Increase flow, 16v head, just looking for data
12-11-2003, 06:24 AM
#16
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Nope, no way you can compress air without heating it up. Adiabatic compress (100% efficient) will still double the intake air-temp at 15psi. A really efficient turbo @ 65% would then heat it up 154%. So if your intake air was 25-C coming in, it will end up being 64-C when it leaves the turbo. Outside if it's efficiency sweet-spot and you're looking at 75-90C easily.
I've read info from several of the grand-daddies of 951 tuning (Gomes, Norwood, etc.) that the 4-valve heads will tend to flow less at low-PRMs than the 2-valve ones, but in the high-end, can easily flow about 2x as much at the same vacuum/pressure level... Of course you have to take into account the ports, and valve-stem size, valve-head shape, cam-timing & lift, etc...
I've read info from several of the grand-daddies of 951 tuning (Gomes, Norwood, etc.) that the 4-valve heads will tend to flow less at low-PRMs than the 2-valve ones, but in the high-end, can easily flow about 2x as much at the same vacuum/pressure level... Of course you have to take into account the ports, and valve-stem size, valve-head shape, cam-timing & lift, etc...
12-11-2003, 04:38 PM
#19
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This might be usefull
12-11-2003, 05:01 PM
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This might be usefull
12-11-2003, 05:33 PM
#21
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OK,
Now let's design a head that uses 8 valves at low rpm's, and then transisitons to the full 16 valves as the rpm's increase!
Is there such a thing?
How does the VarioCam effect this?
Good article!!!
Now let's design a head that uses 8 valves at low rpm's, and then transisitons to the full 16 valves as the rpm's increase!
Is there such a thing?
How does the VarioCam effect this?
Good article!!!
12-11-2003, 06:00 PM
#22
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Originally posted by mslovak1
Now let's design a head that uses 8 valves at low rpm's, and then transisitons to the full 16 valves as the rpm's increase!
Now let's design a head that uses 8 valves at low rpm's, and then transisitons to the full 16 valves as the rpm's increase!
12-11-2003, 07:29 PM
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The GSR's and Prelude's DOHC VTEC also have a two stage intake that uses different length runners to optimize the resonance frequency for both 1000-5800 and 5800-8100 rpm ranges, much like VarioRam... Didn't the 968 also have this, in addition to VarioCam?
12-12-2003, 01:58 AM
#29
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This may be a good time to bring an old idea of mine to the table, so here we go:
A slightly restrictive 2-valve head may actually be a good to have on an inter-cooled turbocharged engine with a high capacity turbocharger.
Consider two scenarios, 1) free flowing head and 2) head with restrictive intake.
Looking at case 2 vs. case 1 it makes sense to just crank up the boost, which will increase the air temperature between the turbocharger and the intake valve. The intercooler will then be able to remove more calories (higher inside/outside temperature difference and slower air velocity) and the air will be cooled further by the nozzling effect (pressure drop) of the intake valve. I am quite sure, that if the thermodynamic numbers are done on these two cases, it will result in more and maybe even colder air mass in the cylinders for case 2. Add more fuel and power is gained.
The extra power consumption by the turbocharger is miniscule. When it works hard, it consumes maybe 4 HP.
I have a suspicion that this is partially why Porsche stayed with 2-valve heads for turbo engines for as long as they did.
Laust
A slightly restrictive 2-valve head may actually be a good to have on an inter-cooled turbocharged engine with a high capacity turbocharger.
Consider two scenarios, 1) free flowing head and 2) head with restrictive intake.
Looking at case 2 vs. case 1 it makes sense to just crank up the boost, which will increase the air temperature between the turbocharger and the intake valve. The intercooler will then be able to remove more calories (higher inside/outside temperature difference and slower air velocity) and the air will be cooled further by the nozzling effect (pressure drop) of the intake valve. I am quite sure, that if the thermodynamic numbers are done on these two cases, it will result in more and maybe even colder air mass in the cylinders for case 2. Add more fuel and power is gained.
The extra power consumption by the turbocharger is miniscule. When it works hard, it consumes maybe 4 HP.
I have a suspicion that this is partially why Porsche stayed with 2-valve heads for turbo engines for as long as they did.
Laust
