my heads

[gombault]

Hi All,

I am new to this forum and have some questions regarding modern day performance motors. Let me start by how I understand it all and “ please” correct me if I am wrong. When the Ducati Moto GP bike came out they said it was a double twin meaning they fired two cylinders at the same time, and those that heard the bike said it sounded like a formula one car. My problem was how can firing two twins sound like a formula one car? Then I was thinking maybe they fired them a couple of degrees apart. All the current formula one car’s and V8 Ferrari’s use a flat plain crank that’s like a double four they also fire two cylinders at the same time. My question is do they have a time difference between firing those two cylinders? Other motors known as big bang motors, like Yamaha fires 90 deg apart but I believe that some other big bang motors fired only a couple of degreed apart. Big bang motors use different crank angles to achieve what they are doing. So then is firing two pistons less frequent at the same time better than having more frequent smaller explosions? Take Ducati for example it was the most powerful 800cc Moto GP bike it was also always the fastest bike and why does all the GP cars use flat plain cranks? So how about changing a Porsche 911 motor in to a double three, firing two cylinders at the same time. Does anyone here see any reliability problems with such a motor? What’s needed for such a motor is new heads. I designed an individual head with its own cams four valves and water-cooled. The two cams in each head are gear driven from a cam drive shaft, this way every cylinders timing can be set individually. The cams will run on sealed ball bearings and all oils for cam lubrication will remain in each head. Having complete single heads will allow for one to make these heads fit no matter how many cylinders you have.

[Flieger]

Individual watercooled DOHC gear driven cams are WAY AMBITIOUS. If you are not using 4 valves, I do not see any real gain.

I suspect the Duc sounds like a Formula 1 car because it revs to like 14000 rpm. It sure does not sound like a "real" F1 car- i.e. one from more than 10 years ago when there was less technical restriction. Ever hear a Ferrari F1 V12? Or a Matra V12 for that matter.

Firing two cylinders at once on the same bank occurs on a V8. It makes for a complex exhaust system because there is too much gas volume coming through the pipes and there are fewer pulses.

The big bang motors were an attempt to allow the smoother inertia torque to make up more of the power cycle to give the tire a chance to "catch up". Yamaha switched to the crazy "long bang" motor to give better throttle response. The "big bang" is too rough. The "long bang" has a better signal to noise ratio between gas and inertia torques and provides smoother midrange torque and finer throttle response at the expense of top end horsepower and a high inertia crankshaft.

Porsche engines are not designed to fire all three cylinders at once. They would shake themselves to bits and not rev very high or make any more horsepower. Each combustion event would have more torque but there would be much fewer of them for every 1000 rpm so the same total torque, or less due to the rough running.

Why don't you ask the Ducati guys? Ducati.ms - The Ultimate Ducati Forum

[lucittm]

It is hard to make a generalization about Porsche engines and how the ignitions work because we have battery and coil, multiple spark, digital (EZ69), 12-plug, Motronic, crank-triggered, and I probably left a few out, ignition systems in our Porsches.

Most of the engines have a single 6-plug distributor, so firing more than one cylinder in a six-cylinder engine is impossible.

The dual plug 12-plug engines were designed to fire both plugs at once in a single cylinder for more complete combustion, again, no chance of firing more than one cylinder at a time.

The newer engines have very complex ignition mapping systems but I don't think the firing order has changed since the beginning of time: 1-6-2-4-3-5.

Am I right on this?

Mark

[Flieger]

Correct. 1-6-2-4-3-5

[dshepp806]

Originally Posted by Flieger

Individual watercooled DOHC gear driven cams are WAY AMBITIOUS. If you are not using 4 valves, I do not see any real gain.

I suspect the Duc sounds like a Formula 1 car because it revs to like 14000 rpm. It sure does not sound like a "real" F1 car- i.e. one from more than 10 years ago when there was less technical restriction. Ever hear a Ferrari F1 V12? Or a Matra V12 for that matter.

