I'm planning to do 2.4 lr pretty soon with a 67mm turbo on stock ecu. E-85 will be my primary fuel and 93 when I'm out of town. I have mixed feelings about the compression ratio on different octanes esp with pump gas. I spoke to 2 different people which came from a dsm background and the other from supra. They both disagreed running high compression esp on 93oct. They said the risk of detonation is pretty high.

One of my buddy's motor will be done by this week, 2.4lr with a 6265 dbb turbo. He's running a 10:5 CR. His primary fuel is E-85 and pump on secondary. I WAS going with 10:5 up until today when the supra dude advising me NOT to go with the high CR. Now I'm confused as f**k

Correct me if I'm wrong, with higher octane, it won't detonate as much in comparison to pump gas in high CR motor, and higher CR creates better power with less boost? Anyone with their secondary pump gas running into issues? or blew their **** up

Does heat actually causes detonation or cylinder pressure? Is there any noticeable difference spool between high and low CR? Thanks in advance.

 

Spool is the same between high and low compression.. The car just feels better with higher compression off boost.

I would stay between 9-10:1 for a good 93/e85 setup. Only go higher if it's a strictly E85 car.

 

For the most part, if your car wont see anything less than 93 oct you could do 10.5:1 CR if it is kept in limp mode... Meaning 20psi for save reasons. My motor is a 10:1 motor. I want to rebuild it and go 10.5:1.

You really shouldn't be listening to what other people from different communities tell you. The Evo is not a Supra and vise versa. I don't tell supra guys what to do...

You are correct, the higher the compression the more power you will make on less boost. In a perfect world, if you up the compression a whole point (9:1 - 10:1) you will up your power about 4%. Not all cars are created equal, but that is a good rule of thumb.

To answer your other question. Higher heat = det. Higher cylinder pressure = heat. They usually follow hand in hand to each other. That is why pump gas can't mask the det that higher cylinder pressure can create. I don't see 10.5:1 on 93 a problem on a lager turbo like you have. If it was a stock turbo, fug no! Stay at 10:1. The larger the turbo, the higher compression on pump you can get away with, due to the increased efficiency of the motor, cooler air charge, better exhaust scavenging.

Now, lets take it another step forward. There are two types of compression. 1) Static compression 2) Dynamic compression. Static compression is really what your piston is (for elementary terms). So on my motor, I use Wiseco 10:1 pistons so my static compression is 10:1 and will never change. Static compression really doesn't mean **** to me. The only compression that really matters is dynamic compression. Dynamic compression can change too. Based off Cam design and HG thickness my Dynamic compression could be 9:1. That is what will determine whether or not I can run pump gas. Basically, I could have 11:1 pistons and still run pump gas if my HG was thick enough.

As long as you are not doing any custom parts or crazy experimental builds you will be fine with 10.5:1 pistons on 93 with moderate boost. I usually like to keep boost below 20psi and just drive the car. I hardly ever boost on pump.

If you would like some help building a motor I would be glad to help you!

Mikey

 

Thanks for the response guys. If I keep the 93 map on limp mode, should I get like a milder tune? Can I still have it fully tuned on pump map? If it should be kept at or under 20 psi for pump, I might as well just run wastegate only and KILL mode on E-85

 

You can get 20psi maybe more on pump 93 with 10:1 pistons

It all comes down to personal preference. A safe tune or a kill tune are both the same type of tune regardless of what fuel you're running.

 

I run wastegate on 93oct. No need in blowing your car up on pump. Then E85 run 40psi

DRCperformance- What are you talking about a safe tune is the same as a kill tune? That is not a correct statement at all!!!

Mikey

 

Mikey what is my dynamic compression (I suck at math).

Static Comp: 10.5:1
HeadGasket: Power Entrerprises
Cams: GSC S3
2.4L block

 

Maybe my wording is off but the point I'm trying to make is a kill tune is a kill tune, E85 pump 93 etc it doesn't matter what fuel. It's still being tuned to the same ragged edge. A pump 93 kill tune is no safer then a e85 kill tune and vice versa. Same goes with a "safe" tune..

 

Lol picking out a number for dynamic compression is not as easy at looking at your parts and doing some quick math to find a number. Dynamic compression is a very complicated number given by a multi-variable equation. One could maybe "guess" within a certain range what your dynamic compression ratio is, but that is about it.

To the OP, go with 10.5:1 or 10.0:1, either one will work just fine if you're not looking for stupid power on pump gas. If you are building the car to run on pump say, 90% of the time, then go lower to 9.0:1.

-Acree

 

I can agree with this.

To me compression should limit your boost but only your timing. 10:1 isn't that high of compression anyway, not these days anymore. If you got 93 octane you don't really have to be that conservative.

The tune is the key in every situation high or low compression.

 

personally i say stay in the 9.0 or 9.5 range its working perfect for me and can have that KILLTUNE LOL on either no worries over here. how much power does one really need more power more money more chances to break **** which leads to more money more downtime and money you could have spent on something else not car related

 

Dynamic depends more on cam timing than anything. Its not a necessarily useful tool for calculating what you have though since it also needs some other variables in there. Assuming everything as close to stock as possible its somewhere near 8.6:1. In the real world it doesnt matter though. Its been awhile since I bothered to calculate it, the last time was when we built Mikey's motor.

I vote for 9:1 myself, we run 8.50s on 9:1 motors. High compression and thin HG area are not good bed fellows.

 

AMF will chime in but his car runs on e85 primarily. Only time it runs pump is if he's going out of state.

 

I view higher compression as a way of having the car perform decent off boost and not having to run as high boost to get the performance you're aiming for.

 

I will be running E-85 primarily as stated in my first post. I just want to run pump
gas safely w/o popping the motor. There's no guarantee that it won't popped running a
low CR, anything is possible. That's why I need to get some Pro advice on which CR is
better OVERALL. I'm just clueless when comes to technical ****. I'll admit to that.
I also think tuner plays an important role too. Haven't decided yet which tuner to go with but English Racing is high up on my list , that's if they willing to tune
it !! Thank you for the response btw!!