Originally Posted by lindy 911 (Post 6767288)

"Originally Posted by lindy 911
If anything over 9.5:1 CR and 95mm+ cylinder bores in a Porsche 911 engine

requires twin plugs to prevent / control detonation,

"You are mistaken. Twin plugs, initiating 2 flame fronts simultaneously, simply results in reaching PEAK cylinder pressure sooner. That's why the timing advance is retarded vs a single plug engine. In one respect you are correct, without retarding the timing the engine would likely be more subject to knock/ping. Obviously there is also the potential for a more complete "burn". Which is why my '93 Ford Ranger's 2.3L I4 uses 2 plugs/coils/drivers. Clearly not for HP."

how would one live without detonation with only one box if your statement is true about only one plug firing? Mine leads a very happy, detonation free life with very hard driving for a street engine. It's 10.5:1 CR with twin plugs driven by one MSD 6AL.

IF BOTH PLUGS WERE NOT FIRING THE ENGINE WOULD DESTROY ITSELF. PERIOD.

Stock ingnition timing for a '78 SC is 26 degrees +-2 degrees BTDC @ 6,000 rpm, not 35 degrees.
My twin plug is running 28 degrees all in at 3,500 rpm. I'm runing MORE timing that stock, not less

"NOT..!"

I have pulled the upper and lower plug leads on #1, attached two plugs and grounded them to the engine case. I started the engine, and although it ran a little rough on five cylinders, and clearly observed both plugs firing. Not only were they firing, they were firing bright blue. When I revved the engine the spark becomes constant to my eye, but both plugs fire all the way up to 6500 rpm. How does one account for that if they are both not firing?"





With all due respect, it's obvious to me that you don't know much about a 911 combustion chamber. The reason for twin plugs on a 95mm + bore and anything over 9.5:1 CR in a 911 is solely to prevent detonation. The hemispherical head and the offset postion of a single plug does not allow the flame front to catch unspent fuel before it detonates on the opposite side of the dome. Two plugs are required to start two seperate fronts so neither side ignites due to detonation events. PERIOD.

IF BOTH FLAME FRONTS WERE NOT BEING INITIATED BY THE SPARK PLUGS SIMULTANEOUSLY, THE CYLINDER WILL DETONATE; SIMPLE AS THAT.

You said in a previous post that two plugs won't fire with the set-up I have; two coils being driven by one CDI (MSD). I said they will and they do. Obviously I understand that I can't see what's happening with the spark at anything over idle, but I can tell you that both plugs do spark. You have said repeatedly that they will not, cannot spark. YOU MY FRIEND ARE THE ONE WHO IS MISTAKEN.

Originally Posted by lindy 911 (Post 6765951)

The only thing that changes from one box to two is the current to each coil. One box splits the available current across two coils where two boxes supply maximum available current to each coil. When each coil runs at a higher current the resultant higher spark energy builds a better fire (read HP). So, once again, there is a correlation between spark energy (current to the coil) and horse power.

This is the third time someone has posted a similar claim substantiated by dyno runs. That's proof and NO JOKE.

Originally Posted by brads911sc (Post 6767344)

Lindy, my .02.

Obviously wwest disagrees with the need to have a Kuehl setup with AC in the deep south,

No, I have ALWAYS taken the position that the factory A/C capability is inadequate, even here in the Pacific NW, at least on the "dry" side of the state. My actual position has been that adding dual radiator fans to force airflow through the rear lid condensor provides enough addition A/C capability.

The counter-argument to that has been "not in the deep south" to which I have made no response other than I don't know, but maybe.

he disagrees with people like Henry at Supertec on your setup. you can probably find 500 threads where he has disagreed with someone we all consider to be a true expert, and he was dead wrong on most of them.

Wwest jumps on every thread about every topic... and states as fact things that have been proven over and over to be wrong by the experts... Most of it is based on google search. he presents alot of "ideas" that are just not fact although it does make for some good entertainment and thought provoking questions... :D It does all non professionals on here a disservice though, because I have no idea what the right answer is sometimes... and alot of people could make mistakes that could result in alot of empty wallets based on his "facts". So i find it annoying. he is the resident "troll".

I would just ignore most of what wwest states as definitive.... you have a great setup. if it were me Id probably copy kents setup so I could run 2 MSD's, but I have no idea on whether you could do that or not. Seems like $200 would be worth a 15% bump in power and more peace of mind if it were technically possible...

And now you go and state that you agree, because you admit you cannot say otherwise, with my position on the need for dual CDI modules.

We may all disagree with Loren at times, and some of his posts are self-serving... but at least he understands the technology that he is speaking about...

Originally Posted by wwest (Post 6767494)

I don't understand how it is that Loren can be the go-to repair GURU for Bosch CDI boxes and yet not understand the technological theory, but the fact of the matter is he does not.


"I have had access to the Bosch CDI schematics since about a week prior to sending mine to you for repair..."

Originally Posted by wwest (Post 6767460)

Lindy, please go back and read Kent's post, #231. He states that he ran his twin plug engine on a dyno with, and without, one of the 2 CDI boxes enabled.

