MR2QIK
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Re: What compression ratio should I run?
2013/08/24 11:08:01
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It'll be fine. Annoying when the wrong part arrives though....
MR2QIK - "The Little Car That Could"  320rwkw @ 19psi (pump fuel, no giggle gas) 11.96 @ 116mph (with 228rwkw)
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dwyer125
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Re: What compression ratio should I run?
2013/08/24 13:20:24
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running bp98, will this limit the boost I should run? or will be just down to how low I can get my intake temps?
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just_ace
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Re: What compression ratio should I run?
2013/08/24 13:24:36
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how much boost are you wanting to run exactly? more than 20psi?
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dwyer125
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Re: What compression ratio should I run?
2013/08/24 13:32:52
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yeah i wouldn't mind going a bit over 20. if i could build it for 24 then I know I'd be safe just running less and could go up to that if ever wanted.
Or am I dreaming at 24?
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MR2QIK
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Re: What compression ratio should I run?
2013/08/24 14:06:39
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I wouldn't go over 20 personally, but 22psi should be ok. It'll just be more prone to detonation. Keep in mind Gen2's are around that comp from factory. Only talking a small difference either way.
MR2QIK - "The Little Car That Could" 320rwkw @ 19psi (pump fuel, no giggle gas) 11.96 @ 116mph (with 228rwkw)
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dwyer125
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Re: What compression ratio should I run?
2013/08/24 14:10:50
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You said the compression ratio will affect my turbos efficiency range. Is the difference between 8.5 and 8.8 going to be negative in this case?
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MR2QIK
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Re: What compression ratio should I run?
2013/08/26 12:41:20
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To directly answer your question, no. The difference between the two is really minimal & you'd still be able to get your turbo into its efficiency range. That wouldn't be the case if we were talking 9.8:1 for example.
It's a trade off. The turbo you're getting will be in its efficiency range somewhere between 20-24psi (approx). With both comp ratios, you'd probably still want to limit it to 20-22psi on 98pump fuel. So you either get a bit more response, especially off boost (higher comp), OR a bit less prone to detonation (lower comp). 3SGTE's respond well to more timing (during tuning) but are held back on pump due to detonation. Conversely, given the milk bottle displacement, response is always welcome where possible. The additional delay in getting the other gasket helps sway towards response in your case.
I just get annoyed at the amount of wrong parts that get sent out these days. Amazes me how many sellers can't get such a simple thing correct. 4 of my past 5 KFC runs weren't even correct......LOL
MR2QIK - "The Little Car That Could" 320rwkw @ 19psi (pump fuel, no giggle gas) 11.96 @ 116mph (with 228rwkw)
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track_mr2
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Re: What compression ratio should I run?
2013/08/27 08:09:18
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Are you sleeving the block? I heard the 3S blocks are prone to cracking if you run more then 16psi constantly unless sleeved?
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dwyer125
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Re: What compression ratio should I run?
2013/08/27 09:27:51
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Not sleeved. I couldn't imagine the engine sitting on 22psi for that long, just random squirts of acceleration.
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MR2QIK
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Re: What compression ratio should I run?
2013/08/27 10:08:56
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It's not that black & white. Tune is a big variable. 20psi in that case though. Will still go quite well.
MR2QIK - "The Little Car That Could" 320rwkw @ 19psi (pump fuel, no giggle gas) 11.96 @ 116mph (with 228rwkw)
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track_mr2
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Re: What compression ratio should I run?
2013/08/27 10:11:15
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Might be worth contacting a 3S specialist like Niel Bates about it. If the block is the limiting factor then running forged pistons isn't much good. When I spoke to them they told me not to run anymore then 16psi without having the block sleeved as it will crack. I've read of a quiet a few 3S cracking blocks.
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MR2QIK
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Re: What compression ratio should I run?
2013/08/27 10:27:08
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I've cracked a 3S......twice. Sleeved & 40thou over. If you tune it a bit rich & don't go as aggressive on timing, it should be ok. There's been 40thou over 3S MR2's that have run into the 10's. The key is not to get greedy or hung up on the numbers too much. If it makes 255rwkw but is safe, then so be it. Don't fall into the trap of chasing near 300 and playing lottery with the block.
Block issues tend to begin at around 280rwkw on a GT30 sized turbo (IMO). Overbored blocks are naturally more vulnerable than others. You can run 20psi on a CT20B & you'll break the turbo or have cooling issues without block issues.
There's no proven sleeve for the 3S, unlike with Honda B-series, Nissan SR20's etc. so I don't believe it's a viable solution for the motor unless someone puts the development into one. Maybe a bit better, but not nearly as comfortable as a 5S block.
MR2QIK - "The Little Car That Could" 320rwkw @ 19psi (pump fuel, no giggle gas) 11.96 @ 116mph (with 228rwkw)
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track_mr2
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Re: What compression ratio should I run?
2013/08/27 11:06:22
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What brand of sleeve were you using when you cracked the block?
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MR2QIK
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Re: What compression ratio should I run?
2013/08/27 12:11:43
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I honestly can't remember now. Tristan & the machinist took care of that part as I originally didn't intend to sleeve (long story).
Sleeves could work ok, but I don't know of any for the 3S (ie like a Dart). Given the 5S is a cheapish & fundamentally stronger block, I don't see a reason to look elsewhere.
As far as I know, the rally guys used a different TTE block instead of a modified 3S block.
MR2QIK - "The Little Car That Could" 320rwkw @ 19psi (pump fuel, no giggle gas) 11.96 @ 116mph (with 228rwkw)
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track_mr2
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Re: What compression ratio should I run?
2013/08/27 13:13:07
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I was speaking to an engine builder about it and he said he will only use Darton sleeves which are expensive, like almost $1000aud but he can get other sleeves for less then $150. Depends which sleeves you got.
When its time to rebuild my engine I'm going for the Darton sleeves option as I already have bought a set of pistions and rods before knowing about the 3S cracking issue. I'm not after crazy power though, just usable track speed.
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