Supercharged GS400 tuning/ performance questions
07-28-09, 11:51 AM
#106
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sorry I probably meant the a/f ratio, on that -20, I'll see what it reads in a min next time I go out for a black.
that's what I thought about the bov, I'v been doing research on the BLV valve I have and it will do what I want it to, but some have expressed concerns about the fact that if say I limited my boost to 6psi w/ the blv and reached 6 psi @4500 then the sc would still be compressing air from 4500 to redline and bleeding off the exess-something about more parasitic loss due to this. so once you reached 6psi the engine would still have to work to spin the sc but not get anymore boost, then you would get less hp-not sure on that, if it would equalize or what woul happen
a solution was to use a limiting pipe or tube, a restrictor tube I think it was called. the issue with has something to do with having the tube matched to the sc/ engine-I think, in addition to keeping the tube from limiting boost too much.
I'm still trying to understand the parasitic losses of the blv (say if I wanted to make 10lbs from 3500 to 6k), and how/ what would the effects of a restricor plate, etc.
this is where I got most of my info from-vette forums
You should try a restrictor on the supercharger inlet instead.
* A passive unit with no moving parts.
* It does not restrict flow during WOT at lower engine speeds.
* WOT at higher engine speeds it creates a slight vaccum at the supercharger inlet. That vaccum is mutliplied by the supercharger pressure ratio. Let's say that you had 14.7 psi max boost before the restrictor with atmospheric pressure at the supercharger inlet ( Pressure ratio = 2 ). A slight vaccum, 2.5 psi, at the supercharger inlet will result in ((14.7-2.5)/14.7) x 2 = 1.66 total pressure ratio. 0.66 * 14.7 = 9.7 psi boost.
* With less dense air the supercharger will rob less hp from the crank. This will reduce belt slip at high RPM as the supercharger only has to compress the air used by the engine and only to the boost level required.
* If you dump air after the supercharger to reduce boost then the air flow thru the supercharger will increase and more hp will be robbed from the crank. This is not a good idea.
Look at this Vortech compressor map.
One example.
You have the pulley ratio set so the supercharger has 40.000 rpm when the engine is at 6000 rpm. The supercharger working point is somewhere along the red '40.000' line depending on the air flow thru the supercharger.
The starting point is the blue dot in the middle. Pressure ratio is 1.8 ( = 12 psi boost ). The supercharger flows 850 CFM.
You want to reduce boost to 10 psi at 6000 rpm on the engine.
If you add a Pressure Relief Valve to reduce boost you will move to the right along the red '40000' line. A pressure ratio of 1.7 will give you 10 psi boost. As you see the air flow thru the supercharger has increased to 1050 CFM. At the same time the engine uses less air because of the lower boost, about 800 CFM. About 250 CFM goes out thru the Pressure Relief Valve.
With a restrictor on the inlet inlet you move to the left along the red '40.000' rpm line instead. You reduce the air flow to 800 CFM, same as above and that reduces boost at the engine to 10 psi. The vaccum before the supercharger will be about 0.8 psi = 1.6 InHg. Not much.
The supercharger will require a lot more HP from the crank to compress 1050 CFM at 65% efficiency compared to 800 CFM at 70% efficiency.
You need those hp more at the wheels.
Information about restrictors: http://www.raetech.com/Restrictors/R...r_Function.php
that's what I thought about the bov, I'v been doing research on the BLV valve I have and it will do what I want it to, but some have expressed concerns about the fact that if say I limited my boost to 6psi w/ the blv and reached 6 psi @4500 then the sc would still be compressing air from 4500 to redline and bleeding off the exess-something about more parasitic loss due to this. so once you reached 6psi the engine would still have to work to spin the sc but not get anymore boost, then you would get less hp-not sure on that, if it would equalize or what woul happen
a solution was to use a limiting pipe or tube, a restrictor tube I think it was called. the issue with has something to do with having the tube matched to the sc/ engine-I think, in addition to keeping the tube from limiting boost too much.
I'm still trying to understand the parasitic losses of the blv (say if I wanted to make 10lbs from 3500 to 6k), and how/ what would the effects of a restricor plate, etc.
this is where I got most of my info from-vette forums
You should try a restrictor on the supercharger inlet instead.
