The block is an 84.5mm B18C5 with basically a whole ITR top end but with CTR cams (not much difference, I know)

I'm confused about all that "dynamic compression" talk and such, and would like to know a decent CR to run this on the street with 94 octane.

There is going to be Hondata, so is 13.1 too high and will I see any advantages with it??? or should I stick with like 12.1???

 

http://www.c-speedracing.com/howto/c.../compcalc.html

enjoy

 

dynamic compression is the compression when the motor is running, static compression is when compression is measured w/o the motor running...cams can lower you dynamic compression throughout the rev range due to overlap; both sides of valves are open at the same time, hence the terms valve overlap, you lose "compression" during this time, but overlap to an extent is good for NA applications as it creates a stronger than normal vacuum that can suck intake air in and suck exhaust out...anyway, you want a compression ratio your engine management can support in the environmaent the car was built for....pump gas and good tuning? 12.5:1-13:1 compression is fine especially with hondata...you can go higher if you go with a stand alone engine management that is not as slo as hondata...

 

the big bore 84.5 will ping on 93/94 octane even with 10 degree advance timing an aftermarket managemnet system is not gonna help, high octane fuel is the only thing that will ... or bigger cams too also helps along with the rollerwave design pistons.

also, makes no sense to go high compr 84.5mm and cant run at least 32 adv timing, so try to either go big cam or go max 12.5:1 compr dome.

greg

 

hmm, im sorry but i disagree CHEETAH. A high overlap cam setup and a precisely tuned engine management will allow for a 13:1 cr setup on pump gas, even with the large overbore. Compression dynamics change ALOT when the the motor is running, overlap kills compression, even if its minutely. Greg, being from the NYC/North Jers area, I know you've seen plenty of cars on the street running 13:1+ on 94 octane throughout the years, and lasting. Sardis Campondonico tuned many during some of my time spent @ dyno sessions up there.


[Modified by builthatch, 2:40 PM 12/3/2002]

 

I'm curious too...

 

hello builthatch, yes you're right, any good tuner can get a car running with high compression like 13:1 motor, its pretty tough and the rings take a beating because the motor always pings but never heard, just visual by the plug tips ... but I assumed the poster was a daily driven car with limited knowledge who wanted to run that high compression with CTR cams ... this is playing with fire, especially on a 84.5mm bore motor ... but look at this scenario (practical point of view - nothing techinical):

1) its pretty inefficient if he plans on runnign 94 all the time and can go a max of 22 to 25 advance (because it'll ping anythign past that (even with enough overlap to dial in cam timing) .. ideally oyu want to advance as high as 32, can't imagine motor will handle 32 on 94 octane evne with hgih degree of overlap ...

2) go past the sweet spot of the motor by giving too much overlap will equate to much less power on the motor by simple "bleeding"

with #1 and #2 in mind, would you prefer to go high compression so high with motor toned down until you're ready to race or you prefer to be practical and use a lower compressive and take full effect of the motor on 94 octane ?

I guess its up to the individual.

Greg

 

Cheetah, I agree, I see what you are saying; I always am thinking in terms of said toned down race motor that is literally on the ragged edge when run with pump gas; I agree that in terms of the original poster's plans, you have the better idea...

 

Cheetah:

So, what is max compression you would run daily-driven on 94, using a stand alone like the AEM EMS?

84.5mm bore and Jun Stage III's.

 

I wouldn;t go anywhere past a 12:1 dome for JE/SRP/Arias, etc and about 12.2:1 max for the Endyn rollerwaves ... especially with the Jun 3 cams, they are not as big ont he overlap as a Toda spec B and C, so your dynamic compr will still be low.

Also, with 12.2:1 you'll make gobs of power ... the AEM is a nice unit BTW.

Builthatch, I knew exactly what you were thinking dont worry ... ****, I run 15:1 on my DelSol with a reprogrammed Honda ECU that I custom did to cater for it, but I've been told I'm not a sane individual either ... by wife and friends ... so who knows.

Greg