MPH vs RWKW

clontarf_x · 18-05-2006, 08:39 PM

Well, as I’ve never had my car on a dyno or raced it at the track I’m not really sure how these relate. I keep hearing everyone refer to ¼ mile MPH as a measure of real RWKW but I don’t really understand how it works.

I guess my question is how do you work out RWKW from MPH and does it actually always tell the truth? I would have thought that a dyno would be a more accurate way to tell but everyone always seems to ignore the dyno numbers and look at MPH from the drag times.

Also, is it possible to then look at MPH and work out RWKW?

So, for me, I have a dead stock AU3 XR6 VCT, what MPH should it run if I have 110RWKW? What about if I had 120, or 140 or 160? Is there a set formula?

Sorry, but its just something that has had me wondering......

XR6-VCT-2000 · 18-05-2006, 08:46 PM

um , ill start it off , although im sure there is more to add ;) -- roughtlly .. here goes ..

RWKW measured on the dyno is a pretty acurate measurement of the power to driveline/trough the diff to the rear wheels etc etc ... but an acurate sorta measure at that for basing all cars on against each other performance wise .... ( every car is tested under the same conditons roughly - with the dyno )

On the track ... a 1/4 mile stip ... you have things like weather ( heat /cold , rain etc etc ) - traction , weight of the driver , heaps of conditions effecting the overall performance of the car ... eg - whats the point of having heaps of rwkw if u cant keep traction and apply that power to increase your times ... i think thats sorta on the track of the questin u asked ..lol

Mark351 · 18-05-2006, 08:48 PM

Have a go and work out your cars baseline!

clontarf_x · 18-05-2006, 08:48 PM

Fair enough, but is there any real way to measure someones RWKW from their MPH over the 1/4 Mile? The reason I ask is my mate always says his car is more powerful than the car he races based on his higher MPH....

pks54 · 18-05-2006, 08:57 PM

check this out

http://www.angelfire.com/rpg/dangrou...horsecalc.html

Racecraft · 18-05-2006, 08:59 PM

Quote:

Originally Posted by clontarf_x

Fair enough, but is there any real way to measure someones RWKW from their MPH over the 1/4 Mile? The reason I ask is my mate always says his car is more powerful than the car he races based on his higher MPH....

and if his car is of similar weight he is right

AWD Chaser · 18-05-2006, 09:13 PM

The simple answer is:

the dyno will test a cars power to the wheels,

the 1/4 mile will test how fast the engine can push the car, driver, and any other weight in the quickest time to the finish.

Some cars have a better take off then others. A dyno shouldn't really be used as a performance comparison (although it does give you some idea on where your car stands to others), but rather is used for tuning. You can see what mods or how you tune your car makes more power, or less....

Casper · 18-05-2006, 09:14 PM

Interesting.. the calc isn’t actually too far off on my car. I keyed in some numbers based on my car and known MPH/RWKW and its not far off. So I extended it out to see what the results would be.
Car weight:

3440 pounds (1560kg) – Standard AU weight

92mph = 129rwkw approx (very similar to what I’ve run in the past)
93mph = 133.5rwkw
94mph = 138rwkw

etc etc. Not sure how accurate it is now though..

150rwkw will get you around 97mph
160rwkw will get you around 99mph

Whitey-AMG · 18-05-2006, 09:17 PM

Quote:

Originally Posted by clontarf_x

Fair enough, but is there any real way to measure someones RWKW from their MPH over the 1/4 Mile? The reason I ask is my mate always says his car is more powerful than the car he races based on his higher MPH....

The TRAP speed is always a good indicator of the potential amount of HP a car will have. The 1/4 mile time is a bit trickier as there are so many variables. A less powerful car although identical in weight may get a better 1/4 mile time because it hooks up better, or the driver can just drive it better. Just look at peoples 60" times and you'll see what I mean. Some people have major difficulties in hooking up........ or they up shift at the wrong time etc etc.

If I had to choose, I'd say there would be better accuracy in gauging HP from the trap speed ( MPH ) than on the actual 1/4 time.....

My 2C

FS5 · 18-05-2006, 10:26 PM

going to the track is a good indicator of how your car is goin .but its not the be all end all ,i have found personaly that your times can vary .given the air temps and especialy the RA readings.if you compare simalar cars ,say one runs in melbourne and one runs at townsville there would be at least a 1sec difference in the times threy run.
the trick is to go to the track and get a couple of base runs .do your mods than take it back and run it in similar conditions .then compare the difference.

Casper · 18-05-2006, 10:27 PM

Quote:

Originally Posted by FS5

going to the track is a good indicator of how your car is goin .but its not the be all end all ,i have found personaly that your times can vary .given the air temps and especialy the RA readings.if you compare simalar cars ,say one runs in melbourne and one runs at townsville there would be at least a 1sec difference in the times threy run.
the trick is to go to the track and get a couple of base runs .do your mods than take it back and run it in similar conditions .then compare the difference.

I dont think he's talking about the ET's, as you said, too many variables. The MPH on the other hand is pretty consistant, I am pretty sure thats what he's referring to.

FS5 · 18-05-2006, 10:51 PM

it goes for mph too .with my car i have picked up 1and a 1/2 mph in the last 3 months , without doing anything .in feb out at willowbank xr6 turbos were only getting 90/91 mph now we all know these cars hammer .

jonbays · 19-05-2006, 08:48 AM

The TS MPH is a very good indicator of the power to weight of a car.

