Short stroke, big bore, or long stroke small bore

[beached1]

I have recently destroked my 454 to a 427. Mainly because I got a killer deal on a forged steel crank and I like the idea of having a more durable bottom end. Then to compensate for my loss of Cu inches, I went with some forged pop up pistons. This is where I started to think that almost by default, I may be heading in a much better direction. In relation to a jet drive unlike a street application, if all things being close to or equal, wouldn't a shorter stroke work much better? Let's say for example you could have a choice or either having a short stroke big bore or a longer stroke but smaller bore but each would achieve roughly the same cubic inches. Wouldn't the shorty move a jet much more rapidly? A jet not only needs torque and HP but RPMs as well. In my case I have lost CU's but gained comp (pop ups). With a better crank and rods, I think I have put togther something that will not only give me more reliability but more usable horsepower where I need it most. Just thought I would post this and see what you guys think. I will let you know if my changes helped me at all soon.
Thanks,

[kojac]

I have been talking to engine builders and other jetboaters and they all tell me big cubic inches.
But I agree with you and tend to think that if you were to build a shorter stroke, Bigger bore, and longer rod motor similiar to prostock configuration but not necessary that extreme you would be better fitted to a higher rev motor. I think this would raise the torque curve. Of course bigger cubic inches does make torque.
I just question if big cubic inches {big stroke and Bore} will put you in the rpm band that is better for jetboats.
I think a better answer is 427 stroke 4.620 bore, 7.9 rods or as long as you can get to fit in the block, and a long duration cam with decent compression would be a perfect combination for a jetboat application. You would need a full port job on good heads to maximumize the combo. If anyone out there has the dyno on his computer I would like him to run the combo with this cam spec. Lift .714 intake and ehaust 270 degrees intake 276 degrees exhaust @.050 112 degree centerline. Or if you have already built a similiar engine combination Let us know how it worked. Just My .02
Kojac...

[bobz]

torque is the answer and thats why they picked olds and ford 429 motors lots of power and low rpms. the pump is most efficent the lower the rpm and "aa" impellor. less cavitation more water.

[wideopen545]

stroke plus cubic inch makes horse power i thought

[cyclone]

Having a motor with a Larger bore and shorter stroke reduces piston speed and friction. Less friction equals more power. A good example is the Gen VI 502. GM used a siamese bore to increase the standard 454cid bore from 4.251 inches to 4.4460 inches. Combining the larger bore size with a standard 454 crank yielded a 502cid motor that made more power without increasing the piston speed and friction.

[77charger]

i ran a 460 before i now run a 429 which is a short stroke and more compreesion too.I would say that the 429 is better for me there was no loos in power only gained and fell better reving the short stroke to the 429. A 460 to a 429 (bbf)is like a 454 to a 427.(bbc) same bore for each make but make shorter strokes

[Boater Bill]

I think its neat that you went the opposite direction most of us would go. It will be fun to see how it responds in your ride. Did you put those good heads on?

[HOSS]

I personally would rather a shorter stroke for RPM capability. A 396 will out rev a 454 any day. It really comes down to what is your NORMAL operating rpm range PERIOD. A motor needs to be built for your personnal driving habits. No matter what surface or conditions. I personally have a heavy foot especially after I get 12 Bud lights in me. And we all know that time and alcohol kind of overlap if you will. So if sober you are at 3400 for 15 min. Then loaded you will be at 4200 for 45 mins minimum. Again, what motor do you think would live longer?
I know, I inserted foot, someone has done 8g on pro whatever and Slick for 24 hrs straight. Get real. I agree with destroking and deals are there since the masses are going in the other direction. Cost is the final frontier, not technology. Ok, you say, " whatever you do to a small motor you can to a big motor therefore you can`t beet cubes". I agree 100%. But if I can get by with 10 to 14g as opposed to 35 to 55g and feel safe as to longivety and idle quality, there is no comparison. And juice, well lets just say I`d rather benn using my boat than in the driveway fixing it.

[bajaruner]

Long stroke, big bore,= more torque, and horsepower at a lower RPM.
Long life engine, and big power = happy owner, fast boat, and more time to drink beer!
There no replacement for displacement!
Nuff said.

[HBjet]

beached1, good job on your choice to go the other route then most of us. I knew a few guys that can sell you a Panther pump if you really want to spice things up... http://free.***boat.net/ubb/smile.gif
Just messing with you bud, It will be interesting to see who it runs this year. Didn't you get some pump work done this year too?
HBjet