VVT/non VVT parts interchange?

[ericjon262]

can anyone clear the air on what parts interchange between the VVT motors and the non VVT motors?

do the heads bolt on? internals? intakes?

Thanks-

Eric

[SappySE107]

valve springs, retainers, keepers.

[ericjon262]

valve springs, retainers, keepers.

will the heads bolt up at all? or are the bolt patterns different? do the VVT heads flow better than the non vvt? does anyone have side by side pictures of both?

Thanks-

Eric

[NateD4]

I can check. Ive got a 3400 And 3900 block and heads here. I can tell you the cranks are interchangeable.

Which parts do you want to know about?

[ericjon262]

mainly the heads, if they flow better, if they bolt on and the coolant ports are close to the same, I can make them work I'm mainly concerned with the VVT 3500 heads, because the 3900's heads are designed or the larger bore.

[ericjon262]

will the heads bolt up at all? or are the bolt patterns different? do the VVT heads flow better than the non vvt? does anyone have side by side pictures of both?

Bump? Anyone?

[WrathOfSocrus]

The VVT blocks have the cylinder bores further apart to accept being bored out to over 4L (i forget the exact quoted spec). That plus the U flow coolant means they won't bolt up. Basically the only direct swap parts are what Ben listed above. It may be possible to make certain parts interchange like the crank, but it would require other custom parts to make it work.

[ericjon262]

I've heard quite the opposite, my understanding is that the bores are offset from the crank centerline, which is alot different than bore centers, and if someone would post some pictures, that would settle it 100% for me. I understand the heads probably wouldn't be a direct bolt on, and may not be any better at all, I'd just like to see 100%.

[WrathOfSocrus]

You asked for anyone and you got it. If you want 100% then go buy one and find out.

[3400-95-Modified]

The Cometic MLS headgaskets were made following the VVT design for the non VVT 3500 and 3400's when they first came out and they wouldn't work, I owned a set I had to send them back. Ben also answered you and I'm sure he's tried or measured every combo. If you still don't like that answer then do what WrathofSocrus said.

[NateD4]

I'm pretty sure the VVT heads will fit the 3400s. I forgot about this post and didn't check yet.... I can say with 99.9% certainty that the bore spacings are the same.

When you read about the 2mm bore offset on forums and publications regarding these engines what they are talking about is offsetting them away from the cam. This means if you intersect the axial centerlines of the bore they intersect below crank centerline. I'm pretty sure this is what I'm seeing. I've almost got the whole block mapped out to .002". I'll have to cross check this against my Chevy Power block drawing from the Gen I blocks. GM was nice enough to publish a mostly dimensioned drawing.

As I mentioned I'll have to put the heads side by side and see if they fit a 3400 block and check the gasket for bolt hole spacings. Unfortunately my 3900 block is out for measurement at the moment.

[NateD4]

If my information is incorrect, then I'm going to have to seriously look into why the 3.1/3.4 crank I have fits perfectly in the block. If bores are offset that can create some piston skirt loading problems. Perhaps they are, but I seriously doubt it.

[NateD4]

Just checked a 3.4 Gasket against a 3.9 VVT head. The bolt holes and dowel holes line up. Bore size of course is different on the gasket.

Looks like the bore spacing is the same. The cylinders appear to have almost no water jacket between them.

So to answer your questions:

Block is interchangeable.
Cylinder Heads are interchangeable with the right rocker sand gaskets, though you may have valve clearance issues as the 3.9 Valves are larger.

Pushrods: unknown
Lifters on non DOD probably are interchangeable (not totally sure).
Camshaft, partially interchangeable. you have to match the timing sprockets to the right cam, but lobe and bearing spacings should be the same (I'll have to compare the two side by side).

Crankshaft main bearing diameters are interchangeable.

Rod journals are larger on the 3.9, so rods won't fit a non 3.9 L crank.

Oil pans are different. Despite looking like the 96+ 3400 oil pan, the bolt hole layout on the 3.9L is different than the 3400.

3.9L rocker arms are a better design than 3400 (cast vs stamped). Ratio is approximately 5.2-5.3 by a my crude measurements.

Valve covers are also interchangeable.

Intakes will probably fit. I'll have to check I have 3100, 3400 and 3900 intakes. I'm guessing the port size is the major difference.

Hope that helps a bit.

[ericjon262]

I found this thread a while ago, it was very useful.

http://60degreev6.com/forum/showthre...4223-3900-Info

[SappySE107]

No Nate, the 3900 heads are not going to work on a 3400. 3400 heads are not going to work on a 3900. Rocker arms are 1.7:1 stock for a 3900, and are not compatible with a 3400.