Firing two cylinders at once on the same bank occurs on a V8. It makes for a complex exhaust system because there is too much gas volume coming through the pipes and there are fewer pulses.

The big bang motors were an attempt to allow the smoother inertia torque to make up more of the power cycle to give the tire a chance to "catch up". Yamaha switched to the crazy "long bang" motor to give better throttle response. The "big bang" is too rough. The "long bang" has a better signal to noise ratio between gas and inertia torques and provides smoother midrange torque and finer throttle response at the expense of top end horsepower and a high inertia crankshaft.

Porsche engines are not designed to fire all three cylinders at once. They would shake themselves to bits and not rev very high or make any more horsepower. Each combustion event would have more torque but there would be much fewer of them for every 1000 rpm so the same total torque, or less due to the rough running.

Why don't you ask the Ducati guys? Ducati.ms - The Ultimate Ducati Forum

Nice read,..thanks.

Doyle

[gombault]

I was thinking more like on a Porsche firing piston one and four, then have two and five on exhaust and then three and six on fire. You would require different valve timing for such a motor. All F1 teams useV8 flat plain crank motors and fire two pistons at the same time, even the V8 Cosworth had a flat plain crank with good results in endurance racing. I don’t think that the revs on the GP ducati would give it that sound, the V twin Ducati used in SB would not rev much less and its sound could never be compared with a high pitch screamer like a F1. My heads are 4 valves.

[Flieger]

The engine will run smoother with a 60* crank versus 120* crank. With all the Aluminum and Magnesium smoother is better. You do not get any more torque when averaged over 4 revolutions. The increase in each peak of torque will not get any more acceleration. The stated reason for big bang was to give the rear tire a rest to regain its static (higher) traction friction level. This is more important with a single, round tire on a lightweight machine with lots of power. On a 2000+ pound car with two wider rear tires and not much more power, there is no need to "rest" the tire. The extra vibrations are just harder on the motor. The motorcycle manufacturers even said that it was too extreme for sport bikes. With advances in metallurgy, it may be doe-able now, but it still will run rough, especially at low revs.

If there was an advantage in firing two cylinders at once, then Porsche would have done it on one of their GT3 RSR motors, which have four-valve, water-cooled heads.

[Flieger]

Maybe I am worng. Did you know how the 908 was plagued with chassis, alternator, and exhaust failures due to their first firing order? In their second season, they switched to a flat plane crank and that reduced the vibrations.

I think the difference is between an 8 and 6 cylinder. I have heard that flat 6 and 12 have 'perfect' balance, without counterbalance shafts. There is something about 2,4,8,10.

I believe the flat 12 in the 917 fired two cylinders at once since it had the same planes as a flat 6 crankshaft but had two rods on each throw.

Anyway, I just do not see the advantage of firing two at once.

[gombault]

Hi Flieger,
I think it was the other way round. The first F1 and 907 Porsche used a flat plane crank. The 907 2.1 motor was reasonably successful with the flat plain crank, it was when they made the 3 liter they developed vibration problems. Porsche then changed to a 90 deg cross plain crank for the 908. I don’t think the 917 fired two cylinders at a time, as a 12 cylinder 60 deg crank will only have two pistons on TDC at a time. The Ducati GP is a four-cylinder motor and like all four cylinders (except for some big bang motors) you have two pistons on TDC and two on BDC, up to now everyone was firing one piston at a time. I think Ducati was the first to fire both pistons on TDC at the same time and they must have seen the advantage in that. Remember this Ducati was not classifies as a big bang motor. Big bang motors cranks are offset.

[Flieger]

According to Fere's The Racing Porsches, the Typ 771 flat eight used a flat plane crank and was fine. The first 908 used a different firing order for a simpler exhaust and had vibration probems. They switched to a flat plane crank, had less vibration, but a little less power due to the more complex exhaust and the drivers did not like it. The lap times were faster with the flat plane crank, though, so they had to live with it.

