Can someone please educate me on a couple of things?

First, is a 4.125 or a 4.25 stroke crank going to fit inside a Mk. IV 454 block without any cutting? This is a late 70's short deck block with 4 bolt mains.

Second, what is the advantage to running a longer than stock connecting rod? On a stoker are they pretty much necessary?

Any help is appreciated!! :chevy :flag

 

The 4.25" stroker crank will fit, however it does require clearencing for the connecting rods. This entails grinding at the bottom of the cylinder walls.

You really want to keep an eye on your rod/stroke ratio when building a stroker. If you use a 6.135" (stock length 427/454 rod) on a 4.25" stroke crank you have a rod/stroke ratio of 1.44. You would have to shift the motor by 6000RPMs otherwise the piston speed would be to great and your motor won't last very long. Thus the need for a longer connecting rod, then you start messing around with wrist pin heights and whatnot....then I'm out of my element.

Maybe someone a little more knowledgable could help out, I've said about all I can say on this topic. :D :cheers:

 

Thanks for the reply Bence. If I'm not mistaken you built up a pretty stout 454 a while back. How'd that motor turn out?. I was impressed that you did most of it yourself.

Thanks for the info on the rod clearance and ratio. I gather the lower the ratio the less you can rev it safely? I have seen some piston/rod combos even with the same stroke (not just 4.25's), that involve different size rod lengths and I can't understand how they affect the motors performance and longevity. I can see that one advantage to a longer rod is less piston weight, but I bet you gain some weight with the heavier rod so maybe weight savings isn't the point. Another mystery for someone like myself. Thanks for the help.

 

Interesting... On the 512ci currently in the roadster. It has a 4.25 stroke, bored .125 using 6.135 rods and on the strip the shift points are normally set at 7000 rpm, and the motor is holding up quite well.

 

marky mark:
The motor turned out great! Ran a best of 12.40 @ 116mph. I have since switched to 4.11 gears and 11.5" ET Streets. With some tuning I am hoping to get the MPH up to around 118-119. I'm also hoping for 11s come spring.

As 70PurpleLS7 pointed out it's not that you can't safely rev it to a higher RPM. The stock 454 with a 4" stroke has a rod/stroke ratio of 1.53 and with a 4.25" crank it will have 1.44. Comparing the two at 7000RPMs, the 4.25" stroker motor will have a greater piston speed at 7000RPMs than the 4.0" stroke motor. The higher piston speed would indicate more stress on the rods and pistons. FYI if you want to go the stroker route EAGLE has a stroker kit to make a 454 into a 496....hmmmm the kit lists a 6.385" rod. The 6.385" rod gets the rod/stroke ratio back up to a 1.50...closer to that of a 454.

The longer rod supposedly put the piston rod combo at a better angle whenever it's thrust back up towards the combustion chamber....I'm really not sure about this part so maybe someone else could chime in. If you do decide to go the 496 route (which I was contemplating) get ready for a boat load of torque :yesnod:.

70PurpleLS7:
That's not to say that it will come apart right away. It may last a while, but with time the piston speed will be too great. 1.44 is not a good rod/stroke ratio by anymeans. The redline on my 454 should be around 6750 taking into consideration my rod/stroke ratio...I've had it to 7000RPMs. The bottomline is that RPM kills parts faster than anything...even moreso with a motor with a lower rod/stroke ratio.


[Modified by bence13_33, 6:25 PM 2/27/2003]