distributor advance curve? (x-flow)

[Ian7]

ok, Kent engine owners, any idea what advance curve is built in to your dizzy's?

general wisdom suggests a street tuned engine wants about 14 degrees at idle and 36 at what upper rpm?;

do we agree?

is the ideal curve linear with rpm, or.... ?

 

cheers

Edited September 8, 2009 by Ian7

[lowflyer]

The advance is going to depend, in most cases, on the condition of the distributor. Since it's a function of the condition of the springs inside, plus the cleanliness around the weights, plus any wear in the shaft.

 

The 36 degrees is about as far as you want to run it, especially if you're using pump gas. I used to run my FF Cortina engine at that advance, but I was using 100 LL aviation gas.

 

The advance is easy to check if you use a timing light with an advance feature, and have the use of a friends foot or hand to operate the throttle. If it all comes in at once, check the condition of the springs inside. You can also buy different springs to alter the advance, as well as changing the weights slightly by grinding.

 

Try setting it at 34/35 at 4000 rpm, then go back to idle and check what you have there. You can use a piece of graph paper and map the advance by running the engine from idle up to the 4000 rpm setting (at which point all the advance should be in) and write down the total setting at 500 rpm increments. You might notice that the timing mark will jump around at 4 grand, but that's just the slop in the gear/distributor shaft/etc.

 

After that, just drive and make sure you don't have any preignition/detonation sounds from the engine (not that you will be able to hear them!).

 

Ken Edney

Chandler, AZ

[Ian7]

Thanks.

Mapping the existing was straight forward. I'm looking for a majority opinion of what might be the best compromise curve.

I have a ridiculous curve in my Caterham-supplied dizzy; total advance in this thing is only 10 degrees !! the third party supplier of the dizzy to Caterham even confirmed that they told Caterham their spec was crap :-)

... so it either idles fine, runs like sh*t, or vice versa, depending on where I set it.

Looking for opinions before the rebuild starts .

[lowflyer]

If the total advance (you didn't say if has just a mechanical or both mechanical and vacuum) is only 10 degrees, then yes, you definitely have a problem.

 

Can you see the advance weights when looking down into the dizz? Any chance that they are rusted or otherwise stuck? If you have a vacuum unit, then the vacuum diaphram could be shot.

 

What is the distirbutor you're working with. Is it an old Lucas unit or something else.

 

More info might lead to a better conclusion.

 

Ken

[Ian7]

Yeah, sorry, previous post lacks info.

This is a non-vacumm mechanical dizzy with an electronic trigger box inside it.

Its a Lucas converted by Aldon in England.

Aldon confirms it has only 12 degrees total advance PER CATERHAM SPEC !! which Aldon tells me they have advised Caterham is wrong but to no avail....

 

my intent is to recurve it so I get 12 idle 34 or so at 4000, but curious if its possible or even desirable to be non linear with rpm (if its just weights, then I guess its non linear with square of rpm due to basic centrifugal force physics)

[lowflyer]

O.K., now I have a better picture.

 

Can't understand why they limit the total advance to only 12 degrees. If you wanted to run up to the "magic" 34/36 total advance, you would have an initial setting of 22/24 degrees.

 

Can't imagine the car would start at that.

 

I think your best bet is to find a shop with an old fashioned Sun Distributor machine. This won't be easy, since nobody even knows what a distributor is any longer. They can set up the advance for just about anything you want.

 

Try the biggest "hot rod" shop you can find in your area and ask if they have such capabilities, or know of anyone that does.

 

Ken Edney

Chandler, AZ

[TheDingo8MyBaby]

Ian,

 

Do you have the Super sprint motor?

 

12-14 degrees is good for idle.

 

The timing should be somewhere around 34-36 at 4000-6000 RPM and seems to vary with the Aldon from what I've read.

 

When does it start advancing the idle? I reccomend advancing from 1000 rpm as opposed to the 1500-2000rpm caterham spec'd.

 

I would reccomend sending it in to Rob at Aldon. He should be able to determine what would be best.

[Ian7]

thanks for input.

 

Rob at Aldon already offered to put in anything I want. Shipping cost is stupid, still trying to find alternatives. Mind you, now that season is ending, I can send it "slow boat inexpensive" ...

[lowflyer]

I shouldn't "hit a guy when he's down", but... these are the kinds of things that led me to buy the Stalker.

 

Can you say, "Made in America"?

 

I had been down the "waiting for my ship to come in" with parts when I built my hot rod Cortina engine.

[bball7754]

Ian - I've been putting off dealing with the same issue on my Crossflow. I also have the Aldon Ignitor with the Unleaded advance curve, which as you said seems to max out at around 25-25 degrees advance.

 

Other than sending to Aldon to be corrected, I guess a new Pertronix might be an option.

 

It's on my list of winter projects. I'm likely going to go with shipping to Aldon. Sounds like Rob is the man to contact.

 

Steve

[TheDingo8MyBaby]

Maybe we can get a group deal going and package all of our distributors together.

 

Or perhaps I could just pick up the 3D ignition I've been dreaming about installing.