Different cam profiles on the same engine? 1

[globi5]

Are there examples of engines that used different cam profiles on different cylinders of the same engine?

Obviously due to variable valve timing this would be an obsolete way to flatten the torque curve, but have engine designers in the past ever produced engines with different cam profiles on the same engine?
(Example: 1st and 2nd cylinder peak at 3000 rpm and 3rd and 4th cylinder peak at 5000 rpm.)

 

[kitabel]

Yes, read Vizard's Mini engine development stuff.

 

[MikeHalloran]

On a Harley, the front cylinder is cooled by air, and the rear cylinder is cooled by accident. On some models, the rear cylinder's timing is retarded a couple of degrees to compensate.

Similarly, the old VW bug's flat four has slightly retarded cam timing on the cylinder whose airflow is impeded by the oil cooler.



Mike Halloran
Pembroke Pines, FL, USA

 

[patprimmer]

Air Cooled VW flat 4s have even valve timing, as each lobe works 2 cylinders.

They have the ignition timing on # e cylinder retarded 2 deg distributor. This is built into the distributor cam.

# 3 is the front RH side when viewing the engine from the rear of the car. It is the cylinder that is under the OEM oil cooler, and runs hotter as in the factory set up, the oil cooler steal some of # 3's cooling air.

I found that if I removed the OEM cooler and fitted a much bigger, remote cooler and reworked the air ducts to even out and maximise the airflow, I could raise the compression about half a point, and slow the cooling fan, or use a smaller fan and therefore pickup both fuel economy and power you could feel in the seat of the pants.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[MikeHalloran]

Well, I knew _something_ was retarded. Please refrain from the obvious response. ;-)



Mike Halloran
Pembroke Pines, FL, USA

 

[icrman]

I think that is one of the secrets in some racing engines.
I read some place that some stock car engine builders have been doing that for years. To compensate for different induction flow charateristics, and other cyl to cyl variables.

 

[Marquis]

The Mercedes Benz 5 litre V8 tripple valve twin plug engines with cylinder deactivation have different cam profiles on different phase firing cylinders.
This is to do with the cylinders which de activate.

It is rare to have this phenomenon on a modern production road engine as it could lead to un even amounts of residual gas content at idle speed/ or even different power contributions from each cylinder- this would not only lead to a rough idle, but could also make it difficult to calibrate good equal EGR rates per cylinder....

 

[swall]

Mike--that was a good one, about the Harley rear cylinder being "cooled by accident". As a long time motorcyclist, I will remember that one the next time someone brings up Harleys (of which I own none).

 

[KrisB4]

It is more common to vary ignition and/or fuelling on different cylinders.
Eg cyl. #2-3 have richer mixture than #1-4 due to worse cooling.
IMO different cam profiles on differen cyls is not so good idea if you're after max power or efficiency (widely understood), as it will always mean compromises.
To make for different working conditions of each cylinders it is much easier to vary timing/fuelling (especially as it is done by the same ECU) saving the same cam profile (easier to manufacture) or each cylinder.

 

[SomptingGuy]

One other consideration in this thread is that there are some engines out there with different pin offsets on different cylinders, giving different piston motions and heat release rates. I'm thinking narrow-angle V engines, where the cylinder centre lines do not meet at the crank centre.

 

[evelrod]

Well, it may or may not be a good idea...I'll leave that up to the individual. However, I use a Kent SP 310 scatter pattern camshaft profile on my 1380cc Austin Mini Cooper race engine. Several mfgrs make such profiles including Kent of the UK and APT of California. Several enging builders use them to good effect and other builders, of equal reputation, I might add, do not. I have managed to massage several extra hp and a 'gob' of torque by playing with the timeing on #1 and #4.

Pat, FYI, I used a VW exhaust profile on a 1594cc Lotus twincam engine's ex cam along with a 'custom' intake profile to develope in excess of 205hp with 50mm Webers, way back when. VW forged piston blanks, too. Fancy that.

Rod

 

[GregLocock]

Hi Rod What rpm was that 205 hp?

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[evelrod]

I'll have to go by memory here, Greg. It was on the AVO engine dyno in the 80's...the power came on around 6500 and kept pulling pretty well to around 8500 where we got a distinct upward peak to ~9000 or a bit over. Rev limit was set at 9500 but in actual race trim, I have seen 10,000 on the tell tale when the cars owner forgot to shift out of second on the start of a race at Riverside (didn't break anything). I do recall that the cyl head was by Brian Hart and had 34mm ports just upstream of the intake valve...pretty big as our current ex F2 head is only 30mm. Then again, I am only hoping for ~165hp with Cosworth L-1's and 14:1 CR with 40DCOE31's for vintage racing.

Oh, one more thing, the 50mm carbs were ok on the dyno but did not work on the track at all and we switched back to 45DCOE9's with 40 or 42 chokes as I recall. I think we "estimated" that the hp was something like 185/195 with the 45's.

Estimates based on a bad memory ;-( ?

Rod