Optimum rpm for change-up (Mk2 172)?

[gh172]

I tend to change up at around 6000rpm in my 172 - it's high enough to catch the next gear at 5000rpm and any higher seems a bit stressful to me . Pointless bouncing off the limiter IMHO - gone beyond any useful power by then. I have the Group N ECU with raised limit anyway, and my nerves couldn't take running it that high every time

Planning to fit a sequential shift light shortly, so just wondering where to set the shift point for optimum changes without blowing the engine...?

/G

 

[LegoHead]

limiter works for me.

 

[gh172]

Power and torque will be falling away by the time you reach the limiter (not to mention lack of mechanical sympathy). That's why the shift light - if you have one - is set somewhere more optimal.

/G

 

[LegoHead]

Its fun to hit limiter occasionally, but I would also like to know optimal gear change, mainly 1st to 2nd to 3rd, dont care about anything higher at the moment.

 

[Dan@SJM]

limiter works for me.

learn to drive it then

 

[_Tom]

I take mine to just before the limiter..

 

[LegoHead]

handbags at forty paces. Its my car and I wil drive it how i f**king well like.

 

[Danny P]

That little green gearlever light works well about 6800rpm

 

[lucky]

I guess you need to have a run on the rollin road to see what your power/torque curve is like really. My car doesn't make peak power till right at the 7500rpm limit, so you've got to rev the tits off it to get the best out of it. Just my opinion anyway

 

[McBunny]

Power and torque will be falling away by the time you reach the limiter (not to mention lack of mechanical sympathy). That's why the shift light - if you have one - is set somewhere more optimal.

/G

it doesnt have an optimum point shift light

it has an ooh f**k the limiter is coming light

 

[Ali]

about 7k, is where i hit peak Bhp.

 

[gh172]

That little green gearlever light works well about 6800rpm

Ain't got one of those (phase 2 172)

 

[gh172]

I guess you need to have a run on the rollin road to see what your power/torque curve is like really. My car doesn't make peak power till right at the 7500rpm limit, so you've got to rev the tits off it to get the best out of it. Just my opinion anyway

Cheers - I reckon most will be similar, so I started another thread about RR graphs, hoping to get some examples.

/G

 

[lucky]

I'll post a pic of mine on there for you.

 

[thedoc]

my power peak's just before 7000rpm, so shift light comes on at 6800rpm ish when warm, thats my optimum...

 

[The Hoff]

Indeed, about 6,800/7,000 produces best results as this drops you nicely back onto the powerband for continued acceleration. However in first, on anythig buy perfect road, i will normally shift to 2nd at around 5,000 as otherwise you just A-Get knocking/traction loss B-Hit the limiter as first is so rapid. Thats said i take 2nd/3rd right upto 6.8/7k if im thrashing.

 

[MarkCup]

It's different for every gear I think.

If I change up before 7000k from 1st, I'm then below 5k in 2nd, and it takes a second or two to really get going.

2nd is lower, about 6800 or so, and it gets less for each gear.

In 4th, about 6200 gets you into the meat of 5th's torque.

 

[gh172]

my power peak's just before 7000rpm, so shift light comes on at 6800rpm ish when warm, thats my optimum...

Thanks for posting the graph. Torque is most relevant for acceleration, and yours is falling away from 6000rpm on, so maybe I'd be changing earlier. As long as you were still in the torque band for the next gear (e.g. 5000rpm).

/G

 

[izibizi]

like lucky said, its all about where your cars peak power is

and you need to go further for about 200-500rpm to get everything from your car

I shift where the lights go on, around 6800 I believe

 

[g18llo]

Thanks for posting the graph. Torque is most relevant for acceleration, and yours is falling away from 6000rpm on, so maybe I'd be changing earlier. As long as you were still in the torque band for the next gear (e.g. 5000rpm).

/G

As you same, and in basic terms, torque is acceleration, bhp is top speed. It is more complicated than that, however, in the context of this conversation people should pay attention to the point where most torque is produced.

Also, the point where most torque is produced is also the point where the most engine wear/stress/damage occurs too, not at the red-line as some think.

Regards

 

[Dan@SJM]

if your optimum change is the limiter, you are loosing time, as by the time youve changed, add that up, through gears 1,2,3 it'll equate to about a second loss, rev to the limiter, but dont hit it, i change around 7100 when im racing it, but notherwise there is no need to hit the limiter, can cause damage.

