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Old 07-23-2010, 02:06 AM   #1
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Default High compression plus boost?

I have been thinking of the idea...I think a lot when my car is in the shop--more so on how to spend more money.

Would it be worth the benefit over risk to run high compression pistons on pump meth? And if so would I be able to get away with say 15 pounds of boost?

Discuss...

Also, if anyone wants to build me a short block PM me
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Old 07-23-2010, 02:14 AM   #2
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This is a neverending argument on other forums. Seen this dilemma come up earlier in a few threads, but let me take a crack at it:

higher compression = a bit better throttle response, and more power with less boost, but your margin for error in tuning, detonation, etc etc etc is much smaller. Something doesn't go according to plan and you got yourself another paperweight block or pistons.

Honda's get away with higher compression engines on boost but they have one VERY important ingredient that miatas don't: FLOW.

Their top ends flow more than hustler on day 3 of his period.

take the s2k motor: high compression + high flowing head + hefty turbo = 450+whp on some ridiculously low pressure level like 12psi.
We can only dream of something like that.

Last edited by 18psi; 07-23-2010 at 02:27 AM.
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Old 07-23-2010, 06:16 AM   #3
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The problem with high compression turbos is heat. The added heat from the turbo can be removed with an intercooler or water injection - when you compress the charge inside the cylinder, there's no way to remove extra heat. More heat in the chamber means you are required to run less timing, and the power levels start to fall. When you look at Hondas and such stuffing boost into high-compression engines, it's always big turbos and low boost - that combo is required to keep the intake charge heat as low as possible so they can still use 11:1+ compression.

Knock the compression down and suddenly the heat goes away, which means you can run more boost, smaller turbos, and more timing. Low compression Miata motors make serious torque because they can run lots and lots of timing - and timing is where you make power. Hustler's proven it, I've proven it by making 300tq through a stock '99 intake manifold at only 18psi.

I don't think pump+meth won't be enough to run MBT on a high compression motor at 15psi.

You have PM regarding the shortblock, we can easily assemble a duplicate of the motor powering my race car for you.
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Old 07-23-2010, 12:12 PM   #4
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A turbocharger is a much more efficient compressor then the motor is, might as well make use of it.
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Old 07-23-2010, 01:12 PM   #5
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When you say pump meth, do you mean meth injection, or did you mean pump eth(anol).

We are advising customers these days who are looking for an e85 build to go 10:1 or higher. We have a couple 12:1 cars out there, and while the tune has to be really tight, the fact that ethanol is the fuel still makes it a bit forgiving. If it's an occasional ethanol car with some pumpgas running through it as well, then we typically advise folks not to go over 9.5:1.

Edit: I just read you sig, which says "pump/meth"...the lack of the slash in your post confused me. If you are on meth injection I'd say stick to a lower compression (below 10:1) in the event you run out of methanol. Even with boost cut protection if you run out anything over 10:1 might be too high for pumpgas.
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Old 07-23-2010, 02:11 PM   #6
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Thanks for all the replies, I heard the same thing with E85 you can get away with more and E85 likes to be run on a bit high compression. I just don't know where I should turn for more power? I am running custom ground 264 Crower cams but maybe that's not enough, maybe the Kelford 272 turbo cam, or 280 will suit me better?
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Old 07-23-2010, 02:26 PM   #7
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I can only speak to Kelford vis a vis DSM/EVO 4g63 motors, but they are on the whole making more power and operating more smoothly at lower rpms when compared to other cams. We have a number of customers using them in EVOs and DSMs with larger turbos (GT35Rs and larger) and they love them.

There is a cam test from a few years back that's frequently cited as it's pretty solid, and was performed by AMS. Kelford 272's and a variety of other cams were tested against stock EVO cams on a dyno, with essentially no other variables changed. Kelfords gained 80whp over stock with only a 100rpm delay in spoolup, and as was stated by the tester: "I like these cams, great street manners, power delivery, and top end power!" Here's a link to the test: http://forums.evolutionm.net/evo-eng...-cam-test.html
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Old 07-23-2010, 02:30 PM   #8
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80whp is a HEFTY gain. very nice
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