Twin Plug 1883 Advance Curve & Ignition System Advice Needed

[Ron LaDow]

Bill,
I wouldn't bet that the geometric model is workable in all circumstances but I would bet it'll get you in the ballpark as a starting point. Mine had the "9.25:1" pistons which are just about the smoothest dome you can find; lumps are going to distort that 2-D picture.
Per Jacques, I wouldn't attempt to establish a base-line tune on an engine with major mods without a dyno.

[C J Murray]

Here are a couple of examples of modern ignition maps to give you an idea of what Jacques is referring to.

http://www.tuneboy.com.au/Products/Prod ... uneedit_3D

http://forum.205gtidrivers.com/index.ph ... opic=67871

There is no point in going to a modern mapable ignition on a carb equipped engine so that means you need fuel injection. With that combination you can run bigger cams and the FI butterflies can be much larger than on a street driven car with carbs. Expect to spend many hours on the dyno with your laptop in hand. Does that really make sense when the basic engine is such a relic and will never produce big power anyway? More displacement and attention to details will give the chassis as much as it can handle without adding the computer controls. Oh, and twin plugs are a waste of time and money.

[Jacques Lefriant]

Hi CJ
"waste of time and money" Where is the fun/romance in that? hell yes go for it and if you learn something in the process so much the better. Seriously if we combine our efforts we should improve the relic for the greater good. Thank you for all the insight/advice you have given me.
KTF
FCF
AMDG
jacques

[Ron LaDow]

"Oh, and twin plugs are a waste of time and money."

Neener, neener, neener!
It’s axiomatic that talk’s cheap, so let’s get some skin on the line.
Ante is $1K; checks held by third party.
You build the best 356 engine you can, single-plug, coil/distributor ignition, carbureted. Get it to The Stable, where we can spend enough time on the dyno to tune it to the best output we can find.
You or I will disassemble it to make the heads available for machining, and I will pay for having the heads machined for the second plug.
We will then reassemble it with second hole plugged and re-establish base line on the dyno.
We will then fit a Pre Mat twin-plug kit and again find the best output we can find on the dyno with *only* this modification; no other enhancements other than tuning changes.
1) If we show at least 5% increase in torque values between (and inclusive of) 3KRPM and 5.5KRPM, I win and you lose.
You lose the ante, the shipping cost, the machining costs and the dyno time costs. And just to keep the bet even, whatever value you state up front to make your heads good again.
2) If we do not, you win and I lose.
I lose the ante, the shipping costs, the machining costs, the dyno time costs and the cost of making your heads good again.
This offer is open to anyone with a 1720cc engine making at least 85HP at 5.5KRPM or an 1883cc engine making at least 95HP at 5.5KRPM. And the offer is good until 9/1/12.

[Jacques Lefriant]

Hi Ron
I am confused are you implying that the 2nd plug mods are detremental to the engine runing single plug? i realize that you have to use a cold plug in the idle hole in order not to create a hot spot. you may win your bet but it only goes to show how the combustion chamber needs to be improved and the need for a better ignition system that can fire richer mixtures. I think we would be better served by piston/head mods than adding a lot of complexity. i am looking for someone to try my pistons which will require no incremental costs except for minor head machining. but i do like the the twin plug look.
Keep at it
jacques

[Jacques Lefriant]

Hi Ron
Wow factor aside i think one should be concened with the incremental costs involved i building their engine. also one should be concerned with the longevity/cost per mile and overall costs.going from 82.5 to 86 is a usually zero cost upgrade in performance and not usally negative in overall costs. i am a big believer in your full flow oil filters and better air filters. in most cases i don't think that the performace increases with the twin plug warrant the cost sorry.
jacques

[Vic Skirmants]

Not to mention the fact that there is one individual, not Ron, who is producing twin-plug heads that require the removal of two pushrod tubes on each side to remove the bottom spark plugs.
I had a local customer who insisted on twin-plug heads. After a two-year wait, he finally received them. I figured I would flow-test them to see how they stacked up to the standard heads, or my race-prepped heads. The numbers were hardly any better than a cleaned-up set of stock heads. Then I realized, while pulling the lower plugs out, that this would be impossible with the pushrod tubes in place. I told the customer I would not use those heads. Instead, I prepped a set of heads with my race combustion chambers, and everybody is happy.

[Vic Skirmants]

There certainly are benefits to a twin-plug set-up. More complete combustion, etc.
HOWEVER, I agree that for our engines, the gains versus cost ratio needs to be examined for an individual to decide if they really want to go that route. But then again, the extra "bragging rights" also have to be factored into the equation.

[C J Murray]

Shorter, stiffer advance springs are available from MSC industrial supply. If you replace the worn pins in the advance with slightly larger than stock pins you can increase the distance between the pins at rest which has the same EFFECT as a shorter spring. I do both.

[C J Murray]

Every modified engine project should start with a careful questioning of what the user intends to do with the car and what their driving style is as well as the maximum budget. The most important modifications are the ones that will impress the owner of the car and that is where you spend the money first. The more you spend the harder it is to see a gain. In other words, the most obvious mods are done early and result in big gains while adding to the basics is progressively more expensive for less progressive increases in power. The most important advice of all is to not go too big with cams and carbs.

