3900 heads on the 3500~!

[farmerz24]

so has anyone tried this yet and do you think it is possible? i guess the only issues would be if the head spacing between the two heads are different as then there would be a gap between the heads when laying down the LIM. other issue would be the heads on the bores themselves as isnt the middle cyl on the 3900 shifted outwards slightly?

anyways, just thought id ask, as the 3900 bigger valves and ports are sure nice! id like to see it when GM comes out with the 3 valve heads for this motor (if they do)

[CNCguy]

I bolted the 3900 head to the 3100 block and visually, the head location in relationship to the LIM was correct. The distance from deck to deck is the same on the 3900 engine compared to the 3100. From that aspect, I believe the top end will a direct swap.

[farmerz24]

hmmm, so cnc guy any other issues you can think of? i guess the 3900 BLOCK is still better than the 3500 due to the fact of increased bore diameters as well as the oil squirters on all 3 banks of cyl (minus the fact of the VVT).

Im intersted in seeing how well this wold work as i beleive the 3900 topend is alot bigger and will flow more air.. but i guess if your swapping the 3900 topend you might as well swap in the motor..

[CNCguy]

hmmm, so cnc guy any other issues you can think of? i guess the 3900 BLOCK is still better than the 3500 due to the fact of increased bore diameters as well as the oil squirters on all 3 banks of cyl (minus the fact of the VVT).

Im intersted in seeing how well this wold work as i beleive the 3900 topend is alot bigger and will flow more air.. but i guess if your swapping the 3900 topend you might as well swap in the motor..

Beside valve clearance to piston/cylinder wall the only other issues that I see are pushrod length and the cooling system return.

To me, the complete swap is the way to go if you can find an engine at a decent price. Esp for W-bodies as its almost a drop in. When you compare a 50% increase in power over a 3100, it seems like a pretty good value for the money compared to other performance improvements. But, thats just my opinion.

[AaronGTR]

You can't do this. The 3900 cylinder bores are offset, not inline. So the combustion chambers won't line up properly with the cylinder bores in the block on the 3500. That and they are bigger in diameter.

[farmerz24]

the cyl bores are offset, not inline. But, i beleive they only shifted them 1mm correct? if so i would think this would still work, no?

[3400beretta]

You can't do this. The 3900 cylinder bores are offset, not inline. So the combustion chambers won't line up properly with the cylinder bores in the block on the 3500. That and they are bigger in diameter.

How do you know? Have you done it? I didn't think so.

Im also very interested to see if this will work. Its a work around for us until the VVT is figured out. It will fix the LIM gasket problem, and really show the potential of the 3400/3500 with those nice big ports and valves.

[CNCguy]

You can't do this. The 3900 cylinder bores are offset, not inline. So the combustion chambers won't line up properly with the cylinder bores in the block on the 3500. That and they are bigger in diameter.

Yes they did offset the bores but they are still inline. The bores were moved outwards by 1.5mm to enable some chages in the canshaft area. It's true that the valves wouldn't be in the center but not by much. Thats why I question the valve to piston clearance when putting the heads on the older engines. I would check it out but I don't have a 3500 engine to play with.

[farmerz24]

so if the bores are offset but still inline, do you mean they have been moved outward when comparing to the bolt hole spacing?? IE, they are 1.5mm over from center where center is the center of the measurement taken between the bolt hole spacing for the head bolts?

CNC guy, what dimentions are you looking for?

[bszopi]

Here is his pic from the 3900 Info thread:



IIRC, that is the 3900 head gasket on a 3100 block. You can see how the bore CL is shifted down some.

[El_Diablo]

will the valve system itself work on the car though? do the pushrods line up with the rocker arms? what about length in comparison? i really dont care to use VVT or the variable runner length system used in the upper intake which brings up another thing, whats the lower intake like? its it simular to the 3500 and 3400 lowers? will we be able to swap the intakes out at all?

[AaronGTR]

How do you know? Have you done it? I didn't think so.

Im also very interested to see if this will work. Its a work around for us until the VVT is figured out. It will fix the LIM gasket problem, and really show the potential of the 3400/3500 with those nice big ports and valves.

I don't have to do it to know it's likely to have problems. Having larger valves as well as larger bore diameter could not only cause interference with piston to valve clearance but also valve to cylinder wall. If you remember that the 3400/3500 valves already take up so much room that there isn't much space to put a larger valve in those combustion chambers, it stands to reason. Plus the larger combustion chambers on smaller bores is going to change the quench area. I don't like the idea of that at all.

Then there is the question of potential you brought up... people seem to be exploring the potential of these engines already with 3500 top end swaps. It hardly seems that the port and valve size of the 3900 is needed without the extra half liter of displacement. IMO without forced induction all that is going to do is lower the air velocity in the ports and lose torque. Especially without being able to take advantage of the variable cam timing and variable intake manifold the 3900 has.

And what LIM gasket problem are you talking about. With the revised gasket and proper installation there ARE NO PROBLEMS anymore. Case in point, I've been running mine for 57,000 miles with no problems at twice the stock HP level.

Bottom line is, I didn't just blurt out some stupid opinion like you seem to think. I've thought this thru and it doesn't seem worth the headache or cost to me to get the 3900 stuff to work for questionable benefits. It's just too much of a different animal from the 3400/3500. The 3500 top end swap seems like a much more justifiable option.

[farmerz24]

throw that 3900 head gasket on a 3500 and take a picture and see what it looks like. maybe all you need is a .020 or .040 overbore to address the piston to valve and piston to wall issues.

[3400beretta]

But you haven't done it, so you don't know for sure. You said it CAN'T be done, and you have no proof of that, only speculation. Im not saying that it can, or that its a good idea, but its definately worth looking into. And yes I am going forced induction with my next project, so I can definately use the benefits of the larger valves and ports. Also, many still believe that there will be a problem with the LIM gaskets, I am one of those people. I think GM also thinks there is still a problem, otherwise they wouldn't have redesigned the whole coolant routing system, eliminating the passages through the lower intake manifold for the new 3500 and 3900.

[onefastV6]

But you haven't done it, so you don't know for sure. You said it CAN'T be done, and you have no proof of that, only speculation. Im not saying that it can, or that its a good idea, but its definately worth looking into. And yes I am going forced induction with my next project, so I can definately use the benefits of the larger valves and ports. Also, many still believe that there will be a problem with the LIM gaskets, I am one of those people. I think GM also thinks there is still a problem, otherwise they wouldn't have redesigned the whole coolant routing system, eliminating the passages through the lower intake manifold for the new 3500 and 3900.

Although I don't think that the LIM gasket is much of an issue anymore, I certainly don't feel that it is an ideal design.

By saying that something can't be done or could be a problem and isn't worth it, doesn't help the community. I commend Ben, Marc and the others here that continue to think outside of the box for the benefit of the community.

As Farmerz24 has stated, if possible it would be interesting to see the 3900 head on the older 3500 block.