 

[howie p]

Ain't got one of those (phase 2 172)

my Y reg MK2 172 has the shift light!!

 

[skinner]

You need to get a graph for your engine, and the gear ratios then work out the torque after the gearbox for each gear. Change gear when torque in the current gear has dropped below the torque in the next gear, or if you have hit the red line. A bit crude but basically about right.
IMO for a 172 you should change at the red line.

 

[gh172]

my Y reg MK2 172 has the shift light!!

I've never bothered to work out which do and which don't. Mine has the light in the normal place, but it has never come on (and I have hit the limiter!).

Y reg Mk 2... I got mine registered on 5/9/2001 and always thought it was one of the first Mk2s into the country, so I'd never see one on a Y plate. Then I saw one the other week. Yours must be late August or something?

/G

 

[LegoHead]

Does hitting the limiter cause damage, not sure it does. As I understand it, it limits fuelling or something to prevent more revs to engine. It does slow you down if you are going for quick 0-60-100 times.

 

[Dan@SJM]

it can damage the engine, pointlessly hitting it, ive seen pistons, and rods go through the block because of someone pointlessly hitting the limiter. its there to prevent damage, not to be hit on every gear change.

 

[gh172]

Big transmission shock as well

 

[Fred@BTM]

it can damage the engine, pointlessly hitting it, ive seen pistons, and rods go through the block because of someone pointlessly hitting the limiter. its there to prevent damage, not to be hit on every gear change.

thats what its there for to prtect the engine from over reving!!!

i'm always using the limiter on track, can be useful

 

[George k]

The power curve in the RR post suggests that you need to go to max rpm. What gives you acceleration is in fact the excess of power available over power required, so in fact the power curve dominates (diesels have massive torque, but in general are not as quick as a petrol car with less torque but more power!); it also depends on the rpm drop between gears, as regardless of how good the torque curve is, you do not want to drop too far down the power curve. Often the best change point is slighly past peak power so that you drop back to an equivalent point before peak power. you can work this out from the gear ratios and an spreadsheet, not that they are in my Trophy handbook, but you can make a good guess by checking the drops by changing up at half max rpm, i.e 3,600.

 

[Dan@SJM]

thats what its there for to prtect the engine from over reving!!!

i'm always using the limiter on track, can be useful

Yes it can be useful, but its not to be in use all the time the engine is on, as i said ive seen pistons and rods go through the block, just because some t**t has been sitting it on the limiter, caused my 19's engine to go.

Ive infact got a con rod from a 5's engine that went through the block.

heres a pic of my 19's con rod that got bent due to my mum driving it and kepping it on the limiter too much.

 

[Paul J]

my 19's con rod that got bent due to my mum driving it and kepping it on the limiter too much

FPMSL @ Racer mum

 

[Paul J]

Rev drops for 182 are:
1-2 - 3125
2-3 - 2291
3-4 - 1481
4-5 - 1192

 

[Dan@SJM]

yea, asked her to do a 0-60, but she seemed to forget to change out of 1st

 

[Fred@BTM]

lol, you should've seen how we ran in our new engine!!!!

thats not a bent rod, i'll get yoz to post a pic of a properly bent rod!!!!

 

[RobertCL]

Rev drops for 182 are:
1-2 - 3125
2-3 - 2291
3-4 - 1481
4-5 - 1192

So you've got to rev it to 4000rpm in 1st before you change into 2nd (working on the basis that idle is ~1000rpm)

My 172 certainly isn't like that.... or have I misunderstood something here:S

 

[Paul J]

Robert; put your gear ratios and final drive into the calculator on www.gearboxman.co.uk

 

[Dan@SJM]

lol, you should've seen how we ran in our new engine!!!!

thats not a bent rod, i'll get yoz to post a pic of a properly bent rod!!!!

I know thats not how bent they can be, but that is the result of bouncing off the limiter.

 

[RobertCL]

Robert; put your gear ratios and final drive into the calculator on www.gearboxman.co.uk

Interesting. I'll give it a go if I can find out what the 172 gear ratios are...

 

[RobertCL]

Aaaahh. Now I understand

If I change gear 1st to 2nd at 2000rpm, the drop is only 893, if I change at 6500 the drop is 2902.

Obvious really since its a ratio has been a long week:sleepy: