1 5/8" or 1 3/4" headers?
1 5/8" or 1 3/4" headers? I'm getting ready to build a set of shorty headers. The collector will be 2 1/2" feeding a 7875 turbo. Which size do all you guys recommend? They will be very short in length. Looking to make max around 700 whp.
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Joined: Mar 2014
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From: Ohio
A 2.5" collector has a rough area of 4.9 sq in.
A T4 flange has a rough area of 6 sq in.
8 - 1 5/8 primaries have a total area of 16.583125 sq in.
8 - 1 3/4 primaries have a total area of 19.2325 sq in.
The answer is yes.
A T4 flange has a rough area of 6 sq in.
8 - 1 5/8 primaries have a total area of 16.583125 sq in.
8 - 1 3/4 primaries have a total area of 19.2325 sq in.
The answer is yes.
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Joined: Jul 2013
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From: Portland, Oregon
I would personally go with the 1-3/4" primaries just because of the added volume of exhaust a turbo'ed engine makes.
The smaller 1-5/8" would probably help the turbo come online faster due to the increase of the exhaust gas' heat and velocity, but I think it may also be more prone to increasing backpressure, as well.
My vote, for what it's worth, is the 1-3/4" primaries.
The smaller 1-5/8" would probably help the turbo come online faster due to the increase of the exhaust gas' heat and velocity, but I think it may also be more prone to increasing backpressure, as well.
My vote, for what it's worth, is the 1-3/4" primaries.
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Joined: Jan 2012
Posts: 557
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From: Bowling Green KY
I don't think it will make any difference at all, it's not like a tuned effect such as in a long tube NA header. The smaller tubes will have more velocity, but the velocity in the collector, and at the turbo, will be the same either way. I don't think higher velocity in the primaries makes a difference here.
I think its like having a 1/2 inch valve on a tap, it doesn't matter wither you put a 2" or a 4" hose on it, it will flow pretty much the same since the hose isn't the choke point. Same deal here with the primaries. Maybe if you were talking a larger displacement engine, but both your choices are oversized compared to going through that little flange. I think Joe's math says it all. You could save some fab work and go truck manifolds? Can get a nice set for about $80, and they are proven? They don't look as cool though. You could also probably buy a generic set of shorty LS headers cheaper than you can make them. I'm not sure why that is, but when price the nice laser cut flanges, collectors, some tubing and some mandrel bends, it almost always costs more than buying headers. You burn your time, current, rod, argon, and abrasives for nothing. The exception here would be the really nice ones like the Kooks, but they are nicer than headers I'm capable of making, so that kind of makes sense.
I think its like having a 1/2 inch valve on a tap, it doesn't matter wither you put a 2" or a 4" hose on it, it will flow pretty much the same since the hose isn't the choke point. Same deal here with the primaries. Maybe if you were talking a larger displacement engine, but both your choices are oversized compared to going through that little flange. I think Joe's math says it all. You could save some fab work and go truck manifolds? Can get a nice set for about $80, and they are proven? They don't look as cool though. You could also probably buy a generic set of shorty LS headers cheaper than you can make them. I'm not sure why that is, but when price the nice laser cut flanges, collectors, some tubing and some mandrel bends, it almost always costs more than buying headers. You burn your time, current, rod, argon, and abrasives for nothing. The exception here would be the really nice ones like the Kooks, but they are nicer than headers I'm capable of making, so that kind of makes sense.
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I don't think it will make any difference at all, it's not like a tuned effect such as in a long tube NA header. The smaller tubes will have more velocity, but the velocity in the collector, and at the turbo, will be the same either way. I don't think higher velocity in the primaries makes a difference here.
I think its like having a 1/2 inch valve on a tap, it doesn't matter wither you put a 2" or a 4" hose on it, it will flow pretty much the same since the hose isn't the choke point. Same deal here with the primaries. Maybe if you were talking a larger displacement engine, but both your choices are oversized compared to going through that little flange. I think Joe's math says it all. You could save some fab work and go truck manifolds? Can get a nice set for about $80, and they are proven? They don't look as cool though. You could also probably buy a generic set of shorty LS headers cheaper than you can make them. I'm not sure why that is, but when price the nice laser cut flanges, collectors, some tubing and some mandrel bends, it almost always costs more than buying headers. You burn your time, current, rod, argon, and abrasives for nothing. The exception here would be the really nice ones like the Kooks, but they are nicer than headers I'm capable of making, so that kind of makes sense.
I think its like having a 1/2 inch valve on a tap, it doesn't matter wither you put a 2" or a 4" hose on it, it will flow pretty much the same since the hose isn't the choke point. Same deal here with the primaries. Maybe if you were talking a larger displacement engine, but both your choices are oversized compared to going through that little flange. I think Joe's math says it all. You could save some fab work and go truck manifolds? Can get a nice set for about $80, and they are proven? They don't look as cool though. You could also probably buy a generic set of shorty LS headers cheaper than you can make them. I'm not sure why that is, but when price the nice laser cut flanges, collectors, some tubing and some mandrel bends, it almost always costs more than buying headers. You burn your time, current, rod, argon, and abrasives for nothing. The exception here would be the really nice ones like the Kooks, but they are nicer than headers I'm capable of making, so that kind of makes sense.
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Joined: Mar 2014
Posts: 7,192
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From: Ohio
I would personally go with the 1-3/4" primaries just because of the added volume of exhaust a turbo'ed engine makes.
The smaller 1-5/8" would probably help the turbo come online faster due to the increase of the exhaust gas' heat and velocity, but I think it may also be more prone to increasing backpressure, as well.
My vote, for what it's worth, is the 1-3/4" primaries.
The smaller 1-5/8" would probably help the turbo come online faster due to the increase of the exhaust gas' heat and velocity, but I think it may also be more prone to increasing backpressure, as well.
My vote, for what it's worth, is the 1-3/4" primaries.