are the advance curves of a Griff/Chim different to a Rangie

[Aussie John]

If they are is it just the bob weights and springs? How do I remove the weights? cheers, John.

[blitzracing]

A modified engine (ie tuned) needs a different advance curve, that can be changed by altering the springs in the dizzy. Its a very time consuming job, as you would have to use a rolling road for each power run and measure the torque, then change the springs- that involves a complete dizzy strip down, and re run the test. You cant use the method of listening for detonation on the RV8 to see if the timing is too far advanced- it simply does not knock, but the torque drops off, The whole concept of altering the timing mechanically is too horrible to contemplate. You have other options though.

You can use the Aldon Amethyst system- http://www.aldonauto.co.uk/shop/product.asp?strPar...

This keeps the stock dizzy, but you lock the weights so they cant move, and the box of electronics to map the timing. I tried this system early on, but there where some bugs in the system, that have now been resolved for the RV8 according to Aldon. Ive got mine wired in, but not controlling the timing at the moment, so I can switch back to the stock system very easily if needs be- I just want to make sure the triggering is 100% reliable before I lock the weights.

There is the megajolt system- http://trigger-wheels.com/store/contents/en-uk/d35...

More advanced and does away with the dizzy completely and uses wasted spark and 4 coil packs- basically a megasquirt system without the fuel control

Or the 123 ignition. http://www.rimmerbros.co.uk/Item--i-RB7459E123

Beautifully engineered electronic mappable distributor that retains the coil, but is very pricey, but just slots in with minimum bother.

[carsy]

I can definately recall Rob Robertson saying they were just a boggo Rangie item, not modified at all.

[davep]

There are 35DLM8 Rangie distributors and then there are other 35DLM8 Rangie distributors:

http://www.rimmerbros.co.uk/Item--i-GRID800071

So I presume the springing, weights and therefore advance curves do differ. What was fitted to TVR engines is anybody's guess.

With this in mind I sent an inquiry to Rimmers asking which of the 35DLM8 distributors on offer would suit a pre-cat 4.3 Griffith given it's a performance Rover V8, EFI and non-cat, their response was forget 35DLM8 and fit a 123Ignition dissy, which they also happen to sell.

On a 35DLM8 I stripped down the compression and return springs were definitely different lengths/rates, also the weight plates didn't strike the end-of-travel posts at the same time, whether this was intentional and TVR specific or not, I don't know. Real Steel do spring kits for Rover V8s giving different advance curve options.

[Aussie John]

I have got a Rangie one apart now and Sardonicus has kindly offered to send me the guts of a Chim dizzy; the springs are both different strengths in the Rangie although the weights appear the same at first glance, it's an interesting subject.

[Speed 3]

Aussie John said:

are the advance curves of a Griff/Chim different to a Rangie

Think you'll find the Rangie is far more boxy than the beautiful curves of a Wheeler era TVR

[QBee]

Speed 3 said:

Aussie John said:

are the advance curves of a Griff/Chim different to a Rangie

Think you'll find the Rangie is far more boxy than the beautiful curves of a Wheeler era TVR

....but I'd love to turn up at a horse show towing my horse trailer behind the Chimaera.

[blitzracing]

Having given up with the Amethyst Ive pulled the dizzy mechanics to bits to see what can be done. I don’t know about the TVR, but the G33 has a standard Range Rover dizzy so far from optimised for a light weight car revving up to 6000 rpm. The stock Range Rover timing curve is designed to be safe pulling a two tonne car in any conditions, and keep the emission low by keeping the timing more retarded than needs be for best power.

Pulling the top off exposes the bob weights- and they are stamped with the number of degrees mechanical advance- in this case 10’. This equates to 20’ on the crankshaft as the distributor runs at half the crank speed. Its generally accepted for the RV8 engine the maximum advance needs to be 34’ for the 3.9 and 36’ for a 5 ltr for peak power. With only 20’ being available, this means you will have to set the idle timing at 14’ to reach 34’ total which is really too advanced at idle so the bob weight stops need modifying.

In this photo you can see the advance plate is hard up against the spring stop (near the 10 stamp) at full advance, and at the bottom there is still about 1.5mm clearance, so only the top plate is having any effect. You can also see that Lucas have heat hardened just that area. You cant remove the assembly to file it anyway, but it is possible to get a Dremel type tool in there with a small grinding stone and remove some metal. I fitted a large cardboard protractor ( Downloadable http://www.machinerycleanery.com/MachineryCleanery... to the upper shaft, and locked the gear wheel at the base. With the springs unhooked you can then rotate the upper shaft and see how many degrees it will move between stops against a reference pint on the protractor. I ended up grinding near 1mm off, and that gave me an additional 2’, that equates to 4 crank degrees.




So the timing should now be 10’ static + 24’ total advance = 34’

In terms of modifying the spring rates I think best to leave alone for the timebeing at least, as the low speed behaviour becomes poor if you add to much additional advance- 10’ static is fine, 15’ makes the engine less smooth and reduces the torque, so I don’t believe the stock springs are far out. However simply grinding the one stop plate allows the advance to continue another 4’ beyond the point the Range Rover timing would have peaked and from my experiments with the Amethyst its certainly worth getting those few extra degrees.

All we need to know now is did TVR bother to alter the dizzy or not?.