Port Timing

[oldskool]

Can someone tell me if the port timing for a +4mil long rod crank and a +4 mil short rod crank is the same. I think I know, but I would like to hear the experts. Thanks

[Finch]

same as long as you use right piston per application. but i could be wrong lol

[Finch]

Good to know.

[oldskool]

False finch. Short rod and long rod cranks use different port specs their minimal differences but still changes are made to the cylinders to match which crank it you run

I believe you, but I dont understand since the top of the pistons are going to be at +2mil at TDC and +2 at BDC when using 795's for 115mm rod and I guess standard for 110mm rod

[Finch]

see i had a on going talk about this with my 392 long rod cub with 573 pistons every one told me it was wrong and this and that and should run right.. but squish was right and ran mean so im not to sure

[Coupelx]

The piston is at a different location in the bore due to the different angangle of the rod.

[Coupelx]

The pin hole is higher to compensate for the longer rod. Its simple. The longer dwell means the piston spends time at tdc and bdc.

[oldskool]

The pin hole is higher to compensate for the longer rod. Its simple. The longer dwell means the piston spends time at tdc and bdc.

Makes sense now. Thanks fellows

[Coupelx]

Depending on the piston used for the long rod setup it has a different crown profile.

[oldskool]

Depending on the piston used for the long rod setup it has a different crown profile.

You have to have domes cut for the pistons you are going to run(795) right?

[AKheathen]

you should have domes cut for either, just for better match, but you don't have to. in real-world, different motors are going to re-act differently, but, aside from the dwell time, the blow-down and some other timings and time-area will be effected a little. this should translate into a slight shift in the power being a little more or less peaky, but i don't think it will really make the motor "not run right" to a huge extent. ideal dome design might be a little different, since the small change in dwell time will effect squish velocity some. just remember, all these effects could add up, but not going to really turd a motor out. it should still scream either way.