Lets talk Apex pistons and compression

[kingtut]

So after rebuilding my sled after 3 years of it breaking (see my long list of threads on here if you want a good story) I found out that I may need new pistons. In a previous post I mentioned I did a compression test which came back 30, 30, 120, 30. Then used a bore scope to check if the valves where seating correctly, thus the thought of a broken ring.

This is a new animal to me that i'm comfortable attacking even though I do have quite a bit of questions.

What is normal compression ratio and compression for naturally aspirated sleds vs boosted sleds?
My best cylinder was at 120psi
What brand pistons are trustworthy out there for turbo applications?
So far i've found JE and Wiseco brands
What compression ratio to use (normally running pump gas which is 91-93 in my area with the ability to dump in some race gas or E85 if I want to have fun)?

How far should I if at all bore out the cylinders for the new pistons?
According to the Wiesco site they offer a 74-76 bore size with different compression ratios
Will I need a retune If I bore out the cylinders?
I currently have a pure logic controller and would have to learn how to reprogram it.

Any questions for me please do ask.

 

[maim]

10:1 for trail running. for racing with good gas 13:1. without turbo or supercharger of course.

 

[kingtut]

I confuse myself on compression. With lower compression pistons can't you fit more air/ gas mixture in there meaning more power at same amount of octane?

 

[maim]

only if you force more air in there ie turbo/super charger. naturally asperated will only draw in so much, so the lower compression acually hurts performance wise.

 

[kinger]

11:1 CR is stock, you can shim the head to get down to 10:1 or pistons. I would only use JE pistons and remember your cylinders are nikasil plated, honing and boring are not recommended. If the block is bad get a new block to start with and go straight up drop in pistons. If you want to bore then you need a special machine to bore then send it off to get plated again. (ie big time $$$).

Are you going boost or NA? What fuel do you want to run? At 10:1 CR you can run 10-11 lbs on 91 fuel. That is a 250hp machine. If you want more power you need more boost and more octane.

 

[kingtut]

I'm going to stay boosted with 91-93 octane since that is readily available. I believe I have a tune that I can choose to run e85, however that requires screwing around even more. So essentially you are saying if my cylinder walls are screwed up it is cheaper just to get a whole new top end.

 

[kinger]

Correct its really expensive to repair the block. When you can get running engines for $1500-2000 I would look used vs repair. Lower to 10:1 and run 10-11 psi and she will love it!

 

[kingtut]

Just curious what psi can be ran with a 10:1 running e85? Local area has it all over in case if I want to have a field day.

 

[jimmyhighway]

10:1 piston with 2 headgaskets I've been running 102-105 octane at 1200'.

 

[kingtut]

10:1 piston with 2 headgaskets I've been running 102-105 octane at 1200'.

What would be the equivalent piston with just 1 head gasket.

 

[kingtut]

Also what is normal compression for you guys. I'm getting 40-70 with oil in the cylinders. Seriously a sad day here with snow coming in 2 months.

 

[ClutchMaster]

Just curious what psi can be ran with a 10:1 running e85? Local area has it all over in case if I want to have a field day.

Well my evo is 10:1 comp and I'm running 40psi boost on E85, 830 horsepower. Pump gas I could probably run up around 25~26 psi but that would be with a lot of timing pulled and a very rich tune.
What you can get out of pump gas on a turbocharged engine depends largely on how much the hotside of the turbo can flow and compression ratio. Not sure what you guys top out at with on pump gas? But I've seen evo's that are 2000cc (2.0L) run upwards of 650hp on pump fuel. So roughly half of that would be 325hp with 1000cc. Now in theory you should be able to do a little better than that just because your motors are smaller.
Now if I were going for maximum horsepower I would go with a 9:1 compression ratio. That should allow for a safe boost limit around 5psi more than a 10:1 comp motor.
With E85 you should be able to max out almost any turbo you throw on. That being said if you know the lbs/min the turbo can provide, then it's roughly 100hp for every 10lbs/min. Example would be a standard GT2871 cast wheel is around 40 lbs/min= 400hp.

 

[jimmyhighway]

What would be the equivalent piston with just 1 head gasket.

I think someone makes 9.5:1 piston possibly JE

 

[jimmyhighway]

Also what is normal compression for you guys. I'm getting 40-70 with oil in the cylinders. Seriously a sad day here with snow coming in 2 months.

Have never checked compression, however I perform a leak down every year. My cylinders range from 4% to 7%.

 

[princesledalot]

I thought an .080 shim was 9:1 cr?