I knwo alot of people have about 9:1 comp ratio for there B18c turbos but I was thinking a 8.5 is there anything wrong with this can having a comp ratio too low be bad will it effect anything when boosting. Also I understand that having a comp ratio that low I would deff need a upgrade in cams. I here ITR cams are the best because of the overlap and I wont lose any top end power but is the torque curve going to stay the same throughout the powerband which are what hondas are known for??

 

Lower static compression and bigger cams means even less "off boost" torque.The 8.5:1 won't have to much effect at boost but will make the engine slower in vacuum.

 

so i would just be better to go 9:1

 

I would go 8.5 or even lower. Thermally (burn stability) it's stupid to use the compression of the motor to make power rather than the turbo and intercooler system.

 

remember that before boost comes in, you're going to have a 8.5:1 compression n/a B18C though.

Wouldn't a motor with higher compression require less boost to make the same power also?

 

but if you have bigger cams wouldn't that compensate for the lower compression by opening the vavlevs longer and farther

 

.5CR isn't going to make that much of a diffrence on or off boost.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GSE980 &raquo;</TD></TR><TR><TD CLASS="quote">but if you have bigger cams wouldn't that compensate for the lower compression by opening the vavlevs longer and farther</TD></TR></TABLE>

You have it backwards.Bigger cams require more static compression because of longer durations.Less time for the engine to make compression.Engines with too low of a compression ratio become very inefficient.They typically have a less than complete burn.

 

just remember every point of compression is 10 hp less. so its really not that big of a diff. power levels will be basicly the same when you hit boost so don't even worry abt it. i would go 8:1 or 8.5:1 for pushing the limits on pump gas.

 

i have 9:1 and its great.

 

Go 10.9:1, 84.5mm ls/vtec gt35r turbo and really good tuning and you wont care about waiting till 6k to get boost.

 

I'd go with 8-8.5:1 on a turbo engine and 10.5:1-11:1 on a N/A engine
Lower compression with a turbo engine and your off boost performance is horrible and higher than that, its susceptible to knock.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tshracing &raquo;</TD></TR><TR><TD CLASS="quote">Go 10.9:1, 84.5mm ls/vtec gt35r turbo and really good tuning and you wont care about waiting till 6k to get boost.</TD></TR></TABLE>


haha...your turbo is much too big if you spool at 6k

 

Jojo carlos (professional driver) runs a 14:1 compression motor turbo. Ive seen 12:1 compression turbo and its all about the tuning.

 

My car doesnt spool at 6k, i meant to say that with a setup like this you wont care if it does.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tshracing &raquo;</TD></TR><TR><TD CLASS="quote">Jojo carlos (professional driver) runs a 14:1 compression motor turbo. Ive seen 12:1 compression turbo and its all about the tuning.</TD></TR></TABLE>

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tshracing &raquo;</TD></TR><TR><TD CLASS="quote">My car doesnt spool at 6k, i meant to say that with a setup like this you wont care if it does.</TD></TR></TABLE>

the higher compression is the more power you make. it is also harder to tune. if you have the money for tuning then do what you want. bet jojo has deep pockets for tuning.

and the op is asking bought low compression turbo not spool time.

 

I have low compression setup, About 8:1 in dohc zc. Turbo is sc50 .48turbine, full boost @ 4000rpm. It pulls great on lower rpm:s too, i think because i can run 10-15 degrees more ign. advance vs. stock ign. Oh and boosting 27psi with pump gas.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by joppe &raquo;</TD></TR><TR><TD CLASS="quote">I have low compression setup, About 8:1 in dohc zc. Turbo is sc50 .48turbine, full boost @ 4000rpm. It pulls great on lower rpm:s too, i think because i can run 10-15 degrees more ign. advance vs. stock ign. Oh and boosting 27psi with pump gas. </TD></TR></TABLE>

i call straight out bs!!!!!!!!!!!!!

 

You can call what you want. I live in finland and we have pretty good quality pump gas. I dont remember exactly advance i have but, about 20deg. in 20psi. You can watch my setup in http://www.jolpa.1g.fi

 

I dont mind paying for the good tuning. Doesnt matter how much it cost.

 

My car is streettuned

 

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

i call straight out bs!!!!!!!!!!!!!


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

did u notice he has a sc50 which is a small turbo. that turbo prolly maxes out at about low 400s whp so that sounds about right 27 psi would be about maxing out that turbo. so why do u call bs. if he said sc 61 27 psi pump gas then u can call bs

 

so running a 8.5 comp. wouls the ITR or CTR benifit more than the sayyyy crower turbo cams ???? Im understanding that lowert your compression your lose low end power but then it make up for it high end. so is it better to have a solid low end(higher comp.)
to work with than losing soo much . or am i just over analizing things

 

A stock 4g63 is like 7.7:1 and they dont feel bad out of boost even with a big hybrid. Make power with boost not dynamic compression. It doesnt matter what all out racecars run, different application.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bailhatch &raquo;</TD></TR><TR><TD CLASS="quote">A stock 4g63 is like 7.7:1 and they dont feel bad out of boost even with a big hybrid. Make power with boost not dynamic compression. It doesnt matter what all out racecars run, different application.</TD></TR></TABLE>

4G63's are torquey motors, more stroke, more displacement. You won't see them rev to 9000+ RPM and there is a reason why. The changes in compression are barely noticeable because it is still probably making 120+ ft-lbs of torque without any boost

Hondas suck when you kill the compression like that... It's no different than driving a damn Geo everytime you are off boost. Higher compresssion just doesn't only improve power at vacuum regions, but it also improves partial boost regions (initial 2-4 psi of boost). It also improves your throttle response so it won't feel like as if you are stepping on a sponge when you hit it off the line Now add the same fixed percentage of power increase when boost is starting to build and you'll really see a difference in powerband and midrange. 0.5CR is still a significant amount IMO, and there are enough 9.0:1 CR Hondas making big power on pump gas unless the power goal is like 900WHP...lol