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picked up a 3500, Took it apart on tuesday night and took some pics.
Here's what it all looks like.
3500 on crate, my 3400 on the stand.
Block:
underside of 1/2/3/4 bores.
underside of 5/6... Oil squirter. Only reason I can figure for only 5 and 6 getting the oil squirter is that years back in the 3100 dessiel piston slap days 5/6 were the two culprits of slap and colapsing. Possible GM's remedy for piston slap from these two cyls. However why not all cylinders? Who knows... GM does odd shit. Wouldnt be hard to fab a hardline to work a squirter system to feed all 6 though.
3400 block bore spacing:
3500 block bore spacing:
I had thought I had read something at one point about how GM moved the camshaft up in relation to the block to gain more room for the larger bore. So I measured both blocks
3500:
3400:
Nothing has changed there in terms of the cam. I measured both blocks from where the #1 main cap sits to the cam retainer bolt hole which is centrally located around the camshaft bore.
Front Bolt Bosses:
Note the lack of AC compressor bolt holes compared to the 31/400 blocks:
3400 bolt bosses front:
3500 block front mount profile:
3400 block front mount profile, as you can see the 3500 block bolt bosses stick out further from the block by about an inch:
3500 Rear bolt bosses:
Rear bolt boss spacing has changed for the two that are closest to the edge of the block. The two inboard bolt holes are still the same bolt spacing:
3400 bolt bosses rear:
Crankshafts:
Grabbed up some spare cranks from my stock for comparison pics.
2.8L 2.99 stroke crank left, 3500 Crank 3.312 stroke center, and 3400/3100 crank 3.312 stroke right.
Crank Rod journals are now 2.250 inch (way too big in my opinion) up from the old 2.0inch journals.
Crank Casting Numbers:
The 58X or whatever it is now Reluctor wheel
Rod/Pistons:
Rods are now 5.9 inch long center to center up from previous 5.7 Inch.
Rod BE's are now 2.375 inch diameter up from 2.125inch previous rods.
Heads:
3100 head to the left, 3500 to the right:
Chamber has been reshaped. I don't have specs on the Valve sizes yet.
I dont have the exh manifolds they had to be swapped onto the new engine. However as you can see from the carbon build up different port shape on the manifold however. The genral "D" shape profile is still used though. I dont know how much its changed in terms of sizing yet.
Took a stock 3400 exh gasket that I had and compared the port locations.
GM has changed the relationship between the bolt holes/ports.
This is with the bolt holes lined up on gasket/head. however you can't really see the port.
Lining up the one port (the rest dont line up like this though) as you can see the gasket does not line up with the head. So 3500 manifolds are a must with the heads.
Intake ports are slightly different
3500 lower intake manifold
I'll try and get more info when I can as per some of the measurements that I havnt had a chance to take.
Here's what it all looks like.
3500 on crate, my 3400 on the stand.
Block:
underside of 1/2/3/4 bores.
underside of 5/6... Oil squirter. Only reason I can figure for only 5 and 6 getting the oil squirter is that years back in the 3100 dessiel piston slap days 5/6 were the two culprits of slap and colapsing. Possible GM's remedy for piston slap from these two cyls. However why not all cylinders? Who knows... GM does odd shit. Wouldnt be hard to fab a hardline to work a squirter system to feed all 6 though.
3400 block bore spacing:
3500 block bore spacing:
I had thought I had read something at one point about how GM moved the camshaft up in relation to the block to gain more room for the larger bore. So I measured both blocks
3500:
3400:
Nothing has changed there in terms of the cam. I measured both blocks from where the #1 main cap sits to the cam retainer bolt hole which is centrally located around the camshaft bore.
Front Bolt Bosses:
Note the lack of AC compressor bolt holes compared to the 31/400 blocks:
3400 bolt bosses front:
3500 block front mount profile:
3400 block front mount profile, as you can see the 3500 block bolt bosses stick out further from the block by about an inch:
3500 Rear bolt bosses:
Rear bolt boss spacing has changed for the two that are closest to the edge of the block. The two inboard bolt holes are still the same bolt spacing:
3400 bolt bosses rear:
Crankshafts:
Grabbed up some spare cranks from my stock for comparison pics.
2.8L 2.99 stroke crank left, 3500 Crank 3.312 stroke center, and 3400/3100 crank 3.312 stroke right.
Crank Rod journals are now 2.250 inch (way too big in my opinion) up from the old 2.0inch journals.
Crank Casting Numbers:
The 58X or whatever it is now Reluctor wheel
Rod/Pistons:
Rods are now 5.9 inch long center to center up from previous 5.7 Inch.
Rod BE's are now 2.375 inch diameter up from 2.125inch previous rods.
Heads:
3100 head to the left, 3500 to the right:
Chamber has been reshaped. I don't have specs on the Valve sizes yet.
I dont have the exh manifolds they had to be swapped onto the new engine. However as you can see from the carbon build up different port shape on the manifold however. The genral "D" shape profile is still used though. I dont know how much its changed in terms of sizing yet.
Took a stock 3400 exh gasket that I had and compared the port locations.
GM has changed the relationship between the bolt holes/ports.
This is with the bolt holes lined up on gasket/head. however you can't really see the port.
Lining up the one port (the rest dont line up like this though) as you can see the gasket does not line up with the head. So 3500 manifolds are a must with the heads.
Intake ports are slightly different
3500 lower intake manifold
I'll try and get more info when I can as per some of the measurements that I havnt had a chance to take.
I forgot to mention that. along with the fact that the exterior where it presses onto is still the same diameter of the old 7x reluctor ring. Now isn't that just convenient 
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