Turbo V8 - Bore or Stroke?

[88hurstolds]

I'm building a turbo motor out of an Olds 350 DX Diesel Block. These blocks are very stout and can handle just about anything you can throw at it and are capable of a 440 ci bore using a stock crank with no issues since the cylinder walls are very thick.
I'm looking to generate 600-700hp out of this motor and possibly bore it out to 442ci. or grind a custom forged crank to achieve said cylinder volume. Do turbo motors generally not like longer stroke? Is it better to bore the block out to gain the extra cubes? i.e. is it better for turbo motors to be oversquare or undersquare?
Just starting out so bare with me on the stupid questions...

 

[KL Mallender]

As I recall, Mondello was (is) one of the leading Oldsmobile builders in the country, I found this: Mondello Performance Products-440 Olds Stroker Small Block

As far as the bore/stroke decision, I would think head decision would dictate what your shortblock needs will be, if head flow is restricted there would be little reason for high-rpm (short stroke) choice, but a bigger bore should help head flow if shrouding is a problem, always a compromise isn't it? LOL.
Good luck with your build, Olds engines are a stout breed.

Kevin.

 

[novaderrik]

i don't think it really matters much, except a longer stroke will give more low end torque to carry you until the boost comes in.

 

[Blazer406]

IMHO, the old addage applies.... there is no substitute for cubic inches.....

With that said.... I think (if memory serves me) you have to put a 425 crank in there to get the big cubic inches out of that block.

Also....I wouldn't get way out of whack with my rod length to stroke ratio.

After digesting all that.... you only want 600 - 700 HP?

You could do that with a stock 350 ci diesel based motor...... there are guys on here doing it with 231 ci and pump gas and alky..... with relatively poor flowing heads. It shouldn't take more than 14psi on a 350ci motor to make those HP numbers you seek if the combo is right.....

 

[88hurstolds]

Thanks guys, I've got a better understanding now.

I've met Joe Mondello a couple of times, he's an extremely nice man and does some fine work.

I definately want to keep the rod lenght to a minimum to avoid bent rods and reduce rotation weight. I wasn't sure if a longer stroke motor is deamed toast when you start adding boost since these Olds motors are known for this.
I figured I'll bore the crap out of it, put in main spacers and run a smaller journal crank. Most guys put spacers in and run a forged 330 small block crank in these since the DX 350 has a big block main journal diameter.
The less surface area the better on the crank surfaces but isn't it better to have a larger bore to allow for more surface contact with the incoming pressure? After all Force = Pressure * Area

I found some good specs to help me calculate what would be optimal for converting an Olds motor to become a turbo motor, I figure if I stay with the bore/stroke ratio and keep the compression ratio down, now time to do some math

Here is a nice article I found as a baseline:

TA Performance Aluminum Turbo Buick V6 Block - Air Fuel Management, Engine Tech Specs - Hot Rod Magazine

 

[Blazer406]

Let em re-state.....

If you are only looking for 600-700 HP..... save the $$ and just build a stock displacement diesel based motor. You should be able to get the power you need without spending any $$ on boring or stroking..... custom pistons etc.

I'd be looking for some 8.5:1 to 9:1 forged pistons for your motor.

I definately would not want to run main spacers for a smaller diameter main. The stock diesel rods had full floating pins too.

Downside is there is only 10 head bolts.

Even at 700 HP.... you are going to need the extra $$ on trannys and sticky tires.... and rear end parts......