In preparation for this bigger engine, I did a bunch of timed acceleration runs to gather baseline info for comparison.  I am now at the point where I evaluate each modification to the engine by performing three different timed runs, each in a unique location.  Those runs include one 2nd gear pull to 7500 rpm on a paved agricultural road, one 2nd gear pull to 7500 rpm on a level freeway on-ramp, and a final 3rd gear pull to 7500 rpm on a paved agricultural road.  If the 2nd gear pulls are duds, I don’t waste my time with the 3rd gear pull.  The 3rd gear pull is the gold standard.  If the modification is a success, it is very evident on that 3rd gear pull.

The 94mm engine I replaced ran good.  It has my Stage II ported head, a Wiseco piston, Web 340b camshaft, a VM38 carburetor, a K&N cylindrical air filter, a 3” flywheel, and a Mac 1.79” exhaust header with a modified LS650 muffler.  It’s best 3rd gear pull from 4000 rpm to 7000 rpm was 7.72 seconds.

The acceleration benchmark for the 97mm Big Bore is 7.72 seconds.  If it won’t beat 7.72 seconds, it’s a dog.

These are the temperature gages.

The oil temperature is read right off the oil gallery, so I am getting a good measurement of the temperature of the oil being fed to the engine.

The compound gage is liquid filled and reads both pressure & vacuum.  It can handle the vibration from the big thumper.   This shows the instrument cluster.  Air/Fuel ratio, engine speed, oil pressure (liquid filled), crankcase pressure, cylinder head temperature, and oil temperature should be sufficient to keep an eye on things.  The GoPro camera records the parameters so I can review later.

Now that I knew I had lubrication, I screwed in the compression gage and cranked away.  It pumped a solid 200 psi.  I expected that would go up a bit once everything bedded in.

The next day I started the break-in.  I break-in my engines by lightly accelerating and then chopping the throttle completely, then repeat.  It’s a constant cycle, accelerate, chop, accelerate, chop…  I’m sure it drives anyone behind me nuts, but a man’s gotta do what a man’s gotta do.  The plan was a solid 500 miles of that nonsense.  The hobby-lathe bore-job would need to be handled with kid gloves.  The cylinder is flimsy, and I probably didn’t have the best surface finish.  I didn’t want it seizing.

Right away things seemed on the warm side.  The oil temp and CHT came up rapidly, much faster than the 94mm.  I stuck close to home and kept the speeds low, constantly workin the throttle.  I would put about 10 miles on it and then come home and let it cool.  Everything seemed to be working well.  It was quiet.  The vibration seemed lower than the 94mm.  Then I noticed a little oil around the right rear corner of the cylinder head.

I wiped it off and took it for another short ride.  It wasn’t a fluke.  It had a leak.  Observing it running in the garage it looked like it was coming out of the area adjacent to the oil feed slot in the cylinder.

I continued to wipe it up and go for short rides.  Once I was confident that it wasn’t going to melt-down I took it on the freeway.  What a mess.  By the time I got back home oil was all over the right side.

I tried doing an air test.  I used a bicycle pump attached to the breather.  I could pump it up to 3 or 4 psi and it would remain pressurized above 2 psi for at least 15 seconds or so.  It just wouldn’t make bubbles when I applied soap solution.  Even when I continuously pumped, I couldn’t make bubbles.  Only thing I could figure was that the oil passage was full of oil, so no air was gonna bubble out.

The engine would have to come out to fix that leak, but I wanted to get it broken-in and also wanted to do some acceleration tests.  I didn’t want to drag that engine back out until I knew there weren’t other problems that needed correction.
 
Situations like this always bring out the stone-axe in me.  I figured I could patch the leak good enough to finish the break-in and testing.  JB Weld to the rescue.  It took several iterations and I ended up with the entire right side of the head epoxied to the cylinder, but it held good enough to start doing some serious riding.

I spent the next 350 miles testing and tuning.  It ran best with a 210 main jet.  The 3rd gear acceleration test was not disappointing.  It ran from 4K to 7K in 6.17 seconds.  That’s an improvement of 1.55 seconds faster than the 94mm Wiseco engine.  Very gratifying.

I didn’t have any 3rd gear acceleration data for the 94mm tight-quench (TQ) engine, but I did have videos of some of my LSR attempts that showed 3rd gear operation from about 5500 rpm up past 7000.  That allowed me to time 3rd gear from 6K to 7K.  The tight-quench engine was faster than the 94mm Wiseco engine, so I thought it would be interesting to compare the 97mm to the tight quench.  BTW, the TQ engine dynoed at 41 HP.  The 97mm pulls 6K to 7K in 2.83 seconds.  The tight quench pulled it in 3.28 seconds.  The big 97mm is .45 seconds faster 6K to 7K.

Since I was in the mood for testing, I decided to see how the big engine would like a bonafide exhaust system.  I threw on a complete Mac system.  After a bit of tuning I settled on a 230 main jet.  It was a tossup between the 220 and 230.  I didn’t have the benefit of the air/fuel meter with the Mac system.  The Mac exhaust was good for another .23 seconds.  It now pulled 4K to 7K in 5.94 seconds.

I must admit, it loved that open exhaust system.  The engine really woke up (and so did my neighbors).  The mid-range was killer.  But man, that thing is just too darned loud.  Looks like I have a new project.

Here’s a look at the Mac Attack.  It’s a nice lookin exhaust, but too loud.