The V8 Owners Forum -

"If it still isn't good enough, you need more cubes. So you could bore it to 3.9 whilst it's in pieces."
Chris.

I read this in a reply to another thread.

My queery is, is it possible to bore a 4.4 p76 block out to take 3.9 pistons ? standard bore is the same as a 3.5 just a longer stroke to get the extra capacity.

I have the complete internals of a 3.9 and a 4.4 block.

What capacity would it be ?

1st post so any help appreciated.

muzzz.

The 3.9 pistons are 3.7" dia, compared to 3.5" dia for the 3.5l and 4.4l engines. I am not sure if the liners will stand a +200 overbore!! When you do this with a 3.5, you need new liners, so I presume that the 4.4 will be the same.

Chris.

as far as I am aware the 3.5/4.4 had new lines to go to the 3.7 bore, the ally cores in the blocks are big enough to ttake the larger liners but the liners won't take the extra boreing. I presume you are asking this because you have a ready supply of these blocks but not easy access to the 3.9 bore blocks? These blocks hada reputation for splitting down the valley when tuned, I can see many reasons why they should in theory produce a better engine than the 3.7 bore block, better rod:stroke ratio, better clearance around the skirt area, I think it is simpler to get the buick 300 crank into this block. There is a better selection of rod/piston combinations as there is more room for taller compression heights of some of the pistons that willfit with a less radical rebore, one of the reasons few pistons were available for the 3.5 rover bore size. However you may have to come up with a way of strengthening the block, there were kits to do this for the 3.5 block that basically bolted webbing across the valley.
this sounds a veryinteresting project
best regards
Mike

Thanks Chris and Kiwicar,
I have a p6b auto that I have owned for 7 years and about to give it a little rebuild to pass onto my son. The motor at the moment is a healthy 3.5 10.5/1 slightly tweeked, as I mentioned before I have a complete 3.9 minus block and a p76 4.4 short motor, i just wanted to see if it was possible to make a larger capacity motor using all the bits I already have.
I have had a couple of quotes to resleeve the 4.4 from 3.500 out to 3.700 but at $1900 ozy dollars it's not really feasable financialy when I can pick up used LS1's for that sort of money, (if the modified vehilce laws here would allow it)
I'm thinking now of getting hold of a good 3.9 and just build up a warm unit.

Thanks for the info gents, till next time, cheers.
Wayne.

Hi
I would not go further than the warmed over 3.9, put much more than 200bhp into the P6 diff and it will give up on you they are not very strong!
Sounds a very cool firstcar for your som by the way!
best regards
Mike

g'day kiwi,
He helped me over 9 months to build it up out of 2 wrecks, 10 year old throwing spanners like a pro, put his name on it then.
I think I will take your warnings and source out a 3.9 to play with, at least being auto it shouldn't punish the diff too much, I hope.
thanks for your input mate .

cheers, muzz.

Hi
Good to see you got you lad started at a good age, I was mucking around withcars from about 8 or 9, my brother found if he got me to work on the underside of his cars he didn't have to jack them up, he just slid me underneath!
Can you post some pictures up of the car at some stage? it would be good to see it.
Best regards
Mike

yeah kiwi I will when I can, nothing special though, just a p6b with a little attitude.
muzz.

Every P6 is special! I am biased though as I drive one everyday

+1 for pics please.

A couple of forum contributors have put 4.6 engines into P6Bs with good results, one of whom is in Sydney..

Robrover wrote:A couple of forum contributors have put 4.6 engines into P6Bs with good results, one of whom is in Sydney..

Did they do something to the final drive? I broke several differential drive shafts on my standard 3500S.

My 3.5 auto P6 snapped a diff shaft - I couldn't believe how puny they were.

PO

plastic orange wrote:My 3.5 auto P6 snapped a diff shaft - I couldn't believe how puny they were.

PO

They are soft, particularly if you spin one wheel and suddenly it grabs hold. If you habitually light it up, then it's only a matter of time. A few guys have fitted the Jag LSD to the P6 with a cradle and it fixes that nonsense...

If anybody is looking for a good 3.9/5.0 block - fully top hat linered with ARP studs included (now impossible for liner slip) - PM me