🔧 BUILD Upside-down M90 GTP build thread

[GTPpower]

So I haven't done anything with this other than think about it. But, I am fairly certain that one or both head gaskets never sealed, or the Pistons are not sealing well. There has always been tons of blowby at wot, and the oil seems to get very dirty really quick.

So, I really don't like the cometics mls gaskets and I would love to go back to a stock style gasket. I have a l32 in storage with a chipped piston. I sent out a few messages to companies about some higher compression Pistons. Yates has a set that would give me about 10.1:1 compression. But, I think JE can build a set that will do 11-12. We will see what I get back from them. There is a decent chance I will be dropping off this block at the machine shop for a bore and hone along with new bearings.

 

[v6buicks]

Oh dang. I thought you still had stock head gaskets on this thing.

I remember Intense sold Diamond pistons in custom compression ratios, but they were a pretty penny. ZZPs JE forged "high compression" option is supposedly 9.9:1 instead of 9.5 if that's good enough. They're a lot cheaper too.

 

[GTPpower]

Oh dang. I thought you still had stock head gaskets on this thing.

I remember Intense sold Diamond pistons in custom compression ratios, but they were a pretty penny. ZZPs JE forged "high compression" option is supposedly 9.9:1 instead of 9.5 if that's good enough. They're a lot cheaper too.

Yeah I looked at that. Actually had one of the zzp employees reach out to me that he has a set of the 9.9's for sale privately. But, I would have to bore the block a little, which means a complete rebuild. So I was looking to bump it even a bit more since I would have to do that work anyways.

 

[v6buicks]

I gotcha. You planning on assembling everything yourself?

A guy yesterday was posting his 4.2 stoker LN3 all over Facebook, and it made all excited to see more built up short blocks. I wonder how similar the bearings are between our stuff and the old 109 stuff because it would be nice to just drop my stuff off at one of the trusted Buick builders if it ever came down to it.

 

[GTPpower]

I gotcha. You planning on assembling everything yourself?

A guy yesterday was posting his 4.2 stoker LN3 all over Facebook, and it made all excited to see more built up short blocks. I wonder how similar the bearings are between our stuff and the old 109 stuff because it would be nice to just drop my stuff off at one of the trusted Buick builders if it ever came down to it.

I would probably have a machine shop put it together. It would be fun to do it myself, but I'm not sure I have the time to do it, or the skills with the tiny clearances gm specs.

 

[v6buicks]

I would probably have a machine shop put it together. It would be fun to do it myself, but I'm not sure I have the time to do it, or the skills with the tiny clearances gm specs.

Totally understandable. I'd do the same.

I follow Steve V's Automotive on Facebook. It's a one-man shop who specializes in turbo Buicks. He'll do just about anything from complete engine builds, light restoration, transmission rebuilds, and general maintenance. He just doesn't really mess with rust and body work. Anyway, he makes a lot of videos when he builds engines for people. Some of the techniques he has to use to get the bearing clearances AFTER a line bore are insane. "X" size bearings, mixing bearings of different brands, and picking from collections of partial sets seem to be the ways to getting those engines right and reliable. I bet its also the reason why so few people have had much time on their garage floor 3800 rebuilds. I never realized how much extra guess, check, measure, and remeasure goes into these engines with such tight tolerances.

 

[GTPpower]

Totally understandable. I'd do the same.

I follow Steve V's Automotive on Facebook. It's a one-man shop who specializes in turbo Buicks. He'll do just about anything from complete engine builds, light restoration, transmission rebuilds, and general maintenance. He just doesn't really mess with rust and body work. Anyway, he makes a lot of videos when he builds engines for people. Some of the techniques he has to use to get the bearing clearances AFTER a line bore are insane. "X" size bearings, mixing bearings of different brands, and picking from collections of partial sets seem to be the ways to getting those engines right and reliable. I bet its also the reason why so few people have had much time on their garage floor 3800 rebuilds. I never realized how much extra guess, check, measure and remeasure goes into these engines with such tight tolerances.

Nice. I'll have to check him out. Sounds pretty interesting.

