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Mon Mar 30, 2009 10:13 am

Hello,

I have searched this, but to no avail... :)
What are the maximal practical RPM's for an 40HP - STOCK - engine ?
As well for a 1300 , 1500 and 1600 dual and single ports ... all stock :)

THANKS :)

Mon Mar 30, 2009 11:13 am

A stock non-counterweighted crank is good for only 4,500 to 5,000 rpm maximum. However, as a practical matter, you will start losing power before then. If you look through the owner's manuals available here, you will find that the 40 hp made peak power at 3,900 rpm, the 1300 at 4,000 rpm, the 1500 at 4,200 rpm, and the 1600 SP and DP at 4,400 rpm. Thus, as a practical matter, there's no need to rev much over 4,500 for any stock engine, as hp begins to drop off before then.

Mon Mar 30, 2009 11:22 am

Built and tuned correctly, a stocker can drive and maintain 4000rpm for extended periods.

My old 63 buS got 31.1 mpg doing 4000rpm @ 65mph on its last long highway drive. They really seem to sing at that rpm.

Mon Mar 30, 2009 11:41 am

Mon Mar 30, 2009 12:27 pm

4501. The price is right!

Mon Mar 30, 2009 12:28 pm

4572 :wink:

Mon Mar 30, 2009 12:31 pm

[Drew looks at Chris ominously] "Are you sure?"

Mon Mar 30, 2009 12:35 pm

$1 :lol:

Mon Mar 30, 2009 1:04 pm

Mon Mar 30, 2009 2:39 pm

My stock uncounterweighted crank went to 7,000 all the time but 8,400 ONCE!!!!!!

Mon Mar 30, 2009 3:26 pm

Jeff Gill wrote: My stock uncounterweighted crank went to 7,000 all the time but 8,400 ONCE!!!!!!

Don't buy used engines from Jeff...

Check.

Mon Mar 30, 2009 5:32 pm

Flywheel came loose after that, bearings and crank where still good though. Im not saying it is the correct thing to do but when your young and dont have the money, you tend to do things like that, and I dont sell them

Mon Mar 30, 2009 7:00 pm

Jeff Gill wrote: Flywheel came loose after that, bearings and crank where still good though. Im not saying it is the correct thing to do but when your young and dont have the money, you tend to do things like that, and I dont sell them

I think Kook was just being funny. :wink:

Wed Sep 17, 2014 6:17 pm

A stock crank can be balanced to 8000 rpm without the need for counterweights. Why use them if you don't need them. The cranks are forged and quite able to handle that speed. But in stock mode, 4200 should be about right so you don't pound out your bearings.

Wed Sep 17, 2014 8:02 pm

Stock valve springs can't handle over 4500 RPM's either.