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CR adjustment for supercharger

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Old 08-28-2004, 09:38 PM
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Default CR adjustment for supercharger

if i'm going to supercharge my Civic Si, which has a K20A3 engine, do i need to lower my CR at all? if i do, how low do i need to lower it to?

i'm trying to boost it up to at least over 300 hp
Old 08-28-2004, 09:53 PM
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Default Re: CR adjustment for supercharger (Inisharu D)

You're not making anywhere close to 300whp with a supercharger without custom pulleys, forged internals, block work and good tuning. You should aim for 180whp with a bolton JRSC or 200 with the "racing" JRSC.

300hp is a tall order on the K20A3 and you'll find that a turbocharger will get you there far faster and with far less tuning. Either way, the money you're going to need to spend is going to be insane. My suggestion is get a K20A (JDM) and swap the motor and tranny. Sell your perfectly good K20A3 ($2500 in the local paper, I'm sure) and you'll have 200ish whp for under $3000 with no tuning required and much better reliability.
Old 09-02-2004, 12:09 AM
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Default Re: CR adjustment for supercharger (Archidictus)

is it possible to tune any of the K series to 300 whp with a budget of 10 grand?

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Inisharu D &raquo;</TD></TR><TR><TD CLASS="quote">if i'm going to supercharge my Civic Si, which has a K20A3 engine, do i need to lower my CR at all? if i do, how low do i need to lower it to?

i'm trying to boost it up to at least over 300 hp</TD></TR></TABLE>

i've thought of that, but sorry, a 215 hp civic does not satisfy me
Old 09-02-2004, 01:20 AM
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Default Re: CR adjustment for supercharger (Inisharu D)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Inisharu D &raquo;</TD></TR><TR><TD CLASS="quote">is it possible to tune any of the K series to 300 whp with a budget of 10 grand? </TD></TR></TABLE>


The short answer is yes but you'll want to do what the other guy suggested and get another motor as the K20A3 isn't nearly as sturdy as the K20A2 (RSX type-S) or the K20A (JDM). Any particular reason why you wanted to go supercharger vs turbo? A turbo would certainly help you reach your goal a lot easier...
Old 09-03-2004, 04:10 AM
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Default Re: CR adjustment for supercharger (00Red_SiR)

even with a turbo, wouldn't the compression ratio be required to be lowered with any K series engine?

if i have to lower a K20A engine imported from Japan, wouldn't it be alot cheaper to buy a K20A3 engine which is cheaper and have the CR lowered already?

and the point in getting a supercharger instead of a turbo, is that a supercharger has no lag like the turbo does since i'm planning on a root supercharger, i'm supposing that it doesn't steal as much hp as a centrifugal.

about the sturdy part, how is a K20A any more sturdy than a K20A3??

K20A CR = 11.0:1
K20A3 CR = 9.8:1
Old 09-03-2004, 09:58 AM
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Default Re: CR adjustment for supercharger (Inisharu D)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Inisharu D &raquo;</TD></TR><TR><TD CLASS="quote">even with a turbo, wouldn't the compression ratio be required to be lowered with any K series engine?

if i have to lower a K20A engine imported from Japan, wouldn't it be alot cheaper to buy a K20A3 engine which is cheaper and have the CR lowered already?

and the point in getting a supercharger instead of a turbo, is that a supercharger has no lag like the turbo does since i'm planning on a root supercharger, i'm supposing that it doesn't steal as much hp as a centrifugal.

about the sturdy part, how is a K20A any more sturdy than a K20A3??

K20A CR = 11.0:1
K20A3 CR = 9.8:1</TD></TR></TABLE>

If you're shooting for 300hp you'll need to reduce the compression ratio for sure with boost. The K20A3 may be cheaper but it has a weak crankshaft compared to the K20A2 or K20A. The A2 head flows considerably better than the A3 head as well which is an important factor for making the power you want. You'll need to change the stock rods too once you run more than 6-7 psi of boost as they are a weak link.

A supercharger may not have any lag but they do create a parasitic drain on an engine especially a small displacement one and tend to limit max power output. A roots type blower will easily consume as much as a centrifical supercharger or more since they are generally a heavier mass to turn. The tend to be great for torque but loose in the top end when compared to a centrifical charger. As far as I know I don't think anyone is making a roots type blower for the K series civic's that'll give you the power you want. A JRSC certainly wasn't designed to give that kind of power on a K20.

