This thread pisses me off....Compression has little to nothing to do with spooling a turbo. Displacement on the other hand has much to do with spooling a turbo. A 1.8L will most likely have a gt28rs in full boost well below 4k in any gear but first. My guess would be around 3.5k.

I spent a megaton of money on my turbo 2.9 vr6, and it was almost underivable with power delivery.

So you don't get your fucking queer as panties in a bunch look at this dyno. http://forum.miata.net/vb/showthread.php?t=258097

Hmmm, just like a thought....3.5k rpm. I must be a fucking genius, oh wait no, I just happen to know shit about motors...

wouldn't less higher compression create more heat, and more energy in exhaust gas means more spool.

this is what I want to avoid:
http://i23.tinypic.com/23lfw3c.jpg

I've seen enough dynos in my life to know that it will not make any tangible difference in spool. The only thing it will do is make the car a little more peppy off boost. Considering where that turbo will have full boost can you honestly tell me that fucking matters? Even on the highway you will have 250lbft of TQ at what I wouldn't even consider high boost whenever you want it.



edit:: The above post is just an example of a poorly put together setup. I would put 0% blame of that power curve on the pistons. ZERO PERCENT!!!!!

http://www.digthechick.com/FUN/crash-kick-in-nuts.gif


what turbo are you running?

Yes. I remember in the corrado how I had to change gears before boost because it would smoke the tires at 4500 rpm...but you had to rev it that high becuase it was such a slug off boost.

Also, on the actual thread topic, wiseco will make you a piston at any damn compression you want. They run their business based on one offs. Its just places like race engineering that buy large quantities of pistons so people like me can get them in 3days. If you ordered through Wiseco directly even to get an "off the shelf" piston you would have to wait the same 3 weeks as your custom piston. The reason being that they have no "off the shelf" pistons. They are all made to order.

gt2860rs

fuck!!!! I'm trying to get the motor built next week. Everything is rushed now because I'm moving.

I'm done man, you can do whatever the fuck you want with your motor. I've tried to help you in numerous threads of yours. You're just like a friend of mine, probably worse, in that you just don't trust anyones advice. Even when you ask someone else something, you don't trust their answer or experience. I'm done giving you any of my advice....

for one thing, your 1.8L will spool it well below 5K, for another, you can add timing advance to make up for the loss of compression. for a third, you're insane.

Sure, 9.0 over 8.6 is a 1.6% reduction in spool time. If you normally spooled at 4,000 RPM's, you would drop that number down to 3,936 RPM's. Energy is the key word. It takes energy to spool a turbo. Retarding the ingnition timing will reduce the power the engine is making, but increase the energy going into the exhaust and cooling system. That extra energy in the exhaust would help to spool the turbo. Makes since to me to retarding timing at certian times to help spool the turbo. Once it's spooled, then run as much timing as you can.

Rushing an engine together is the WRONG thing to do. Period. You need to do it once and do it right. I've already explained what's important on building and break-in so you know you can't rush this thing together. Let's stop beating that dead horse. I think the members of this forum are in agreement that you need to do some learning on your own. Quit whining.

Your advice is valued, but other people disagree. TDR swears up and down that he hated the 8.6 pistons in his car, and promptly switched them to 9.0. So far, that's the only real work experience I've heard of from miatas, and I've never seen a real comparison of static compression ratios.

I don't want my car to drive like an MSM, even though that car is at 9.0 and makes 8psi at 4500rpm.

I'm not moving in the miata. That would take a while with a 10-hour commute.

does anyone actually have experience with a low compression motor?

Not in a miata, but a VW. 8.5:1. It really isn't a slug off boost, it's all in the timing and fueling. If I can find it after work I'll post the dyno charts.

Currently I help with a 8.6:1 20V drag car running a SC61, which is a massive turbo for a VW motor. With a ton of advance down low and pulling some fuel we were able to get it to fully spool at ~5,000 rpm.

8.6:1 is not going to be a problem. I'd venture a guess you could drive two identically prepped cars; one with 8:1 and one with 9:1, and you'd be hard pressed to be able to differentiate.

So with a .4 bump in compression it would have gone from 135lb/ft to 465 in 690rpm. How has the situation been improved?