Hello turbo people, as the title suggest I'm looking at doing an engine rebuild and just would like some input from people with more first-hand experience than my none.

Basically my engine has bad compression on a cylinder due to bad rings, but because replacing rings is going that deep anyway I decided I'd like to do an engine bore/rebuild. Basically the plan so far is upgraded rods, race bearings, forged pistons, stronger head gasket, and ARP studs. With all these fancy zoom bits I was planning on running the stock 9.0:1 compression ratio, on a 84mm overbore. Eventually Id like to go turbo, however because this build is already going to be a pretty penny, it wont be immediate by any means. Now my hesitation came after I called the machine shop I plan on using for the boring. While talking to the machinist who claimed to have 20+ years experience machining/tuning engines he said that if I plan on running a turbo with up to 15psi (ill probably leave it at 9 for most of the time, just 15 if I see a mustang who needs beating) on the engine running stock compression on pump gas (92 octane where I live), Im probably going to blow my engine. Doing research on the internet and here it doesn't look like alot of people blow engines running below 15psi, assuming they have a good tune.

Basically my question to the boost guru's on here is what would you recommend? Running lower compression on N/A for a little while while I wait for funds just to have the peace of mind once the boost is there? Or will I be fine with stock compression and still get some bonus pony's while I'm waiting for turbo funds?

Any input is highly appreciated, Thank you boost people and feel free to make fun of me if this is a retarded post

 

is this a 1.8?

for pump gas + boost you want low comp, likely 8.6:1, but not for the really stupid reason the builder gave you, but because you'll get better torque by being able to run more spark advance before you reach the det limit

 

Find another machine shop please, the guy who runs yours is utterly incompetent

 

Yeah its a '95 1.8l.

So basically your saying running the same boost on a 9:1 vs 8.6:1, the 8.6 would be able to handle more spark advance meaning more torque, but would this increase spool time or does it all end up with the same **** aside from my torque numbers? Sorry for the noob questions, I appreciate your help man thank you.

 

same spool on pump, these engines are ancient and don't have variable cam trickery, opening up flow from both sides is where you gain spool

this all assumes pump gas.

if you use e85, throw all that out the window and run as high compression as you can making huge power and torque everywhere

 

Run as far away from that idiot of a machinist as you possibly can.

There's a small chance he might be able to assemble an engine properly, but that's should be the extent of your communication, and you should probably be as specific as you possibly can, because again, Philistines and all.

 

Devil's Advocate: You don't have to know anything about a turbo miata to be able to successfully bore and hone a pretty standard and un-special decades old closed deck iron block milquetoast motor.

Just don't take tuning advice from him. You do that from a tuner. You also wouldn't take a block to be bored to your tuner.

 

I like arbitrary numbers too!

 

What wrong with that? I started at 10.63 psi. Now Im pushing 23.1415926 psi, but only I am beating down a 1995 NSX 6 speed, with air-conditioning, power steering and wider tires.

 

^Wisdom.

The machinist I took my stuff to builds american hot rod motors. While he had a lot of tips and tricks, I just gave him the specs I wanted (after searching this site, and probing build threads and forum recommendations and experiences). He did what he was paid to, and did a pretty damn good job as far as I've been able to tell. Same guy that slapdashed Soviet's motor. His name is Bob. The machine shop is dingy and janky looking under a Napa auto parts.

 

I had similar experience in my town. Machinist wanted to narrow up the valve seats and a few other pushrod v8 stuff. I said no thank you. Just factory specs or what te part manufactutlrer suggests please. Thats what they gave me.

 

And the Prince of Band-aids has returned to bless us with his knowledge.

 

Meh. If he claims that 15psi will blow up the motor, you have to question his knowledge of engines in general, which includes the realm of properly boring and honing an engine.

 

You have to question his knowledge of forced induction in general, which is a much smaller and newer piece of the pie compared to what 99% of the work that 99% of the machines outside of the Miatas-only machine shops in California do. In most of the country, the machine shops are staffed by people who are still convinced EFI is voodoo magic and they pray every Sunday at church that their deity will continue to protect them from such evils.

Again, OP is talking about a block bore/hone. I agree with you a point: If he's looking for a Miata expert, go somewhere else. I don't know what OP's knowledge base is like or what he's actually looking for, but it doesn't sound like he's looking for a one stop shop that will put together his motor, install it, and t00n it. My only sentiment is that i saw nothing there that would scare me away from having something so simple and un-specific as a bore/hone.

 

As long as you give him specs to follow and he follows them to a tee, there's no problem.
The one issue I have with people like that is that if you don't give him specific instructions or he doesn't follow em, he could hog out the bores like crazy or not use a torque plate, or use some ghetto rigged plate from some other car, or gap the rings too loose or too tight, PTW clearance, etc etc. stuff they generally think "applies to all engines" when it's not that simple or easy. Different engines require their own different approaches.

 

Not to mention the different material characteristics of piston alloys etc

 

OP, I have an idea. Rather than spend the money on building a motor right this second, why don't you buy a used 1.8? Tiger Japanese - Home this is where I got mine. Use the left over money to buy turbo bits for your car. I ran 10psi for years with no issues. Then, save some money and build your other motor. Keeps the car running, gets turbo goodness sooner, and ends with a built motor.

 

not a bad plan, unless he's tired of the power and wants big boy power

 

he already said he is going to have to run it NA for a while until he can afford a turbo kit. Going this way he will save 2-3k and still have a running car. For 3k he can get a turbo kit and engine management. Then he can send off his blown motor to get built

 

best part is, he can run 15psi on a stock block!