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Old 01-07-2012, 01:57 PM   #1
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Default 11 to 1 Comp w/ Boost

I was looking to raise the comp, then I thought of the F20c and its 11/1 comp ratio. I was thinking of running no more than 14 psi on on it, but just enough to make 250-270hp. What do you guys think?
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Old 01-07-2012, 02:07 PM   #2
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When guys boost the f20c they usually add a block spacer to lower the compression. Your room for error on the tune is very small if you are running high compression. Yes, if you get it right you will make more power, but the chance of blowing your motor is high.
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Old 01-07-2012, 02:10 PM   #3
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It's not a good idea.
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Old 01-07-2012, 02:13 PM   #4
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If you can run E85 all the time, go for it. Pumpgas, a bit borderline.
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Old 01-07-2012, 02:16 PM   #5
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Im also at 4300 ft alt and maybe add alcohol inj above 8psi
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Old 01-07-2012, 02:22 PM   #6
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Quote:
Originally Posted by wittyworks View Post
When guys boost the f20c they usually add a block spacer to lower the compression. Your room for error on the tune is very small if you are running high compression. Yes, if you get it right you will make more power, but the chance of blowing your motor is high.
I haven't one S2000 turbo kit come with a spacer or a new head gasket
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Old 01-07-2012, 02:34 PM   #7
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Quote:
Originally Posted by 1993ka24det View Post
Im also at 4300 ft alt and maybe add alcohol inj above 8psi
If you set up a failsafe boost/timing cut for when the alcohol runs out then sure. I personally don't like the idea of running out of something that prevents my car from blowing up. Do you have easy access to E85? My friends shop builds a lot of high comp 4g63's, but you can get ethanol on every other corner here so they build specifically for it. A couple of 12:1's have gone out the door there.
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Old 01-07-2012, 02:45 PM   #8
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Okay here ya go:
http://www.s2ki.com/s2000/topic/9090...#entry21146790

Here's a power chart for FI s2k's. As you can see, when people start to get into higher power levels for that motor, they generally LOWER the compression ratio, with a head gasket spacer. Yes, there are some people still running stock compression ratio, but I bet when they blow their motors, the rebuild will be a lower comp motor.
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Old 01-07-2012, 02:46 PM   #9
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Btw, thread jack, we should make a power chart on this site, it's a great way for noobs to see what they need to hit certain levels.
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Old 01-07-2012, 03:01 PM   #10
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I wish it would be easy to install a F20c, it would be enough hp/torq that I would need in NA form. I am so used to higher hp engines. I will see if I can find some decent 10:1 comp pistons.
I also found a Honda Civic running 12.5:1 comp + 40-50 psi on E98
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Old 01-07-2012, 03:06 PM   #11
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If I could start this all over, from scratch, I'd probably have a Honda engine in my Miata.
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Old 01-07-2012, 03:16 PM   #12
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http://www.s2ki.com/s2000/topic/9090...t__p__21147325

------- 400whp out of that car on 12psi, I make 250 at 11psi. lol @ Mazda
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Old 01-07-2012, 03:51 PM   #13
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s2000's heads flow more than a miata head can even imagine flowing. that helps them in more ways than one. tons of flow = less likely to det.

you throw compression like that on our truck motor and your "cushion" against det is non-existant
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Old 01-07-2012, 04:03 PM   #14
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What I might do is get 9.?:1 comp then shave the deck to 10:1 comp
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Old 03-21-2012, 03:00 PM   #15
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At 9.5:1 on crappy CA gas I have to pull timing WAY back, even at low boost levels. like 7-8* by 12psi
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Old 03-21-2012, 03:07 PM   #16
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y8s hit 257rwhp on a dynapak at 9.5psi on his '01. that's 10:1?
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Old 03-21-2012, 03:43 PM   #17
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Quote:
Originally Posted by wittyworks View Post
When guys boost the f20c they usually add a block spacer to lower the compression. Your room for error on the tune is very small if you are running high compression. Yes, if you get it right you will make more power, but the chance of blowing your motor is high.
omfg, Im hope theyre not doing something so damn stupid.


OP,

Of course you can run boost on 11.0:1, thats not even very high compression if youre a competent tuner.
The stock cam profile is going to limit the boost quite a bit due to the high dynamic compression created by having so little overlap, but with a more aggressive cam profile you can run more.

The F20C has a pretty radical cam profile compared to the BP, which is why you see people running so much boost on top of 11.0:1 compression.
Another example would be Fords new 5.0L modular motor which has VVT on both intake and exhaust camshafts. Tuners have been using the VVT to lower dynamic compression in boost by creating more overlap.


Heres what I suggest.
Dont get 11.0:1 pistons, and dont deck the block. Instead, mill the head to increase the area of the quench pads in the combustion chamber. With the right pistons you can get your desired compression ratio and have improved quench over stock. In other words you can run the same boost with more compression without detonation.
Id also suggest getting a good cam grind if you have the budget for it. I know Web has a good grind they offer but you may also want to check and see if Colt offers one.

Last edited by Full_Tilt_Boogie; 03-21-2012 at 03:54 PM.
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Old 03-21-2012, 04:03 PM   #18
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10:1 here. 93 for the street(~350whp) and vp113(~500whp) for the track.
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Old 03-21-2012, 04:59 PM   #19
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Keep in mind his location. He is at least 2psi short of most of us across the MAP. and that region is noted for having a higher effective elevation. A typical day could be 5000 to 7000 ft air the engine is breathing.

op - Will you be traveling much to lower elevations? 11 might be too much. I could see 10 working well, but no more. However, some of the fuel you get in that area is not the best from my experience. (Alb-Hobbs area) And if you do go lower elev, it will get into trouble real quick.
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Old 03-21-2012, 05:21 PM   #20
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Quote:
Originally Posted by halfdemonpyro View Post
At 9.5:1 on crappy CA gas I have to pull timing WAY back, even at low boost levels. like 7-8* by 12psi
Plugged cat or tiny exhaust. On a [email protected] I was able to run ~12-13* at peak torque and ~20* at redline on a stock BP4W motor and CA91. That was with a cast manifold and 3" catless exhaust.

The increased head flow of the BP4W means that a 99-00 9.5:1 longblock will actually take more timing than an identical setup on a '94-95 8.8:1 longblock.
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