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Discussion Starter #1
I just recently bought some P30 (JDM B16A) Pistons. I have a GSR motor and the car is going in the shop within two weeks. My plan is to put the pistons in the GSR block which will create 11:6 compression with stock head gasket and no milling. I was wondering if I went with a 2 layer head gasket, I'd be at 11:9 cr. Would that be safe? Would running street gas be ok? I need help in deciding if I should stay stock head gasket and be at 11:6 cr or 2 layer head gasket and be at 11:9, and which would be more ideal/safe. I really want to go 11:9 cr, but don't know much about compression. Any help is much appreciated. Thanks.
 

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where do you live, what is the best octane you can get, if your in cali and can only get 91, drive around with some octane booster until you get it tuned
 

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it should really be dependant on what cams you are using, and what your goals are. why run more compression than you need to... you'll just run into tuning headaches the higer you go, and it'll be useless if your cams don't warrant that high of a compression level.
 

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Discussion Starter #5
oh sorry, i forgot to mention. I'm running skunk2 intake manifold, aem type r cai, skunk2 stage 2 cams with prospec valvesprings and retainers with skunk2 cam gears, with DTR headers and a Hayme exhaust. and highest i can get is 100 octane, but thats 5 dollars a gallon, so i don't think i'll be buying 100 octane often.
 

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with the sk2stg2's you need to run around 11.6 CR. anything higher and you'll be undercamming the engine's potential and you'll spend more time and money tuning the fuel. at 11.6:1 you should have more than enough margin error to run regular pumpgas premium as long as you tune it properly.

why time of engine management are you planning on?

got any more info on the prospec valve stuff?
 

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Discussion Starter #7
all i know is that the prospec valvetrain that i have has the exact same spring rates as the skunk2 valvetrain.. They were copycats made for Rob at thunderalley back in the days in San Jose. so you think i should stick with 11:6 instead of 11:9?
 

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nospeedlimit143 on Feb/09/04 said:
with the sk2stg2's you need to run around 11.6 CR. anything higher and you'll be undercamming the engine's potential and you'll spend more time and money tuning the fuel. at 11.6:1 you should have more than enough margin error to run regular pumpgas premium as long as you tune it properly.

why time of engine management are you planning on?

got any more info on the prospec valve stuff?
wrong, 12:1 is ideal for those cams w/ a ABDC valve clsoing degree of 49. you want ~20% cranking pressure over stock.
 

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DefiantGSR on Feb/09/04 said:
wrong, 12:1 is ideal for those cams w/ a ABDC valve clsoing degree of 49. you want ~20% cranking pressure over stock.
i guess i'll have to show my work. seriously, if this isn't right, let me know what i'm not doing right here. i used the dynamic compression calculator available on rbracing-rsr.com as found in the articles. the specs i used were for stock GSR bore, stroke, and rod length. i also figured them at 0 ft.
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cranking pressure at 10:1 static CR = 176.12 PSI

176.12 x .20 = 35.244 (20% of stock cranking pressure)

176.12 + 35.244 = 211.344 <--ideal cranking pressure for ABDC - 49 degrees

cranking pressure at 11.6:1 static CR = 218.68 PSI
----------------------------------

from those figures... it looks like 11.6:1 is pretty much right on the mark. 12:1 yeilds 228.68 which is almost 30% higher than stock cranking pressure.
 

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Discussion Starter #13
thanks nospeedlimit143. i'm trying to go allmotor, but the thing is.. i'll only be hitting 13's with this setup.. is there anything else i can get done that will get me into high 12's? i'm getting a type r tranny with custom clutch..
 

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nospeedlimit143 on Feb/10/04 said:
Quote: DefiantGSR on Feb/09/04 wrong, 12:1 is ideal for those cams w/ a ABDC valve clsoing degree of 49. you want ~20% cranking pressure over stock.
i guess i'll have to show my work. seriously, if this isn't right, let me know what i'm not doing right here. i used the dynamic compression calculator available on rbracing-rsr.com as found in the articles. the specs i used were for stock GSR bore, stroke, and rod length. i also figured them at 0 ft.
----------------------------------
cranking pressure at 10:1 static CR = 176.12 PSI

176.12 x .20 = 35.244 (20% of stock cranking pressure)

176.12 + 35.244 = 211.344 <--ideal cranking pressure for ABDC - 49 degrees

cranking pressure at 11.6:1 static CR = 218.68 PSI
----------------------------------

from those figures... it looks like 11.6:1 is pretty much right on the mark. 12:1 yeilds 228.68 which is almost 30% higher than stock cranking pressure.
you want cranking pressure of 20% over a stock engine. that means gsr cams(40 ABDC) and 10:1 in his case. that will give you a cranking pressure of 191.12 PSI. 191.12+ 191.12(.2)= 229.42. now, plug in 49 degrees for the skunk2 cams...to get ~229 cranking pressure, that requires ~12:1. Toda sells 12:1 CR pistons for their 50 ABDC degree toda spec B cams. not a coincidence.


here you go. thank you, come again.
 

