focusrrx87

How do you work out top speeds of car's? Taking in to account drag efficiency, gearing ect. As the new astra vxr-r has a claimed top speed of 170mph which seems a bit ott for a 300bhp hatchback as does the new focus rs and it's claimed 165mph, can these actually be achieved? Or are they recorded on a rr?

turbotoaster

alot of them get access to an oval for testing, mostly performance stuff will be tested on an oval where you in theory have unlimited amount of time to get up to the top speed, or VAG group use a 5mile straight

mostly rod works his out from 0-top speed achieved in 1.5miles which is a bit different.

if you want to work it out for a car with unlimited room(like manufactors claims) then you need to know wheel horsepower, gearing and CO of the car, little things like width of the tyres etc can be factored in, but wont make a huge difference.

if you can give us an example of a car that you dont know the speed of, we could probably work out a rough estimate if theres CO avaliable for it

155lee

iTrader: (10)

theres a thread in the escort turbo section about a guy claiming 150mph from 200 bhp.im doubtful.

andy130

iTrader: (2)

WHAT? you need to learn how to READ

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?

Rod-Tarry

In the UK its the max you can reach in circa 1.5miles. With the facts i have on gearing, Power etc i have an ever improving excel spreadsheet that will tell me the Max at 1.5miles very accurately, including the best gearing to use. Given 5 miles the 206 mine reached at Woodbridge would be well the other side of 225 with the Power available. Unless a distance is given comparing Topspeeds is pointless.

155lee

iTrader: (10)

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.

Karlos G

iTrader: (4)

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.

J1mbo

iTrader: (1)

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 !

155lee

iTrader: (10)

but 'most' rst's have standard fuel ecu's dont they so will never see 150.

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.

Karlos G

iTrader: (4)

Yeah when I had 17's on mine and a 3.52 FD I hit around 160mph at 6900rpm, now with 16's and a 4.29 FD I can only do 144mph! lol
So just fit bigger wheels or a longer FD! lol

J1mbo

iTrader: (1)

6900 my rods would buckle,bend and fall out the sides at that lol !!

Karlos G

iTrader: (4)

lol Classic!
Thankfully my little CVH has PEC rods and Wossner pistons

turbotoaster

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

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

exactly

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

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

J1mbo

iTrader: (1)

lucky git, would love them in mine, but then id need a gearbox to handle the added power !

turbo toaster: here is a graph of my engine

i would have expected a drop to possibly 220/230 by 6500 if the boost was held in

power losses i am not sure

fwd escort

as above 205/40/17's

see what you can do !!

focusrrx87

Lol you know to much. thanks for the help and info, i was just asking as some claims seem to be a bit optimistic, there's no point me really tryin to set a top speed with my car. Lol hardly gonna set any records. When iv got my print outs I'll let you do some number crunching as you seem to like it. Lmao

Karlos G

iTrader: (4)

I only put them in mine for peace of mind, and maybe future proofing for if I want more power later lol
You running 252bhp on stock rods and pistons! Poor thing!! lol
I've limited myself by only running a .36/50 T3 because of the old gearbox probs, what turbo you on to make 252bhp Jimbo?

J1mbo

iTrader: (1)

bloody right i am lol !

its perfect mate it gets absolute death everywhere, 6200 in every gear and she is mint bless her

recently had head off and all pistons are still exact amount out top of the deck as on the build sheet

its revs that kill them though, hence not taking it to 6500 on dyno and i stay off the limiter !!

im on a 55 trim t3 (2wd cos) in a .48 housing

and you can see the boost on the graph

Karlos G

iTrader: (4)

Thats interesting, almost the same boost as me but an extra 20bhp, shows the difference a .48 makes! Still plenty left in that then too, 2bar FTW! Really push those stock internals!! lol

Also you make 25psi by 3040rpm, thats amazing on that turbo!!!
What cam have you got? Head work?

J1mbo

iTrader: (1)

the 48 makes a hell of a difference

much laggier though

the original engine i had was on std head and cam and .36

gave 220bhp at similar boost

this one, i wanted to use the same boost as i knew the internals coped well before so set about gaining power with out boost !

nick waples had the head

slightly bigger cam

and the .48

lovely engine pulls very strong but it is a little laggy, but hey whos below 3/3.5 when having a blast

Karlos G

iTrader: (4)

I wouldnt say thats laggy at all Jimbo! The engines i've mapped with .48/55 T3's have all made peek boost at around 4000-4200rpm, although they both had standard heads and cams, and my .36/50 doesnt make peek until around 3000rpm!

