A while ago I posted about the results from dynoing my MGB with the mildly ported cylinderhead.
It didn't seem to gain me much power, and I lost a little in driveability. I took my old cylinderhead to my machinist to have him look over. With about 30,000 miles on it, the exh valves for cyls 2 and 3 were a bit worn. He cleaned those up quick telling me that siamesed exhaust valves were always the first to go and I'd need a full valve job in 10-20,000 miles. He also expressed a little surprise that I had put 18,000 miles on my MGB in the past year. (Of course I only put 18,000 miles on it, I have another car and a motorcycle. But he seemed to think that was a lot of miles, not few.)
As luck would have it, Terry Barnard, who owns the dyno that I originally tested my car on was leaving on vacation for a few weeks and couldn't help me tune the car with the stock head, but told me of dynospot racing at Evelyn and Calderon in Mtn View. They told me that an Air Fuel Ratio test would be $125 and that they were free about 3PM. They mostly specialize in ricerockets and didn't really know much about MGs, so I basically did the tuning while they ran the dyno.
In short, the mixture looked good, so I adjusted the timing. I started out at 74 hp and 86.6 ft-lbs of torque and my adjusting the timing to 17 degrees at idle (with vacuum adv attached) and 31 degrees full advance I brought her up to 75.3 ho and 88.7 ft-lbs of torque. Note that my best run with the ported head was 75.5 hp and 90.8 ft-lbs of torque.
I wanted to find out how much power, if any I lost by adding the airfilter: stock air filter
my overal results for the day:
To my surprise, it leaned the motor out a litte and gave me 76.1 hp and 90.3 ft-lbs of torque.
Note that the second day was cooler, on the same model dyno, but a different dyno and I was using street tires rather than DOT legal race tires, so the tests aren't perfectly equatable. The important thing to note is that without a more radical cam and more compression (and the race gas to make use of them) the ported head cost me money, power and driveability.
I suspect that someone with a more radical cam, and higher compression, or a supercharger which would help mix air and fuel, would be able to make use of the added potential airflow of my cylinder head. The porting, hardened seats and valve work cost me $560. It also has a new thermostat and the housing as well as the temperature sender. The head has 1,000 miles on it. Is anyone building a race motor and interested in making me an offer on it?
Last modified 04/11/01
