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mpersell

A question for GT and other E85 performance guys

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Dodge has made considerable mods to the 4.7 v8 in the 2008+ model years. 

 

The engine now has 2 plugs per cylinder, higher compression ratio and valve timing to take advantage of the compression ratio.

 

I know the higher compression ratio helps but does the dual plug help without making considerable timing changes?

 

The horsepower gain on gasoline with these design changes was considerable, from 245 to 302.

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I can garuntee it's still detuned, and will likely take very well to ethanol. Gas by itself in anything is a waste, no matter how efficient it is. Find the compression ratio and the cylinder head flow rate and I'll be able to tell you a lot more. If you find what other changes they made, I can tell you what should be possible.

 

I really hope factories will step up their driveline engineering efforts. The motors do fine, but I don't want a collection of broken driveline parts.

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The newer 4.7-liter V-8 features two spark plugs per cylinder, a  9.8:1 compression ratio, and better port flow; but it has a new slant/squish combustion system design.

 

Refinements included significant revisions to the induction system, reduced reciprocating mass via a lightweight piston/rod assembly, and reduced accessory drive speed. The peak hp is obtained at 1000 more rpm so it looks like better flow in the heads and manifold.

 

Driveline is the same as 345-380 hp hemis so it should stand up well to normal and rated operations.

 

I can garuntee it's still detuned, and will likely take very well to ethanol. Gas by itself in anything is a waste, no matter how efficient it is. Find the compression ratio and the cylinder head flow rate and I'll be able to tell you a lot more. If you find what other changes they made, I can tell you what should be possible.

 

I really hope factories will step up their driveline engineering efforts. The motors do fine, but I don't want a collection of broken driveline parts.

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That's a pretty good combo, IMO. The compression is a good compromise. I wondered if it was at like 11:1 or anything. Bolt-ons and a reflash should make 400hp+.

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and its still a factory FFV motor.

 

That's a pretty good combo, IMO. The compression is a good compromise. I wondered if it was at like 11:1 or anything. Bolt-ons and a reflash should make 400hp+.

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I know the higher compression ratio helps but does the dual plug help without making considerable timing changes?

 

Yes it reduces the likelihood of misfire, and reduces sensitivity to detonation by reducing combustion time.

By starting the combustion in two locations the time it takes to burn off the fuel is cut roughly in half, which reduces the time for low quality fuel to undergo pre-flame decomposition reactions that can result in detonation.

 

Dual spark was used extensively in high performance aircraft 60 years ago, for the same reasons (and reliability).

 

The one side effect to dual ignition that many folks are unaware of is, that if you increase performance and put a cutting edge tune on the engine, and if you have a failure of one spark plug that cylinder can very rapidly go into severe detonation due to the single off center ignition point.

 

Good ignition wires and replace spark plugs before they fail on those engines if you are pushing them hard.

Dual spark is good from the standpoint of emissions and efficiency as much of the engines improved efficiency is the increased thermal efficiency of a higher compression ratio and reduced frequency of misfire or partial misfire.

 

All engines experience a high percentage of incomplete combustion or out right misfire even when they are running well due to random variation in ignition and in cylinder burn condtions.

 

Larry

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I've used dual plugs in the methanol drag racing engines but that was 25 years ago.  We used it there to make sure we burned the fuel we were shoving down the engine's throat.  Burning 10-12 gallons of methanol in a quarter mile pass was not unusual. We used a single distributor drive with dual magnetos and one plug fired slightly after the other.

 

I think the design for the new Dodge engine is for a combination of power and emissions.

 

It looks like the engine will be available in Ram half tons, Dakotas, Durangos and Jeep Commanders.

Dual spark was used extensively in high performance aircraft 60 years ago, for the same reasons (and reliability).

 

Good ignition wires and replace spark plugs before they fail on those engines if you are pushing them hard.

Dual spark is good from the standpoint of emissions and efficiency as much of the engines improved efficiency is the increased thermal efficiency of a higher compression ratio and reduced frequency of misfire or partial misfire.

 

All engines experience a high percentage of incomplete combustion or out right misfire even when they are running well due to random variation in ignition and in cylinder burn condtions.

 

Larry

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