ON A DYNO...WIDE OPEN THROTTLE...FULL ENGINE LOAD.

And the twin plug mode indicated a 15HP "gain".

Originally Posted by wwest (Post 6767468)

You seem to have missed, overlooked, an important point in Kent's post. He was using dual CDI "boxes", one of each set of plugs.

Originally Posted by brads911sc (Post 6767358)

Therein lies the problem to 95% of your posts... Why dont you talk to experts like Henry, Steve, hell... even Loren, instead of making things up based on Google searches... you my friend are dangerous. So much of your information is dead wrong. I hope no one actually sets up their car based on your posts. Good luck.

Originally Posted by brads911sc (Post 6767358)

Therein lies the problem to 95% of your posts... Why dont you talk to experts like Henry, Steve, hell... even Loren, instead of making things up based on Google searches... you my friend are dangerous. So much of your information is dead wrong. I hope no one actually sets up their car based on your posts. Good luck.

Originally Posted by wwest (Post 6767551)

Yesterday, after I wrote the dessertation on the Bosch CDI..

Originally Posted by kent olsen (Post 6766410)

Just a clarification of my post. My engine ran on the engine dyno with one MSD firing one spark plug, and 35 deg advance. Then we hooked up both plugs run by two independent MSD's and the timing set at 28 deg, that was when we saw a 15 hp increase. That justified the twin plug claim to develop more horsepower.

I looked at the possibility of one MSD firing thru two coils and both plugs mainly because of space to mount the Coil/MSD units. Mike at J&B, and the tech service at MSD and Mallory agreed there would be a slight loss in horsepower.

To muddy that even further, I run the bottom plugs with a Mallory MSD and top with the standard MSD/MSD.

Originally Posted by LJ851 (Post 6767567)

Thread summary:

1) CDI boxes will create sparks and run the ignition system of a 911, there are many options.

2) One high voltage CDI (MSD,etc.) will fire two plugs in one cylinder with slightly reduced spark energy. Herin lies the debate.

3) Two CDI boxes will fire two pugs in one cylinder with maximum spark energy.

4) Multiple sparks--- MSD has them. Oh, and Ferrari as well.

5) Isn't it great we have so many options for fueling, sparking, and personalizing our 911s?

Originally Posted by mytoy (Post 6767574)

wwest
Perhaps you should read thoroughly through the post and understand what was said before twisting the information for your arguments. If you read the statements made by Kent he clearly states that the difference of 15 hp was a direct correlation between a single cdi unit firing a single plug and dual cdi units firing two plugs. Nowhere was there a correlation between one cdi unit firing two plugs and two cdi units firing two plugs. There is no definitive correlation of how much HP would be lost if he was to use only one cdi unit for firing dual plugs. That test was never carried out on the dyno. There was only a statement made that there would be a slight loss of power using one cdi unit to fire dual plugs. How much is a slight loss, 2-5 Hp or more nobody knows as this was never determined in the testing.

Originally Posted by LJ851 (Post 6767567)

Thread summary:

1) CDI boxes will create sparks and run the ignition system of a 911, there are many options.

2) One high voltage CDI (MSD,etc.) will fire two plugs in one cylinder with slightly reduced spark energy.

3) Two CDI boxes will fire two pugs in one cylinder with maximum spark energy.

4) Multiple sparks--- MSD has them. Oh, and Ferrari as well.

5) Isn't it great we have so many options for fueling, sparking, and personalizing our 911s?

Originally Posted by calling911 (Post 6767361)

What I dont get is since wwest reverse engineered the bosch ignition box from a schematic, why on earth send it out for repair?

Context below.

I've done audio amplifier repairs where as a result of my inability to fully understand the circuits I've simply replaced all the components.. and I am STILL way ahead of sending it out (this is for high end gear).. maybe the bosch components are hard to find.. that would explain it I guess.. but if not, why wwest did you send it out since you have all this knowledge???

See below...

Anyway off topic.. my point was very similar to brads911sc.. this thread could fool people not in the know to spend WAY too much money on an ignition with a minimal to no return for it..

3 years ago, McCall id, had I known what I now know regarding the POOR design of the Bosch CDI, I would NOT have hesitated purchasing an MSD CDI plus the MSD blaster TRANSFORMER. As it happens all I was able to do POST the Bosch repair was design an input voltage limiting circuit and wiring harness that my nephew could install.

thats why this thread needs to be stomped out..

Originally Posted by MBruns (Post 5786585)

We have dyno tested this on a very good 2.0 HSR race engine using single MSD box driving 2 Blaster coils and it ran and seemed OK until we read the power #'s compared to 2 boxes,2 coils. This engine made north of 230 HP on the 2 box setup and lost almost 15 HP on the single box split signal to 2 coils. we have repeated this test on various sizes and levels of build, non made equal power with the single box.

Mike Bruns JBRacing.com

Originally Posted by brads911sc (Post 6767588)

Exactly. Which is why this whole discussion is so pointless. We are dealing with a few bloviating buffoons.