Speciffically the difference between 9.0:1 and 10:1 on a 1.8/stock head w/ sc61? I know the car will make more power and spool sooner but how much sooner? Any dyno charts would be great. I trust my tuner alot but im not looking to run race gas and Ill prob be on forged rods/pistons but stock sleeves.


Modified by BoostedGSRBubble at 9:12 PM 10/29/2003

 

higher comp works wonders BUT its "harder" to tune.
smaller window for screwing up

 

I have b16a2 stock bore 8.8:1cr and a Precision SC50 and spools slow as hell and has no guts!

 

This has been a constant arguement among turbo guys for years and years, some say lower boost higher compression, others say higher boost and lower compression....... You can't have both, for example, a 12:1 compression ratio and 20lbs of boost would be ungodly, but it just can't really be done..... I'm sure it could be done, but many problems arise: 1- damn near impossible to have it reliable, 2- damn expensive, I think some F1 - not FI, but F1 formula cars run V12s with a lot of compression and "small" turbo's...... but then again, they have 20 million dollar budgets..... In my opinion, I'd always go with 9:1, if not slightly lower, and more boost...... I think this way has more potential

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by spoolinlude &raquo;</TD></TR><TR><TD CLASS="quote">This has been a constant arguement among turbo guys for years and years, some say lower boost higher compression, others say higher boost and lower compression....... You can't have both, for example, a 12:1 compression ratio and 20lbs of boost would be ungodly, but it just can't really be done..... I'm sure it could be done, but many problems arise: 1- damn near impossible to have it reliable, 2- damn expensive, I think some F1 - not FI, but F1 formula cars run V12s with a lot of compression and "small" turbo's...... but then again, they have 20 million dollar budgets..... In my opinion, I'd always go with 9:1, if not slightly lower, and more boost...... I think this way has more potential</TD></TR></TABLE>

12:1 and 10+ pounds of boost can be done.... if you're running meth That would be very hard to tune for a street car even running C16 all the time. You'd make a lot more power running a 9:1 motor and more boost, and the difference in spool time is almost nonexistant going from 9:1 to 10:1, and so is the power difference down low. If you're going to build a street honda, go 9:1.

As far as F1 goes, I don't think so. Since I think it's 94 all F1 cars are 3 liters naturally aspirated. You might be thinking of cart, but their engines are all produced by ford/cosworth, are 2.7? Liter DOHC V8's and run on meth.

 

ill say go with 9.1.
yes it will spool a tad slower and yes you will need more boost to get
the same amount of power of the 10.1 motor, but leaves you room
for tuning error, bad tank gas, ect.

 

I'll argue with both the 9:1 and 12:1 guy and say go 10:1 or 10.5:1 and be the happy medium. Obviously you cant have BOTH, but you can have right in the middle. A good standalone + 10:1 compression = great power out of boost, and awesome power in boost, not to mention quick spool. You won't regret it if it's street driven, and if tuned right, it will do great on the track.

 

how much power do you plan on making anyways? street or drag?

 

Well the limits of gas and stock sleeves seem to be 400whp. So, id like to be 380-390, as close as i can get and have my tuner feel the car is safe. Street car which will see some 1320 action.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BoostedGSRBubble &raquo;</TD></TR><TR><TD CLASS="quote">Speciffically the difference between 9.0:1 and 10:1 on a 1.8/stock head w/ sc61? I know the car will make more power and spool sooner but how much sooner? Any dyno charts would be great. I trust my tuner alot but im not looking to run race gas and Ill prob be on forged rods/pistons but stock sleeves.


Modified by BoostedGSRBubble at 9:12 PM 10/29/2003</TD></TR></TABLE>It would be impossible to have meaningful dyno results on compression change.
The current trend on some of the faster cars is to lower the compression and turn up the boost.
I get the c/r question every day. If the car will ever be run on pump gas, use 9-1 c/r. On racing gas only, 9.7-1 to 10-1 seems to work ok.
If you have the proper sized exhaust, your turbo will spool quickly and compression ratio will not be an issue. Most guys on the street over turbo and blame their problems on other issues.

 

An engine with a higher compression will spool faster, increase the power band and make more power. If I was going to run pump gas all the time I'd run 9:1. Race gas 10:1. Or if you want to run alot of boost, like I am(35psi) then I'd run 9:1CR.

art

 

I'm running 9:1... due to living in california with our brutal 91 octane...

spooling really isn't a huge issue. i have full boost relatively quick. and even with 9:1 it spools quicker than it did with 10:1 compression and smaller exhaust.

 

I beg to differ from the rest of the guys about compression. My outlook on street applications is 10:1 is the perfect compression. 10:1 isn't hard to tune with boost on pump gas. Well then again, we have 94 octane here in Ny as compared to 91 in Cali. That might be the deciding factor on compression. If you live anywhere but Cali then go 10:1 compression, however if you live in Cali then stick to 9:1 because of the lower octane.

All my turbo street are running 10:1 compression without any problems, maybe I'm just have luck with it. I personally run a tad big higher than 10:1 on pump gas doing 1 bar, on a daily basis. When it comes to track or dyno I just put some c16 in the tank and off I go. The most boost that I have tried so far is 21psi on c16 and the motor sounded pretty damm good. It was just humming on the dyno.

