Ported 390xp vs. Ported MS460

[Mattyo]

ok.... but doesn't the same analogy fit for F1 cars vs muscle cars? same hp, just one is better for something vs something else. short stroke revs higher but w/ less torque.

 

[MG2186]

That is my question and does the rod-stroke ratio make as much difference as it does in in a 4 stroke application. No one seems to ever look into that aspect of chainsaw engine performance


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[jmssaws]

A mm of rod length will make more power than a mm of bore.

I'll take a extra mm of stroke everytime

 

[MG2186]

A mm of rod length will make more power than a mm of bore.

I'll take a extra mm of stroke everytime

Are you referring to longer stroke or a longer rod because if you have longer stroke doesn't always mean you have a longer rod, actually it's quite the opposite in most applications. That is why everybody makes over length rods for Chevy's. The optimum rod-stroke ratio has always been 2:1 if possible to achieve in the application

 

[jmssaws]

Stroke.

A longer rod is good too,takes angle away and helps bearings.

 

[jmssaws]

A mm of stroke makes more power than a mm of bore.

 

[MG2186]

Stroke.

A longer rod is good too,takes angle away and helps bearings.

Yes and makes more torque, anytime you can straiten the rod angle is always a big advantage! Develops more torque and does relieve stress and load off the bottom end

 

[sawfun]

The dwell time is increased thereby allowing more time for fuel entry into the cylinder. Anytime the crank can rotate more degrees while the piston is at BDC, this occurs.

I don't know if this is still being given used but in some very high rpm 8 cylinder applications, a short rod was tried in the early 80's. It may have been in 180 degree V8 engines. Rod ratio vs fuel burning speed likely plays into it as well. So does over vs under balancing.

 

[MustangMike]

As mentioned above, a different stroke will play with the port timing in a 2 cycle (unlike in a 4 cycle, where the cam dictates it).

Also, in cars, most now have longer strokes vs bore because they (for some reason) seem easier to comply with emissions.

With the newer technology in rod & piston strength, an overbore engine (for high RPMs) is no longer as important.

And, as my brother (who is a PE) points out, chainsaws must have an overly strong rod as you can change pistons w/o re-balancing, and they don't blow up at high RPMs.

 

[MG2186]

When emissions started playing into how engines were designed they went towards more stroke and shorter rods. The 454 had a horrible rod-stroke ratio compared to a 396 & 427. A SB 400 is even worse! This all started in the mid 70's


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[MustangMike]

I think the (short lived) 429 Ford was one of the worst offenders. The stroke was only 3.59 (compared to 3.78 in a 390). The 429/460 engine family, and 351 Cleveland/Boss 302 engine family were designed by former GM employees who defected to Ford. (and had canted valves like the Big Block Chevy).

 

[MG2186]

I was told the same thing by an engine builder that the 460 was very similar to a 454 in its build design that makes sense now


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[MustangMike]

The reason the Boss 429 engine was not a big hit at NASCAR was not because it did not produce enough power, and the aluminum heads made it just as light as the Ford 427, but due to the bigger bore size, the engine block was longer, so with both engines against the firewall, too much of the 429 extended in front of the front wheels, which hurt handling and launching. In short, the car was not designed for the engine. A lot of racers ripped it out of their 69 Talladega's and put the 427 back in the car.

 

[Chainsaw Jim]

ok, so the 460 and 064 have 52mm pistons... does the 064 have a longer stroke?

whats the 390's excuse? 55mm bore makes sense vs the 460 that its faster. .... doesn't make much sense that the 064 is that much faster than the 460 based on bore size

It's a 54mm top end from an early 066.

 

[Hedgerow]

A 064 is awesome and a 390 isnt

Yes. 064's, like 372's and 346's are just mo bettah than they're counterparts.

Though I have run a couple 390's that were pretty special..

 

[mdavlee]

Yes. 064's, like 372's and 346's are just mo bettah than they're counterparts.

Though I have run a couple 390's that were pretty special..

52mm bore is where it's at

 

[Hedgerow]

9010's a 52 mm bore too..

Even longer stroke.

 

[Chainsaw Jim]

9010's a 52 mm bore too..

Even longer stroke.

I imagine a 54mm top end on it would be a freak show.

 

[Hedgerow]

I imagine a 54mm top end on it would be a freak show.

Idk.
I think I'd rather have the 52..

But that's just a hunch.

 

[MG2186]

Yes. 064's, like 372's and 346's are just mo bettah than they're counterparts.

Though I have run a couple 390's that were pretty special..

My 2186 ain't as fast as 064/066 but I still love it, dam bit sexier for sure!