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fordfreak ef
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 Posted: Tue Feb 12, 2008 7:34 pm Post subject: |
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| 66 coupe wrote: |  dyno comps...
put it on the track, thats where the real numbers are |
im a track hore.. well.. in tha past anyhows... so that cannot be directed my way!...  |
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BigCav
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| Posted: Thu Feb 14, 2008 1:38 am Post subject: |
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| 4dlvr wrote: | | according to my physics teacher the torque curve will drop but the peak kw number should slightly increase |
your teacher is sadly mistaken and should go back to uni i think.
that theory is on motors revving harder, as power is a result of rpm and torque, if rpm increases so does power etc
however at the treads where a dyno is reading the motors not physically making any more power at the motor because of big wheels is it.
u can dyno tune your car in first gear or in 5th gear u will get the same rwkw, so what would changing the rolling circumfrence do, absoluty nothing as its the same thing as different gearing.
u will lose power with those 20's, not because ratio's and speeds have changed but because you have greater rolling resistance due to the additional weight in the wheels.
i ahve experiance with dyno's, i have been tought a little by the dynodynamic's trainer and he says the same.
iv physically had experiance with running a vl on 14's then again on 19's
if u wont the most power fit a set of stocko's on but you will lose very few kilowats with the rims.
the vl went from 92 to 90 from memory |
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Steady ED
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| Posted: Thu Feb 14, 2008 3:02 am Post subject: |
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| BigCav wrote: | | u can dyno tune your car in first gear or in 5th gear u will get the same rwkw, so what would changing the rolling circumfrence do, absoluty nothing as its the same thing as different gearing. |
In theory.
In practice, and theres a thread where we tested it on FPV_GTps dyno with my Sprint, there was a slight variation between gears.
Roughly 5kw spread from memory, testing 1st to 4th gears.
5th oversped the dyno so we had to abort the run. |
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dc_todd
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| Posted: Thu Feb 14, 2008 11:25 am Post subject: |
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just changing to 20's with no other variables being changes would not have a forseen effect, however, variables like the rotating mass, the quality of the rubber to width of the tyre will all effect the output.
a 20" rim would have a higher static mass than a 17" rim meaning the car has to work harder to spin that mass thus absorbing a small amount of power, the tyre width would have a similar effect as the traction footprint increases again the power required to rotate that footprint increases. As the overall rolling diameter is increased it will have a similar effect to changing diff ratios, though not as dramatic it will still have an affect. I have seen cars that normally run 235/45/17's pull figures around the 150kw mark, those same cars on little cheese cutter 14" steelies with smaller diameter wheels gain as much as 15rwkw's with nothing else being done. purely because the rotating mass is reduced. |
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BigCav
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| Posted: Thu Feb 14, 2008 1:31 pm Post subject: |
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| Steady ED wrote: | | BigCav wrote: | | u can dyno tune your car in first gear or in 5th gear u will get the same rwkw, so what would changing the rolling circumfrence do, absoluty nothing as its the same thing as different gearing. |
In theory.
In practice, and theres a thread where we tested it on FPV_GTps dyno with my Sprint, there was a slight variation between gears.
Roughly 5kw spread from memory, testing 1st to 4th gears.
5th oversped the dyno so we had to abort the run. |
yes there will be, i was tlaking more of a theoretical thing lol
the reason there is a spread is because in lower gears there is more mechanical advantage in the gearbox and less resistance depending on your gears etc
the slight difference in resistances and variables between gears at 4000rpm can make a big difference at your rear wheels |
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fordfreak ef
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| Posted: Sun Feb 17, 2008 5:52 pm Post subject: |
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| i left my 20's on for yesterdays ford/holdne dyno day and i pulled my best ever figure's ... go figure!! 174.7 RWKW.. |
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Tocchi
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| Posted: Mon May 12, 2008 1:07 pm Post subject: |
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slightly different that power related. more tune
im getting the EF re-tuned this thursday, at the moment its got the 295/50/R15s on the rear.
if i get it tuned with these on, and then switch to standard FTRs (for when i sell it, or other, etc) would the tune be affected. (even slightly)
due to the fact when its tuned on the 295 it needs more effort to turn them, rather than 225/R16s which it would turn easier |
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Nigel
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| Posted: Mon May 12, 2008 3:38 pm Post subject: |
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You'll probably find that Larger wheels will affect your acceleration a bit, but not your overall power.
The problem is the inertia of the bigger wheel. It takes more to make it spin faster - keeping it at that speed though is no problem.
I didnt notice 17's on my EB (not too much), but I did notice my little ford escape (3.0 V6) when I went from Factory 225*16's to 255*18*65's. Noticably less takeoff, but so much better traction. |
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Steady ED
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| Posted: Mon May 12, 2008 4:21 pm Post subject: |
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| Tocchi wrote: | slightly different that power related. more tune
im getting the EF re-tuned this thursday, at the moment its got the 295/50/R15s on the rear.
if i get it tuned with these on, and then switch to standard FTRs (for when i sell it, or other, etc) would the tune be affected. (even slightly)
due to the fact when its tuned on the 295 it needs more effort to turn them, rather than 225/R16s which it would turn easier |
Nah, the only way it could is if it brought up some weird load they hadn't tuned for.
They'll load it up on the dyno anyway, I doubt the rim/tyre combo would be able to provide more load on the street then they can on the dyno. |
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Nigel
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| Posted: Mon May 12, 2008 4:58 pm Post subject: |
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You would have more traction with bigger tyres....
would explain the power |
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Tocchi
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| Posted: Mon May 19, 2008 2:14 am Post subject: |
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update on the 295s on dyno
ended up running with them
the gearbox shat itself lol (auto)
made a pathetic 257rwhp @ 5000rpm and 500Nm @ 1450rpm |
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fordfreak ef
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| Posted: Mon May 19, 2008 10:06 am Post subject: |
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| Tocchi wrote: | update on the 295s on dyno
ended up running with them
the gearbox shat itself lol (auto)
made a pathetic 257rwhp @ 5000rpm and 500Nm @ 1450rpm |
sad to hear... what box you going to do now? upgrade btr?? |
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FordFairmont
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| Posted: Mon May 19, 2008 10:11 am Post subject: |
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| fordfreak ef wrote: | | Tocchi wrote: | update on the 295s on dyno
ended up running with them
the gearbox shat itself lol (auto)
made a pathetic 257rwhp @ 5000rpm and 500Nm @ 1450rpm |
sad to hear... what box you going to do now? upgrade btr?? |
i think he's going a T5 |
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fordfreak ef
Cruise Moderator
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| Posted: Mon May 19, 2008 10:23 am Post subject: |
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| t5 are not as strong as the BTr's.. but i guess one could always upgrade the T5.. a t5 driven sensibly can last awhile.. even behind boosted applications if driven with care... |
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Iron Horse
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| Posted: Tue Sep 02, 2008 7:51 am Post subject: |
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| Rim size has nothing to do with it , it's the rolling circumference that will alter the figures . 20's would have a low profile tyre fitted that would have a similar height to the standard wheels that came on the car . Unless the Dyno guy's are uploading the "actual" rolling circumference of the tyres you are paying for a lie . The rollers are measuring twisting torque transmitted by the wheels , cars need to be tested in direct 1-1 . A set of 4-1 diff gears will give a huge output figure compared with a set of 3-1 gears in the same car . That's why 3.55-1 ratio diff gears are used for towing and 2.78-1 ratio for cruising and economy , it's all about twisting torque . |
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