Turbo kits today, when properly matched to an engine have little or no lag. They are more efficient at making power and far more capable at making the 300 hp you're looking for especially with intercooling. Most roots type blowers aren't available with intercooling and that's a big issue when pushing high boost numbers to make big power. A turbo will give you far more tunability and reliability at the power levels you want.
Old 09-03-2004, 10:15 AM
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Default Re: CR adjustment for supercharger (00Red_SiR)

bull **** the compression ration doesn't need to be lower.


compression and 'boost' do the same thing, in different ways.

check this out, say we have two motor's same everything on them, (turbo, ect) the only difference is one has 9.8:1 and the other has say 8.8:1. now tune them properly ON THE SAME PSI and that 9.8:1 motor will make more HP and TQ at the same PSI.

9.8:1 isn't that high of compression at all, in fact its boost ready compression, you just need to find a good tuner.

FI, does just that FORCE AIR into the cumbustion chamber. more air= more fuel= bigger boom= more HP.

high compression pistons, take away empty space and fill it up with metal, thus creating a smaller area and getting the alil more fuel and air into it= more power.


i don't see why your even worried about this because you will need to build that bottom end to take that hp and tq. K series motor can take what they have just fine, but when you throw more at it they don't last long
Old 09-03-2004, 10:25 AM
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Default Re: CR adjustment for supercharger (slammed_93_hatch)

Thanks slammed. I don't even bother to fight the higher cr+ less boost makes the same hp as lower cr + more boost, but with better off boost performance argument anymore.
Old 09-03-2004, 10:26 AM
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Default Re: CR adjustment for supercharger (slammed_93_hatch)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by slammed_93_hatch &raquo;</TD></TR><TR><TD CLASS="quote">bull **** the compression ration doesn't need to be lower. </TD></TR></TABLE>



<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by slammed_93_hatch &raquo;</TD></TR><TR><TD CLASS="quote">
compression and 'boost' do the same thing, in different ways.

check this out, say we have two motor's same everything on them, (turbo, ect) the only difference is one has 9.8:1 and the other has say 8.8:1. now tune them properly ON THE SAME PSI and that 9.8:1 motor will make more HP and TQ at the same PSI. </TD></TR></TABLE>

yes that is true and that's why I was saying to reduce the compression ratio. The more power you want to make the less compression you have to run and vice versa. He's not going to make 300 hp running 9.8:1 compression on 6-7 psi of boost!
Old 09-03-2004, 01:27 PM
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Default Re: CR adjustment for supercharger (00Red_SiR)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 00Red_SiR &raquo;</TD></TR><TR><TD CLASS="quote">



yes that is true and that's why I was saying to reduce the compression ratio. The more power you want to make the less compression you have to run and vice versa. He's not going to make 300 hp running 9.8:1 compression on 6-7 psi of boost!</TD></TR></TABLE>


HOLLY **** DO YOU NOT SEE THE ignorance in this statment.

not once did i say he would be getting to 300 hp on 9.8:1 compression on 6-7psi.

he would be able to make 300whp with 9.8:1 compression qwith lower boost then with 8.8:1 compression all else be equal.

besides PSI/ boost is relative to alot of other things. so you can't really just throw out a number.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Ricey McRicerton &raquo;</TD></TR><TR><TD CLASS="quote">Thanks slammed. I don't even bother to fight the higher cr+ less boost makes the same hp as lower cr + more boost, but with better off boost performance argument anymore. </TD></TR></TABLE>

LET THE IGNORANCE STOP PLEEAAASSSSEEEEEE
Old 09-03-2004, 01:57 PM
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Default Re: CR adjustment for supercharger (slammed_93_hatch)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by slammed_93_hatch &raquo;</TD></TR><TR><TD CLASS="quote">check this out, say we have two motor's same everything on them, (turbo, ect) the only difference is one has 9.8:1 and the other has say 8.8:1. now tune them properly ON THE SAME PSI and that 9.8:1 motor will make more HP and TQ at the same PSI.</TD></TR></TABLE>

If you make 300 HP on a 9.8:1 motor you might make 290 HP on the 8.8:1 motor. Read an article in a mustang mag, they dropped the compression on a motor from 10:1 to 8:1. Power dropped from 400 to 360 naturally aspirated, then when they slapped a positive displacement blower on power dropped by like 12%, but keep in mind when they were running a blower with a fixed rotor speed and a fixed level of airflow. With the same pulleys they were seeing a full pound of boost more on the 10:1 motor than they were on the 8:1 motor. With a turbo the boost controller would automatically compensate for this, so some of the added benefit of the power the higher compression makes would be gone right off the bat, and if you want more power the 8.8:1 motor will make more power on pump gas. Race gas, sure, the higher compression motor might make more power once you max out the compressor, but on pump gas there is no way a 9.8:1 motor will make more power than an 8.8:1 motor.
Old 09-03-2004, 03:15 PM
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Default Re: CR adjustment for supercharger (Chip)

that makes no sense.

oct ratings are how hot it has to be to ignite i have seen plenty of 300+ wheel HP cars on pump gas with 9.5:1 CR.


