Twin Plug = More fuel??

[126coupe]

Once I twin plug my 2.5L race engine will I be able to throw more fuel in there?

My guess would be yes, more fuel = more power??

Opinions?

[Steve@Rennsport]

Twin-ignition, in and of itself, doesn't require more fuel.

Twin-ignition does require different timing specs from idle to redline and this means the advance curve & total timing.

Air-fuel ratios should be 12.8-13.0:1 at WOT for best power for air-cooled N/A engines.

[tctnd]

The challenge when trying to extract additional power has never been "more fuel". More air, or specifically, more oxygen is the difficulty because it is in the form of a gas (and in the case of air, only a 20% concentration) which takes up a lot of space relative to it's energy content. Big ports, hot cams, supercharging, and nitrous injection are all intended to get more oxygen into the combustion chamber; getting enough fuel is easy, metering it is the hard part.
regards,
Phil

[Eagledriver]

To simplify what's been said already, twin plugging does nothing to increase the amount of air entering the engine. Since the amount of air is the same the amount of fuel should be the same as well.

-Andy

[126coupe]

So twin-plugging my already "proven" 2.5L 10.2:1 Race engine, which after 40 hours of high reving (5,000-8,000) and showing no bearing or piston ring/cylinder wear , no detonation, no valve guide wear (race fuel only)is not worth the $$$$???
The only change I am making to this engine so far is to go from a 60 Cam to an 80 Cam.

To twin-plug or not is the question?

Opinions Please

[DW SD]

twin-plugging is a preventative measure against detonation, which can destroy an engine in a hurry. Detonation is caused by high compression ratios and the use of non-sufficient octane fuels.

A larger cam should reduce your effective compression ratio. I would venture the opinion, while not an expert, that if your high revving race engine does not detonate currently (based on the condition of the engine provided) and you continue to use the same quality of fuel, that you don't need twin plugging.

Increasing the compression ratio will increase power extracted from a given amount of air and fuel, but the risk of detonation increases. Where the threshold of risk lies, I do not know. An expert will probably know. Henry or Steve Weiner would likely know that information from the top of their head.

[sww914]

More correct air/fuel mixture, properly combusted, = more power.
More fuel= too rich, improper combustion, less power.

[Steve@Rennsport]

Originally posted by Minkoff
To twin-plug or not is the question?

Opinions Please [/B]

Take a look at this: http://www.rennsportsystems.com/2a.html

Twin-ignition affords using less total ignition advance to perform the same amount of work and this results in more of the cylinder's gas pressure being utilized to make HP.

Further, ignition two flame fronts provides more efficient combustion as the pistons approach TDC. These lazy hemispherical chambers that have little or no natural turbulence or squish that create nice homogenous mixtures.

Aside from the financial hit by doing this, there is no downside and in fact, a great many benefits even for those using race gas.

[914efi]

High compression requires high octane 'race' fuel which burns more slowly. High rpm requires fuel to burn quickly. To burn more quickly, twin plugs can be used to essentially cut in half the time required for combustion since you have two flame fronts. Driveability is supposedly enhanced(per B.A.), but total power may not be.

[911pcars]

If it hasn't been said directly or indirectly yet, twin plug ignition allows one to use higher compression ratios for increased volumetric efficiency without detonation or need for special, high octane fuel. This translates into more torque and power out of a given qty. of fuel - all good. If high octane fuel is available, increase the compression ratio for even more power.

Even with lowly 91 octane premium fuel available today, most modern engines have fairly high compression ratios. Current Porsches are what? 11 or 12:1?

Sherwood

[Steve@Rennsport]

Originally posted by 911pcars
Current Porsches are what? 11 or 12:1?

Sherwood

964-993's actually range between 10.5-10.8:1.

The water-cooled models are slightly higher at 11.1:1 but with those water-cooled heads that afford excellent temperature control and their pent-roof chambers with centrally-located plugs, their flame propagation characteristics are almost ideal.

[Henry Schmidt]

Twin plug engines produce more horse power/ torque everywhere, throughout the RPM range.

They (twin plug engines) will burn fuel more efficiently and therefore can use more fuel if all other things are equal.

Because you are burning fuel more efficiently the cylinder pressures are higher at all RPMs and higher cylinder pressures equal more power/ torque.

Imagine adding ignition timing to the point of near detonation. At that point your horse power is optimized.
Twin plugging allow for more effective ignition advance without detonation.

A simple test. Dyno test your twin plug engine with one set ( lower) of plugs shut down. Set the ignition timing to it optimum setting.

Now connect the second set and optimize the ignition setting. Rejetting is often required. Dyno test again. Your findings will be clear. More horse power at every RPM, with any fuel, guaranteed.

[Carrera3.5L]

Originally posted by Henry Schmidt
A simple test. Dyno test your twin plug engine with one set ( lower) of plugs shut down. Set the ignition timing to it optimum setting.

Now connect the second set and optimize the ignition setting. Rejetting is often required. Dyno test again. Your findings will be clear. More horse power at every RPM, with any fuel, guaranteed.

Did just that, about a 20 whp difference on my motor with the timing advanced for single ignition and than retarded for twin ignition...

Ralph

[BK911]

So basically with twin plug you can reduce the amount of ignition advance without detonation, which results in more power.

And if you still get the same amount of air into the cylinder, and have more efficient combustion, you should be able to reduce the amount of fuel.

So more power and better fuel economy?

[gumba]

What would be the typical total engine advance for a twin plug? On the Electromotive HPV-1 you can advance or retart from 3 - 8,000 rpm, what is the benefit/purpose of that.

[Carrera3.5L]

Originally posted by gumba
What would be the typical total engine advance for a twin plug? On the Electromotive HPV-1 you can advance or retart from 3 - 8,000 rpm, what is the benefit/purpose of that.

On my mild Motronic street motor with 91 octane it is only 22°

Ralph

[gumba]

HMMMMM? On my 3.4 race motor 10.5 comp, 46mm Webers, etc. I'm at 28d at 3,000 and down to 26d at 7,000 using 50/50 pump/100octane race. Is this too high?

[Steve@Rennsport]

Originally posted by gumba
HMMMMM? On my 3.4 race motor 10.5 comp, 46mm Webers, etc. I'm at 28d at 3,000 and down to 26d at 7,000 using 50/50 pump/100octane race. Is this too high?

Not knowing what cams you have, its hard to make firm recommendations, but 28 deg at 3K is FAR too much and thats costing you power as well as putting your pistons & rings at high risk.

Try:

10-12 deg at 1K
18 deg at 3K
25-26 deg at 7K.

[gumba]

Thanks for the response. I'm using DC80 cams.

[Henry Schmidt]

A good place to start for most race engines
5-7 degrees stactic
15 degrees at 2500
24 at 4800
28 at 6500