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High Compression and Supercharging vs. Engine modification


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#1 OFFLINE   Shelby2809

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Posted 01 February 2010 - 12:24 PM

I feel like I know a lot about cars and how things work... truth is I don't really understand why the new 5.0 engine and its high compression ratio is bad for Supercharging. Maybe someone with a stronger knowledge of this could help explain it to me.

My second question, based on my knowledge of high compression engines is, why not upgrade the cams, intake (including porting and polishing the heads), and exhaust instead of supercharging this engine? It seems like that would be a safer way to get more HP and make this new GT350 very unique in the aftermarket Mustang world.

Thank you in advance, I'm very interested to understand this a bit more.

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#2 OFFLINE   DutchGT500

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Posted 01 February 2010 - 02:09 PM

Faster way for detonation when there is too much boost. F.e. when people smaller pulley the SC.
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#3 OFFLINE   Son of GT

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Posted 01 February 2010 - 04:51 PM

In a nutshell, you generally don't want to force air and fuel under pressure (boost) into a high compression engine because the higher pressure will sooner or later wreck havoc on the valve train, head gaskets, heads, piston rings, connecting rods, rod bearings, and crank bearings. You could also end up bending the crank if it was not hardened. You could stretch the head bolts, and the intake manifold could also lift off the head too.

Additionally, and as Patrick (Dutch) stated, forced induction into a already high compressioned engine also causes detonation to occur, and that would destroy the tops of the pistons among other internal components.

A simplistic, "Mr. Wizard" way of putting it would be to take a balloon and just blow it up with your lungs until it's almost ready to pop. It would probably take you 25 to 40 puffs and about a half a minute to blow up an avarage sized balloon until it popped. Now take another, but smaller balloon and fill it with air from an air compressor. It would probably take you less than 15 seconds to fill it before it popped.

Perhaps that's not the best example I could give you, but I believe that it gives you a broad idea of the differences between a low compression engine and a high compression engine.

The GT350 is being supercharged under the care and guidance of Ford Racing, and essentally the boost pressure on the 5.0 and whipple combo will be quite low, but god help those folks who decide to increase the boost after they get the car home from SA.

It's the same thing with the Dodge Hemi engines too. Mopar says not to supercharge those engines either, but I have seen a few Challengers that have been supercharged with low boost Paxtons and Novi chargers in spite of that warning.

Hope this helps.

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#4 OFFLINE   Shelby2809

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Posted 01 February 2010 - 05:11 PM

Thanks for the replies, that helps to understand why you should apply to much boost to that motor.

What about the second question... if its not good to apply too much boost, why not increase intake and exhaust flow to increase the power in these motors instead? From other posts, I'd venture to say, intake, exhaust and cams would cost about as much as a supercharger (maybe a few hundred $ less)? Wouldn't that be a better way to go? Thanks again,

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#5 OFFLINE   Son of GT

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Posted 01 February 2010 - 05:21 PM

Thanks for the replies, that helps to understand why you should apply to much boost to that motor.

What about the second question... if its not good to apply too much boost, why not increase intake and exhaust flow to increase the power in these motors instead? From other posts, I'd venture to say, intake, exhaust and cams would cost about as much as a supercharger (maybe a few hundred $ less)? Wouldn't that be a better way to go? Thanks again,

Jim



That would be a better way to go Jim, but then the car (engine) would not meet 50 state emissions requirements, and SA can't let a car out of their facility unless it meets all federal and state emission and safety requirements.

I, living in California, could not do any of those mods to my car without violating about 15 laws that say I can't.

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#6 OFFLINE   Shelby2809

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Posted 01 February 2010 - 07:17 PM

That would be a better way to go Jim, but then the car (engine) would not meet 50 state emissions requirements, and SA can't let a car out of their facility unless it meets all federal and state emission and safety requirements.

I, living in California, could not do any of those mods to my car without violating about 15 laws that say I can't.



Gotcha, that makes sense. Maybe they'll do an "R" version this way... hint hint.

Thanks again guys... see how my brain goes when I'm on the road for work, all I think about is these cars and what we could do with them.
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#7 OFFLINE   DubbsFaris

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Posted 01 February 2010 - 08:30 PM

Yeah, SAI is bound by manufacture licensing to not do that kind of engine work....that said....YOU could after you buy it....

I had the high compression explained to me as this...your 5.4 boosted becomes a high compression engine when you add the supercharger. The way the 5.0 is put together already gives you that high compression rate without a supercharger. At some point, every engine has its compression limits....or to put it more accurately, SOME component or components will fail.
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