Darwin's back...what the...?

[Darwinskeeper]

Just got Darwin back from the shop last Friday. As great as it is to have my wagon back on the road, I'm now faced with a little mystery. While I was having the short in the turn signals fixed, I also had several changes made that I thought would improve efficiency. The Comp Cams 252H (206/206 [email protected]; .425/.425 lift; 110 sep) stick was replaced with a new Crower Level 1 (182/190 [email protected]; .386/.387 lift; 114 sep). The stock rocker arms were replaced with Comp Magnums with 1.52/1.60 ratios. A 195 deg thermostat was added and a distributor recurve kit was added. The problem is that my mileage seems to have dropped a bit. During some recent road tripping/testing I recorded 18.5mpg on a tank on a 170mi trip that was 98% highway. Last Summer's road trip ended up netting tankfuls in the 20-24mpg range. In other words, I did all this work to improve fuel economy only to see it drip. ](*,)

I'm now trying to figure out what's wrong. I've already noted that the tire pressure was a bit low (in the 28-32psi range), I have since brought the pressures back to 35psi. I have also removed the spoilerette that is under the radiator. The one on Dar takes a lot of abuse and is in danger of falling off. Those things may help, but I don't think they explain the difference.

I am wondering if it is possible that sitting in the shop has caused the gas in Dar's tank to decompose and possibly clog the fuel filter a bit or leave deposites on the carburetor. I am going to run the tank down to 1/4 or below to get rid of any bad gas and then change the fuel filter.

Other possibilities are that the recurve kit was installed in a way that reduced distributor advance and that the cam/rocker arm combination is making things worse.

Any thoughts or suggestions?

 

[malibu795]

err put it back to the previous setup....

 

[mhamilton]

The recurve kit may be the problem. I know the 305 and 229 do not like more advance, and economy is best with the stock timing curve. The 350 and 4.3L may be able to take more timing, but not sure if it will help or hurt your economy.

Tire pressures doesn't seem bad at 28 psi. Agree about the front air dam, not a huge aerodynamic gain compared with the brick of a front end. It's more important for low speed cooling (not recirculating the hot air back around).

Not sure what to make of the cam change. It's closer to the stock profile, and the stock engine could do better than 18 mpg highway. Might as well start with the easy things, and see how it does with OE timing.

 

[mhamilton]

Was just looking at the Crower catalog. They do offer the same cams for the semi-odd V6 and 4.3L. The Level 1 offers more lift and intake duration... but why in the world did they trim exhaust duration? Could be due to the lobe centerline, wanted to have the valve closing earlier, but seems odd.

Also could be all that extra lift. The Crower is already more than stock, plus the extra ratio rocker arms, the valves are spending more duration at 0.05in.

Just things to consider if the timing doesn't help mileage. But my experience, the "recurve" doesn't work well for a driver's rpm range. I tried a recurve kit on my 229 once, it was a dog on the highway, and I also saw an economy drop.

 

[79Elky]

Regarding timing advance on the 200 and 229...

When I got my '79 Elky, the engine block appeared to be a commercially-rebuilt as it had some sort of aluminum tag pinned onto a driver's side front boss on the block. The engine and transmission (3 speed manual) were very clean and freshly painted orange. Eventually, I discovered the heads have bad valve seals; #4 cylinder oil-fouls and the plug must be used with one of those oil-fouling adapters. It would foul and not fire within just 2000 miles. Not having time and the Elky being my daily driver, I just put up with the anti-fouling adapter. My mpg, with about 25% city, 75% highway, was usually about 18 mpg.

I also have an '88 fullsized Crapice wagon with Olds 307 V8. I've taken it to the strip a few times just for sh*ts and giggles cool.gif I discovered that when I advanced the timing by 4 to 6 degrees, I not only picked up considerable low-end torque but the mpg also increased from 18 highway to, on occasion, 22 mpg. That dropped the ET from around 18.8 to 18.15 or so, so it wasn't just a seat-of-the-pants impression.

After a year or so of driving the '79 Elky around, I tried advancing its timing, too. I eventually advanced it 6 degrees and found the bottom end torque was WAAAYY better, and the mpg, just like the big heavy wagon, also increased, now hitting 22 most the time and a best, so far, around 24.

I also have an '83 Malibu wagon with 229 and, I guess, 200C transmission. That engine locked up before I had a chance to try the same timing advance trick but I swapped the engine/transmission from my junker '84 Elky into it. My son used to drive the car from home in Connecticut to school at Virginia Tech and he just wouldn't keep track of the mpg, so I've no real idea what the original '83 drivetrain did, nor how the '84 engine did once I advanced the timing. He did remark the "new" engine seemed much more "powerful"; it no longer downshifted to 2nd when going up a long hill on I-81 down in Virginia, and he could even pass most people. I cautioned him not to overrev the thing but I'm sure, being 20 yrs old, the music that engine made at 3500 rpm probly was too much of a siren's call for him to ignore :lol:

Anyway... so he graduated and took a job out on the West Coast, buying his own car and leaving me the 'Bu again. Since getting it back, I've had several opportunities to drive it for several weeks and play with the timing. With the timing stock, it would never do better than about 18 mpg and interestingly, it didn't seem to matter whether it was on the street or highway: 17 to 18 all the time no matter where it was driven. Then I advanced it 4 degrees and hey el presto, mpg increased to around 20, once hitting 21.1 on a long highway drive. Raised it another 2 degrees and omi.... 20 was now the worst it'd do, and it did 22.5 several times with 25% city, 75% highway, most of the highway at 75 to 80 mph where the rpm is well over 2500.

All of the above engines are WELL-USED except probably the '79 Elky's 200 which, as I mentioned, appeared to be a fresh short-block when I first got it. I know for a fact the Olds 307 has over 300K miles (I put 150K on it myself); the '83 Bu, when I bought it, already had over 200K according to the prior owner and my son and I've put over 100K on it since I bought it; the '84 Elky odo was over 100K but the prior owner had no idea whether that was once-over or twice (from the frame rotting, it appeared closer to over 200K); and since I suspect my '79 Elky's block is a rebuilt short-block, who knows what it's got but I've put 90K on it myself in the past 3 years.

So the possibility exists that advancing the ignition timing as I did was making up for well-worn loose cam timing chains and consequent retarded ignition timing. I've never heard pinging or detonation on any of those engines with the advanced timing.

Just one guy's experiences.

 

[Darwinskeeper]

79 Elky,

Thanks for the info. Since the mpg on both Darwin and my 80 Elco were in your "before" range 17-19mpg, I'm planning to get a timing light so that I can see what effect playing with the timing has on my mediocre mpg. ](*,)