From what I understand if you are going for big turbo power and not running E85 you should go with 8.6:1 pistons. You will not be det limited and you can throw a **** ton of timing at it and make phenomenal power. I remember this discussion somewhere on this forum. I believe both Hustler and Savington said that 8.6:1 on pump gas will allow for the most head room.

 

This. I've never built an engine, but the TSE pistons page recommends 8.6:1 for their turbo builds. That's what I got, because Savington has probably built more turbo miata engines than just about everyone else on here. The MSM is 9.5:1 because it is an awful hack job that is more marketing than engineering.

 

Like Ryan G said, if you think you might want to go for big power later, you want to start with lower compression. 9:1 is a nice medium because you've got enough compression that it runs good off boost, but it's not too high of compression. If you go 9.5:1 you won't be able to run as much boost down the road. Yes you'll have more area under the curve, quicker spool like you said, but the headroom isn't there if you go higher compression and don't run E85.

 

Dont be afraid of timing, timing is good. Timing is wholesome. Super conservative timing burns exhaust valves.

 

Well. It sounds like a plan.

 

Won't be able to run as much boost? Are you're talking more than 20psi? There are members here that have made 350whp on 9.5:1 w/ pump gas @ 20psi. I guess the Idea is you don't have to run as much boost if you have higher compression... The seesaw could go back and forth all day on this discussion though. It's preference. 8.5:1 all the way to 10:1 are all doable on pump gas. 10:1 having the smallest margin of error. 9.5:1 in my opinion is not a terrible option though.

 

I'm not putting a solid number on boost. If you want to run high boost, you will run it higher and safer with low compression. 9:1 is a great combination for this, as illustrated by the many cars that are well-built this way. There are members here who are putting out over 300 whp on a 1.6 with a 2560, but it's not the easiest/safest/best way to go. Yes you can make mad powers on 9.5:1 but Erat likes to play it safe, and if you're gonna put out lots of power safely, you're better off to go lower compression.

 

Yeah, i want to be able to drive this car cross country, beat the **** out of it, then drive back.

Sustaining 35mpg highway would also be nice.

 

The higher the static compression, generally, the better the BSFC.

In that case, if your goal is higher cruising mpg's then go for the 10:1 CR...

 

This is also true. Lower comp will mean lower MPG. It can still be quite good, but I can't see 35 mpg. 30 though, sure.

 

lol@ talking about MPG when building a high horsepower turbo engine.

What snail are you thinking about running Erat? Waiting on the TSE kit like me?

 

Why lol at MPG when building a high horsepower turbo engine? If you do it right, there's no reason you can't have decent MPG when you're not on it, and amazing power when you are. Yeah if you're talking about 500hp then sure, that's pushing it.

Dillon, did you ever ride in Bryan's car? Is yours the fastest Miata you've ridden in? you might have to take mine for a spin when the weather clears up (if I still have it). 300hp would be fun but I don't really feel like I need any more than I have right now. 400 hp just seems silly!

 

Yes, you can have your cake and eat it too...

 

I netted 35mpg with me, a passenger, and a full trunk of stuff returning from the dragon. Oh, and i had a good crosswind. I drove like an old man 65mph, and ever got into boost. But still. What's "high HP". To me high is like 500hp. But a normal 300hp (what i seem to be pretty reasonable) should still get great gas mileage just fine. I did all that ^ on 200hp. Nothing in my setup will change except engine internals. I don't see how my MPG would be affected except positively with the upped CR.

Going to keep the gt2560, with FM log manifold i currently have on it. I bought a bigger intercooler from Bryan, just waiting to hear back from him.

I'm not going to build around MPG, that's silly. But i wouldn't be mad if i could retain my 35mpg highway. Like i said, i want to be able to drive this thing somewhere. Nor am i shooting for 500hp.

My car is not the fastest miata i've been in. I was in a built engine, gt2860, begi S4 car on 30psi. BUT like all begi manifolds he blew a crack in it (on what i believe he said was his 4th manifold). Though, when i rode in it, we were on the dragon, so all the power was not usable. But it did feel good. Still haven't been in Bryan's, not sure i want to ruin his seats.

My main dilemma will be: Do i want to try and make the 5 speed last, or just shoot for the stars, blow it up, and find a 6 speed... Hmmm. Also my clutch is rated for 318ft/lb... We'll see.

 

Well damn... that sounds like a tall order buddy.

My car has never seen higher than 25mpg, even on a whole highway tank.


And a fun and highly useless comparison, my MX6 makes more power, has a MUCH lower compression ratio (7.8:1), weighs more, and is shaped like a brick. 41mpg on the highway.

 

If you run ALLOFIT out of that GT2560 your clutch will definitely be fine (still overkill actually) and unless you beat it your 5-speed should survive. But running ALLOFIT at 9.5:1 will not be easy to tune.

 

Why don't we all drive these ugly things? Sounds like magic.

 

Sounds like your MX6 has a better tune than your miata...

 

My MX6 runs horrible piggybacks that if i were to go into full detail of, would bring down the wrath of the MT.net gods upon my brow.

My MSM was tuned in-house by FM, the gods of turbo Miatas.

 

I thought your MX6 had like three HKS F-con units, or something like that.

I don't think FM are gods of turbo Miatas...