-werks.com/partlist/979/

What about some Sanders Shorties?

dfree383 wrote:What about some Sanders Shorties?

Just checked them out. It's nice they have dims listed. All of them are still too wide (or deep) though. I only have about 3" between head and upper control arm. Very tight.

Those mild steel donuts are pretty ingenious. Never knew they were made. Looked at a couple of dealers and can't find them on their websites. Must be a special order.

I'll find out this weekend what I can get a hold of. Few phone calls to make.

3" is actually quite a bit IMO you need to get some manifolds and fit them the see how much space you have. Then compair to something like those sanders.