Now to your motor!
No doubt you will use the larger capacity oil pump and big bore oil
pick up,
along with enlarged and radiused oil galleries (don't forget to try your mains
shells in and check the oil hole alignment with the oil gallery hole). Plus
you may choose to fully groove your mains bearings or risk cross drilling your
shaft. Plus we understand, you will use studs instead of bolts to tie the
caps on. Under sensible conditions, we believe this should work well and be
reliable.
As for cutting down you mains from 3" to 2.55", you are a brave man.
On the
down side, that's a lot of iron to buzz off a cast shaft. On the positive
side, Buick nodular shafts are wonderful things and when was the last time you
saw one break? The idea of big diameter mains is to increase the rigidity of
the shaft and stop whip, then in turn block flex. Apart from chopping out the
main bearings, this also causes cylinder walls to crack and in your case
release the sleeves. (Nasty!)
On problem with big mains is the bearing speed and the friction they
produce.
Drag racers, chasing that extra couple of ponies, cut down the Buick 455
shafts, we understand, get away with it. The 455 has a delicate and light
"thin wall" block which relies on the cranks huge mains for rigidity. So it
might work for you, all you can do is try and see.
I suggest you seek professional advise on the crank from a race crank
maker.
However, you might start with as a radius as big as possible at the end of
each cut down journal, even if you have to bevel the edge of the bearing
shells. A ruff cut down then a crack test and shot peen before the final
clean up also helps. Another trick is to "roll the fillets" as per the Buick
V6 Turbo engines. That is, roll the end radius. This is however a job for a
specialist who most importantly is interested in your project. As for a
cross-drill, I prefer it to grooved shells, but in your case seek a second
opinion.
Now, the big bore to 3.7". You are damned if you do and damned if you
don't.
If you stick to the 3.5" bore, all the available heads will be restricted in
the breathing by valve shroud. A move to a bore of around 3.7" fixes this
very well. However there is not enough metal in the P76 block to hang onto
the big sleeves under severe duty when the block is bored out to accept them.
Some blocks by chance have more metal and end up in big bore but otherwise
stock motors that don't get a beating and in these cased, when fitted to a car
and not a four wheel drive, they give good service, provided the rest hangs
together.
So, in your case, you are stepping out into the unknown. You are using
a
longer stroke and bigger capacity, which will change the whole character of
the motor. The torque and horsepower points and the motors ability to rev.
Plus by using the long rods of the 350, your rod ratio will still be fair at
around 1.65, but will yield more power down low. Then again, the longer rods
and stroke will require a shallow piston (or lower pin height). Buick
discovered that this works very well in its new generation V6. It gives less
thrust against the cylinder wall. This decreases friction which increases
power and reduces heat and wear. In your case this factor would help your
sleeves.
The all up result of your modifications is that there will be bundles
more
torque and horsepower, which in turn will increase the stresses and loads on
your block. However, these will come in at different points in different
areas and at different rates. So there is only one way you will find out, and
like the turned down crank, you will just have to try it. Now a word of
warning and some advice. Firstly, only let the best machine shop in town do
your work, The sleeves must be fitted spot on. The radiuses on the crank
must all be as generous as possible and all clearances must, and I mean must,
be spot on.
As you may know, a build sheet is a must for this type of project. In
your
case an exercise book would be ideal. You must list and record every
operation. That is, what you used, who supplied it, who machined it and so
on. Then you must list all sizes and check everything yourself. Friend can
help, but not interfere. Then if you have a problem or are unsure of
something, you check the book.
Now, to the heads and cam. Buick 300 are your best option. I agree the
exhaust valve should be enlarged and that the ports should be cleaned up and
flowed. I also agree to a point that with 331 cubes to feed, they will
struggle a little. However, this is a lowish rod ratio. So, it will take
it's biggest breath down low and give you huge port velocity. This in turn
with less valve shroud from the big bore should produce monster torque, but I
feel that 5000 maybe 5500 rpm will see it out. Remember to get hardened valve
seats for the exhaust and bronze valve guide liners to handle unleaded fuel.
Plus to aid breathing and drop your compression, remove as much metal as you
can from around the valves. With the ports, you can only clean them up and
flow them a little, as the walls are thin. The general consensus is 1\16 of
an inch. Which means you can enlarge a port 1\8 of an inch each way. You can
also cut the guide down a little in the port, but don't over do it as they are
important for heat transfer.
Now oil and the cam. If you look at the P76 block, the provision for
the oil
ways to the heads are cast into the block. You simply drill it out with a
"long" drill from the engineering supplies (not cheap)… of course you must be
spot on with the angle. A simple jig is best. I use a piece of "onsize" tube
bronzed to a plate at the right angle. I bolt the plate to the block face and
carefully drill down, of course I punch and start the hole first. Then, in
your case use "Felpro" Buick 300 composite head gaskets with the oil hole.
The composite ones seal much better and button down at 40 thou, giving lower
compression than the "tin" 20 thou.
You can then use the stock Buick rockers, shafts and pedestals, with
the P76
push rods. They will be more than adequate for the revs you will be pulling.
As for the cam, start off with a big grind to help feed those ports. But
don't go overboard and not too much overlap. You need a cam that will work
for you down low. Lift is more important in a long stroke motor. Remember a
cam out of a 215 will work fine in a big capacity motor. Read up on cams and
seed advice. You may try several grinds before you get it right. Also
remember "big cams" work your valve gear hard, so do monster valve springs.
So don't go off to heavy with either. As you say, late Buick V6 and our
Holden run roller tappets which give quick lift and in turn longer duration,
without excessive overlap. This could be worth investigating. However, once
again, they work the valve gear very hard and require big springs. This in
turn could cost you reliability.
As for spark and fuel, well you can't beat the 350 electronic
distributor, I
would start with a 64 Buick 300 inlet with the later Carter carby (65 on).
You will need to use spacer plates to make it fit. Plus you will need to
enlarge and match the manifold port runners to the ports.
A couple of final points, no doubt you read Kurt's fabulous MG V8
Newsletter
and as such you would have read his article on high torque starter motors. I
think it would be safe to say you will need one. Next your balance man will
no doubt want you to stick with the 350 balancer and will tell you that metal
is easier to grind off the shaft than put it on. Also less weight you have
running around inside your motor, the less stress. So, get as light a set of
pistons as you can. Buick 350 rods are cast like the V6 and 300 rods.
Buick\Olds 215, Rover and Buick 455 rods are forged, so are the P76. However,
the 350 rods are reported to give excellent service and respond well to a
polish and shot peen (remember if you do your own polishing, you work down the
beam of the rod and not across). Also there are many books and articles on
porting, cams and so on. Find them and read them. Nothing beats doing you
homework.
We hope the last few pages of dribble will be of some help to you.
Your e-
mails to Kurt indicated that you have done a lot of research and that you
project is well advanced. We are most interested and like you, we have done
endless research over the years on what fits what.
Please keep in touch and let us know how each stage works out.
Kind regards and the best for the new year.
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OK, that's the letter folks. Tough stuff for sure.
Greg
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