If you know the race weight you can fairly accurately predict the rwkw.

It is of course actually a good measure of the average power in the useable rev range on the strip not actually the peak that you get on a dyno so a better indicator of overall performance.

TS will vary from day to day as its affected by temp altitude pressure etc just like a dyno but without correction factors in the software obviously.

My best TS in the wagon is 91.8mph and it weighed in at 1650Kg at WSID scrutineering so Caspers numbers are pretty well on the ball as i average just a bit over 90mph mostly.

Casper · 19-05-2006, 09:25 AM

Quote:

Originally Posted by jonbays

The TS MPH is a very good indicator of the power to weight of a car.

If you know the race weight you can fairly accurately predict the rwkw.

It is of course actually a good measure of the average power in the useable rev range on the strip not actually the peak that you get on a dyno so a better indicator of overall performance.

TS will vary from day to day as its affected by temp altitude pressure etc just like a dyno but without correction factors in the software obviously.

My best TS in the wagon is 91.8mph and it weighed in at 1650Kg at WSID scrutineering so Caspers numbers are pretty well on the ball as i average just a bit over 90mph mostly.

In a few weeks when I get the car up and running again I'll take it to the track and test the theory again. It should run around the 93-93.5 mph mark based on rwkw. Will be interesting to see how close I get.

Jut on another comparison. A BA ute with more weight and around 190rwkw runs around 99-100mph. Based on weight this would fall into the right mph/rwkw comparison too.

jonbays · 19-05-2006, 12:47 PM

Quote:

Originally Posted by Casper

Jut on another comparison. A BA ute with more weight and around 190rwkw runs around 99-100mph. Based on weight this would fall into the right mph/rwkw comparison too.

Weight is a big factor most people ignore (except for unopened commodore drag racers)

Next time you see some WRX with the big tailpipe driving round with a car full of people take him on and see what happens!

You will find it bogs down real bad off boost.

Small turbo cars suffer more than V8's but 100kg is like 10rwkw!

Casper · 19-05-2006, 12:49 PM

I agree. The formula only works when correct weight is applied (within reason).

Thats why it takes a BA ute 190rwkw to get 100mph and an AU sedan only about 165-170rwkw to get the same TS.

Mark351 · 19-05-2006, 01:57 PM

Which car has the standard weight of 1560kgs?

Casper · 19-05-2006, 02:21 PM

Quote:

Originally Posted by DeathXR

Which car has the standard weight of 1560kgs?

Official Ford factory figure for an AU I6. Give or take a 10 or 20kgs. I've never weighed my car but using that calculation it actually worked out reasonably close.

Tornado · 19-05-2006, 05:48 PM

The calc is very close.

TS - 98.79
lbs - 3968
ET - 14.15886

This gives me 332HP (248kw)

DanXR6T · 19-05-2006, 06:06 PM

For those who have commented about different MPH values for winter vs summer etc, and so how its not an accurate measurement, well it is an accurate measurement - in summer if you have a lower MPH because of the heat - your engine is making less power in reality - anything like a dyno that uses correction factors to adjust for variations is giving theoretical power.

Engines do make more power in winter than summer and so have higher MPH values - I know most people know that but its clear that by reading this thread some people are a little confused.

Dan.

clontarf_x · 19-05-2006, 06:26 PM

Axeman82 held aloft his mighty sword and said <>:

Nyar!

DanXR6T · 19-05-2006, 06:33 PM

Quote:

Originally Posted by clontarf_x

Axeman82 held aloft his mighty sword and said <>:

Nyar!

Too much D&D for you?

/me rolls a double one, his intelligence score gets a -10 penalty for the next two posts...

Casper · 19-05-2006, 08:17 PM

Quote:

Originally Posted by Tornado

The calc is very close.

TS - 98.79
lbs - 3968
ET - 14.15886

This gives me 332HP (248kw)

Pretty close as that calculator works out engine KW. I then took the "Cheats" conversion method of engine KW = rwHP (yes I know its not accruate) and then converted that to RWKW. That equals about 185rwkw which, on the 40 degree day you ran is probably pretty accruate I think.

Casper · 19-05-2006, 10:37 PM

Quote:

Originally Posted by Tornado

The calc is very close.

TS - 98.79
lbs - 3968
ET - 14.15886

This gives me 332HP (248kw)

lol, just for fun I just did the same calc on Grunters TS from the timeslip database.

I says 344hp(256kw) so converting that using the old hp to kw trick thats about 190rwk. Then I reasiled that the database also holds the owners rwhp amount. In this case Grunter had actually put in 260rwhp as his amount.

The calculator and conversion from fwkw to rwhp is pretty much spot on (4hp different). I'm suprised actually, usually the converters are way off.

Casper · 19-05-2006, 10:41 PM

hhaha, sorry to post again but this conversion calc is fun. I just did it again on my car using the exact mph of 93.54 and a weight of 3440lb's. It came up with 244hp(engine). So then I punched in 244hp and 3440lb into the converter below for ET and it came back with 14.959seconds. The ACTUAL time was 15.024. The total difference, 0.065 of a second. I'm impressed!

clontarf_x · 20-05-2006, 12:20 AM

That is pretty damn accurate I'd say ;)