19 replies to this topic

[onepablo]

I've asked this question at other BBs, but so far have not gotten a satisfactory response. My query is this: What gives the old Porsche air-cooled engines their distinctive "rat-tat-tat" sound? I know its a complex mixture of different sounds, but is there any source that plays a major role in that rather unique sound? I've searched the TF, and the only thing that suggested a source was an old post on 2-stroke kart engines...namely, resonance caused by vibration of the cooling fins.

[Melbourne Park]

Well, I guess boxer engines firstly sound different. The WRX engine, a four cylinder, sounds really fantastic. The 911 also was air cooled which would have made it noisier, not just because of the sound of the power absorbing fan, but also because the engine rather than having internal water channels had external fins, which would mean that rather than absorbing sounds by using water channels the air cooled engine would have emitted sound via the cooling fins. IMO.

[desmo]

Agreed. Cooling fins.

[eldougo]

The sound form a air cooled motor is more (Noiser or Ratter) because the piston firing is not dulled by a layer of water as in a water cooled motor and this tends to increase the overall Rat-tat-tat sound .This is at lower RPM however once the Revs go up who cares they sound just Great.

[Yelnats]

I can't say I noticed a drastic change in sound when motorcycles when from water to air cooling. Similarly when snowmobiles underwent the same changes.

[Melbourne Park]

Originally posted by Yelnats
I can't say I noticed a drastic change in sound when motorcycles when from water to air cooling. Similarly when snowmobiles underwent the same changes.

There's quite a change now with the 996 engine though. Even with the water cooled heads there was a change. But the engine grew in both power and refinement. I also have a vague recollection from reading a book 20 years ago, that the fan back then was absorbing 30 kw or something huge like that. Fan technology has improved greatly with computer technologies, and such changes would have changed the sound as well as the air cooled engine gained in refinement. I've driven an old 911E lately, an early one, a good hot up car, and its sound really pleasant. They got a bit harsher as they got more powerfull, then they got more powerfull and got quieter. Also there was more insulation between the engine bay, and the body was quieter, different heating etc. The 90's ones were really very refined. My comments are based on being inside the car ...

[zac510]

Originally posted by Melbourne Park
The WRX engine, a four cylinder, sounds really fantastic.

You will find that is more to do with the exhaust manifold configuration than the layout of the engine. Cylinders 1, 2 and 3,4 are paired up with inequal length pipes.

[Melbourne Park]

Originally posted by zac510


You will find that (the XRX engine sound) is more to do with the exhaust manifold configuration than the layout of the engine. Cylinders 1, 2 and 3,4 are paired up with inequal length pipes.

But I've not known another 4 to sound like the WRX's engine. I should say, not the standard XRX engine, but ones that have been worked on a bit. Actually, I liked the sound of a Triumph TR4 (for some reason, nicer than the TR3s similar Fergerson tractor engine). But the WRX can sound almost like some kind of V8 ... I can't but help think the layout has something to do with it, at least the apportunity to tune the exhaust more easily is there with such a great IMO layout.

[marion5drsn]

Zac410; Do you mean unequal? What is the firing order of this engine? This layout sounds a little weird! There are two firing orders according to Bosch Automotive Handbook. 1-3-4-2 & 1-2-4-3. This might account for an unusual pipe length. M.L. Anderson

[indigoid]

Apparently Subaru have changed their exhaust layout in newer (2004) models, and they don't sound nearly as distinctive anymore. More powerful though

[Powersteer]

Well air-cooled engines do not provide double glazing like liquid cool one does. Air-cooled engines are very loud at high rpm, most noticable when the exaust is very well silent.

[zac510]

marion5drsn, I thought it was 1, 3, 2 ,4 ! Who knows now? The new engines that indigoid refers to have extractors that join 1&4 and 2&3 in a conventional manner. I read in a press release that it was more difficult to set the extractors up like this.

