Top Speed results with Hyper 7 and RB WS7ll...

mtrsprt · #1 10-01-2003, 09:25 AM

Well, I set the GPS on the wing with rubber bands and let her rip.

Speed with 15T clutchbell and OFNA Adheris tires was 46.3mph(74.51kph)

Speed with 15T clutchbell and OFNA stock Ultra LX tires was 50.7mph(81.59kph)

Fuel used was 20% Trinity Monster Horespower fuel, with carb settings at 4.5 out on the HSN, and 5.25 out on the LSN.

My goal was to reach 50mph(80.47kph), and I have succeeded.

NOTE: The stock UltraLX Pulsar tires are taller than the ones I have on mine and also balloon out ALOT.

OldskoolGT · #2 10-01-2003, 09:45 AM

mtrsprt,

Did you ever clock your car with the stock 13 tooth clutch bell? If so, what was the speed?

StevePond · #3 10-01-2003, 10:17 AM

That's a cool experiment, but don't put too much stock in the speed readings you're getting. The margin of error on a GPS receiver is pretty considerable, so the distance you need to travel before you get a somewhat accurate estimated speed is many consecutive miles (not a lot of back and forth).

mtrsprt · #4 10-01-2003, 02:29 PM

Steve, thanks for inquiring. Do you know how far I ran WOT? It was a close to 600ft. I did back to back runs after resetting max speed on the GPS, until there was no further increase of speed. After doing all the calculations, the results were within 1% accuracy with the GPS results, ie: engine RPM/final drive/primary drive/tire diameter(with some balooning factored). etc, you know what I mean

mtrsprt · #5 10-01-2003, 02:34 PM

OldSchoolGT, Yes, previously I have tested the stock 13T clutchbell, but it was with the 8-port engine. The results were 37.9mph. With a 15T clutchbell, it was 42.3mph. Definately real world figures here, not some exaggerated figures.

Example: A Kyosho MP7.5 with an equivelent racing engine(Nova SBK), will require a good 35000 engine RPM under load, to aquire a speed of about 40mph, given that the final drice ratio is 11.6:1(same as the Ofna Hyper 7).

So, when someone tells you there buggy does 50mph with a 13T clutch bell, they better hope their engine is hitting about 45,000 RPM under load, or their tires are about 5.6" in diameter

OldskoolGT · #6 10-01-2003, 02:56 PM

Thanks for the info mtrsprt. I had always thought that a buggy with stock gearing could do about 35 mph based on the engine reaching around 30,000 rpm, and your test confirms that. Some magazine (not RCCA) reported that the MBX5 top speed was 46 mph, which I found hard to believe based on my own calculations.

mtrsprt · #7 10-01-2003, 03:47 PM

There was also another article I have heard of saying that the OFNA Ultra LX pro hit 46mph also I think. I do not think this is possible. It was done on radar supposely. Even with the Ultra balooning tires, and the stock gearing, the engine would have to reach about 39,000rpm. Sorry, no Force .25 can pull that kind of RPM's under load.

mtrsprt · #8 10-01-2003, 03:50 PM

Quote:

Originally posted by StevePond
so the distance you need to travel before you get a somewhat accurate estimated speed is many consecutive miles (not a lot of back and forth).

I was not looking for an estimated speed, but looking for max speed recorded by the GPS unit over a 600ft straight. The signal was very strong in front of my home, and the GPS was registering about a 16ft accuracy level. At accuracy levels below 50ft, it can get your max speed reading over a shorter distance. Surely the 600ft was sufficient.

DerekB · #9 10-04-2003, 02:27 PM

Quote:

Originally posted by OldskoolGT
Thanks for the info mtrsprt. I had always thought that a buggy with stock gearing could do about 35 mph based on the engine reaching around 30,000 rpm, and your test confirms that. Some magazine (not RCCA) reported that the MBX5 top speed was 46 mph, which I found hard to believe based on my own calculations.