* A passive unit with no moving parts.
* It does not restrict flow during WOT at lower engine speeds.
* WOT at higher engine speeds it creates a slight vaccum at the supercharger inlet. That vaccum is mutliplied by the supercharger pressure ratio. Let's say that you had 14.7 psi max boost before the restrictor with atmospheric pressure at the supercharger inlet ( Pressure ratio = 2 ). A slight vaccum, 2.5 psi, at the supercharger inlet will result in ((14.7-2.5)/14.7) x 2 = 1.66 total pressure ratio. 0.66 * 14.7 = 9.7 psi boost.
* With less dense air the supercharger will rob less hp from the crank. This will reduce belt slip at high RPM as the supercharger only has to compress the air used by the engine and only to the boost level required.
* If you dump air after the supercharger to reduce boost then the air flow thru the supercharger will increase and more hp will be robbed from the crank. This is not a good idea.
Look at this Vortech compressor map.
One example.
You have the pulley ratio set so the supercharger has 40.000 rpm when the engine is at 6000 rpm. The supercharger working point is somewhere along the red '40.000' line depending on the air flow thru the supercharger.
The starting point is the blue dot in the middle. Pressure ratio is 1.8 ( = 12 psi boost ). The supercharger flows 850 CFM.
You want to reduce boost to 10 psi at 6000 rpm on the engine.
If you add a Pressure Relief Valve to reduce boost you will move to the right along the red '40000' line. A pressure ratio of 1.7 will give you 10 psi boost. As you see the air flow thru the supercharger has increased to 1050 CFM. At the same time the engine uses less air because of the lower boost, about 800 CFM. About 250 CFM goes out thru the Pressure Relief Valve.
With a restrictor on the inlet inlet you move to the left along the red '40.000' rpm line instead. You reduce the air flow to 800 CFM, same as above and that reduces boost at the engine to 10 psi. The vaccum before the supercharger will be about 0.8 psi = 1.6 InHg. Not much.
The supercharger will require a lot more HP from the crank to compress 1050 CFM at 65% efficiency compared to 800 CFM at 70% efficiency.
You need those hp more at the wheels.
Information about restrictors: http://www.raetech.com/Restrictors/R...r_Function.php
Last edited by gs400 civi; 07-28-09 at 12:06 PM.
07-31-09, 10:32 PM
#111
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hey I've just got a hold of a supercharged gs400, and I need somewhere to have it tune in the tx/ west tx area.its currently using an SAFC for A/F control I also have some questions
so far it has the supercharger, 3.76 lsd, 3" exhuast from the cat back, w/ the last resonator deleted.
I want to get the S&S headers but my question is does anyone/ can you do anything about the cat area between the two? that seems like it would be the bottlneck in the exhuast system.
I'm also interested in a higher stall torque convert 2800 or 3000?.
another thing I was wondering about is that a turb can spoolup at say 3000rpm's and hold that pressure to redline but a sc setup only make max boost at wot, can you use a different pully setup on an sc that will have the sc spin to full boost at 300 then us a blowoff valve or some kind of valve to let off the extra pressure so you could have full boost at a lower rpm and hold it from 3000 to wot?
the last thing is the intercooler, I want to replace it cause I hit a rabit on the way home and it dented it, can/ should I go larger? where to buy?
Can someone help w/ these questions? please
so far it has the supercharger, 3.76 lsd, 3" exhuast from the cat back, w/ the last resonator deleted.
I want to get the S&S headers but my question is does anyone/ can you do anything about the cat area between the two? that seems like it would be the bottlneck in the exhuast system.
I'm also interested in a higher stall torque convert 2800 or 3000?.
another thing I was wondering about is that a turb can spoolup at say 3000rpm's and hold that pressure to redline but a sc setup only make max boost at wot, can you use a different pully setup on an sc that will have the sc spin to full boost at 300 then us a blowoff valve or some kind of valve to let off the extra pressure so you could have full boost at a lower rpm and hold it from 3000 to wot?
the last thing is the intercooler, I want to replace it cause I hit a rabit on the way home and it dented it, can/ should I go larger? where to buy?
Can someone help w/ these questions? please
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