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 Post Posted: Fri Apr 28, 2006 3:55 am 
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What is the limit for crank stroke in a GM Gen IV block? Would a 4.25 stroke be ok? Am I correct in that a 4.25 stroke with a .060 overbore equals 524cu. in.? Thanks!

-Tanner
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 Post Posted: Fri Apr 28, 2006 6:40 am 
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Tanner wrote:
What is the limit for crank stroke in a GM Gen IV block? Would a 4.25 stroke be ok? Am I correct in that a 4.25 stroke with a .060 overbore equals 524cu. in.? Thanks!

-Tanner
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Yes you can use a 4.25 stroke, It might take a little bit of grinding on the pan rails and bottoms of the opposing cylinders. Some blocks dont need any grinding, some do.

no it does not make it 524 C.I. it would make it 496 C.I.


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 Post Posted: Fri Apr 28, 2006 7:45 am 
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Thats what I run, pan rails were good to go. I had to clearance the bottom of the cylinders as you said. I am running eagle rods, some rod may clear though.
Greg


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 Post Posted: Fri Apr 28, 2006 2:54 pm 
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So what is the max dependable stroke crank that you can through into a GM block? Clearing the cam would be the limiting factor, correct?

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 Post Posted: Fri Apr 28, 2006 4:15 pm 
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Tanner wrote:
So what is the max dependable stroke crank that you can through into a GM block? Clearing the cam would be the limiting factor, correct?



Tanner for the stock Mark IV block 4.25 stroke crank is about the limit....if you are using the tall block you can go up to I think 4.50.....but the to go any higher you would have to go with an aftermarket tall block..... :-k

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 Post Posted: Fri Apr 28, 2006 6:50 pm 
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That's what I needed to know, thanks!!!
\:D/
-Tanner

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 Post Posted: Sat Apr 29, 2006 8:02 am 
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Hello
A .060 over BBC with a 4.5 in crank gives you 526 cubes. I also was trying to find out about the 4.5 in crank in a BBC(truck block 10.2) a little while ago
I have 454 pistons with the pin up .250 and a .400 long rod (6.535)
I will be a while before I do mine, so I would like to hear how your combo works out for you
take care
Tom


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 Post Posted: Sat Apr 29, 2006 12:50 pm 
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I won't be using a tall deck (truck block). From what I'm being told a 4.325 is about as far as I can go in the short deck. Reason for stay with the short deck is to keep the same header locations. :-$

I have decided to grab a 4.25 crank and run with it!

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 Post Posted: Sat Apr 29, 2006 6:30 pm 
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[quote="Tanner"]I won't be using a tall deck (truck block) Reason for stay with the short deck is to keep the same header locations. quote]

With a 10.200 Tall Deck block the header location will change some, but they will only be .200 higher and .200 wider its not as bad as it sounds

And you can fit a 4.500 stroke crank in either style of the production blocks.


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 Post Posted: Sat Apr 29, 2006 8:43 pm 
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There are some advantages to running the tall block. you can put a longer rod in it and still use a standard short deck piston with the 1/4 stroker the longer rod takes some of the side presure off cylinder walls. the early 427 truck block was a bit tougher in the cylinder wall area too. Back in the day, all the fuel burning guys would drool when they saw an old grain truck lol.

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 Post Posted: Sat Apr 29, 2006 9:27 pm 
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Bubstr wrote:
There are some advantages to running the tall block. you can put a longer rod in it and still use a standard short deck piston with the 1/4 stroker the longer rod takes some of the side presure off cylinder walls. the early 427 truck block was a bit tougher in the cylinder wall area too. Back in the day, all the fuel burning guys would drool when they saw an old grain truck lol.



And now you cant give the Truck Blocks away. I had a chance last year to buy 7 brand new ones for 480 $ ea. and in a week I couldnt find a single person interested in one.


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 Post Posted: Mon May 01, 2006 7:46 am 
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Interesting, when I put my ideal 496 into the DynoSim and then switch out the crank to a 4.5 stroke, the only thing it does is lose 20hp and gain 20 lbs foot torque. Kind of anticlamactic, I was expecting quite a bit more change than that from the 26 c.i. worth of change.

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 Post Posted: Tue May 02, 2006 7:19 pm 
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Tanner wrote:
Interesting, when I put my ideal 496 into the DynoSim and then switch out the crank to a 4.5 stroke, the only thing it does is lose 20hp and gain 20 lbs foot torque. Kind of anticlamactic, I was expecting quite a bit more change than that from the 26 c.i. worth of change.



How can it gain torque and loose HP ? Peak Torque at a lower RPM ?
and how did it compare throughout the entire RPM range not just peak ?

Try some more lift on the cam or 1-2* wider lobe sep.


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 Post Posted: Tue May 02, 2006 8:02 pm 
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you increased the stroke which increases torque. in your case the hp was maxed. and dont forget those programs use engine combos that made hp and torque and may not register all cid factors. in other words they used the same cid motor to determine hp but substituted the torque for the increased stroke. these programs are only base lines to build an engine and actual #s may be significantly diffrent. tony. \:D/ \:D/ \:D/ \:D/

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 Post Posted: Wed May 03, 2006 4:28 am 
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I realize it's just a baseline, I was just surprised it didn't give a higher results through the power curve. Given keeping the same heads, cam and all other internals, what do you guys guess a real world improvement someone would realisticly see going from a 4.25 stroke to a 4.5?

-Tanner

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