Frankenmotor assembly questions

[Zandr]

I'm new around here, so my apologies if this is the wrong section. [Please move as appropriate]

A few years ago, I had a Frankenmotor long block and reversed 5spd built for my Vanagon. Life got in the way for a bit, so I've only now gotten back to the project and am swapping parts over.

The existing motor was a bog stock Phase 1 EJ22. The new motor is a Phase 2 EJ25 block (6+2 bellhousing pattern, 311 castings), with Phase 1 EJ22 heads (dual-port exhaust, SOHC).

So far so good, until I tried to install the intake manifold from my EJ22. Somehow the heads are too close together, by a few mm. Searching this forum and others tells me two things: a) all EJ motors have a 201mm deck height, and b) if I use this combination, the intake will be "too wide" and I'll need to slot the holes in the manifold.

I guess my first question is... how can both of those be true? If the deck height is the same, how do I have such a large difference in width? Gaskets and machining won't add up to what looks like about 3mm.

As to getting a motor put together, I'm ok with slotting the manifold, though I'm a little concerned about the ports being misaligned. But is that the right answer? Is there a different manifold I should use instead?

Finally, would a different 2.5 bottom end avoid this? As we also race a Subaru powered Beetle in Lemons, I have a pretty good boneyard to go shopping in.

Many thanks,
-Zandr

[GeneralDisorder]

What pistons are you using? You need 25D pistons and it looks like, based on your head gaskets you are using 251 block and gasket thickness. The compression ratio on that combo is too high and it will suffer from severe detonation. The ECM will yank out your timing and kill the performance. 

Looks like those heads may have been decked. There shouldn't be a significant fitment issue with more or less stock block, heads, and intake. 

If you have plenty of parts to shop then the combo you want is a 255/257 rotating assembly, #5 thrust block, and 25D heads. Shave off about 0.020 on the heads, run 257 gaskets. You will need eccentric idlers for the timing belt, and you will have to enlarge the holes on the 25D intake. Very exceptional power band from that combo. 

GD

[Zandr]

I don't know what pistons are in there. This was built for me professionally a few years ago, and I don't know what I did with the paperwork. They knew what I was doing with it, since they were building the reversed 5spd for me at the same time.
Is there a way to ID the pistons without splitting the case? I'm not averse to pulling the heads to take some measurements, and the bog-stock EJ22 is on a stand right next to it.

Do 331 castings point to this being a 251 block? Searching for casting numbers rarely yields much info, which seems odd to me, I guess it all comes down to how the castings were machined. That would have been a hell of a deck to cause this much misalignment... Like more than 0.030 off all four surfaces.

EJ25D heads are not an option, because this thing needs to look like an EJ22. That includes the number of cams.

[GeneralDisorder]

251 pistons are flat top, while D pistons have a square dish in them. 

The problem I see is that 25D pistons are what you need, but it's essentially impossible for it to have D pistons with those thin head gaskets. The D piston requires a 0.051" gasket (IIRC) or the pistons hit the cylinder head. Of course they could have done custom pistons or mixed and matched rods or something but it certainly wouldn't be stock. If it turns over and it's made of stock parts then it's likely a 251/253 and the compression will be stupid high. Like 11.5 or more if heads and block got decked. Would run on E85 but not using the stock ECU

GD

[Zandr]

I'm fairly certain this is built out of OEM parts. I can probably see the dish through a plug hole with a borescope, but it sounds like I really need to measure piston height at TDC to know what I'm dealing with, and I should probably put it back together with thicker gaskets.

I'll contact the shop on Monday and see if they still have anything in their files, but that doesn't seem too likely.

Thanks for the help, I'll keep you posted.

[nvu]

the intake holes were slightly narrower when i put together my ej22 with ej257 block.  drilling the intake holes slightly larger got it to fit.   

[Zandr]

As an academic matter... does that mean that "All EJ motors have a 201mm deck height" is false?

[heartless]

6 hours ago, Zandr said:

As an academic matter... does that mean that "All EJ motors have a 201mm deck height" is false?

from the factory, they probably all do have the 201mm deck height.. so no, it is not false.

any machining work done down the road will change that, however..

i am not an engine builder, but common sense says that if you are machining warped heads to sit flat, and possibly machining the block mating surface as well, you are taking material away and that will affect other things.

[Zandr]

4 hours ago, heartless said:

any machining work done down the road will change that, however

Yeah, I understand that. Next weekend when I can get back into the shop, I'll measure exactly how far off this thing is. But as I said, it would be rather more than 0.030" off all four surfaces to get here. Here's one of the other posts I found that suggested there was more of a difference than just machining.

"Running an ej257 block on '98 ej22 heads here. It'll work. ... Use the intake manifold from the EJ22, it'll be slightly longer, the bolt holes are 1-2mm off. Drill out the manifold holes 1mm larger to make them fit."

There was another that had the oddly specific reference to a 1.8mm difference, but I'm not finding that right now.

 

[Zandr]

I've made it back to the shop and poked a borescope through a plug hole. Pistons have valve relief, but are not the big square dish of the D pistons. Piston tops are stamped 0.50, which is consistent with the 0.020 overbore that the builder mentioned. Still waiting for other details, but it seems like this is probably a stock EJ251 bottom end?

Given that, with these gaskets, I'm probably in the 11.3:1 range before any machining. Sounds like the right answer here is to go to a 0.051 or 0.056" gasket, which would drop me down to the mid 10's. Seem right?

Thanks again for the help, it is appreciated.

 

Edited July 26, 2020 by Zandr
typo

[GeneralDisorder]

You can go with a thick gasket, but that was the entire reason for the HG failures on the 25D. Gasket is too thick. Also absolutely destroys your quench and if you expect a full timing curve at mid 11's it's going to be a real detonation prone engine with poor quench.

Subaru's DO NOT HANDLE detonation. They want a lot of timing, and detonation kill rod bearings FAST. You want to do everything in your power to prevent it. So if you have a standalone you can run it on so you can pull a bunch of timing out of it..... that's not going to run for beans on a stock ECM.

GD

[Zandr]

Yeah, that's why I want to get out of the 11s. These things have a pretty good track record in Vanagons, this one just seems to have been put together with the wrong gaskets for the application.

Thanks again!