Delanoso's 2.9L Build

[Delanoso]

Turns out the guy who tuned my ecu is no longer with the dyno shop, which makes me even more suspicious that he slapped a tune in there with out ever putting the car on the dyno. My shop is concerned that there's a forged M52B25 crank in there instead of the B28. He's also concerned that cam timing has been retarded by decking but at least we have an adjustable cam gear to correct that. We'll likely get it in the shop next week to pull the covers and oil pans to see if we can measure or see casting numbers. First thing though, he wants to try swapping out the AFM just in case that's causing the power loss as well as the idle issues. I feel like we've been through three of them already though so I don't have much confidence in that.

[digger]

doubt its a 75 mm crank in there....anyway you said the shop built the engine how would they not know what crank is in there......

[AWDBOB]

Pull a plug, find TDC, and stick a socket extension in there. Mark it at TDC, and then rotate the motor. Easy way to measure stroke in just a few minutes.

[Delanoso]

doubt its a 75 mm crank in there....anyway you said the shop built the engine how would they not know what crank is in there......

I'm not sure really. My understanding is that they measure everything before the put it together. Some of the parts were from a kit, some of the parts were bought separately. I know they used separate M52 135mm rods because of the shape and he says they were weighed and measured for balance. You'd think in that process they'd measure the crankshaft as well. His thought is that a forged shaft in a kit designated for the block/head combination might go unnoticed because it was part of a kit where an M20 cast crank would stand out. Still seems kind of unlikely to me unless the actual tech who built it didn't put 2+2 together on 2.9L = 84mm crank.

Pull a plug, find TDC, and stick a socket extension in there. Mark it at TDC, and then rotate the motor. Easy way to measure stroke in just a few minutes.

That's a fantastic way to do it myself. Aaaaand now I feel dumb. I'll do that tonight.

[ForcedFirebird]

I see you are using Ross pistons. Was the stock 885 crown shape used?

[ForcedFirebird]

I see you are using Ross pistons. Was the stock 885 crown shape used?

[e30sh]

What kind of torque #'s should a 2.9 make at lower RPM's?

[digger]

I'm not sure really. My understanding is that they measure everything before the put it together. Some of the parts were from a kit, some of the parts were bought separately. I know they used separate M52 135mm rods because of the shape and he says they were weighed and measured for balance. You'd think in that process they'd measure the crankshaft as well. His thought is that a forged shaft in a kit designated for the block/head combination might go unnoticed because it was part of a kit where an M20 cast crank would stand out. Still seems kind of unlikely to me unless the actual tech who built it didn't put 2+2 together on 2.9L = 84mm crank.

That's a fantastic way to do it myself. Aaaaand now I feel dumb. I'll do that tonight.

the pistons would be way down the hole (almost 5 mm) and it'd be obvious. plus a typical 75 mm stroke m20 doesnt normally make 150 tq at 2500 rpm its normally like 130 if its lucky.

[digger]

What kind of torque #'s should a 2.9 make at lower RPM's?

160ish rwtq is the ball park where id want it to be on a fairly mild 2.9L build for the street. The camshaft and exhaust can really reduce that big time though if you arent careful

[e30sh]

Did they mention anything about the machine work required to fit the 84 mm crank? Any chance they had an ETA crank lying around?

[Delanoso]

I see you are using Ross pistons. Was the stock 885 crown shape used?

That's actually a good question. I assumed that they were the same crown shape just adjusted for increased compression.

[Delanoso]

the pistons would be way down the hole (almost 5 mm) and it'd be obvious. plus a typical 75 mm stroke m20 doesnt normally make 150 tq at 2500 rpm its normally like 130 if its lucky.

The gap at the top of the block was one of the things that I talked about with the owner of the shop. Doesn't seem likely that a guy who builds M20s all day every day would miss something like that - or measuring the crank to make sure he has what he expects.

Also, I was wondering about the low end torque numbers for a 2.5. Hard to find anything conclusive and a NA 2.5 because those dyno plots don't get posted very often ForcedFirebirds dyno thread has some to look at but they're frequently modified. Hearing that torque on a 2.5 is significantly lower makes me feel better about the internals. That would mean it's tuning, which I can correct with the MSPNP.

[Delanoso]

Did they mention anything about the machine work required to fit the 84 mm crank? Any chance they had an ETA crank lying around?

They had *my* eta crank lying around for certain. But that's a cast crank and the owner feels like that would be a very unlikely mistake when we were putting in a forged crank. There's also the actual piston size. If they're 84mm instead of 85mm that could explain some of it too. The shop has verified the order - we ordered the right things and the supplier records show they shipped the right things. Now it's a matter of verifying those parts. Monday, I'm making an appointment to take the car in next week for all the inspections. He continues to offer to pull the engine out and measure cylinders if he has too. Hopefully it doesn't go that far.

[e30sh]

Did you try the stick in the spark plug hole to measure stroke?

How easy is it to see the spacer that these cranks need when you remove the balancer?

[Delanoso]

I tried the spark plug measurement and couldn't get anything that I felt was accurate enough to trust. I got several different marks for what should have been TDC. It's probably my measurement because there shouldn't be that much difference over several degrees before and after. Same thing with BDC. Whatever the case I didn't get anything I felt was reliable enough drive a conclusion.

The shop owner said he definitely saw the spacer at the end of the crank before they covered it up with a bunch of pulleys and covers. That's one reason he thinks there a chance that it's an M52B25 crank - it's either that or a B28.