holy crap! compression #'s

IJ.

Grumpy Old Man
Mar 30, 2005
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I come from a land down under
Dats: There's a tradeoff between gains from increased boost/less detonation using a thicker HG and inefficient burn from incorrect squish you get.

I've run a 3mm MHG in the past on a fresh uncut block and head and you do lose some drivability/response/economy but I lived with it as I was pushing 30 psi through it.
 

Datsrboi

Loud pipes Save Lives
Jul 31, 2007
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Haltom Texas
www.cardomain.com
IJ. said:
Dats: There's a tradeoff between gains from increased boost/less detonation using a thicker HG and inefficient burn from incorrect squish you get.

I've run a 3mm MHG in the past on a fresh uncut block and head and you do lose some drivability/response/economy but I lived with it as I was pushing 30 psi through it.


I am willing to give up on ecomomy for more controlled performance rather life sucking high compression.
 

suprasman01

N Y0 Ca8in3t eatin Y0 C3
Dec 19, 2006
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Ohio,
Josh, you would be better off running a "leak down" or
"cylinder differential" test. This actually is a better way anytime, but trying to build the proper compression at a slow rate of turn ie. socket and rachet is not going to give you the desired result. You will have a certain amount of blowby past the rings, even on a new engine, and to try to "turn" it by hand, by the time you have reached TDC the blowby will own you and your results will be LOW...
JoelD
 

Adjuster

Supramania Contributor
Personally, I think for most people, a slightly higher static CR on mild boosted engines is a better setup around town. (More responsive.)

High boost pressures are detonation prone if the right amount of fuel is not added, and some coatings can help out here to limit heat transfer, and improve heat rejection. In theory of course, and in practice, my 9:1 CR sure is fun around town, and yet makes plenty of power on boost too.

One of these days, I'll do a compression check, and see where it's at across all 6... :)
 

Halsupramk3

Member
Apr 4, 2005
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Mississippi
i have a 9:1 CR and my cylinders are 170 but #6 is 165. great response around town. spools sp61 easy.

adjuster what boost on pump gas and what timing are u using?
 

Adjuster

Supramania Contributor
Hal, I'm actually still putting it all back together on the T70 :) Perhaps this weekend I'll have it up and running on the Maft Pro.

On my prior setup, Bolt on T4 60-1 DBB Chra, Lexus meter, 550's and the Emanage/E-01, it was very happy on pump gas at mid lower 20psi. I generally added 30% Toulene if I was running more than 21lbs boost, and it was very strong up in the 25psi range, but started acting like a CT26, running out of top end over 5000rpm.... (Thus, the larger turbo.) At 25psi, there was basicly little to no traction in first, and most of second, and part of third if the ground was dusty or damp in any way.... I was constantly hitting FC too, even with the Hz clamped by the Eman at 1450hz... Sucked big time... Especially if I floored it in a higher gear, and allowed the turbo to build boost.. it would FC almost instantly... But the wideband showed it to be rich under all WOT conditions, and running just right at idle and crusing around town. (Even with the FC problem, it was a blast to drive, so much more tourqe, you can tool around in 5th geat at 35mph, and it does not complain, lurch or make much fuss... :))

The bolt on T4 was great on a stock engine, but on the stroker, it was too small.

It will be interesting to see how the Maft Pro stacks up compared to the Emanage/E-01. I liked the E-01's screen, and ease of use, but the new setup has a 4" inlet, and nothing but an airfilter, so speed density should be interesting. Also I went from 550cc injectors, to 780cc injectors, so the air flow scale should give me quite a jump in head room before FC is hit, but I am interested to see how much it advances timing, and if it will be reasonable on pump gas, or if I'll have to turn down the boost to run pump gas, and only turn it up when the Toulene is added to the tank. (I can get 98 octane as a result of 30% added to stock pump gas...)

Perhaps in the future, some methanol or water injection system might find it's way on my car, but for now, I just want to get it running again, and drive it more than work on it. :)
 

Halsupramk3

Member
Apr 4, 2005
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16
Mississippi
good info adjuster. i may try toulene this week as i need to make sure i dont have knock. i have a few spikes at just 11 psi on the sp 61 with 9:1 cr. I will turn up the boost tho with the higher octane.
So you cant say what exactly the timing is since your still with the stock ecu? when are you going to bust a nut and go aem? You may have some trouble getting a decent idle with the piggy back if maft pro cant reduce the injector duty cycle lower than what the stock ecu minimum. with that big of a set up timing will be a great area to explore for power and safety reasons.