That must be great on the roads!

J1mbo

iTrader: (1)

bloody hell ! well in the car full boost is 3500 to be fair but yes it is great!

my old .36 engine was well on boost for 3000 bit before id say

sooooo punchy !

lacked up top but this new engine changed that

Karlos G

iTrader: (4)

Yeah I know.. shit isnt it!! lol
I am tempted to try a .48 on mine and see how it feels, my head was done by NMS and i've a Newmans with solids so should flow nicely!
But as you say .36 is proper punchy almost there instantly!

J1mbo

iTrader: (1)

it is i would happily go back to a .36 as now ive calmed down and dont race anything within 5 yards of me id be happy

i love the way you put your foot down you go

the .48 is a couple of second wait, and if your not in boost threshold then its bad !

but for you go for a .48, your engine spec should love it and give very good power on it

you may also find that it makes it much more efficient and not need much more fuel for the gain in power

my 36 engine had a set of escort cossie small turbo (im on t2 << high imp) on 100 duty at 225 hp ! very inefficent

Karlos G

iTrader: (4)

Yeah it'll be a laugh to try, would be nice to see 270-280bhp @ 28-30psi!
I'm running Siemens Deka IV's 630cc High Imp on Megasquirt at about 65 % so have plenty of headroom, could fuel a mission to Mars with those fuckers!! lol

focusrrx87

Thread hijacker's! Lmao

J1mbo

iTrader: (1)

bloody ell im using 440cc inj with plenty spare

but like i say when you get rid of .36 it makes it much more efficient

wish i had steel rods and good gearbox so i could crank up the boost lol

J1mbo

iTrader: (1)

oops

sorry

Karlos G

iTrader: (4)

Sorry!
440cc really?! I was using Astra VXR 480cc ones but they topped out at around 230bhp, shows just how much the VE and BSFC changes by going .48!!
I'm fitting a SportKa box with Puma Racing LSD as it's the strongest, cheapest, youngest (11k miles), almost direct fit box I can find and it has a hydraulic release bearing built in too!
Hopefully that will last a little while, I have already snapped a main shaft and broken teeth off the input shaft on a couple of BC box's! lol

J1mbo

iTrader: (1)

Id bet you could stick a 48 on there go back to them injectors and youd be fine !

im sure its 440 im on

focusrrx87

lol no worries at least your talkin about interesting things. And it hasn't turned in to the usual arguments.

Karlos G

iTrader: (4)

Yeah your probably right!
There was some guy on here that was going to give me one for the price of the postage but it never happened, might have to start looking about!
Makes a nice change doesnt it! lol

J1mbo

iTrader: (1)

aye get on the case im sure you'll love how freely it will rev up top

turbotoaster

ok jimbo, lets have a crack at this then

the mk5 escort has a CO of 0.39 which is actually about as slippery as a people carrier so thats not gonna help to start, but due to you running the car lower that will be a little better, probably around 0.36

Just had to research your gearbox ratios

3.15 1.91 1.28 0.95 0.76
Final drive 3.82

so assuming your tyres are new(ie not worn so smaller diameter)

at maximum power you will be doing in theory 145mph and at 6500rpm if your prepared to rev it that high you will be doing 156mph

power losses through your transmission should come about 214whp

with that in mind the 145mph shouldnt be an issue but as you go past peak power, your losing power and also the air pressure is increasing, pretty dramatically with your heavy drag shape, from that i work out you will be able to hit 151mph with along enough distance

J1mbo

iTrader: (1)

cool ! like i say 146 was possible in a fairly happy distance, i didnt wanna hang it in there too long

but i tried working this out got 153 at 6500 so want far out

and tbh i think it should piss 150, it has the power there for sure just a bigger 5th would be nice

will have to give it a go, see if i can break 150 on sat nav !

thanks for that !

im sure my co would be as std if not worse as i run a rs500 splitter and 4 canards on front but still it gets there happily