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VR6 Helix clutch failed (x2!)

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Post by boost panda on Tue Nov 02, 2010 5:18 am

Yes I know this is old and IIRC Pete doesn't even have a VAG car at the mo.

I'm just wondering whether it was the torque that killed it.

The R32 dials in ~170lbft just above idle (1500rpm) and the VR6 peaks at about 190lbft? so the clutch is under way more strain than it should have been from the off.

Yeah, Helix says its rated to 300hp, but HOW do they actually rate that? peak? the jerk through a drivetrain as drive is taken up from 0lbft to over 100 when pulling off has a lot more inertial forces in than going from 250lbft to 280 at peak torque curve.

My thoughts, mull it over Very Happy
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Post by boost panda on Tue Nov 02, 2010 5:19 am

Forgot to mention, obviously 100lbft is peak torque around idle and would represent a hard start, but still might be worth thinking about.
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Post by pete_griff on Tue Nov 02, 2010 9:33 am

what you say is true, however...

the lower gears are obviously the easiest for the engine to use, so put less strain on the clutch - and i would say that's generally when the revs are going to be low as you're accelerating from standstill...

also, turbo cars such as Kev's are running the same clutch as mine was and turbos deliver the torque in a much more aggressive slug than any N/A engine - his hasn't let him down yet...

tbh, i still don't know the exact cause of the issue.
i can't explain how or why, but i'm pretty certain it was down to the aftermarket flywheel. i recon if i had retained the oem item i wouldn't have had any dramas.
big shame really as i still sorely miss the corrado. i'm very happy with my BM now though and hopefully plan to hang onto it for a good while yet...

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Post by boost panda on Tue Nov 09, 2010 12:52 am

Kev doesn't have a standard gearbox though, does he? I thought he had a longer FD or something.

I'm surprised that a flywheel killed a clutch though. Perhaps the lightenedness of it meant it span up too fast for the application. The beauty of an OEM wheel is that it obviously has all that extra weight to kind of limit things a little bit.

Glad you're happy with the Bimmer now though Very Happy
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Post by kevhaywire on Tue Nov 09, 2010 8:56 am

Standard box with shorter final drive (from the G60), so the car is easier to move in all gears Very Happy It's how the VR6 should have been from the factory imo, but some folk would complain about mpg.

I've had a few Helixes over the years, 2 on the VRT and a couple on my old MK2s. They all worked well. They take some bedding in though!



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Post by boost panda on Tue Nov 09, 2010 12:09 pm

AH ok, so your 70mph in 5th is at higher revs than normal, say 4000+?

I am yet to experience the joys of an uprated clutch. Are they vicious?
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Post by kevhaywire on Wed Nov 10, 2010 2:21 am

70 in 5th is 3000rpm with my diff mate, so not exactly 'busy' but puts it nearer the main meat of the torque band. The standard gearing is crap. You have to drop to 4th gear at 70 to pull away with any vigour!

The Helix organic is far from vicious! It's just like stock, but heavier on the pedal.

I've tried a couple of 'streetable' American clutches and they were feckin awful.... REALLY stiff pedal and juddered like a ****, and I mean, undrivable at low rpm judder.

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Post by boost panda on Wed Nov 10, 2010 3:31 am

Ah of course, I always forget the diff! My knowledge of gearing is horrific, I got 20% in my gears coursework, it's all voodoo to me. Trying to work out the ratios between suns and planetary gears in epicyclics made my brain melt :/

I think most clutches are organic these days aren't they? Or at least have some organic compounds in.

I've only ever had stock clutches. I remember taking about 2000 miles off my golf one trying to pull out of my drive back in Southampton. I thought i was in 1st but was actually in 3d (stupid worn bushes) so I booted it and saw all this smoke. I thought it was odd to wheelspin so much, and then about 5secs later I got the smell. Oh dear.

Clutch lasted about 2 months more, lol.
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Post by kevhaywire on Wed Nov 10, 2010 4:41 am

20% Laughing

I'm exactly the same with engine angles mate. Where to fire an injector in the otto cycle confuses the feck out of me, especially when DTA bloody do it 0 + 360 to -360 - 0, instead of 0 - 720 deg!! It bakes my noodle!

You get all manner of friction materials mate.... sintered bronze, organic bits of rope and fish bones, good old asbestos (where permitted!) and so on....

Paddle clutches are generally the worst for low speed drivability. Instead of one circular disc mating with the flywheel and pressure plate, you have 4 or 6 little pucks and the grab is instant usually, so to modulate it usually kicks off a lot of judder. Having said that, the smoothest uprated clutch I've ever tried was in an Escort RS Turbo.... that had a Helix 6 puck in it!

I once deliberately burned out the clutch of a hire car by slipping it on the motorway. Killed it one journey Laughing

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Post by boost panda on Wed Nov 10, 2010 4:46 am

Yeah I have an engines coursework at the moment which measures cylinder pressure against crangle and that's all -360 to 360!

