More Top End?

[ARTZ]

will a car acheive higher top end speeds with power alone or does gearing need to be changed to go faster..

For instance if a GTST tops out around 240 how much faster would it go with same gearing but double power..

[iplen]

Too many variables, eg.

* If a car with standard power hits the rev limiter in top gear (unlikely) then you can quadruple the horsepower, it will get there quicker, but will still not go any faster, because the motor is turning the same gearing as fast as it can.

* If we take the same car and with all of the engine work decide to rev it 1000rpm harder, so increase the rev limiter, it will go faster, but not because of the horsepower

* If the car however does not have the grunt to turn top gear to the limiter then more horsepower will make it faster.

[SlowSkyline]

it depends if 240 was at the top of 5th or not... if the cars geared to top out at 200 no matter if its putting out 4ty million rwkws it will still top out at 200...

[luvpsi]

exactly its all about the gearing

[syfon]

All about the gearing my friend. Put a taller ratio in your diff, i.e., a 3.73 and your top speed will be higher. From what i know R33 GTS-T manuals come with a 4.11 and autos come with 4.44

[KezR33]

One this topic, will shorter gearing give you faster acceleration, or will both cars accelerate at a similar pace? What's the advantage of short gears?

[ARTZ]

exactly that.. Older muscle cars always had lower gear like 3.08 thy would put 4.11s in for drag racing.

These days 4.11s are pretty standard and they have better gearbox gearing so its not reving so hard on the freeway

[KezR33]

I thought so, explains why Monaros are so slow!

[ARTZ]

pretty sure newer monaros are 4.11 or 3.9

[syfon]

I thought so, explains why Monaros are so slow!

my dad used to race his HG monaro (308 gts) @ ravenswood raceway back in the day....his fastest time was a 13.2, mildly worked making about 325rwhp....was running a 4.11 diff ratio.

[KezR33]

pretty sure newer monaros are 4.11 or 3.9

3.46

My mate has one and he reckons doing a 100kph if you put it in 6th the car nearly stalls.

[ARTZ]

my dad used to race his HG monaro (308 gts) @ ravenswood raceway back in the day....his fastest time was a 13.2, mildly worked making about 325rwhp....was running a 4.11 diff ratio.

haha. Mine had a HJ Monaro with a well worked 308 but 3.08s in the rear was good for 14sec. But fully loaded with a trailer would sit on 160km happy to do 200 fully loaded with no trailer

[syfon]

haha. Mine had a HJ Monaro with a well worked 308 but 3.08s in the rear was good for 14sec. But fully loaded with a trailer would sit on 160km happy to do 200 fully loaded with no trailer

nice

my brothers 308 hg gts is running about 350rwhp and that ran a 12.9sec with slightly taller ratio than the 4.11

[scathing]

will a car acheive higher top end speeds with power alone or does gearing need to be changed to go faster..

Power:weight ratio determines low-speed acceleration (for a certain set of gear ratios).

Power:drag determines high speed acceleration/top speed (for a certain set of gear ratios). At a certain point wind resistance becomes so high that it relegates inertia due to mass to a relatively negligible amount when determining the maximums.

Speed is a factor of engine speed and gear ratio (in the gearbox and final drive) so the amount of power you're making does not have a direct relationship.

As others have said, if you're hitting the rev limiter in top gear with your existing power, all that adding more power is going to do is mean you will get to that speed in a shorter time.

However, if with your existing power you're not able to rev out top gear (which will be due to drag) then adding more power will increase your top speed. Of course, if adding more power meant increasing drag (say if you needed to open up the front of the car to get more air onto your heat exchangers) then your gains might not be as high as you'd first think.

One this topic, will shorter gearing give you faster acceleration, or will both cars accelerate at a similar pace? What's the advantage of short gears?

Shorter gears may give you faster acceleration. It depends on the situation. Shorter gearing will give you better acceleration in a certain gear, but note that your ground speed in that gear at a certain RPM will be lower. Whether its worth it or not is up to the conditions.

As an example, with the stock 3.5 FD in my car I'd be able to hold 3rd gear all the way around Wakefield after the main straight. With my new 3.9 I keep having to grab 4th and use about half its rev band (and then back into 3rd for some corners). Every time you change gear you decelerate while your engine is disconnected from your wheels, as drag and parasitic loss still act upon your car. Those extra gearchanges have actually cost me laptimes (both in terms of outright time and consistency) at Wakefield Park.