I'll send you the complete file from our radar gun and software because our MBX-5 reached 45.3mph to be exact. We didn't base our speed on calculations, yet rather an expensive piece of electronic equipment called a radar gun!

mtrsprt · #10 10-04-2003, 02:46 PM

Then the engine used in the MBX-5 was reaching a higher RPM than my WS7. Also, do you remember what was the final drive ratio of the MBX-5 was????

DerekB · #11 10-04-2003, 03:24 PM

Quote:

Originally posted by mtrsprt
Then the engine used in the MBX-5 was reaching a higher RPM than my WS7. Also, do you remember what was the final drive ratio of the MBX-5 was????

All that information is listed in our reviews, including weather conditions. We have a final gear ratio of 11.79:1 (this doesnt account for tires (final roll-out))

Nitro engines aren't all exactly the same and the amount of variables (weather, fuel, altitude, friction and such) make it hard to say any two cars in different locations will be the same speed. The only thing I'm going to double check is the highend needle setting which we have lsited at 1 3/4. This seems a little low, but it wouldn't have reach such a high speed if it were too lean.

mtrsprt · #12 10-04-2003, 03:38 PM

Quote:

Originally posted by DerekB
This seems a little low, but it wouldn't have reach such a high speed if it were too lean.

On the contrary. The engine will reach an absolute maximum RPM only when it is on the edge of a VERY lean A/F ratio. Which of course as we know, detremental to the little engines where the lube is in the fuel supplied. Highest RPM's will be right before the engine bogs from missfirig, because of insufficient fuel.

mtrsprt · #13 10-04-2003, 03:41 PM

Quote:

Originally posted by DerekB
(this doesnt account for tires (final roll-out))

This is one of the most important factors here. Some tires after balooning will have a much higher rollout measurement.

Like my findings. Over a 4 mph gain in top end just from a tire/rim swap.

DerekB · #14 10-04-2003, 05:14 PM

Quote:

Originally posted by mtrsprt
On the contrary. The engine will reach an absolute maximum RPM only when it is on the edge of a VERY lean A/F ratio. Which of course as we know, detremental to the little engines where the lube is in the fuel supplied. Highest RPM's will be right before the engine bogs from missfirig, because of insufficient fuel.

I'm fully aware of the limit of fuel and speed. We always tune the engine to the limit and richen it slightly so the engine doens't starve at full throttle.

I also understand tire diameter increase affecting overall topspeed. But my hole point is why did you say you doubted that the car acheived the speed we put?

DerekB · #15 10-04-2003, 05:16 PM

Quote:

Originally posted by StevePond
That's a cool experiment, but don't put too much stock in the speed readings you're getting. The margin of error on a GPS receiver is pretty considerable, so the distance you need to travel before you get a somewhat accurate estimated speed is many consecutive miles (not a lot of back and forth).

Steve, Im not sure this is true. I think Road and Track or C&D now use a GPS system to do a figure 8-skid pad test. GPS is now very accurate after de-militarization of accuracy.

mtrsprt · #16 10-04-2003, 05:34 PM

Quote:

Originally posted by DerekB
But my hole point is why did you say you doubted that the car acheived the speed we put?

It wasnt me that doubted it so much as Oldchool put it.

The tires could have brought the MBX-5 up 4 mph from where a 4.25" tire would normally be.

Do you remember what engine was used in it?

My WS7ll is basically pulling a good 35,000 rpm under full load, which I am very pleased with, because the bottom and mid-range is excellent.

StevePond · #17 10-04-2003, 06:11 PM

The latest information I have on GPS systems says the best possible margin error on a standard GPS is 10 to 100 meters. The Garmin unit posted here has a minimum margin of error of +/- 15 METERS, not feet. This means that your 600 foot run can easily produce a 15% error in speed.

DPGS is the only more accurate solution, but as far as I know, it's not available in compact handheld GPS units. DGPS equals Differential GPS, where the U.S. Coast Guard transmits a correction signal to make DPGS receivers more accurate because super tankers cant really afford to use equipment that can be in error by as much as 1000 feet.

