Performance header design-Am I doing it right???

TheDullCarbide

TheDullCarbide

Active Member
#1
#1
To start off, I am working on a Greyhound 212 with the governor intact and the governor spring cut to give me 4400rpm no-load. I have about 1.5-2 degrees timing advance by slotting the holes in the coil pack and moving it down. It has a Comet TAV2 that engages at 2200 rpm and accelerates at 3900 rpm. I also cut out all the gas tank emission BS.

Other than that, it's a bone-stock Greyhound 212.

I want to make a scavenging header to target 3900rpm. I calculated 0.420" ID at 7' 3" long.:confused: I don't think that sounds correct at all, but I would have no trouble actually building something like that.

I want to know if it's better to use this design or just make a free-flowing exhaust like everybody else likes.
 
TheDullCarbide

TheDullCarbide

Active Member
#3
#3
I know about those 1" pipes and it seems those act as free-flowing headers for low rpm engines like mine and actually have scavenging around 7500rpm. Since my target is so low, the formula calls for that thin and long header.

The formula I used was on wallaceracing (sucks I can't post links yet). I also backed it up with other calculators like this.

I wonder about that small I.D. though...will it completely choke out the engine when I'm below 3900 rpm and not scavenging?

I just thought I'd run the idea past the experts before I make a decision.
 
W

WLB

Active Member
#4
#4
I wouldn't call myself an expert but I had a Superflow flow bench back when I had my shop and used it quite often on a wide variety of heads and cylinders (I flowed two strokes as well). I tried some supposedly torque enhancing small diameter stuff on a 5 hp Briggs flathead when a friend's son raced them and it killed flow and added many seconds to his lap times.
I'm not sure what formulas you are using but your dimensions seem way off base. I can't imagine how restrictive an exhaust .4 diameter 7 feet long would be. I would make the pipe whatever diameter matched the exhaust port the best and experiment with length from there. If the port shape is a D try to form the pipe to that shape for at least several inches, gradually blending to round. If the pipe is smaller than the port where it bolts on, the ledge will produce turbulence--not good. A LITTLE bit larger at the junction doesn't hurt but smaller does. Regardless of what any formulas say, you have to work with what the engine manufacturers give you unless you can alter it by welding. JB Weld won't last long in an exhaust port:laugh:
 
TheDullCarbide

TheDullCarbide

Active Member
#6
#6
WLB said:
I wouldn't call myself an expert but I had a Superflow flow bench back when I had my shop and used it quite often on a wide variety of heads and cylinders (I flowed two strokes as well). I tried some supposedly torque enhancing small diameter stuff on a 5 hp Briggs flathead when a friend's son raced them and it killed flow and added many seconds to his lap times.
I'm not sure what formulas you are using but your dimensions seem way off base. I can't imagine how restrictive an exhaust .4 diameter 7 feet long would be.
Click to expand...
Yeah, I was afraid of that. It's awesome to hear somebody use a similar header in practice (I'll bet it sounded hilarious). I guess the free-flow header is the next best option. Thanks guys.
 
TheDullCarbide

TheDullCarbide

Active Member
#10
#10
So could I use 7/8" ID, 4' long tubing for a header? And about the JB weld, haters can hate but I've never touched the stuff. Nothing beats a true bead of weld.
 
minibikin'

minibikin'

Sho-nuff
#11
#11
I'm just curious where you're getting this insane length from? Are you going to loop this two or three times? A 4' header is going to vibrate and stress crack plus need tons of support. That would make your bike about 7 1/2' long overall??


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TheDullCarbide

TheDullCarbide

Active Member
#14
#14
minibikin' said:
I'm just curious where you're getting this insane length from? Are you going to loop this two or three times? A 4' header is going to vibrate and stress crack plus need tons of support. That would make your bike about 7 1/2' long overall??
Click to expand...
This header is actually going on a Ty-Rail gokart and I have a lot of room for snaking, bracing, and looping the pipe.

WLB said:
The example I mentioned was nowhere near as small as .4 or as long as 7 feet. Something like .750 and 20 inches and it still killed hp.
Click to expand...
So I guess the 0.42" x 7 1/2' is off the table. But then do I go with the 0.875" x 4', the free-flowing header, the stock exhaust, or some other forth design? I'm very lost here.:confused1:
 
minibikin'

minibikin'

Sho-nuff
#15
#15
Did you look at the pipe max program? I don't mean to sound arrogant, but I just cannot see the benefit of running something so long that it will actually be restrictive? There is torque and power in the correct diameter and length. Companies like F&B and Robertsons dump test their pipes. Maybe you should ask them for some advice?


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TheDullCarbide

TheDullCarbide

Active Member
#16
#16
minibikin' said:
Did you look at the pipe max program? I don't mean to sound arrogant, but I just cannot see the benefit of running something so long that it will actually be restrictive? There is torque and power in the correct diameter and length. Companies like F&B and Robertsons dump test their pipes. Maybe you should ask them for some advice?


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Click to expand...
No, I haven't downloaded pipe max. I just thought that there was a better pipe out there than the simple free-flowing one. I could just do a 1" x 20"-ish pipe and call it a day.
 
minibikin'

minibikin'

Sho-nuff
#17
#17
Yep. You can run wax on the length of the pipe and see where it's stops burning when you fire the engine. That can help you tune the length...[emoji1303]


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TheDullCarbide

TheDullCarbide

Active Member
#18
#18
minibikin' said:
Yep. You can run wax on the length of the pipe and see where it's stops burning when you fire the engine. That can help you tune the length...[emoji1303]


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Click to expand...
Wow! Never heard of that one before. So I could run any diameter (probably 7/8"-1"), and cut it where the wax stops burning after running it at rpm? If that works, I'm all over it!
 
FOMOGO

FOMOGO

#19
#19
Paint it white with the cheapest spray paint you can find and it will burn the functional part of the pipe clean and you can cut off the rest. We used to paint header collector extensions on the drag car white and after a couple of passes you knew how long they needed to be.

This will only work with an open pipe. If it has a muffler you are peeing in a funnel.....

Doug
 
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