Race Video from July 4th at Roebling

[lancer360]

...

[Rick Ross]

Nice video and sound quality.

Were those F500 or F600 cars that you were racing? You seemed to have a massive hp advantage.

[jim murphy]

Nice video and sound quality.

Were those F500 or F600 cars that you were racing? You seemed to have a massive hp advantage.

Regional F500's and CF's and regional FF's against a national level F6 driver (Clint McMahan #34) so there were some lap time differences between Clint and the rest of the group. The 600cc MC's turn out about 125HP to the Rotax's 110HP but weigh about 50 pounds more. Clint says that the CVT's will out accelerate the MC's having to shift but both drivetrains have about the same top end. The true test will be when top notch national F5's and F6's run against each other.
The proposed F600 ruleset includes individual inlet restrictors which were not being run at this time. Please vote FOR the MC drivetrain in F500 by emailing the CRB asap.


Edit: The above post was general comments about the race - now the video with Chris Ross. Chris has progressed very well since he started in F500 now F600 and this video shows this.

Jim

[Marshall Mauney]

Enjoy

1st half

http://www.youtube.com/watch?v=GFPrYTmwyeI

2nd half

http://www.youtube.com/watch?v=vvszV_3NcYk

Looks like you had a lot of fun! Does Roebling still chew up tires within a few laps?

[jim murphy]

The track was repaved in the late 1980's (got rid of the seashells in the pavement) and again several years ago so the tires don't get chewed up quite as bad. Clint ran R35's this weekend and had the left rear blister slightly along the outer edge during the Saturday race. There is a photo of him lifting the inside front wheel at Turn #3. Since there were no more R35's at the track we swapped the tires and added pressure for Sunday - no more problem.
The other problem is sand blowing across the track. If you look closely along the outside of the track you will see berms of sand used in place of tire walls. This helps safety but causes sand to be on the track especially when windy (Saturday) so you will see the cars get loose for no apparent reason - it is the sand which is the culprit.

Jim

[lancer360]

Nice video and sound quality.

Were those F500 or F600 cars that you were racing? You seemed to have a massive hp advantage.

Its hard to say how much of a HP advantage we had. Both Clint and I were running our F600's unrestricted and the blue and the yellow F500's don't change their gearing from track to track. When I was following Tom in the blue F500, it seamed like we were pretty evenly matched in acceleration off the corners. It wasn't until we got down the straight away that I started gaining on him and that could have been him running out of gear not HP. Hank in the yellow F500 said he was down on HP as Tom was able to pull away from him down the straight. I don't know much about the engines that were in the various CF's and FF's that were there. They may have been top notch engines or they may have been fairly mild engines.

Jay Novak is making a set of restrictors for Clint so we will both probably run restrictors at the next race.

[Rick Ross]

Thanks, Chris. I did not realize that F500 cars could run out of gear on the straights, or even vary the gearing for different tracks. It still appeared to me that you probably had more hp than the F500's, but perhaps that is to be expected without the inlet restrictor.

How close was Clint to the F500 track record?

[jim murphy]

Clint ran mid 1:12's and his F5 lap record is a 1:11.8.

Jim

[lancer360]

Gearing is important with the 500's with CVT's. Depending on your pipe, the 500 engine turns between 7800-8200 rpm. The CVT ratio range is from 3.x to around 0.8:1. However below 1:1 (overdrive) the efficiency drops off significantly robbing HP. So with a CVT at 1:1 the jack shaft is turning the same rpm as the engine. Depending on which tire you are running and the track you ultimately should change the final drive sprockets to adjust the ratio between the jack shaft and the rear axle so that you hit your top speed at your braking zone at the end of the fastest straight away. If you are geared to low, the CVT will drop into overdrive giving you a bit more speed, but well below what you could achieve if the final drive was set to keep the CVT at 1:1.

According to the dyno work, we probably have around 10 hp more (unrestricted) than a top level national 500 engine. Neither Tom nor Hank have dynoed their engines so we don't know where their engines stood.

[tedsimmons2]

[FONT=Verdana]Chris Ross wrote:

Quote:
Neither Hank nor Tom change their final drive gearing for this track.


I’m curious how many people running two strokes change their final drive ratio from track to track? I understand to truly optimize your lap times a final drive change may be necessary. But what criteria do you use to decide when a change would be required with a CVT? I understand Roebling Road is a very fast track. However, unless Hank and Tom were running a very short track with extremely limited top speed in their previous race, I don’t see how the final drive ratio would have made the significant difference that is clearly obvious in the video. My limited experience shows the two stroke/CVT combo to be less sensitive to final drive ratios then a MC powered engine running up through 6 gears in the transmission.

In some parts of the video corner exit speeds appeared to be more or less equal. Acceleration was advantage Rotax out of the corner but top end was hands down in favor of the MC engine. I’m not buying the final gear ratio theory. Down on power for Hank maybe but what about Tom was he down on power too?

Until you install the IIR, on track video comparisons with two stroke engines are interesting but meaningless (but please keep them coming). A much better indicator would be Clint’s MC lap times vs. Clint’s Rotax times. In this race Clint’s MC times where about one second slower than his previous two stroke times. Part of the equalization process will involve resolving the on track differences between the two power plants and transmissions. That won't be done on a dyno.
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[captaineddie1975]

Sure would be nice to see the videos ......

[jim murphy]

The national drivers (who go to the Runoffs) like Clint change their final drive at every track they go to - Clint did it when he had a 2 stroke and he does it now with the MC.
If we went to a track where we had never been to before we would test on Friday for both clutching and final drive ratio - now with the MC it is only ratio. The frequent changing of the final drive was one reason of many that we changed to a chain drive - this made it much easier to change the ratio. Now Clint has 3 drive sprockets and 3 axle sprockets along with different length chains to give him a complete range of ratios for every track in the SE. Having the right ratio is absolutely critical to running up front because it is just no fun at all to get left behind down the straights when you know you have about the same HP as the rest of them.

Jim

[bsmeal]

Sure would be nice to see the videos from Roebling --They are marked Private on U-tube. Will good links be provided?