Best revs for max speed on a 6 speed

[250horses]

Now Ive had my 6 speed for a week, my old na took off at 5000 rpm and had a strong power band right upto 6600 rpm.

 

The TT seems to go best with changes at 5800 rpm.

If you bring it up to past 6000 rpm, I reckon it slows down.

Obviously its on full boost at 5800 so the extra revs make no difference.

 

So my point is as follows:

 

 

What do U reckon the best revs are to change gear on a 6 speed TT

[Andrew]

I'd say 7000 revs :flame Dev

 

1st and 2nd 6500 - 6800, 3rd 6500 and 4th 6000 - 6500. Always felt when stretching 3rd and 4th to red line from 6000 revs I wasnt gaining any power.

 

UK specs and J-specs are geared slightly different I believe.

[tbourner]

Redline.

Not all the time obviously only when you're going for it (which really shouldn't be ALL the time!!).

 

 

If you say the max power is at so n so, so change then, you're WRONG.

 

 

Look at the area under the curve of a dyno chart, changing at full power will mean the area under it is less than changing at redline, because changing after the max power point will mean you get that particular point right in the middle of each gear's rev range.

[merckx]

Definately not the Red line, you'll get the max speed out of each gear but not max acceleration.

 

If you look at a dyno plot, torque and power levels have started to drop well before the red line.

 

I have a quick glance at the rev counter but change up before the red line, more because you get a feel for when it's right to change than anything else.

 

Difficult to focus on the revs when you're going flat out

 

Maybe the guys who have experience with running on the 1/4 mile could give us a definate answer!

[tbourner]

I didn't mean exactly on the rev line, it's easier to say that though. I usually change IIRC at about 300-400 revs below redline.

 

 

You want the top revs in the low gear, and the new low revs in the next gear to be equal distance from the peak on the power curve, so changing at that point is wrong.

That way you get the max AVERAGE power of the gear through the rev range that you use.

 

Torque is largely irrelevant at full throttle, at least from 2nd gear upwards, as you're already moving so the momentum is already put into the mass of the car.

[merckx]

Torque is largely irrelevant at full throttle, at least from 2nd gear upwards, as you're already moving so the momentum is already put into the mass of the car

 

But momentum is directly proportional to your speed, so to double your speed you also have to also double your momentum.

[AJI]

Realy you should be changing very shortly after the torque curve starts to fall off. This occurs at 5700rpm ? (is that right?) I can't remember how a standard TT graph goes but from memory I think it rises steeply just after 2000rpm, levels off at 4600rpm and then starts to fall off again at 5700rpm.

I'm running a non-standard TT with around 400bhp and I can definately feel a drop off in acceleration after 6000rpm.

So I'd say from my experience change at 6000rpm to get the most out of the torque.

[250horses]

Well if max torque is around 5700 rpm that makes sense to my theory that It seems to pull faster when I change at around 5700 rpm.

Any Santa Pod 1/4 miles out there who can advise ???

[Digsy]

You actually need to plot the cascade curves for torque at the rear wheels in each gear (sort of like a dyno torque curve, but at the rear wheels) against vehicle speed. If you do it for each gear, you will end up with what looks like a load of torque curves almost nose to tail, but overlapping slightly. The points where the curves cross are the optimum (theoretical) change up points.

[Digsy]

This is an example of what I am on about.

 

Its a bit simplistic because the changeup point would always be at the redline. Doesn't always work that way for car gearing.

[Ian C]

Stock J-spec cams I'd say shift at 6000, you can feel the power fall off beyond that. 256in 264out cams, change up somewhere north of 6500, it pulls strong up to the rev limiter but I've timed the acceleration and it slows down a bit between 6500 and 7000. Not a lot though.

 

-Ian

[Supragal]

Originally posted by Ian C

I've timed the acceleration and it slows down a bit between 6500 and 7000. Not a lot though.

 

-Ian

 

he actually has.... and has video footage also i believe

[tbourner]

Originally posted by merckx

But momentum is directly proportional to your speed, so to double your speed you also have to also double your momentum.

 

 

Sort of, but we're talking about acceleration not top speed (Yes I know the thread title says different, but why are we discussing it then - it'd be as far as your bhp could carry the needle up, to get max SPEED!!).

Anyway, the torque doesn't affect your acceleration anywhere near as much as BHP does, so you shouldn't even bother considering the torque curve. It would from a standing start, or from a constant speed, but when you're accelerating it's effects (especially in a car like the Supra) will not make enough of a difference.

 

 

As for BHP, check the attached:

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.

[Ian C]

Gears are a ratio so the earlier you shift up the less rpms you drop, so it's not entirely a linear relationship.

 

Torque is everything - horsepower is merely a calculated number from measured torque. You should change up at a point where power is just past peak, and the upshift drops you back into your torque peak.

 

-Ian

[Tom]

Originally posted by Ian C

Gears are a ratio so the earlier you shift up the less rpms you drop, so it's not entirely a linear relationship.

 

Torque is everything - horsepower is merely a calculated number from measured torque. You should change up at a point where power is just past peak, and the upshift drops you back into your torque peak.

 

-Ian

 

So is Torque the most important thing then for when looking at a cars stats?

