Why use a distributor?

[85HOT-T]

Originally Posted by DonWG

The only way I see that charge affecting EGT is if the ignition is missing and a/f is being pumped into the exhaust system. Maybe someone can add their observation of what happens to exhaust temps when it's obvious that ignition missing is taking place.

I by no means is an engine expert but what I would see happening if the stoke misfired and dumps into the exhaust the heat in the exhaust manifold pipes would ignite that mixture and raise egts, which brings us to the previous post of lower egts. If you ask me what I have logged in my head from this topic is high rpm misfire. That is the concern with the stock DIS. Now what I have to bring to the table is if RJC's dual coil system has two coils, that means it should handle high rpms no prob. Only reason I bring his up is the debate of the stock system. So now the question is will dual coils do it, is the distributor setup oboslete now?

[speeder]

OK, I can buy the fact that misfires raise EGTs in a waste spark system. Two of the stock igntion systems in a 6 coil arrangement would still misfire as badly as the stock system, but probably not contribute to the EGT problem. The E-motive provides the benefits of multiple coils and high performance ignition drivers.

A coil dwell of 2.5 Ms from a single coil sounds pretty short for a high revving, high output motor. And this at only 6000 RPM and decreasing with revs. With several EFI systems I have worked with, I have wound up with much bigger dwell times at higher RPMs for best performance. No doubt that the Mega -Joule, flamethrower MSD boxes help with a distributor and single coil, but I think that this is running the ignition system on the edge, where the slightest problem in the secondary circuits can cause big problems. I see multiple coils being a big benefit in setting optimum dwell times.

Being an electrical engineer, I trust (quality) electronics over mechanical things and brute force high voltage systems. To me, more coils don't add unnecessary complication when they can eliminate long ignition wires and caps/rotors. The whole secondary system is under much less stress - everything less critical.

Still, ya can't argue with what works for folks, and obviously the distributors do work. As a long-time lurker here, I'm amazed at the results some guys on this forum get.

I do have to admit to "the more electronics the better syndrome" - that's just how I roll.

[cdsttype]

I THOUGHT BUT MAYBE I AM WRONG THESE WERE TURBO CARS
I ALSO THOUGHT WE HAVE BEEN FIGHTING AN AGE OLD PROBLEM
OF BACK PRESSURE IN THE CYLINDER YOU SPEAK LIKE THE EXHAUST
STREAM ON YOUR ENGINE IS ISOLATED

[DonWG]

Something else to think about in the scenario that the waste spark is igniting anything at the top of the exhaust stroke. Let's say the a/f mixture went through the ignition cycle without lighting off. Now the piston drops and uncompresses the mixture.

When this occurs, isn't some of the heat from the previous compression now drawn out from the decompression?

When an a/f mixture is decompressed, does some of the mixture condense into larger droplets from the previous vaporized state, due to the drop in pressure and temperature?

Isn't most of the charge expelled from the cylinder way before the 24 or so degrees before TDC of the exhaust stroke? In fact, most likely past the turbo by this point with a short runner exhaust system?

The piston speed is very slow by 24 degrees BTDC exhaust stroke. In tuned exhaust systems, the charge would have exited the primary tube and a low pressure pulse would have traveled back up the primary and would be pulling residual and the next intake charge into the chamber by this time. Assuming a large overlap camshaft and the unburned charge would be traveling at the same speed through the primary tube as a higher volume and pressure burned charge, which I realize it wouldn't.

I would think that if the charge that was expelled from the cylinder did light off, it lit off way before 24 degrees before TDC ex somewhere in the exhaust system from exhaust system heat.

[DonWG]

Originally Posted by cdsttype

I THOUGHT BUT MAYBE I AM WRONG THESE WERE TURBO CARS
I ALSO THOUGHT WE HAVE BEEN FIGHTING AN AGE OLD PROBLEM
OF BACK PRESSURE IN THE CYLINDER YOU SPEAK LIKE THE EXHAUST
STREAM ON YOUR ENGINE IS ISOLATED

Dont' quite understand what you're getting at. How do you feel exhaust bp plays a part in all this?

[DonWG]

Originally Posted by 85HOT-T

I by no means is an engine expert but what I would see happening if the stoke misfired and dumps into the exhaust the heat in the exhaust manifold pipes would ignite that mixture and raise egts, which brings us to the previous post of lower egts. If you ask me what I have logged in my head from this topic is high rpm misfire. That is the concern with the stock DIS. Now what I have to bring to the table is if RJC's dual coil system has two coils, that means it should handle high rpms no prob. Only reason I bring his up is the debate of the stock system. So now the question is will dual coils do it, is the distributor setup oboslete now?

