Best replacement distributor cap and rotor?

[Ken A.]

Re: Best replacement distributor cap and rotor?

All the rotors on the market have an air gap of .125, except the K & B rotor, which reduces this gap to .035. This applies to all GM style caps from 58-74. Copper/brass offer no performance gains, they just corrode easier than the aluminum that GM spec'ed the cap with due to the wells the wire terminals were inserted into.

[Leif A.]

Re: Best replacement distributor cap and rotor?

All the rotors on the market have an air gap of .125, except the K & B rotor, which reduces this gap to .035. This applies to all GM style caps from 58-74. Copper/brass offer no performance gains, they just corrode easier than the aluminum that GM spec'ed the cap with due to the wells the wire terminals were inserted into.

Ken,
Who distributes your rotor? Checked LIC and Paragon and their parts aren't identified as to where they come from.

[Timothy B.]

Re: Best replacement distributor cap and rotor?

Thanks Douglas. I don't know about the specific product you mention, but I purchased the MSD 5500 cap/rotor kit a few years ago. The materials and construction look robust, featuring brass terminals and a high quality rotor. They're black so look stock from 2 feet away.

Mark,

The MSD cap and rotor parts I have seen are stout pieces. I remember you can adjust the rotor tip and rotor phasing on there part but if me memory is correct I recall them being red in color.

[Gene M.]

Re: Best replacement distributor cap and rotor?

All the rotors on the market have an air gap of .125, except the K & B rotor, which reduces this gap to .035. This applies to all GM style caps from 58-74. Copper/brass offer no performance gains, they just corrode easier than the aluminum that GM spec'ed the cap with due to the wells the wire terminals were inserted into.

Ken,
GM used aluminum as a cost avoidance. I'm sure you will find the brass copper has less electrical resistance. The major benefit is the fitting of the brass terminals on the plug wires into the distributor cap. As it is well known the copper/brass does not get along with aluminum. The length of time or life of the cap in most Corvettes gets attention well before the contacts has expired life. So that is not a concern. Also aluminum under sparks creates a white crud that is high in resistance and builds up. The copper/brass just burns away fairly clean.

[Donald O.]

Re: Best replacement distributor cap and rotor?

Don, the extended tip is just a figure of speech, all the current replacements have a larger gap between the rotor tip and the posts on the cap. As Gene states they gap is near correct , there is no contact like you might think.

All the rotors on the market have an air gap of .125, except the K & B rotor, which reduces this gap to .035. This applies to all GM style caps from 58-74. Copper/brass offer no performance gains, they just corrode easier than the aluminum that GM spec'ed the cap with due to the wells the wire terminals were inserted into.

OK. So then how does the spark plug get the juice to spark? Inductance? Hall effect? Does it arc across the gap just like the plug?

[Larry M.]

Re: Best replacement distributor cap and rotor?

Does it arc across the gap just like the plug?

Yes..............

Larry

[Donald O.]

Re: Best replacement distributor cap and rotor?

Would a wider and closer rotor provide a hotter and longer spark then?

Don

[Douglas L.]

Re: Best replacement distributor cap and rotor?

Would a wider and closer rotor provide a hotter and longer spark then?

When talking about spark plug gap, the wider the gap the hotter the spark but the shorter the spark duration. A coil only has so much energy to give up, voltage increases until the gap is jumped(the larger the gap the higher the voltage) but the more voltage needed to jump the gap the more energy is used to jump said gap so the duration is decreased. I'm not totally sure on this but Id image that the larger the gap under the cap the less energy is left over to jump the gap at the spark plug.

I cant speak for anyone else but I bought a cheap repro 308 cap(I wasn't aware of the K+B one at the time) and it caused a high rpm/load misfire due to the excessive gap between the cap and rotor. I also bough a cheap off shore repro 287 coil that exhibited the same problem.

[Ken A.]

Re: Best replacement distributor cap and rotor?

At the time of the switch to aluminum, it was more expensive than copper. The conductance properties is a neglible issue

[Ken A.]

Re: Best replacement distributor cap and rotor?

Both mentioned companies buy quite a few.

[Larry M.]

Re: Best replacement distributor cap and rotor?

When talking about spark plug gap, the wider the gap the hotter the spark but the shorter the spark duration. A coil only has so much energy to give up, voltage increases until the gap is jumped(the larger the gap the higher the voltage) but the more voltage needed to jump the gap the more energy is used to jump said gap so the duration is decreased. I'm not totally sure on this but Id image that the larger the gap under the cap the less energy is left over to jump the gap at the spark plug.

I cant speak for anyone else but I bought a cheap repro 308 cap(I wasn't aware of the K+B one at the time) and it caused a high rpm/load misfire due to the excessive gap between the cap and rotor. I also bough a cheap off shore repro 287 coil that exhibited the same problem.

Bill Clupper did a Restorer article on this some years ago and pointed out the issues with the "shortened" rotor tip and solid lifter (high RPM) cars. Don't have the Restorer Issue handy, but someone should be able to provide..........or I can try and find it for you.

Larry

[Donald O.]

Re: Best replacement distributor cap and rotor?

Eight years ago, Joe Lucia recommended the Accel 8124 cap/rotor set.

Today, any opinions about choices for top-shelf cap/rotor sets? I'm not worried about judging, but prefer a stock looking black cap. My short list:

Accel 8124
MSD 5500
ACDelco C349 Professional (cap only; I couldn't find a cap/rotor set. Cap looks nice, but their rotors look marginal, IMO)

Others?

I prefer cap/rotor sets, thinking the rotor tip length is matched to the cap.

Is the Accel 8124 a kit or just a cap or a rotor?

[Donald L.]

Re: Best replacement distributor cap and rotor?

The Accel 8124 is a cap & rotor combo. The newer Accel rotors , the ones whose coil wire contact has a concentric flat surface exhibits the wider gap tang.. The older Accel rotors coil contact area has an oval surface and the gap on the tang has the closer gap.