High compression worth it?

[Weston]

Anyone want to give me any realistic power/torque gain estimates for going to about 11:1 compression (vs stock 9.2:1) on a LS with I/H/E?

How big of a gain are we really talking about, in terms of power and 1/4 mile times?

I'd really like to go FI, but the all motor route doesn't require me to dump $2k into it to get started, so I'm considering it even though FI is a big advantage up here...

[Mr. NoSkills]

not enough sadly.

you'd be faster with your 9.2:1 plus nitrous while saving up for your turbo kit then you would be on just 11:1 all motor.
i can't give you exact numbers, but it's not much.
thing with all motor is you've gotta have it all, even more then turbo. you can't really get away with just pistons or just cams.

[TheBlackKnight]

Originally posted by tdjb-potc
not enough sadly.

you'd be faster with your 9.2:1 plus nitrous while saving up for your turbo kit then you would be on just 11:1 all motor.
i can't give you exact numbers, but it's not much.
thing with all motor is you've gotta have it all, even more then turbo. you can't really get away with just pistons or just cams.

I agree with you on this one....If you go all-motor to get anything, you'd need the whole package...pistons, rods, cams, and everything else...you'll spend more to go all motor than you would to go FI and geat better results with FI. the nitrous kit is a good idea...but not for autocross....If you want to save money to go FI don't spend unneccesary money on high compression items, when if you want big FI numbers you have to go lower compression.

[V8SpankR]

With our thin air NA just doesn't see the gains you might get at sea level,just go FI.

[Slava]

UP here you maybe get like 20 horspower I did 11.1:0 with my H22 and I didn't feel all that much difference.

[hsunchen]

Weston, I ended up with a 10.8:1 C/R for my minime hybrid using forged pistons (Ross).

I originally had the pistons made at a 12.8:1 C/R, but under more intelligent advising, I realized that my power gains would be minimal (there are diminishing returns with compression - there is a lot more HP to be gained going from say 9:1 to 10:1 than going from 10:1 to 11:1) and that I really would need to running on higher than 91 octane pump gas to have any reliability or ignition advance.

If you want power, unfortunately FI is the way to go. I wanted to build an "inexpensive" N/A minime for the CRX, b/c I already have one gas-guzzling (13 mpg!) turbo car.

The bargain basement D16 hybrid is still well into the 4-figure range already - no labor costs, just internal parts and machine work . . .

[john]

There are always tradeoffs. Higher compression == more heat == more likely to knock/etc. Higher octane can help out a lot with high compression motors.

And you'll get a NICE bump in power on the bottom end.

[dsmsv8bro]

10-15 percent gain per point of comp you go up, approx, but then you have to use race gas depending on how high you go. i am just over 11 to 1 on an aluminum headed 6.9 liter motor so with aluminum heads you should be able to run the same. but like they said you can turbo it easier with lower comp ratios.

[hsunchen]

Hey Weston, or anyone else who is comtemplating C/R, this link is an incredible help once you've cc'd the head, micced the bore, etc to get your stats.

http://www.knology.net/~jediklc/D.htm

It's set up for Civic motors, but you can substitute any of the parameters for any motor setup.

[Weston-work]

Here's one for B-series engines... They left out the B20A's though.

http://www.c-speedracing.com/howto/compcalc/compcalc.php

[Kahulia]

The mini-me is 10.8:1 and there was a difference. But that could just be because of the VTEC.

[hsunchen]

Update: My C/R is going to right around 11.1:1 with a 2.0 mm Greddy headgasket. Cost of HG? $180!

Cost of OEM D16Y8 headgasket if I'd just made an intelligent decision when ordering the custom pistons - around 35 bucks.

Stupid, stupid, stupid . . .

Kinda a case of not "think many times, order parts once."

[allmotor_civic]

I agree with alot that has been said so far (especially your last line John), but one thing people often tend to over look about Colorado is that when there is less static air pressure there is a higher tolerance for high compression (if you over look the heat effects of edges on highly dome'd (sp?) pistons). It has been my experience that even 12.5:1 on 91 at altitude is perfectly okay for a streetable Honda...so long as you have a strong fuel system. So 11:1 is just fine.
Now about your 'plans/idea', if you feel strongly about going the all motor route, then if your already tearing into the block and replacing pistons and bearings, I would invest in a decent set of rods (Eagle comes to mind as an inexpensive set) and a block guard. This gives you a strong base for future upgrades.
However 11:1, even at sea level, is considered rather minor as far as an upgrade. Power output; with larger cams, a better header (trust me the header is the key to top end power reguardless of additional mods in the all motor world), either a Skunk2 manifold (port matched) or ITB's, and a really worked head leaves you in the 160-190whp range depending on parts and budget...many LS's have made well beyond the 2 century mark on 12:1.
If you looking for just a great daily driver then I would steer clear of the N/A. I have a not-so-daily driven race car because of my lust for N/A power. I'd just buy the new Greddy kit and have a reputable tuner help you dial in the E-manage and just have fun boosting on the stock block...
Later,
Dan
P.S. hsunchen, why are you dropping your compression that far by means of a headgasket? I would tend to think that 11.5-12:1 would be better suited to your minime especially since your also going to gain a bunch of hp based off the oversized headflow and cam dynamics...but then a gain I tend to test the limits of streetablility.

[hsunchen]

Originally posted by allmotor_civic

Dan
P.S. hsunchen, why are you dropping your compression that far by means of a headgasket? I would tend to think that 11.5-12:1 would be better suited to your minime especially since your also going to gain a bunch of hp based off the oversized headflow and cam dynamics...but then a gain I tend to test the limits of streetablility.

I have had so many problems with getting another car to run ('91 MR2T, built motor, turbo upgrade, cams, etc) that I want to avoid any detonation-related issues.

I understand the tolerance level of high compression is better up here, but still - I plan to beat on this motor, and it's possible once in a while my wife might put mid-grade gas in it or whatever.

I'm aiming to put down 135 whp. Hopefully the increase in displacement will do a lot of that (going from 1590 cc's to 1654 by boring .050" over) and that the oversize valves in the Y8 head, high compression, a decent 4-1 header and highflow cat & catback will do that rest.

My other choice was an A'pexi 1.5mm headgasket, which would have put C/R right around 12.1, again I'm going to err on the side of safety just so I am safer overall and can run advanced timing at the track with race fuel.