I was in B&N browsing throught the car section and read a few sentances about shifting race cars. The guy stated that the optimum speed was obtained when shifted between the maximum HP and maximum torque based upon the dyno.

I know most of the lude drag racers are shifting at redline (7400) or above to get the best 1/4 time. (I know a lot of people shift around 8k or higher depending upon their mods.) Based upon the dynos that I have seen for the lude, the shift would occur somewhere around 6500rpms or so??? If that was done, I don't think the 1/4 mi time would be better.

Just wondering what your thoughts were on this? Maybe it is more important for "true" race cars on the track rather than street cars?

 

ludes peak at 6800-7000 in stock format.

People shift higher in 1st becuase you will drop out of VTEC....which will seriously kill your speed.


And the shift from 2-3 puts you below the torque peak so........

 

Most books and other sources also state that engines get their peak volumetric efficiency at peak torque. However this is not true of most VTEC, VVTI and similar motors.

If I was to follow the logic of shifting between peak torque and HP that would be a bad idea. Each time I shift I will not only fall out of VTEC but in the next gear I will be at a lower HP.

Think of it this way:

Do I shift at 7500/8000 RPMs (~200/190 HP) to stay in VTEC so that in the next gear I am at 6000 RPMs (~170 HP)

Or do I shift at 6800 RPMs (~180 HP) and drop out of VTEC so that in the next gear I am at 4000 RPMs (~140 HP)

The first example is the way to go because you dont lose as much power in between shifts. You only drop from 200 to 170 as opposed to 180 to 140.

(those numbers are just a quick guesstimate)


[Modified by BlueShadow, 5:59 PM 2/1/2003]

 

Yeah, I guess the Vtec is the difference here as it plays a huge part in HP for this particular engine. Lowering the crossover with the Vafc will keep us in the Vtec range, but only to a certain point. (We cannot lower it tooooo much) I have my crossover at 4700 now.

Guess it's sacrificing HP near the redline for better HP on the next gear...

 

Its all about GEARING........

 

Sure you can lower your VTEC X-over so you dont have to shift at a higher gear but in the next gear you will still be at a lower HP when compared to shifting at a higher RPM and being at a higher RPM (and higher HP) in the next gear.

 

I tried explaining this to some people a while ago. They were all like "don't shift that high, you loose power up in that RPM", which might have been true, but I still had MORE power at that higher RPM than if I had shifted into the next gear (IE> dropping out of VTEC or being damn close to doing so). It's a balance, you have to find where the benefits of the higher RPM's HP drop off point gets to be too great, but where the next gear's RPM drop doesn't take you out of your power band.

 

Yup, I've said the same thing myself...IE. would you rather lose 15 HP at the higher RPM by shifting high or 30 HP at low RPM by shifting to low?