Built motor guys chime in

[CoolRex]

Well I went to a Subaru meet in Greenville, SC this weekend and met a guy with a built motor. Juanmedina has a 06/07 WRX with Forged pistons and built heads. Car ran nice and didn't sound loud at all but I did notice one thing. When he first cranks up the car it shakes like CRAZY! Like the engine mounts are shot but they aren't. Once the idle stabilizes it purrs and idles like stock and doesn't shake a bit.

So I'm asking does forged pistons make the engine do that or is his idle not quite optimized and needs smoothing out? He is still on a rough break in tune and is running on E-85.

[calmnothing]

I rode in someone's car with forged pistons and it was kind of like that until the engine got warm. I thought the car was broken.

[CoolRex]

Yeah me too! He cranked it up and I was like ????????? that not normal.

[Alex]

Balance is off maybe?

[CoolRex]

That what I was thinking. He went with simple dropins. Made a big stink on Nasioc when the engine wasn't breaking in but he was breaking in on E85 which is a no no. Switch to 93 octane and the rings started sealing.

[slowwrx]

Some motors I've seen are like that, the last two Subaru motors that I have seen leave Batlground were not. They both started up very quietly and ran smooth.

Also that is total bullshit that you can't break a motor in on E85, if anything it would be easier to break it in on E85 because it has less lubrication properties. Don't believe everything you read on the net.

[CoolRex]

Originally Posted by slowwrx

Some motors I've seen are like that, the last two Subaru motors that I have seen leave Batlground were not. They both started up very quietly and ran smooth.

Also that is total bullshit that you can't break a motor in on E85, if anything it would be easier to break it in on E85 because it has less lubrication properties. Don't believe everything you read on the net.

I disagree with you there Matt. Rings need to get hot to expand and seal. HomemadeWRX (Micah), Maxwell Power, Ron @ Raw Performance and Topspeed all don't recommend doing that purely because it runs much cooler than 93 would. It can be done but not recommended unless you have the breakin tune just right to create the needed heat. But that's another discussion.

[slowwrx]

Originally Posted by CoolRex

I disagree with you there Matt. Rings need to get hot to expand and seal. HomemadeWRX (Micah), Maxwell Power, Ron @ Raw Performance and Topspeed all don't recommend doing that purely because it runs much cooler than 93 would. It can be done but not recommended unless you have the breakin tune just right to create the needed heat. But that's another discussion.

Let me see if I can find a nice way to put this that won't offend anyone. There is so much more to this than simply saying you cant do that because thats honestly fucking ridiculous.

From my 16th birthday till I was close to 22 I spent almost every weekend at the dragstrip and a lot of my friends ran Alcohol cars. None of them broke them in on gasoline. Mind you I have heard of people doing it but not many.

If you were to keep everything the same and just adjust the fueling so that it would run on E85 then it would run really cold. However if you were to adjust things correctly then you would also be advancing the timing a lot more therefore giving the fuel in the cylinder a longer burn time, therefore transferring more heat into the cylinder walls and rings.

I assume that everyone here knows that E85 is higher octane and therefore actually burns slower therefore giving the flame front more time to travel down the cylinder, therefore allowing you to run more timing and lighting the mixture earlier.

You can't simply just say you can't do that because you most certainly can. Thats part of the reason I don't post on Nasioc anymore, to many people think these cars are mythical beast unlike any other automobile on the planet and none of the rules seem to apply.

Also a couple of things to think about

The auto ignition point for gasoline is 536 degrees

The auto ignition point for Ethanol is 725 degrees

If its better to seat the rings with hotter fuel why not just run 83 octane

[slowwrx]

Its really all totally related, if he had told his engine builder what kind of setup he is running then the engine builder should have set up the Piston to Wall Clearance and the Ring Gap and Type accordingly. Its really neccesary to your original topic, but if you want to just go sling some parts in a block and call it built then just do that if you want to do it right then take the time to learn about expansion rates of pistons, ring gaps, piston to wall clearance, compression rate, Temperature of combustion, etc...

Theres a lot more to this stuff than most people think and I know very few tuners that even really know enough about it. Most guys that do know about this stuff don't go into detail about it because most people don't get it and or don't care.

Judging by your "Okay Thanks have a nice day post you fall into that category or maybe you just don't understand how important this stuff really is.

Honestly if you just want to make 400 to 500hp throw some drop ins, in it and call it a day, if you want more than that you better start educating yourself and you can skip most of the other Subaru forums, go by some books on engine building, tuning etc.... Most of those books are going to be about V8s but everything directly relates.

[CoolRex]

Matt please go back and read my first post man. I was simply asking why in the world was his engine shaking so bad.

He flat out ghetto built (used drop ins, 3 seperate unrelated installers, and flat out BLASTED Topspeed for something they didn't do wrong) that engine which is why Topspeed is not taking responsibility for tuning that car.

But again my original question was could the shaking be tuning related or a matter of unbalanced parts/poor build. Not breaking in an engine on E85.