Regardless of what type system it is, it must be capable of putting out the initial voltage level to jump the spark gap in extreme cylinder conditions. You could be using 6 coils per cylinder and if the necessary voltage level isn't there, no spark. The answer is making sure that the system you use has the reserve voltage capacity to do the job you're demanding from it.
The distributor is just a tool used to distribute the voltage to the plug. It's perfectly fine to do this without a distributor.

If I were going to bother with converting to COP, at the very least I would keep the secondary wires as short as possible. The real advantage of COP would be using no secondary wire at all. The coil directly on the plug. In that situation you've vastly eliminated the chance for secondary voltage leaks. Without that worry, you can now pump up the secondary voltage level without worrying about the previous problems I mentioned. If you use COP with long secondary wiring, you've restricted your secondary ignition voltage level to the limit of what the secondary wiring can handle. That would be the same level as most any other high performance ignition system. That would be a waste of time to me.

The secondary wires are the weak spot that limits how much kv level you can get away with in your secondary system. That is what limits me with my particular w/s system. The system is quite capable of putting out some massive kv, but then I just end up blowing it out the wires all over the place. Cross firing then becomes a big problem. That is why I decrease my spark gap with my system. To keep kv levels down to what the secondary wires will allow me to get away with. Also keeps from straining the coils. Longer coil life.

When you start pumping up your secondary kv, a single coil is going to see a lot of heat. More coils allows this heat generation to be shared. So less heat per coil. More coil life.

[cdsttype]

I Would Agree With Your Theory On The Valve Timing Events
On A Single Cylinder Engine But With A Manifold Or Collector
And Multiple Cylinder Engine Back Pressure Will Certainly
Play A Role In What Left In The Cylinder At The Extreme
Ratios We Run Compared To An N/a Engine There Is Fuel Left Over
The Fastest Turbo Cars That Are Tuned Well And Live Leave
Leave A Black Trail That Is Fuel

[DonWG]

Originally Posted by cdsttype

I Would Agree With Your Theory On The Valve Timing Events
On A Single Cylinder Engine But With A Manifold Or Collector
And Multiple Cylinder Engine Back Pressure Will Certainly
Play A Role In What Left In The Cylinder At The Extreme
Ratios We Run Compared To An N/a Engine There Is Fuel Left Over
The Fastest Turbo Cars That Are Tuned Well And Live Leave
Leave A Black Trail That Is Fuel

Yes it's fuel. But is it at an a/f ratio that can be burned? You need fuel AND oxygen to burn the fuel. Or fuel and a catalytic converter.

[cdsttype]

Why Use A Distributor?
That Was Your Question Was It Not.
You Good Some Good Information.

1.more Reliable Rev Control Very Important When Trying To
Win A Race.
2.when In An Actual Buick Class Race Tsm Tso Tsl Tse
Rules Very Tight No Cop Ignition Which Would Be My
First Choice.
3.because Of Tight Buick Class Race Rules Looking For Any
Edge In Horsepower By Lowering Egts And A More Aggressive
Tune. Is There Better Horse Power Gains Elsewhere Yes
But We Cant Take Advantage Of Many Of Them Because Of The Rules.
4.in Super 16 Which Is Run What You Brung I Also Would Not Use
The Dis Because Of The Short Dwell Time And Poor Coil Saturation
At High Rpm
5.in An Open Class Low Rpm Application You Could Run Dis
If Your Okay With So So Rev Control
6. Complication And Price Should Not Be A Factor To The Guys
Who Run The Dist Because Most Guys Who Run One Have Over
50k In There Cars And Are Competitive Buick Class Racers.

[lazaris]

"Something else to think about in the scenario that the waste spark is igniting anything at the top of the exhaust stroke. Let's say the a/f mixture went through the ignition cycle without lighting off. Now the piston drops and uncompresses the mixture.

When this occurs, isn't some of the heat from the previous compression now drawn out from the decompression?

When an a/f mixture is decompressed, does some of the mixture condense into larger droplets from the previous vaporized state, due to the drop in pressure and temperature?

Isn't most of the charge expelled from the cylinder way before the 24 or so degrees before TDC of the exhaust stroke? In fact, most likely past the turbo by this point with a short runner exhaust system?"

