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I have a few questions about 2 main issues.

The first issue being gear box. I run a completely standard gear box/diff/drops. Im looking to upgrade. I have been reading articals such as turbo daves strait cut verses helical and now im left confused.

I think basically the artical says given suffecient lubrication around vital area's a well built helical box is the dogs thingys. Or have i got the wrong end of the stick? Please enlighten me!!


And also, i have a very low compression turbo engine, 10cc pistons, 30.5cc head chambers. I run at highish boost with a MED T3 cam shaft.

so basically my standard metro turbo ignition system is no longer acurate, or is it??? What are the experts advice on ignition system mods/ upgrades. For example what does that 200bhp mini williams run?

Go on guys, amaze me with your technical knowlege!!!!

Expert: 'X' is a has been; 'Spurt' is a drip under pressure.

So, now we've got that out of the way...

I claimed in that article that Factory helicals are far superior in strength than the SC gears you purchase from the many specialists, and i still stand by that.
The problem is that they (helicals) DO generate large axial and twisting forces about the gear axis (the axial force being the greater component).
This is the greatest problem therefore, the bearings - there is simply veryu little that can easilly be done to counteract this (other than what i mentioned i'd like to try about pressure feeding the idler). So, the easy way out is to fit SC gears, accept the vastly reduced life, increased noise, greater swarf build-up as they wear, etc.... But use the Stock bearings.

For the turbo, there is another factor to consider... These engines make lots of low-down torque. Hence, can pull a taller first gear much more easilly than a 286'd 1293 putting out the same peak power.
For the Drag strip aswell, it has been proven that the ideal total 1st gear / FD combined ratio is between 8:1 and 9:1 (8:1 for 10", 9:1 for 13").
The std turbo FD and 1st gear is (i think) 10.6:1 Might not sound an awfull lot, but it is - especially if you have a high (and wide) torque from your engine...

So, SC 'GEARS' will NOT last longer than helicals. Nor are they 'stronger'.
However, in a high performance Mini Gearbox, the bearings will (theoretically) last longer with the SC gears as they are not being exerted to the same 'damaging' twisting and axial force components as experinced in a helical transmission. Of course, when a bearing fails, it usually damages a gear - so the helical gear is often blamed, when in reality, it was the bearing designed for a 40lb/ft 998 engine that was just pushed too far.




As for ignition, this, along with gearboxes, is a fave subject of mine!!!

Peak power is just that. PEAK! All you need to get the highest peak power figure in any Petrol engine, is a dizzy running No mecahnical advance, NO vacuum advance, and No fancy electronics.
All you do is run the engine up on a rolling road or dyno until peak power is reached, swing the dizzy a little more, adjust the rpm to the point at which by adjusting the dizzy just enough, and gettign the revs just right, your engine makes peak power. How fantastic is that? And so simple!!!

Unfortunately, that means you DONT have the best power at every RPM and load site everywhere else. Also, (with a hi-boost turbo) you can end up running not much advance at all at 7000rpm and 20psi (as an extreme example). If you have a locked up dizzy, this means you are also running this same advance at 3000 rpm when you are pootling up an A-road on the way to the shops - result, bad economy, excessive heat generated in the turbine, increased turbine spool-up time, etc...

To get the best all round advance, you need a few things:
1) a RR operator who knows how & cares enough to 'tune' your dizzy's advance curve by changing/ modifying bob weights and springs in situ.

2) My preffered method whilst retaining a dizzy - Using a Dizzy testing machine. With this, you run your engine up on a set of rollers with a locked dizzy, and note (using a strobe light) what advance is required to acheieve full power every 1000 rpm. You then plot the advance against RPM, fit a dizzy into the machine, and by adjusting springs, bob weights and stops, you achieve as close to the advance curve as you need. The dizzy is then fitted back into the engine and the advance checked. Using the vacuum advance complicates it a little more, but is still pretty straightforward.

Finally,
3) My much preffereed method for a turbocharged engine; mapped ignition, preferebly wasted spark.

Jukka, is, in my opinion, one of the best people to speak to about Dizzy's, simply because he has done quite a few of them! I have to confess, i've only ever been involved with one engine build using 2) - no rolling road operator seems to be bothered with it anymore, so long as there is a nice big power figure at the end...

Hope this answers some of your questions?

Edited by turbodave16v on 20th Jan, 2004.

Again, I have to admire how well Dave explains the helical box vs. s/c box features. I have used the same helical box since 1996 and am yet to break anything. The trick is careful setup during assembly and changing the bearings every time the box is dismantled. The gears are strong, especially those dating back to pre A+ time. I am currently using 15 psi boost with helical box and drop gears and still intend to keep it that way. I will most likely pull the engine apart next winter and have planned to experiment the car at 20 psi on rollers just for fun...

