USDM Fits/Jazz 1.5 vtecs are 10.4 compression rate and the JDM honda Jazz GD1 1.3L is 10.8

can anybody pls enlighten me why do some cars have higher compression rate when modified via N/A and when u turbo the ride it should have a lower compression?
someone told me dat if u wanna turbo our rides and they must have low compression 10.4 but wat i got is a 10.8 on my ride which is not Vtec.
pls enlighten me in the advantages and disadvantages of low and high compression rate
sorry still a noob... i hopin u guys are catchin my drift?

 

Your engine's compression rate depends upon the fuels that are common in your area. Here in the U.S. we have a fuel chemistry that varies by state and county. Fuels using ethanol in the mix require a higher compression rate than fuels with no ethanol. Summer vs. winter oxidation chemical additives also require different compression rates (usually higher) than countries where these chemicals are not used.

 

ok. but how does low or high compression play a roll in performance?

 

in a nutshell, our engines with higher compression will never see high boost in a turbo. Without going into dynamics which some of it I won't even understand, the lower the compression, the more boost you can run. The higher the compression, the less boost. We all know 30psi is more fun than 5psi.

Good luck.

Kris

 

Another way to explain it is, higher compression generates more power with smaller displacement up to a point. But higher compression also causes detonation, or "knock", requiring more anti-knock additive and higher octane fuel. Above 14:1 compression ratio, you don't need spark plugs because the heat of compression ignites the air/fuel, and you now have a diesel engine.

The compression ratio of your engine is part of its design, along with all of the computer controls, ignition system, timing, and the gear ratios of your drive train. Everything works together as a system. You can change some of each part of the system to increase power and speed to a point, but that usually upsets the balance in other components of the system.

You can cram a little more air/fuel into the combustion chambers with turbo or supercharger systems, but they have to be engineered and sized to help the existing design parameters of your engine. Simply increasing your compression ratio to gain power won't work without also changing your cam, fuel, fuel delivery, ignition, timing, and computer controls.

 

Yeah! What he said! I figured since Manx chimed in earlier, he would elaborate more! But yeah, if you can find low compression slugs for the L15, you can turn the boost up more than what you would want to with the stock compression.

Kris

 

Hey Kris!

Here's another idea. If you want to be really fast off the line with no engine mods, run 12 " wheels and tires if you can get some with the right bolt holes. But then your gas mileage would suck along with your top speed. You wouldn't have to spend money on lowering springs either.

 

He he he! I love little wheels! I remember on my old SRT-4, I would spin 26" slicks through 3rd gear. It was awful.

Wait...was that a knock? I was just commenting that your knowledge would explain a lot more than what I could have.

Kris

 

I never knock people who don't deserve it, and would not knock you. I knew that you would already know about the downfalls of small wheels.

 

u could still run high boost with high compression if given the right turbo setup

 

True, but you are getting into a fairly intense build then or a smaller turbo. Me, I went 8.5:1 on my old car and ran a GT3775 at 28psi all day long and 500whp. The innards held up great because it was all forged. For a Fit though, I wouldn't run over 10psi regardless if I am pumping a liter per minute worth of fuel.

The pressure will get to it eventually. My SRT-4 was an 03 and they are decently built motor's factory with Mahle pistons with the skirts coated, oil squirters etc...I put a .50 trim and tuned a 11.8 AFR and ran around 24psi at 450whp. After 5 months, 3 ring landings gone.

Anything is possible with the money, setup, and tune. But for an out of the box kit like AJR, GReddy, Blitz, or any others, 10psi would be max I would run period!

If they made good innards for the L15, I would have already went nuts...Just to enjoy the lag of a huge turbo and then shred the tires with a little baby motor!

Sorry we got off topic...I think Manx hit it on the head though with his explaination.

And Manx, no worries! Just thought I said something wrong!

Kris

 

pressure is only a measure of restriction, not your motor's limit. 15psi on a small turbo may equate only 230whp (for example), but with an adequate tune, theres no worries on stock innards. HP level is where your engine is weak on. you can blow your motor with say GT42 @8psi (ie. 300whp). Turbo lag is just foreplay.

these newer honda's are stronger than you may think. i push 17psi daily on my base rsx, for well over 2 years now. stock CRV motors have seen 32+psi and over 600whp reliably. dont forget all the other K's now.

we had a 11.5 CR RSX-S make over 500whp on pump. 793whp on C16.

the key to boosting with high compression is getting rid of ALL backpressure. that means you need a really good flowing manifold, DP, exhaust, etc.

all in all, psi is not your measuring tool to where u designate your stock "limit", its HP value. 12psi from Company X turbo may only give 210whp, which is still relatively safe on these L-series. past the 250whp mark is where i'd start thinking about build. Most companies are putting smaller turbos with their kits anyways.

yah, we're getting off topic.

 

Are you 100% sure that the l15's stock internals can take 200whp? I don't wanna blow my motor lol

 

so high compression on N/A engines does produce more power if the internals are built proper, am i right? i wanna go N/A first and make as much power out of my engine.
Turbo.... i would love to do that, but i know i will just have to stick to a low boost probably 5psi because of the higher compression ratio we have on our rides.

The reason i asked about compression is because i see many N/A tuned cars out there with high compression and i also plan on port and polishing the heads and probably using oversized pistons, which i know would generate a higher compression than wat i already have.

oh and btw i only plan on achieving 140 whp N/A and without Nitrous.
140 whp is my Target.

 

yes, i'm pretty damn confident.

azkikersfit, the higher compression, the higher octane fuel you will need. too high, and you will not be able to run 93 octane. N/A is always harder to make power, and will also cost more, but is also sometimes fun.

again, y our compression ratio is still relatively safe for boost.

 

Yo!!!
03DSM-RSX, Manxman, Claymore and Fit4Kris.
thanks alot u guys, now i know wat i gotta do. I know i can always depend on guys like u in Fitfreak for some info, even though i got a JDM.
muchas gracias!!

 

High compression pistons require less boost to build horsepower.
However it also takes a lot less psi before it starts detonation something terrible.The only difference is if you are running forged pistons and rods.
Then you can a considerable amount of boost.
but for stock internals that are high compression you would have to run a lot less boost to keep it safe.otherwise you have a time'bomb situation.The more boost you run on stock,high compression the closer you are to a blowup.
You have to take a lot into consideration.
Tuning is going to have be an exact science. and you are going to have to consider running octane additives (octane-boosters) when you are planning to really run your boosted,high compression stock engine.
So tune your car on regular pump gas and then race with some race-gas or other additive.
we run d-15 sohc engine on stock internals with up to 15 p.s.i daily drivers.However we all know that the compression ratios vary for these engines.
however for stock b16 it is 8 - 10 p.s.i for the stock internals.unless you lower the compression ratios by changing the pistons to say b18a.

 

for my 115a I am planning to run 5- 8 ps.i.I have already changed the clutch to an A.C.T clutch and flywheel that i took out of a 99 civic.I replaced the disc witha brand new one. it was remarkably bigger than the dinky fit one. the l15a fit clutch/pressure plate & flywheel is remarkably smaller in diameter than the d15/16 clutch setup.
I had to skim the inside of the flywheel to get it to work.
But it is now in 3 months and going.Its just the manifold that is the 'breeder'.I cant even cut the factory one as the pipes/runners are teh size/diameters of cigarettes.(STIFLING)