Quick question: bored out 3400 w/ LX9 heads???

[2.8-350TBI]

Hi guys, Ihave a quick little question for those with experience in these motors...

I had a couple ideas and wanted to know if 3500 heads would work on a 3400 bored out to 95 millimeters (3.6L), and if the 3400 block itself will hold up to 95mm bores, since the 3500 has a 94mm bore...

[IsaacHayes]

I'm pretty sure that's over the safe limit of .060" over... You don't have to bore it to use the heads though.

[bszopi]

Boring the 3400 block 3mm over is effectively boring it 0.120" over. Can it be done? Yes. Have people done it? Yes. Would I trust it for any decent power levels? Heck no! As stated, the 3500 heads will work on the 3400 block with no issues, so I wouldn't bore it over any more than 1.5mm (0.060").

[2.8-350TBI]

Okay, now I have time to write more...
Thanks for showing interest in my ideas.

The idea I had in mind was to build a big-bore short-stroke "2800" if you will.

The crankshaft I would use is a genIII with a 66.7 mm (2.6 in) stroke from the 2.5L chinese LB8 engine.

To achieve 173 cu.in., the bore would have to be 95mm's (which forces me to use the 3500 block), up just one mm from the 3500's 94mm bore, which I assume is still safe.

Of course, I would have to use custom rods and pistons, but lets put that aside for now...

The real question is this: Will the short-stroke genIII crank be usable in the (HighValue) 3500 block???

[2.8-350TBI]

Nevermind, the short stroke crank wont fit in the 3500 block, back to the thinking board...

[robertisaar]

there is a gen 4 2800...

factory boosted too, i believe in a Saab?

[2.8-350TBI]

there is a gen 4 2800...

factory boosted too, i believe in a Saab?

Its the high feature engine, DOHC.
All I can say is expensive...

To be able to use off the shelf parts, a 3400 block bored to 93.5mm (0.060" over) w/ the 66.7mm crank, I will end up w/ a 2748cc engine, damn, imagine how high that thing could potentially rev...

Its all genIII stuff, so I suppose it could be frankensteined...
Plz correct me if im wrong...

[IsaacHayes]

Yes, been talked about MANY times, no one has gone through with it.

For a real nice setup,

* 3400 block
* 2.8 crank
* Custom pistons to work with the 3400 bore and 2.8 crank (high compression here would be good too. Lower velocity with short stroke means more resistance to pre-ignition)
* Healthy cam (to bleed off some compression and make power too)
* 3500 top end for maximum breathing
* Headers

That would be a high revving powerful small displacement motor.

[Superdave]

for a true "2800" just throw a 2.8 crank, 2.8 RWD pistons and stock rods in a 2000+ 3100 with a ported top end and enjoy.


the gen2 2.8 crank will work in the LX9 3500 block, with modified small journal SBC rods and custom pistons it'll make a helluva screamer. You'll still make more power just by leaving the displacement alone or increasing it. Trust me, my 3500 bounces off 7K way too fast as it is.. i couldn't imagine something that revs faster.

[IsaacHayes]

Yeah but then you miss out on the "big bore short stroke" and also the LX9 heads...

Wait, I thought you couldn't put a gen3 crank in a gen 3.5 (lx9) ?

[robertisaar]

if you're looking for high flow heads, look to the latest DOHC motors, not the OHV... they'll beat us up top every time...

[Superdave]

Yeah but then you miss out on the "big bore short stroke" and also the LX9 heads...

Wait, I thought you couldn't put a gen3 crank in a gen 3.5 (lx9) ?

why not?



same main bearing size, same bearings, etc...

[IsaacHayes]

Then why haven't people done this and used a 3.1/3100/3400 crank and rods instead of a crank trigger? Just no one has is the only reason?

[robertisaar]

3.5 haz forged crank...

[IsaacHayes]

No one has broke a 3.1/3.4 crank yet have they?

I swear I thought there was some reason it couldn't be done.