rattlecan
rattlecan New Reader
12/6/21 3:57 p.m.

I have a high milage (195k) 1995 NA8. The engine is currently torn down and I'm going through inspecting everything. I'm rebuilding for mild boost. I don't intend for this car to ever have more than 210hp. Probably more like 175 to 200 with a stock ECU for CARB. I've been told time and again these engines can handle 200-225hp on stock internals and that the weak link is the rods. Everything inside the engine looks really good. I'm sending it out to the shop to be professionally measured next week. I was anticipating it looking worse and needing to bore for a larger aftermarket piston. However, if everything is in spec I am considering

A) stock pistons and rods

B) stock pistons and forged rods

C) Aftermarket pistons and forged rods

Mostly this car is for street and autoX (for fun, not Nationals). I want reliability and not to have to deal with excessive slap, oil consumption, etc that can come with aftermarket pistons. Right now I am headed towards option B, stock pistons and forged rods. However, I don't want to do all this work and skip the pistons if they're recommended. Should I do aftermarket pistons while I'm in there, or am I creating a potential headache for no good reason? Also, if I do pistons the general community consensus seems to say Supertech due to their alloy not expanding as much as the Wiseco, even though the Wisecos are stronger. The Manley H-Beam rods appear to be the clear winner in the world of popular opinion. Although everyone knows what they say about opinions. 

I should probably also add that this is my first complete engine rebuild. 

Keith Tanner
Keith Tanner MegaDork
12/6/21 4:09 p.m.

Stock internals will have no problem with that power level, with reliability measured in decades. A good build using stock parts will be fine. Use good bearings, that's the most likely place you'll discover the heartache of cheap parts.

rattlecan
rattlecan New Reader
12/6/21 4:19 p.m.

Thanks Keith, the parts will be coming from you, so I'm sure they'll be great

 

z31maniac
z31maniac MegaDork
12/6/21 5:37 p.m.

I would probably do the rods just because I've never known anyone, not worried about hp:weight classing that doesn't eventually want to turn up the BOOOOOOOOOOSSST. 

Keith Tanner
Keith Tanner MegaDork
12/6/21 5:41 p.m.

You'd be surprised. The majority of our customers are happy to run at what they've been told is a safe boost level. Coincidentally, engine destruction is relatively rare in our customer base.

Pete. (l33t FS)
Pete. (l33t FS) MegaDork
12/6/21 6:05 p.m.

An aside, the piston materials that don't expand much tend to be weaker than the materials that need more cold clearance.

Old timey forgings that needed .005" clearance could practically be hammered into a saddle shape and not break.

NickD
NickD MegaDork
12/6/21 6:08 p.m.

My '99 1.8L has stock rods, pistons, bearings, oil pump and head gasket and I'm pushing 245whp with a Rotrex blower. I did put ARP head and main studs in but it was kind of a "while I'm in there" thing. From what Gary at Track Dog told me, the real killer of parts is RPM. When I said my engine has stick internals, he told me it'd live happily ever after as long as I kept it below 7500rpm. The stock cams run out of breath and then power curve noses over it 7000rpm, so I have no reason to twist it that hard anyways. I've beat on it like it owes me money for 3 years now and its still holding together. 

Keith Tanner
Keith Tanner MegaDork
12/6/21 6:34 p.m.

Loads on the rods increase exponentially with RPM, this is true. They're responsible for accelerating and decelerating that big slug on most of the strokes. That also beats on the rod bearings. You can also get into problems with vibrations taking out the oil pump, so a good damper is a good plan. But with a stock ECU like the original post, you're limited to a stock redline so this isn't an issue.

I know the HLA cars will hit valve float at about 7800, which can cause valvetrain problems in the medium term - a set of valve springs takes care of that.

I think a large percentage of rod failures under 250 rwhp come from detonation, which is a fault of the tune and setup and not the strength of the internals.

codrus (Forum Supporter)
codrus (Forum Supporter) PowerDork
12/6/21 6:42 p.m.
NickD said:

My '99 1.8L has stock rods, pistons, bearings, oil pump and head gasket and I'm pushing 245whp with a Rotrex blower. I did put ARP head and main studs in but it was kind of a "while I'm in there" thing. From what Gary at Track Dog told me, the real killer of parts is RPM. When I said my engine has stick internals, he told me it'd live happily ever after as long as I kept it below 7500rpm. The stock cams run out of breath and then power curve noses over it 7000rpm, so I have no reason to twist it that hard anyways. I've beat on it like it owes me money for 3 years now and its still holding together. 

Well, the REAL killer is detonation. :)

As for limits on boost level, one difference to be aware of is that the boost curve of a centrifugal blower doesn't produce the big belt of midrange torque that a turbo does, so at the same max boost level a rotrex is less likely to turn the rods into bananas.

I agree that stock parts should be fine for a 200 hp turbo, although I would probably look for a good used block instead of spending the money on doing a machine shop rebuild.

 

rattlecan
rattlecan New Reader
12/6/21 7:50 p.m.

In reply to codrus (Forum Supporter) :

I'm doing the rebuild for two reasons. 1) Lower mileage engines are getting tough to find. These cars are 25-30 years old now, most of what I'm finding is around the same mileage as mine, if I can find anything at all. 2) I really enjoy wrenching and I've always wanted to rebuild an engine, so here I am. I like the idea of getting to know every part of the car.

 

APEowner
APEowner SuperDork
12/6/21 9:46 p.m.
Keith Tanner said:

...You can also get into problems with vibrations taking out the oil pump, so a good damper is a good plan...

What does a vibration induced oil pump failure look like?   Do the pump gears chatter and wear excessively or is there some kind of catastrophic failure?

Keith Tanner
Keith Tanner MegaDork
12/6/21 10:11 p.m.

The sintered oil pump gears come apart, followed by basically the rest of the engine because now there's no oil pressure. You can get upgraded gears but I like to address the root cause first.

If you put an undamped billet "underdrive crank pulley" on a turbo Miata, you'll never have to change the oil again.

Keith Tanner
Keith Tanner MegaDork
12/6/21 10:12 p.m.

In reply to rattlecan :

Both very good reasons. I'd probably do the same.

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