One of the draw-backs of the 851/888 series has been the air-box. They respond very well to opening the air-box, but, the 888 fuel tank still causes a lot of restriction. Lifting the front of the fuel tank on an 888 can gain 3-4 HP on the dyno, even with an open air-box.
Beside the the obvious displacement boost, caused by a 2mm stroke increase, the 916 has a well designed inlet system. (Well, from an air-flow standpoint. The air filtration system can be a little iffy.)
The 916 exhaust pipe diameter, also offers a power increase over that of the 888.
All of this results in the 916 being able to produce over 100HP (at the rear wheel.)
From my experiences with 3 944cc 4-valve, and 1 984cc 4-valve, and some tests of different exhaust systems, my feeling was that we could get in the mid-teens for power with a high-compression 916 with the same head work as the others. All of these engines used stock cams. Frankly, I like the characteristics of stock cam engines for street use. They have broad, flat torque curves, they don't eat up the valve train, and they can make a satisfying amount of power.
I've had a set of JE 916 drop-in pistons sitting around since last summer, and finally, Troy Drury decided that he could stand a little performance increase.
Last year Igor Gorodinsky did an engine like this for Josh Golden. Although we didn't talk about the particulars, he did say he'd used the 35mm inlet, 30mm exhaust, valve sizing that I've used on several of these other stock cammed engines.
A little aside here. I never had the privelege of meeting Igor, although, I did talk with him often. I miss him, as a lot of others do.
Initially we intended to just do the drop-in-and-cam-timing thing, but a friend of Troy's suggested he do the port improvements too. (Good idea, I thought, but it isn't my money.)
Troy had an Arrow intermediate system, and wanted to gut the air conveyors, using an over-the-velocity stacks air filter. So, away we went!
The following chart shows the before and after. Before is with the stock mufflers and after is with the Arrow intermediate system, oversized valves, cam timing, and high compression pistons. And, the appropriate chip changes.
We're not done with this one either. The ignition timing is quite retarded, to be safe with the high compression pistons. The CR calculates to be 11:1.
A comparison with a 944cc 888, shows that the exhaust pipe size of the 916 seems to help at the top of the power band, whereas the small pipe and extra displacement really help the 944 at the torque peak.
One characteristic of these larger valve, stock cam engines, which pleases me, is the way they carry the power out the top-end, without the help of extra duration and lift. I've built one of the three 944s without the porting and the power was disappointing. But, a lot ot the torque was there.
As we fine tune this 916, I'll update this report.