 

[JST_A_3800]

checking in GTPpower

 

[Turbocharged400sbc]

for higher compression check how far out the hole your pistons end up and all you have to do is yank the thick shim in an MLS set to get down to .030 quench clearance and bump compression up substantially

I gotcha. You planning on assembling everything yourself?

A guy yesterday was posting his 4.2 stoker LN3 all over Facebook, and it made all excited to see more built up short blocks. I wonder how similar the bearings are between our stuff and the old 109 stuff because it would be nice to just drop my stuff off at one of the trusted Buick builders if it ever came down to it.

the "tall deck" LN3 (pre SI/L27/L67) shares much with the on center 3.8, those witht he later roller rocker 94/95 heads would be a good beast.

i personally would like to toss the SII pistons and smallwer MOI SII crank into a 94/95 SI block with rebushed chrysler 440 rods to end up with a nearly indycar territory 1.98:1 rod/stroke ratio and cap it off with the bettter symetrical port SII heads with a custom LIM/intake

sticking point is that i have to turn a cam blank witht he SI journals/lobe spacing (EIIEIE) but have it ground with the SII lobe phasing (IEIEIE)

 

[v6buicks]

for higher compression check how far out the hole your pistons end up and all you have to do is yank the thick shim in an MLS set to get down to .030 quench clearance and bump compression up substantially




the "tall deck" LN3 (pre SI/L27/L67) shares much with the on center 3.8, those witht he later roller rocker 94/95 heads would be a good beast.

i personally would like to toss the SII pistons and smallwer MOI SII crank into a 94/95 SI block with rebushed chrysler 440 rods to end up with a nearly indycar territory 1.98:1 rod/stroke ratio and cap it off with the bettter symetrical port SII heads with a custom LIM/intake

sticking point is that i have to turn a cam blank witht he SI journals/lobe spacing (EIIEIE) but have it ground with the SII lobe phasing (IEIEIE)

I think I just learned a few things here. 94/95 S1s had roller rockers? Are you suggesting that the LN3s were off-center? I didn't think any of this was the case.

 

[Turbocharged400sbc]

the cylinder heads were make with stands that bolted on the early roller rocker fulcrum units, an early version of the SII stuff intake and exhaust valves are positioned differently, the SII is symetrical, each cylinder identical in port layout/chamber etc. the SI was EIIEIE where the cylinder heads are asymetrical with some intake ports/etc not shaped/positioned the same in relation to the bore centerline.

refering to the buick 3.8 stuff it is an on center rod/crank layout from the factory for the LG3+ 3800's

 

[Turbocharged400sbc]

off center 3.8's are offset from the bore centerline to the crank bearing journal centerline

 

[GTPpower]

I would really like to go back to a stock style head gasket while I still have a bunch of compression.

I'm working on making a deal on an engine with 11.5ish:1 compression.

 

[Turbocharged400sbc]

Say what

 

[GTPpower]

I want compression.

 

[GTPpower]

Did a leak down test today.







So, according to that, head gaskets, valves, and rings are all good, right?

 

[v6buicks]

Looks good to me.

 

[sktchy]

am i wrong as usual or is that a lil on the low side?

 

[sktchy]

Nevermind I guess if your using air and that's not actual compression?

 

[GTPpower]

Yeah, it's a leak down, not a compression test. There are a couple cylinders that might be a tad low, but still normal from what I can tell.

 

[sktchy]

Looks good for another season then lol

 

[GTPpower]

The problem is that it doesn't make power yet, and I don't know why. I was better on head gaskets.

 

[sktchy]

Don't feel bad mine didn't seem to be makin what i think it should, still kind of has a weird miss I haven't tracked down and last time I had it out it didn't wanna idle after sticking my foot in it but otherwise seems to run and drive fine. I haven't really had much ambition to mess with it since getting it running again tho.

 

[JST_A_3800]

whats it make on an actual compression test nick? mine is stupid low

 

[GTPpower]

I didn't actually check compression. I couldn't find my gauge so that didn't get done. Yours was like 130ish right.