 

Ehh i was just guessing about the F1 cars, I didnt really know....... but I still say 9:1 is better on the street, even with high octane...... it just seems more reliable.... which is what i said earlier..... and seems to be everyone elses view

 

im running 10.5cr on my sohc (still on break in period) and will be boosting 12-13psi out of tdo4.. 93 octane and good tune on aem ems.

possible? yeah!... low cr + boost is a thing of the past thanks to modern/better/cheaper ways of tunning, people have a hard tiem of letting go older 'proven' stuff.

 

Colin, Im curious how much power you've safely tuned out of street hondas running 10:1 C/R.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ekb18c &raquo;</TD></TR><TR><TD CLASS="quote">I beg to differ from the rest of the guys about compression. My outlook on street applications is 10:1 is the perfect compression. 10:1 isn't hard to tune with boost on pump gas. Well then again, we have 94 octane here in Ny as compared to 91 in Cali. That might be the deciding factor on compression. If you live anywhere but Cali then go 10:1 compression, however if you live in Cali then stick to 9:1 because of the lower octane.

All my turbo street are running 10:1 compression without any problems, maybe I'm just have luck with it. I personally run a tad big higher than 10:1 on pump gas doing 1 bar, on a daily basis. When it comes to track or dyno I just put some c16 in the tank and off I go. The most boost that I have tried so far is 21psi on c16 and the motor sounded pretty damm good. It was just humming on the dyno. </TD></TR></TABLE>


yeah I'm also a fan of higher compression and mild boost. I live in MN and we can get 93octane at almost every other gastaion. I would personally go with forged pistons 9.5cr and 6-10psi on stock sleeves and 93 octane. If it was sleeved 84mm I would go more with 10.1cr 8psi on 93 octane all day and 14psi with 110octane on race days

just me though. Although lower compression does give me more peace of mind when i'm traveling and not have to worry if that state/city/town has 93 octane... lol know what i mean.

 

meguir's ITR runs 20 lbs of boost on stock internals...and that's supercharged and turbocharged....

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ekb18c &raquo;</TD></TR><TR><TD CLASS="quote">I beg to differ from the rest of the guys about compression. My outlook on street applications is 10:1 is the perfect compression. 10:1 isn't hard to tune with boost on pump gas. Well then again, we have 94 octane here in Ny as compared to 91 in Cali. That might be the deciding factor on compression. If you live anywhere but Cali then go 10:1 compression, however if you live in Cali then stick to 9:1 because of the lower octane.

All my turbo street are running 10:1 compression without any problems, maybe I'm just have luck with it. I personally run a tad big higher than 10:1 on pump gas doing 1 bar, on a daily basis. When it comes to track or dyno I just put some c16 in the tank and off I go. The most boost that I have tried so far is 21psi on c16 and the motor sounded pretty damm good. It was just humming on the dyno. </TD></TR></TABLE>The original question was about spooling as compared to compression ratio. You may be having quick spooling results because you pick the right sized turbos for your applications. The higher compression may be a bonus or it could hurt you if you had a spike and hurt the motor.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by earl &raquo;</TD></TR><TR><TD CLASS="quote">The original question was about spooling as compared to compression ratio. You may be having quick spooling results because you pick the right sized turbos for your applications. The higher compression may be a bonus or it could hurt you if you had a spike and hurt the motor. </TD></TR></TABLE>

Oh right, sorry for going off on a tangent. Yes, higher compression will help you spool up a turbo faster. However as with anything, too much will hurt you. =P

 

I was under the impression that high cr + lower boost is = to low cr + high boost - as far as power and ease of tuning. Or is it only to a certain point? It is just more pressure either way right?

 

i think 10:1 is nice to have for a daily street car becuase of the low end and so u don't need to go in to boost all the time

 

i have 8.8:1 in my motor. motor doesn't start making any power until Vtec. Spools slow so i'm going to get a EBC, hopefully that will help.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by BoostedGSRBubble &raquo;</TD></TR><TR><TD CLASS="quote">Speciffically the difference between 9.0:1 and 10:1 on a 1.8/stock head w/ sc61? I know the car will make more power and spool sooner but how much sooner? Any dyno charts would be great. I trust my tuner alot but im not looking to run race gas and Ill prob be on forged rods/pistons but stock sleeves.
</TD></TR></TABLE>

i have seen this sort if thing argued many times on many forums... but nobody ever puts up any math to back up their claims, and nobody ever understands the thermal limits of efficiency that gasoline has.

as per the gas faq at: http://www.repairfaq.org/filip...E_008, once your compression ratio reaches ~17:1, you can't make any more power by increasing the c.r.

i believe that law of physics applies to both normally aspirated and boosted motors, pump gas and race gas, etc.(??).

so when you achieve 17:1 effective c.r. on a boosted motor running any kind of gasoline, the only way you'll make more power is by increasing the overall volume of air/fuel ratio... which means you'll need less static c.r., and more boost volume.

it's all about the total combustion area.

i guess that if you never went to the track, and you had access to 93 octane pump gas, 10:1 static c.r. would be fun.

but in san diego county, they can permanently confiscate your car for street racing, and the gas is only 91 octane... it's a good place for 9:1 c.r. :-)

 

and btw, your car will not spool sooner with 10:1... because the exhaust gas volume will be basically the same as it would with 9:1 static c.r.

why? because changes in static c.r. do not affect the amount of cfm the engine consumes in normally aspirated mode... it uses about the same amount of a/f mixture regardless... so there can't be much of a change in exhaust gas volume.