GT6 Distributor

[MARK]

I bought a distributor at IWE for my tr6. On cleaning it up I have found it is for a GT6 not a TR6 !!!!

My TR6 is modified with sports exhaust and lightened flywheel running on triple 40 DCOE Weber carbs.

In its present state is the GT6 dizzy likely to work in my car without modification? I do have a spare TR6 dizzy which has broken casting and would be able to transfer weights and springs over to GT6 dizzy but are the cams different?( Both 6 cylinder). Thoughts please

MARK

[stuart]

Talk to Martin Jay http://www.distributordoctor.com/

Stuart.

[Guest ntc]

Mark

Put it in and try it

[MARK]

Thanks Stuart

Spoke to Martin this morning. He said advance curb and cam would be wrong and suggested that I send it to him for altering to TR spec. I did not want bombard Martin with many questions as he was obviously very busy and called me back amongst a number of calls.

I have since wondered why cams would be different as both are 6 cylinder unless profiles are different.?

Has anyone tried GT6 dizzy on a TR6?

I would suppose that most TR6 advance curves are somewhat out anyway with modern fuel and modifications we have done.

Anyone come up with a good compromise of Dizzy springs and weights for both PI and on webers on mildly modded TRs ?.

MARK

[MARK]

Hi Neil

Will be trying it on car as soon as I can but building work and plastering on my house is making it very difficult to get to my car !

Trying to build up some knowledge in meantime!

MARK

[Nigel Triumph]

GT6's were fitted with Delco distributors in the factory, not the usual Lucas.

 

Is your really a Delco (steel body, compared to alloy body for a Lucas dizzie)? If it's Delco, the advance weights and springs are different, not interchangeable with Lucas, so re-curving a Delco for a TR6 would be difficult.

 

 

Nigel

[RogerH]

Hi Mark,

my chum Bob with TR6 and triple webers found that the dizzy bob weights were actually back to front so they always did nothing but the car went very well (sort of). Fitting the correct dizzy with working bob weights made an improvement but not earth shattering.

 

Stick the GT6 in, if you can, and see what happens.

 

Roger

[Peter Cobbold]

Give it a go, I expect it to work well.

GT6 and TR6 have similar combustion chamber shape and compression ratio and you are on carbs not PI. The 2.5 vs 2 litre is not too important: the effective compression of the GT6 will be a tad better, but only a degree or so less advance different, if that.

(The above does not apply to the TR6 PI)

 

Spark timing to the nearest degree is only important if the engine is on the verge of knocking. Otherwise it can be timed with 5 crank degrees too much, or 5 deg too little, advance and the torque dropped will be only 1% of max., undetectable. See slide 60 of IWE talk, and preceeding slides.

 

Peter

[Peter Cobbold]

Thanks Stuart

Spoke to Martin this morning. He said advance curb and cam would be wrong and suggested that I send it to him for altering to TR spec. I did not want bombard Martin with many questions as he was obviously very busy and called me back amongst a number of calls.

I have since wondered why cams would be different as both are 6 cylinder unless profiles are different.?

Has anyone tried GT6 dizzy on a TR6?

I would suppose that most TR6 advance curves are somewhat out anyway with modern fuel and modifications we have done.

Anyone come up with a good compromise of Dizzy springs and weights for both PI and on webers on mildly modded TRs ?.

MARK

Mark, He might be thinking its a PI TR6, which will be different frmm the GT6 for reasons that dont apply to your Webers. For the PI peculiarity see IWE talk slides 91 -100. The PI runs markedly retarded to try to abolish the pinking upon flooring the throttle.

 

Try the GT6 disy, set the static to around 10BTDC. Then try 5 BTDC and then 15BTDC I dont think you'll find much difference. 10-12 BTDC is about right for a 9.5:1 head.

Unless you have a trick cam with very late inlet valve closing ( or the GT6 did and the disy was adjusted to suit) it should work fine.

Peter

Edited July 25, 2016 by Peter Cobbold

[BlueTR3A-5EKT]

at least if it is a GT6 unit it has a mechanical tacho drive take off.

[MARK]

Thanks very much for all the words of wisdom gentlemen ! My car was originally CR PI but was converted in past to triple webers. If that makes any difference to any advice already given. Cam shaft is unknown but car goes well compared to standard PI.

Seems only way forward is to give it a try in the car! The dizzy in question is a 22D no 41168B and seems to be in very good condition.

Looking at TR6 distributors they seem to be made in two parts. The main bowl part and the part with the tacho drive. Martin the Dizzy Doctor said they were made in two parts but re-cast together? They often break apart at this point. (one of mine has) Anyone know about this or has repaired one so broken?

[Guest ntc]

Mark

The webers make all the the difference tis why I said try it

[poolboy]

A Vacuum Gauge hooked up to the intake manifold might give you a clue about the cam...not saying it will identify specifically which one but should give indications.