[ckkl]

Originally posted by Melbourne Park


But I've not known another 4 to sound like the WRX's engine. I should say, not the standard XRX engine, but ones that have been worked on a bit. Actually, I liked the sound of a Triumph TR4 (for some reason, nicer than the TR3s similar Fergerson tractor engine). But the WRX can sound almost like some kind of V8 ... I can't but help think the layout has something to do with it, at least the apportunity to tune the exhaust more easily is there with such a great IMO layout.

The WRX does sound quite unique and awesome and I've always assumed it was from the boxer configuration (I believe the 6-cylinder Subarus also make similar noises, though they're far less popular -- those with free flowing exhausts anyway).

But as for the comparison to a V8... you make it sound like a compliment that the WRX sounds like the supposed higher-end V8 but we all know the best V8s sound like inline 4s ;)

[Randall Aase]

The firing order for Porsche 6 cyl Boxer Motors is 1 6 2 4 3 5 this will allow the aspiration periods to complement one another for the 3 cyl on the drivers side and the 3 on the passengers side.
The cyl banks can be paired up and installed into a collector like the Cosworth Flat Plane Cranks.
The street versions of the later type have a rather complicated Cat. sys. and the two outlets are routed to the opposite sides of the vehicle , hence the thump. On racing versions we bring the outlets together and produce a great racing sportscar sound.
Best regards

[marion5drsn]

To zax510; Woops! I gave the firing order for an inline four. :

The firing order for a flat four is 1-4-3-2 with 1 & 2 on the same side, right, and 3-4 on the other,
left, and only one firing order. Bosch.
Now the question is, how did they number the one that you are talking about?

If they numbered it like the 6 cylinder Corvair it would be 1 & 3 on the left and 2 & 4 on the right.
One must also remember that the Corvair is turning the wrong way, in relation to the output.

M.L. Anderson

EDIT; Subaru fires 4 cyl., 1R- 3R-2R-4R
Subaru fires 6 cyl., 1R-6L-3R-2L-5R-4L

[Melbourne Park]

Originally posted by Randall Aase
The firing order for Porsche 6 cly Boxer Motors is 1 6 2 4 3 5 this wil allow the aspiration periods to complement one another for the 3 cly on the drivers side and the 3 on the passengers side.
The cly banks can be paired up and installed into a collector like the Cosworth Flat Plane Cranks.
The street versions of the later type have a rather complicated Cat. sys. and the two outlets are routed to the opposite sides of the vehicle , hence the thump. On racing versions we bring the outlets together and produce a great racing sportscar sound.
Best regards

Originally posted by marion5drsn
...
M.L. Anderson

EDIT; Subaru fires 4 cyl., 1R- 3R-2R-4R
Subaru fires 6 cyl., 1R-6L-3R-2L-5R-4L

Strange that Subaru did not copy the firing order of the Porsche ... I wonder why not?

[marion5drsn]

To Melbourne Park; Randall Aase did not state the physical layout of the cylinders! This is why the Corvair turns the “wrong way” as it is behind the rear axle and to get it to turn the ring gear and the pinion wheel the correct way you have to turn it to the counterclockwise. It turns the wrong way. If you tried to hand crank one (not possible) you would have to do it “Left handed.”
The Porsche engine is in the front of the axle is it not? There fore it probably turns the “right way”, that is to the clockwise direction if you had to hand crank it (not possible”).

The Porsche is numbered to the DIN standard (Dumb) but is numbered #1 right at the front, # 2 in back of that with #3
right rear. # 4 is on the left in the front with 5 left, 6 left rear.

M.L. Anderson

[Randall Aase]

Sorry,
I forgot the original question was about old Porsche engines.
The 6 cyl firing order M.L. Anderson described is for a 914-6 middle motor.is
Mine is for a 911 where the engine is the closest thing to a rear end accident.
Cyl. 1 is furthest back drivers side and 6 furthest forward passenger.
This will allow a clockwise rotation and the Trans Rang gear is situated in relationship to the pinon to allow proper dirve to the dirve line.
Best regards

[McGuire]

Originally posted by Randall Aase
Best regards

Any relation to the famous Porsche Aases?

[Randall Aase]

Yeah, I guess you can't hide behind a name spelled like mine