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31 replies

igintion timing for high comp engine based on roller

matgmatgMember
Team Hi,
4907 is on the road again incl. German TÜV ..no issued as they loved the car...woow as all brand new! incl. 305 on the rear!
so now I am doing all the "final" adjustments. Here now the ignition timing topic.
- I did follow the guidelines per sticky (TX George et al), well always some deviations.

Status:
1) engine full overhauled, bore 4.02 (custom Ross pistons) compression static app. 10.3, Trick flow heads, Edelbrok dual plain (modified!)
2) Holly 650 (so far)
3) ignition single point (one) system
4) Crane parts all over.. full roller , limit 6000 (can get you the cam details)

did run the car for 25 miles to go for TÜV / MOT was running rough after just static timing set up, based on this wimpy "PIONTER" precision!
Today I now used a ignition flash device to get better facts and adjusts.

Starting point:
1) vacuum tube OFF the distributor
2) engine run in the garage for 15 min, Oil pressure good, water temp did go up but have a fully modified cooling , no worries all top class (again learned from sticky)
3) engine idling very rough at MEASURED 5 dreg. adv.

Mods:
1) move the distributor/hence pointer settings back and forth.
2) Settled at a nice 800 rpm idle at about 15 degr. advance? Can move it up and done with better & worth idle ..

SO...What is correct?
1) From my sense it is a question of the cam used.
2) I ASSUME : at idle move the advanced back as much as possible (near 10 degr.) for a DECENT idle at 800? OR NOT????

Need please some advice based on experience


Matthias
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rockyrockyMember
Agree

That should give you about 16* at idle.

You are looking for about 36* total (mechanical advance only).

You can decide if you want to connect the vacuum advance or not. Sometimes it can give you too much advance in Highway driving conditions.

I am not running vacuum advance per the recommendation of my engine builder.

Rocky
bosswrenchbosswrenchMember
Matt, did you absolutely find TDC mechanically first? And what harmonic balancer are you using? If stock, it's almost a sure bet the outer ring where the timing mark is, has shifted towards retard as age and oil leaks break the bond it once had. Then you'll be trying to set timing to the wrong point on the crank rotation.

NOS balancers are 45+ years old and even new replacement ones sometimes have Windsor or SBF timing marks. Parts store employees that know what a 351-C is are getting rarer by the day, and some will insist that 351-Windsor parts are "equivalent" because their erroneous catalogue says so.
matgmatgMember
Tx for help & comments...

I will double check the TDC per finger in spark hole #1. (did check also the rockers for #1 to be loose - valve closed)
The damper is a brand new ATI for Cleveland. Bloody expensive.
I will def stick with timing light.

My issue is, I do not know how SMOOTH a Cleveland should idle with a modern cam . I guess should be decent with a lob sep. of 112??

Crane Hydro roller 52 9551
Range 2500 ...6000
Intake at 050 224
Exhaust at 050 232
Advert in 286
Advert. out 294
lob sep 112

As said I did play with the distributor setting at IDLE rpm between 5 deg and say 20 deg. advance according the ATI scale.
Idle was app 800 rpm (as a starting point, it can go lower). At <=5 deg it is not nice, kind of "lazy" picking up rpm. At 20 deg at idle it gets really rough, this is what I had first by setting the static timing.

If I give it 10...to 15 deg at idle it runs decent/acceptable, at a steady rpm. (I still have to close the vacuum tube for this measure!!) WHICH ONE TO CHOOSE 10 or 15 in respect to higher rpm/more advance driven by distributor characteristics?
I can check the advance at higher rpm per Chuck's statement app. 35 deg max to expect.

Matthias
rockyrockyMember
Hi Matthias - at 800 RPM, you should not have any mechanical advance yet. So you should block off vacuum to the distributor, but you should measure it at the carburetor.

I believe your mechanical advance should be “all in” at about 2800 RPM. The ignition advance should smoothly increase as you increase the throttle above idle.

Good luck - keep us updated!

Chuck
R rene4406Member
the most important thing is not to have knock at full load, not the regularity of idling.
For this is what George recommends:
Set the ignition timing to the following spec: 16 ° to 18 ° initial advance; 20 ° centrifugal advance fully in between 2800 to 3200 rpm; this equates to between 36 ° and 38 ° total advance. Street engines (operated at partial throttle) should have 10 ° vacuum advance connected to ported vacuum. In spite of what you may have read elsewhere, a combustion chamber of fixed design (Cleveland factory), used with a piston dome of fixed design (flat top), with a similar dynamic compression ratio (8.0 or less), and with a fuel of fixed octane (91 US / Canada), shall require the same ignition calibration.

http://pantera.infopop.cc/eve/...0045562/m/4591090956

The idling advance will be ............... what it will be based on your distributor and you will adjust your idle with the carburetor

The value of the maximum advance can vary depending on the dynamic ratio, how much do you have?
rockyrockyMember
While I agree with everything that has been said...

It is possible to limit the mechanical advance capability of the Motorcraft (Duraspark) distributor easily.

This can allow you to set the maximum advance of 35* (or whatever you choose), and then still have a 16* idle advance, by only allowing 20* of Mechanical advance.

This is done by shimming the dvance limit stops inside the distributor.
V 4vandproudMember
with 8.3 DCR you'll be lucky to run 30* maybe less w/o ping / detonation

here's a tutorial on the workings of the distributor

http://www.reincarnation-autom...tructions_index.html

don't miss the 2nd page! notice in George's link you posted the 10L slot, it's discussed in my link here too. if you don't have the 10L slot or modified equivalent your total advance will limit your initial adjustment. you can also close the slot further past the 10L width and make your own 8L slot, or 6L slot etc Wink
matgmatgMember
we will see..did go back into my design work ..
I used a spread sheet and the crane cam is recommened for 9.5 to 10.75 Static. If I use Deg duration which is 284 or 360 - 284 = 74 it gives me 7.55 Dynamic. I got confused as I was playing with different cams 2 years ago when I kicked off my engine work. So hope all working fine.
Here is my metric: Comments?

Matthias

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