Delanoso's 2.9L Build

[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]

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.

[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?

[digger]

Is the oil pan off ?

[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]

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]

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?

[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.

[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.

[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.

[digger]

The leak likely won’t affect power as it is a big proportionate of the idle airflow but at wot it’s insignificant. It could affect the global trims but I’d not expect it to be a big effect. Atleast with the new ecu you will know you have the right fuel and timing and that way you’ve extracted all that cAn be had with that combo

[ForcedFirebird]

I'm with Digger on this one. Since you are measuring WHP/dyno power at WOT, a vacuum leak won't affect overall power (significantly, anyways - too many details to extrapolate), but, will make idle and lower partial throttles a mess.

However, with the stock ECU and the suspicion that it wasn't going into the WOT maps, I would say the intake leak would affect it MORE. The NB o2 sensor would be throwing all kinds of wonky voltages, and since the ECU was staying in closed loop, it would read this feedback, and respond accordingly. The stock ECU was a marvel for it's time, but as many of us know, everything has to be tip-top for it to work correctly. Modern (and even slightly less archaic) systems have "plan B's", or fail-safes in place for when sensors are out of range, or absent all together.

[digger]

It raises another question why the dyno operator never plotted out AFR for the OP. That should be rule number one always plot AFR. A wideband up its ass is good enough even with cat(s)

[Delanoso]

I'm with Digger on this one. Since you are measuring WHP/dyno power at WOT, a vacuum leak won't affect overall power

Assuming it was actually going into the WOT maps, correct?

However, with the stock ECU and the suspicion that it wasn't going into the WOT maps, I would say the intake leak would affect it MORE. The NB o2 sensor would be throwing all kinds of wonky voltages, and since the ECU was staying in closed loop, it would read this feedback, and respond accordingly. The stock ECU was a marvel for it's time, but as many of us know, everything has to be tip-top for it to work correctly. Modern (and even slightly less archaic) systems have "plan B's", or fail-safes in place for when sensors are out of range, or absent all together.

If it *wasn't* going into the WOT maps, then that means two things: First, the manifold leak would kill low end power. Second, the fact that it wasn't going into open loop means it wasn't ever making peak power potential at any RPM. If both of those things are correct, then the engine would suffer at low RPMs and at high RPMs, correct? That would look like a double whammy at full throttle/low RPMs ie a drag run, right? What affect would you expect just open loop to have on a dyno plot? Another thing we found yesterday when I calibrated the TPS is that the lock nut for the throttle cable had fallen off and the cable was loose. What are the chances the WOT switch wasn't making contact because of that?

Digger, I'm still not sure it's seen a dyno other than the one time I had it on there myself. I found out recently that specific dyno may have trouble getting AFR readings, which is probably why he didn't put them on the run he did for me. It sucks not to know where the good people and equipment is around here. Atlanta is too huge not to have many of both.

Should have more info later today after we get the manifold back on and try cranking it again.

[ForcedFirebird]

Correct. If the switch wasn't being triggered, you lose that ~9° of timing at MBT, as well as the ECU stays in closed loop and uses the o2 feedback. In the race cars running stock DME's, I always delete the o2 sensor just to avoid this very situation. Look at the AFR's before/after on the first two plots: https://www.r3vlimited.com/board/for...ad#post9875136 as you can see, the ECU is oscillating along with the o2 readings. When cruising, this is fine, but when going through the RPM's very quickly in WOT, the oscillations become clear.

As far as the leak affecting power in itself, probably not since the dyno is measuring power output after you hit WOT (physically the TB is wide open), so vacuum leaks become moot since you will be hitting near atmospheric kpa in the manifold anyways.