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Old 10-26-2010, 04:31 PM   #1
RicersWetDream
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2014 Forester XT

Default Compression Question

I've tried searching and can't really get a solid answer.

I'm currently building an EJ25. Stock crank and case bored to 100mm (slight scuffing on #2). The list is quite long but in a nutshell I'm building the entire rotating assembly to include manley h-beams, acl race main and rod bearings, mild head work, 20g-xt 10cm^2, E85, and all supporting mods.

Right now the top pick on my piston list is the Wiseco 100mm as they seem to be a good bang for the buck, and they come with the skirt coating.

My only concern is the 8.9:1 CR they have.

My goal for the car is to run the 20g to it's limit on E and try to hit 400whp/400tq, but I am more than happy with high 300's and a nice fat power band. I don't want the car to just shoot up to 400 and drop off.

I'm concerned that if I get pistons with a higher CR like the Wiseco's, I'll be limited in the boost and timing I can run and affect my ability to make the most out of the turbo. I know there will have to be some timing and boost pulled to avoid detonation, but does the higher CR make up for the loss of peak boost and timing? On the contrary, does E85 take a lot of the worry out of running a higher CR?


C/N: Will I be able to make the max the 20g with 8.9:1 pistons on E85?
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Old 10-27-2010, 02:50 PM   #2
UP2MTNS
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Default

What heads are you running?


and I would say 'yes' to your question on maxing out the 20g. (but I don't know if you'll actually hit 400whp) E85 is basically like race gas. i'm switching over to it on my 9:1CR hybrid build w/a 20g turbo, although my goals are different because I have a 34mm restrictor, etc. But I've seen rally cars with 10:1 CR on E85 making crazy torque.
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Old 10-27-2010, 02:55 PM   #3
explicithero
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I can tell you that I was running a stock block with stock everything but injectors pump and header back exhaust with a blouch 18g with 8cm housing making 408 wlb/ft of torque and about 389 whp on e85. Motor lasted 40k before I got a clogged injector that fried a piston ring. That set ups was so fun it was like instant power.
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Old 10-27-2010, 03:54 PM   #4
UP2MTNS
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Quote:
Originally Posted by explicithero View Post
I can tell you that I was running a stock block with stock everything but injectors pump and header back exhaust with a blouch 18g with 8cm housing making 408 wlb/ft of torque and about 389 whp on e85. Motor lasted 40k before I got a clogged injector that fried a piston ring. That set ups was so fun it was like instant power.
out of curiosity, what injectors/pump were you running and do you know the cause of the clog?

(I'm currently running 800cc injectors +walbro pump and since I can't make big peak HP due to the restrictor, I'm hoping I can get away with using them)
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Old 10-27-2010, 05:58 PM   #5
RicersWetDream
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Stock 09 WRX heads (49.5cc?). They will be PnP'd, bc stage II single avcs cams, supertech dual coil springs and Ti retainers, and stock valves/guides if they're still good (if not, supertech on both).

I believe the wrx heads are about 2cc's smaller than comparable STI heads (51.5 cc?), and I believe Wiseco has these pistons rated based on the STI head cc. The compression could be a couple tenths higher if that's the case.

Regardless, I know E85 will allow me to run the setup knock free, just not sure if I can run as much boost and timing as I need/want to make the most of the 20g or slightly larger turbo.
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