block boring ???

[tjbecht]

can a 2.8 block 89mm piston bore be bored out to 92mm piston bore and drop in the 3.4 pistons on the stock rods and a 3.1 crank from the spec that is the only differences 2.8 and 3.1 have differnent strock and the 3.1 and the 3.4 have different bore 89mm vs 92mm any help would be helpful

[robby1870]

3mm overbore is WAY too much. GM says .060-.080 over is max. 1.5mm is about .060 over

[v6h.o.]

It has been done, but the result is you are left with hardly any material on the cyl wall's. which is just a case of asking for trouble or failure. Not a recommended practice or recommended setup to do.

and yes, 2.8/3.1L share the same bore, 3.503
2.8L stroke is 2.99inch
3.1L and 3.4L share the same stroke 3.3122
the 3.4L which is a specific cast block unto its own has a 3.62 inch bore.

[oil pan 4]

The normal wall thickness is 4.5mm.
If you bore it 3mm you take 1.5mm off each side and leaves you with 3mm walls.

[chucksterdesertdog]

Sleeving is the alternative to boring and should result in proper wall thickneess for sure. I suppose the argument is that it is cheaper to get a 3.4 block.

In my case, I have an old 2.8 aluminum block just for weight savings and am looking for sleeves now since there are no 3.4 aluminum blocks.

[TurboZ24]

If you have the aluminum block, it was intended too run a 2.8 crank, so you would be hard pressed too reach the 3.4 displacement with the 2.8 crank. You could get a custom crank and run the max stroke, which I believe was 3.2".

[TheProfessor]

dude
are you talking about the aluminum 60 degree bowtie block

[Doward]

IF so, the 3.1 rotating assembly drops right in... resleeve it, and boom - 3.4 aluminum!

[geoffinbc]

If this is the GM performance block you are talkng about then you can safely bore it to 91mm

Aluminum Bow Tie V6/60º engine blocks have rough-bored 89mm (3.504") cylinders which can be safely overbored to 91mm (3.582"). Light alloy Bow Tie blocks have bosses for both front-wheel-drive and rear-wheel-drive engine mounts. The starter motor can be installed on either side of the block. The cylinder walls are non-siamesed, and the cylinder deck height is 8.820". Cylinder bore range is 3.525-3.582"; crankshaft journal diameter is 2.65"; all sump type is wet. This block has a 2-piece crankshaft seal and a design maximum stroke of 3.20". It is bossed for front or rear drive engine mounts. Intended for professional competition.

[donk_316]

It can be done. Runs fine no issues after 3000 kms.

[chucksterdesertdog]

My aluminum block is not the current bowtie catalog block since mine has small mains. I understand from the former owner that it is also 11# lighter than the bowtie block!

It wil prob need sleeves anyway since I am not too keen on trusting the circa 1985 silica treated (or whatever) alumium cylinder walls. The cylinder walls, on the other hand, do look very thick and might accept boring and sleeving rather than total replacement with cast iron barrels.

I just hope there is no significant relief needed for the larger crank throws.

The oiling to the lifters Y's off the main feed to the crank main mains. Is this the oldest style or the better oil feed? I'm not sure what the prefered "priority feed" looks like.

chuckster

[RacerX11]

It sounds like you bought the prototype GM aluminum block listed for sale a while back. IIRC, it is simply an early iron block design that has been cast in aluminum, so it has the smaller 2-bolt mains, and earlier style oil galleys. The priority feed system has 3 oil galleys when looking at the front of the block, while the early style uses only 2. Good luck.

Marty

[chucksterdesertdog]

It is the prototype block I got from Jonathan Mcreery.
The oiling method doesn't bother me since that should be just an end of life issue when the lifter bores are worn.
High volume pump and roller lifters should help the lifter bore life along with relatively low RPM use of this motor.
The entire lifter galley is also removeable.

I think that perhaps the block is not exactly like an aluminum version of the 2.8 in other respects.
The aluminum cylinders which seem fairly thick walled are open chamber for the top half of the water jacket.
They are 0.272" thick (7mm).

I'm getting the mains bored for the larger crank journals. About a 77 thou larger radius.
Current plan is to get to 3.4L displacement and use 3.1 heads and intake. Long primary hearders and stock or mild street cam profile.

I also don't plan running it w/out a lot of work to the pan for oil-control and maybe an accusump. My current 88 4cylinder car that the V-6 is going into makes more cornering-force than any of my previous two 88's. Mostly advances in tire technology.
The Michelin Pilot Cup tires I use now are lots gripier than the old TA's or even the KD's. They also test a little better than the Yok 032R track tires and are a lot quieter.

Would like to get 160 HP crank minimim, anything above that is gravy. Mainly this motor is for low weight. I've owned several other 88 fieros with suspension set up almost exactly the same way, and I could always feel the handling difference between the 2.8 cast iron motor and the cast iron 2.5 liter. 360 vs 300# approximately.
I race an F500 SCCA formula car and I don't care for more than about 50-55% on the rear wheels of any car that I am going to drive hard.


Chuckster

[donk_316]

That block is a piece of GM history and should be left alone... my opinion.

You should just buy a GM perf aluminum block instead of machining a rare (possiblely one of one) block.

[geoffinbc]

If you do not have priority main feed oiling you cannor run hyd roller lifters. The crank will starve for oil.