there isnt anything bad about high compression, like breaking parts or anything right?...The only thing holding us back is the gas we use?

 

High compression ratio = more power = more stress & heat.
Glenn

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by D-CeReaL#4 &raquo;</TD></TR><TR><TD CLASS="quote">there isnt anything bad about high compression, like breaking parts or anything right?...The only thing holding us back is the gas we use?</TD></TR></TABLE>

It depends. If you have to use a huge piston dome, it will impede airflow and hurt the engines ability to breathe a little bit. You always want to match the available octane to your compression, not try to strecth the ability of the octane to meet your 12.5:1 build just because someone told you it would be ok with a good tune on 91 octane.

Higher compression doesnt necessarily have to produce more heat. The right amount of fuel in the upper RPM range should cool things down quite a bit.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by LsVtec92Hatch &raquo;</TD></TR><TR><TD CLASS="quote">

It depends. If you have to use a huge piston dome, it will impede airflow and hurt the engines ability to breathe a little bit. You always want to match the available octane to your compression, not try to strecth the ability of the octane to meet your 12.5:1 build just because someone told you it would be ok with a good tune on 91 octane.

Higher compression doesnt necessarily have to produce more heat. The right amount of fuel in the upper RPM range should cool things down quite a bit.</TD></TR></TABLE>

 

Really high compression is hell on your bearings -- the force pounds them and ruins them faster. Also the heat is much greater because your compressing the air into a smaller space pushing all those molecules together making heat. There is also a point (some people think otherwise though) were you reach a plateau, and no matter how high you make the compression you just won't make any more power because even the best fuel cannot support it.

 

shouldnt be hard on bearings if you know how to set your timing properly. No harder than lower compression and bad timing.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by d16dcoe45 &raquo;</TD></TR><TR><TD CLASS="quote">Really high compression is hell on your bearings -- the force pounds them and ruins them faster. Also the heat is much greater because your compressing the air into a smaller space pushing all those molecules together making heat. There is also a point (some people think otherwise though) were you reach a plateau, and no matter how high you make the compression you just won't make any more power because even the best fuel cannot support it. </TD></TR></TABLE>

 

nothing wrong with high compression, i have almost 13.0.1. on pump gas. all this crap on bearings and not making any more power is false, u will be fine dont miss a gear.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by jrthecow311 &raquo;</TD></TR><TR><TD CLASS="quote"> i have almost 13.0.1. on pump gas</TD></TR></TABLE>

Ill assume you mean 13.1:1, and thats bull. Can you go past 30% throttle on 91 octane without pinging?

 

he said almost that means 12. something

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by LsVtec92Hatch &raquo;</TD></TR><TR><TD CLASS="quote">

Ill assume you mean 13.1:1, and thats bull. Can you go past 30% throttle on 91 octane without pinging?</TD></TR></TABLE>

i had a 13:2:1 motor and with the timing at 10 degrees it would ping on 100 octane.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DC2Hybrid1 &raquo;</TD></TR><TR><TD CLASS="quote">i had a 13:2:1 motor and with the timing at 10 degrees it would ping on 100 octane.</TD></TR></TABLE>

So you agree with me that this guy if full of **** right?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by LsVtec92Hatch &raquo;</TD></TR><TR><TD CLASS="quote">

So you agree with me that this guy if full of **** right?</TD></TR></TABLE>

with him running pump gas and the car running fine; i agree with you 110%!!!!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by DC2Hybrid1 &raquo;</TD></TR><TR><TD CLASS="quote">

i had a 13:2:1 motor and with the timing at 10 degrees it would ping on 100 octane.</TD></TR></TABLE>

I have a 14.x:1 motor that I run on 100 octane all day at 16 degrees of initial timing and 32 degrees of total timing advance and have zero pinging. Were you using stock gsr cams with that compression or what????

 

12.5:1 on 91 octane here. Daily driven and runs fine

 

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

I have a 14.x:1 motor that I run on 100 octane all day at 16 degrees of initial timing and 32 degrees of total timing advance and have zero pinging. Were you using stock gsr cams with that compression or what????</TD></TR></TABLE>

no, i was using skunk 2 stage 3 cams

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by jrthecow311 &raquo;</TD></TR><TR><TD CLASS="quote">nothing wrong with high compression, i have almost 13.0.1. on pump gas. all this crap on bearings and not making any more power is false, u will be fine dont miss a gear.</TD></TR></TABLE>

my guess is hes one of those guys that bought some big dome pistons and they are called 13:1 but when actually calculated out with head volume, PTDH, gasket thickness etc it runs only 12:1.
i was a sucker at one time. bought some 12.5:1 pistons. actual CR after everything figured in 11.3:1.

 

I know that 1 2 NV is one of the few on here with actual real world experience that i can vouch for.

Would you say high 12s compression is possible with zero pinging on 91 octane?

 

well i only know of what i have seen posted. there are very few built high compression motors where i live. ill give an example of what i have personally seen in the past.
my friend bought some pistons, exact same CR but for a 84mm CRVTEC motor. we both had B16 heads. i sold him my 310cc injectors and he pinged like crazy. i know his compression was slightly higher due to the longer stroke of the 89mm crank but id say around 11.7:1 VS my 11.3:1. we put my ECU into his car, both on 92 octane and his damn motor would ping anyways, we even backed off base timing and it still pinged.
when i build my street motor im still goin to shoot for 12:1 and i think its possible. countless ppl on HT agree that you could even run up to 12.5:1 but i wont take that chance.

 

I think even 12:1 will require a compromised tune, im betting youd get more area under the curve from a 11.5-11.7:1 engine. Just my .02.

What octane will you be running?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by LsVtec92Hatch &raquo;</TD></TR><TR><TD CLASS="quote">I think even 12:1 will require a compromised tune, im betting youd get more area under the curve from a 11.5-11.7:1 engine. Just my .02.

What octane will you be running?</TD></TR></TABLE>

i agree 92 here where i live.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by LsVtec92Hatch &raquo;</TD></TR><TR><TD CLASS="quote">I think even 12:1 will require a compromised tune, im betting youd get more area under the curve from a 11.5-11.7:1 engine. Just my .02.

</TD></TR></TABLE>

This sounds good. I remember reading in the WD-40 B series shootout that all of the builders were only running 11:1 CR I believe. One of them even said something like, "we could probably run 11.5:1 but it might detonate on a hot day." or something like that. 12:1 would need a pretty good tune, it would also help w/a real high cr to have some big cams that would relieve a little bit of cylinder pressure thus lowering the dynamic CR. Maybe this could help in a scenario that's on the edge of pinging or not.

If you think what I said sounded like bullshit, I'll look for the quotes.

 

No, what you said was correct, im just wondering if you understand the concept of dynamic compression, or are you just quoting what you read in that magazine or here on HT?

 

I was pretty much just quoting what I read, could you enlighten me on the details of dynamic cr or guide me to where I could learn more about it, I would really love to know.

edit: I thought it had something to do with, (this is all theoretical) if cams had long duration, etc. that slightly carried over into the compression stroke, then some cylinder pressure would be relieved which could help lessen the chance of detonation due to preignition by excessive heat/pressure. I would venture a guess that duration wouldn't be the only possible factor, I'm trying to search.

 

Yep, you pretty much got it.

 

Nice, thanx!

Sorry to change the subject.