What's the difference between 13/4" and 17/8" headers?
Thread Starter
Drifting
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From: When I say who is the masta you gotsta say Shonuff
What's the difference between 13/4" and 17/8" headers?
I've noticed that kooks offers both.
Besides the 1/8", what's the difference performance wise?
Besides the 1/8", what's the difference performance wise?
Le Mans Master
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From: Montreal Qc
Re: What's the difference between 13/4" and 17/8" headers? (Conjunctivitis)
The 1-7/8" are for bigger cubed engines, apparently if used on a stock N/A car, they will hurt performance, at least that's what I've read. 
Melting Slicks
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Re: What's the difference between 13/4" and 17/8" headers? (Conjunctivitis)
Some of the guys have been successful on stock cubes but they are highly modded--Kooks can make anything you want, I have talked to them about a 2" header to be used with c5r heads and sheetmetal intake--
Drifting
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From: If you can see the car behind you, your not going fast enough
Re: What's the difference between 13/4" and 17/8" headers? (Conjunctivitis)
That 1/8 of an inch is a big difference lets look at it like this...
The Area of a 1.75 in. tube is 2.40 in. That is enough for a 346 or even a 383 but would restrict the airflow put out by bigger motors such as 402, 408, 418, 422, 427, 436, and 441...
The Area of a 1.875 in. tube is 2.88 in. that is over 4/10s of an inch! That would be too much for a 346 or 383 but would satisfy the needs of the bigger engines like the ones I listed above...
That 4/10 of an in. can result in up to 30 - 40 CFM differences... That could make a world of difference...
The Area of a 1.75 in. tube is 2.40 in. That is enough for a 346 or even a 383 but would restrict the airflow put out by bigger motors such as 402, 408, 418, 422, 427, 436, and 441...
The Area of a 1.875 in. tube is 2.88 in. that is over 4/10s of an inch! That would be too much for a 346 or 383 but would satisfy the needs of the bigger engines like the ones I listed above...
That 4/10 of an in. can result in up to 30 - 40 CFM differences... That could make a world of difference...
Team Owner
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From: S.W. Ohio. . . . . . NRA Life Member
Re: What's the difference between 13/4" and 17/8" headers? (NJ99FRC)
That 1/8 of an inch is a big difference lets look at it like this...
Depends on the engine's mods... and the intended useage.
general rule-of-thumb is... where (what RPM range) you want the benefit to occur. If you want it at lower RPM's ... then the smaller diameter is better for that.
If you want the power increase to happen at a higher RPM (1/4 mile drag enthusiasts), then the larger diameter is best suited.
Despite all the mathematics, this is how it pans-out on the street/strip.
.
[Modified by Mike Mercury, 10:44 AM 7/3/2004]
Le Mans Master
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From: Flower Mound TX
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Re: What's the difference between 13/4" and 17/8" headers? (Mike Mercury)
That 1/8 of an inch is a big difference lets look at it like this...
maybe not...
Depends on the engine's mods... and the intended useage.
general rule-of-thumb is... where (what RPM range) you want the benefit to occur. If you want it at lower RPM's ... then the smaller diameter is better for that.
If you want the power increase to happen at a higher RPM (1/4 mile drag enthusiasts), then the larger diameter is best suited.
Despite all the mathematics, this is how it pans-out on the street/strip.
maybe not...
Depends on the engine's mods... and the intended useage.
general rule-of-thumb is... where (what RPM range) you want the benefit to occur. If you want it at lower RPM's ... then the smaller diameter is better for that.
If you want the power increase to happen at a higher RPM (1/4 mile drag enthusiasts), then the larger diameter is best suited.
Despite all the mathematics, this is how it pans-out on the street/strip.
I think that is the right way to look at this...it is not just geometry.
Drifting
Joined: Oct 2002
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From: If you can see the car behind you, your not going fast enough
Re: What's the difference between 13/4" and 17/8" headers? (Mike Mercury)
That 1/8 of an inch is a big difference lets look at it like this...
maybe not...
Depends on the engine's mods... and the intended useage.
general rule-of-thumb is... where (what RPM range) you want the benefit to occur. If you want it at lower RPM's ... then the smaller diameter is better for that.
If you want the power increase to happen at a higher RPM (1/4 mile drag enthusiasts), then the larger diameter is best suited.
Despite all the mathematics, this is how it pans-out on the street/strip.
maybe not...
Depends on the engine's mods... and the intended useage.
general rule-of-thumb is... where (what RPM range) you want the benefit to occur. If you want it at lower RPM's ... then the smaller diameter is better for that.
