Another Header Question
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434 Posts
I always thought that the bigger the better but ask to see if the 2" will fit without any problems on your 70 from the guys here
Michael
Michael
The 1 7/8 prob would be perfect for the torque and would prob shift the torque curve down depending on where your peak torque is,but the problem is finding a company that makes a 1 7/8 BBC header. I too was faced with the dilema... The Only 2 I found were Patriot and Hooker Super Comps. The Patriots were reasonably priced $145 raw uncoated, $345 ceramic coated. The Super Comp Hookers $ 509 painted black, $739 ceramic coated.
I called Summit and Jegs, they said it was a 3 week wait for the Patriot H8024 and H8024-1(1 7/8).... So I called Pertronix which makes Doug and Patriot headers and they said they only had 5-6 in the warehouse but could not promise me that they were not all ready spoken for..... From my understanding the 1 7/8 is not readly kept on the shelf. You order them from the vender then they send a request to Pertronix, then the 1 7/8 header actually comes from Pertronix... So go figure, more wait time for your headers. But Summit and Jegs had the H8026 and H8026-1 on the shelf, so I went with the H8026 uncoated....
There are some other companies that make a 1 7/8 but it will be custom, so get ready to shell out the doe:thumbsup:
I called Summit and Jegs, they said it was a 3 week wait for the Patriot H8024 and H8024-1(1 7/8).... So I called Pertronix which makes Doug and Patriot headers and they said they only had 5-6 in the warehouse but could not promise me that they were not all ready spoken for..... From my understanding the 1 7/8 is not readly kept on the shelf. You order them from the vender then they send a request to Pertronix, then the 1 7/8 header actually comes from Pertronix... So go figure, more wait time for your headers. But Summit and Jegs had the H8026 and H8026-1 on the shelf, so I went with the H8026 uncoated....
There are some other companies that make a 1 7/8 but it will be custom, so get ready to shell out the doe:thumbsup:
Problem is Flowtech does not make a 1 7/8 header for a Chevelle or at least A body, I called em already........
they are for:
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2,098 Posts
imho....dont think that .125 will make that much difference. if it is a track use mostly deal the 2" would flow better in the higher rpm range....
my 496/600 hp motor has hedmans 1.75....it hauls it !! but mostly street use....
my 496/600 hp motor has hedmans 1.75....it hauls it !! but mostly street use....
Doug,
I have 1 7/8 super comps. On the dyno, the difference between these and the 2 1/4shop headers was that the tq curve moved up about 500 rpms (I will check that when I get home to see if I can find the exact number).
The 1 7/8 fit great, but snug. I had to clearance the flange on my scatter shield. Very easy to get to the spark plugs. This is with 063 iron heads. Very tight with a DB mini starter. Had to wrap the starter in that heat shield stuff, but it did fit. No issue with a stock starter. Also, great clearance, etc., for shift linkage.
This is with my 69 though.
I have 1 7/8 super comps. On the dyno, the difference between these and the 2 1/4shop headers was that the tq curve moved up about 500 rpms (I will check that when I get home to see if I can find the exact number).
The 1 7/8 fit great, but snug. I had to clearance the flange on my scatter shield. Very easy to get to the spark plugs. This is with 063 iron heads. Very tight with a DB mini starter. Had to wrap the starter in that heat shield stuff, but it did fit. No issue with a stock starter. Also, great clearance, etc., for shift linkage.
This is with my 69 though.
Would the 11130flt or 31130flt work for el camino? they are 1 3/4"
CHEVELLE 64-74 396-454 11130FLT 31130FLT 1-3/4”x3”
http://www.holley.com/BrowseCatalogs.asp?Catalog=Flowtech&Page=5
Thanks for all the great info guys.I currently have 1 3/4 very restrictive old headers with issues on the Elky.Just want to get the most performance,or bang for my buck,as I said mostly track duty at high rpm's.Don't care about street torque,I have my Chevelle for that.
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1,794 Posts
Here are two quotes from Joe Sherman about header size and horsepower:
"I must have done this same dyno test 20 or 30 times.If the engine is really 500 Hp ( not 600 plus ) the 1 & 3/4 with the 3 inch will be the best. Once in a while, the bigger pipes will help out. My testing has shown that the 1 & 3/4 is very good up to 600-625. If you can rev the engine way up ( 7500 or higher ) then the bigger dia starts to get better. Usually the collector needs to be in the 20 to 25 inches long ( from the end of the 4 pipes )"
JOE SHERMAN RACING ENGINES
"the headers are way too big for that kind of HP. I have found that 1 & 3/4 size works very well on most engines up to 700 HP. Are you all done with the dyno testing at this point ??"
JOE SHERMAN RACING ENGINES
My advice is research header size thoroughly. If you anticipate making over 700 HP, maybe go 1 7/8". Although a large header may make higher numbers on a dyno, a smaller header will accelerate the car better. If you keep going to bigger and bigger headers, and stay in the same RPM range, eventually your car will slow down. Listen to Joe.
"I must have done this same dyno test 20 or 30 times.If the engine is really 500 Hp ( not 600 plus ) the 1 & 3/4 with the 3 inch will be the best. Once in a while, the bigger pipes will help out. My testing has shown that the 1 & 3/4 is very good up to 600-625. If you can rev the engine way up ( 7500 or higher ) then the bigger dia starts to get better. Usually the collector needs to be in the 20 to 25 inches long ( from the end of the 4 pipes )"
JOE SHERMAN RACING ENGINES
"the headers are way too big for that kind of HP. I have found that 1 & 3/4 size works very well on most engines up to 700 HP. Are you all done with the dyno testing at this point ??"
