Another one for all you techies.
Discussion
Just wondering if you guys think this might be a viable solution to the age old problem of turbo lag and supercharging. I have seen a few motors running both a turbo and supercharger but all seem to be running the blower first and then the turbo. I was thinking, could you run the turbo into a normal fixed displacement supercharger (roots type)? I cant see it not working as all the supercharger is moving is moving a fix volume of air, regardless of the pressure it is at!
There would be some issues with efficiency, roots type blowers can put a lot of heat into the charge, and as its already compressed, this may increase the problem. To counter, you could run an intercooler after the turbo and then a charge cooler after the supercharger. Also there is water/alky injection which would help a lot.
Anyway, what are your thoughts? Could this be the answer to lowering spool up and still running loads of boost? Or am I barking up the wrong tree (again)?
Thanks Chris.
There would be some issues with efficiency, roots type blowers can put a lot of heat into the charge, and as its already compressed, this may increase the problem. To counter, you could run an intercooler after the turbo and then a charge cooler after the supercharger. Also there is water/alky injection which would help a lot.
Anyway, what are your thoughts? Could this be the answer to lowering spool up and still running loads of boost? Or am I barking up the wrong tree (again)?
Thanks Chris.
I think it's OK. A Roots blower does no actual compressing itself; it stuffs a fixed volume of air per rev into whatever's downstream of it, and the pressure rise depends on the flow characteristics of the downstream system. So I think that if the Roots blower is fed with air from a turbo at the same pressure as you would be expecting the supercharger to produce if it was running from atmospheric pressure at the inlet, the blower rotors would no longer be transferring any energy to the air, and the turbo would be doing all the work.
Detroit Diesel two-strokes all have a Roots blower as a scavenge blower; there are also turbo versions and I think they do something similar to the above.
The disadvantages are that you get all the problems of a turbo installation AND all the problems of a supercharger, in return for probably not that much gain in efficiency, which is probably why it's not done more often.
Detroit Diesel two-strokes all have a Roots blower as a scavenge blower; there are also turbo versions and I think they do something similar to the above.
The disadvantages are that you get all the problems of a turbo installation AND all the problems of a supercharger, in return for probably not that much gain in efficiency, which is probably why it's not done more often.
Screw blowers are the way to go with turbo like efficiency (+80% Adiabatic).
G-Laders can't produce enough boost, Pressure Wave have heating issues, Vane blowers are extinct. Rootes 4th generation are pretty good but struggling to hit 60%. Boost limited to about 12PSI.
Screw blowers are the future. Sadly my mini has a Rootes 4th gen (1966 mini)
Turbos are good, but no cigar. I suppose you could offset the lag/power consumption of a supercharger by using a turbo combo, but I would rather go with simplicity. Haynes used to do a Silver "Handbook of Turbocharging and Supercharging". It is a properly written text for engineers. I haven't totally lerned it yet but screw blowers are the go.
G-Laders can't produce enough boost, Pressure Wave have heating issues, Vane blowers are extinct. Rootes 4th generation are pretty good but struggling to hit 60%. Boost limited to about 12PSI.
Screw blowers are the future. Sadly my mini has a Rootes 4th gen (1966 mini)
Turbos are good, but no cigar. I suppose you could offset the lag/power consumption of a supercharger by using a turbo combo, but I would rather go with simplicity. Haynes used to do a Silver "Handbook of Turbocharging and Supercharging". It is a properly written text for engineers. I haven't totally lerned it yet but screw blowers are the go.
Thanks for all the responses. I agree that screw type blower (such as the Whipple) are the way forward, but they are still limited. They would require a HUGE amount of power to develop say 30psi, whereas turbos can make this easily. Also as turbos become cheaper to produce, more manufactures are turning to them. Also they allow you to adjust what level of boost you want.
The ideal solution would be to run a supercharger (be it roots or a screw type) at say 6-7psi, then let the turbo take over and produce say 15+psi. You may have to set the pressure after the turbo slightly less as the supercharger would be compressing air already pressurised. This way you have all the advantages of a supercharger, but still the boost potential of a turbo. Also lag would be none existent and spool up of the turbo would be much quicker as you have 6-7psi from just past tick over. The only problem would be the blower, and if it “let you do it”.
So if the supercharger was producing 1bar (hypothetical and to help with the maths), and the turbo was producing 1bar before the supercharger, then the combined pressure (neglecting losses) would be 2bar and the intake. Is this right?
So what do you think, could this 2 stage boost work? If it did work then think of the potential. How about a 2.0ltr producing 600+bhp and still being as driveable as stock!
Thanks again Chris.
The ideal solution would be to run a supercharger (be it roots or a screw type) at say 6-7psi, then let the turbo take over and produce say 15+psi. You may have to set the pressure after the turbo slightly less as the supercharger would be compressing air already pressurised. This way you have all the advantages of a supercharger, but still the boost potential of a turbo. Also lag would be none existent and spool up of the turbo would be much quicker as you have 6-7psi from just past tick over. The only problem would be the blower, and if it “let you do it”.
So if the supercharger was producing 1bar (hypothetical and to help with the maths), and the turbo was producing 1bar before the supercharger, then the combined pressure (neglecting losses) would be 2bar and the intake. Is this right?
So what do you think, could this 2 stage boost work? If it did work then think of the potential. How about a 2.0ltr producing 600+bhp and still being as driveable as stock!
