mattmak wrote:
I'm not seeing how this measures the chamber volume. Chamber height is not the only variable in the volume of the chamber. Shape and diameter also are part of it. Am I missing something in envisioning how this could work?
Matt, go and look at the SST60 spec sheet posted on another thread....look at the cylinder head diagram...it shows the pocket depth of the head that produces the 28.5 cc volume. In coming up with the 160 lb compression rule MANY heads were cut different amounts and race tested to find one that would make the SST60 less performance equal to the other motors in the class. The actual tests showed there was little difference on the race course between an SST60 with 150 compression to one with 160 compression. The T group decided on 160. So for the SST60 head 30 to 30.5 cc will produce 160 compression on a spec SST60.
Also, for go/no go for jets, what happens if the jet's orifice is out of round: for example the max diam round gauge that goes through is 72 but it flows like a 76 because the jet orifice is oval (modded by a cheater!)
We know that the orifice in the jet should be round......if it is oval it is not legal regardless of its size.Matt as a point of interest here is some more history on the 56 compression testing.
The boat we used for race testing was Dave's 411 Critchfield...with the pure SST60 motor it ran 73.7 mph on GPS.
Dave ran a different cylinder head every race day.
I had done some GPS readings at Waterford on a number of boats running the fishing motor. Riley's boat running a bone stock non rebuilt 56 with a 160 compression head ran 70.5 mph........other boats ran 64 to 68 mph.
My goal was to get Dave's boat to run 67 to 69 mph. Jimmy Allen needed a boat to race at Waterford.....i assembled a blue printed pure stock fishing motor with a 155 lb compression head. Jimmy ran it and said it was the best boat he had ever raced...he won every heat that weekend....I got the boat back and GPS tested it at the cottage the following weekend. It ran 68.2 mph, but the acceleration to top end was super compared to the SST60 power heads we were testing. Finally I got the SST60 to perform at Dunnville. Dave won one day of racing and finished top 3 the other. The motor made for great racing. It lost 2 boat lengths out of every turn due to the acceleration compare to the fishing motor and made up the 2 lengths in the last 1/4 of each straight.