Lets talk compression!

[Black_Bullet]

So, from conclusion of general consensus, DSMer's have shunned high compression for a long time normally staying around the stock 1g-2g ratios, and not likely going higher than 9:1 compression.

In a lot of other car circles, ( i.e. muscle, honda, toyota etc.)
high compression, high boosted engines are'nt so uncommon.
What most people dont understand is that running higher compression doesnt mean your limited to X amount of boost. Normally it simply means you now require more retarded ign timing and as long as you have a good tuning system ( i.e. Dsmlink,AEM,Dsmchip) and good enough octane fuel; running high compression ratios shouldnt be a tuning nightmare as some make it out to be.

Now dont get me wrong, 8-9.1 CR's are great for pump gas only cars , and it leaves a lot of "slop" room in the tune for less experienced tuners, but for those of us trying to have intense setups, perhaps, a lot of us are leaving a lot on the table by not venturing to higher CR's.

It seems a lot of the guys who are making really big numbers on their particular turbos ( 16gs, 30r's,35r's for example) are running higher than norm CR's, and I recall reading info that shops like Magnus, and TPG prefer higher compression...

For those who get to run their car full time E85, it may be a great idea to bump up the compression significantly. I am considering it myself. Though I dont plan on building this motor or running full time E85 until sometime next year once this cars not a DD anymore.

Originally I was directed towards 9.0:1 comp pistons, but recent thinking has me almost enthusiastic to try out as high as 10.0:1 CR. having a much more efficent engine, better gas mileage, easier to find MBT with timing, and less overall timing needed, and making more power on less boost...
(Given, it'll be a E85 or race gas only car when its not a DD.)

Now I cant say that super high compression would be ideal on a 9 second, 50+psi setup, who knows? But I can say that for what I am trying to do ( staying E316G ) it may be very benefitial, especially with my goal of over 400awhp on this turbo.

Some quick CR info:
Engine Compression Ratio - Tech - Popular Hot Rodding Magazine


So opinions...

 

[BoredDSM]

If some people go 8s on just 8.8:1 compression ratio why not? It is safer and easier to tune. Jumping to that high of a compression would be harder to tune and harder to daily drive in my opinion.

 

[BootlegGreg]

Valve timing and timing failure can be a horrible reality with high compression. You will definitely need to degree the cams and have a rock solid timing belt setup. On the plus side you can run 20lbs and make upwards of 400-500 horse on racegas easily. This will allow the turbo to have a much longer and happier life for sure. SR20 guys have been making easy power on low boost for years like this.

 

[bastard dsm]

yea i think if your on strait e85 then i would go high comp, more hp per lb of boost.

 

[Black_Bullet]

Valve timing and timing failure can be a horrible reality with high compression. You will definitely need to degree the cams and have a rock solid timing belt setup. On the plus side you can run 20lbs and make upwards of 400-500 horse on racegas easily. This will allow the turbo to have a much longer and happier life for sure. SR20 guys have been making easy power on low boost for years like this.

Wouldnt we be screwed if we had a timing belt issue anyways?
I mean hell if I skip a couple teeth on my stock 1g compression id still bend valves.

I know there is a point of going too high, but Im thinking that the average DSM setup probably is a bit low.
(Once proper fuel, timing control, and supporting mods are there.)

Also since Im more interested in the tuning aspect of this, im thinking I should've put this thread in the Tuning Engine Management section. Plus Id probably get more views there.
Perhaps a mod can move it for me?

 

[Black_Bullet]

yea i think if your on strait e85 then i would go high comp, more hp per lb of boost.

Since I burn my own eprom chips, Id probably keep a spare chip in the car set for a 93 oct tune to swap in just in case I got caught somewhere with no E85. Since theres not much e85 stations in my state yet that would be important for me.

Though all Id have to do ( without dropping boost level ) is just richen it up in the 10s and drop the timing a lot, and it probably could handle 10:1 comp on pump gas. At least enough to drive normal till I got to more ethanol.

Theres a guy I know local who had a 2g awd and was running high compression ( higher than 9:1 ) running on 93 octane and 22psi with 60-1 and he was making really good power with less than 14degs peak timing advance, no knock...
I think its all in knowing what kind of timing advance to play with for your CR...

 

[BoredDSM]

Since I burn my own eprom chips, Id probably keep a spare chip in the car set for a 93 oct tune to swap in just in case I got caught somewhere with no E85. Since theres not much e85 stations in my state yet that would be important for me.

Though all Id have to do ( without dropping boost level ) is just richen it up in the 10s and drop the timing a lot, and it probably could handle 10:1 comp on pump gas. At least enough to drive normal till I got to more ethanol.

Theres a guy I know local who had a 2g awd and was running high compression ( higher than 9:1 ) running on 93 octane and 22psi with 60-1 and he was making really good power with less than 14degs peak timing advance, no knock...
I think its all in knowing what kind of timing advance to play with for your CR...

