Centrifugal cam advance, anyone? - Fuel Economy, Hypermiling, EcoModding News and Forum

beatr911 · 02-04-2009, 11:12 AM

Franco used to sell a centrifugal cam advance for VW's years ago. See this link: Franco Industries: Manufacturing and Sales of Automotive Performance Products.

This seems like a great idea for FE. VWVortex poster G60Jetta2dr says:

I am currently running the Franco cam gear.

I have the before and after dyno pulls on the wall next to my monitor. Yup I gained no horsepower.

I did however go from 184.2 ft/lbs peak to 204.6 ft/lbs.

Before the cam gear my motor had a torque bulge above 175 ft/lbs from 3400 rpm to 4700 peaking at 184.2 ft/lbs.

After the cam gear the torque bulge above 175 ft/lbs is from 2300 rpm to 5200 rpm peaking at 204.6 ft lbs.

Before the cam gear my motor made 150 ft/lbs from 2500 rpm to 3400 rpm then ramped up above 175 ft at 3500 rpm. Now my graph is above 150 ft/lbs when the dyno starts plotting at 1700 rpm.

I very pleased with it.

Llew.

...So it doesn't make much horsepower, but the low speed advance gives a big boost in torque - and right in the FE driving sweet spot. For all us that want to optimize the engine for higher torque in the low speed range but not sacrifice top end power for the occasional high loads, this seems like the perfect solution.

Has anyone tried one of these and measured FE gains? I want one, may need to be custom, for my Ranger.

TestDrive · 02-04-2009, 11:51 AM

Will have to think about it more, but off the cuff - it looks plausible.

some_other_dave · 02-04-2009, 10:26 PM

I think the main difficulty is trying to match the amount of advance at various RPMs with what will actually help the most at that RPM.

Pretty cool, though! Like VANOS, but much cheaper and easier and simpler! And not computer-controlled for all circumstances, of course.

-soD

almightybmw · 02-05-2009, 02:16 AM

interesting. I'm sure the vehicles its applicable on is limited. Useful for older engines that don't have fancy VVT or such. Would be interesting to see this on various vehicles, especially ones that have awesome FE and ones that have poor FE.

Frank Lee · 02-05-2009, 02:57 AM

Gotta wonder why these cheap, simple devices weren't put on at the factory?

ncs · 02-05-2009, 10:01 AM

There's a patent on it, but it looks like it's ok.

Centrifugal control assembly for camshaft advance and retardation and suppression of cyclical vibration - Patent 5609127

Going by the pictures, that cam gear is huge. I suspect there's only enough gear space on single overhead cam belt driven engines for a mechanism like that. Chain driven cam gears are much narrower, and belt driven dohc gears are smaller. To make a smaller version, the weights would have to be made out of a heaver metal which could drive the cost up too much. Lifespan of the springs might be a problem too.

Also, it only provides 7 degrees of variation. Modern active cam timing has 35-40 degrees.

beatr911 · 02-05-2009, 10:46 AM

Yeah, it was only available for VW SOHC engines. I think belt drive SOHC engines because the cam gear is big enough to house the weights.

Frank, I wonder too. Spring advance has been used for decades in distributors without major problems. The complexity issue doesn't add up because DOHC, 4 valves per cylinder with VVT or vtech or something is certainly more complex. Must not have gone OEM because greater gains were had in just going to 4 valve heads with VVT in the future.

Ford put alot of re-development into the 2.3 (S)OHC engine when everyone else was deep in to a parellel line of DOHC engines. This item seems like logical develoment that should have happened if a MFR was sticking with SOHC for some time.

Daox · 02-05-2009, 10:56 AM

Well, its also not very flexible. Ideally, you want to control cam advance based upon rpm and load, not just rpm.

beatr911 · 02-05-2009, 11:57 AM

Daox, agreed for where we are with todays engines. These things originally came out in like 1985. Manufacturers were still really struggling with meeting emissions and O2 sensors were only recently widespread.

Ideally we'd have infinitely adjustable fuel, spark, cam lift and duration independently for intake and exhaust, compression, bore and stroke, but we're not there yet iether.

beatr911 · 02-05-2009, 01:37 PM

Had to dash off to a meeting. Finishing the thought...

Carburetors are still made and being refined for old engine applications. Fixed timing single cam engines like the metro, vw, ford 2.3, etc are still around just like the old V-8's and will continue to be around for some time. Because a sophisticated modern VVT retrofit is not really an option, this centrifugal cam advance idea seems like a solid incremental improvement for the older engine designs.