SRX 1108 Race Sled Buildup

How much fuel does that pump flow? The Mach Z pulse pump that you were using pumps 65 litres per hour, and is more than sufficient.
 
Nice. We went out today to do some testing. It was a slower day today.

My trail sled ran 135.3 mph.
Doug's Apex ran 127.4, and it was running 132 out with you guys on Saturday.
 
Well, I'm heading to Iantomasi to dyno the 1136 motor on Thursday, April 15th and do some playing around. It previously built 263.3 corrected hp, but there have been big changes since then, so we'll see what it makes now :)
 
You should make your hp, you work your butt off on that sled.
How long of dyno pulls do you make with your sled? I'd do some long pulls, or the same time it takes you to run your top speed runs. See if you have any lay down issues with a long run. Better to find it and fix it in a nice dyno room then a cold day on the lake.

Good luck and keep us posted
 
Nah, Iantomasi runs a Stuska dyno, so the runs are short. I am betting that we don't find the issue that I am having with the motor laying down. I doubt we'd find it on our track dyno either, but I have a very good idea as to what it is, so I'll address it during testing next season. I'll post results when I return.
 
I am back from the dyno. We found a few issues down there, but none of which were causing my issues. Gerry also loaded it up for an 8 or 9 second run on two of the passes, and we could not get the motor to lay down. Therefore, the issue is not in the motor, and things are continuing to point to the possibility that pressure is being created under the hood when travelling down the track, which is pressurizing the carbs, resulting in a very rich condition, and causing the motor to lay down part way down the track. Simply venting the carbs up by the handlebars will fix this, if that is in fact the issue.

It is hard to compare the power it is now making because he has changed his dyno setup since the last time I ran this motor down there. The dyno is now reading somewhere in the neighborhood of 3-4% lower than his previous setup. My motor produced 261.x hp a few runs while we tested various things, which, in comparison, would put it in the 270hp range on his old setup, so there is some improvement in power over the last time I dyno'd it. If I were on another dyno such as down at Dynotech, I probably would have produced in the 280 hp range because his setup reads higher, or if I went to Jaws, it would have read lower. However, that isn't what I was trying to do.....I needed to compare gains from previous numbers.

Iantomasi still figures it should make more power than it is currently making. He things that the motor doesn't have enough case volume with the small Yamaha crank cases for the 83mm pistons I am running, and wants me to pull it apart and measure the case volume. If that is correct, and the case volume is too tight, there could be more power to be made. :)

All in all, it was a successful day. We found a few small issues, and the motor came home running, so I am happy.
 
More case volume

If case volume is the issue, how will you create more case volume?? Don't you already have the cases all hogged out as much as possible?

Madmatt
 
There is a small amount of volume that could be obtained from the transfer areas on the sides. The only other option would be to build a larger reed spacer.
 
valin said:
I am back from the dyno. We found a few issues down there, but none of which were causing my issues. Gerry also loaded it up for an 8 or 9 second run on two of the passes, and we could not get the motor to lay down. Therefore, the issue is not in the motor, and things are continuing to point to the possibility that pressure is being created under the hood when travelling down the track, which is pressurizing the carbs, resulting in a very rich condition, and causing the motor to lay down part way down the track. Simply venting the carbs up by the handlebars will fix this, if that is in fact the issue.
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Thats cool you did get a long pull. The carb pressure issue will only happen if you run a air box of some sort. If the bell mouth (opening) of the carb and the float bowl vent tubes both feel the same pressure, everything works fine. So if your running a air box, your better off drilling holes in the air box next to the bell mouth and putting the vent tubes in that way. If your running open carbs with just filters and run the vent tubes to the bars, you will push fuel out the vent tubes and the bowl, lean down (I have done that, not good). I have run the tubes both ways and like them in the air box best. Polaris runs them to the air box with check valves on stock sleds, Yam never did and they know they run rich stock.

I did see when fuel would stay in the float bowl vent line and cause all kinds of issues. You would think the fuel would drain out one way or the other, but it didn't. So you had to blow out each vent line and the sled would run fine. Most times this happen when you tip the sled on it's side to work on the track or rear skid, or off the trailer full of fuel.
 
I am not running an air box. I am running open carbs, no filters. At the moment, the vent lines are only roughly 5" long, and are vented to just below the carbs. I am not sure if the pressurizing issue will only happen when running an airbox, since I have never encountered this happening before. Gerry Iantomasi told me that he has seen this circumstance before, and it was cured by venting up by the handlebars. It's definitely something to try when I am able to get out to the test track again.
 
Gerry is a very smart guy and seen way more then me, so I,m not knocking what he wants you to do. How about if it does lay down at the track, just take the hood off and make a run. If the problem is gone, then run the lines to the bars. I just don't want to see you hurt the motor because it could go way lean fast. I'm sure you are making pressure all sleds do, yours would be alot with a top speed run. But with open carbs and vented to the same pressure it won't be a issue. If you are making pressure under the hood you will cause low pressure in the float bowl by running the float bowl vents to the bars. The fuel will flow (or be drawn, sucked) to the low pressure area (float bowl lines) and not up the venturi.
 
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Well, I got around to measuring the case volume today, and it is way too tight for the displacement, as we figured. It is currently sitting at 830 cc's of case volume, and needs to be in the 1050 range. Acutally, the volume is just about perfect for a 780 or 835...........damn tight Yamaha cases. :o|


Now I just have to figure out how to find 200 additional cc's of case volume. There isn't much carving that can be done to the cases, so pretty well the only way I can enlarge them is to cut off the intakes, and run skidoo 809 intakes and spacers. It won't be enough, but it will help.
 
Hope this isnt a dumb question but what about a bottom end from a 1200-1300 CC yamaha triple CYL wave runner. Case has to be huge
 
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