Also, note that S/C box and 13" wheels will put quite a strain to clutch, especially with numerically low diffs like 2,95 to 3,21. When choosing the transmission, think carefully where you are going to use the car. Track, drag strip or normal traffic. Once the engine is sorted you?ll have more than enough torque with good spread over the rev range. You will note that you can use numerically lower final drive n/a engine ever could, and still retain loads of acceleration. I have got sub 7 sec timing from 0-100 km/h with 2,95 diff. This is measure with an acceleration meter, not with stop watch.

Now, turbo engine with s/c box, 3,7 diff and 10" wheels will make for a lot of gear changing, every 2 to 3 seconds. You?ll end up doing something like 4000 rpm at 65 mph. If you love it, that?s the way to go.

As for dizzys, Dave?s method is the way to go if you find an enthusiastic operator who loves to tinker. Most don?t. I have used common sense when modifying the dizzy. I have a load of old lucas dizzys and have removed the internals. The centrifugal weights have a degree figure stamped on. Say, 10 or 15 or 16 degrees. This tells you the amount of maximum advace in the mechanism. These are distributor degrees so you have to multiply by 2. I have used 10 degree stuff. OK, an example: let?s guesstimate that your engine has a good intercooler, good cam, low CR and 15 psi boost. ASSUMING the engine is otherwise set up, runs rich enough etc. I would guesstimate that the total advance would be around 28 crank degrees. Now, with 10 deg internals the mechanical advance from dizzy is 20 degrees at the crank. So, your static advance equals to 28-20 = 8 degrees BTDC. OK, in real life it?s better to start at 6 or even less.

Now, again we come to where you are using the car. For road use I would retain the turbo advance vacuum. This is different from n/a vacuum pots. Anyway, what you achieve is better low rpm drivability. If you don?t believe, try it. It will not harm the engine, but you?ll find out the the engine hesitates.

Whether your retain the vacuum or not affects the dizzy spec. The dizzy internals define the max mechanical advance available and the approximate static setting. The primary and secondary spring combination define the rate of advance relative to engine speed.

Usually the primary spring is weaker, secondary stronger. Now, the idea is to swap the springs until you find the best curve. Rolling road and dizzy machine is the fastest way to do it. I have used common sense, lots of guessing and gut feeling to set the engine up. Without vacuum unit you would have to use a weak primary spring to get enough advance at low revs and very strong sec spring to limit the advance during boost. With the vacuum retained the primary spring can be a touch stronger since the vacuum pot will advance another 20 degrees at low rpm (high vacuum conditions. Once the engine boost is developed the vacuum pot is inactive.

As for Metro turbo dizzy, their curves are very conservative, remember that it is for 9,4:1 engine. With intercooled low CR engine there is more tolerance against pinking and most likely the timing could even be advanced at lower revs. Anyway, each engine is unique so you have to listen to your engine. Try small changes, see how it feels and if it runs better make another change. If the engine pinks, BACK OFF immediately and retard the timing. Rolling road is the best place for these total timing trials but a lot of initial work can be done on the road. Most of the "experts" have done years of work with their engines and this is where the "expertise" comes from.

Hope you are still awake...

Jukka

On 21st of Jan, 2004 at 08:19am jukka said:
Again, I have to admire how well Dave explains the helical box vs. s/c box features. I have used the same helical box since 1996 and am yet to break anything. The trick is careful setup during assembly and changing the bearings every time the box is dismantled. The gears are strong, especially those dating back to pre A+ time. I am currently using 15 psi boost with helical box and drop gears and still intend to keep it that way. I will most likely pull the engine apart next winter and have planned to experiment the car at 20 psi on rollers just for fun...

Also, note that S/C box and 13" wheels will put quite a strain to clutch, especially with numerically low diffs like 2,95 to 3,21. When choosing the transmission, think carefully where you are going to use the car. Track, drag strip or normal traffic. Once the engine is sorted you?ll have more than enough torque with good spread over the rev range. You will note that you can use numerically lower final drive n/a engine ever could, and still retain loads of acceleration. I have got sub 7 sec timing from 0-100 km/h with 2,95 diff. This is measure with an acceleration meter, not with stop watch.

Now, turbo engine with s/c box, 3,7 diff and 10" wheels will make for a lot of gear changing, every 2 to 3 seconds. You?ll end up doing something like 4000 rpm at 65 mph. If you love it, that?s the way to go.

