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Leveling the field: Applying turbo tech to a Vortech

S

SoopaCooga

Veteran CEG'er
Joined
Jun 19, 2001
Messages
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Fairfax, VA
We all know that forced induction devices work by compressing air, and that a supercharger is a belt-driven compressor, whereas a turbocharger is an exhaust-driven compressor. A centrifugal supercharger (e.g. Vortech, Paxton, Procharger) is an interesting animal in that its compressor is quite similar to that of a turbocharger. Because of these similarities, we may be able to borrow some turbocharger technology to improve the performance typically obtained from the centrifugal supercharger. :ponder:

Can turbo tech be applied to a supercharger? To find out, let's compare the typical processes for choosing a compressor. Let's say we want mild boost of 8 psi max.

The output of a centrifugal supercharger is dependent on engine speed (i.e. RPM). The faster the engine spins, the faster the supercharger spins, forcing more air into the engine. If we don't want to exceed our maximum pressure of 8psi, then we size the compressor and its pulley so that peak boost is made at peak RPM. The downside is that we don't get our full 8 psi until the red line.

Since it's not belt-driven, a turbocharger isn't constrained by engine speed. How then do we keep from pressurizing the engine above our 8 psi max? If we attempt to solve this problem in the same manner that we did the last time, then we would choose a compressor and turbine such that the pressure produced would not exceed our max. [The turbine is analogous to the supercharger pulley.] However, this is not what is typically done. Instead, the pressure is kept below maximum through the aid of a wastegate. The wastegate allows us to choose a compressor that outputs more pressure than our maximum, which is desirable so that we reach our maximum boost sooner. This is why a dynamometer chart for a turbocharged engine shows a characteristically flat torque curve, versus the peakier curve of the centrifugal supercharger. When comparing dynos from a Honda S2000, this becomes painfully clear! :laugh:

In theory, the dyno chart for the centrifugal supercharger could also be flattened out by using a wastegate. The wastegate would be setup to vent boost once we reached peak pressure, allowing us to use a compressor/pulley combo that could exceed our maximum pressure, which would in turn let us reach maximum boost sooner. :D

I got this idea from an article in Muscle Mustangs & Fast Fords. I hope I inspired everyone to buy a Blackcoog kit. :)
 
Say we have a centrifugal supercharger with smaller pulley (~15psi at max rpm) and a wastegate set to 10psi. At high rpms you are producing 10psi because you are dumping anything over that. Keep in mind you are still producing 15 psi at the supercharger outlet so the air temps will go up and there will be more hp lost to drive the supercharger harder which may or may not be signficant.
 
Blackcoog said:
Say we have a centrifugal supercharger with smaller pulley (~15psi at max rpm) and a wastegate set to 10psi. At high rpms you are producing 10psi because you are dumping anything over that. Keep in mind you are still producing 15 psi at the supercharger outlet so the air temps will go up and there will be more hp lost to drive the supercharger harder which may or may not be signficant.
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you're right, the supercharger will always be less efficient than the turbocharger, so there's a threshold below which it won't make sense to add the wastegate. but the idea is that you can reach 15 psi sooner - and maintain it longer - than otherwise, making your power curve less peaky.
 
This is already being done all over the place.. nothing new here.. this is almost as new of an idea as allowing the supercharger to free-spin on a clutch when not under load so it isn't making boost or dragging the FEAD, etc.
 
Ray said:
This is already being done all over the place.. nothing new here.. this is almost as new of an idea as allowing the supercharger to free-spin on a clutch when not under load so it isn't making boost or dragging the FEAD, etc.
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Well, I may have missed a previous discussion on the subject here, but I never came across it in a "supercharger vs. turbocharger" thread, such as this one. Why has nobody here tried it on their Vortech? It appears viable - and may be more desirable - now that more CEG'ers are pursuing power through forced induction.
 
Well, he has since sold the car and the Vortech, so unless you were just going to pick his brain on it or something, then take all I am saying with a grain of salt...
lol
 
I searched, but could not find where WorldTour installed a wastegate on his supercharger. Here's a rundown of the WorldTour setup from what I found:

1. Installed Vortech on 2.5L with 3.5" pulley (8 psi)
2. Installed Vortech on 3.0L with 3.5" pulley (4 psi)
3. Swapped pulleys on the 3.0L [unless I misread] to get 10 psi
4. Sold the Vortech kit on Ebay.

Did I miss anything?
 
I dunno, personally.

I left my "Worldtour financial recordbook" in my other jacket. I could be wrong, I guess.. I know he spoke of the application and its helpfulness, but it was right before he sold the car that he told me about it... maybe he was just saying what he wanted to do, a few days before the "sell" bug hit him?
 