There will always be the guy but you never know how hard it is until you try yourself. Keep in mind you have to flush your tank and keep it full with ethanol. Running half and half is kinda hard to tune for. Chips wouldn't even be sufficient for tuning like that. You would probably need dsm link or ems with you to do that. To me it just seems kind of worthless if your stranded in a place and without e85 and you gotta load up different maps do run a different type of gas.

 

[Black_Bullet]

There will always be the guy but you never know how hard it is until you try yourself. Keep in mind you have to flush your tank and keep it full with ethanol. Running half and half is kinda hard to tune for. Chips wouldn't even be sufficient for tuning like that. You would probably need dsm link or ems with you to do that. To me it just seems kind of worthless if your stranded in a place and without e85 and you gotta load up different maps do run a different type of gas.

Oh I was just trying to make an example.

It wouldnt be that big a deal for me, I can do everything DSMLINK can do.
Actually I have superior timing/ fuel control over dsmlink v2.
I burn the chip at home computer because I dont have a laptop yet, but plan on having a laptop by xmas so id be able to do it in my car, and I could always get a Ostrich emulator.

I keep spare chips in my car in a cd case in the glove box now as it is.
My ecu has a ziff socket... Takes literally 1-2 minutes to swap a different chip in the ecu.
Im pretty capable when it comes to tuneing as well, and goal is to make this car a E85 only car when its NOT a DD anymore... The pump gas chip could be just in case.
With good fuel and the high compression Im speaking of, Im starting to get really interested in seeing what this evo316g setup could really do, and I already have an idea!

Would be nice if someone who actually tunes on high compression would enlighten the conversation!

 

[Bud92gsx]

There is one guy that I met that was running stock compression on E85 in a 1G. But he had cams, an safc, 950's, a walboro, and an eprom ECU. You shouldn't have to run higher compression because of detonation. Also E85 burns hotter than regular pump gas, so why would you want to run higher compression and have a chance of detonation while your burning hotter than stock? You could use colder plugs, but would only help to an extent.

 

[My1GLaser]

I am running an 18g6SL2 at 26 psi on pump with 11.7-12 AFR and 21* timing using DSMLink with 0 knock on 9:1 CR.

 

[JusMX141]

Are we talking piston compression ratios with the stock head and deck height, or ACTUAL compression ratios?

 

[Freerevving]

some people consider 8.5:1 compression ratio to be "perfect" for turbo... especially people who are converting.... others have to deal with whatever they can afford.

 

[Kevin Jewer]

I run 9.5:1 on the RWD (it came with those pistons), and I've run 10:1 on my old 2g. The 2g was a clast on pump gas. You have to tune accordingly, but it's no different than the way you tune now. You'll get away with slightly less timing, but power will be the same. Most of the guys making big power on very high boost are also running high compression, and it's been that way for as long as I can remember.

 

[Bud92gsx]

I mean you can do it on any compresion is what he's saying I agree. Also what ever you can spend. I mean this guy is runing 9's, and running higher comp. 1st gen dsm run way lower comp and boost the hell out of them on stock comp..He doesn't have to run 40 PSI to get good numbers. That's why he's on 26 PSI. Good freakin work man!!

 

[rhamlinii]

I mean you can do it on any compresion is what he's saying I agree. Also what ever you can spend. I mean this guy is runing 9's, and running higher comp. 1st gen dsm run way lower comp and boost the hell out of them on stock comp..He doesn't have to run 40 PSI to get good numbers. That's why he's on 26 PSI. Good freakin work man!!

Yeah, everyone keep there boosted high compression motors. I'd continue to spray my car untill something works better with my low compression motor.

 

[Black_Bullet]

There is one guy that I met that was running stock compression on E85 in a 1G. But he had cams, an safc, 950's, a walboro, and an eprom ECU. You shouldn't have to run higher compression because of detonation. Also E85 burns hotter than regular pump gas, so why would you want to run higher compression and have a chance of detonation while your burning hotter than stock? You could use colder plugs, but would only help to an extent.

Umm, well E85 is WAY more detonation resistent than regular petroliuem.
Thats why you hear people maxing out their turbos with high ish timing advance knock free.

I am running an 18g6SL2 at 26 psi on pump with 11.7-12 AFR and 21* timing using DSMLink with 0 knock on 9:1 CR.

Sounds nice, any numbers?

Are we talking piston compression ratios with the stock head and deck height, or ACTUAL compression ratios?

Anything good for conversation...

I run 9.5:1 on the RWD (it came with those pistons), and I've run 10:1 on my old 2g. The 2g was a clast on pump gas. You have to tune accordingly, but it's no different than the way you tune now. You'll get away with slightly less timing, but power will be the same. Most of the guys making big power on very high boost are also running high compression, and it's been that way for as long as I can remember.

Your posts havent failed me yet .

Yeah, everyone keep there boosted high compression motors. I'd continue to spray my car untill something works better with my low compression motor.

