Dizzy question

[TvrToe]

4L Chim, Serp engine. Just bought a replacement for my Lucas 35DM8 dizzy (2 pin male connector to a separate ignition amplifier). The new one arrived today (oh joy!) but it is the one with the amplifier attached to the dizzy i.e Lucas 35DLM8 type, which has a 3 pin male connector.
Question is can this be adapted to make it a 35DM8? What goes on under the tamper proof cover inside? Does anyone have a wiring diagram?

Thanks in advance

[nawarne]

In my opinion, fitting the 'older' style of dizzy would be a retrograde step.

Might be worthwhile going back to the supplier and highlight the difference as per your original post.

With the amp mounted on the dizzy, it is, again imho, subjected to far more heat stress making it more liable to break down as the engine temp rises/over time.

Possibly, other more knowledgable folk will be along and add to what I've said - BUT the change of position of the amp to a heat sink plate away from the exhaust must have been done for a reason.

Nick

[nawarne]

In my opinion, fitting the 'older' style of dizzy would be a retrograde step.

Might be worthwhile going back to the supplier and highlight the difference as per your original post.

With the amp mounted on the dizzy, it is, again imho, subjected to far more heat stress making it more liable to break down as the engine temp rises/over time.

Possibly, other more knowledgable folk will be along and add to what I've said - BUT the change of position of the amp to a heat sink plate away from the exhaust must have been done for a reason.

Nick

[TvrToe]

Thanks for your thoughts Nick. I'm still waiting for a reply from the supplier. I hadn't planned on splashing out on an ignition system overhaul just yet. Almost tempted to strip down the old unit to see if its repairable.

[GreenV8S]

The only difference between them is where the ignition amp goes. If you didn't get what you ordered obviously you're entitled to get it changed, but it doesn't seem like a big deal either way.

[blitzracing]

I think the ignition amp was moved on the later dizzy to reduce the heat it was subjected to, although there are some minor changes to the rotor assembly as well. The biggest advantage to the earlier set up is the cost of the amps, as the earlier type is used on the Metro an can be had for £10-25 new, but it may be more prone to failure in the very hot TVR engine bay. The two and three pin amps are interchangable, and Ill send you the wiring if you drop me your email. DO MAKE SURE you get the wires around the correct way or it pops the amp. In terms of upgrades I recently bench tested a "50kv" amp, but it produced a slightly lower voltage (27kv) than the LUCAS unit (30kv) at 5500 rpm, but it has a longer spark burn time, although I doubt you would notice any difference for the price.

Mark

[big geoff]

Blitzracing Mark the lucas one was fitted to the Ford CVH engine which was a lean burn engine good power and mpg due to the angle of valves and shape of piston crown which needed a controled detonation hence the length of spark time .

[blitzracing]

The "50kv" unit is a bolt on after market goodie sold by one of the RV8 tuners, although it never reached anywhere near 50 kv under test, as this is dependent on the coil type and available dwell, not the amp, as after all this is just a switch. What it did do was prolong the spark for nearly a millisecond longer at 5500 rpm than the lucas unit, but at the expense of ultimate HT voltage. This is due to the way it divided the very limited charge / discharge time avaiable for firing 4 plugs per revolution at high RPM. Basically it gave the coil less time to charge (with subsiquent lower HT) but longer for the spark to burn, before it started the next coil charge period. The performance was identical to the Lucas at lower RPM. As you say long spark durations are supposed to be better on lean burn engines, but I dont think the RV8 ever came into that camp!

[TvrToe]

Happy ending; It works
For anyone interested: once I bit the bullet and removed the dust cover inside the dizzy, the solution was obvious. I needed to retrieve the 2 pin plug from the old unit,to match my cars wiring; so cut the leads close to the impulse pickup and removed. Did the same on the new dizzy. Soldered the old connector to the tails from the impulse pickup in the new dizzy and sleeved with heatshrink sleeving. Refitted the dizzy using a photo taken before the old one came out, to ensure the new one went back the same way. Fired up first time; brilliant! Doing it this way saved £100 over the correct dizzy;if I could have sourced one!

[2005lyndon]

hi sorry to hijack an old thread, im just changing the amp on my mgb gtv8 project in a vain attempt to get the bloomin thing to fire,haynes manual diagnozed the last one as faulty im looking for a wiring diagrm to change form the two pin to the three pin amp, for the 35dlm8 dizzy

thanks

lynd

[SILICONE KID]

You can have mine for £20.. only done 35000 miles with new OE cap.

[SILICONE KID]

Straight out my engine when i had the megasquirt fitted.The bracket is still on the engine to retain the plug.You can re use your own.I can post ,dont think it will cost more than £4.The dizzy cap is new (OE)

Edited by SILICONE KID on Thursday 13th January 23:54

[blitzracing]

2005lyndon said:

hi sorry to hijack an old thread, im just changing the amp on my mgb gtv8 project in a vain attempt to get the bloomin thing to fire,haynes manual diagnozed the last one as faulty im looking for a wiring diagrm to change form the two pin to the three pin amp, for the 35dlm8 dizzy

thanks

lynd

Drop me your email address, Ill send you a daiagram.

[2005lyndon]

done cheers

[2005lyndon]

received thanks