Ignition Retard Under Boost

[topcatcustom]

Hi, is there a rule or guide line as to how much retard the ignition should have under boost, whether it be per lb or rev related?

Running about 6psi (on the gauge) and rev limit will not be any more than 6500 tops.

[kiwicar]

hi Tom,
a general rule is 1 degree at the distributor for 1 Lb boost, but as I posted on your other thread I would just dump out about 5 or 6 degrees of additional vac advance over what you would normally have off the vack advance and use a conservative mechanical curve that comes in late.
Best regards
Mike

[topcatcustom]

Ta Mike, I'm going to try using the vacuum advance to retard for boost, I have 3 different vac cans, they are something like 6, 7 and 8 degrees so wasn't sure which to use as a starting point.

I do have an MSD BTM but didn't have any joy with it when I was trying to start the car for the first time so I disconnected it and haven't tried again, though I will hook it up again before I go messing around! If it is kaput I dont fancy spending £300+ on a new one as I am only running low boost and not professionally.

[Eliot]

£300 for an add-on ignition box?! megajolt or megasquirt doing just ignition will give you a fully mappable ignition.
as noted mike says, allow about 1 to 1.5' degrees of retard per pound of boost. Phil (extraefi) has first hand experience of boosted rovers and may chime in.

[daxtojeiro]

Me chime in ?

If youve got an EFI setup then you will need to sort out the fueling by either having the Lucas chipped or by going with an aftermarket ECU, there is no other way and the Lucas simply will not fuel for the blower without it.

Of course if you have a carb then forget the above

Personally I feel youd be far better with wasted spark and a full mappable system, for the sake of 4 or £500 for it all I wouldnt mess about.

Up to you though,
Phil

[topcatcustom]

Thanks for the input Phil- but I'm staying old skool and happy with my carb and dissy for now! The combo has worked ok since the 60's on the scene so it'll do me on this one!

[daxtojeiro]

Thanks for the input Phil- but I'm staying old skool and happy with my carb and dissy for now! The combo has worked ok since the 60's on the scene so it'll do me on this one!

Thats cool, as you say Im sure its up to the job.

I'm thinking of going for a blower again now, all this talk about them has made me miss mine

Ohh, as for the question, the rule of thumb is cut 1 deg for every 2 psi of boost, certainly worked ok for me up to 8psi on my old 3.5, hotter plugs too if I recall,

Phil

[DaveEFI]

Thanks for the input Phil- but I'm staying old skool and happy with my carb and dissy for now! The combo has worked ok since the 60's on the scene so it'll do me on this one!

Jaycar do a programmable ignition unit that can be used with an existing dizzy and will alter the advance curve either way to your requirements . It has an optional MAP sensor and should do what you want to the vacuum advance too.
The only snag is it uses its own hand held programmer rather than a laptop.
But is pretty cheap for the DIY kit - under 100 quid complete. It would be very easy to install it so it could be disabled and revert to the original ignition setup.

[JP.]

hi Tom,
a general rule is 1 degree at the distributor for 1 Lb boost, regards
Mike

Thats what I run too.
Have advance set at 38 total at 4000 rpm ( 14 initial & 24 advance).
BTM module is set at 1' retard / 1psi

[topcatcustom]

Cheers for the input guys, I took the car for a spin last night with the 8deg vac unit on and it drove superbly, it is going on the rollers on saturday so may experiment with a different unit and more/less timing then.