Hot cams and advanced ignition

[Lutz Kramer]

Last week I started a thread with the headline "Ignition timing with Pertronix Ignitor and strobe light" (https://www.britishcarforum.com/bcf...iming-with-Pertronix-Ignitor-and-strobe-light) since I thought the phenomenon with my car was corresponding to these issues. With the help of some experienced forum members I found out that this was not the case. So I started this thread to draw the attention to the more likely reasons.

When I checked the ignition timing of my AH 3000 BJ8 with a strobe light I found it was set at 45° BTDC at idle and about 65° at about 4500 rpm. Nevertheless the car is performing excellant! It's running perfectly at idle as well as at high rpm. I hear you say:Then leave it as it is and don't touch it. Yes, you're right and I dont't really want to touch it, but I would like to know what is going on here.

Whenever I change the timing towards the standard setting of 15° BTDC at idle the engine stalls.
I really checked everything:
- changed the strobe light
- did a static timing
- took out the Pertronix and put in the old Mallory twin contact distributor
- checked the TDC mark on the pulley with position of #1 piston
- checked the timing between camshaft and crankshaft and so on.
Everything was OK!

When I was ckecking the timing between the camshaft and crankshaft I took alle the data of the valve lifts at all positions of the crank, I mean every 10°. All of a sudden I realised that there must be a hot cam in the engine which I didn't know. The data I found tell me it's a 290° or 288° camshaft.



So my questions are:
Does a hot or racing camshaft require an advanved ignition and if so, how far should the igniton be moved to "early" for a BJ8.
And what about my setting of 45° BTDC at idle? Don't you agree, that this setting cannot work even with the cam I have? But if so, what is the reason for my car still performing so well?

May be there are some specialists out there who are experienced with hot cams and racing cars and know what is going on here?

Best regards from Germany
Lutz

 

[HealeyRick]

Lutz,

You might find this article of interest even though it's a bit vintage. https://www.healey6.com/Technical/Dyno.pdf Those motors weren't seeing the same kind of advance you're running. If I were in your shoes, I'd book some time on a "rolling road" or "chassis dynamometer" as they are know in the States. It should be simple enough for the operator to set your distributor so the motor produces its best power and give you the settings so you can reproduce it in the future.

 

[Bob Claffie]

I suggest somewhere along the way someone put on an incorrect balancer which has the timing mark in the wrong position.

If your real timing was set at 45* the car would neither start nor run.

Another alternative is the wrong indexing of the ignition wires in the cap

 

[DerekJ]

Lutz,

There is no way those numbers of 45 deg and 65 deg can possibly be correct. Something is wrong in the way you are measuring the advance. The car would not run at those advances. You say the car is running perfectly, well that is all you need to know. If you want to further optimise the advance do it the old fashioned way. Keep advancing the ignition little by little until the car starts 'pinking' under load, then back it off by a degree or two and that will be fine and set for your particular car. If you want more precision take it to a rolling road plus they will give you a correct advance reading.

 

[Lutz Kramer]

Lutz,

You might find this article of interest even though it's a bit vintage. https://www.healey6.com/Technical/Dyno.pdf Those motors weren't seeing the same kind of advance you're running. If I were in your shoes, I'd book some time on a "rolling road" or "chassis dynamometer" as they are know in the States. It should be simple enough for the operator to set your distributor so the motor produces its best power and give you the settings so you can reproduce it in the future.

Rick, thanks a lot for the link. This article is very interesting and useful even it's a bit vintage. But aren't our cars vintage too? So far I haven't thought about playing with the needles and spark plugs. But since the car is running perfectly there is really no need to do so. It's just a matter of finding the reason for the phanomenon. But interesting to see that the guys in former days were also setting the ignition more or less at max rpm and not at idle and took care it wouldn't exceed 40° BTDC. But as I mentioned before, mine is idling at 45° and reaching 65° at 4500 r/min! Usually no engine is running with those settings!

 

[Lutz Kramer]

Hi Bob, I'm sure the balancer is sitting correctly, not because I put it on but i checked it with a piston stopper. By the way the mark for TDC on my car is a notch located on the pulley which the balancer is rivited to. I mounted a piston stopper into #1 spark plug seat.