As for dizzys, Dave?s method is the way to go if you find an enthusiastic operator who loves to tinker. Most don?t. I have used common sense when modifying the dizzy. I have a load of old lucas dizzys and have removed the internals. The centrifugal weights have a degree figure stamped on. Say, 10 or 15 or 16 degrees. This tells you the amount of maximum advace in the mechanism. These are distributor degrees so you have to multiply by 2. I have used 10 degree stuff. OK, an example: let?s guesstimate that your engine has a good intercooler, good cam, low CR and 15 psi boost. ASSUMING the engine is otherwise set up, runs rich enough etc. I would guesstimate that the total advance would be around 28 crank degrees. Now, with 10 deg internals the mechanical advance from dizzy is 20 degrees at the crank. So, your static advance equals to 28-20 = 8 degrees BTDC. OK, in real life it?s better to start at 6 or even less.

Now, again we come to where you are using the car. For road use I would retain the turbo advance vacuum. This is different from n/a vacuum pots. Anyway, what you achieve is better low rpm drivability. If you don?t believe, try it. It will not harm the engine, but you?ll find out the the engine hesitates.

Whether your retain the vacuum or not affects the dizzy spec. The dizzy internals define the max mechanical advance available and the approximate static setting. The primary and secondary spring combination define the rate of advance relative to engine speed.

Usually the primary spring is weaker, secondary stronger. Now, the idea is to swap the springs until you find the best curve. Rolling road and dizzy machine is the fastest way to do it. I have used common sense, lots of guessing and gut feeling to set the engine up. Without vacuum unit you would have to use a weak primary spring to get enough advance at low revs and very strong sec spring to limit the advance during boost. With the vacuum retained the primary spring can be a touch stronger since the vacuum pot will advance another 20 degrees at low rpm (high vacuum conditions. Once the engine boost is developed the vacuum pot is inactive.

As for Metro turbo dizzy, their curves are very conservative, remember that it is for 9,4:1 engine. With intercooled low CR engine there is more tolerance against pinking and most likely the timing could even be advanced at lower revs. Anyway, each engine is unique so you have to listen to your engine. Try small changes, see how it feels and if it runs better make another change. If the engine pinks, BACK OFF immediately and retard the timing. Rolling road is the best place for these total timing trials but a lot of initial work can be done on the road. Most of the "experts" have done years of work with their engines and this is where the "expertise" comes from.

Hope you are still awake...

Jukka

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Hi,
This is a great post, a bit more I've learnt!
Cheers,
Gavin :)

Edited by Bat on 17th Jun, 2007.

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That was 3 years ago lads....!

Would say Experts, maybe Sperts lol. Wow Lots to read on here.
SumpNut , if its any help.

I'm running Straight Cut box and drop gears without any problems over the past years (not now mind) yes what Dave is saying is spot on about the gears, i can't see mine lasting long with the side loads the helicals make, which is a shame as the quaility of the gears them selfs.

As for ignition, i'm using the STD metro electroic set up, with dizzy. And it's locked, as we have found it to be a smoother ride.
We had done many tests over the years and have found NO gain in throttle responce or turbo lag, by using the Vacum advance or adding timing down at the bottom end of the rev range, but this isn't the norm by the sound of things, it just seems to be my car, as others have found more timing down the bottom helps things.

Best 1/4 mile 13.2 seconds @116 mph
First 5 port miniturbo to make over 200 bhp on a carb?
First 5 port miniturbo to make over 200 bhp on Injection?

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I was always tempted to try an A-series gearset on mine, as the gears were visibly thicker than the A+. I never had any old A-series boxes about though.
I could easily destroy the input drive gear in no time with the A+...( not the drop gears, but the internal gear attached to the lower drop, plus corresponding laygear )

After destroying 4 or 5 A+ gearsets, I eventually went to a Tran-X gearset. This proved pretty good, with only once breaking 2nd gear in the many miles I did.

Same as above, all I ever had was a welded electronic dizzy. I did upgrade my coil to a Crane Hi-6 setup at one point, but never had any real problems either way.

On the gear thing...I checked the website I got my T56 from. I think they only charged me something like $350 to have the gearset cryo treated, so wasnt too bad.

Id liked to have tried a mapped ign setup, but that stuff was beyond normal people back then.
Welding the dizzy was free lol.

but as said, with low CR, you want reasonable timing down low, then on boost, it may lower....I think I recall I had circa 24-28 deg all the time.
I dont recall ever using the vac advance too...although cant say for sure.


@ miniwilliams....did you ever get the missfire sorted ?

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will