Indirect interest xpost: Laycock moved to El Cajon, CA

[steveg]

Laycock de Normanville technology is now owned by Gear Vendors, Inc. of El Cajon, CA [source Wikipedia]:

https://www.gearvendors.com/index.html

The site has lots of interesting setups on classic cars, such as Leno's Bentley Speed Six and LaFrance fire engine.

Evidently our overdrives can be used in very high-horsepower setups such as dragsters and supercharged musclecars.

There is a lot of information about the theory and practice of over/underdrives.

No financial interest - just enthused about the site. Always happy to see somebody actually, you know, Doing Something here in California.

 

[57_BN4]

They have some pretty big fuel economy claims there. "not uncommon for blown car to get 100% better fuel economy"

The Ford road tests done in 1957 recorded an increase in fuel consumption with OD due to the engine being 'off cam' at cruise plus the increased mechanical losses in the gears.

 

[Bob_Spidell]

Makes sense. It takes the same HP to move a car of given weight and drag characteristics at a given velocity regardless of the gearing. IOW, if you're running at lower RPM, it takes more torque to produce that same HP, and more torque requires a larger throttle opening (hence greater fuel consumption).

I expected (hoped for) a 1-2MPG highway mileage increase when I installed a 3.54 diff in my BJ8. In reality, I might have gotten a half-MPG increase (and some of that may have been expectation bias).

Also, it appears to me that GV's high HP claims are for their own design O/Ds; have always heard an A-Type Laycock O/D is good for about 200HP.

 

[HealeyRick]

They have some pretty big fuel economy claims there. "not uncommon for blown car to get 100% better fuel economy"

The Ford road tests done in 1957 recorded an increase in fuel consumption with OD due to the engine being 'off cam' at cruise plus the increased mechanical losses in the gears.

I can see how their claims could be true. They aren't talking about 20 mpg cars getting 40 mpg. Look at the cars in their testimonials. Big block blown cars with really deep gears. Probably getting 3-6 mpg. Drop their highway speed by 1000 rpm and you'll see some high percentage gains in mpg. 'Course now you're getting 6 mpg instead of 3 mpg.

 

[57_BN4]

Bob- your diff change isn't quite the same because you aren't adding gears, bearings and hydraulics into the transmission system. I read that it takes about 25hp to achieve cruise speed and lets say 1hp is lost in the overdrive. 1/25hp is a 4% loss you don't have with the diff change. Your half mpg is about 2.5% improvement vs 4% reduction with OD. [completely unscientific analysis there]

No properly designed engine is 22-28% more efficient when operated 850rpm less than it would otherwise. If this were true OEMs would have hyped it for years and certainly not gone to the trouble of fitting a different ratio diff to the od equipped vehicles.

The website FAQ reads like something written by a technician in overalls during his smoko break

 

[steveg]

I and two fellow Healey drivers have found that by decreasing freeway speed from 70mph+ down to 62mph - our fuel consumption changes from around 16 to 22mpg - this decrease is less than 850rpm. This is approximately 38% better mileage, more or less. There must be a sweet spot for mileage that the OD tries to reach. Also unscientific, but observed.

No properly designed engine is 22-28% more efficient when operated 850rpm less than it would otherwise. If this were true OEMs would have hyped it for years and certainly not gone to the trouble of fitting a different ratio diff to the od equipped vehicles.

The website FAQ reads like something written by a technician in overalls during his smoko break