Boost Loss
11-06-2008, 05:32 PM
#21
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Join Date: Apr 2008
Location: NJ
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BTW just out of curiosity, what type of application did you tell them you were running? I mean maybe they thought you were building a track only car or something. And although the companies you mentioned do have good reputations, I would recommend going to DSS, Livernois, or CHP for some additional advice. Even a good performance shop or engine builder can clarify things up a bit more for you because I personally think youi're gonna blow your engine up if you run that setup...
11-06-2008, 11:29 PM
#22
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Join Date: Feb 2006
Location: Virginia
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i built the engine in my brothers miata earlier this year. it came from the factory with a c/r of 9.5:1 and me and him installed a FM voodoo s/c kit on it and at 6psi he made 183hp at the wheels. a few weeks later he broke a connectiong rod. we built his current engine identical to the prior one but with c/r of 8.5:1. he took back to the dyno to get tuned and layed down 178hp at 6psi. so like i said, he "lost" 5hp from the lower c/r but no boost. thats would be how i know.(i know that sounded sarcastic, but i wasnt trying to be)
Boost is masured in psi (pounds per square inch) which is a measurement of pressure. Superchargers create a positive pressure. According to the laws of physics pressure is decreased when volume is increased and pressure is increased when volume is decreased. Altering the compression ratio does not alter the volume of an engine so it has no effect on boost. The only thing that would make sense to me is that perhaps the increased dish of the piston would allow for more volume in the cylinder walls which could possibly lower your boost. If that is true (and it was just an idea, I could be wrong so don't jump all on my case) then you could possibly see a minor decrease in boost. However it would be VERY minor and insignificant. I have never heard a reputable company recommend anything more than a 9.5:1 CR for boosted applications and most recommend no more than a 9.0:1 (for a STREET application) so maybe you heard wrong or misinterpreted what they were telling you. 10.5:1 is very excessive for forced induction and you would be stuck under a limited amount of boost AND you would probably run into problems in hotter weather. I would seriously doubt the reputation of anyone who said to run that configuration. And consider this, if you ran a lower CR you could keep adding more and more boost and you will surpass the limits of a high CR engine with boost by a very large amount. Now if you're only going to be using only race gas with an aftercooler and meth injection then your pockets must be very deep so go ahead and do your thing. Otherwise you're gonna crack those pistons. But to get back on point, no a lower CR will not have a significant or even noticeable effect on boost and no a 10.5:1 CR should not be used with a forced induction application...
BTW just out of curiosity, what type of application did you tell them you were running? I mean maybe they thought you were building a track only car or something. And although the companies you mentioned do have good reputations, I would recommend going to DSS, Livernois, or CHP for some additional advice. Even a good performance shop or engine builder can clarify things up a bit more for you because I personally think youi're gonna blow your engine up if you run that setup...
Last edited by Sxynerd; 11-06-2008 at 11:39 PM.
11-06-2008, 11:50 PM
#24
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11-07-2008, 03:41 AM
#25
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Ok, that does make sense. However I do not think you're gonna lose anything significant. I mean you are not increasing volume by any significant amount. If you increase the dish of a piston by 5 cc's and multiply that by 8 cylinders then you would have an extra 40 cc's of total volume increase. That relates to an extra 2.5 (approximately) ci. I don't think you're gonna lose mad boost by going from 281 ci to 283.5 ci. BTW, my car had 9.0:1 (17 cc dish pistons) CR with ported heads, stage 3 cams, bored .020, aftermarket intake set-up, and a vortech aftercooler set up and I still had 15 lbs of boost...out of curiosity, how much boost do you think you're gonna lose...??
11-07-2008, 08:11 AM
#26
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Ok, that does make sense. However I do not think you're gonna lose anything significant. I mean you are not increasing volume by any significant amount. If you increase the dish of a piston by 5 cc's and multiply that by 8 cylinders then you would have an extra 40 cc's of total volume increase. That relates to an extra 2.5 (approximately) ci. I don't think you're gonna lose mad boost by going from 281 ci to 283.5 ci. BTW, my car had 9.0:1 (17 cc dish pistons) CR with ported heads, stage 3 cams, bored .020, aftermarket intake set-up, and a vortech aftercooler set up and I still had 15 lbs of boost...out of curiosity, how much boost do you think you're gonna lose...??
I wanted a real answer for you guys, not the canned "you wont loose any" because I know that dropping compression does. Some of the most reputable Mustang Companies in America all agreed that boost level can be affected by compression. (**** Livernois, I wont call them)
Last edited by Sxynerd; 11-07-2008 at 08:13 AM.
11-07-2008, 09:15 AM
#27
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Join Date: Dec 2005
Location: Kentucky
Posts: 2,406
There is an article in the new 5.0 where they build a 2v with an F1R.
They explain that higher compression in that particular motor helped produce power and torque down low.
I agree that high compression and boost is not crazy, its just hard to make it work with pump gas. In theory you could run lot's of compression and lots of boost, but only without any timing..
I would be that adding more timing on a lower compression setup would equal more horsepower than the added compression ratio in a higher compression setup.
They explain that higher compression in that particular motor helped produce power and torque down low.
I agree that high compression and boost is not crazy, its just hard to make it work with pump gas. In theory you could run lot's of compression and lots of boost, but only without any timing..
I would be that adding more timing on a lower compression setup would equal more horsepower than the added compression ratio in a higher compression setup.
11-07-2008, 10:14 AM
#28
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Join Date: Sep 2008
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Boost is the level of pressure in the manifold and is created by restriction in the heads, cams, exhaust and intake. The intercooler is before the manifold and restricts the amount of air that can be forced into the intake which makes a lower boost pressure.
11-07-2008, 04:51 PM
#29
2nd Gear Member
Join Date: Apr 2008
Location: NJ
Posts: 451
There is an article in the new 5.0 where they build a 2v with an F1R.
They explain that higher compression in that particular motor helped produce power and torque down low.
I agree that high compression and boost is not crazy, its just hard to make it work with pump gas. In theory you could run lot's of compression and lots of boost, but only without any timing..
I would be that adding more timing on a lower compression setup would equal more horsepower than the added compression ratio in a higher compression setup.
They explain that higher compression in that particular motor helped produce power and torque down low.
I agree that high compression and boost is not crazy, its just hard to make it work with pump gas. In theory you could run lot's of compression and lots of boost, but only without any timing..
I would be that adding more timing on a lower compression setup would equal more horsepower than the added compression ratio in a higher compression setup.