Thanks again Chris.
this is right, if you wanted to run really high boost (like 2bar +) on most engines , then you would have to back off timing a lot or run low comp. but most suppercharged engines using roost run low com anyway. also the air entering the supercharger would be around abbient, thanks to intercooling and water/alky injection. also this injection would would help reduce det. and drivablity would be as good thanks to the blower sorting boost out at low rpm.
also there are ways to help with both these problems. thermal coating the chambers will instantly reduce det. and may give you a few more ponies. hot roders in the states are really getting into coating and in an article i read they said that there is little on an engine that cant be coated. take a look on www.hotrod.com for more info.
so some on, do you guys and girls think this system could work? we can worry about the problems later!
thanks Chris.
also there are ways to help with both these problems. thermal coating the chambers will instantly reduce det. and may give you a few more ponies. hot roders in the states are really getting into coating and in an article i read they said that there is little on an engine that cant be coated. take a look on www.hotrod.com for more info.
so some on, do you guys and girls think this system could work? we can worry about the problems later!
thanks Chris.
I'm no expert inthis field at all - but why not go for something like the anti-lag systems on WRC Cars?
www.kiwisport.net/techtalk.html
"[snipped]
So the biggest problem with turbos, which all WRC cars use, is that they take a short amount of time to spin up to useful speeds - this is called lag. It is noticeable in most road going cars below about 3000rpm, below this point acceleration is 'sluggish' and above it acceleration comes as expected. No driver wants this but it is a fact of any turbocharged engine and it's performance. The engineer's problem is how to minimize the lag. Lancia's Group B car used a supercharger at low revs, which has no lag, and then the turbo higher in the rev range - but that's another story.
Current technology gives engineers the chance to minimize turbo lag through the use of electronic wizardry and stronger mechanical parts. When the driver backs off the throttle the engine management computer advances the ignition timing by around 40 degrees and continues to feed fuel into the combustion chambers. By moving the ignition point like this most of the fuel remains unburned as the exhaust valves open and the mixture is flows into the exhaust manifold. Obviously the manifold is extremely hot and the unburned mixture explodes creating a huge force, driving the gas through the turbo and hence keeping it at a usable revolution speed. Once the driver pushes the throttle down again the computer changes the ignition and fuel settings back to normal and the boost is available for maximum power.
Most WRC teams use anti-lag systems of this sort which are driver adjustable. The explosive force of the detonation in the exhaust manifold near the turbo is enough to damage the already abused components in a rally car. So when the drivers are moving between special stages they turn it off or to a minimum. This sort of system in a road car would destroy the turbo and exhaust manifold in a matter of minutes and regardless, is probably too noisy for most countries vehicle regulations.
"
and sounds super sweet!
I also hear they have an anti-lag for the anti-lag now too but not sure how that works.
best
Ex
Some stuff on Cosworth Antilag here
www.wrc-cosworth.org/tech/tuning/antilag.html
www.kiwisport.net/techtalk.html
"[snipped]
So the biggest problem with turbos, which all WRC cars use, is that they take a short amount of time to spin up to useful speeds - this is called lag. It is noticeable in most road going cars below about 3000rpm, below this point acceleration is 'sluggish' and above it acceleration comes as expected. No driver wants this but it is a fact of any turbocharged engine and it's performance. The engineer's problem is how to minimize the lag. Lancia's Group B car used a supercharger at low revs, which has no lag, and then the turbo higher in the rev range - but that's another story.
Current technology gives engineers the chance to minimize turbo lag through the use of electronic wizardry and stronger mechanical parts. When the driver backs off the throttle the engine management computer advances the ignition timing by around 40 degrees and continues to feed fuel into the combustion chambers. By moving the ignition point like this most of the fuel remains unburned as the exhaust valves open and the mixture is flows into the exhaust manifold. Obviously the manifold is extremely hot and the unburned mixture explodes creating a huge force, driving the gas through the turbo and hence keeping it at a usable revolution speed. Once the driver pushes the throttle down again the computer changes the ignition and fuel settings back to normal and the boost is available for maximum power.
Most WRC teams use anti-lag systems of this sort which are driver adjustable. The explosive force of the detonation in the exhaust manifold near the turbo is enough to damage the already abused components in a rally car. So when the drivers are moving between special stages they turn it off or to a minimum. This sort of system in a road car would destroy the turbo and exhaust manifold in a matter of minutes and regardless, is probably too noisy for most countries vehicle regulations.
"
and sounds super sweet!
I also hear they have an anti-lag for the anti-lag now too but not sure how that works.
best
Ex
Some stuff on Cosworth Antilag here
www.wrc-cosworth.org/tech/tuning/antilag.html
dont worry, i had already thought of it 
anti lag is a great thing, dont get me wrong, but for road use it is a little too sevear on the turbo. even rally cars turn the "bang Bang" off on the raod sections to save the turbos. also with anti lag on the EGTs go through the roof! this puts greater stress on the manifold and the turbo itself. i read an artile on it once and it was very nicly discribed as instead of using a gloved finger to spin it, using a hammer!
there are other forms of anti lag that are les stressful than the bang bang type, but these are less effective.
the supercharger and turbo is the only solution that i have sean that would be road usable and not require constant turbo rebuilds.
thanks Chris.
anti lag is a great thing, dont get me wrong, but for road use it is a little too sevear on the turbo. even rally cars turn the "bang Bang" off on the raod sections to save the turbos. also with anti lag on the EGTs go through the roof! this puts greater stress on the manifold and the turbo itself. i read an artile on it once and it was very nicly discribed as instead of using a gloved finger to spin it, using a hammer!
there are other forms of anti lag that are les stressful than the bang bang type, but these are less effective.
the supercharger and turbo is the only solution that i have sean that would be road usable and not require constant turbo rebuilds.
thanks Chris.
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