Compound induction
Originally Posted by 96SCTA
Yeah,, Im pumped that i got somthing new to think about.
My motor is out of the car right now. I am doning the build up . I was thinking 383 LT1 all forged set up. But If i am going to run this much boost. I may just stay with a 355 LT1 so i can turn up the rpms even more. I will have to go with real low comp pistons. like 8.5:1. Right now im still on the stock compression ration. With 9-11lbs of boost. (never consistant)
The question that i really need to find out is how much can a v8 handle.
My motor is out of the car right now. I am doning the build up . I was thinking 383 LT1 all forged set up. But If i am going to run this much boost. I may just stay with a 355 LT1 so i can turn up the rpms even more. I will have to go with real low comp pistons. like 8.5:1. Right now im still on the stock compression ration. With 9-11lbs of boost. (never consistant)
The question that i really need to find out is how much can a v8 handle.
TECH Enthusiast
Joined: Aug 2003
Posts: 596
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From: Downers Grove,IL
It would be sort of a silly thing to do as the primary reason this is done in some forms of racing( tractor pullers) is because a single turbo just can not handle the pressures these guys run without damage.
I believe you would not need much boost from the turbo to the blower. 7psi would be enough and if the right turbo is used temp rise into the blower would not be to extreme.
You could slow down the blower speed as well to keep it in it's best efficiency range and maybe 1 good intercooler would still workout.
Say you normally run 10psi boost with the blower at max rpm. That's a 1.68 pressure ratio. If you increase the pressure going into the blower from atmospheric pressure (14.7) to 7psi boost(21.7), then the new boost would be 21.7 psi.
If you boost the blower inlet pressure to 10psi from the turbo and keep the same blower speed, then your looking at 26.8psi out of the blower if my math is correct. So managing final boost levels would be very tricky. If the turbo wastegate EVER malfunctioned it's probably instant meltdown time.
The problem I have with this is you need a pretty large turbo.To make 7psi into the blower that is normally making 10psi, means some serious cfm rates!
It's going to take a big turbo and at that point why even bother as you won't need the blower anyhow and no way any gasoline motor can handle the pressures this sort of system is designed for..
Maybe the better idea is to just run it in parallel. Increase the flow and you increase the boost. Right now I have a g-trim for instance. It'll handle maybe 1000cfm. Just adding a small turbo capable of 1000cfm in parallel puts it beyond a YSI trim easily in potential flow. You'll still suffer the 80hp or so loss from blower drag and still be down in power per boost compared to an ALL turbo system. But it will be ahead of a single large ALL belt driven setup.
Just a pretty darn complicated (and probably heavy)setup is the down side.
Steve
I believe you would not need much boost from the turbo to the blower. 7psi would be enough and if the right turbo is used temp rise into the blower would not be to extreme.
You could slow down the blower speed as well to keep it in it's best efficiency range and maybe 1 good intercooler would still workout.
Say you normally run 10psi boost with the blower at max rpm. That's a 1.68 pressure ratio. If you increase the pressure going into the blower from atmospheric pressure (14.7) to 7psi boost(21.7), then the new boost would be 21.7 psi.
If you boost the blower inlet pressure to 10psi from the turbo and keep the same blower speed, then your looking at 26.8psi out of the blower if my math is correct. So managing final boost levels would be very tricky. If the turbo wastegate EVER malfunctioned it's probably instant meltdown time.
The problem I have with this is you need a pretty large turbo.To make 7psi into the blower that is normally making 10psi, means some serious cfm rates!
It's going to take a big turbo and at that point why even bother as you won't need the blower anyhow and no way any gasoline motor can handle the pressures this sort of system is designed for..
Maybe the better idea is to just run it in parallel. Increase the flow and you increase the boost. Right now I have a g-trim for instance. It'll handle maybe 1000cfm. Just adding a small turbo capable of 1000cfm in parallel puts it beyond a YSI trim easily in potential flow. You'll still suffer the 80hp or so loss from blower drag and still be down in power per boost compared to an ALL turbo system. But it will be ahead of a single large ALL belt driven setup.
Just a pretty darn complicated (and probably heavy)setup is the down side.
Steve
started a thread asking how to calculate compound pressure ratio.
https://ls1tech.com/forums/forced-induction/257954-experts-how-calculate-compunded-psi-s.html
It's all about pressure ratios. Say your first compressor (turbo or SC) has a PR of 3. That gives you 29.4psig of boost though this formula, assuming your at sea level (ie. 14.7 = Atm):
(Atm+Boost)/Atm = PR
For your second compressor your Atm would be the product of your first compressor (29.4 here) plus 14.7 (to switch it from a gauge pressure to an atmospheric pressure). So use the same formula above but with 44.1 as your secondary Atm. So with a PR of 2.5 for our second compressor, the final boost pressure would be 66psig. Now go tractor pulling!
https://ls1tech.com/forums/forced-induction/257954-experts-how-calculate-compunded-psi-s.html
It's all about pressure ratios. Say your first compressor (turbo or SC) has a PR of 3. That gives you 29.4psig of boost though this formula, assuming your at sea level (ie. 14.7 = Atm):
(Atm+Boost)/Atm = PR
For your second compressor your Atm would be the product of your first compressor (29.4 here) plus 14.7 (to switch it from a gauge pressure to an atmospheric pressure). So use the same formula above but with 44.1 as your secondary Atm. So with a PR of 2.5 for our second compressor, the final boost pressure would be 66psig. Now go tractor pulling!
Last edited by Richiec77; Jan 5, 2005 at 05:51 PM. Reason: spelling
Staging Lane
Joined: Nov 2004
Posts: 76
Likes: 0
From: Apopka, FL
Originally Posted by Richiec77
started a thread asking how to calculate compound pressure ratio.
https://ls1tech.com/forums/showthread.php?t=257954
It's all about pressure ratios. Say your first compressor (turbo or SC) has a PR of 3. That gives you 29.4psig of boost though this formula, assuming your at sea level (ie. 14.7 = Atm):
(Atm+Boost)/Atm = PR
For your second compressor your Atm would be the product of your first compressor (29.4 here) plus 14.7 (to switch it from a gauge pressure to an atmospheric pressure). So use the same formula above but with 44.1 as your secondary Atm. So with a PR of 2.5 for our second compressor, the final boost pressure would be 66psig. Now go tractor pulling!
https://ls1tech.com/forums/showthread.php?t=257954
It's all about pressure ratios. Say your first compressor (turbo or SC) has a PR of 3. That gives you 29.4psig of boost though this formula, assuming your at sea level (ie. 14.7 = Atm):
(Atm+Boost)/Atm = PR
For your second compressor your Atm would be the product of your first compressor (29.4 here) plus 14.7 (to switch it from a gauge pressure to an atmospheric pressure). So use the same formula above but with 44.1 as your secondary Atm. So with a PR of 2.5 for our second compressor, the final boost pressure would be 66psig. Now go tractor pulling!
Actually, in tractor racing circles they are running 3 and 4 turbos in series/compound to run boost pressures upwards of 250 psi ...
Originally Posted by hangslo
Actually, in tractor racing circles they are running 3 and 4 turbos in series/compound to run boost pressures upwards of 250 psi ...
Jesus. How do they keep the heads on!!?? Probably have to weld them at that point.
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TECH Fanatic
Joined: Sep 2002
Posts: 1,112
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From: BLOOMFIELD, NY
Originally Posted by MIGHTYMOUSE
in series the pressure adds, flow stays the same
in parralel the flow adds, the pressure stays the same
in parralel the flow adds, the pressure stays the same
So will you see much of a power gain from running them in parralel. Is it worth it.
