Many may remember that it was around this time last year when I picked up the 1990 VFR750 project bike. The motor was partially tore down and the plastics were busted up. As I evaluated the motor, I found it had a spun rod bearing and a proper rebuild would cost more than double what a used runner would cost.
TOE CUTTER was instrumental in helping me locate a motor on a tight budget. Thanks again to Bweiss and Cundalini for their help too. Those stories are told here:
So I took the 1992 motor from Sac-Cycle Salvage and put it in the 1990 frame. I used the 1990 49 States carbs with stock jetting to start. The motor was put in with all the stock equipment (PAIR valves, headers, collector, air-box, and snorkel). I normally like to see what I have before changing a bunch of stuff around and then chasing ghosts to find the problem. TOE pointed out way back then that his failing aged memory believed there was a difference in the cam shafts. This was confirmed in the factory service manual but I chose to leave the motor as it was.
In the following photo page 1-6 of the Factory Service Manual, you can see as much as 20deg difference in cam timing from 3rd generation to California cams. You can also see at the bottom that the 3rd gen uses 36mm carbs.
The following photo shows carb numbers and jetting for 3rd and 4th gen along with California. Page 1-7 of same manual.
This photo is the real doozy. Page 1-8 of the manual shows as much as .090 more in Intake cam lift over the California model.
So I got the bike running and purring pretty well. Rode it all summer but the more I got used to it I felt it seemed a bit pig-ish. I had a local racer who used to own a 4th gen jump on and see what he thought. His report was that it felt about right.
Winter came along and some prodding by TOE CUTTER finally got me to get off my ass and dig out the 3rd gen cams from the original motor. Up to the closest bike shop with a Dyno I went to get a base line run before making any changes.
For fun, we ran two pulls on the bike. One with PAIR valve operating as designed, and one with the hoses pinched. The graph below shows both runs over top each other. Statistically there shows no change with the charts virtually identical. This is taken at 4900 feet with stock jetting(49states), K&N filter, Yoshi pipe, California cams, and a reported 12,000 miles on the motor (unverified).
The numbers are far from impressive. Home I went to tear it back down. Here's a photo of a California cam and a 49states Intake lobe next to each other. Some local shops warned me that our altitude did not always agree with more aggressive cams. Since this is a factory camshaft, I was not concerned.
And so finally, here are the semi-final results. The 3rd gen cam set compared directly to the California camshafts resulted in approximately 5 additional horsepower and 2.5 lb/ft more torque. Another important thing to notice however is that the fuel mixture became more rich.
So, a direct swap was five more HP. But to honestly compare apples to apples, I'd have had to adjusted the jetting to bring the air/fuel mixture back to the same as the first run which would have given even more HP.
Since the last Dyno run, I've pulled the carbs and replaced my #130 mains with #125. I'm trying to bring the mixture closest to ideal for my altitude which is something like 13.1 The seat of the pants gauge says there's an even more noticeable gain than I had from the cams. The Dyno owner said he expected to see 5-10HP additional gain from fixing the jetting. We'll see when the latest cold snap passes. High if -4f tomorrow.
Initial Dyno run cost me $65 and the second run cost $40. I would highly recommend to anyone that they go see their local shop with the right tools (Dyno) to measure properly how your motor is running.