db's 66 Belvedere ***FOR SALE***

[db]

Thanks all, plenty of conflicting info but the general consensus is not to go bigger so I'll stick with the 750, but I'll think seriously about a 750dp.

Dunc you're just a bloody troublemaker- I need LESS options not MORE!!


Meanwhile.... timing. Clearly I can't drive it again til this is sorted.

I have 17 initial, 35 @ 3000, then it sails away to 50-odd.
So it's correct up to 3000?
Do I leave it as is but fit a limiter plate so It won't go past 35?
Should I connect the vac advance or leave it off? I've no carb port so it would have to be be manifold vac.
I've pulled the dissy out now, anyone see anything that would cause my timing to over-advance?

[Pete]

Do you have Vac advance on it?

[db]

There's a vac can on the dissy but the carb only has a manifold vac port, It's never been connected but I tried it briefly yesterday and obviously the timing went even higher!

[Pete]

Good.
Leave that disconnected for now and plug the maifold off.

That is not an adjustable Dizzy.
File and weld up job.

[Dave-R]

17 from 50 = 33 degrees.

I have never seen a dizzy with 33 degrees in it. They are usually about 25.

You didn't have the vacuum can connected up to a vac source when you were checking the timing did you?

[Dave-R]

With those springs it should have been "all in" by 3000 or 3500.

Check they are not sticking.

You only time to 3000rpm after you have made sure the dizzy does not advance after 3000rpm.

[db]

Vac was blocked for all the measurements.
Initial is 17.
By 3000rpm it's 35.
Then it just keeps going...

The existing limiter plate is stamped '13R'
There's one yellow spring which gives light even tension from 0 to full swing.
There's one blue spring which gives NO tension initially until the weight has moved out about halfway then it gives very strong tension.

I can't find pics anywhere of any dissy with a differrent spring on each weight like this?

[Les Szabo]

Paul the 750 will be ok on the street, a 650 or 700 will be ok on the street, anything will work ok on the street, as will an 800/850dp, but only cos you got what you got in your motor.

The 340 in '71 came from the factory with an 800 thermoquad if I'm right!, spreadbore or not, it was 800cfm.

The theorists are technically correct, but once you stick a big solid cam, a race intake, headers, CR, ally heads, gears etc in a 340/360 car, all that theory is CRAP!!, thats why I went as fast or quicker than similar 440 equipped cars on motor way back then, cos I didn't listen to them.

I ran my car on the street a lot with an 850, drove it to and from the Pod, cruised to Tony Dicksons in it, etc., it ran great, had more power and torque and it didn't wash the bores or behave badly ever, it was 2/10ths quicker than any other smaller carb, which has no relevance for you I know, but it speaks for itself for hp, and thats noticeable lower down the rpm range as well.

All I can say is try it as you can borrow one, but give it a fair shot, dare to be different to the masses and mass thinking if you want the Most out of your package and something better than just ok, jus get your timing sorted first.

Les

[Dave-R]

Paul it is perfectly normal to have one spring stronger than the other. The control the rate that the timing comes in. The play on the stronger spring allows the timing to come in faster at the start of rpm rise and then increase at a slower rate.

On a street car you should have about half your total timing in by 2000rpm and the rest by 3000.

[db]

Luckily Les I have been offered a loan of one so if I get chance I may well give it a try

[db]

Paul it is perfectly normal to have one spring stronger than the other. The control the rate that the timing comes in. The play on the stronger spring allows the timing to come in faster at the start of rpm rise and then increase at a slower rate.

On a street car you should have about half your total timing in by 2000rpm and the rest by 3000.

Well that all seems right, The only issue seems to be the limiter plate not doing it's job?

[Pete]

I would run as much initial as possible to keep the engine cool and responsive as long at the engine will start without ripping the teeth off the flywheel (Kickback test).

This would mean in your case that the dizzy would wildly over-advance at 3000 rpm.

You need to limit the travel within the Dizzy - you would do this in a "quality" one by loosening off the torq screws and restricting the number of degrees the base plate could rotate and then tightening the Torqs again.

You will have to find a way of doing this if you are going to use that dizzy; hence my comment about a welder earlier...in essence, the slots are too long....

[Dave-R]

Les you are absolutley right that a bigger carb will work better on the strip.
But you are also right that the "800" cfm Thermoquad was a spreadbore. The smaller primaries work well on the street.

This is why I am a big fan of the six pack. Most of the driving is done on the little center 2bbl which works as the primary. That is only 250cfm in 4bbl terms.
The six pack worked just as well on a 340 as it did a 440 because of that.

Total cfm for the six pack was 964cfm (in 4bbl terms). Pretty damn big for a 340. It only worked because of that little centre carb.

[Dave999]

There's one blue spring which gives NO tension initially until the weight has moved out about halfway then it gives very strong tension.

I can't find pics anywhere of any dissy with a differrent spring on each weight like this?

thats cos your Dizzy has been set up with a performance curve

its a chrysler thing adopted by many others

the first spring would cause a rate advancemnet with RPM assocaited with its strength

faster engine spins wider the weight swings and the more advnce you get

the set up you have gives the dizzy advance curve two slopes

first bit it advances fast on the weak spring

say up to 1500

then the next spring slows the advance RATE down becasue 1) its stiffer
2) its working alongside the first spring

so in the first bit you get X degress of advance per rpm
in the second section of the curve you get something different in degress advance per rpm

this allows you to tune the advance rate up to the maximum advance caused by the mechanism just by changing that 1 strong spring once you are happy you can gun it away from s standstill with your foot burried in the floor on the first spring

it might not suit todays petrol

and its called a curve rtaher than a basic x y graph with a bend halfway up becasue twice the rpm gives 4 times the force on the weights combine that with 2 different springs acting at different times and it gets quite hard to picture

springs are linear devices and the force on the weights is not
Force on the weight=Mass of the weight times the Velocity sqaured divided by the radius of the circle i.e force is linked to velocity squared

Dave

[Dave999]

or to put it another way

you can pile masses of advance in at lower rpms to get ya moving
then allow the last 2-3 dgrees to dribble in very very slowly up to the point where the Bananarama! the stops

useful to avoid advance related detonation at some rpm/load point


Dave