[308] carby 308 and carby 304

[DANNY8]

So apparently the black carby 308's found in VK's and VL's are 304's, is that true? If so wat changes were made to make them 304ci instead of 308ci?

I have a rebuild kit with pistons to suit a red/blue 308....and at the moment I'm on the hunt for another 308 to build up and I wanna use the rebuild kit I already have, so can I use a black carby 304 motor or will it not work?

I'm gonna be using the pistons in the kit, along with A9L rods, so the main thing I guess is the crank which I'd need to worry about.

 

[383 hatch]

The stroke was changed slightly. 308 is 3.062" stroke, 304 is 3.02 " stroke so about 40 thou difference. The pistons you have will be no good in a 304 as they'll be too far down the bore and affect comp dramatically. You need a 308 to be able to use the rebuild kit you have.

 

[DANNY8]

So to change the stroke was it just the pistons which were changed? Or are the rods and crank different as well?

I guess A9L rods are to suit 304, so if the 308 and 304 rods are different lengths I'll run into the same issues with those too hey?

 

[soop]

304 crank has a different throw.

 

[DANNY8]

So the rods are all interchangeable then. So I should have no trouble using my 308 pistons and A9L rods as long as I use a 308 bottom end?

 

[soop]

They will probably fit, but whether or not the lenght is the same is another matter. Which is what I think Bv6 was alluding to.

 

[Clutchy]

Im pretty sure its only in the crank well thats the understanding I got whan I rebuilt my old 308.

 

[ari666]

rods are a different weight so you will need to get a 308 crank balanced to use them

 

[383 hatch]

rods are a different weight so you will need to get a 308 crank balanced to use them

Which you should do when fitting different pistons anyway, so what does it matter?

DANNY8, all Holden V8 rods are the same length, so they're all interchangeable. The only way the stroke of an engine can be changed is by altering the crankshaft throw. Obviously, when the stroke of the crank is changed, if using the same length rods you need a shorter/longer piston to compensate for the decreased/extra throw which is the case in a 308 and a 304.

So, yes you can run a 308 crank, with the later model A9L rods and your 308 pistons no problems, just need to get the rotating assembly balanced which should be a matter of course when building an engine anyway. The cranks can be very tricky to tell apart by looking at them though, as both 304 and 308 cranks have 308 stamped on them, so be careful.

 

[soop]

Ah, there is a notch taken out of one of the counter balances on the 304 cranks!

I'll find a picture for you!

EDIT: I found the photo but my PC keeps having a hissy fit when i try to put it on.

Basically the 304 cranks are missing a casting on the front of the crank, when you see the two side by side its very very obivious.