We have to talk all about cyclic variability. Basically why if an ignition system is set to spark at 20degrees, why aren't the results always perfectly the same?

It is a haedbake, and probably the only module which could strip meof a good degree :@
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Post by boost panda on Wed Nov 10, 2010 4:56 am

Oh, and:

Fifth Gear testing additives

Yes, this is Oxford Brookes. That is the engine lab with all the old racing cars in. We've just taken ownership of Button's old Honda!

That old gearbox the Wynn's bottle is resting on is a TWR from a race spec Volvo.

The dirty old Transit chassis that is shown with Nox has been there for donkey's years! Think it was used for chassis dynamics.

STP additive is in with our Formula Student single seater racecar.

The lab tech is my lecturer. He knows 7.89 f*ckloads about engines, and everything related....but he *just* can't teach it in a way I can understand....it's a real shame, and he rushes through the miserly 1hour a week lecture we have with him. It's my main point on contention at the mo :/

The K series is still about, but we have a Cooper S lump in the engine dyno now.

The other guy is Geoff Goddard aka God. He was chief engineer at Cosworth back in the day, and pretty much has the midas touch. He's my supervisor for my dry sump dissertation.


Just a monumental hijack to say "welcome to my world" Very Happy

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Post by kevhaywire on Wed Nov 10, 2010 5:00 am

Ignition is a nice one!

It's amazing how complicated a piston going up and down can be sometimes.... I think some people make it more complicated than it needs to be though.

For example, I've had no further education or special training in cars, and yet I've been able to install an ECU, stick some random old numbers in it and it makes 400hp, so getting it absolutely c0ck can't be THAT critical Laughing

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Post by boost panda on Wed Nov 10, 2010 5:25 am

LOL yeah! if you can do ECUs and electronics, you're a bit of a hero in my book! Give me the oil parts that move any day! Laughing
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Post by kevhaywire on Wed Nov 10, 2010 7:38 am

It's just luck and some educated guessing mate Wink

I'm amazed I haven't blown the motor yet, which can only mean my timing is very conservative!

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Post by mrbeige on Wed Nov 10, 2010 11:52 am

To be fair, educated guessing can get you 95% of the way to a perfect map, and in reality, that extra 5% isn't a great deal in the grand scheme of things. Timing is a dark art in my mind. However, the good thing is you can hear it when it's drastically wrong.

I do wish I'd done more of an automotive degree sometimes, however, working at the place I do is a good thing.

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Post by boost panda on Thu Nov 11, 2010 12:46 am

Yeah, hearing when it's out is always a good indicator. Just as long as you stop before the pistons melt! :-o

I feel odd doing Msport Eng sometimes. I mean I'm not big into F1, the only 'sport i really watch is Rally and even then I never keep track of who is top, driver teams, peoples names (!) etc.

The only part of the course that really lights a fire under me is the design, and in this I'm incorporating the CFD (Comp Flow Dynamics) we do in Aero and all the stress testing etc.

That's kinda why I'm moaning about trying to make a Corrado in CAD cos i'd like to plot some aero lines over it, and I'd also like to do some calcs to see what weight dist I could get if i dropped an engine behind the front seats.

There, the truth is out. :-o
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Post by kevhaywire on Mon Nov 15, 2010 8:04 am

mrbeige wrote:To be fair, educated guessing can get you 95% of the way to a perfect map, and in reality, that extra 5% isn't a great deal in the grand scheme of things. Timing is a dark art in my mind. However, the good thing is you can hear it when it's drastically wrong.

Indeed. The engine will soon tell you if it's not happy with it's fuelling because it will be riddled with flat spots, sound horrible, be gutless and pink it's **** off.....and that's BEFORE installing AFR and EGT gauges etc! The writing's on the wall! If people can't read the obvious signs, seek another profession / hobby Very Happy

Given that 95% of all petrol engines will run satisfactorily and make power with fuelling in the range 12.5 - 15:1 when hot and 11 - 13.5:1 when cold, you are absolutely bang on, it's not feckin difficult making an engine run smoothly!! It does annoy me a little when tuning houses make out they are some kind of mapping geniuses, but the reality is anyone can do it. The only time I've seen drastic improvements from a remap is when the existing map was so shockingly bad to begin with.

Timing as you say, does require more thought and opinions on what's correct vary enourmously.

My favoured method is the OE torque strategy, which we've discussed before. I.e. keep advancing until the engine makes no more power / torque, then back it off a couple of degrees for safety. This obviously needs to be done on a dyno.

For the home DIY, it's back to the obvious clues. After your changes, does the motor feel more responsive or more sluggish? Does it feel coarser or smoother? Can you hear it pinking? Are the EGTs rising too much etc?
There are also the other obvious things like sensible timing off idle so it doesn't rev it's **** off and of course, sensible timing in boost Very Happy
The rest won't kill the engine if you get it wrong, but if you do stupid things like 100 deg advance when your crank sensor is positioned 78 deg BTDC, then....well.....seek another profession / hobby Very Happy




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