**** there ARE tons of GSR motor with STOCK bottom end, running 350+whp ON PUMP gas.

st00pid is a bad *** tunner.

ricey i see why you gave up, im done i tried im out.
Old 09-03-2004, 03:23 PM
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Default Re: CR adjustment for supercharger (slammed_93_hatch)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by slammed_93_hatch &raquo;</TD></TR><TR><TD CLASS="quote">that makes no sense.

oct ratings are how hot it has to be to ignite i have seen plenty of 300+ wheel HP cars on pump gas with 9.5:1 CR.


**** there ARE tons of GSR motor with STOCK bottom end, running 350+whp ON PUMP gas.

st00pid is a bad *** tunner.

ricey i see why you gave up, im done i tried im out.</TD></TR></TABLE>

I didn't say you couldn't make 300 WHP on pump gas with 9.8:1, I said you can make MORE HP on pump gas with 8.8:1. Everybody I've known who builds a turbo honda with high (9.5:1+) compression, including myself, has been disapointed in the end because they can't turn it up as high as they want to on pump gas. On top of that not everyone has a great tuner available in the near vicinity of their car, so they can't all afford to get a st00pid/mase/torquefreaks/etc caliber guy to tune their car who can put it exactly where they need to be with higher compression on pump gas.

Old 09-03-2004, 03:35 PM
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Default Re: CR adjustment for supercharger (slammed_93_hatch)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by slammed_93_hatch &raquo;</TD></TR><TR><TD CLASS="quote">


HOLLY **** DO YOU NOT SEE THE ignorance in this statment.

not once did i say he would be getting to 300 hp on 9.8:1 compression on 6-7psi.

he would be able to make 300whp with 9.8:1 compression qwith lower boost then with 8.8:1 compression all else be equal.

besides PSI/ boost is relative to alot of other things. so you can't really just throw out a number.

LET THE IGNORANCE STOP PLEEAAASSSSEEEEEE</TD></TR></TABLE>

Talk about making a mountain out of a mole hill... ***shaking head***

If you had read the original post to begin with you'd realise that it's not about the debate between compression ratio vs boost. I already said that I agreed with you about boost and compression! He asked if he would have to lower his compression to get 300 + horsepower and I said yes but notice I didn't say how much?? That's because I wasn't trying to start the big debate that you're trying to create here! Running 300+ horsepower on 9.8:1 compression would be ideal...hell 13.0:1 would be even better! but let's be realistic...it's a lot EASIER (not better) to build and tune a car running higher boost with lower compression than the other way around! running higher compression with less boost IS IDEAL but it also leaves less margin for error where tuning is concerned.

I was giving this guy reasonable advice on how to achieve his goal, I wasn't trying to rewrite the laws of the internal combustion engine! You're not the only one on here that actually has some knowlege about these things so why don't you relax a little and allow others to share some information constructively!
Old 09-06-2004, 10:50 PM
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Default Re: CR adjustment for supercharger (00Red_SiR)

yeah, i agree with you 00Red_SiR, thx for the advice, i appreciate the information i've got.

before i end this, i want to know about the race gas and the pump gas you guys were talking about. what exactly are these?

P.S. can't we all just get along peacefully? we all like cars right?
Old 09-07-2004, 07:42 AM
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Default Re: CR adjustment for supercharger (Inisharu D)

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Inisharu D &raquo;</TD></TR><TR><TD CLASS="quote">yeah, i agree with you 00Red_SiR, thx for the advice, i appreciate the information i've got.

before i end this, i want to know about the race gas and the pump gas you guys were talking about. what exactly are these?

P.S. can't we all just get along peacefully? we all like cars right? </TD></TR></TABLE>

Pump gas is just fuel that you buy at a gas station but usually has a limited octane rating of 91 for supreme. Race gas is a specialized fuel that you can usually buy at the race track or some speed shops. It comes in MANY different formulations but are all typically a lot higer in octane rating (100+ and up). Octane in fuel raises the fuels flash (ignition) point allowing it to be run in cars with higher compression and boost levels, more agressive timing curves etc. Trying to run pump gas in a high compression boosted motor is very difficult without extensive tuning. Lower octane fuel, because of its lower flash point is more likely to preignite and cause detonation and engine damage. With the available types of race fuel out there you have to make sure that the kind you buy is UNLEADED as a lot of race fuels are leaded. The leaded fuels will ruin your cat and O2 sensors pretty quick. Hope this helps..
Old 09-08-2004, 10:23 PM
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Default Re: CR adjustment for supercharger (00Red_SiR)

aight, thx
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