Compare Scenario's 1 and 3.. All else being equal, the more radical, the more fluctuation.

http://www.secondchancegarage.com/public/186.cfm

[john.r.davies]

Here is a comparison of dizzie advance 'curves' from a race engine, two marks of Vitesse, a Herald and a TR6.

It's from Gareth Thomas' "Tuning Manual".

I suppose that the GT6 will not be very different from the Vitesse, but remarkably, the TR6 and Herald curves are as good as the same!

 

The way to tune is by changing the two springs, a fiddly but straightforward job, and the Distributor Doctor sells sets.

http://www.distributordoctor.com/distributor_advance_springs.html

 

John

Edited July 26, 2016 by john.r.davies

[Peter Cobbold]

Here is a comparison of dizzie advance 'curves' from a race engine, two marks of Vitesse, a Herald and a TR6.

It's from Gareth Thomas' "Tuning Manual".

I suppose that the GT6 will not be very different from the Vitesse, but remarkably, the TR6 and Herald curves are as good as the same!

 

The way to tune is by changing the two springs, a fiddly but straightforward job, and the Distributor Doctor sells sets.

http://www.distributordoctor.com/distributor_advance_springs.html

 

John

John, Thank you, I'd been looking for those data. The TR5,6 have odd curves that come in late because of the PI pinking due to lack of 'acceleration charge' ( ie throttle pump). The Herald uses less advance because it is smaller bore- the flame takes less time to cross the chamber. So the similarity is a coincidence. A carb'd 5 or 6 would be like the Vitesse or GT6. Peter

Edited July 26, 2016 by Peter Cobbold

[MARK]

Many thanks for help. Did anyone have any info about construction of TR 6 dizzy. If you look under the bowl of the main part it looks like it was separate. How the were joined ? Anyone fixed one that has broken at that point.?

MARK

[Nick Jones]

Thanks very much for all the words of wisdom gentlemen ! My car was originally CR PI but was converted in past to triple webers. If that makes any difference to any advice already given. Cam shaft is unknown but car goes well compared to standard PI.

Seems only way forward is to give it a try in the car! The dizzy in question is a 22D no 41168B and seems to be in very good condition.

Looking at TR6 distributors they seem to be made in two parts. The main bowl part and the part with the tacho drive. Martin the Dizzy Doctor said they were made in two parts but re-cast together? They often break apart at this point. (one of mine has) Anyone know about this or has repaired one so broken?

 

 

That's actually a Mk1 2.0L Vitesse distributor not GT6, though I'd expect the curve to be very similar to that of the Delco unit used in the Mk1 GT6.

 

Stick it in and try it. None of the standard offerings are going to be right for a 2.5 on triple Webers and non-standard cam anyway.

 

Dizzy Doctor or Aldon will have a good guess at it if you can tell things like what cam is fitted and what the compression ratio is. Otherwise a rolling road and a bunch of weights and springs.

 

Alternatively, junk the clockwork dizzy and go Megajolt / NoDiz for timing setting with a laptop.....

 

Nick

[Gunner1]

Hi Mark,

 

I have just done this. Bear with me, but I have to give you some history. Bottom line is that it will work fine.

 

When I rebuilt my 75 Tr6 engines, I put in a Kent TH2-6 Cam, increased compression and am running a pair of Weber 45 MCHH's so no vacuum advance.

 

I followed the manuals instructions when orienting the distributor drive gear so they lined up with the two distributor hold downs lug (7/16" bolt) and triple checked my cam timing. (TH2-6 cam timing is very similar to PI)

 

I used the stock distributor with pertronix ignitor.

 

When I started the car, it ran like **** at idle. I changed to points...same thing. It ran a bit better as speed increased or if I advanced initial timing to 24 degrees!

 

I had an unmolested 1969 TR6 engine and pulled the dizzy to have a look and found that the drive slot on the gear was installed one tooth to the left of where the book suggested so it pointed towards #5 spark plug, maybe a bit to 4, but not to #6. (and some fettling, lined up my oil pump drive gear)

 

I drilled a hole in the dizzy cap on the 75 and sure enough the distributor was out of phase when lined up the way the manual suggested. (points fired between and not on the plug wire terminals)

 

When I changed the gear orientation, the distributor went into phase. You can adjust it to perfection by moving the vacuum plate and pinning it so the points or ignitor fires right when you want it...just as the rotor starts to touch the plug wire lug.

 

So here comes the part about the GT6 dizzy. I purchased a Delco GT6 dizzy from Accuspark off Ebay (GREAT people do deal with!)

They supplied me with a centrifugal curve graph upon request and it looked very much like what I was looking for. I installed it and it worked great!

Just for fun, I pulled the drive gear and put it in as the manual suggested and it worked even smoother.

 

I compared the angle of the rotor to the angle of the drive at the bottom and it is slightly different than TR6.

 

So, my suggestion, drop it in, if it will not idle, change that gear by one tooth. As for the advance curve, at least on the Accuspark one, it worked very well! I would not alter it.

 

Your observation on the orientation of your drive gear, or even a pic when at TDC would be very much appreciated as I am still baffled.

 

Hope this helps.

Gunner1