asking this becuase i see some build that has the same set up but different comp. ratio. what are the pros and cons for high compression like 12.1 and up? what about 10:6.1 ?

 

i have no idea im going higher then 12.1 hopefully its all good

 

It is pretty simple:

Pros:
More power
Ability to use aggressive cams

Cons:
More prone to detention
Conservative timing (for the reason above)
Bad tank of gas can have fatal results to your engine (detonation)

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by chump2825 &raquo;</TD></TR><TR><TD CLASS="quote">i have no idea im going higher then 12.1 hopefully its all good </TD></TR></TABLE>

Just ask yourself, what you just said...does that sound smart at all? You are doing something without knowing the pros/cons and effects of?

 

does it have anything to with longevity?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ge_itr &raquo;</TD></TR><TR><TD CLASS="quote">does it have anything to with longevity?</TD></TR></TABLE>

if you dont tune for the higher compression, the engine will roast itself.

 

im running 13.5 cr in my fullly built ls/vtec and its my dd and i have no problems BUT i do have to only pump 110 octane which isnt that cheap but watever i like the way my motor pulls!

 

12:1 is easy on pump gas.

I am running 35 degrees of timing at WOT with ~12:1

If I were to do it over again, I would run 13:1

 

You can sefely run 12:1 compression if you have it tuned correctly. I'm not able to get 94 octane at the pump any more, so I'm having my motor tuned again for 93.

Just make sure you have your car tuned at a reputable shop.

 

It's a fine line for street driven cars, considering that race gas is $7 a gallon and rising.

Properly tuned 12.1 will be fine, but above that your looking for trouble if the car isn't a dedicated track car. My cousin runs a 200whp b18c1 with 12.1, ported & polished GSR head with '01 ITR cams with an OBD1 Hondata ecu in an EF hatch.

The car is a true daily driver, without a race gas mix at least once a week the car will ping.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by H-PIMP &raquo;</TD></TR><TR><TD CLASS="quote">The car is a true daily driver, without a race gas mix at least once a week the car will ping. </TD></TR></TABLE>

He needs a bit larger cams.

I was knock central until I upped my cam size. Stock ITR cams hold in a lot of dynamic CR and with anything more than ~11.5:1 you're going to be running conservative timing.

 

Go to a higher 13:1 compression and tune thing on E85. That stuff is 106 octane, burns cleaner, cooler, and costs less than regular unleaded (if you can find it). The only downside is that you will loose mpg (-25%) since it takes a much richer a/f mixture with e85 to burn stoich than gasoline. This means you will also need bigger injectors...

 

i have skunk 2 stage 3 on my car right now and yes i am over cammed. what do you guys think. should i try to sale it and get somthing smaller. or up my compression.

 

you can make a good amount of power from a high compression engine. some of the drawbacks is that if you do plan to to go 12-13+ compression, you might want to look at making the car a track only car unless you can afford 4-5 dollars per gallon of gas. it might be a bit hard finding a gas station with 110 octane as well. if you cant afford to pump it constantly, i suggest not going with such a high compression as you will need to retard timings quite a bit to run 13:1 while running on 91 octane. it might be doable, but you might not be making much power over 12:1 since you will have retarded timings.

what 94eg! said might work as well, although, i havnt seen that stuff in southern california (or maybe i just havnt looked hard enough). Even if it costs less than regular unleaded, you have to add 25% to the cost of it to get the true cost since you're losing out on roughly 25% efficiency.

 

my tuner said 12:1 is easy but the last time i talked to him i didn't mention 12.5:1. is there a big difference there.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 92TypeR &raquo;</TD></TR><TR><TD CLASS="quote">

He needs a bit larger cams.

I was knock central until I upped my cam size. Stock ITR cams hold in a lot of dynamic CR and with anything more than ~11.5:1 you're going to be running conservative timing.</TD></TR></TABLE>

I think he's planning on skunk 2 III's, like the OP has.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by eMpAtHy &raquo;</TD></TR><TR><TD CLASS="quote">some of the drawbacks is that if you do plan to to go 12-13+ compression, you might want to look at making the car a track only car unless you can afford 4-5 dollars per gallon of gas. </TD></TR></TABLE>

Like I said above, 12:1 is a joke on 92 octane. You can run into the mid 30's for ignition timing. Even 13:1 you can do fine on 92 octane.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by eMpAtHy &raquo;</TD></TR><TR><TD CLASS="quote">might be doable, but you might not be making much power over 12:1 since you will have retarded timings.</TD></TR></TABLE>

I'm not trying to be a dick, I promise, but I am tired of hearing this comment from people who have never tuned a high compression motor. You are going to retard timing every time you increase cylinder pressure...that is obvious. But you are imagining some large scale retarding which just isn't happening. What is the difference between 10:1 and 11:1? 11:1 and 12:1? So on and so on.

If your tuner can't figure out how to easily run 13:1 compression on 91/92/93 octane, find a new one.

 

I know this is an old thread but im looking to start up my motor, got around 12.2:1 CR. Should i pour in a couple gallons of 100 octane to get up to around 93 octane until i can get a proper tune. Right now i have a chipped P28 from mtber (phearable.net). Or should i pour in a couple more gallons of 100 Octane and get around 95 Octane.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by all-mtr-teg &raquo;</TD></TR><TR><TD CLASS="quote">I know this is an old thread but im looking to start up my motor, got around 12.2:1 CR. Should i pour in a couple gallons of 100 octane to get up to around 93 octane until i can get a proper tune. Right now i have a chipped P28 from mtber (phearable.net). Or should i pour in a couple more gallons of 100 Octane and get around 95 Octane.</TD></TR></TABLE>


It sucks that guys have such shitty gas in cali. Does anyone in your area sell 100 cam2? I don't know what your final octane rating will be but. 25% 100 oct/ 75% 91 oct mix per tank should be fine for a street car.

Oh, and don't waste your money on 114 or 116 octane. That's total overkill, not to mention any cop that gets behind you will have tears in his eyes from the burn. Cops know what race gas coming out of a catless exhaust smells like.

 

i think its not so much about the actually rating on the compression ratio that is important, i think what 92typer is talking about is cylinder pressure. it does make sense that regardless of how high your compression ratio is, your cylinder pressure can also be low, therefore causing no detonation.

your cam gears can be tuned for more or less cylinder pressure to a certain extent. we all know this.