Oh yea, ignition curve, Ron is a good source of info about maximum and idle timing numbers. With a single plug engine I have found that a smaller range of advance where the full advance remains at stock and the idle at 2 or 3 degrees advanced works well and that stiffer springs make things more stable without significant changes in the point where maximum advance is achieved.

[Vic Skirmants]

"smaller range of advance"; like in a 009 distributor?
Yes, I use these in my race engines, AND in street-driven cars.

[Ron LaDow]

Jacques,
Yes, there are cheaper ways to find power. And finding yet more power gets yet more expensive. But do your *absolute best* and I can stick a second plug in there and find more yet.
Not only peak power, but spread across the range, per the offer. It's not a matter of initiating the reaction in a rich mixture, it's moving peak reaction pressure to a more favorable crank/rod geometry; I'm betting that physical laws always win.
Just to make it clear, my offer is made without rancor toward anyone. I simply state that whatever you do with a 356, adding that second plug to reduce the spark lead will improve it. And I'll willing to put my money behind the claim. I could be proven wrong; all it takes is someone to successfully put their money behind the opposing claim.
And thanks, Vic. Whatever you had, those heads were *not* per the Pre Mat drilling spec.

[Jacques Lefriant]

Hi Ron
the laws of physics do not change depending on what coast we are on but i am mistified since the definition of work is force thru distance and a tdc we have almost no movement and the rod/stroke effects are noticible at max piston velocity and movement which occurs much latter. Increased displacement, cam changes , combustion ratio and induction/exhaust are inexpensive ways of getting more power. don't get me wrong i love twin plug motors but i think combustion chamber mods may have more bang for the buck. A good crank fire system is an improvement for the twin plug 4-Cams i work on but try to sell anyone on it. the 911 guys jump on it since it is better than any twin plug dizzy. How much of the improvement you attribute to the second plug is due to the ability to run richer mixtures and greater BTU fuel?
jacques

[Ron LaDow]

"How much of the improvement you attribute to the second plug is due to the ability to run richer mixtures and greater BTU fuel?"

None.
You, Cliff, Vic and others are far better at maximizing that and other issues than am I. The second plug does nothing to help that, it simply takes the best you guys can accomplish and uses it better.
I ask you to imagine the crank/rod angles as the mixture reacts. At some time during that reaction, there is a peak pressure on the piston dome, maximally pushing the piston down and thereby rotating the crank.
It doesn't take trig computations to recognize that if the peak pressure is at, say, 10* ATDC, it is far less effective in rotating the crank than if it happens at, say 20* ATDC. In all likelihood, the optimal peak pressure would occur when the 'rod angle' (rod C/L-to-crank moment-arm angle) is at 90*. Given the 356 rod length, that's (guessing) 40* ATDC.
If you must initiate the reaction >30* BTDC, the peak pressure is going to occur much earlier, which is the reason I'm not joking in wishing I could sneak a 3rd plug in there.

[Mario Bellettato]

A twin plug 356 engine does go better than a single plug one, the issue is what better means to you and what kind of engine you are thinking at. If you are happy with a Dame and drive your 356 like an old lady do not think of it, as well as (probably) if you are a serious racer. Beyond the HP/Torque gains the whole "temper" of the engine changes. When Alfa Romeo developed its twin plugged racing engines back in the 40s & 50s (they had been constant winners), the goal was a broader usable RPM range, power increase was a welcome side effect. Following "go advance, go rich" you probably get much HP, but the engine get wilder and wilder. I do not build racing engines, therefore I talk about hot street engines, what I really love. In my experience with a good twin plug system you can get 7K RPM with 24° advance or even less (twin plugged engines showed to be less advance sensitive). I tested the engine on Dyno and the HP/torque increases were significant, even bigger than what Ron is granting. The engine I tested was a big bore C block, with custom crank (standard stroke), Carrillos, 7008 Elgin cam, 10:2 CR, custom exhaust, slightly ported heads, 40 weber carbs with 12" stacks. What I really loved was the smooth power it performed from 1800 to 6400 RPM, an outstanding sense of power on long hillclimbs. Even kicking down the gas in 4th gear at 2000 RPM it accelerated quickly with no empty hole. The system we developed (3 units) after a long testing with two Ducati motorcycles technicians probably was extremely expensive, we made it for fun, so did not count hours, trips, waste materials and so on, but the result was very good (again in my opinion). Everybody can decide if a twin plug system is cheap or expensive, depending on his own judgement, but I would not say it is a waste of time and money: you get a significant increase of HP/Torque, the engine run cooler (combustion is faster), the rods work with a far more favourable angle, the car is more enjoyable and engine lifespan is not shortened. Good systems are almost "bolt on" type, you can go back to single plug and ordinary distributor without problems. Coming to racing engines I have no experience and great respect for some members who wrote before me, so the solution probably is not good for allout racing.