JOE SHERMAN RACING ENGINES
My advice is research header size thoroughly. If you anticipate making over 700 HP, maybe go 1 7/8". Although a large header may make higher numbers on a dyno, a smaller header will accelerate the car better. If you keep going to bigger and bigger headers, and stay in the same RPM range, eventually your car will slow down. Listen to Joe.
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6,401 Posts
A certain red chevelle claimed 1.75 headers well into the tens.
True Ken, but it all comes down to the combination..... Everybody's is different as we know. Say a guy has his motor dyno'd and the dyno uses 2" headers, peak torque 4000rpms. Then he uses 1 3/4 headers peak torque may be 3500 now.... His torque curve will shift lower not in power but shift down the torque curve. Now with this shift down the curve he may loose some top end HP. If he still wants his motor to still build along that curve or later, a larger pipe may serve him some justice via a 1 7/8" or 2" or larger cam.... 1 3/4 most say is perfect for street because on the street most normal guys don't rev the engines up to 6000 or 7000+, well there are some crazy guys that do it on the street so I will tentatively make that statment....lol
Not to say the 1 3/4 won't get the job
Not to say the 1 3/4 won't get the job
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1,794 Posts
I had a DZ years ago and put 1 7/8" headers on it because they were a bargain. They were MUCH better than stock manifolds. But I always felt 1 5/8" would have been a better choice. Don't get me wrong. The 1 7/8" pulled hard with that engine, but they were 36" long. And, FWIW, the collector is the most important part.
There is a lot going on in a set of headers. You have a slug of exhaust going out, a pressure wave caused by that, that travels at a given speed because of the temperature of the exhaust gas; then another wave returning up the pipe at a different speed, because the air in the pipe is no longer as hot as the exhaust gas. Each wave has to get to the right place at the right time to make a set of headers "work". Those waves are augmented by primary tube length and collector length. The speed of the gas in the pipe is important; not just getting it out of the pipe. Gas speed, wave speed, and temperature of the gasses all work for you or against you. There are more to headers than "Letting it breath".
When an engine "comes on the pipe", it means the headers are working best at that particular RPM, cleaning exhaust gas out of the combustion chamber without over-exhausting. Exhaust gas dilution is a huge power killer. That's why a good intake valve seal is so important. You must keep burnt gasses from diluting the next intake charge. Likewise, you want to be sure the headers will do their job in pulling as much residual gasses out of the combustion chamber as possible. In my opinion, the best way to do that is by having the gas speed in the pipe high enough to do some work, as opposed to just being blown out into the world.
I'm certainly no expert on this, and from what I have read, neither is anyone else. You can only take one set of parameters at a time, and try to make a set of pipes that work with those parameters. All the figuring will get you close, but only testing will get the best results. My experience has been to err on the small side, because as I said, gas speed must be high enough to make the pipe "work".
There are some good books with lengthy formulas for finding the right diameter and length of exhaust pipes, but it is still cut and try. Seems no one has figured out how to think like an engine.
Joe Sherman says he has made over 740 HP with 1 3/4" headers, and going larger hasn't made much difference at that power range. I will never see 740 in my life at the rate I'm going, so I have to take his word for it. I have witnessed over 700 hp in dyno pulls with that size headers, and the engine builder didn't think he needed anything larger. (NASCAR type 350 stuff from about 15 years ago.)
I'm not trying to say anyone is right or wrong about header sizing. I'm trying to say: Don't pick 2" pipes because they are big and look cool. Do some research and find some combos close to yours that are running well. Go to a track and look around. See what people are running in the power range you are expecting to attain.
There is a lot going on in a set of headers. You have a slug of exhaust going out, a pressure wave caused by that, that travels at a given speed because of the temperature of the exhaust gas; then another wave returning up the pipe at a different speed, because the air in the pipe is no longer as hot as the exhaust gas. Each wave has to get to the right place at the right time to make a set of headers "work". Those waves are augmented by primary tube length and collector length. The speed of the gas in the pipe is important; not just getting it out of the pipe. Gas speed, wave speed, and temperature of the gasses all work for you or against you. There are more to headers than "Letting it breath".
When an engine "comes on the pipe", it means the headers are working best at that particular RPM, cleaning exhaust gas out of the combustion chamber without over-exhausting. Exhaust gas dilution is a huge power killer. That's why a good intake valve seal is so important. You must keep burnt gasses from diluting the next intake charge. Likewise, you want to be sure the headers will do their job in pulling as much residual gasses out of the combustion chamber as possible. In my opinion, the best way to do that is by having the gas speed in the pipe high enough to do some work, as opposed to just being blown out into the world.
I'm certainly no expert on this, and from what I have read, neither is anyone else. You can only take one set of parameters at a time, and try to make a set of pipes that work with those parameters. All the figuring will get you close, but only testing will get the best results. My experience has been to err on the small side, because as I said, gas speed must be high enough to make the pipe "work".
There are some good books with lengthy formulas for finding the right diameter and length of exhaust pipes, but it is still cut and try. Seems no one has figured out how to think like an engine.
Joe Sherman says he has made over 740 HP with 1 3/4" headers, and going larger hasn't made much difference at that power range. I will never see 740 in my life at the rate I'm going, so I have to take his word for it. I have witnessed over 700 hp in dyno pulls with that size headers, and the engine builder didn't think he needed anything larger. (NASCAR type 350 stuff from about 15 years ago.)
I'm not trying to say anyone is right or wrong about header sizing. I'm trying to say: Don't pick 2" pipes because they are big and look cool. Do some research and find some combos close to yours that are running well. Go to a track and look around. See what people are running in the power range you are expecting to attain.
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