crankshaft interchange

[dohcfiend]

for once this isn't for me. a friend of mine has a 2.8 in a 92 cavi i think anyway can u swap in a crank from a 3.4 dohc? are there any diferences in rod lengths, like will it make it a 3.4 then?

[dykz34]

I think that you can put the 2.8 crank in a 3.4 DOHC block and it will be de-stroked. Therefore, if you put the 3.4 DOHC crank in the 2.8 block, won't it whack the pistons on the heads?

[grandprixgtp_91]

i know that the 3.4L DOHC and the 3.1L have the same cranks because when my brother got his motor rebuilt his crank was so screwed up they put in a 3.1L crank in his 3.4L DOHC and it runs perfect. but of course this has nothing to do with what you were asking,lol.

Jake

[dohcfiend]

^ u are correct sir.

i should have done this be4 i posted the thread but i looked at the specs. if i put a 3.4 crank in a 2.8 block it is a 3.1.

as long as the rods are the same length it should be np. does any1 know the rodlength of the 2.8 and 3.4? o well if nothing else i can get the rods and crank from the 3.4 and put it into a 2.8 to get a 3.1 at least.


i am fairly certain the 60* family all have the same deck height(well at least up to 94 anyway).

[TheProfessor]

correct me if im wrong but
if you used a stroked crank you need the rods and pistons for a 3.1 not a 2.8
other wise youll nail them on the head
fun fun

[Rhedalert]

^ u are correct sir.

i should have done this be4 i posted the thread but i looked at the specs. if i put a 3.4 crank in a 2.8 block it is a 3.1.

No. the 3.4 is bored out 3.1. 2.8 is a destroked 3.1. Therefore you will have a compression ratio of about 6:1. you could even run 81 octane gas!

[firechiken]

Or olive oil

[dohcfiend]

so the rod lengths are different between 2.8 and 3.4? but the rods maybe the same between 3.1 and 3.4 cause it looks as if the 3.4 is just an overbored 3.1?
so to pull this off i will need 3.1 pistons? can't help the guy with that.

[Rhedalert]

Rods are all the same. The crank and pistons are different in the 2.8 vs 3.1. The 3.4 has different pistons for the bigger bore.

[RidgeRunner]

Rod lengths are all 5.7" for the 2.8, 3.1, and 3.4 engines.
Piston compression height is different between the 2.8 and 3.1 engines.

If you want to use a 3.1/3.4 crank in a 2.8 or 3.1 block, you will need some sort of 3.1 pistons.

If the 2.8 in the Cav came from an 87-89 car, and thus has aluminium heads, you'll need 3.1 pistons from an aluminium head 3.1 to keep the compression ratio close to stock.

[dohcfiend]

kewl, thanx. i will relay that on.

[pocket-rocket]

I was told that the DOHC crank and 3.1 crank are not the same. They look exactly the same, but have different casting and part numbers.

[grandprixgtp_91]

yeah the part numbers are different , but it works just as good as the 3.4L dohc, because my brothers car runs better than ive ever seen it, so i know it restored his power. so yeah the 3.1l crank works perfect in the 3.4L dohc.

Jake

[pocket-rocket]

I would only do this if the engine remains stock. The TGP crank might be a better idea then the DOHC crank possibly. There was a discussion on it, because it and the DOHC were supposed to be special cranks from what I had heard, over the standard 3.1. I don't know though, it has been a while since I heard anything about any of it.