4.0 Pistons on 4.6 Rotating Assembly - Rebalance?

StangGT5

Well-known member
Feb 4, 2019
295
130
Atlanta, GA
For those of you who have swapped 4.0 pistons onto a 4.6 crank and rod set, do you suggest having the assembly re-balanced?

I know it's probably unnecessary since there's only a small dish difference and 4500rpm is high RPM for these engines. Still figured I would ask. I've always rebuilt to stock, but this time I'm going with ported heads, a Crower 229 cam, and pistons from the 4.0 that is getting replaced. The 4.6 I'm using looks like a red block too.

20200910_214318.jpg
 

StangGT5

Well-known member
Feb 4, 2019
295
130
Atlanta, GA
When researching RV8 head work, I came across information from the swapped MG crowd. According to them, oversize valves don't help the RV8 much unless you have a heck of cylinder head. The exhaust port design on these heads is laughable, so they're probably right.
 

logan_gibson

Well-known member
Dec 20, 2016
258
47
Alabama
The ques

The question is, do oversized valves reduce engine torque at the lower RPMs used for off-roading or daily driving?
When researching RV8 head work, I came across information from the swapped MG crowd. According to them, oversize valves don't help the RV8 much unless you have a heck of cylinder head. The exhaust port design on these heads is laughable, so they're probably right.
" both the inlet and exhaust port pockets should be opened up to match the valve seat diameters. "

As to the torque, I cant say. Its just what you find when looking at building stroker engines.
 

Swedjen2

Well-known member
Sep 12, 2018
594
127
California
When researching RV8 head work, I came across information from the swapped MG crowd. According to them, oversize valves don't help the RV8 much unless you have a heck of cylinder head. The exhaust port design on these heads is laughable, so they're probably right.
Last year, I was researching replacement engines for a D2. I was looking at the ACR 4.8 Short Stroke. I emailed the owner a few times about his big valve heads. He said it adds 5 hp above 4500K.
Since I'm not going to enter the Dakar Rallye, I don't need the big valves.