BTW - the accuracy of the GPS improves as it receives signals from more satellites, but at their best, standard GPS units still won’t produce speed results nearly as accurate as a stop watch and a calculator, or a good piece of radar equipment. I'd be interested in reading more about what type of equipement whatever car magazine is using for testing. I don't think it's a run of the mill GPS, or at least I hope it's not...

mtrsprt · #18 10-04-2003, 06:26 PM

Steve. Is it the speed at which you dont believe? Because 50.7mph is perfectly believable isn't it?

Along with the engine RPM and final drive calculations, theres no reason to belive that the buggy was actually traveling any faster than it was.

The GPS systems are now more accurate after they passed that law or whatever it was for thesystem that was previously only allowed to be used by federal users(Coast Gaurd etc.) to be now used by civilians back in 1998 or around that time.

I had plenty of room for the GPS to pick the unit up multiple times for an accurate measuement.

asc · #19 10-04-2003, 10:26 PM

Well,

I was intrigued by this topic. I just so happen to own the exact same GPS unit as the one pictured on the first page of this post. With the cooperation of my wife (rolling her eyes) I conducted an experiment to determine the accuracy of the calculated speed vs. the speedometer in my car.

Results?

This GPS is amazingly accurate, especially if you are receiving a signal from a satellite overhead and one just over the horizon. Try it.

The algorithms used to calculate speed are independent of those used to fix a spherical position. I was involved with the initial fielding of GPS in the military back in 89. Rockwell Collins made a unit which integrated into our direction finding/ signal jamming mobile field equipment. These GPSs increased our accuracy 10 fold. We had access to the encyphered military frequencies and could obtain spherical coordinates down to about 6 inches accuracy. We were made aware of the intentional error factored in the (civilian available) signals from the satellites but speed calculations were not subject to variation due to the error.

Hate to go against an administrator on this one but I believe the speed results are very close.

mtrsprt · #20 10-04-2003, 11:37 PM

Quote:

Originally posted by asc

Hate to go against an administrator on this one but I believe the speed results are very close.

I'm sure Steve knows, that being an administrator for this forum, doesn't mean he has to know everything there is to know about any subject.

I moderate a few message boards, and I do not know everything there is to know about all topics.

mtrsprt · #21 10-04-2003, 11:44 PM

They ought to use GPS instead of radar.

The margin of error is greater with handheld radar.

BTW. I actually measured the distance of the WOT run, and it was roughly 860ft

Good thing the WS7ll was at a comfortable 230*F

Toyotatogo · #22 10-04-2003, 11:52 PM

Still slower than my big block .15 rc10gt project......... lol

Oh wait I never got a chance to test that thing yet .........

OldskoolGT · #23 10-05-2003, 12:19 PM

DerekB,

I did some more calculations, and with some reasonable estimations (35K rpm, tires expanding to 125 mm) a top speed of over 40 mph does not seem so unbelievable now for a buggy. Although I never would have guessed that my X5 might have been doing close to 40 mph at the end of Action RC's 165 foot straight.

You guys should try doing some top speed runs with some tires that don't expand. It would be interesting too see what kind of rpms these engines are reaching.

mtrsprt · #24 10-05-2003, 12:49 PM

Quote:

Originally posted by OldskoolGT
I never would have guessed that my X5 might have been doing close to 40 mph at the end of Action RC's 165 foot straight.

Are you serious? They said it was 165ft??????????I need one of those engines!!!!!

mtrsprt · #25 10-05-2003, 12:52 PM

Quote:

Originally posted by OldskoolGT

You guys should try doing some top speed runs with some tires that don't expand. It would be interesting too see what kind of rpms these engines are reaching.

Any kind of top speed run would make the magazines sell like hotcakes. Kids LOVE top speed #'s. Take 3 cars, 6 of the most sought after .21's, a GPS, and a radar gun to a good straightaway. Spend about 4-6 hours on the test. Print a 5 page article in the magazine!!!.