Don,

What I think you maybe missing in regards to left over exhaust to ignite, is the overlap , especially with bigger duration cams. The new fresh charge being pumped into the chamber during this overlap, some of it goes out with the exhaust. Cant help it. Lobe separation angle also plays a part here. When this happens I can see why it may raise EGT's. There may be enough fresh A/F to burn.

[BlownV6]

The fastest Buicks on the planet all use a distributor!!! What more can be said??? Please correct me if Im wrong, but thats just how it is. Matter of fact the fastest cars on the planet all use distributor caps and wires.
Just my observation!!! Mike

[DonWG]

Originally Posted by BlownV6

The fastest Buicks on the planet all use a distributor!!! What more can be said??? Please correct me if Im wrong, but thats just how it is. Matter of fact the fastest cars on the planet all use distributor caps and wires.
Just my observation!!! Mike

Excuse me. Are you including the import crowd? Lets start talking about hp/cu. in. What did Honda eventually do with their F1 turbo car? They eliminated the O/H cam driven distributor caps and the secondary ignition wires. C.O.P.!

[DonWG]

Originally Posted by lazaris

"Something else to think about in the scenario that the waste spark is igniting anything at the top of the exhaust stroke. Let's say the a/f mixture went through the ignition cycle without lighting off. Now the piston drops and uncompresses the mixture.

When this occurs, isn't some of the heat from the previous compression now drawn out from the decompression?

When an a/f mixture is decompressed, does some of the mixture condense into larger droplets from the previous vaporized state, due to the drop in pressure and temperature?

Isn't most of the charge expelled from the cylinder way before the 24 or so degrees before TDC of the exhaust stroke? In fact, most likely past the turbo by this point with a short runner exhaust system?"

Don,

What I think you maybe missing in regards to left over exhaust to ignite, is the overlap , especially with bigger duration cams. The new fresh charge being pumped into the chamber during this overlap, some of it goes out with the exhaust. Cant help it. Lobe separation angle also plays a part here. When this happens I can see why it may raise EGT's. There may be enough fresh A/F to burn.

I'm following your reasoning. But is this the sort of thing usually taken into consideration when tuning a big naturally aspirated V8 with monster cams on an engine dyno? I don't believe so. When watching a F1 engine on a dyno, do you see exhaust flame out the exhaust during a power pull? No. You do see it during coastdown overrun. So fuel can definitely be ignited by a hot exhaust system, but why do you only witness it on a dyno during overrun? Or during special turbo spooling techniques? If fuel was being burned in the exhaust or during the exhaust stroke, wouldn't exhaust valve durability become a problem? We've all heard of how an exhaust gasket leak can cause burned valves.

I wasn't missing the big overlap deal. It's just that most TR cams in use are designed with zero or negative overlap numbers.

[BlownV6]

Originally Posted by DonWG

Excuse me. Are you including the import crowd? Lets start talking about hp/cu. in. What did Honda eventually do with their F1 turbo car? They eliminated the O/H cam driven distributor caps and the secondary ignition wires. C.O.P.!

Donnie , I knew that would ruffle your feathers!! Wish you could have made it to BG I would love to have meet you and seen your car!!! When speaking of drag racing , Facts still are that distributors rule!!! Mike

[lazaris]

"wouldn't exhaust valve durability become a problem? We've all heard of how an exhaust gasket leak can cause burned valves.

I wasn't missing the big overlap deal. It's just that most TR cams in use are designed with zero or negative overlap numbers."

I think exh valve durability is already a concern. Thats why I prefer Inconel on the exh side as does Manley in blown applications.

Most TR cams may have less overlap but not the faster ones that usually use a distributor. Maybe thats why they see the EGT difference.

[lazaris]

"When watching a F1 engine on a dyno, do you see exhaust flame out the exhaust during a power pull? No. You do see it during coastdown overrun. So fuel can definitely be ignited by a hot exhaust system, but why do you only witness it on a dyno during overrun?"

I believe you only see during overrun because of the pressure wave/pulse causing fresh air to be introduced into the pipe thus igniting the unburned fuel.

[DonWG]

Originally Posted by lazaris

"When watching a F1 engine on a dyno, do you see exhaust flame out the exhaust during a power pull? No. You do see it during coastdown overrun. So fuel can definitely be ignited by a hot exhaust system, but why do you only witness it on a dyno during overrun?"

I believe you only see during overrun because of the pressure wave/pulse causing fresh air to be introduced into the pipe thus igniting the unburned fuel.

We'll explore this one more. Got to run for now.