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Old 01-04-2005, 05:41 PM   #1
AlbanianImpreza
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Question Compression ratio question.

i was having a talk with a friend of mines and he goes to me his friend is running 28 psi on a SE-r with a compression of 9.5:1...which i feel is complete and utter BS because it totally doesnt coincide with the 18.7:1 ECR that your allowed to have without your engine blowing out.

so the question is am i right? or do i have a hole in my thinking? if i do plz tell me why and how and such. and if hes right what would he have to do to make that true. would he have to do any air to fuel ratio changes or what?


thanks for you help.
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Old 01-04-2005, 05:59 PM   #2
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He would be running around 27:1 ECR. Thats high. He also wouldn't be using pump gas, and chances are he would have to have MAJOR bottom end work done to sustain that power.

If I were a betting man, I'd say its BS.
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Old 01-04-2005, 06:01 PM   #3
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I really don't know too much on the subject, but I don't think that the engine just blows from compression. I think the 18:1 rule has more to do with the type of fuel being used and what not. Ie - Since the highest octane we get is 93 at the pump(at least most of us), if we go higher then 18:1 we will have to start retarding the timing a lot in comparisson to when the compression is below that(more the higher the compression) and what not to try and keep the fuel from detonating. Since the octane rating tells us how much pressure/heat a fuel can take b4 spontaniously combusting, many of us are limited by the fuel. That doesn't mean that we can't run higher then 18:1 though, even on 91 octane. The timing would just need to be retarded more and what not to avoid det. There are other things which can be done to avoid det also, which can help people run higher compression on lower octane fuels(like water/alch injection). Not sayin that the guy's running 28psi with a cr of 9.5, but I'm pretty sure it's possible.

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Old 01-04-2005, 06:33 PM   #4
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CDvma, what kind of bottom end are we talkin bout, cost wise?
and yes on pump gas

and hippy so ur telling me if i retard my detonation i can get more psi? but arent u gonna be having the piston hit the valve? or wouldnt the Rpms be way too low to do anything? cuz if u retard the det. then ur retardin the rpms also. so?
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Old 01-04-2005, 06:41 PM   #5
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The timing I'm talking about is the ignition timing(when the spark plug fires). You're not retarding det. Retarding the ignition timing is just making the spark plug fire later. Generally, the sooner the spark plug fires(upto a given point), the more power and engine will make given all other things being equal, but the more chance there is of detonation. By retarding the timing we basically take load off of the engine at the cost of power. A lot of the time the compramise of more boost to less advanced (more retarded)timing equals more power then less boost and more timing.......... Point being, retarding the timing is common practice for people who run higher compression then most people would. I dunno how good an explination this is, or how true all of it is, but you get the point.

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Old 01-04-2005, 06:45 PM   #6
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so wait if u do this are u telling me it doesnt even give power because it imbalanced? or again am i getting it rong?
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Old 01-04-2005, 06:51 PM   #7
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Old 01-04-2005, 07:04 PM   #8
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Quote:
Originally Posted by AlbanianImpreza
so wait if u do this are u telling me it doesnt even give power because it imbalanced? or again am i getting it rong?
Wrong. The point was that most engines don't just blow up from running a lot of boost. If you can keep the engine from blowing up(by retarding the timing, or whatever), then you can run whatever boost you want. I don't think 28psi is that unbeleivable.

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Old 01-04-2005, 07:22 PM   #9
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Quote:
Originally Posted by AlbanianImpreza
They only ran 17 psi for the run, and claim it normally does 20. Thats a lot different than 28

I suppose its possible, but I dont know how the bottom end is liking it. I dont know anything about Nissan motors, but I've heard they are great for power. My dad owns a 300zx TT and I know some people pull insane power from the stock bottom end. SR20s are popular from what I gather, I think they also like power but making an NA motor turbo probably wont last long with that much power and a stock bottom end. 28 PSI would definitely require some reinforcement, as at that kind of pressure the cylinder walls would probably warp (most engines I've heard of require sleves at > 25 PSI).
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Old 01-04-2005, 07:33 PM   #10
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sorry about the 28 my friend likes to embelish i guess, but sleeves? i never heard of these. what are they just metal sleeves?
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Old 01-04-2005, 09:21 PM   #11
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steel cylinder sleeves to reenforce the block
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Old 01-05-2005, 09:28 AM   #12
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Quote:
Originally Posted by AlbanianImpreza
which i feel is complete and utter BS because it totally doesnt coincide with the 18.7:1 ECR that your allowed to have without your engine blowing out.
"allowed to have?"

that's funny.

there are no rules in this game. sometimes stuff works amazingly. sometimes it blows up for no apparent reason. if you keep thinking in absolutes you'll never get anywhere!

if he's a fantastic tuner and has good octane fuel then there's no reason to doubt it. if he seems like an idiot who couldn't find his way out of paper bag, total BS. catch my drift?

ken
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Old 01-05-2005, 12:45 PM   #13
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From the link it looks like he's running the non turbo block (i.e. it's a SR20DE, not a SR20DET). Unless he is running water injection I would really doubt he could run even 20 psi.

Plus I don't understand why he is running a Wolf 3D and e-Manage.
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Old 01-05-2005, 02:32 PM   #14
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so he needs water injection to pull this out his ass or what?
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