The next 066 top end

Toying with several ideas for the next 066 top end.

Blue is a stock NWP BB. 174 intake, 170 exhaust, 30 blowdown

Red is same except transfers raised to 26 blowdown. Brad Snelling had suggested that I try raising the transfers. Good call, Brad. :msp_thumbup:


I'm also looking at a custom head for an OEM jug, but it's going to be tough to beat the BB. More later.

Here's a particular OEM jug I've got laying around. It has good plating all the way to the top, well shaped ports, and port widths are already maxed out as it comes from the factory. However, the combustion chamber is HUGE (10cc) so compression will be low.

Blue is the OEM jug with squish set to 0.020". 158 intake, 168 exhaust, and 20 blowdown.

Red is the same jug fitted with a custom 7cc head.

By comparison, the factory claims 6.8 - 7.2 HP, depending on the year. MOTA is known to be wildly optimistic at high RPM, so I look at the 10,000 RPM power, where you're actually going to be cutting, and ignore the 13,000 RPM stuff.


Comparing the BB to OEM:

Blue is the NWP BB with transfers raised to 26 blowdown.

Red is the OEM with 7cc head.


As much as I'd enjoy making a custom head, it appears that it's easier to get power out of the BB.

The bad news is that I haven't found any more easy gains beyond what I've already shown you.

Did you happen to try 20° of blowdown? BTW, that's a super low intake! See what raising that up to 160° duration does.

Will have 158 intake later tonight, will try 20 blowdown tomorrow night. On the BB, I mean.

Blue is the previously posted NWP BB with 26 Blowdown.

Red is the same except intake magically changed from 174 to 158.


Well, that didn't go as expected. 158 intake SOUNDS good and 174 intake SOUNDS crazy, but 174 intake works better at normal cutting speeds.

Wow, that's a lot of intake, but Mota seems to like it. Looking forward to seeing what the transfer changes make.

Tweaking the blowdown on an otherwise stock NWP BB.

violet is stock (30 degree blowdown)

blue is 26 blowdown

red is 21 blowdown


Looks like 26 blowdown is closer to optimal.

This jug has actually had the intake and exhaust widened, so I'll rerun the 26 blowdown with the wider ports.

Too much intake isn't a good thing I just tried a saw of mine that had a LOOOOONNNNNNNNNNNGGGGGGGGG intake duration, it sounded like an old hand-crank tractor. In a nut shell, that top end is gone.

Both of these are the NWP 066 BB with transfers raised to 26 blowdown.

Red is ported (exhaust 2mm from skirt, intake 3mm from skirt)

Blue is stock intake and exhaust


So porting helped a wee bit, and didn't hurt anything.

mtngun said:

Looks like 26 blowdown is closer to optimal.

Click to expand...

Looks like 21 BD was equal to or higher than 26 at all times.

blsnelling said:

Looks like 21 BD was equal to or higher than 26 at all times.

Click to expand...

True above 7000, but the difference is tiny.

If you were building a race saw, you'd take any little gain you could find.

Since the crazy 174 intake duration worked better than expected on the BB, let's see how the OEM jug likes more intake duration.

Violet is the ported BB with 26 blowdown

Red is the OEM with custom head and 170 intake, otherwise stock 168 exhaust and 19 blowdown.

Blue is the OEM with custom head and 165 intake, otherwise stock.


Now the OEM jug is nipping on the heels of the BB. I'm thinking to go with the OEM setup, since I have everything I need to make it, while I'm short a piston for the BB.

Note that very little low end power was lost despite the high intake duration.

This beats guess porting. :cool2:

Thanks for all the hard work and info sharing. It certainly helps explain why my 066BB runs so well. It has:

Exhaust 168
Intake 174
Blowdown 25

It is by far the strongest 066/066BB I've run.

mtngun said:

Both of these are the NWP 066 BB with transfers raised to 26 blowdown.

Red is ported (exhaust 2mm from skirt, intake 3mm from skirt)

Blue is stock intake and exhaust

So porting helped a wee bit, and didn't hurt anything.

Click to expand...

Maybe I'm reading wrong, but why does it show on the right, the HP and torque way less then what the graph shows?

parrisw said:

Maybe I'm reading wrong, but why does it show on the right, the HP and torque way less then what the graph shows?

Click to expand...

Will, the HP and Torque numbers in the boxes on the right show the power at one particular RPM -- where the cursor is placed. I usually place the cursor at 10,000 rpm, but on that chart the cursor happened to be randomly placed at 4,918 rpm when I captured the screenshot. :msp_rolleyes:

mtngun said:

Will, the HP and Torque numbers in the boxes on the right show the power at one particular RPM -- where the cursor is placed. I usually place the cursor at 10,000 rpm, but on that chart the cursor happened to be randomly placed at 4,918 rpm when I captured the screenshot. :msp_rolleyes:

Click to expand...

Ok, thanks. Kept wondering WTF?? I'm used to seeing just peak HP and torque graph numbers.

Once again great info. I've recently seen a ported cylinder with really long duration, longer than normal, seems some cylinders respond well to this.

A fixture for holding jugs ...... and pistons, too. :msp_wink:


There's no going back now ....


Dialing in the bore before making the final cuts.


Jug is done.


That's as far as I got this weekend. This is new territory for me, so I'm going real slow. :msp_rolleyes:

mtngun said:

A fixture for holding jugs ...... and pistons, too. :msp_wink:


There's no going back now ....


Dialing in the bore before making the final cuts.
Jug is done.


That's as far as I got this weekend. This is new territory for me, so I'm going real slow. :msp_rolleyes:

Click to expand...

That looks pretty good! How would you do a Husky Jug?

Sweetness. Looks like fun.