crazyman03 Posted June 22, 2012 Author Share Posted June 22, 2012 (edited) I know turbos are on manual trannys.. Would an electric supercharger be bad on an automatic? Edit: since the boost doesn't change depending on how much rpm youre at?? -Justin Edited June 22, 2012 by crazyman03 Quote Link to comment Share on other sites More sharing options...
iceageg Posted June 25, 2012 Share Posted June 25, 2012 (edited) I don't know that an electrically driven supercharger would be any more or less strain on an AT than an MT. You would certainly have boost more readily availible but would always be getting 100% power draw to keep it going unless you rigged a way to modulate it. You would have to use a centrifugal supercharger and make sure you are within its cavitation limit to avoid boost stacking at partial throttle settings. I wouldn't try this setup on a carburated engine. Edited June 25, 2012 by iceageg Quote Link to comment Share on other sites More sharing options...
porcupine73 Posted June 25, 2012 Share Posted June 25, 2012 Interesting. Just curious, is there a surge curve for superchargers or turbos? Quote Link to comment Share on other sites More sharing options...
iceageg Posted June 25, 2012 Share Posted June 25, 2012 There most certainly is. It varies wildly from model to model. For instance, a traditional roots twin screw supercharger is positive displacement and will build more and more pressure at nearly any rpm if the flow is blocked off. Other twin screw style blowers like whipple units are not positive displacement and do allow for some backpressure. Centrifugal blowers and turbos provide the most flexibility here. The blower that we have sold the most of for aircraft is designed to produce a maximum of 21lbs of boost, but will not "stack" boost if it is operating below 14lbs output which is well beyond what we produce with our aviation kits. Instead of drawing more or constant power during this period of restricted flow, they draw less power to turn it. Have you ever held your hand over the end of a vacume? Listening to the electic motor you can hear it speed up. That is because it isn't flowing any air. In much the same way a boat propeller cavitates if you spin it too fast in the water an air compressor will begin to spin more freely when there isn't enough air to compress. To Crazyman's question, the electric motor would turn the blower at a constant speed creating say, 8lbs of boost. If the throttle was closed, the engine would still be operating under vacume. The 8lbs of boost is essentially waiting behind the butterfly at the trottle to jump in. While the 8lbs of boost is built up between the throttle and the supercharger the compressor is effectivly whipping the air it has into a froth the way a boat propeller does in the water requiring less power to turn it. Open the throttle and you instantly receive boost and create a load on the supercharger as it gobbles up more air to feed your hungry engine. The superchargers and turbos do have a point in their efficiency however where this no longer holds true and they start to build up pressure between the throttle and the compressor. Best case scenario here is one of your duct couplings pops and lets out the excess pressure. Worst case you break mechanical parts and have a new project to rebuild in your spare time. Quote Link to comment Share on other sites More sharing options...
crazyman03 Posted June 25, 2012 Author Share Posted June 25, 2012 ...Best case scenario here is one of your duct couplings pops and lets out the excess pressure. Worst case you break mechanical parts and have a new project to rebuild in your spare time. Well then.. that's a bit of a difference! would a BOV work? it would be funny to hear it sitting there whistling at a stop light lol Could you possibly wire a switch to the throttle that when the throttle is open that it starts the supercharger? there wouldn't be any back pressure to shove down its throat, but it wouldn't sit there and spin and damage anything and/or blow the ducting.. cant have that.. its my DD! I'm looking for a little UUMPH and some MPG while i'm at it! -Justin Quote Link to comment Share on other sites More sharing options...
iceageg Posted June 25, 2012 Share Posted June 25, 2012 Crazyman, lets back up a bit. How much boost are you looking to dump into your DD? Using a system that is designed similar to our aircraft kits you would still be looking at 25-33% more power and be well within the limits of boost stacking. You would also be looking at a 8HP electric motor instead of something closer to 15 or 20+ to achieve the 14-21lbs of boost that are going to cause problems. Directly to your question, I am not sure a standard BOV will release enough pressure for a supercharger or turbo that is continueing to build boost instead of spooling down. You would almost certainly have to dial back the electric motor when the trottle closed if you wanted to push big boost in this manner. And adding a supercharger will rarely improve your gas mileage. Your foot will just get heavier. Quote Link to comment Share on other sites More sharing options...
crazyman03 Posted June 25, 2012 Author Share Posted June 25, 2012 ...And adding a supercharger will rarely improve your gas mileage. Your foot will just get heavier. this is very true! Ok, how about this. I'm looking for a bit more uumph out of my engine, maybe a little MPG, but I dont have the time/money to drop another engine with a turbo & intercooler into my car. The Electric supercharger seemed appealing because I would be able to "switch" it on when I want the uumph, and then off if i'm just doing some OTR traveling. What I'm looking for is something that I can use to boost what I already have but keep stable enough to not damage anything. -Justin Quote Link to comment Share on other sites More sharing options...
