New T Class proposal

sheuninck · **Posted:** October 25th, 2013, 12:15 pm

if you guys need engine specs / amalgamation sheets other than below to support inspections, I can send what I have.
http://www.apba.org/resources/formula-v-spec-sheet-2924
http://www.apba.org/resources/sst-60-spec-sheet-2920
http://www.apba.org/resources/sst-45-spec-sheet-2922
http://www.apba.org/resources/sport-c-spec-sheet-2923
http://www.apba.org/resources/2013-modi ... anual-2435
let me know,
steve

Hounddog · **Joined:** April 3rd, 2012, 1:52 pm **Posts:** 3140

Hounddog wrote:

We are working on a go-no go gauge that is inserted thru the spark plug hole and goes to the side of spark plug. There would be a different guage for each motor. The inspector positions the gauge in the cylinder, you manually turn the flywheel, if the power head can go thru the full stroke cycle, it passes. If it stops when the piston hits the guage, your DQ'd.

Just an up-date on this gauge. The first one has been tested and several T racers have been e-mailed and shown pictures and test results. We will need to decide if there will be one spec head for all 56 powerheads be they SST 60, bridge port fishing or oval port fishing. Or have a separate measurement [gauge] for each. The current gauge measures a 28.5 cc minimum head [head volume has to be larger]. This measurement does NOT included the head gasket. This is a LARGER measurement than an SST 60 head which includes the head gasket. We think that this head spec should work for everyone. The Tech spec changes made in 2013 allowed the fishing motors to be modified so that they were close or maybe even better than the SST 60 blocks. By having the larger volume head we solve the varied compression results. Plus we only need one head.

DoktorC · **Posted:** November 1st, 2013, 10:03 am

Wouldn't it be easier to just make an agreed upon procedure for the compression test? Crank for a count of 8 with the throttle plates closed...that way we know what compression is in the motor...as per the rule. There's too many variables and ways around the piston stop.

Hevi Kevi · **Posted:** November 1st, 2013, 10:42 am

A while ago I had ordered an "On" "Off" timer off ebay that was adjustable from 0-15 seconds. The plan was to set up a box with it's own battery, solenoid, timer set at maybe 3 seconds, start button and wires with alligator clips to put on ground and starter terminal. Open up the throttle, press the button and it does an exact set time every time. Unfortunately, I was out for a few days and before I had a chance to get to the post office, they sent the timer back to the sender. I never bothered to get another one and finish it. Just a thought if people wanted to stay with the compression test. The plug doesn't seem like a bad idea so long as it is set at a height that evens the SST-60 and fishing 56ci engines out. I just wonder how it would work with the 49 and the Yamaha or a merc if someone was to use one. I'm guessing they would all need something different?

hec2buck · **Joined:** August 22nd, 2013, 4:13 pm **Posts:** 273

If you consider using a 70 hp, 56 fishing motor or a SST-60, 56 block, and the port height variations from the stock motor to the SST-60, and then factor in the tolerances allowed on the ports, there is no way a pocket depth gauge will work. You may require a pocket depth of 0.530" on a stock 70 hp, or a pocket depth of 0.440" on a SST-60. If you consider the +/- 0.035" port height tolerance on the exhaust ports on any given motor, you end up with a potential of .070" difference from the low to the high of the spec. That's over 1/16". If your at the high end, or low end, the pocket depth of the head could change as much as 0.060"-0.080". That is just the variation on a given motor. Then you go to a SST-60, and the exhaust and intakes are closer to the deck, and still have a tolerance of +/- 0.035".

If the rule says 160 psi, that covers it all. Two racers with the same SST-60 motor, but different port heights within the spec., could see a variation of 5-15 psi on a compression gauge. If both racers wanted 160 psi, then the one with the higher box stock compression would probably do nothing, while the racer with the 15 psi lower compression would cut his head to achieve 160 psi. That would change the pocket depth of the cut head to 0.015"-0.020" less. Perhaps more.

Lastly, using a pocket depth gauge will require pulling heads, wasting costly gaskets etc.

