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I mentioned to Dave prior to the latest test just how varied the compression readings can be. Dave did some more testing yesterday on my SST 60 powerhead. He tested it cold with light oil and got readings around 175 lbs. If you load the motor and use storage oil the readings jump over 200lbs. He tested the leak down as well 77-78/80. He measured and cc the head. When you include the gasket the head and gasket is to SST 60 Spec. On Dave Whittington's SST 60 the smallest head I ran was 30.5 and cold it read 155. Dave Elsey test a number of heads on my SST 60 and got different numbers. Example a 29.5 head on the same motor read 150. Another 30 head read 160.
The POINT IS....The compression will vary head to head and cylinder to cylinder.
The compression ratio is more important in my view.
Based on the measurements a stock SST 60 head on a fishing motor is 10 to 1 ratio.
It doesn't matter if the gauge reads 135-145-155 or 160.
If that motor runs on premium pump gas it will perform well and last.
If you need race fuel and the motor doesn't last. Then it is costing you more money.

I will let guys smarter then I am comment, but have always been told that calculating compression ratio's on two strokes is a waste of time because of the ports, a four stroke with valves is a different story.

I would expect the compression to come up on the fresh fishing motors after break in.

X2

12:1 compression ratio and use that exhaust port as a relief lol

The other option we have is just have a spec head for each powerhead and forget about the compression reading. The only reason the compression rule was put it the rules in the first place was to detune the SST 60.

If it's 160 max, build it so it doesn't blow over 160 when it's tech'd. Doesn't really seem like rocket science to me. All the other factors are things we can play with to build the engine how we want it to be. I like that option. As long as we know it doesn't crank over 160 on Top Gun's compression gauge after it's been run (no assembly oil and what not) and it's cold, then it's legal.

I bit of clarification about heads.
SST 60 head measurement of 28.5 includes the gasket
Here is the depth and CC of the actual head.
Pocket depth closely relates to head chamber cc’s.
21cc =.405”
23cc =.440” SST60 minimum
25cc =.470”
27cc =.505”
28.5cc =.525” SST60 minimum including head gasket ??
30cc =.550”
31cc =.565”
32cc =.583”
33cc =.598”

So the actual head is 23 cc. plus the gasket volume to arrive at 28.5

LC to answer your question of compression ratio 4 stroke to 2 stroke. 2 stroke is more accurate. The tuning and over lap of valves is the big difference.

I have no problem with the 160 rule...it's not perfect by any means but it is reasonable and simple to apply to our level of racing...if this was a national event or for money you'd probably have to refine things and have tear downs and then you could incorporate all the specs you want.

I was simply pointing out that compression ratios in a two stroke are not necessarily a valid measurement tool for figuring out what head to run, sometimes you just have to pull the plugs and look to see what the plugs and piston look like. You have shown on the fishing block that there is a huge variance between blocks and people should take notice that they simply just can't throw any head on a block and run the shit out of it cause she just might pop!

So, I was reading through the engine rules and according to what I read, we are all illegal. When we were at the 2013 boat show meeting for the engine rule changes, we all agreed on lightening of the rotating assembly, and that working of the ports was open, so long as no ports were added (finger ports). Here is what is in the rules.

- No removal of material from the powerhead for any reason other than recognized (by the manufacturer) repair

- Engines may be blue printed, but measurements must not exceed that engine’s spec sheet.

We are removing material from the powerhead for porting and lightening so that should be omitted and weights and ports will be outside the engine's spec sheets.

Maybe that should be changed with:
-Ports may be modified so long as no ports are added (ex. finger ports)
-Lightening of the rotating assembly is permitted but must be done with OEM parts (pistons can be from any manufacturer)
-Bore and stroke must remain stock (up to .040" overbore allowed)
-tuner may be modified. Any length or shape may be used - I believe this was in the previous rules but maybe missed for these ones

Hopefully I'm not missing anything. I'm not trying to stir anything up but if we don't clarify what we have already discussed and understand amongst ourselves, in the rules, we may have a problem as new racers come into the sport and like I said, we are all illegal with the rules we have up now. Also, it will be easier to promote and potential racers can view the "real" rules online and not be in for any surprises once they go to race.

Just an FYI the only engine spec sheet for the 56 is the sst60 specs...so...don't go beyond the sst60 lol

[quote="Hevi Kevi"] Here is what is in the rules.

- No removal of material from the powerhead for any reason other than recognized (by the manufacturer) repair This applies to low emission motors and four strokes per the rules and we don't have any currently running in the classes

- Engines may be blue printed, but measurements must not exceed that engine’s spec sheet. Are you looking at the current rules as I don't believe "but measurements must not exceed that engine's spec sheet" is contained in the current rules

/quote]