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At the CBF meeting in Feb a motion was passed to move T Class out of the stock outboard group and create a new category similar to what Drags and Thunder Cats are.

For now we have named the new category "V Production Runabout" (VPR) and T Class will be a division within that category. Having T Class as a division will allow us to add new divisions like COR etc in future to this category if we desire.

Attached is a draft of the CBF 2013 T Class Rules in pdf.

What Jake, Don and myself tried to do was simply recreate the rules we raced under last year in stock outboard plus incorporate the agreed changes that the T group had discussed before the CBF meeting. Nothing else has been added or changed. Some language for certain parts of the rules was borrowed from the Thunder Cat rules...thanks Andrew.

The rules as they stand are 99% there. One or two items needs some minor editing but figured best to get a draft out for people to have a read of. I think Gig was looking to get a group of T guys together to discuss the rules one last time and make any agreed on changes before we submit to CBF for consideration.

Happy reading.

Cheers,

Looks Good to me! Thank you VERY much Paul - you have done a great job!

Yes sir...that was a big job. Thank you for stepping up and getting this together for us.

Just a thought, since almost everyone is using the 56 omc would there be something that could be done to make the 49 a little more competitive? Like maybe a rule that would allow anything under 50ci to have say 180 or 185 compression or less minimum weight maybe. I don't know how the extra compression would make it compare to the 56 but I'm just thinking out loud here...

We actually tried a few things with the 49 OMC. The regular stock 49 motor is approximately 150 lbs compression. We put a 160 head on one and the motor quickly developed a ring gap problem. We are not 100% sure if it was a water problem or the added compression. The gain was not worth the risk, so the motor was put back to stock. There were two reasons for the 160 lb rule when we looked at the OMC 56 models. There are 4 different 56 blocks in the class. We wanted to first reduce the performance of the SST 60 blocks. In 1994 Rob Gordon raced a stock 120 to 130 compression 56 motor in EP against the 49 OMCs. That race should soon be up on this site to view. It is a LeMans start and the 56 shows the torque difference off the dock and leads for a few laps, only to be caught and passed by several 49's. That is the other reason for the 160 rule. We wanted to get a little more performance out of the 56 fishing motor so it could race with the 49. Jake runs a 49 as do several others. Jake is going to run his 49 this year. The weak sister has been the yamaha. The best run we have recorded is 67 mph. We have 56s running 68 to 73 mph. What does this mean in the race, NOTHING!! We have had 62 mph boats win and 68 mph boats finish 5th in the same race.

OMC 56 COMPRESSION RESULTS

Thanks to the Dave Elsey's hours of testing and charting we have a good understanding of what head to run of the fishing motor and the SST60. REMEMBER THE RULE IS 160 lbs. MAXIMUM. You cannot be over. These are the SUGGESTED specs and you should be legel. However, if you have decked the block or done other alterations, you will get a different read and you cannot be over 160.

Compression Gauges:
There was 5 lbs difference between the old style gauge and the modern accurate gauge.

Head Gaskets:
OMC Hd Gasket .040” gasket .045” Fire ring Used 0329836
Sierra Hd Gasket .050” gasket .058” Fire ring Used 18-3836
WSM Hd Gasket .040” gasket .050” Fire ring New 505-07
With head studs you can crush the gasket an extra .005” Result ~ 6lbs on compression test.
There is ~ 12 lbs less compression with the Sierra gasket.
Each engine is unique, the compressions varied ~ 7 lbs from engine to engine with the same head.

Results:
Suggested heads
An SST-60 legal engine ~ 30cc head . This was on a blue printed powerhead

Fishing motor 24 to 28.5 cc head. The difference is due to the difference between motors.
Based on actual racing the 28.5 cc has provened to provide the best performance with excellent motor life.


True actual full stroke Compression Ratios are as follows;
9:1 32.7cc
10:1 28.5cc
11:1 25.0cc
12:1 22.5cc
13:1 20.5cc
28.5cc gives a reasonable ratio for pump premium gas. (Regardless of compression readings)

Pocket depth closely relates to head chamber cc’s.
21cc =.405”
23cc =.440”
25cc =.470”
27cc =.505”
28.5cc =.525” Legal limit SST specs
30cc =.550”
31cc =.565”
32cc =.583”
33cc =.598”
Head gasket @ .040” = 5.3cc
* All cc’ing was to the top of the spark plug threads as specified in the SST rules.

All the motors ive build , when you put a 28.5 cc head on them you get around 130 psi comp??
Were did you get these numbers??

It's all pretty complicated for but a humble school teacher. You T850 guys better get this sorted out! ... T750 is pretty easy though. Stock 60 OMC = 155-160lbs

If its any help, the Gieger Tech head motor I was so graciously loaned last year was 155lbs on my Princess Auto gauge! I suppose that was a 21cc head? Man, I miss that motor...

Ya Dave....it looks more complex than it is...Don/Dave have provided a good guideline for someone new but you still have to plug the gauge on to it and make sure you've got less than 160...too much less and you cut some more off...easy pease...

OR buy a Yamaha...no one seems to care what the M.R.S skunk works is up to (Which is actually just changing diapers so...it's no big deal...)

For Dave's last series of tests he used two fresh rebuilt production cast fishing motors. We had used 3 others in previous tests. As stated in the post we have seen a wide difference in the compression reads on the fishing motors. That is why there was a range from 24 to 28.5 in the head suggestion. You could have a 28.5 head and get in the 130's with some motors. I believe we had one at 137. That is why the math for the actual compression ratio is most important. Based on the cylinder volume 10 to 1 is where the motor should be to run on premium pump gas. If a racer runs a 21 cc head and it reads 160, it would be legal.
We can only suggest. You get different compressions also because of oversize bores, different head gaskets and torque on the head bolts. This is never going to be an exact science.