like it says, looking to change a few things about my all motor set-up and was wondering what the highest compression ratio was that would be safe to consistently run 91 octane. thanks!

p72 block and head

Already searched and i found a lot of different answers... thanks

 

anyone?

 

i have a 12.5:1 cpr and i daily drive on 93 octane

 

Do you want it to last 40k or 140k if the latter run 11.0 IMO. Dan

 

It's such a vague and IMO pointless question. Are you gonna make more power with a 12.5 cr tuned vs. a 11.5 tuned?? Chances are your tuner is gonna be able to work with the motor and squeeze more power out of it with a more friendly c/r compared to working with a motor that he/she has to constantly fight detonation.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by spooncivic16 &raquo;</TD></TR><TR><TD CLASS="quote">i have a 12.5:1 cpr and i daily drive on 93 octane</TD></TR></TABLE>

i don't have 93 i have 91

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Dan Ruddock &raquo;</TD></TR><TR><TD CLASS="quote">Do you want it to last 40k or 140k if the latter run 11.0 IMO. Dan</TD></TR></TABLE>

not too worried about it lasting more than about 40-50k

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by clean rice &raquo;</TD></TR><TR><TD CLASS="quote">It's such a vague and IMO pointless question. Are you gonna make more power with a 12.5 cr tuned vs. a 11.5 tuned?? Chances are your tuner is gonna be able to work with the motor and squeeze more power out of it with a more friendly c/r compared to working with a motor that he/she has to constantly fight detonation.</TD></TR></TABLE>

how is it pointless or vague? its a simple question, whats the highest and safest comp ratio i can run on 91 octane without detonation. is your suggestion 11.5 then?

As far as more details, it will be tuned at Church's with s200 on a p28 if that matters.

 

i'd say 13:1 is about the maximum for premium pump....91 is kinda on the low side of premium gas.

 

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

https://honda-tech.com/zerothread?id=767014
https://honda-tech.com/zerothread?id=1451743

https://honda-tech.com/zerothread?id=353980

https://honda-tech.com/zerothread?id=184093

https://honda-tech.com/zerothread?id=564214

https://honda-tech.com/zerothread?id=939241

Did you try to search ther is a lot of info about Pump gas and Compression?</TD></TR></TABLE>

thanks a lot

 

i run 12.3 comp on 91 daily...it's fine as long as it's tuned...

 

most people includeing myself have lsvtec's with pr3 or p30 pistons with compression from anywhere around 11.3 to 12.1 and run on 91 octane with no problem

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by dohcMONSTER &raquo;</TD></TR><TR><TD CLASS="quote">
how is it pointless or vague? its a simple question, whats the highest and safest comp ratio i can run on 91 octane without detonation. is your suggestion 11.5 then?

As far as more details, it will be tuned at Church's with s200 on a p28 if that matters.</TD></TR></TABLE>

its vague because you dont even mention what other components you will be running such as camshafts. static compression is one thing, but you also have to think about dynamic compression.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Manuel &raquo;</TD></TR><TR><TD CLASS="quote">You can run 12.5.1 CR on 91oct detund the motor but you now the higher you go on compression you get closer to detanation the engine</TD></TR></TABLE>

Keep in mind that a lower compression ratio motor with more advance will almost always make more power than a higher compression motor in which the timing has to be retarded.

 

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

Keep in mind that a lower compression ratio motor with more advance will almost always make more power than a higher compression motor in which the timing has to be retarded.</TD></TR></TABLE>

True Here is some of my rantings that I have posted else where but it is relevant.

How does he know there is no detonation just because he can't hear it does not mean it is not there, some detonation is inaudible. Some times the problems don't show up till latter. Wow 95 ron we use the ron + motor /2= X method here which make comparing diffucult. I would say limit it to 11.5 and you should be ok. Don't use ctr pistons!!! As far dynamic vs static compression way too much importance is made of that here is a I wrote about this in another thread.

The more you push cr to the edge the more fuel you will need suppress detonation. In my opinion if you need to back off timing or run a fat A/F you have too much cr. You will get better fuel mileage and the same performance with a cr that allows you to run a factory A/F and timing that is why Honda set there cr where they did. Here is another bit of my rantings that might help you about a prevalent myth.

Myth's get started with some truth and cams vs compression is an old debate. When you increase the duration you will lose cranking compression and a compression test proves this. It is the later intake valve closure and not overlap that causes this. So the conventional wisdom is to increase the cr to compensate for the loss. But it is not that simple, none of us drive our cars at starter cranking speeds and what is happening at high rpm is much different than what is happening at idle speeds. When an engine comes onto the power band of a cam (peak volumetric efficiency point) the late intake closure bleed off stops happening because the velocity in the intake runners becomes high enough to over come the piston pushing anything out, it is called ram effect. This is the main reason big cams will make more power. In the days of no vtec adding cr would help a lot in motors with big cams when the engine was below the cams power band of the cams but with vtec there is no need for this. So what's my point, the point is the cr should be 90% weighted toward what fuel is being used and not the cams. Dan