NoahDL88 Posted June 25, 2012 Share Posted June 25, 2012 Ok, how about this. I'm looking for a bit more uumph out of my engine, maybe a little MPG, but I dont have the time/money to drop another engine with a turbo & intercooler into my car. You can go fast, reliable and cheap, pick two. Unless you want to spend real money, a tune-up will net you more power and MPG then anything else you can do for your engine. You have to pay to play. Period, end of story, full stop. If you want to go faster make your car lighter and clean it out, bump up the psi a couple of pounds in your tires and make sure all your fluids are clean and at the appropriate level. If you want to actually go faster you will have to spend actual money, a set of cams and an exhaust will be the best bang for your buck. Bottom line, you will never be as fast and reliable as a WRX, if you want speed and reliability get one, and in the long run it will probably be cheaper. If you don't have the money for a well engineered and designed turbo don't give up reliability for cheap parts, or you'll be spending a great deal more on getting your car running again purchasing stock parts. This forum is littered with threads like this, please search through them, you'll see that there is little to be done with no money or time. Quote Link to comment Share on other sites More sharing options...
iceageg Posted June 25, 2012 Share Posted June 25, 2012 Noah is right with his pay to play statement. Even with substantial fabrication skills and know people who can get you the parts you want at a discount you are still looking at four figures to assemble a turbo or supercharger system before you tune it. You can piece this sort of thing together from left over parts at a junk yard and ebay used components but you will never achieve any level of reliability that way. You also mentioned an attraction to the electric drive supercharger so you can shut it off when you don't want it. Keep in mind that when it is shut off your engine will have to suck air through the supercharger and all of its plumbing. It is similar to driving around with a really dirty air filter. You will end up with less power when it is turned off, and more power when it is engaged. Probably a larger issue is you will need to run two tunes for your engine depending on whether it is engaged or not. This will require some sort of piggyback ECU at the very least if not something more exotic like MegaSquirt. In the end if you are dedicated to the idea of a supercharger and reliability you are better off either sticking with an always running electricly powered unit or a traditional belt driven one, either pushing about 3-4lbs of boost. Then spending the $$ to get quality parts so it stays together. Quote Link to comment Share on other sites More sharing options...
iceageg Posted June 25, 2012 Share Posted June 25, 2012 One benefit you do have Crazyman is that you reside at 5000-6000' elevation. Your engine is starving for more power on its stock internals. You could go with 3-4lbs of boost and have your engine back to just a little more than it would have been at sealevel anyway. The stress on the engine internals should be negligible. Just something to consider if reliability is truely at the top of your list. Quote Link to comment Share on other sites More sharing options...
WoodsWagon Posted June 26, 2012 Share Posted June 26, 2012 You also mentioned an attraction to the electric drive supercharger so you can shut it off when you don't want it. Keep in mind that when it is shut off your engine will have to suck air through the supercharger and all of its plumbing. It is similar to driving around with a really dirty air filter. There are clutched roots type superchargers. Mercedes and Toyota both used them. Most belt driven superchargers have a bypass valve so under light load they aren't compressing any air. The toyota clutched one had an electric bypass valve. When the supercharger was off, the bypass was open. I have one out of a Previa. Fast, cheap and reliable are possible. The key is water/meth injection. It eliminates the detonation and superheated intake air temps for $2 a gallon. The systems are cheap to set up compared to most engine management solutions. An electric supercharger could be very straightforward. Supercharger turns on, bypass valve shuts, water/meth injection starts. Have it trigger by a throttle switch at WOT. Quote Link to comment Share on other sites More sharing options...
NoahDL88 Posted June 26, 2012 Share Posted June 26, 2012 The key is water/meth injection. It eliminates the detonation and superheated intake air temps for $2 a gallon. "Water/Meth is a crutch used when the system wasn't designed correctly in the first place." Corky Bell Quote Link to comment Share on other sites More sharing options...
WoodsWagon Posted June 27, 2012 Share Posted June 27, 2012 If that's his quote, then his "maximum boost" book has probably set water/meth back decades. It works, and it works well. Sure it's a crutch, but when you're dumping lots of boost into an engine not designed for it (high compression ratio) it does a great job. Dumping fuel in and retarding timing as you increase the boost is just as bad of a crutch. It also makes your fuel economy go down the drain. It's a heck of a crutch that lets you put 12.5psi into a 9.6:1 comp ratio engine from a severely overspun roots supercharger with no intercooler. Oh, and no tune or larger injectors. A crutch that continues to hold a highly abused engine together after 30k miles like that, including towing heavy loads cross country. Don't knock it until you've used it, water/meth works miracles. Quote Link to comment Share on other sites More sharing options...
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