Just a thought, but here is my idea. The argument I hear most of the time for turbo over supecharger is that the engine spends more time at max boost resulting in more power under the curve where a supercharger only produces max boost for a short time at max RPM. Could you pulley your supercharger for higher a higher boost level than you need but vent the extra psi through a blow off valve so that you would see max boost for a longer duration? For example, say I want to use a T-Trim to achieve 6 psi, could I use a pulley combination that would produce 10 psi but have a blow off valve set at 6 psi to vent the excess pressure or would the extra heat from compressing the air negate the effects having max boost earlier? This might be a stupid question because I think if it would work there would probably be alot of people doing it already, never hurts to ask though.

 

Ive been REALLY thinking about this for the last few weeks.... youd have to use something similar to a wastegate, instead of a BOV, to vent it.

I was actually thinking about a all in one unit for a SC application.. a wastegate/BOV all in one. Regulate boost and upon coming off WOT to then completely vent.

Im sure we arent the only ones thinking about this cause when mentioning it both people I talked to said they had thought of the same thing.

Overclock the SC to see a higher, X, PSI @ lower RPMs then vent it but maintain X PSI all the way to redline. A lot of people use bigger SCs then needed anyways for efficiency, D1SC for example, so overclocking it woudnt be that big of a deal, IATs wouldnt suffer much cause the motor would still only see X PSI AT the motor, the rest would be vented pre manifold.

 

This has been discussed many times before. The problem is that you build up alot more heat because the compressor is run out of its best efficiency range. Also, there are max speeds for superchargers. Most people aim to spin it the max speed in the base case anyway.

Mike

 

HEY breakmyfootoff, change the title to this thread to something else to generate more views on this topic... I want some discussion on this.

Maybe "Boost controller on a SC?"

Yeah but if you have say a D1SC, with a normal set up, most stock motor cars arent going to run more then 7-8psi, the D1SC is pretty damn efficient at that PSI, right?

So lets say with a 8# pulley when you hit the throttle, WOT, at 3KRPM you make 3psi, 4KRPM you make 4-5psi, 5KRPM you make 6-7psi, and by 6K youre making your 8psi. *dont know if this is accurate real world, just an example.*

Lets say with this device we are discussing about, boost controller, that your goal is 8psi across the board. Find out what pulley would be required to generate round about 8psi @ 3KRPM or so, lets say its a 12# pulley *I have no idea what pulley would be required, this is a guess.*, then vent a gradual 4#s of boost starting from 3KRPM all the way to redline.... that way you make 8psi from 3K-6KRPM.

Lets say that would work on a D1SC with a 12# pulley... isnt the D1SC still pretty efficient at that kind of boost? Especially since they are either twin SMICed or in some cases FMICed. Not to mention if you vent those 4#s prior to the manifold, of course, wouldnt venting compressed air cause a rapid cool down? Kinda like a aerasol (sp?) can? Ever noticed on a small BBQ the propane canister is frosted when you use it, the compressed propane inside isnt cool but once you vent it the contents become COLD. I dont know if that would apply here but I dont see why not.

If the SC youre using is capable, and can produce that PSI you need to make, then all it would take is developing something like a wastegate to gradually bleed boost vs rpm.

I dunno.. I think it could work.

 

it will work, there are people that have done it. But you have to have a big enough blower to move the extra air that you are venting off. Keeping it in the efficiency range is very important. In the 12psi example above if you are sending 8psi into the engine and 4psi into the atmosphere. Since you are moving about 50% as much air out to the atmosphere as you are into the engine. So if your engine takes 750cfm(~525hp) the blower is pushing 1125cfm(~775hp). If you have a big enough blower to keep that in the efficiency range then you're good to go. Using a wastegate would be your best bet.

 

The D1SC is efficient at 12 psi and ~60 lb/min, but not necessarily 8 psi and 90 lb/min. Your idea puts it in a totally different place on its compressor map than putting all the boost through the motor.

Also, depressuring gas does cool it off, but the only gas that gets cooled is the gas escaping through the valve, so that won't do you much good.

If you want to fix the low-rpm lack of boost, install a higher stall converter.

Mike

 

Yeah I knew you could match a converter to the boost but in my case Id have to install a A4 with it. M6 here..

Hmmm I just think this would be a great thing to have for the SC guys and seems it wouldnt be TOO incredibly hard to make work.

Maybe the vented air could be directed back onto the charge pipe after the venting point, cool off the pipe itself, or even onto the IC surface to have make that vented cooled air help out some how.

 

I don't think you'd see any benifts by venting the hot air back on the intake piping. I've never seen air vented from a compressor get to cold. Venting certain liquids or propellants (sp?) may cause an extreme temp drop, but I can't see staight air having enough of a temp drop to cool the intake piping.

If you're going to pulley up the compressor, why waste the extra boost by venting it anyway. Your already heating it up a bit, and it probably taking more hp to turn the compressor pulley at the higher speeds. Seems like it is leaving a lot of hp on the table at the higher end of the rpm range, which the motor should be in for most of the time, when making a pass.

Personally, I think rpm dependent boost isn't really a bad thing. Especially if you're talking about streetcars, where traction is usually an issue.

 

Why can't you match your launch rpm to the boost you want? Seems like a 6speed would make that easier.

 

If its a stock M6 unit and/or 10 bolt under there... i dunno how long it would enjoy that sort of launch (assuming he caught traction).

 

When you depressure a gas, it does cool down.

However, if you pressure up a gas from ambient 14.7 psia/60 deg F to 8 psi, the temperature rises to 130 deg. F, assuming 100% efficient compression. If you depressure that to ambient, the temp drops back to 60 deg F.

Now, if compression is less than 100% efficient, then the temp will rise beyond 130 deg. F and, consequently, when you depressure it the temp will be above 60 deg. Since superchargers are in the 70% range, the depressured boost would wind up being hotter than ambient.

Mike

 

Well, how would launching with more boost be any better for the 10 bolt, or any easier to get traction?

 

The reason I'm wanting boost at a lower rpm with a supercharger is not soley for drag racing, drag racing is not my primary concern. I'm thinking that something like this would provide awesome part throttle response and driveability.The way most superchargers and turbos are set up only provide their best performance under WOT with a heavy load on the engine. The reason I'm wanting to go this route is that a supercharger provides a certain amount of boost for a given engine rpm, a turbo is spooled more by exhaust gas volume than rpm. For example, maintaining a speed of 60 mph at 2500 RPM at light or part throtle will not cause the turbo to spool up and provide boost, you would have to have the throttle open more to allow a larger volume of air into the engine which in turn would generate a larger volume of exhaust gasses which would then spool the turbo and provide boost. With a supercharger set up to provide 10 psi at 6500 rpm it would still provide 4 to 6 psi at 2500 rpm regardless of throttle position or exhaust gas volume (the 4 to 6 psi is an estimation) . My thinking is that a setup like this would provide more power throughout the rpm range with better throttle response and make the car more responsive and more fun to drive in all situations instead of just at WOT in a straight line with slicks and a prepped racing surface.

 

If it compromises peak power for a little low-end response, I'M OUT. I'd bet that 9 out of 10 enthusiasts here wouldn't do it either. Sounds like you need a stroker or roots blower.

Mike

 

Why would it? A roots would be exactly that.. low end with less peak and complete fall off up top. This wouldnt do that... it would hit peak boost early and hold it all the way to redline, just like a turbo.