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850 / S70 & V70 '96-'99 / C70 '97-'05 General Forum for the 850 and P80-platform 70-series models |
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Dyno Run 850R 1996 with RICAViews : 14175 Replies : 223Users Viewing This Thread : |
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Mar 16th, 2012, 18:57 | #51 | |
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Mar 16th, 2012, 19:24 | #52 | |
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Frankie - the OP got a BHP figure because MAHA measure tyre drag. I don't know whether this is because transmission drag is very low by comparison - anybody have a suggestion? I notice that on some dynos they coast in neutral with no transmission drag and other others just dip the clutch and leave it in gear. I suspect tyre drag is higher than transmission drag but thats just a hunch - it will certainly be quite high on a twin roller set up like a MAHA. All other dynos measure something as drag too - your results at MAHA and HLM are both valid if taken in context and Bens post should help explain the differences. They should both arrive at the same flywheel figure even if the wheel figures are wildly different - again refer to Bens post as it makes clear why wheel figures are not the holy grail. HLM use a very large roller with less rolling resistance than twin smaller rollers so tyre drag WILL be different. Comparing WHP figures between any dynos is fundamentally flawed unless the dyno is identical and all other conditions are identical. Neither MAHA or HLM is wrong and for tuning purposes where you might check for power changes after a new modification either is reliable - stick with one dyno and keep anything that may effect drag constant eg. tyre type and tyre pressure. MAHA have a good reputation with car manufacturers because their fly figures compare well with engine dyno results - to rubbish them in light of the above and Bens post is misleading. I acknowledge that HLMs dyno yields accurate fly figures too so no bias intended.
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Mar 16th, 2012, 19:38 | #53 | |
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Mar 16th, 2012, 19:53 | #54 | |
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Gear choice - it affects wheel power but not flywheel power if drag is being measured accurately. The only comparable constant is fly power. It would be interesting at the next dyno day (wherever that may be) to run a few cars in 3rd 4th 5th (6th) and see what happens - the engine power isn't altering but drag will change hugely with the varying wheel speed. If the dyno is accurate at measuring anything it should show equal fly power every time with very different WHP. Hope this helps.
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Mar 16th, 2012, 20:38 | #55 | |
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Mar 16th, 2012, 20:53 | #56 | |
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In theory it should make no difference because drag is drag and will be measured as such on dyno. Thinking it through - for example if you ran in 3rd in my car and reached 90mph then 6th and reached 180mph then the tyre drag loss added to the 6th gear run would be much higher than the that added to the 3rd gear run. However torque at the wheels is much higher in 3rd than 6th so you can see how you end up with the same result when you add high wheel power to low drag (3rd) as low wheel power to high drag (6th). I suspect that it made more difference to run in 4th years ago when dynos were inertial drums only and calculations of drag were in fact guesstimates. Also, in practical terms it may be safer to run in a gear that isn't spinning the roller at ~200 mph (my car would at 7000rpm) while 3rd would result in tyre slip ie: compromise of speed and traction.
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Mar 16th, 2012, 22:06 | #57 | |
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I've never expected Hamish to as you so quaintly put it, Kiss my Ass. I'm afraid, I respect fully those who "tell it as it is" - however, what I don't respect is that the guy has ripped off a great many people, and is generally full of pi$$ and wind. Not only that, but let's not forget the crap that he spewed forth about Water Injection, or the fact he's banned from the VOC forums - for very good reason. Put it like this, he's probably an adequate mechanic - but he's playing at the rest of it, and doesn't even attempt to understand things that he "knows" won't work As for VPC being friendlier - I'm sure it is, that's clearly why Emlyn upped and left...
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Mar 16th, 2012, 22:32 | #58 | |
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Mar 16th, 2012, 22:38 | #59 |
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Mar 16th, 2012, 22:40 | #60 |
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chinese whispers mate, he is who he is i suppose but he knows what he's doing. i know chris is watching hello mate
Last edited by t5frankie; Mar 16th, 2012 at 22:42. |
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