Delanoso's 2.9L Build

[Delanoso]

Got the car into the shop today - wideband, TPS, IAT with new intake and the new ECU all went in easily enough. We made one wiring mistake on the wideband but figured that out quick enough. Then I spent a couple hours working with ForcedFirebird chasing our tails until I suggest we put a smoker on the car. Turns out there was a vacuum leak in the intake boot, which we could have caused today. On the other hand, there was another massive leak in the intake manifold gasket near #1. As in, you could hear it hissing over the rest of the noise in the shop. That 100% explains why it would never idle correctly. How much would that have affected peak power with the tuned stock ECU? Is that likely to be 20-25whp? The MS ECU wouldn't really idle at all because its relying on non-existent pressure in the manifold.

Not my favorite outcome but I did get to be there to help identify issues first hand and I'm certain it'll perform much better once we have it back together.

[e30sh]

A compression test.would be quick and easy and at least give you some info. I would still pull the pan back off vs. head removal. You should be able to see the details with one of those miniature cameras.from the bottom side.

[ForcedFirebird]

Actually since it is stroked, the compression goes up when using the same pistons and adding stroke (more swept volume), so you end up right about 9.3:1, and 9.7:1 with the block shaved.

So, if you factor in you started with 10.1:1 pistons, then you will have about 9.7:1 if they didn't shave the block. Still respectable.

Our car has 190psi with 9.4:1 81mm crank and 272. I just did a comp check on it and pulled it because we have a hole that's down >10psi.

[Delanoso]

My maths went in uncharted directions.

So, if it's an 84mm stoke and stock i pistons on 130mm rods it's actually a low compression 2.8L - 8.8:1 minus whatever .5mm of compression would do. That's something less than 190psi, closer to the stock 160psi mark?

[digger]

Oil pan is back on the engine. It may have to come back off.

That dyno chart looks uncomfortably familiar. So if I understand things, 130mm eta rods, 84mm crank and stock pistons would put the piston tops 3.5mm below the proper deck height. If it's 130mm rods with the custom pistons it's 5mm below the deck. A compression test should give us a clue - what would you expect the results to be for about 10:1 2.9L?

No 4.5mm extra throw if 84 stroke less 5mm rod is net 0.5mm below deck.

10:1 272 cam around 190psi

[Delanoso]

Oil pan is back on the engine. It may have to come back off.

That dyno chart looks uncomfortably familiar. So if I understand things, 130mm eta rods, 84mm crank and stock pistons would put the piston tops 3.5mm below the proper deck height. If it's 130mm rods with the custom pistons it's 5mm below the deck. A compression test should give us a clue - what would you expect the results to be for about 10:1 2.9L?

[digger]

Is the oil pan off ?

[ForcedFirebird]

I dyno'd a local's 2.8 that didn't shave the block (84mm crank, eta rods, stock .5mm over pistons, 272 cam, stock exhaust) and it made 161whp/167wtq with a stock ECU (note the AFR's after 5500rpm):

https://www.r3vlimited.com/board/forum/e30-technical-forums/engine-drivetrain/m20/378740-forcedfirebird-s-m20-dyno-thread?p=6950667#post6950667

Since the pistons are custom, they very well could have been made to use 140mm rods, so rod lenth doesn't mean much in this case. If they were stock pistons, we could deduce what was used.

Was a compression test ever done?

[e30sh]

The i piston with e rod is a common recipe with the 84mm crank. Not saying that's what they did.

I would think you could look through the bottom and see some piston detail with just a flashlight. If not,, you can get a Lizard cam for you smart phone and stick it in there. Factory pistons have casting #'s on them underneath.

e rod is 130mm
i rod is 135mm
early M50 is 135
Tu rod is 140mm 2.5 / 135 mm for 2.8

Your rods appear to be the earlier ones...just can't id the length from the pic.

[Delanoso]

We haven't pulled the head to verify the bore. Is there a way to do that with the head still on?

If the crank is the correct 84mm then the deck height math makes getting the other stuff wrong more difficult. Custom pistons on e rods would be 5mm below the deck - that should stick out pretty clearly to an experienced engine builder. They'd have to be modified stock pistons on e rods in a stock block to not stick so far out of the block that the head wouldn't go on. You can see the piston shape from underneath and they don't appear to be stock.

Once again, correct me if I've got the scenarios wrong here.

[e30sh]

Did you verify bore? They didn't stick i pistons on e rods did they.? We know the rods are not the Tu rods you were supposed to get?

[digger]

All the 75 and 81mm cranks I have come across have "H75" or "H81" cast into them. The only way I have been able to identify (without measuring) the longer throw cranks is by the casting/forging numbers. It might be different in other countries?

There are different 84mm versions but don’t know about others. I know the 75mm stroke were forged at some point it may be in the e90/92 only

[ForcedFirebird]

I don’t doubt the 84mm are those forging numbers but it maybe the case that the smaller cranks use the same forging but get machined differently. I don’t know if that is possible or correct but raising as a possibility. I have seen pics that suggest the m52b25 crank is actually cast so idk

All the 75 and 81mm cranks I have come across have "H75" or "H81" cast into them. The only way I have been able to identify (without measuring) the longer throw cranks is by the casting/forging numbers. It might be different in other countries?

[digger]

I don’t doubt the 84mm are those forging numbers but it maybe the case that the smaller cranks use the same forging but get machined differently. I don’t know if that is possible or correct but raising as a possibility. I have seen pics that suggest the m52b25 crank is actually cast so idk

[Delanoso]

I saw this post as well as a few others.

https://www.bimmerforums.com/forum/s...-Crank-casting

I feel pretty good about the number being correct.