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iydkydg on Feb/10/04 said:
thanks nospeedlimit143. i'm trying to go allmotor, but the thing is.. i'll only be hitting 13's with this setup.. is there anything else i can get done that will get me into high 12's? i'm getting a type r tranny with custom clutch..
a little giggle gas, higher final drive gear, weight reduction, racing slicks.

check the rules at the track(s) you will be running at. at certain points you need to implement safety devices (ie. cage, helmet, etc.)

if you are looking for a streetable setup, there's not much (within reason) that you can do. when you get into more agressive cams and higher than 12:1 CR you throw streetability right out the window.
 

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Discussion Starter #16
Originally Posted By: Michael Delaney

if you know how to fuel tune on a dyno using a wideband O2 sensor for realtime AF ratios and can reprogram your ECU, you can use 91 octane in 12.5:1 CR motors. Having an accurate oil temp gauge or water temp gauge or readout also helps. You'll need to upgrade the fuel delivery (injectors and pump once you get up to 12:1). those stock 240 injectors won't do the job for you.

if you are running a stock ECU (I don't care if it's OBD1 or not..because it makes no difference anyway because the fuel tables and ignition tables are identical to the OBD2's despite the hype) and can't fuel tune then you can't run 12:1 with 91 octane and have a decent powered motor. It'll run like sh*t and detonate.
Most people who don't have access to fuel tuning don't push past 11.5:1 (the stock ECU can handle that with a VAFC and FPR).

If this is so, why do shops never reccommend going over 11:7 cr? My friend wanted to put ctr pistons in his b16 block and the shop he went to said no.
 

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DefiantGSR on Feb/10/04 said:
you want cranking pressure of 20% over a stock engine. that means gsr cams(40 ABDC) and 10:1 in his case. that will give you a cranking pressure of 191.12 PSI. 191.12+ 191.12(.2)= 229.42. now, plug in 49 degrees for the skunk2 cams...to get ~229 cranking pressure, that requires ~12:1. Toda sells 12:1 CR pistons for their 50 ABDC degree toda spec B cams. not a coincidence.


here you go. thank you, come again.
yea, thats where my mistake was. i wasn't plugging in the right number for stock ABDC closing angle.

my appologies.
 

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nospeedlimit143 on Feb/10/04 said:
Quote: DefiantGSR on Feb/10/04you want cranking pressure of 20% over a stock engine. that means gsr cams(40 ABDC) and 10:1 in his case. that will give you a cranking pressure of 191.12 PSI. 191.12+ 191.12(.2)= 229.42. now, plug in 49 degrees for the skunk2 cams...to get ~229 cranking pressure, that requires ~12:1. Toda sells 12:1 CR pistons for their 50 ABDC degree toda spec B cams. not a coincidence.

here you go. thank you, come again.
yea, thats where my mistake was. i wasn't plugging in the right number for stock ABDC closing angle.

my appologies.
no problemo. were all here to share and correct info.
 

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aah... more info to share about the P30's.

if you use P30's with GSR crank, rod length, and head with a modified 2 layer head gasket, you will get a 11.98:1 static CR.

looks like they are still an option.

another set of pistons i was looking into were the PR3(B16A) pistons since they have a dome volume of +6.01 compared to the 6.93 that the P30's have. pretty much is going to come down to price and availability. i'm not of fan of having JDM parts for the sake of JDMness, but more concerned with cost vs. performance.
 

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Discussion Starter #20
yeah i hear you.. cost was a big issue of mine.. i got my jdm b16a pistons for 91 dollars shipped. i just received it today, and they are in perfect condition. so it depends when and where you get the pistons at. i mean for 50 dollars you can probably grab some usdm b16a pistons, but for 40 more, why not get jdm which will bump your compression up more. just my two cents.
 
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