Can raising your engine shift RPM increase your TOP SPEED?

[Frostbite]

I remember reading a section in the setup notes on my Heavy Hitters and I wanted to ask this seasoned bunch of riders about the validity of it. I don't have the notes with me but there was a section on "turning engine RPM into speed".

Basically, the recommendations said something to the effect of spinning your engine close to the high end of your engines optimum shift speed to squeeze a few more miles out on top end speeds.

Of course this makes me wonder....................(I seem to wonder a lot) if running our sleds at the higher end of the recommended shift speed may give you lake racers a few more miles per hour on top end?

My particular sled seems to just love 10,400 to 10,500 RPM. I see some folks hitting the rev limited (usually guys riding their turbos for the first time).

With the horse power and torque curves as flat as they are on the RX-1 why not run closer to 11,000 and get a few more mph out of the sled?
It really doesn't look like there is that big of a penalty to pay in either horsepower or torque (as in a two stroke powerband) for exceeding the recommended 10,200 RPM Yamaha suggests.

We have all seen the gearing charts and the theoretical top speed listed for each set of gears is directly proportional to the engine RPM. The higher the engine RPM the higher the "theoretical" top speed. I'm sure there are things to be considered like drag and surface conditions but it MAY be worth at least talking about.

Honesty, I just like to watch as some of you REALLY smart guys start a discussion (and sometimes disagreement) that is usually WAY over my head

Frosty

 

[LazyBastard]

It doesn't help to spin faster, because POWER is POWER. Aim for 10300-10400 rpm and you will achieve the best top speed. You go any higher than that, power drops off, so driveshaft torque drops off and speed decreases. Modified engines may have their peak power elsewhere. Freddie's air kit makes peak power at 10700-10800, so thats where they clutch to.

 

[Frostbite]

I can't believe it!

Either I completely missed the boat or read the wrong posts on here but this is the first time I have read that the ECP kit should be clutched to 10,700 to 10,800.

I was wondering why the higher I had my shift speed (above 10,200) the more power I seemed to have. If his kit likes the higher RPMs that makes good sense.

See more RPMs = more speed

Frosty

 

[Frostbite]

Why does everything we talk about always have to revolve around the ECP kit?

Beacuse they work!

 

[LazyBastard]

I have yet to see any evidence of that as everybody appears to be too chicken to come up here and race me. I have NEVER raced this sled - *everybody else* is also too chicken.

 

[SUPERTUNER]

It doesn't help to spin faster, because POWER is POWER. Aim for 10300-10400 rpm and you will achieve the best top speed. You go any higher than that, power drops off, so driveshaft torque drops off and speed decreases. Modified engines may have their peak power elsewhere. Freddie's air kit makes peak power at 10700-10800, so thats where they clutch to.

LB is giving good advice here but the truth of the matter is that with my air kits, peak power is achieved by 9200 RPM's and pretty much flatlines to the rev limiter which hits a real 11,100 give or take. The tach will read around 10,800 RPM's at the rev limiter.

Spinnig the RPM's higher will increase top speed but like LB says..power is power and the torque drops dramtically after 9000 RPM's.

I am sitting here looking at a dyno graph as I type this of a stock airbox versus the ECP air kit.

Torque with the stock airbox at 9000 is 72.8 foot pounds...air kit at 9K = 80 foot pounds. 9500/air kit 76.4 Ft Lbs., airbox 69.6, 10K/air kit = 72.5, airbox = 70, 10.5K/air kit = 69.2, airbox = 67.8,11K/air kit = 63.4, airbox = 63.9

I agree that a loss of driveshaft torque diminishes speed. If you were on perfectly flat and very smooth ice and were revving the engine to lets say 10,800 it would MPH slightly faster than 10,500 RPM's. Hit one little bump though and you speed goes into the toilet because the engine cannot recover and grunts too hard, backshifts albeit too late and wastes all that stored energy/momentum you had and won't recover in time.

 

[Snowman269]

I have yet to see any evidence of that as everybody appears to be too chicken to come up here and race me. I have NEVER raced this sled - *everybody else* is also too chicken.

Did I read CHICKEN????????

Difficult to find you without narrowing down your location from this: "Location: Somewhere in that frozen wasteland north of the border."

Where should us Cha-Ch-Ch-Chickens go?

Mines stock, that equals to I'm losing the race. But a day riding is a day riding. I'm into having fun!

 

[Frostbite]

Freddie, are you officially saying to clutch for 10,750 while using your ECP kits? If so, I need to pull some weight off of my heavy hitters (since I'm sold on my spring combination) to get my RPMs up to that mark.

From reading your data on from the dyno I see your ECP kit is higher on torque at all but 11,000 RPM.

How much more does the torque increase (roughly) when the EVAC kit is added to your ECP kit for each given RPM.

Frosty

 

[RX-Dave]

On a note here, I tested my factory tach to a Digatron SN54, and at 10,500 factory tach RPM, it is running 10,200 on the Digatron. So, if it is running best at 10,5 - you are actually only spinning it about 10,2 - right where yammy says it is "all-good"

 

[Frostbite]

I guess that means I should be spinning 11,000 to equal the 10,700 to 10,800 that the ECP kit prefers?

Frosty

 

[SUPERTUNER]

Freddie, are you officially saying to clutch for 10,750 while using your ECP kits? If so, I need to pull some weight off of my heavy hitters (since I'm sold on my spring combination) to get my RPMs up to that mark.



No, I am not saying clutch for 10,750 RPM's unless you want to set high MPH at a radar run. You will experience the benefit of increased fuel mileage spinning the engine at a slower speed and also have more torque which is desireable when trail riding where back shifting and upshifting are constant.

"How much more does the torque increase (roughly) when the EVAC kit is
added to your ECP kit for each given RPM.

Frosty

"

There is only a little and on some sleds no torque/power gain at top revs. On 2 stroke engines the peak torque is only 200 or so RPM's behind peak power. On 4 stroke engines, the peak torque is 2500 to 300 RPM's behind peak power! This is why Yamaha underdrives the primary clutch. It is in an effort of keeping the primary driveline in more of the "meat" of the torque.

To answer your specific question about the increase in torque...at 3200 RPM's the non evac makes 46.9, evac makes 49.0. 5700...non evac = 66.5, evac = 73.4, 7500 non evac = 79.1, evac = 81.5, 9400 non evac = 75.3, evac = 76.8. After 9500 RPM's the lines lay on top of each other.

This means that there is little gain by revving higher RPM due to the fact that you make the same torque with or without the evac. The evac just gets there quicker and geared properly, you will experience more time to accelerate due to the evac making "quicker power".

 

[Frostbite]

Thanks for that info Freddie but I'd still like to know if I should pull a little weight out of my Heavy Hitters and aim for a higher (10,700) shift speed?

Maybe it should be 10,900 if the tachs are really off by 200 RPM?

Frosty

 

[RX-Dave]

Note: I am not trying to tell anyone where to clutch their sled, just saying, some people may want to calibrate their sleds like I did with a more accurate device.

 

[SUPERTUNER]

Clutching your engine for 10,300 to 10,500 will get you about all the performance you could obtain from a stock air kit equipped engine.

Revving to a "real" 10,700 RPM's will get you 1 or 2 more MPH. This is good for the $1000.00 win prize at the radar run.

Revving the engine a little lower than 10,700 will keep you recovering better from the loss of torque. I mailed a dynosheet to Mr. Sled. He should be posting it this week. It will all be clear when you see the dynosheet.

Freddie

 

[Frostbite]

Thanks freddie. Is he posting ECP and ECP plus EVAC?