Turned the piston clockwise till it was stopped and made a mark on the damper/pulley. Then turned the piston counterclockwise until it was stopped again by the piston stopper and again marked the pulley. The middle of the distance between the two marks corresponded exactly with the TDC factory mark. So, no problem here.

In additon, when the TDC mark is aligned with the pointer sitting on the chain housing, the rotor of the dizzy is pointing to #1 plug wire.

But I agree with you, if my timing is set at 45° at idle the car for sure should neither start nor run!

Lutz

 

[Lutz Kramer]

Lutz,

There is no way those numbers of 45 deg and 65 deg can possibly be correct. Something is wrong in the way you are measuring the advance. The car would not run at those advances. You say the car is running perfectly, well that is all you need to know. If you want to further optimise the advance do it the old fashioned way. Keep advancing the ignition little by little until the car starts 'pinking' under load, then back it off by a degree or two and that will be fine and set for your particular car. If you want more precision take it to a rolling road plus they will give you a correct advance reading.

I agree with you! When I set the timing I was using the method described by you. When I bought the car three years ago, I was not able to set the timing to the standard parameters neither with a strobe light nor by performing a static timing. So I did it manually and have been running the car with these settings for more than 5000 miles even crossing several mountain passes in the alpes with an altitude of 10.000' and more.

Next thing I want to do is to visit a Bosch station to have them ckeck the ignition system.

 

[Bob Claffie]

Ok, you proved my idea about the bad balancer didn't work.

Lets try another trick. Hook up your timing light to each other ignition wire. One of the other five SHOULD come up really near to your goal of 15*. If so, that wire should be going to cylinder #1. If that proves out you should be able to ROTATE the distributor AND change the location of the wires.

What you will find out now is that with the distributor cap off, AND with #1 cylinder at top dead center that the rotor IS NOT pointed at the #1 wire location.

 

[vette]

Lutz, I believe Bob Claffie is on the right track. Given that everything else has been checked, his idea is the only way I can think of that you would get such timing readings. Bye the way, I don't think your cam spec are so radical as to give you very much timing variation need. I don't know which of your degrees is applied to intake or exhaust but, You also may not have figured for the measurement at 50* of rotation. Most cam measurements are at 50* of rotation. So subtract 50 and you have
240* & 238*. As an example I have a Bored & Stoked 383 ci engine in my 1970 Vette. The cam I installed has 224* in, and 230* exh. I have my timing set at 15* at idle (800 rpm) and full advance is about 35*.

 

[vette]

Accidentally Posted twice.

 

[Lutz Kramer]

Lutz, I believe Bob Claffie is on the right track. Given that everything else has been checked, his idea is the only way I can think of that you would get such timing readings. Bye the way, I don't think your cam spec are so radical as to give you very much timing variation need. I don't know which of your degrees is applied to intake or exhaust but, You also may not have figured for the measurement at 50* of rotation. Most cam measurements are at 50* of rotation. So subtract 50 and you have
240* & 238*. As an example I have a Bored & Stoked 383 ci engine in my 1970 Vette. The cam I installed has 224* in, and 230* exh. I have my timing set at 15* at idle (800 rpm) and full advance is about 35*.

Here are my measuremnts taken for the valve lifts:

 

[Roger]

Not sure about that. With a 6-cylinder engine, in one revolution every 120 crankshaft degrees a cylinder fires, and the same on a second revolution for the other 3 cylinders.
So if you have 15deg advance, they fire at 15, 135, and 255 degrees. No other time, and not 45 degrees.

 

[Lutz Kramer]

Not sure about that. With a 6-cylinder engine, in one revolution every 120 crankshaft degrees a cylinder fires, and the same on a second revolution for the other 3 cylinders.
So if you have 15deg advance, they fire at 15, 135, and 255 degrees. No other time, and not 45 degrees.

I don't understand your argument, Roger! May be my fault.
If #1 zylinder fires or would fire at 45° BTDC the next three zylinders would then fire at 165°, 285° and 405° (which is again 405° - 360° = 45° BTDC). But I agree, if you say 45° BTDC, never ever, since no engine should be able to run with such a timing.

 

[Lutz Kramer]

I just want to to let everybody know that I gonna be on vacation until 24th of October and therefore cannot reply to messages during this time. For the 25th of October I have an apointment wit BOSCH to find out if there is anything wrong with the ignition. Thereafter I will get back to you to let you know if there are any news.

