Best revs for max speed on a 6 speed

[Suprash]

Originally posted by Thorin

not read it all but some people seem to be under the impression that you're best off changing at 6000 or before just because the torque graph starts to fall off around that point... but what about your revs when you change up to the next gear? This may have been posted before but...

 

http://www.boostaholic.com/supra/shiftpoints.html

 

I see your point Thorin, and its a good one, cause if you change earlier you are then lower in the revs on teh next gear.....

[tbourner]

Originally posted by Ashley Willis

I see your point Thorin, and its a good one, cause if you change earlier you are then lower in the revs on teh next gear.....

 

 

Funny, that's what I said too!!

 

 

 

Hence, my little paint jobby to illustrate:

 

http://homepage.ntlworld.com/tbourner/Car%20pics/images/bhpcurve.jpg

As I said before:

Very simplified. Change at the upper RED point and your average power will be less because your revs in the next gear will be at the lower RED point.

Change at the upper BLUE point and your average BHP is much higher, even though the acceleration is starting to die off by that time.

[Thorin]

Originally posted by tbourner

Funny, that's what I said too!!

 

Sorry, I did say I hadn't read it all

[Digsy]

I don't think that Ian was implying that the Supra VVTi is utterly gutless. I suspect he was talking about Honda engines, which I also eluded to in my post.

 

..and on that note, shame on me because VTEC and VVTi are two totaly different technologies. VTEC uses two separate cam profiles and VVTi swings a single cam profile between two valve timing points.

 

Both are comparible in taht they can be used to manage the trade off between top end power and low down torque.

[SimonB]

Originally posted by tbourner

IBut we are essentially talking about a 1/4 mile sprint or similar situation here, where torque works best at the start to get the car moving - after that it's the BHP figure that does the most work.

 

No, torque is the only thing that determines acceleration (along with mass of course). Acceleration = force/mass, where here the force is the toque at the wheels. If you build an engine that revs twice as high say, so produces loads of power but the same torque (like an F1 engine say), that allows you to use a lower gear ratio, so more torque gets to the wheels.

 

People say that power determines your top speed, what they really mean is that torque and gear ratio determines top speed.

 

Have a look at this for an explanation of torque, power, work etc.

 

Nothing to do with when to change gear really though, so sorry for the !

[Digsy]

Originally posted by SimonB

Nothing to do with when to change gear really though, so sorry for the !

 

I think it has everythng to do with it. Good post, dude.

 

Considering the torque going to the rear wheels in isolation is fint until you get to the shit point, then you have to consider where on the torque curve you will drop back to.

 

Anyone plotted the cascade curves yet and worked it out?

[Tom]

I found this on mkiv.com and thought it was a little strange, shouldnt there actually be a curve??? I didnt think there would be that much torque across the whole rev range.

 

 

 

[Digsy]

Its like a billiard table

 

Does look a bit over-simplified.

[SimonB]

Originally posted by Digsy

...until you get to the shit point...

 

Good typo . I hereby define the shit point as the point where your rear wheels start spinning and you start heading for the central reservation...

[Digsy]

PMSL! Well spotted.

 

Especially funny since I pulled someone up for exactly the same typo a few weeks back.

[lust2luv]

This looks a bit more realistic (from mkiv.co.nz):

 

 

Peak torque at 3,600 revs on a TT though - if torque is everything, this would suggest changing up very early, maybe 5,000 revs?!

 

...thinking about it though, that's probably the torque curve in 6th gear??

 

[Digsy]

Cheer for that.

 

Those should be the torque curves from an engine dyno (i.e. at the flywheel). OEMs generally don't use figures at the wheels in publicity.

[Ian C]

Apologies to VVTi Supra owners

 

I didn't mean to diss them and I wouldn't, in fact Toyota are about the only car manufacturer that has used variable valve timing to improve midrange torque rather than chasing high bhp figured, and I respect them for that. What I meant was, and apologies for the minor , that cars like the S2000 and the Civic Type R were gutless. Peak torque at 6000+rpm, and a weedy peak torque at that, to me is not a fun car to drive every day.

 

Phew. And on that dyno plot, I'd change at 6000 and get right back onto the point where the torque curve crosses over the bhp curve.

 

-Ian

[250horses]

Righto, both torque curves show a drop at about 5900 to 6000.

So there seems to be no point in taking a stock 6sp over 6000 rpm. Mine actually seems to stop accelerating with the same vigour at over 6K - at first i thought it was broken. :D

[Thorin]

Originally posted by 250horses

Righto, both torque curves show a drop at about 5900 to 6000.

So there seems to be no point in taking a stock 6sp over 6000 rpm.

 

Except for the fact that if you change up at 6k RPM or before your revs will not be at the optimal point in the next gear when you change up.

[tbourner]

I'm glad someone agrees.