If you want the power increase to happen at a higher RPM (1/4 mile drag enthusiasts), then the larger diameter is best suited.
Despite all the mathematics, this is how it pans-out on the street/strip.
the effect you are talking about is a result of primary length... the longer the primary, the slightly higher the back pressure will be the more low end torque... Shorter primarys are less resrictive and offer a higher range torque curve... I am not exactly a header specialist but im sure you can ask lou at LG or nick at kooks and they could give you a more professional explanation... But I am pretty sure i am on the right track
Drifting
Joined: Jun 2004
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From: Goodyear Az
Re: What's the difference between 13/4" and 17/8" headers? (NJ99FRC)
You want the SMALLEST diameter tube that will not hinder maximum horsepower. Tubing *lengths* are used to tune the torque peak. For a low rpm torque peak of around 5000 rpm with 350 cubic inches, the tubing length of choice is right around 32". Not so coincidentally, LG and SuperMaxx headers both have primary tube lengths of ~32".
If you have a modified heads/cam car with a much higher redline, or a bored/stroked motor, or blower/turbo, you'll need the larger diameter tube to keep from limiting the top end horsepower. The LS6 isn't anything magical -- racers having been doing this for a long time, and unless you have a high horsepower smallblock, a 1-3/4" header is what you need.
The best bet is to simply call LG or Kooks or Stainless Works or Dynotech and tell them what your horsepower goals are and let them suggest tubing diameter.
If you have a modified heads/cam car with a much higher redline, or a bored/stroked motor, or blower/turbo, you'll need the larger diameter tube to keep from limiting the top end horsepower. The LS6 isn't anything magical -- racers having been doing this for a long time, and unless you have a high horsepower smallblock, a 1-3/4" header is what you need.
The best bet is to simply call LG or Kooks or Stainless Works or Dynotech and tell them what your horsepower goals are and let them suggest tubing diameter.
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Verdad Gallardo
Team Owner
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From: S.W. Ohio. . . . . . NRA Life Member
Re: What's the difference between 13/4" and 17/8" headers? (nuke61)
You want the SMALLEST diameter tube that will not hinder maximum horsepower.
it's best for people to put their calculator down and visit the track. That's where the real world opens ones eyes.
Le Mans Master
Joined: Jan 2003
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From: Tyler TX
Re: What's the difference between 13/4" and 17/8" headers? (Mike Mercury)
Cartek did a test said the 1/34 made 5pounds of tq more than the 1/78 but alittle less Hp. I went with the 1/78 so I could mod up to a large stroker setup and have the right header for it .
Safety Car
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From: San Diego, CA "leaf" "tee" "e"
Re: What's the difference between 13/4" and 17/8" headers? (LittleBoyBlu99)
The following books have sections on exhaust systems requiring some back pressure:
1) John Lingenfelter on Modifying Small-Block Chevy Engines - High Performance Engine Building and Tuning for Street and Racing
2) Chevrolet Power - How to Prepare Chevrolet Engines for Maximum Performance
To paraphrase John Lingenfelter, too large diameter primaries will not allow exhaust gases to pick up enough speed to exit the cylinder, thus causing some of the spent gases to recirculate back into the next cycle, and produce less power, especially at low rpms.
The second book was much more about swapping factory parts versus aftermarket parts, and has a pretty weak section on exhaust design.
John Lingenfelter did a lot for us during his lifetime, I just wish things could've worked out so could've done an updated version of his book too...instead we got a LS1 Performance book and a Corvette Fuel Injection Systems book both from other people, and full of fiction, opinion, and errors.
[Modified by leaftye, 2:14 AM 7/4/2004]
1) John Lingenfelter on Modifying Small-Block Chevy Engines - High Performance Engine Building and Tuning for Street and Racing
2) Chevrolet Power - How to Prepare Chevrolet Engines for Maximum Performance
To paraphrase John Lingenfelter, too large diameter primaries will not allow exhaust gases to pick up enough speed to exit the cylinder, thus causing some of the spent gases to recirculate back into the next cycle, and produce less power, especially at low rpms.
The second book was much more about swapping factory parts versus aftermarket parts, and has a pretty weak section on exhaust design.
John Lingenfelter did a lot for us during his lifetime, I just wish things could've worked out so could've done an updated version of his book too...instead we got a LS1 Performance book and a Corvette Fuel Injection Systems book both from other people, and full of fiction, opinion, and errors.
[Modified by leaftye, 2:14 AM 7/4/2004]
