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Old 03-29-2004, 06:26 PM
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Minimum compression for supercharger

whats the minimum requirements for a supercharge to work properly?

like the compression the piston types and can types. Im just kinda of curious.

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Old 03-29-2004, 06:36 PM
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Well I dont know the minimum, but I do know that you can run gasoline on like 6:1, hell it should light just fine if it wasnt even compressed.

Can't run cast pistons, your just asking for trouble there. Either hypereutetic(however spelt) or forged. It is also better to run a cam with more duration on a supercharged motor so the blower is able to push air/fuel into the cylinder sooner. Typical compression is around 7.5-8.5:1 on blown motors.

Other than that simple answer, what exactly do you want to know?
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Old 03-29-2004, 08:03 PM
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I would guess stock or slightly above would be fine for a blower. You don't want high compression with a blown or bottle fed engine without some major bottom end mods, or you will literally have a blown engine with a very ugly hole in the block. Stock bottom ends aren't up to the task of the combined pressure of high compression and bottle or blower.
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Old 03-30-2004, 08:37 AM
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Are you talking a street car? Pump gas? Alcohol? Nitro? This all makes a difference.

I will assume a pump gas engine, If that is the case it will also depend on engine size and blower size.

I would not run lower than 7.5:1 and depending on the type of blower probably no more than 9:1.

If you run 7.5:1 you will have a little less botom end, than say 8.5:1 but, you will be able to run more boost and "should" be able to make more power up top. It is a balancing act and you have to decide what you are looking for.

I am running 8.47:1 in my 388ci SBC with an 8-71 on it. I have seen 10lbs of boost so far and not problems at all. It has an incredable amount of torque and bottom end.

Royce
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Old 03-30-2004, 11:58 AM
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You can run very low compression with a forced induction engine, but it is really not recommended for street use. Anything below 8:1 and you get into hard starting and the engine being a real dog off boost. For full race engines the 6:1 would be a viable option since it will allow more boost without detonation and consequently more power.

Another thing to consider is cam selection when talking about CR. If you try to run a larger cam with forced induction the low end power will suffer even more. My turbo engine is 8.5:1 static compression ratio, but the dynamic is 6.6:1. The engine starts and runs good as is, but I think if compression was much lower it would have problems starting. It was also very hard to get the idle and cranking fuel table set properly. With a carb, it would probably be worse about starting. Just something to keep in mind.....

Chris
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Old 03-31-2004, 10:34 AM
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I would have to agree with turbo-s10. I have never heard of running more duration is better on a blower, infact this is a perfect example of bigger is not always better. A typical street blower cam usually is around 230 to 250 dur @ .050 and somewhere around 112-114 center lobe . I have tried a few larger duration cams with blowers and they didnt work well for street use.
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Old 03-31-2004, 10:58 AM
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I was thinking more along the lines of 280s 290s adv. dur. going up from the 250s or 260s you see in stock factory cams.
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Old 03-31-2004, 12:02 PM
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id stick with between 8.5:1 and 9:1 especially with a non intercooled roots blower.

(with a setup like turbo s10 on the other hand, you could get away with 7:1 with high flowing heads and an intercooler to really take advantage of that enormous turbocharger.. how does 28 pounds of boost strike you chris?)
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Old 03-31-2004, 12:25 PM
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Quote:
Originally posted by deuce_454
id stick with between 8.5:1 and 9:1 especially with a non intercooled roots blower.

(with a setup like turbo s10 on the other hand, you could get away with 7:1 with high flowing heads and an intercooler to really take advantage of that enormous turbocharger.. how does 28 pounds of boost strike you chris?)

Yep, If the S-10 chassis proves itself in the 9 second range and for some stupid reason I want an 8 second street truck I might try to stretch the legs of the big snail one day. With good heads and a cooler it should make 30psi for around 1000HP or more.......problem is that it would probably split my oem block in half. I think I can get to the 9's within a year on the parts I have(plus cooler and a possible head upgrade). Below is a link of a syclone that runs 27psi on a Vortec V6 for 10 second quarter mile times on street rubber after 200 mile drives to the track. One interesting note is that he is doing it with composite gaskets and no orings.......a real testament to efi tuning. One of his buddys is a developer on the VEMS(Versatile Engine Managment Systems) Group that designed the board I am running. BTW, VEMS is the new name of what used to be called Megasquirt AVR group. The group is now running the v3 genboard that is the most powerful diy-efi board designed to date and is alot nicer than many of the aftermarket units.

http://www.beverlyhillsvideo.se/nysy/start.asp


Later,

Chris
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Old 03-31-2004, 01:28 PM
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DUDE no way, ive been messing arround the megasquirt AVR page and the guys seem to work 15 mutes drive away from me, how do i get in contact with some of them, i would really like to talk to someone in person about the VEMS... i still need an efi setup for my stack injection.. arent they from denmark??? by the look of it they are from DTU about 6 miles from me...

Last edited by deuce_454; 03-31-2004 at 01:34 PM.
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Old 03-31-2004, 01:43 PM
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Duece,

Some of them are in Denmark and some elsewhere. They do all the development over the web as far as I know. I will email you the instructions for getting on the developers chat line. I am on there alot lately trying to learn. Right now, we are trying to get one of the hotrod $2004 challenge cars up and running for the race this weekend. He has to load it to the trailer tonight and it has not cranked yet......everyone is busy.

BTW, if you dont get the email, send me an email and I will reply with instructions......dont want to flood the channel by posting it here.


Chris
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