Well, hmm, I guess I have a couple comments I can throw in here.

First, a wastegate on a turbocharger is NOT on the intake air side, it is on the exhuast side to bypass the turbine with excess exhuast flow. A wastegate does NOT bleed off compressed intake air. The OP does not make it clear whether he understands how a turbocharger wastegate works, but it could easy for a casual reader to interpret the post as saying a turbo wastegate bleeds compressor air, rather than exhaust around the turbine.

Second, a device as described, has been used by many people in the past, both on turbocharged systems and supercharged systems. It is essentially the same as a BOV used in a slightly different manner, where it blows off not only in overrun (when the throttle is closed) but also in normal operation to prevent overboosting. It was actually used extensively in the 80's turbocharger glory days of Formula 1, as well as some of the US-based open wheel series with small displacement, high boost racing engines. It was used to ensure that the racing engines did not exceed the boost limits set by the respective sanctioning bodies.

is it relevant to a duratec? Probably not. The fact of the matter is that it most certainly will not play well with a MAF controlled system, and even on a alpha-n system (speed density, common in standalone systems) it is very difficult to calibrate to run well. Further, you are still wasting the mechanical energy required to spin the blower that much faster at high rpm, giving much higher parasitic losses, plus you have the likely decreased adiabatic efficiency (obviously dependant on the particular application) which results in higher temperatures in the compressed air.

In regards to Worldtour's old car, I believe he just had a typical bypass valve for overrun conditions.

In summary, could it be made to work, and improve the power under the curve? Yes. Is it worth it? Probably not, the effort and expense to make it work well would dwarf the actual benefit from it. There are other simpler, and readily available solutions to improve output. Heck, if you are dead set on spending large amounts of money and effort, I think a variable speed blower drive would give more benefit and be easier to tune for, lol.
 
Rara said:
Heck, if you are dead set on spending large amounts of money and effort, I think a variable speed blower drive would give more benefit and be easier to tune for, lol.
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Everything i was gonna say... and my thoughts exactly.
 
Can someone explain a little more please. To my mind, if you put a 'wastegate' on a supercharger system to limit the psi..then the air pressure would stay at a level but the cfm would rise with RPM to the superchargers capacity.The air temperature should level out ..partly because the supercharger would run cooler (at say half its' capacity)... by not creating its' highest rated pressures and having a greater air throughput. Also could you explain that MAF issue too please...if the MAF is after the 'wastegate..why would it be a problem ?. thanks G
 
gorman said:
Also could you explain that MAF issue too please...if the MAF is after the 'wastegate..why would it be a problem ?. thanks G
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The MAF should not be an issue if it is after the wastegate. if it's before the wastegate, then it will have sensed more air than is actually going to arrive at the throttle body if the wastegate cracks open. of course, a blow-through MAF would be preferable if the MAF is to be located after the supercharger (and wastegate).
 
You could still run a suck through MAF if you dumped the over pressured air back into the intake track before the supercharger but after the MAF like a bypass valve. A blow through would be the simplest setup and easiest to tune though. It almost seems like blow thru setups are being preferred more and more because the MAF is closer to the TB giving better throttle response and it makes tuning easier.
 
The problem with putting a wastegate on a supercharger is that it makes no sense.

The wastegate is in the exhaust stream to divert exhaust gas from the turbochargers turbine.
 
Blackcoog said:
You could still run a suck through MAF if you dumped the over pressured air back into the intake track before the supercharger but after the MAF like a bypass valve.
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But then you would basically be compressing the same air twice or even more times adding even more heat into the inlet air. Seems awfully counterproductive.
 
Rara said:
But then you would basically be compressing the same air twice or even more times adding even more heat into the inlet air. Seems awfully counterproductive.
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True, but if you have a correctly sized intercooler and dump the air after the intercooler the heat may not be a problem. I'm not saying it's a good idea but it could be done or probably has been done.
 
Blackcoog said:
True, but if you have a correctly sized intercooler and dump the air after the intercooler the heat may not be a problem. I'm not saying it's a good idea but it could be done or probably has been done.
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Well, it has definately been done. And I do think it is worthwhile in very certain applications, like in racing where there is a very strict boost limit, or something like that. For a street car, where such limits don't exist, just up the max boost a bit and throw a little more fuel at it in the calibration :D Or just use a turbo instead, lol.

But, I'm serious that if someone came up w/ a good, reliable variable speed drive for an SC it would be a major step forward.
 
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