Big Cap to Small Cap
#1
Posted 03 June 2006 - 07:54 PM
Is it a ford v8 cap & rotor,hopefully someone will know.
#2 _Yella SLuR_
Posted 03 June 2006 - 08:43 PM
#3 _Herne_
Posted 03 June 2006 - 09:08 PM
I may be wrong here but something in the back of my mind tells me it's a Commodore cap with a Ford rotor??????
I am almost certain Bruce told me he used Commodore VL/VK??? in my car but I don't recall him mentioning the rotor button and I didn't ask 'cos I assumed it was all Commodore parts - bad to assume
Anyway I am sure someone here will point you in the exact direction.
Cheers
Herne
#4 _Yella SLuR_
#5 _Yella SLuR_
Posted 03 June 2006 - 09:22 PM
My large cap is a tight fit, and if you totally pull the dizzy out, you have to remove the base to get it in and out. Reminds me have to do that soon to get No. 1 180 degrees about.
#6
Posted 04 June 2006 - 09:30 AM
#7
Posted 04 June 2006 - 05:45 PM
#8 _Yella SLuR_
Posted 04 June 2006 - 06:49 PM
Edited by Yella SLuR, 04 June 2006 - 06:50 PM.
#9
Posted 07 June 2006 - 12:03 AM
#10 _devilsadvocate_
Posted 07 June 2006 - 12:46 AM
My thinking would be that the most likely scenario is that the spark leaks from the centre electrode to any of the terminals of the circumference of the dizzy, rather than from one outer terminal to the next. There should be significant half circular shields around each terminal on the underside which should reduce the straight line contact area between the outer terminals and that a"short' is only likely if a layer of conductive grime is present. A short also being more likely on the top where the spark can leak around the seals of leads on the male terminals of the cap.
Of course in a 6, the dist from centre to outside = distance between outside terminals, so to create the same dist between outside terminals in an 8 the cap needs to be 8/6 bigger in radius.
Resistance of the leads will not affect the voltage of the spark across the plug electrodes. Straight wire can be used(with good insulation), however, the interference that is produced will see the guys that control illegal radio signals(whatever they are called) trace down you car, as you will cause interference to everything within 100m) From my measurements the resistance of leads has not changed greatly in the last 35 years, some higher performance leads have lower resistance.
Only limiting factor is if the resistance of the leads is too high, then either coil will not deliver enough voltage for spark to be able to jump plug gap and go through lead or spark will take easier path, perhaps from one terminal to another which isnt connected by such a high resistance lead to its plug.
Edited by devilsadvocate, 07 June 2006 - 12:53 AM.
#11
Posted 08 June 2006 - 12:18 AM
My thinking would be that the most likely scenario is that the spark leaks from the centre electrode to any of the terminals of the circumference of the dizzy, rather than from one outer terminal to the next.
I reckon your rotor button would have to be in big trouble for that to happen.
Edited by rodomo, 08 June 2006 - 12:21 AM.
#12
Posted 08 June 2006 - 12:29 AM
are you saying female caps are better for this than male ones. i always felt that the male one was going to give me a better connection.A short also being more likely on the top where the spark can leak around the seals of leads on the male terminals of the cap.
i hear holden went to the large cap to stop hi energy misfire (internal, one to the next). ford used the same dizzy with the small cap. can any fordies enlighten of any probs.
#13 _devilsadvocate_
Posted 08 June 2006 - 02:06 AM
If youve seen the scorched terminals of a female dizzy cap youll know what I mean.
Leakage from the centre terminal to any of the outside terminals via the top of the cap is always a possibility, possibly leaking(misfiring) to the plug that is experiencing the least compression, or just beginning the intake stroke(possibly requiring far less voltage than the desired plug at the top of the compression stroke), which may not be the terminal thats next in the firing order on the outside of the dizzy.....too late to work that out atm.
A high performance and or compression engine will require higher plug voltages at full power, so its reasonable to suggest it will need a dizzy with wider spacing all round so the spark doesnt jump via an easier path
#14 _switchedon_
Posted 14 June 2006 - 10:59 PM
#15
Posted 14 June 2006 - 11:17 PM
#16 _switchedon_
Posted 14 June 2006 - 11:32 PM
#17
Posted 15 June 2006 - 10:49 AM
When Ford & Holden went to the Bosch HEI system for their V8s, Ford stayed with the old style (smaller) cap & Holden went to the larger diameter one. One of the reasons for this was that Holden went to the super wide 1.5mm spark plug gap while Ford remained at 0.8-0.9mm. Holden also went to 8mm Packard leads. They used the same ignition coil, so Holden obviously had a problem or wanted to reduce the risk of crossfire.
When Holden introduced their EFI V8, the coil output remained the same as the Blue/Black HEI system, but the spark plug gaps were reduced to 1.1 mm & they went back to the smaller cap.
To answer the question on which rotor to use, the best one would be the XD/XE Ford V8 which has the same dissy shaft size as the Holden HEI, but the smaller cap, therefore the rotor is a perfect fit. I believe the EFI V8 rotor would also fit, but have never tried it.
Just remember to reduce your spark plug gap when using the smaller cap. I always use a maximum of 1.3mm gap on any Holden HEI system(6 or V8) in anycase, you get less misfire & longer spark plug life.
Dr Terry.
#18 _Oldn64_
Posted 15 June 2006 - 04:09 PM
Cheers
#19 _Toranamuk_
Posted 07 July 2006 - 11:21 PM
A quick tip from many years in race & dyno testing is to drill a 1/8th hole approx half way down the cap (& at the rear of the cap) between 2 posts.
This lets some air flow through the distributor & helps to discharge the "charged" electrons from the cap/rotor area & eliminate cross firing.
This may sound strange, but check out any of the top "name" brand performance distributors & caps & you'll see the holes.
It's very subtle but extremely important.
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