Hey but who said I wasnt going to spray also.
On top of my other ideas, 50 wet shot is sounding good enough right about now...

 

[tsiAWD91x]

im liking the thread bro i was looking for this same type of imput..good shit, hopfully everyone gives alot of imput

 

[->PrOjEcTGS<-]

There are a lot of manufacturers that use higher compression on their engines with their stock turbo setups. I can think of these:

SAAB 2.0L Turbo - 9:1
Subaru WRX - 9:1
Pre-1987 Porsche 944 Turbo: 9.7:1
1987 Porsche 944 Turbo: 10.2:1
1989 Porsche 944 Turbo: 10.9:1

If manufacturers feel the need that these ratios are "safe" for a DD car. Then why would we even question the thought that someone that monitors the wellbeing of their engine should have to worry about running higher compression? I think it gets a bad review when someone throws higher compression pistons in and trys to run the same amount of boost or more on the same crappy fuel that they were running. Us 1g guys are used to getting away with running high numbers on pump gas since the compression is so low. When you step up to the plate with a 10:1 or the like compression you really need to make sure you are on top of it all of the time.

I'd say do it. That's my plan when this motor blows.

BTW, high compression and big cams + turbo = SICK

 

[My1GLaser]

Sounds nice, any numbers?

Not yet... well any good numbers anyway. I had some major personal sh_t come up and I have only got to track it twice this season.

 

[Black_Bullet]

There are a lot of manufacturers that use higher compression on their engines with their stock turbo setups. I can think of these:

SAAB 2.0L Turbo - 9:1
Subaru WRX - 9:1
Pre-1987 Porsche 944 Turbo: 9.7:1
1987 Porsche 944 Turbo: 10.2:1
1989 Porsche 944 Turbo: 10.9:1

If manufacturers feel the need that these ratios are "safe" for a DD car. Then why would we even question the thought that someone that monitors the wellbeing of their engine should have to worry about running higher compression? I think it gets a bad review when someone throws higher compression pistons in and trys to run the same amount of boost or more on the same crappy fuel that they were running. Us 1g guys are used to getting away with running high numbers on pump gas since the compression is so low. When you step up to the plate with a 10:1 or the like compression you really need to make sure you are on top of it all of the time.

I'd say do it. That's my plan when this motor blows.

BTW, high compression and big cams + turbo = SICK

This is true.
But keep in mind, compression ratio also has to do with the efficiency of the head and engine VE etc.
Our heads might not be as good of some of those cars you mentioned.

Again, for us though, I think that its all in the timing maps!

I wonder whats the highest compression ratio someone has tried on a dsm?
You also have to consider that it takes a lot more effort for the motor to compression the mixture, I dont know if you can go high enough to were its counter productive.
I know there are some super high compression cars that require more powerful starters.

How do you guys feel about the wiseco pistons for a DD high performance/ compression piston of choice?

 

[Bud92gsx]

Umm, well E85 is WAY more detonation resistent than regular petroliuem.
Thats why you hear people maxing out their turbos with high ish timing advance knock free.
QUOTE]

They guy I meantioned befor is running 19 degrees of advance no detonation, no knock, stock 1G compression. Wich is sweet..Wonder if I could run E85, but would need bigger injectors and a logger. I have a super AFC on it's way and a walboro 255, which is still not enough...

 

[Hazard]

There is one guy that I met that was running stock compression on E85 in a 1G. But he had cams, an safc, 950's, a walboro, and an eprom ECU. You shouldn't have to run higher compression because of detonation. Also E85 burns hotter than regular pump gas, so why would you want to run higher compression and have a chance of detonation while your burning hotter than stock? You could use colder plugs, but would only help to an extent.

Please dont post anymore if you're going to spread more misinformation. this post is borderline retarded.

 

[Hazard]

I have been considering tossing together a higher compression motor as well. If you're running E85 all the time and have a solid tune, there is nothing wrong with high compression. People are laying down upwards of 500whp on stock K20a2 honda engines, which are ####ing 11:1.

if your goal is 500whp or less and you can run e85, id say go for some compression.. why the hell not? Just how much is up to you, but in a street car, everything will be more fun. everything is about having a setup that goes well together, from where the intake starts to where the exhaust exits.

 

[Red97Eclipseboy]

I have a 6-bolt bottom-end with a 2g head. I stuck with the 8.5:1 C/R and with my first tank of E85 the other night and a new DSMlink tune for the E85, I run 17psi from a EvoIII16g with 20 degrees of timing with zero knock all the way to 7000. My fuel is a Walbro 190lpm and 650 FICs.

FYI: I didn't change any of my fuel delivery or psi for the E85. We just put the E85 in and re-tuned.

 

[Hazard]

you could probably run that tune on pump gas.. of course you're not getting any knock with e85, e85 is very knock resistant and that's fairly conservative.


running a 190lph isnt going to get you far with e85 though..