67mustang302

Part of it is rod ratio, and the angle of forces relative to the crankshaft position. There comes a point when the change in those forces by going to a shorter stroke is negligable at best, and all you're doing is trading displacement for rpm. An argument could be made that stroking a block out increases the stress on it because of those angular forces etc, but the longer stroke setup generally turns lower rpm to make the same power as the shorter stroke setup, so the increased stress from the higher rpm of a shorter stroke basically cancels it out. Ultimately you're better off by trying to go to lighter pistons for the same setup, or a longer rod ratio for the same setup, but I wouldn't destroke an engine unless it were for a race class that required a certain displacement per weight or had some other rule that made it beneficial.

Some engines could benefit from destroking to make the setup more oversquare, to benefit from a larger piston surface area with the rpm capability of the shorter stroke.

Rajun_Cajun

Destroking it wont help it survive more hp. The limit for our 5.0 blocks is usually around 450ish to the wheels, though there are some out there that are surviving at 600 to the wheels. Just b/c you have less cubes, doesnt mean that you can run more boost/spray, or whatever you prefer. You still have to consider the weak points on our blocks are the main webs. Once you get to that certain stress point, there really isnt much you can do, except for pray that it will hold up. An extremely well prepped block will last longer than if you just throw any old 5.0 block and throw 15-20psi of boost at it. As said above, the correct rod angle comes into play. Too much, and your pistons will tend to rock back and forth in the cylinder.

Pearlkobra12

in NHRA thats what prostock cars do. but thats so they can ring up the rpm's.... doesn't seem to worth it unless your motor is like AMAZING and there is nothing else you coudl possibly do...

Rajun_Cajun

Thats correct. The better the rod angle, the higher RPM's you can turn. There is less binding with the piston and rod.

tooslow5.0

one thing you HAVE to keep in mind is the *rod to stroke ratio* this gets forgot about ALOT! if you dont know what this means, then dont play with engine stroke/destroke. its extremely critical to engine longevity, piston rings, connecting rods, etc..... there is a reason a honda b16 engine can rev to 10k rpms on a stock bottom end all day long, because the rod to stroke ratio is perfect. slap a b16 head on a b20(2 liter) block on the other hand and your snappind con rods all day long. I havent done the math, but id be willing to bet the ol' 289 has a better rod to stroke ratio than the 302, which would in turn make more power reliably.


food for thought.

tooslow5.0

sorry rajun- i didnt even notice that you mentioned it too---you know what your talking about

5spd GT

289: 5.155"/2.87" = 1.79
302: 5.090"/3.00" = 1.69

*Note: I never said anyone was better over the other.

With those "rod ratios", there is NO need to worry one bit.

Stroke it.

Joel5.0

Which is?.......

Rajun_Cajun

This should help you understand everything. Also gets me out of alot of typing...


http://www.fordmuscle.com/archives/2...ker/index2.php

Joel5.0

So higher R:S = engine longevity....... how come I keep working on regular Ford OEM 4.9 I-6 engines (R:S = 1.56) with over 300k miles on the odometer?...... no fuel consumption BTW. Why is it that I had a Toyota 3-TC 1.8L engine (R:S = 1.57) that I drove for +350k miles and revved, almost daily, to 6500 rpms+, dual side draft Weber carburetors, cam, etc?

Go for the cubic inches for power...... R:S ratio is what it is for the different stroker configurations...... or can you build a 347 in a 8.2" deck block with a 1.7 R:S?