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purely theoretical... Can you have too much stroke?
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journeyman
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PostPosted: Thu Oct 08, 2009 1:37 pm    Post subject: Reply with quote

Practical solutions:


Since I have a 9.8 deck 454, the logical thing to do is stick with what is readily available: 4.25" or possibly 4.375" stroke rotating assembly.

Anything else would be cost prohibitive and a LOT of research work.




But I still would love to build a 4" bore 5" stroke tall deck....


Very Happy Someday
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gilletteracing
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PostPosted: Sun Jan 10, 2010 4:51 pm    Post subject: Reply with quote

Piston speed is a good thing, right up to the point of ripping the wrist pin out of the piston. Stroke limits rpm, the more stroke the less rpm you can turn before piston failure.

With any engine you build you want max piston speed or you will end up with an inefficient engine. There is a point of diminishing returns the closer you get to max piston speed. (what you gained in efficiency from 100 to 200 fps piston speed, you wont see the same gain from 200 to 300 fps)

Its all in what your building. Comparing two different 500 cid big block chevys, one in the truck pulling the race car and the other in the race car.

A low rpm, high torque, all in by 4500 rpm (truck engine) i would do a long stroke small bore. The right head for this application is not going to have a 2.400 intake valve so valve shrouding is not a problem. This engine will have a high rod to stroke ratio but with a max rpm of 4500 and a small bore, cyl wall side loading shouldn't be an issue.

Now if your building a 9800 rpm prostock type (race engine), you have to decrease stroke to handle the rpm you want to achieve. Also you will have a serious cyl head with a big valve so shrouding and intake runner flow come into play. You will want as big of bores as possible and a stroke that will give you the piston speed you desire at 9800. Also with the shorter stroke and the longer rod your rod to stroke ratio will be less and less side loading on the block

There is a lot of other factors that play into things but there is something to go by.
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journeyman
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PostPosted: Mon Jan 11, 2010 4:15 pm    Post subject: Reply with quote

In our application the engine will NEVER see 5000 RPM, and almost all it's time will be spent from 1800 - 3500.

In the current project I ended up with a departure from my original intent: ended up with an LY6 6.0 liter.

However, down the road our second 454 will be ready for an out-of-frame, and I am contemplating using a tall deck, small bore block stroked to achieve ~ 454 inches, i.e. 3.935 bore X 4.75 stroke = 462ci
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Big Dave
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PostPosted: Mon Jan 11, 2010 8:41 pm    Post subject: Reply with quote

I never saw the power I thought I would get out of my 582. At first I thought the bores where too thin (punched out to 4.600 which is the max the block will take), but in retrospect I suspect it is a ring seal issue. I attribute this to low drag thin rings and the longer than stock stroke (4.375"). It has been suggested that I would benifit from a vacuum pump but I like a stone stock look as I am attempting to pass it off as a 402 pick up truck motor.

Big Dave
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journeyman
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PostPosted: Tue Jan 12, 2010 12:38 am    Post subject: Reply with quote

Big Dave wrote:
I never saw the power I thought I would get out of my 582. At first I thought the bores where too thin (punched out to 4.600 which is the max the block will take), but in retrospect I suspect it is a ring seal issue. I attribute this to low drag thin rings and the longer than stock stroke (4.375"). It has been suggested that I would benifit from a vacuum pump but I like a stone stock look as I am attempting to pass it off as a 402 pick up truck motor.

Big Dave


So you suspect the brand/style of rings was the culprit in not delivering the power?

Did you have excessive blow by?
Do you think the extra ~10% stroke length gave you too much piston speed?
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Big Dave
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PostPosted: Tue Jan 12, 2010 4:16 am    Post subject: Reply with quote

Actually I think I was a little too generous with my filing the ring gaps for the amount of anticipated nitrous, coupled with ring flutter as the culprit.

Big Dave
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FRITODAVE
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PostPosted: Wed Jan 13, 2010 2:07 am    Post subject: Reply with quote

Gilletteracing your spot on here. The late great C.R. Axtell gave me some great info on this. Piston speeds/stroke is absolutely everything. The forgotten speed secret is "piston speed". It really determines almost everything and is directly related to stroke. An engine's limit in total power is piston speed. Of course power adders and forced induction throws a monkey wrench in. There is a calculation but I think it might have changed in the last few years for whatever reason.
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