Transistorized igintion 427/390

[William F.]

Re: Transistorized igintion 427/390

Pertronix III is said to increase spark energy, multiple spark, keep "dwell" from dropping at high rpm, and has a built in dwell limiter as well as just being an electronic trigger to replace points. Isn't it true that the higher compression engines require more energy than the 9000 V mentioned in another thread, especially if there is a little fouling? Otherwise why do racers use the MSD high energy ignition boxes with high output coils? On a previous L79 I owned, ran with the original Pertronix trigger connected to MSD 6AL box and sure made a difference in eliminating high rpm misses and plug fouling. Didn't have bit of problem with Pertronoix trigger , either. Present L79 has Pertronix trigger module only(not newer III) . Thinking about going to newer Pertronox III and related coil since I do take this car to redline and had some misses till I changed plugs, which is a PTA wit AC.Bottom line, isn't higher output ignition better for the higher output Corvette engines?While Duke likes points, in one post he said original points system was "marginal" as far as having enough energy. as I recall.

[Duke W.]

Re: Transistorized igintion 427/390

It took me 15 years for figure out how to make a Delco single point work to 7000 revs, but once I did that there was no need to reengineer the system.

What's really important in ignition systems is total per spark energy and spark dwell time. The single point only has about half the energy of the TI and HEI, but if the plugs are not badly fouled and the distributor is in proper working order - tight end play, snug shaft bushings, and a wobble free breaker plate, it will work just fine.

I've seen plugs come out of HEI-equipped engines where the ground electrode was worn down to the insulator and the engine still ran, but hopefully all of us are a bit more diligent about changing spark plugs at reasonable intervals.

Lean mixtures need long duration sparks, which is why OEMs don't use CD systems. CD spark energy is good, but dwell time is too short. They are a poor choice for a road engine. Multiple sparks are not worth much because they only occur at low revs and the subsequent sparks are considerably retarded, so if the fire doesn't light the first time, power and fuel economy will take a huge hit.

The key is to have a properly timed spark of sufficient energy and dwell time, which for a road engine means an inductive system.

When the coil ground switch opens, voltage builds at the plug. Some will leak away due to fouling, but that's much less an issue today with unleaded fuel. If the mixture is reasonably correct with unleaded fuel, a conventional two-dollar spark plug should last at least 15K miles, and they can always be cleaned if a little fouled and reused.

If the plug is in reasonable condition a spark will form at about 5 -7 kilovots. Once the spark is established voltage drops to several hundred, and as long as there is not a lot of shunt resistance (plug fouling) that bleeds energy, an inductive should last long enough to light the fire, and a properly assembled distributor will ensure that the plug fires at the right instant assuming the spark advance map is in the ballpark for the application.

"50,000 volts coils" are BS. Maximum open circuit coil voltage should not exceed 30 KV. If more, it could just burn through the plug wire insulation if the plug wire is removed or otherwise becomes disconnected from the load.

Duke

[Timothy B.]

Re: Transistorized igintion 427/390

William,

I helped a friend install a Petronics III in his L-79 and we could not use a timing light to set the timing. The light flashed all over the place from 10BTDC to a few * after TDC. I gave up on it and after calling Petronics they said to use a remote battery just for the timing light but I can't recall if it worked. I posted this before and no one responded with a similar problem.

The only modification on my 67 is the breakerless SE and I am very happy with it. Nothing special except the car runs like it's got new points all the time and no skips like sometimes with points. I do agree with Duke in that points are just fine but I noticed a difference with the breakerless SE. The breakerless is designed to run with the stock resistor and coil using the single coil wire.

[John H.]

Re: Transistorized igintion 427/390

Thinking about going to newer Pertronox III and related coil

William -

You might want to think twice about the Pertronix coil - the other forums are full of posts from owners with reports of multiple Pertronix coil failures, some of which have been replaced by Pertronix two or three times. No reports of coil failures with stock coils.

[William F.]

Re: Transistorized igintion 427/390

Would like to hear more from owners with strong 11.0:1 compression engines-L79's, L72's, etc. who do "pulls" to redline and their their experiences with ignition breakdown problems and their ignition system choices in real life.No fun changing plugs in AC equipped Corvettes.

[Clem Z.]

Re: Transistorized igintion 427/390

check out this website. http://www.davessmallbodyheis.com/

[Mark Z.]

Re: Transistorized igintion 427/390

I don't normally reply but I've been on this board a long time and d--n Duke that was very PC----everything OK?

[Duke W.]

Re: Transistorized igintion 427/390

My back must have not been hurting to bad?

Duke

[Dennis O.]

Re: Transistorized igintion 427/390

My '67 L79 used to breakdown approaching redline even though it was a fresh engine with all new parts. I installed one of the new extended tip rotors, and it now goes to redline no problem. I threw a fan belt yesterday impressing one of my friends. (Ooops!)

[Keith B.]

Re: Transistorized igintion 427/390

Bottom line, isn't higher output ignition better for the higher output Corvette engines?While Duke likes points, in one post he said original points system was "marginal" as far as having enough energy. as I recall.

isn't it true that GM required TI with the higher output Corvette engines from 65-69? they must knew something back then that points were not the best thing to have.

[Kenneth B.]

Re: Transistorized igintion 427/390

isn't it true that GM required TI with the higher output Corvette engines from 65-69? they must knew something back then that points were not the best thing to have.

I am with you. If the TI was not better why did all HP cars come with TI?

[Clem Z.]

Re: Transistorized igintion 427/390

converting to a TI very expensive but there are system out there like i posted above will work for a lot less $$$. if you want to keep your plugs clean you can add a MSD box even with your points. Multi Spark Discharge box fires the plugs many times up to 3000 RPM to keep them clean while around town driving.

[William F.]

Re: Transistorized igintion 427/390

Clem and others,
Where can I hide an MSD 6AL box on my '67 factory air L79 (batt. on driver's side)?Someone in previous post said there's room on driver's firewall just behind battey if I remember correctly. Agree or other better place?
Thanks

[Clem Z.]

Re: Transistorized igintion 427/390

Clem and others,
Where can I hide an MSD 6AL box on my '67 factory air L79 (batt. on driver's side)?Someone in previous post said there's room on driver's firewall just behind battey if I remember correctly. Agree or other better place?
Thanks

why hide it ?????

[Glen C.]

Re: Transistorized igintion 427/390

I haven't done any "pulls" quite to red line recently, but am running the 5005 K66 unit on my L72, which I believe to be 11.0:1. I just purchased the Lectric Limited replacement solid state module, even thought I've had no problems with the original GM piece. Any down side to these replacement modules?

Would like to hear more from owners with strong 11.0:1 compression engines-L79's, L72's, etc. who do "pulls" to redline and their their experiences with ignition breakdown problems and their ignition system choices in real life.No fun changing plugs in AC equipped Corvettes.