So you mean on a V4 that one cylinder at TDC is at the end of exhaust and the other is firing?

I still think it is just more vibration. Think of a Ferrari flat 12, maybe a 5 liter from the 512M. If you had a flat 6 that big, that is like firing two cylinders at once. Everyone would think that a 5 liter flat 6 would run rougher than a 12. Spreading out the impulse makes for smoother running. Similarly, the 968 had, I think, a 3.2 liter 4 when the 911 had a 3.2 liter 6. The 968 needed big balance shafts.

Why would firing two at once in a 911 be better? As I have heard, the MotoGP teams said the tire could "rest" on the longer time between power strokes. It would be like having a twin again, except with twice as many parts.

I always heard of "big bang" being firing two cylinders at once on a 4. Is it firing all 4 at once?! I heard the Yamaha YZR-M1 called "long bang".

[Flieger]

I re-checked Fere. The 771 used a flat/single plane crankshaft. Second order forces cancelled. Each of dual exhausts fed from both banks for extractor. The 908 (early) used a two plane crankshaft (90 degree). Second order vibrations added. Each of dual exhausts fed from single bank for extractor. Severe vibrations. Not bad enough for 1000km race but too bad for 12 hours, 24 hours, let alone road car. Each bank was a separate four cylinder engine as the exhaust saw it.

To smooth the engine and make it more reliable, they switched to a flat plane crankshaft with the complex exhaust.

[Flieger]

Well, the v12 is the clear winner!

[Flieger]

I still think revs has a lot to do with the sound.

[gombault]

I will have to disagree with you about revs being responsible for engine noise. One will always be able to distinguish the difference in engine sound between a flat plain and cross plain V8 engine
Take a look at this site.
Ever wonder why a Ferrari V8 sounds completely different from an American V8??? - Team-BHP
The Ferrari F430 will only rev till 9000 and you will never get a cross plain V8 sounding like this YouTube - Ferrari F430 Scuderia FLATOUT in the city! at 9000.

According to the sound of the 3-litre 908/3 it must have had a cross plain crank YouTube - Porsche 908/3 Laguna Seca CA.
The type 771 was a completely different motor see Porsche 908 K, LH, & Spyder

My original question was more about why would a double twin like the GP Ducati have that high pitch sound? And is it better to fire two pistons at a time?

What I mean is on a V4 like the Ducati all the pistons that is on TDC is on compression stroke and firing.

I would like to experiment with such a motor. The head I am making will allow me to change the valve timing to anything I want. I would also like to be able to set ignition timings individually, either mechanically or electronically. I am busy with ignition components for a 911 motor I am building. Will show some pictures when finished. Somehow I think Ducati get that sound because of a spark offset between the two firing cylinders. They might even have differed valve angles for each cylinder.

[Flieger]

I trust Fere more than the sound on a video. I still think the later 908 used a flat crankshaft, as the 771 did. They certainly reverted to the style of the 771. Have you read his Porsche 911 Story or The Racing Porsches ?

The project sounds interesting, though.

The Carrera GT V10 (derived from Formula 1 and WSC-Spyder projects) used a V angle of 70 degrees, but a conventional 72 degree crankshaft plane offset, if I remember correctly. F1 likes narrow engines.

[safe]

Originally Posted by gombault

I was thinking more like on a Porsche firing piston one and four, then have two and five on exhaust and then three and six on fire. You would require different valve timing for such a motor. All F1 teams useV8 flat plain crank motors and fire two pistons at the same time, even the V8 Cosworth had a flat plain crank with good results in endurance racing. I don’t think that the revs on the GP ducati would give it that sound, the V twin Ducati used in SB would not rev much less and its sound could never be compared with a high pitch screamer like a F1. My heads are 4 valves.

I almost made a big bang engine, by mistake, 2 months ago when I rebuild my engine. I put one camshaft in 180 degrees of. Since I use wasted spark ignition, i guess 1 and 4 would have fired at same time??
Or would it have become a different kind of big bang?