Thanks I'll remeber that
as I'm saving for a tubo ubgrade at this moment
I'll be sure to keep seeing how your project comes along

Boost is not about "mass flow rate", but rather "volumetric flow rate". This is a touchy subject and often results in alot of misconeptions, such as a T4 at 6psi flows more air than a T3 at 6psi. This is NOT true. To create a given manifold pressure you must have a certain volumetric flow rate (typically refered to as CFM's cubic feet per minute). At any give rpm and give manifold pressure you will have the same CFM regardless of which turbo you use. The difference between the two is in the effeciency. At higher CFM's, the T3's effeciency is low, thus, by definition, heats up the air charge much more than the T4 would. So you have two turbos flowing the same CFM, but the T3 is hotter air and the T4 is cooler air. Recall air density. If the two turbos flow the same CFM, then the cooler running T4 is actually delievering more air "mass" to the motor, hince why more power is achieved. This is why sizing the turbo is critical. You want to size the turbo so that it is effecient as possible in the CFM range you plan to use it.

A little off topic, but I wanted to clarify Pseudo's comment as to why turbo size must be considered, and to clarify that boost is pressure which is determine by volumetric flow rate, not mass flow rate.

As for the topic, you have to ask yourself what "fails" the motor? Stress in the bottom end ultimately fails a motor. How do you stress the bottom end? Heat and cylinder pressures? How do you control heat and cylinder pressure? TUNING!!!! Fuel and timing! That is the key. You can probably setup a stock MP3 motor with engine managment and run concervative timing and fuel and probably run 14psi for years, or I could take the same car and screw up the timing and fueling and trash the motor with 5psi. It comes down to tuning! So to answer your question, well it can't really be answered.

I think 14 psi is optimistic. The Miata engine, which began life as a turbo engine and has proven to be extremely heavily built, can live for years at 12 psi. At 15, it shows accelerated wear but not catastrophic failure. This is with a fully programmable, tuned ECU running Miata-specific software.

Given that the FS motor in the Protege is less turbo-biased in design and based on discussions with Mazda, I'd suggest 10 psi as the upper limit for reliable long-term use with proper tuning.

Keith

What makes the miata motor more suitable for turbo? I'm not trying to "start" anything, I simply want to know.

Because what I do know it the miata motors have been being tweaked and turboed for years, so there is alot of experience and knowledge behind miata tuners. The FS owners are just getting started. . .

The FS motor utilizes a cast iron block and aluminum head just like the miata motor (pretty sure on that one). The FS and miata motor also incorporate bottom side piston oil squirters to cool pistons. . . Nice feature for turbo application. The FS motor incorporates a aluminum stiffener which adds alot of strength and integrity to the crank and crank bearing caps. Now the rods and pistons are typically of most N/A OEM stuff, but from a bottom end perspective of the FS, I would say the FS is more than up for handling boost and just as much as the miata motor. I couldn't image the miata rods or pistons being significantly better than the FS's. But never know. Just looking for you input on why you feel the stock miata motor has an advantage over the FS

Keith has conversed with Mazda about the FS motor, and they have stated something along the lines of the crank case will not hold up to more than 10 psi.

Then we are OK. . . because the crankcase should NEVER see 10psi of boost.

Cute :)

Actually, the culprit is the aluminum girdle aka oil pan upper block. The crank is sandwiched between this and the block. Under high boost, this is not rigid enough and the crank is allowed to flex.

The BP Miata engine doesn't have this girdle and this weak spot. The integrated stiffener is only on the ZM engine. I haven't had the chance to pull the pistons and rods from a FS engine yet, so I can't comment on their design. I'm pretty sure there aren't any oil squirters in the FS either - I'll confirm next week.

Granted, this is based on what Mazda has told us. We haven't tried destroying an engine. Everyone, please send $300 and we'll try it :)

Keith

I have had the FS motor apart twice. There IS oil squirters in the FS.

I'll post photos shortly.

Not "ditching" you, but this makes no sense to me. . .

First the crank is held in place by the block and the main bearing caps. On most engines THAT IS IT. The FS has the block and 2-bolt main bearing caps, which is OK, 4-bolt caps would have been nicer, but we also have the addition of the aluminum stifferner as backup. . . This effectively increase the integrity of the bottom end and combats crank deformation. Just doesn't make any sense to me. . .

I personally feel the FS bottom end is a rock at least for a good 400-500whp. Certainly not the stock rods or pistons though.

The Miata engine is an old design, going back to the 80's. I suspect that Mazda has put a lot of effort into removing unnecessary strength (unnecessary for the design parameters) in the newer FS to help with NVH and thus the upper portion of the block is weaker.

People within Mazda say they come apart at 12 psi, so we're going with what they tell us. I'd love to see someone prove them wrong.

Keith

The FS motors do have oil squirters. I have seen them in my motor.

http://www.probenet.com/pics/blockbtm.jpg
http://www.probenet.com/pics/deck.jpg
http://www.probenet.com/pics/piston2.jpg
http://www.probenet.com/pics/pistonbottom.jpg
http://www.probenet.com/pics/pistonside.jpg
http://www.probenet.com/pics/pistontop.jpg
http://www.probenet.com/pics/rod.jpg
http://www.probenet.com/pics/rod1.jpg
http://www.probenet.com/pics/rod2.jpg
http://www.probenet.com/pics/rodbearing2.jpg

I will take some photos of the oil squirters tonight, or at least were they go, I have yet to press new one in yet.

There's no need to offer photographic proof of the oil squirters. I wasn't proclaiming from the mountaintop that it was impossible, merely saying I didn't think there were any. I don't remember seeing any when we had the pan off the last FS here, but I wasn't specifically looking for them.

I assume all those photos above are FS internals compared with aftermarket equivalents?

Keith

I posted them so people could take a look at what the guts of their FS looks like more than anything. Its always nice to see things.

rods and pistons are comparison shots. . . pistons are JE, obviously, OE CR and these were mistakenly built for a N/A application, hince why they look nearly identical to stock. Rods are Crower. . .

such is life in a car with a factory warranty. if mazda doesn't protect their asses. morons will try to push the limits of the engine at mazda's expense. everyone wanted 30-40hp more and they got it.

I highly doubt that you could replicate the MSP for under $20k. I'm sure that you could make a much faster 1/4 mile car with the FM turbo kit, but you still won't have the LSD or larger axles. BTW, the MSP already has an upgraded clutch. Also, with the MSP you're paying for the body kit and the sound system (which SHOULD be an option).

MSP owners should be happy to leave the car stock. For the rest of us, there's FM turbo's and tein or jic coilovers.