Originally Posted by RotorNutFD3S

FWIW, I'm using tri-coated OEM pistons done by the shop Ben recommended. I couldn't justify the cost of forged when no one has had any issues with the OEMs unless due to poor tuning. Also because I daily drive my car and didn't want to risk piston slap wearing the engine any faster than necessary. My goal was a simple mild build to strengthen the weakest points: rods and rings.

Originally Posted by patsmx5

FWIW, I see full boost by 3200 with my GT3271. Very good spool considering how big the turbo is. Journal bearing, 52 trim comp, .78 A/R hotside, mild tune, MBC. I have a 99' motor with extensive head work, but all stock components. Headwork is huge when it comes to spool up. And also the folks Ben noted are running 01 heads, which flow as well as a 99' but have the advantage of VVT.

You can do a 300whp setup with 11.0:1 compression. But you'll have to tune it well. It won't have as much room for error as a lower comp motor. Make sure you have a good tuner if you decide to go high on the compression.

And as far as the bottom end goes, it's not how they hone it. They will bore the engine a certain size as to maintain a certain piston/cylinder clearance. Exactly what clearance they choose is based on the piston type (forged or cast) as well as what the motor will be used for (N/A, turbo, Nitrous). Make SURE you have a very good machinist do the engine that knows how to build race motors. It's critical.

Originally Posted by 18psi

sorry to see your engine go....in for another awesome forged build full of awesomeness I can draw more Ideas from

Originally Posted by Rafa

Sorry to ask dumb questions but; I have to get as much info as I can before pulling the trigger.

When you mention that you see full boost by 3,200rpm with a T3270 my ears perk up. Your turbo is bigger than mine so; what's the secret in your case? Do you have a lot of headwork done on your engine? Are you running a huge exhaust?

About the bottom end; I got in touch with a guy who raced cars locally for many years and retired not too long ago so he set up shop with some big machinery (I've seen them, but I have no clue! ). He works on crankshafts and also block honing with those. He's got a very good reputation here and I can actually get to see what and how he does it. I'll post some pics when that time comes.

Another part of your post convinced me to not go for the highest compression pistons; I can't expect to get the assistance I may need from my local tuner. My car's tune was based on threads and remarks I read on this forum and on road tuning with my oldest son's invaluable assistance. I was pretty pleased. When we took the car to the dyno the first time, it showed 206whp and after 4 passes, my tuner could only get 6 extra whps so I figured we did a pretty good job considering we don't know anything about this.

Many thanks man.

Originally Posted by Rafa

Eric, so you stayed the course with your original goal. Good to hear. Have you finished your build yet? Is your car running already?

To be honest, I would love to follow your path and not overcomplicate matters. What compression are the pistons you selected?

Do you mind if I pm you?

Thanks

Originally Posted by Rafa

Ben, thanks for that explanation.

As usual, I've got some dumb questions:

1) I specifically asked my mechanic about the honing job done locally since that's the part that really worries me. He told me there are good shops here doing it. He said, that this part, along with a good build up, would really reduce the chances of facing piston slap. I understand, from what I've been reading on the subject that the first 600 miles after the build are critical. I plan to follow FM's procedure for it.

2) I trust your judgment on mechanical aspects of Miatas so I have to ask: I already have a small headwork done on my engine (mild porting and **** like that) but I really don't want to deal with a 99 head. Local tuners are not too good and mine just doesn't have the time so I'm on my own in that matter. So; are you suggesting cams and valves?

3) I totally agree with you in regards to the best HP range for our cars; I think anything around 300whp for a dd Miata is just perfect (maybe a little too much in some instances) so that's my ultimate goal. The only issue I still need to resolve (without spending too much extra $) is whether I can get a T3/T4 to produce boost at the right powerband. I don't think I'll be able to see full boost by 3,200 rpm with it. I would love to get my hands on a T2871 but that would mean changing the manifold too and that is totally out of the equation (at least for the next 8 months).

4) I've seen some 11:1 compression forged pistons. My final question is: do you think I would be risking it too much if I buy them?

Thanks

Originally Posted by Ben

Rafa,
The other beautiful thing about aftermarket pistions is you can order them oversized. 1.9 > 1.8 Plus you can order them in whatever CR you want.
It's not a matter of just honing, but of boring the block to proper spec. The proper clearances are extremely critical.

I'm not specifically suggesting more radical headwork, since that's not what your main need is right now. But I recalled that you had some work done in the past.

11:1 aftermarket pistons probably aren't in your best interest. But if you're planning on running stock take-out pistons, I'd not hesitate to score a set of 01+ 10:1 pistons if the price is right. They're going to be the easiest type to find with low miles on them.

Originally Posted by Stephanie Turner

I have a set of MSM pistons here. You want me to see if the owner wants to sell?
Stephanie

Originally Posted by patsmx5

Factory bore is 83mm. Are these used pistons? I would want new oversized pistons if I were you. How are you going to bore the cylinders and achieve correct piston/cylinder clearances otherwise?

Originally Posted by RotorNutFD3S

The bore and stroke is the same across all '94-'05s.
IIRC, the '96 was 9:1 CR.
FWIW, the machine shop that did my motor checked the used pistons I had and said they were fine and honed the engine, installed them, checked everything again, and said it was all great.

Originally Posted by RotorNutFD3S

Yeah, checking the block would be a very good idea to do first before you start buying a ton of parts. However, the difference between your 9.5:1 and the 10:1 pistons is not going to make much difference at all, or so I was told on here when asking about a difference between 0.5:1.

Originally Posted by Rafa

Thanks for that info Eric but I think Pat is right; I don't really know how bad my block is (I haven't even opened the engine yet) so maybe I made a mistake. It wouldn't be the first one, nor will it be the last one.

Ben's suggestion of 2001 pistons is looking better and better with each passing minute.

Originally Posted by patsmx5

Easy way- Buy new oversize pistons and let your machinist build the motor.

Hard way- Buy used pistons and hope:

• used pistons are in good condition with no scores, minimal ring landing wear, minimal skirt wear, etc
• block has never been bored out and all four cylinders have no signs of scratches, scoring, minimal even wear, minimal out of roundness, no grooves, etc.
• The block can be honed (cylinder must be round, no grooves, etc)
• Once honed, the cylinders are all the desired bore as to maintain whatever piston/cylinder clearance you require.

Seeing how cylinder 2 has no compression, I'm gonna take a guess and say you damaged that piston and that cylinder is likely damaged.

Yes people build motors with used stock pistons. Why, I dunno. A competent machinist can build a motor with forged pistons that will not produce audible piston slap. There are factory engines that come with forged pistons that do not produce audible slap and last over 100k miles.