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Power Loss From Engine To Wheels On Stage 3 Mpi


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#1 Chris Jones

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Posted 14 May 2010 - 06:10 PM

Hi, first post on the mini forum so just wanting to say hi to everyone and thanks in advance for replies. Hope to be of help also.

Anyway, a bit about my car and the supposed problem. I bought a completely standard 97 Rover Mpi and have gradually added a Stage 3 tuning kit from Minisport, with a few parts a bit better than their standard lot, also fitted the car with a 52mm throttle body. It went back there to go on the rolling road and came back with 91bhp at the fly (the tester said he could have squeezed a bit more out of it although it would have been a bit fussy around 2k revs), overall he was very happy with the engine. What surprised me though was the loss from the engine to the wheels, which were reading out at 48.5bhp. I thought this to be quite a large loss, as the percentages I've heard thrown around for the loss being quite a bit less than this. Since then I have heard a few people say it does happen sometimes, so yeah... Now I'm not going to get into the number chasing game or anything, but I was wondering what stage of tuning I could go to to try and reduce this a little, and if it actually is worth trying to do so. I also don't want to throw a lot of money into new gearboxes etc if I'm not going to notice much difference. So if anyone has gone down the same route, I would really appreciate some feedback on what they did and ultimately their results. Thanks in advance! :bah:

#2 cooperrodeo

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Posted 14 May 2010 - 09:42 PM

91bhp from a standard MPI with Stage 3. Do you believe that?

#3 nicksuth

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Posted 14 May 2010 - 09:48 PM

91bhp from a standard MPI with Stage 3. Do you believe that?


Yeh !, He did say at the FW not the wheels, I would say it 70ish at the wheels ?

Edited by nicksuth, 14 May 2010 - 09:56 PM.


#4 Dan

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Posted 14 May 2010 - 10:07 PM

Forget about stages of tune, there's no such thing really. If you want to reduce transmission losses, you will have to invest in the transmission components. Tuning other areas won't help.

#5 mykweb

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Posted 15 May 2010 - 08:20 AM

Your luckie to get 91bhp. Most Mpi's barely make the 87 mark.

Not even the JC works mpi's had 90BHP.

Since doing all this top end work has any work been carried out on the gearbox. Dif change, center oil pickup, seals, bearings etc?

Mike

#6 Chris Jones

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Posted 16 May 2010 - 09:51 AM

Yeah I know, was really pleased with the 91, which is why such a big power loss seems a bit of a shame. Nope, all the mods at the minute are top end. I've heard of people putting new diffs in, is there anything I should be looking out for? Looks like I'll be having a word with my mechanic for a little bit of a gearbox overhaul :thumbsup:

#7 nicksuth

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Posted 16 May 2010 - 09:57 AM

What BHP was it indicating at the wheels?

#8 cooperrodeo

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Posted 16 May 2010 - 07:35 PM

If all the mods are at the top end then 91bhp seems to be wildly optimistic.

#9 Chris Jones

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Posted 17 May 2010 - 11:05 AM

Argh, why do people not believe me? Sorry about the bad quality but took this on my phone. It's 91 at the fly, 48.5 at the wheels.

Posted Image

Edited by Chris Jones, 17 May 2010 - 11:07 AM.


#10 hlynur

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Posted 17 May 2010 - 12:33 PM

How is it even possible to measure transmission losses without removing the engine from the car? Surely you would have to run the engine on a test stand and then compare that to the figures from a rolling road after install to see the true losses?

My understanding was that the flywheel figures that you see on these printouts are calculated back from the roadwheels by basically assuming what the transmission losses will be...

#11 cooperrodeo

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Posted 17 May 2010 - 01:01 PM

You have probably got more like 71 at the flywheel.

#12 Sammy D

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Posted 17 May 2010 - 01:04 PM

Transmission losses are calculated on the run down of the rollers.

#13 hlynur

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Posted 17 May 2010 - 01:17 PM

Transmission losses are calculated on the run down of the rollers.


Ah thanks, that makes sense. It's more than just transmission losses that you're measuring in that case though isn't it? You'll also be getting all the drag from the engine. It still doesn't feel like a good assumption to say that this figure means that your transmission losses are excessive. I can see why the figure might be high though. Compared to modern cars a mini with an A series generates a ferocious ammount of engine braking.

Sorry to spam up the thread, I'm just interested :dontgetit:

Edited by hlynur, 17 May 2010 - 01:30 PM.


#14 JonBetts

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Posted 17 May 2010 - 02:04 PM

You shouldnt really listen to the flywheel figures, the rolling road can only accuratly measure the reading at the wheels (even this can and does change from one RR to another), any other measurement is just a calculation and therefore inaccurate. To get a true flywheel figure you need to have the engine setup on an engine dyno machine out of the car.

A RR is only really a tuning tool, and the so called power runs are just a gimmick really to make some money, understandable with the cost of these things! You should think of a rolling road as just a good tuning device and ignore the final power out put but concentrate on the power gains and engine running improvements made from the first run to the last run.

#15 adam_93rio

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Posted 17 May 2010 - 02:33 PM

as the guy said above, i never really care about when people say how much power it did on different RR's etc.
i wouldnt mind knowing mine, but dont see the point in chasing figures, if it drives well then next time you uprate something it drives better than thats all that matters to me




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