Is it safe to shift my SS at 8k if I have had my rev limiter removed with a JET ecu?
Will this allow me to stay in vtec territory between the 1-2 shift and improve my times? Is it true that the 5th gen's tach is off by 600 at the top?

 

If you look at a DYNO chart the max hp in a prelude is produced somewhere around 6900 rpm. So that might be a good place to shift. But if you shift a lil higher then you stay in VTEC longer.
I'd say shift at 6900 for non-drag use.
EDIT: and yes it is true that the 5th gen tach is off by about 600.

 

Thanks, you are right it makes more sense to shift at the point where max hp is made.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Uman &raquo;</TD></TR><TR><TD CLASS="quote">Thanks, you are right it makes more sense to shift at the point where max hp is made.</TD></TR></TABLE>
Well yes and no. There s continuing debate about that. You'll see if some more people ring in on the subject.
-Benefits of shifting at 7200-7600, obviously you have a high chance of staying in VTEC band, but at the same time you're making no additional hp and essentially just reving your engine.
-Benefits of shifting at 6900-7000 your engine will like you more. And if you have a VAFC and if you're a good shifter/driver its possible to stay in VTEC.
I think its pretty much up to the individual.

 

if you want to find the best place to shift:

-take a dyno chart of your car

-starting at like 4,000 RPM, make a chart for each gear. multiply the torque by the gear ratio, and then multiply that by the final drive. Do that for every gear, and in, say, 200 RPM intervals. Fortunately for you, you only have four gears to do this for...

-graph the speed of the car in each gear.

-determine at what point you should shift so that the torque product you found in the next gear is equal to the torque in the current gear.

for example: Lets say at 7500 RPM, you make 105 ft lbs of torque to the wheels. If you shift at 7500 RPM out of first gear, lets say you drop to 5,000 RPM, at which point you make 135 ft lbs of torque to the wheels.

your first gear ratio is 3.31:1 , and your second gear rato is, uh, I guess in that case it would be 2.2:1 (thats not what we have, but lets just say for this example.) lets use our final drive of 4.27:1

1st GEAR AT 7500....3.31 x 4.27 x 105 ft/lbs = 1484lbs of driving force

and you shift into second gear....

2nd GEAR AT 5000.... 2.2:1 x 4.27 x 135ft/lbs = 1268lbs of driving force

so in this case, even though the power is dropping off, the torque multiplication of the first gear makes more 'twisting force' at the wheel then it would in second gear at the same speed.

Normally, you'll take 1st gear all the way to your rev limiter, because 1st gear is usually almost twice is short as 2nd gear (twice the torque multiplication). As far as every other gear, you'd have to figure it out. I'm sure you could look at a dyno of a prelude w/ bolt ons, and use that as your guide. But you'll also need to find your gear ratios.

And all though HP is what matters, when doing these calculations, you'll only use the torque curve.

 

Say for instance that a dyno plot says max hp occurs at 7000 and I want to shift at max hp, do I then shift when my tach says 7600 since it is off by 600 at the top or is this already accounted for in the dyno numbers?

 

your dyno will show the actual engine speed, not what your tach says.

Re-read my post. Shifting at the peak HP will NOT yeild the best results.

 

Thanks, your post was very informative, now all I have to do is find someone to dyno an automatic.