 

and could you explain torque? my kind of understanding is that you need power of the line but torque while you rolling, is this right?

[Suprash]

Torque means everything, torque is what you feel when you stamp on the gas, torque is the real daddy.........

 

What would the point be of having 600 horses and say 250 lb/ft of torque, it would be much better having half of that BHP, 300 and 390 lb/ft of torque.

 

Impressive car stats usually show more torque than BHP, cant remember who now, but someone is running a stock J-Spec and he has something like 350 horses and 391 lb/ft of torque.

[Ian C]

This is why VVTi cars feel utterly gutless. No torque. They get their power by spinning the engine really fast instead.

 

This is from memory so shoot me down if it's wrong Torque is the measurement of work done over time by a twisting force. 1ft/lb is the work done by rotating a one pound weight on a one foot lever for one minute. 10ft/lb is the work done by, say, rotating a 1lb weight on a 10 foot lever, or a 10lb weight on a 1 foot lever, etc etc, so the more ft/lbs you have, the harder you can twist the driveshafts.

 

I can't remember the equation for BHP so you'll have to look it up It should explain the whole torque/bhp multiplier effect too...

 

-Ian

[Digsy]

Originally posted by Ian C

This is why VVTi cars feel utterly gutless. No torque. They get their power by spinning the engine really fast instead.

 

This is from memory so shoot me down if it's wrong Torque is the measurement of work done over time by a twisting force. 1ft/lb is the work done by rotating a one pound weight on a one foot lever for one minute. 10ft/lb is the work done by, say, rotating a 1lb weight on a 10 foot lever, or a 10lb weight on a 1 foot lever, etc etc, so the more ft/lbs you have, the harder you can twist the driveshafts.

 

I can't remember the equation for BHP so you'll have to look it up It should explain the whole torque/bhp multiplier effect too...

 

-Ian

 

I'm not sure I'd go as far as Ian to say "utterly gutless" but it's why you have to keep a Honda VTEC engine on the boil if you want to feel all of the horsies. However, you can use exactly the same technology to get more low-down torque, so saying that VVTi engines are all gutless is a bit too much of a sweeping statement.

 

Torque is the product of force and distance. Time doesn't come into it. The 10lb x 1foot being the same as 1lb x 10 foot is correct....

 

 

 

...except we tend to use Newtons and meters these days

 

Power is torque x revs I think (or something along those lines). I think the torque has to be in Newton-meteres and the revs need to be in radians per second. The power falls out in Watts.

[SimonB]

Here you go, I was actually sad enough to look this up in a thread ages ago:-

 

Ok, I got bored at work and looked this up. Here goes:

 

power = torque * angular velocity.

therefore torque = power / angular velocity

 

angular velocity = rpm * (2 pie / 60)

 

Torque is measured in ftlbs so you have to convert the power from HP to/from ftlbs/second which you do by multiplying or dividing by 550.41 (ish)

 

So:

 

torque = (power in HP * 550.41) / (rpm * 0.1047)

 

power = (torque * rpm * 0.1047) / 550.41

 

Basically, torque is the force that turns the wheels. The more toque there is, the faster the wheels and hence the car will accelerate.

[Ian C]

Originally posted by Digsy

I'm not sure I'd go as far as Ian to say "utterly gutless" but it's why you have to keep a Honda VTEC engine on the boil if you want to feel all of the horsies. However, you can use exactly the same technology to get more low-down torque, so saying that VVTi engines are all gutless is a bit too much of a sweeping statement.

 

Torque is the product of force and distance. Time doesn't come into it. The 10lb x 1foot being the same as 1lb x 10 foot is correct....

 

 

 

...except we tend to use Newtons and meters these days

 

Power is torque x revs I think (or something along those lines). I think the torque has to be in Newton-meteres and the revs need to be in radians per second. The power falls out in Watts.

 

Pah, you know the VVTis I mean Car companies use a technology that could give huge amounts of grunt to an engine to instead give high power figures so it can sell to gumbies. Maybe my perspective is off

 

I stand by my sweeping statements and usage of outmoded units of measurements. Apologies for the time boo-boo

 

-Ian

[tbourner]

I agree with all that everyone is saying, you're not listening to my point.

 

Torque is very important to a car yes, and it's great for 'pulling power'.

 

But 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.

 

Torque is also brilliant for those times when you're sitting at 60mph on the motorway, and someone comes up behind you and you boot it. After that BHP takes over again and it's better to be in the 'BHP high' bracket!

So for maximum acceleration you'll need a reasonable torque curve to get the car off the start line, but keeping it in the maximum BHP cluster will do more good than working out the best average between BHP and torque.

[merckx]

This is why VVTi cars feel utterly gutless. No torque. They get their power by spinning the engine really fast instead

 

You are kidding aren't you?

 

Is that why the VVTI engines have more torque and power then than the earlier cars?

.

1ft/lb is the work done by rotating a one pound weight on a one foot lever for one minute

 

Torque has no relationship with time, basically it is a turning force.

 

Power is the rate of change of energy so the quicker the engine supplies more energy the more power you have

[Suprash]

Ian, are you saying that variable valve timing is useless....????

[Suprash]

Ian, are you saying that variable valve timing is useless....????

[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