corrected compression ratio

what is a nice corrected compression ratio that will allow the motor to rev high and run cool and still produce decent power. i know there is no direct correlation to psi but i find running at 135 psi i get all the above. 150 i get more power but temps start to rise.

the motor in question is aircooled and is for street use.
i am sure before today i have aimed for 6:1 when calculating my head volume but cant remember due to old age.
thanks

Nombre de messages : 351 Localisation : Belgique Date d'inscription : 05/12/2011

corrected compression ratio is useless.

JanBros a écrit:: corrected compression ratio is useless.

JanBros a écrit:: corrected compression ratio is useless.

isnt it a good rule of thumb guide so as to achieve the desired psi?

ie its impossible to test the psi of a head whilst its on the bench but its easy to burette it to get the desired volume.

one of your spreadsheet pages refers to it ??

Nombre de messages : 351 Localisation : Belgique Date d'inscription : 05/12/2011

aljaxon a écrit:

JanBros a écrit:: corrected compression ratio is useless.

isnt it a good rule of thumb guide so as to achieve the desired psi?

ie its impossible to test the psi of a head whilst its on the bench but its easy to burette it to get the desired volume.

one of your spreadsheet pages refers to it ??

because some people (like you) keep using it, I've put it in but have never looked at it

well i wouldnt call it useless. if only to get the desired volume of the head somewhere in the right place. otherwise how the hell do you know how large to machine it?
or are you implying uncorrected compression ratio is the one to use to determine the head volume?

Nombre de messages : 351 Localisation : Belgique Date d'inscription : 05/12/2011

what does the position of the piston have to do with determining the head volume ? if you want to measure it with fluids, the only position that matters is TDC.

JanBros a écrit:: what does the position of the piston have to do with determining the head volume ? if you want to measure it with fluids, the only position that matters is TDC.

i need to know what cc to machine the head to.
luckily by trial and error i now know what cc to make it. but i thought using the ccr formula would help me get the cc's without guesswork.

its looking like a ccr of 5.9 will lead to 8.1cc and cool running.

Nombre de messages : 351 Localisation : Belgique Date d'inscription : 05/12/2011

aljaxon a écrit:

JanBros a écrit:: what does the position of the piston have to do with determining the head volume ? if you want to measure it with fluids, the only position that matters is TDC.

i need to know what cc to machine the head to.
luckily by trial and error i now know what cc to make it. but i thought using the ccr formula would help me get the cc's without guesswork.

no formula or spreadsheet or sim is ever going to tell you what it should be. it's all about playing with it and testing. and than play some more and test some more.

and with more experience, you will have to play and experiment less to get the desired result.

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