[68hotbird]

Looking at combos and wanting opinion. I have a block that is 4.245 I can do either Combo 4.25 stroke bore to 4.350 or use my 4.250 bore and use 4.5 stroke looking for opinion on both combos. Will have high port heads that flow 375-380 ish.

[slowbird]

Bigger bore every time. Also shorter stroke will be easier on rods/pistons

[johnta1]

That may be true, but bigger CID probably makes more HP?

[krisr]

Originally Posted by johnta1

That may be true, but bigger CID probably makes more HP?

Wouldn't the HP output balance out with the extra revs that the shorter stroke should be able to provide? Depends what you're looking for, me personally a shorter stroke bigger bore is my favourite.

[mgarblik]

Will this be NA or a power adder engine?

[Half-Inch Stud]

Originally Posted by krisr

Wouldn't the HP output balance out with the extra revs that the shorter stroke should be able to provide? Depends what you're looking for, me personally a shorter stroke bigger bore is my favourite.

Hmmm yea, using Excel, if you can count you tire roll-out across the 1/4 mile, and multiply the engine turns *4 and * the rear & trans gear & Converter ratio, you would discover the number of Powerstrokes applied.

Then that would reveal the applied power across the 1/4 mile, for combos.

[AIR RAM]

Originally Posted by krisr

Wouldn't the HP output balance out with the extra revs that the shorter stroke should be able to provide? Depends what you're looking for, me personally a shorter stroke bigger bore is my favourite.

Agreed, At the end of the day, big bore, short stroke with a boost specific cam with 15-20lbs of boost will be hard to beat!

SPEED SAFE, NICK

[Bill Eveland]

What about a 4.375 stroke ?

[Scott Roberts]

Go with the larger bore.... not that a long arm cant rpm, but it will take more work... if I had to guess Langer turns 9200 rpm with a 572.... he works for it though....
I would say a higher revving large bore engine would be the way to go.... spread the power out...

[Stan Weiss]

Bore 4.35" - Stroke 4.25" - ci 505.3

Bore 4.25" - Stroke 4.5" - ci 510.7

So you are talking about all of 5.4 more ci's

Bore 4.35" - Stroke 4.375" - ci 520.2

(4.35" - 4.25") / 2 = 0.05" So if I have the room by the exhaust valve I can run a 0.1" bigger intake valve.

Stan

[gman005]

I have a set of 4.350 pistons if you are interested.

[68hotbird]

will be normally aspirated. May even be a pump gas combo before its over.

[mgarblik]

Thank you. Normally aspirated I would build the engine with the large bore. I have built both 4.250 stroke and 4.500 stroke versions. In a reasonably light car, I prefer the 4.250 stroke. 4.500 stroke puts allot of piston out of the bore and is hard on the skirts and piston rings. In a big power adder situation, I tend to go with a little smaller bore in a Pontiac as the potential for a larger intake valve is not as critical and the extra sealing area between bores is more of a factor under boost.