All the clearances had been checked.  The compression ratio had been verified.  Time to put it together and see how it runs.  I followed standard assembly procedures.  Once the engine was back in the frame, I filled the crankcase with Castrol 20W-50 V-Twin motorcycle oil.  Then pre-lubed the top end by filling the reservoir (trough) below the cam lobes with an oil can.

It fired up and ran good.  The idle was a little cobby for a while but eventually it smoothed out.  It felt frisky, was quiet, and the vibration levels were low.  No leaks.
 
I proceeded to break in the new piston.  I checked fuel mileage three times during the break-in.  I was impressed.  On the first mileage check it got 73 mpg.  That seemed like it was too much.  Thought I might have made a mistake.  The second check it got 65 mpg.  Less but still better than I had ever observed on the Savage.  Third check it got 69 mpg. Man, this thing is efficient.
 
After it passed the 400-mile mark, I took it for a long ride (for me). About one-third of the ride  was haulin freight on the freeway, about one-third on 50 mph country roads, and one-third on 40 mph surface streets. It went 114 miles on 1.48 gallons of fuel.  There was nothing gentle about this ride.  It wasn’t an attempt to set a fuel mileage record.  It got a whopping 77 mpg.
 
After it passed the 500-mile mark, I did another long run, only this time I rode it full bore.  Plenty of WOT.  Lot’s of freeway.  After 102 miles it had sipped 1.42 gallons of fuel.  The little 94mm took a lickin, kept on tickin, and got 72 mpg under some pretty aggressive riding.  That made a believer out of me.  It’s not an anomaly.  Five fuel mileage checks and every one showed fuel economy at 65 mpg or better.  The average fuel economy works out to 71.2 mpg.  I guess that gradually-increasing quench zone gets the job done.  My concern over the spherical dish has been put to rest.

How’s the power?  It felt powerful, with a willingness to rev fast, but the seat-o-da-pants dyno doesn’t cut it.
 
In preparation for this project, I did some baseline tests on the 94mm Wiseco Pop-Top.  The intent of the project was to see how the two pistons compare.  So, the two setups would be identical except for the pistons.  Same crankcase, same cylinder, same head, same cam, same carb, same air filter, same exhaust, same ignition, same flywheel, same gearing, etc.  I even used the same old spark plug.  The only thing different was the piston.

The benchmark would be a 3rd gear pull from 4K to 7K at my standard test location.  The 94mm Wiseco Pop-Top engine did that pull in 6.68 seconds.  That’s the benchmark.

The Flat-Top engine did that 3rd gear pull in 5.65 seconds.  That’s impressive.  It’s over a full second faster than the Pop-Top piston.

During the break-in, as I started to ride it a little harder, it was evident that there is more mechanical noise.  The piston clearly rattles a bit.  I can’t help but wonder if the skirt were a little longer would it reduce that noise?  I don’t know what effect that will have on longevity.  It’s not obnoxious but it is unsettling.  As I mentioned earlier, forged pistons make more noise than cast pistons, and I have a bit more clearance than Wiseco recommends.  At this point, I’m not too concerned about the noise.

At a little over 500 miles, I checked valve clearance, inspected the spark plug, inspected the piston with a flexible camera, checked compression, and checked my breather can for oil.  The valves were all .005”.  The spark plug was pretty dark and there was no evidence of detonation.  It’s getting enough fuel.  The piston looks great (what I can see of it), no sand blasting, pitting or missing chunks.  It seems to be doing fine on 92 octane.  Compression has bumped up to 230 psi.  The breather can was dry, no indication of excessive blow-by.

Here’s a look at the plug.  My best acceleration times were with a 230 main jet and the air/fuel meter was in the mid 12s.

That pretty much sums it up.  I want to give a BIG shoutout to Dave & Lancer for collaborating on the project.  Dave cross checked my sketches and calculations.  Lancer worked out the details with Wiseco, and he took the financial plunge and associated risk required to do the special order.
 
I hope you find this report informative.  As usual, I welcome your questions and comments.  I will continue to log miles on the new Flat-Top.  If something interesting comes up, I will update this report.

Mask up.  Stay safe.   Stay well.

Mike

Great write up and results.....as usual!

It is nice that you were able to get a significant power increase by improving efficiency - rather than just going bigger.  More power and increased mpg - that is not often achievable.

It will be interesting to see how long you leave your bike together this time........have you found the power and performance you are looking for?  Or - are you already scheming on the 97mm flat top piston?

DragBikeMike wrote on 02/10/21 at 21:46:22:
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LOL, I used to race with that guy!

Wow!
Great work!
Great reporting and documentation!
Thanks for sharing!!!!