By the same token, at Eastern Creek where I was constantly making 3rd-4th interchanges. I should be able to avoid using 3rd so much now, and getting rid of those gearchanges should mean that I'm quicker at EC (I can't wait to get out there and find out, my Wakefield experiences have gotten me a bit annoyed at this FD).

My car also used to top out 4th gear at the end of the quarter. I'd pretty much hit the cutout just after crossing the line. With the shorter FD I'd now have to grab 5th. It's hard to say whether the extra in-gear acceleration is worth the trade-off on having to make the extra shift (and being more likely to wheelspin out the hole) but I'm suspecting I'm now a fraction slower.

Note that I've got a pretty close ratio box stock. On a car with long ratios, like Falcodores, shortening the FD is probably a good thing for acceleration in most circumstances.

[mad082]

when talking top speed it isn't just about gearing. taller gearing can actually lower the top speed. i think it was the VR HSV GTS that had a top speed of 250kmh in 5th gear and only 217kmh in 6th because the gearing was too tall to overcome the wind resistance. very few cars on the road will actually hit the rev limiter in top gear in stock form. a lot would actually have higher top speeds with fractionally shorter gearing, but car companies don't worry about this sort of thing as they aim for top gear to rev in a nice fat torque range on the highway to give good fuel economy as well as stop you having to drop down gears at the slightest incline. top speed is all about overcoming air resistance and the faster you go the more it takes to go that little bit faster.

as for shorter gearing increasing acceleration, the short answer is yes. this is why first gear accelerates faster than 5th gear. a commodore or falcon with a shorter diff ratio will be much faster than a stock one in a drag race. first gear in an auto commodore (older 4 speed autos) is nearly the same as second gear in a manual skyline (once diff ratios are taken into account).

[Birds]

The first reply to the thread nailed it. Marc's post there has some pretty good information too.

It all depends on what you're aiming for. You set a goal, then you change all the variables to shoot for that goal. If I want to drag people to 100km/h I'll use the standard 4.11 diff in my Skyline because 2nd gear tops out around that and if it was any shorter I'd need another gear change, which will cost me time. If we're dragging to 80km/h I'll put a 4.36 in the car, because even though 2nd gear will now top out around 90-95, I only need 80 of that and the shorter ratio will give slightly better acceleration.

If you calculate it, a standard R33 GTS-T has the gearing to achieve ~277km/h (forget the exact figure). Realistically you'll only get to around 250 because you'll run out of torque. Shorten the diff a bit and you might get 255 thanks to the extra torque of the gearing. Shorten it too much and you'll only get 230 because your car will redline in top gear at this speed. Make it too tall (say 2.5:1) and you'll have a theoretical top speed of 400km/h+ with only enough torque to get to 160-170. But 1000hp behind that ratio and you'll propel the car to around 320. There are lots of variables to it all.

All hypotheticals for the purpose of examples^

[Nee-san]

the wind resistance. very few cars on the road will actually hit the rev limiter in top gear in stock form. a lot would actually have higher top speeds with fractionally shorter gearing, but car companies don't worry about this sort of thing as they aim for top gear to rev in a nice fat torque range on the highway to give good fuel economy as well as stop you having to drop down gears at the slightest incline. top speed is all about overcoming air resistance and the faster you go the more it takes to go that little bit faster.

as for shorter gearing increasing acceleration, the short answer is yes. this is why first gear accelerates faster than 5th gear. a commodore or falcon with a shorter diff ratio will be much faster than a stock one in a drag race. first gear in an auto commodore (older 4 speed autos) is nearly the same as second gear in a manual skyline (once diff ratios are taken into account).

I never thought that I would change my opinion again, but your argument moved me in way that I've never known.

[mad082]

I never thought that I would change my opinion again, but your argument moved me in way that I've never known.

i generally have that effect......

[ARTZ]

yes definatly one of your better posts Marc. While i have your attention, do bike speedos work in cars?

[Nee-san]

I honestly just wanted to get a bit of savage garden in this thread.