Camshaft regrinding for fuel economy
 

I am going to be working on getting my (first car!) 1993 Toyota Tercel running again over winter. While I've been going through some spare parts I have, I found a spare camshaft for it. I know the metro guys see some pretty nice mileage gains from swapping to the XFI cam. I also know that those lucky guys can get their camshafts reground at Delta Cams for $50!

So, anyway, I emailed Delta and asked about regrinding my Tercel camshaft and asked for a quote.

Can anyone recommend any other shops? Anything I should look out for, or is this something that basically any cam shop can do?

Delta regrinds cams for more or less duration and lift all the time and they make new cams from blanks.
They can do it.

Had I known about delta before I rebuilt my diesel I would have had them regrind my diesel cam for more lift and duration.

I used:

American Custom Cam
(626) 963-0011
128 S Valencia Ave # E, Glendora, CA 91741

for the last set I did. Its 75 each. May want to look at changing the LSA also. Of course this is all pointless if you'll be shifting the power band outside of your cruise rpm.

How would one change a profile to improve economy? What is the difference in the Metro XFI to the standard one?

What about extending the intake duration into the compression stroke? Would this be a cam used in concert with a high static compression ratio to get the more efficient power stroke without the detonation issues of high intake charge compression?

That's the most usual setup in the current generation of hybrids. So-called "Atkinson cycle", altough it's not the real Atkinson which actually uses an articulated crankshaft to provide a power stroke longer than the compression stroke. Before hybrids got mainstream, this setup was quite popular in stationary and marine engines, coupled to a supercharger to overcome the discompression generated from the longer intake timing, in the so-called Miller cycle.

Don't they do the "Atkinson cycle" because they do not want to pay royalties for the Otto cycle?

James Atkinson developed the original Atkinson-cycle engine to overcome Nikolas Otto's patent rights, but the currently so-called Atkinsons are actually Otto.

I spoke to the guy here Colt Cams - custom camshaft grinding a while back about a cam for a Metro. He seemed to at least know about the interest in ecomodding, which is more than most shops I deal with. Might be worth an email if nothing else. :snail:

So, Atkinson is actually better, but they only pretend to use it?

While some original mechanical systems are attributed to the various inventors, Otto, Diesel, Atkinson... The heat engine cycle names: Otto, Diesel, Atkinson, Rankin, Brayton each describe a particular thermodynamic cycle, named to honor an inventor engineer or scientist. You can see the wikipedia page for each.

Modern hybrid car engines are closer to Atkinson than Otto. But it isn't the valve grind per se. The intake valve cam is advanced and retarded by an oil pressure driven mechanism that is calibrated to allow the precombustion pressure to be optimized for the engine rpm. In other words, the cylinder is filled with the same air-fuel charge independent of engine speed. Just less than the charge that would knock. The mechanical expansion ratio is about 13:1 but the effective compression ratio is lower.

The key advantage is that for power levels from about 15% of maximum up to full power, the engine output is proportional to rpm, because over a wide band the engine is producing maximum torque - due to having the intake valves providing a nearly constant amount of charge. With this a car can be designed to run with the throttle wide open maximizing thermodynamic efficiency. Instead of reducing power by throttling the intake charge, you reduce rpm.

Lets say you have a car with a 200 hp engine, and you only need 40 hp to cruise (up a grade...)
With an Otto cycle engine, you find a gear ratio that puts the engine at a reasonable rpm and throttle the engine to half or lower of its potential (which reduce effective compression ratio - which reduces efficiency). With an Atkinson like cycle engine, the engine is at wide open throttle and you need to find the appropriate gear ratio for the engine rpm that delivers the required power. The engine rpm will be 1/5 of red line. You need a CVT but you get excellent efficiency.

In the Otto cycle car you can open the throttle to speed up. In the Atkinson cycle car you need to change gear ratios, first going to a higher ratio, the car slows down but the engine rpm climbs, then at the new higher rpm, which is producing more power, you slide the gear ratio up to the speed that uses all the power. You can see that having a big electric motor to give you a boost could allow the car to drive acceptably. So you only see full time Atkinson engines in hybrid cars.

-mort