gze throttle body

rsfire · 02-07-2009, 10:00 PM

Ok, I have a question about the throttle body placement for the gze. I know that it's before the s/c, but why. Most throttle bodies I see on other cars are right before the intake.
Why i ask is because I've just about finished twincharging my 86, but some time down the road i'd like to get a sc14 and a new bypass system and I want to move the throttle after the turbo instead of infront of s/c and turbo. thanks. ask if that doesn't make sense.

div0 · 02-08-2009, 03:40 AM

The problem is that the SC12 and SC14 are positive displacement superchargers. This means that they displace the same volume of air per revolution, and the amount of boost they produce is purely based on the restriction of this flow on the discharge side. With the throttle body post supercharger, the throttle position does not matter when the supercharger is engaged... it is going to pump the same volume of air and force the pressure up high enough to get that volume through the throttle body regardless of the throttle position.

I actually have the throttle body moved after the SC12 supercharger as part of the build stage before the final twincharge build (in progess now). The supercharger is set to engage at 60% throttle and >2000 RPM. It is rather unpleasant to drive, since past the 60% throttle position, the SC comes on hard, and 60%-100% throttle position makes no difference... so might as well floor it whenever the SC is engaged. Similarly the jolt is significant when dropping below 60% throttle position as well.

In addition, with the throttle body after the supercharger, it is necessary to have a blowoff valve to release the pressure when the throttle body snaps closed between shifts or deceleration.

My final twincharge setup will contain a bypass valve around the superchager. I am hopeful that careful tuning of the bypass valve will smooth out this harsh transition.

rsfire · 02-08-2009, 04:13 PM

so having the throttle body before the s/c & turbo should keep it smoother by theory then, right. The only reason i was asking cause down the road i'd eventually like to get an sc14 s/c but my current bypass system wouldn't fit and would be restrictive, i'd also rebuilt my engine and crank up the boost on turbo. But 2 of the supra ones that you have may work instead. hmm, thanks

div0 · 02-15-2009, 07:01 PM

I think having throttle body > S/C > turbo would be smoother, but having the throttle body in front of the turbo sounds strange to me. It seems like the rapidly fluctuating vacuum the throttle body would place in front of the turbo would cause rapid changes in the pressure ratio the turbo would experience. It seems like it would be really easy to throw the compressor into surge when you let off the gas. This is not something a blowoff valve could solve since it would be caused by vacuum at the intake of the compressor instead of overpressure at the outlet.

Has anyone on the board heard of a system running the throttle body in front of the turbo before?

Any luck getting your new twincharge setup running rsfire?

02-07-2009, 10:00 PM	#1 (permalink)
rsfire No Skills Join Date: Aug 2008 Posts: 41 Thanks: 0 Thanked 0 Times in 0 Posts iTrader Rating: (0/0% )	gze throttle body Ok, I have a question about the throttle body placement for the gze. I know that it's before the s/c, but why. Most throttle bodies I see on other cars are right before the intake. Why i ask is because I've just about finished twincharging my 86, but some time down the road i'd like to get a sc14 and a new bypass system and I want to move the throttle after the turbo instead of infront of s/c and turbo. thanks. ask if that doesn't make sense.

02-08-2009, 03:40 AM	#2 (permalink)
div0 No Skills Join Date: Jul 2008 Location: San Jose, CA Posts: 31 Thanks: 0 Thanked 1 Time in 1 Post iTrader Rating: (0/0% )	The problem is that the SC12 and SC14 are positive displacement superchargers. This means that they displace the same volume of air per revolution, and the amount of boost they produce is purely based on the restriction of this flow on the discharge side. With the throttle body post supercharger, the throttle position does not matter when the supercharger is engaged... it is going to pump the same volume of air and force the pressure up high enough to get that volume through the throttle body regardless of the throttle position. I actually have the throttle body moved after the SC12 supercharger as part of the build stage before the final twincharge build (in progess now). The supercharger is set to engage at 60% throttle and >2000 RPM. It is rather unpleasant to drive, since past the 60% throttle position, the SC comes on hard, and 60%-100% throttle position makes no difference... so might as well floor it whenever the SC is engaged. Similarly the jolt is significant when dropping below 60% throttle position as well. In addition, with the throttle body after the supercharger, it is necessary to have a blowoff valve to release the pressure when the throttle body snaps closed between shifts or deceleration. My final twincharge setup will contain a bypass valve around the superchager. I am hopeful that careful tuning of the bypass valve will smooth out this harsh transition. Last edited by div0; 02-08-2009 at 03:54 AM..

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02-08-2009, 04:13 PM	#3 (permalink)
rsfire No Skills Join Date: Aug 2008 Posts: 41 Thanks: 0 Thanked 0 Times in 0 Posts iTrader Rating: (0/0% )	so having the throttle body before the s/c & turbo should keep it smoother by theory then, right. The only reason i was asking cause down the road i'd eventually like to get an sc14 s/c but my current bypass system wouldn't fit and would be restrictive, i'd also rebuilt my engine and crank up the boost on turbo. But 2 of the supra ones that you have may work instead. hmm, thanks

02-15-2009, 07:01 PM	#4 (permalink)
div0 No Skills Join Date: Jul 2008 Location: San Jose, CA Posts: 31 Thanks: 0 Thanked 1 Time in 1 Post iTrader Rating: (0/0% )	I think having throttle body > S/C > turbo would be smoother, but having the throttle body in front of the turbo sounds strange to me. It seems like the rapidly fluctuating vacuum the throttle body would place in front of the turbo would cause rapid changes in the pressure ratio the turbo would experience. It seems like it would be really easy to throw the compressor into surge when you let off the gas. This is not something a blowoff valve could solve since it would be caused by vacuum at the intake of the compressor instead of overpressure at the outlet. Has anyone on the board heard of a system running the throttle body in front of the turbo before? Any luck getting your new twincharge setup running rsfire?