1.8T_EG

... whats the highest compression ratio for a street / daily driven car on 91 octane?... (without too much risk of detonation)... i was thinking 11:1 would be a good ratio to run... can i go higher?... to like 12:1?... what does everyone else think?... anyone running 11:1 or higher on a daily driver?... lemme know... thanks...

( trying to plan next build - high compression h23vtec with nitrous )

EG TYPE-R

I have a friend that has a fully built ls/vtec and he is running 12.5:1 on 91 octane. It works fine and has awesome power.

Sportmode

how bad does mileage get when you raise compression say about a point (10:1 to 11:1)
I probably wouldnt go higher than 11.5:1 with proper tuning if it is a daily driver.

EG TYPE-R-
is your friends car his daily driver?

NSX Bob

You can run a lot higher than 11.1, but tuning is the real key to avoiding detonation.

boosted hybrid

13.5:1 on my built all motor engine. I havent run it yet to find out what octane it will start pinging at. I plan on running it on 93 + a mixture of toluene to yield approximately 100 octane. If you have the maps tuned, its the same deal as forced induction anything is possible.

Here is a shot of the cylinder head:



B16a head, portflow P&P, skunk2 springs, retainers, ferrera .5mm oversized valves, ferrea broze valve guides, ef-1.com "killer" cams.

Here is a shot of the header:



Block is due back from GE anytime now.

Sportmode

i agree that anything is possible, but i would like to know who is compression levels of 12:1 or higher in their only form of transportation, Especially here in cali where the highest octane we get is 91.

msilbernagel

That a Bisimoto header?

sshaikh01

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Sportmode &raquo;</TD></TR><TR><TD CLASS="quote">how bad does mileage get when you raise compression say about a point (10:1 to 11:1)

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thats what i wanna know

EG TYPE-R

like i earlier stated my friends car has 12.5:1 on his only car and he lives here in cali i should have said. 91 octane. he knows that the engine wont last too long but it will last a while when properly tuned and built which it is. ls/vtec

boosted hybrid

The more compression an internal combustion engine gets (otto cycle), this is not including the diesel cycle, the more efficiency it gains. More efficiency=more power. More power=more gas. Its a trade off. If we had alot higher octane gas available, you could run the air/fuel mixture leaner without detonation problems. 12.5:1 is not a problem even on 91 octane. You guys have to realize that with turbochargers the dynamic compression of the engine is through the roof. We counteract that by giving the engine more fuel, as well as taking out timing. A super high compression engine is not different. You have to run colder plug with a tighter gap to compensate for pre-ignition of the mixture (this is due to the nature of heated air in super high compression), as well as backing out some timing. High compression will still show significant gains even when the timing is reduced.

chet

i've seen quite a few higher compression motors in this area. (i consider anything over 12:1 high compression)

and it seems like you need a standalone system to really make the motor run properly without detonation. i guess that goes without saying but people still insist on trying to run just a vafc with over 12:1 compression and at some point problems will exist.

for daily driven, i like around 11:1 compression. with good tuning you can be in the 190-200whp range and still have excellent reliability.

dfoxengr

12.5 with tuning...

msilbernagel

&gt;Quote, originally posted by Sportmode »
&gt;how bad does mileage get when you raise compression say about a point (10:1 to 11:1)
&gt;&gt;thats what i wanna know

Efficiency increases with compression, and efficiency means doing more with less, such as more energy released from the same amount of gas, so more HP per gallon, so more miles per gallon...

What causes mileage to decrease with compression is a heavy foot that wants to do something with the extra HP!!

How much -- I suppose it could amount to a MPG or two. It is 'knowable', sort of, as I've seen numbers somewhere which translated compression ratio to a % increase in power.

Mark

NiiS

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Sportmode &raquo;</TD></TR><TR><TD CLASS="quote">how bad does mileage get when you raise compression say about a point (10:1 to 11:1)
I probably wouldnt go higher than 11.5:1 with proper tuning if it is a daily driver.

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Just to give you an idea, I had a stock JDM GS-R w/ 10.6:1 cr and my milage was decent, I jumped to ITR`s and to ~11.6:1 and I did`nt notice a huge difference in fuel consumption....It also has to do with how you drive the car tho...

respectblades

nice cylinder head there

na200whp

im runing 12.78 to 1 on 93 pump gas.like stated above with more fuel and a little less timing it will be fine but it also helps if you are using a anti-detonation piston like endyne's rollerwave and some combustion chamber work on the cly head.

junya16

run 11:5:1 all day long on pump gas, no problems

1.8T_EG

so with tuning and 91 octane gas, 12.5:1 is not out of the question?...

also, this might sound n00b and i doubt it is possible, but is there a way to up the compression ratio on the fly?... like between street trim and track trim?... i am sure the answer is no... so the only other way to up the power for the track is to run more advanced timing right?... the only reason i ask is because i am used to turbos running in street trim and track trim and i was wondering if there was anything like that in the n/a world... thanks...