I would like to thank all of you for the efforts and help that I have been received so far.

 

[vette]

Lutz, I hope you have an excellent vacation. I believe Roger may be talking about my comparison of the V8 engine to a 6 cylinder engine. I have to say which might become obvious real quick that I am not a cam expert. I made my remarks because over a 2 year period that I was more or less designing the spec for my new Vette engine, I noticed that many of the cam spec and head flow measurements were consistent for a certain level of a performance engine, whether it was a 6 cyl. or a v8. None of it is cast in concrete but for base comparisons there is similarity. About Lutz' measurement tables. I'm not sure I understand them, but if I presume to understand some of it I would be drawn to his first values in MM under the Exhaust column and see that at .20MM he is indicating 130* crankshaft rotation & 65 * of cam lobe opening. My puny little mind can't even comprehend all that data. I apologize for being block headed. But just so we're on the same page I want to quote the definition of cam duration: " Duration @.050" is a measurement of the movement the cam follower, In Crankshaft Degrees, from the point where it's first lifted .050" off the base circle on the opening ramp side of the camshaft lobe, to the point where it ends up being .050" from the base circle on the closing ramp side of the camshaft lobe. " ( Cam Spec Terms - Lunati Power ). Beyond all this cerebral, scientific, engineering stuff I don't think the cam is the problem. Do the test that Bob Claffie suggested.

 

[Roger]

I am saying that Bob Claffie's test is suspect.
He suggests that one pot will fire at 15 deg. If one does, then two will and the others at 135 and 255 degrees. There wont be one at 45.

Talk of camshafts is irrelevant.

 

[Lutz Kramer]

Ok, you proved my idea about the bad balancer didn't work.

Lets try another trick. Hook up your timing light to each other ignition wire. One of the other five SHOULD come up really near to your goal of 15*. If so, that wire should be going to cylinder #1. If that proves out you should be able to ROTATE the distributor AND change the location of the wires.

What you will find out now is that with the distributor cap off, AND with #1 cylinder at top dead center that the rotor IS NOT pointed at the #1 wire location.

Bob, I definitely will follow your advice and perform the test you suggested? But before, just one more thought!
It's proved that the pulley together with its time mark for TDC are mounted on the crank correctly and there is no doubt which wire is leading to plug #1. Now, when I hook up the strobe to that #1 plugwire and the strobe flashes then at this time a current pulse is definitely running through that #1 wire and fires the engine (plug). And I at first hand could see this taking place at 45° BTDC. So far so good!

Now, I come back to your suggestion. Wouldn't you agree, that it makes no difference whether I just turn the dizzy from 45° to 15° or whether I connect #1 sparkplug wire to that point of the dizzy cap where the wire is connected I with your method found to be the one that fires at 15°? And if so, the engine would stall, no matter where #1 plugwire is conncted to on the dizzy cap, as long as it is the one that fires at 15° BTDC and not at 45°. Sorry for my english, which is not qualified for technical explanations, but I try my best!

But anyhow, I will try your suggestion to find out if there is may be a logical error in my thoughts.

 

[Lutz Kramer]

Bob, before I go on vacation I want to let you know what I found when I performed the test you suggested. I hooked up my strobe to every sparkplug wire to find out which one is firing close to 15° BTDC. I still can't believe what I found. People must believe I'm crazy!

The strobe flashes for all 6 wires at 45° BTDC of #1 piston??? So, usually I'd assume the strobe is trash. Not in this case, because the other day I tried a strobe of a different manufacturer with the same result and I did a static timing with the same result, at least for piston #1. What is this now???

Best thing to do is to go on vacation and then let BOSCH take care of it!?

 

[John Turney]

Question for when you return (Hope you have a great vacation, BTW), what kind of plug wires do you have?

Reason I ask is that I have the bumblebee wires on mine, which are non-resistor wires. They caused interference with my strobe light. I had to replace the #1 wire with an old resistance wire to make it work properly.

 

[Bob Claffie]

My ORIGINAL POINT was to assure that at TDC the rotor was pointing at the #1 wire location in the distributor cap ! No more and no less. If in fact it was pointing at #1 my other theory is no good. If it wasn't pointing at #1 the orientation of the distributor and it's wires is suspect. In my opinion the camshaft question is a red herring and is of no consequence