Originally Posted by
focusrrx87
Cheers for that so in the real world your not gettin 170mph from the astra? Ok let's say 300bhp focus mk1 and a 300bhp Calibra turbo, seeing as the Calibra is much sleeker and has a 6 speed box it'll have the better top speed right?
it having 6 gears doesnt make any difference to the car.
its the top gear ratio thats important, but thats not to say the longer it his the better.
what you need to do is accurately work out where the car makes it most horsepower, for that you need to put it on a dyno.
From the dyno graph you can see where it makes peak power, but more importantly when the power drops off.
say you had 300bhp and it made it at 6000rpm, then the power dropped off to 240bhp by 7000rpm.
Now going off your 5th gear, tyre dimensions you would hit 170mph at 7200rpm.......do you think you could hit 170mph with around 230bhp....i dont think so either.
But you say you have 300bhp.....well thats not at 170mph(7000rpm) more like 155mph(6000rpm)....hence thats all the speed you will do
Now if your engine made 300bhp at 6000rpm but 301bhp at 7000rpm, its alot more likely you will get to your 170mph, even though in theory you have only made 1bhp more than the other setup.
The only way you can help the other setup is changing the gearing/tires so that when you hit 6000rpm your doing 170mph
Also i mentioned power at the wheels because thats the most important, top speed doesnt know whether your fwd/rwd/4wd, it just knows how much power your putting to the ground, an accurate persective would need wheel power.
If you want to know how fast you can theoretically go(not brunters) id need an accurate dyno graph with whp and your cars CO of friction
Originally Posted by
155lee
why?i can read fine but i dont believe everything i read.i have had a 200 bhp rs turbo which would never reach 150 mph on any road.check the stats in the middle of performance ford which they print every month,most rs turbos struggle to do 150 mph and thats big power 1's.if somebody tells you they seen 150 on a set of 20 odd year old rst clocks i would take that as nearer 130 mph.
Of course its different in performance ford, they are doing it on a short airstrip where you need alot more power to hit that speed, we are talking about traditional top speeds with manufacture distances.
For example, ill need 550whp to hit 200mph at bruntingthorpe due to the short distance, but stick me on an oval or the german 5 miles straight and 200mph can be achieved with 450whp....both examples assuming your car is correctly geared so 200mph is dead on peak power.
like mentioned before, top speed doesnt care what car you have, its not a fickle mistress, if the car is slippery enough and the gearing matches the power perfectly then over course it will do the speed with a long enough distance.
On a motorway i did a gps approved 141 in a 175bhp renault 5 turbo, which is shaped like a brick.....if i tried to do that at brunters i would have got no where near due to room
Originally Posted by
Karlos G
Lee thats because stock RST gearing, Rev Limit, and wheel size wont do 150mph
lol
You need to change one or all of the above.
exactly
Originally Posted by
J1mbo
it would with 17's !
mine will do a genuine 150 with 17's 205/40/17
and a 6500 rpm limit
ive had it round to 146 on sat nav on a testing ground and it wernt off the limiter
i think 200hp would pull it, just take a long time !
there you go, bein a ford has no disadvantages, if jimbo posts up a dyno graph with expected transmission loses we can probably work out his max top speed aswell
Originally Posted by
focusrrx87
ok rod say over 5 miles, 300bhp mk1 focus mtx75 box, 205/40/18 7000rpm limit. I'd say about 155mph. Never really been in to top speeds ect but your threads interest me and i met turbotoaster the other day got me interested in how it's all achieved.
i could need you to find out the CO before i could be more accurate, i tried looking online but couldnt find it.
its not a bad shap and looking at other cars with similar shape im guessing its 0.32, remember though, the lower your car is the less its CO(lower=better)
assuming your transmission uses around 15% of the power would leave you with 255whp...again a guess because we need more data.
ill use this graph of a near 300bhp focus to give us a rough idea, but again id need a graph from you to actually properly work it out
we will just add 15bhp all over the graph, so take that in mind when im tell you info.
looking at the graph it hits 300bhp at 5700rpm and slowly drops to 290bhp at 7000rpm(you limit)
now the mtx75 box from a focus rs has these ratios.
0.85 fifth gear with a 3.82 final drive, from that and your tyre size i can tell you what speed you will be going at what rpm(this is in a vacuum so no drag)
6000rpm 134mph
6500rpm 146mph
7000rpm 157mph
Now from you estimated CO and 255whp you should be able to hit your limiter with enough room as you will be making 230whp which is ok.
now you need to decide how has you want to go as thats your lot at the moment, you will have limiter/gearing/tire size holding you back.
Hope this helps, i know its a bit long winded so if you have any questions im more than happy to help.
In regards of what Rod mentioned when he comes out with speeds, these are all from brunters by using previous cars as examples, ie he already knows there power and CO hence the difference in power between cars(saphs,evos, rs turbos) which he has a large excel info pack can easily be used to help