Hey all,

I am rebuilding my 1.6. the machine shop needs my new pistons before they can start the work. Supertech sells 2 79mm piston sizes. one for 8.8-1 and one for 10.6-1 I am leaning towards 10.6-1 but would that require E85 all the time due to the higher compression or would I get away with 93 which is freely available in my area. From my understanding, the higher compression can help spool quicker which is obviously a good thing but I feel there would be reasons to go with the lower compression too right?

Please help lol!

Thank you!

 

Yes it would spool faster/reduce the lag. But would it be that huge of a difference from running 8.8? I doubt it.

10.6:1 compression and mild amount of boost sounds like a disaster on pump gas. If you're trying to get a faster spool, get a better turbo instead, and run the lower comp pistons.

I'm running a EFR 6258, and 8.6 pistons. I start spooling around 2k~, How much sooner do you need to spool?

 

I need an idle spool! No for real, you info is great, it's exactly what I needed! Thank you! I just wanted to make sure I wasn't missing out on performance!

 

Performance wise, even if you did decide to run the high comps and run lower boost, in most cases you wont make more power vs lower comp and higher boost levels without running into some sort of det. As lower comp and high boost would be more efficient.

 

Another vote for low comp pistons. I have 8.6:1 in mine with an EFR6258 like JakZe, but my spool is slower because my turbine wheel looks like this:

Hey, that's not quite right...

 

My sincere condolences.

 

What the hell went through your turbo to cause that

 

Looks like something came out the engine (valve/piston/ring chunks). Maybe the previous motor died spectacularly?

 

Run 8.8s for pump gas. While the 10.6 extra spool sounds nice, it is less nice than not being able to run 93/91 octane. Going exclusively E85 sucks if you aren't running a racecar you trailer into the track.

 

Best guess is that the previous owner of the turbo had something go through it, turbo was purchased second hand. Never took the turbine housing off prior to installing on my car, so didn't notice the damage. Comparative dyno runs show identical turbo performance now as right after it was installed, so it's been like this the whole time I've owned it. It's made it through a number of track days, so I figure I'll run it until it catastrophically fails.

 

That's hilarious! Can't you get new turbine and compressor wheels for fairly cheap?

 

No...unfortunately. That is a fancy wheel. Last I looked into it, it was difficult to get new turbine wheels for the EFR series. Easier to order a new core, just expensive.

 

Higher compression pistons do not increase spool! Once the exhaust valve opens there is no compression being made, turbo spool is dependent solely on the pressure ratio between the manifold and the downpipe. The pressure ratio can be increased by increasing EGT, which you can do with timing/fuel (pressure and temperature are related).

What higher compression DOES do is help you make more torque off-boost at the expense of becoming more knock-limited while in-boost, hence the need for E85. With more compression you need the ignition timing to be even more precise and your tuner will need to spend more time tuning for various conditions, particularly things like coolant temp and MAT.

No need to reinvent the wheel on these things, they've been figured out for years, take advantage of the existing knowledge present on this forum and many others.

 

Miata engines like timing. You can make more power with the same amount of boost on lower compression pistons because you can run more timing. 10.6 is def too high IMO. 8.8 is proven, its almost the same as the stock compression and you might gain like 5hp under the curve with the higher compression pistons, at the expense of power up top since you’ll have to pull more timing to prevent det than you would with the 8.8

get the 8.8

 

I ran 10:1 ST's in "another life" and can't say that the results were noteworthy. Following that science experience I switched to 8.5:1 Wiseco's (after the ST's broke a ring land on cyl's 1 & 3 because of fatigue cracking at the valve reliefs) and saw no appreciable loss in power. In fact, 95RedM said, I was able to add timing without fear of detonation with the Wiseco's.

I would NEVER consider 10.5:1's on a turbo engine.

 

Thanks a ton from everyone, I actually did order the 8.8-1s and will be dropping them off at the machine shop this week. I am boring out a mm from the original block and doing manley h-beam rods, acl race bearing, arp main and head studs as well as an ati damper. I don't intend to run crazy power off this yet but it will definitely give me more opportunity. I still need a new rear end, trans, clutch and turbo to do more than 200whp~.

 

My 2560 looked like that after a throttle body screw broke and went through the motor. Car still ran fine and there wasn't a huge change in boost response, but it did make a lot more whistling.

--Ian

 

I have a bone stock 1.6 with a kraken manifold and TD04-13T. It starts making positive pressure between 1600 and 1700rpm. I haven't gotten to try it yet, but I also managed to get my hands on a lower overlap 1.6 automatic exhaust cam that should help with that even a bit more. Duno what turbo you plan on running though.

 

That is the one problem with the EFR.

Borg Warner is extremely proud of the Gamma-Ti turbine wheels are over $500 and looking at over $200 to replace it, that is if the ceramic bearings aren't screwed.

New complete center section is around $850. Don't ask how I know.