If anyone has radical port heights that require a pocket depth of say 0.385" to achieve 160 psi, than I can promise you that individual will have no acceleration off the exit pins, and an extremely peaky power band, good only for top end.

p man · **Posted:** November 1st, 2013, 11:04 am

hec2buck wrote:

:D If you consider using a 70 hp, 56 fishing motor or a SST-60, 56 block, and the port height variations from the stock motor to the SST-60, and then factor in the tolerances allowed on the ports, there is no way a pocket depth gauge will work. You may require a pocket depth of 0.530" on a stock 70 hp, or a pocket depth of 0.440" on a SST-60. If you consider the +/- 0.035" port height tolerance on the exhaust ports on any given motor, you end up with a potential of .070" difference from the low to the high of the spec. That's over 1/16". If your at the high end, or low end, the pocket depth of the head could change as much as 0.060"-0.080". That is just the variation on a given motor. Then you go to a SST-60, and the exhaust and intakes are closer to the deck, and still have a tolerance of +/- 0.035".

If the rule says 160 psi, that covers it all. Two racers with the same SST-60 motor, but different port heights within the spec., could see a variation of 5-15 psi on a compression gauge. If both racers wanted 160 psi, then the one with the higher box stock compression would probably do nothing, while the racer with the 15 psi lower compression would cut his head to achieve 160 psi. That would change the pocket depth of the cut head to 0.015"-0.020" less. Perhaps more.

Lastly, using a pocket depth gauge will require pulling heads, wasting costly gaskets etc.

If anyone has radical port heights that require a pocket depth of say 0.385" to achieve 160 psi, than I can promise you that individual will have no acceleration off the exit pins, and an extremely peaky power band, good only for top end.

Very well put!

Hounddog · **Joined:** April 3rd, 2012, 1:52 pm **Posts:** 3140

The 2013 tech rule changes really changed the compression readings. Originally when I tested stock motors. I did get minor differences between similar blocks. I never got different readings other than a lb or 2 testing the same block from one day to the next. I did exactly as Todd mentioned in his post. I cut the heads on an individual bases to get close to 160. Even though the heads were cut different the performance of the motors were consistent and equal. The 2013 rule changes really changed the readings. Dave and Kevin saw wider ranges. They also found that changing the head on a motor that was 10 lbs over [170 and above] back to 160 dropped the performance of that motor back 2 or 3 mph.

hec2buck · **Joined:** August 22nd, 2013, 4:13 pm **Posts:** 273

I ran the same tests and found no difference in top end with the 10 psi higher compression. However, the acceleration was definitely better with the higher compression. In once instance, I saw a slight drop in top end with the higher compression. I lost about 0.6 mph.

Hounddog · **Joined:** April 3rd, 2012, 1:52 pm **Posts:** 3140

hec2buck wrote:

I ran the same tests and found no difference in top end with the 10 psi higher compression. However, the acceleration was definitely better with the higher compression. In once instance, I saw a slight drop in top end with the higher compression. I lost about 0.6 mph.

The higher compression makes a difference with the SST 60 blocks and the high ported fishing motors. A good SST 60 motor is 175 to 180 compression. I changed the heads on several SST 60 motors. One motor was raced with 5 different heads. After 2 years I put its original head back on the motor and the boat ran exactly the same as it did originally. I had to adjust the jetting to suit the heads. The speed range was from 61.4 mph to 73.2 mph. The head and jetting were the only changes. Oddly enough the quickest ET to 61.4 mph was the lowest compression head, had no top end.

hec2buck · **Joined:** August 22nd, 2013, 4:13 pm **Posts:** 273

It's hard to accept a difference of 12 mph with just a head change and jets to suit. A 56 cid in T-850 is roughly a 70 mph boat. A 45 cid in T-750 is roughly a 58 mph boat. That is also a 12 mph difference; boats are the same. The horsepower difference between the 56 and the 45 is about 35 hp ( 95 hp & 60 Hp ). So what you are saying is that going up 15-20 psi in compression with jetting to suit, is worth 30-35 hp? I so wish that was true.

In testing, we went from 170 psi down to 152 psi ( as checked at Waterford, On. ) and we actually picked up a tad bit of top end, but lost acceleration. Just sayin' what we experienced.

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New T Class proposal

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