Head flow vs Turbo
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Head flow vs Turbo I tryed a search but found nothing. I am reserching turbo kits & I see people using stock heads on their turbo motor & getting good results. Is this because of velocity? How does it work? Would a stock head work better than a ported head on a street turbo motor?
I would go ported.
You want to force in as much air as possible, right? So larger ports should help aid this. Take a stock headed turbo 346, then add AFR 225 or TFS 225 and you will gain some good power.
You want to force in as much air as possible, right? So larger ports should help aid this. Take a stock headed turbo 346, then add AFR 225 or TFS 225 and you will gain some good power.
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Turbo's are funny. Any given turbo will support a certain amount of hp and it will make as much boost as it needs to get there. For instance, the popular T76GTS has made just under 1000 rwhp on a 355 at 22 psi boost, and been just over 1000 rwhp on 180 cid at 45 psi boost.
So, with any given turbo, you can make the same amount of power with stock heads as you can with ported heads, but it will take more boost to get there. Conversely, alot of guys, including myself, are trying to maximize power on motor alone using head flow, cam selection, intake manifold, and cid, so that you can make more power at lower (safer) boost levels.
Mike
So, with any given turbo, you can make the same amount of power with stock heads as you can with ported heads, but it will take more boost to get there. Conversely, alot of guys, including myself, are trying to maximize power on motor alone using head flow, cam selection, intake manifold, and cid, so that you can make more power at lower (safer) boost levels.
Mike
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What is the relationship between increased head flow and decreased boost required to produce a given HP? For example, would a head that flows 20% more require (as a first-order approximation) 5/6 (inverse of 120% = 6/5) the original boost, or is the relationship more complex?
Originally Posted by LILS
What is the relationship between increased head flow and decreased boost required to produce a given HP? For example, would a head that flows 20% more require (as a first-order approximation) 5/6 (inverse of 120% = 6/5) the original boost, or is the relationship more complex?
its gets alot more complex.
just one example would be the compressor efficiency... you change where that compressor is at, and the efficiency changes... so the charge may be hotter or cooler, so the density changes... ect...
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Yes, efficiency would change some with the change in boost, but if the difference in charge temperature were offset by a corresponding change in charge air cooling, how close would we come to the "required boost is the inverse of head flow" rule? Are there other significant factors that would similarly have to be compensated for in an effort to isolate the effect of changed head flow, all else being as nearly equal as possible?
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Originally Posted by LILS
What is the relationship between increased head flow and decreased boost required to produce a given HP?
FIhp = NAhp*(boost1+14.7)/14.7
FIhpported = NAhpported*(boost2+14.7)/14.7
So, if FIhp = FIhpported, then:
NAhp*(boost1+14.7)/14.7 = NAhpported*(boost2+14.7)/14.7
Solve for boost2:
boost2 = NAhp*(boost1+14.7)/NAhpported - 14.7
Example: If an LS1 makes 380 hp with stock heads and would make 410 hp with ported heads. Your initial boost level is 10 psi and you want to add ported heads and reduce boost to get the same power level.
boost2 = 380*(10+14.7)/410 - 14.7
boost2 = 8.2 psi.
So, if ported heads add 30 hp over stock heads, and you're running 10 psi, then you can port the heads and lower the boost by 1.8 psi and get the same power.
Of course, these are gross approximations.
Mike
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Originally Posted by engineermike
Turbo's are funny. Any given turbo will support a certain amount of hp and it will make as much boost as it needs to get there. For instance, the popular T76GTS has made just under 1000 rwhp on a 355 at 22 psi boost, and been just over 1000 rwhp on 180 cid at 45 psi boost.
Mike
Mike
Originally Posted by FUroundeye
So engineermike, are you saying that the guys who jump up and down about a 408 making too much backpressure for a T76, and therefore will be outperformed by a 347 w/ a T76, are wrong?
I may be wrong, but i see turbos not as boost makers but air blowers. it's not how much boost a turbo makes, it's how much air it can throw. Isn't it true that each horsepower made needs the same amount of air to be made regardless of engine size? which means if a turbo is flowing as much air as it can with unported heads or lower ci, then it will not flow more air with ported heads or bigger ci? Could ported heads reduce heat by increasing efficiency therefore increasing power?
-also... the smaller motor probably makes more power because it is lighter than the 347 and both pump the same amount of air.
-also... the smaller motor probably makes more power because it is lighter than the 347 and both pump the same amount of air.
Originally Posted by engineermike
Turbo's are funny. Any given turbo will support a certain amount of hp and it will make as much boost as it needs to get there. For instance, the popular T76GTS has made just under 1000 rwhp on a 355 at 22 psi boost, and been just over 1000 rwhp on 180 cid at 45 psi boost.
Last edited by Mike454SS; Oct 20, 2006 at 03:47 PM. Reason: forgot some words in one of my sentences
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Originally Posted by FUroundeye
So engineermike, are you saying that the guys who jump up and down about a 408 making too much backpressure for a T76, and therefore will be outperformed by a 347 w/ a T76, are wrong?
Note that I was running 383 cid with my T76GTS, but then switched to 363, and then my current motor is 388.
Mike
