Lizard928

I saw the thread on the sound of the cars and was thinking.
How would a 928 sound if you ran a wasted spark system, and hooked up one of the cams 180 deg out of rotation......

Technically, you would just be having your compression stroke 180 deg out on the crank. You would still build pressure, you would still ignite in (wouldnt be possible with stock ign system). But how would it affect power, vibration, responsiveness, exhaust note?

Would this give more of a ferrari V8 sound?

Thoughts on this.

hacker-pschorr

Did you drop one of your new cams on your head?

Lizard928

nope!

Thinking about it you could actually run it with the factory ign system, you would just have to change that arrangement of plug leads.

I think the idle would become rougher, but its hard to say.

svp928

I think you be making a "big-bang" firing order, with 2 cyls firing at the same time, and a longer gap between firings....almost the opposite of a flat-crank, ferrari-style firing order...sounds more like a harley..

928mac

In a word, Nope

But I understand what you are thinking

here is a good artical

http://www.circletrack.com/enginetec...ing/index.html

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James Bailey

Just pull the plug wires off one bank and you will hear what it sounds like

Lizard928

Brad,

I know that it will fire those cylinders. Your link is to a pushrod motor, which this would simply not be possible to do this to. I know a fair bit about cams.
But basically what I suggested was to change the firing stroke of one bank. This would only be possible in an OHC V8 engine.

The idea is that when the piston hits TDC, one of the pistons fire, then on the next revolution, the other side fires. This would change it so that when the engine hit TDC both cylinders would fire at the same time.
Now Ferraris use a flat plane crank in their cars meaning that all lobes are on the same plane. Or more simply put they all oppose one another. But I am not sure if they oppose their timing events like our motors, or if they fire them at the same time as well. But if each cylinder was producing 50bhp, instead of a crank journal taking 50bhp, then next round taking 50bhp, it would take 100bhp on that stroke, but the next go around it would have nothing. This would effectively make it more like a 4 cyl at idle with the vibrations I would imagine. But what of possible power output? More less? Exhaust note? More like a ferrari, or more like a 4 cyl?

This is what made me wonder.

76FJ55

It would sound as James said. At least the exhaust pulses would match those of a single bank though the tone and volume may different as there would be a larger volume of exhaust as you would have 2 cylinders firing at the same time. They would not be even as it would with a flat plane crank. firing order would be (1,6), (3,5), (2,8), (4,7), (1,6) the firing events would happen at 0, 90, 270, 540 crank degrees in relation to the current 90 degree interval between cylinders you would now have an interval of 90, 180, 270, 180, so not evenly distributed. The 1,5 journal would see both pistons in the power stroke simultaneously though 1 would fire 90 degrees before 5. Interestingly this leave the (2,6), (3,7) and (4,8) journals with 270 degrees between firing events and therefore not having both pistons in the power stroke simultaneously, the rod journal loading may actually be better though the overall crank loading would probably suffer as the max to min peak between firing events would be much greater. Interestingly in a cross plane even firing engine three of the four rod journals see 90 degree firing events and therefore have both pistons in the power stroke at the same time.

The flat crank is of course a totally separate case, and spinning the cams 180 will still leave you with a 90 degree firing spacing, it will just change between either 90 deg between rod journal firing events and 270 deg between firing events. one of the big differences in sound between the cross plane crank and the flat crank is in the alternation between the banks based on firing order, the cross plane crank fires R, R, L, R, L, L, R, L and the flat plane crank fires R, L, R, L, R, L, R, L. This is why you will never get the 928 with dual exhaust to sound like a V8 Ferrari.