Truck Tonneau Covers and Mileage?
 

So I'm thinking about building a tonneau cover for my truck. I found some good plans online the other day. My main reason would be to help with gas mileage. Does anyone know roughly how much of an improvement in mileage a cover usually makes? I've read 10% but that's from the manufacturers. Although if I could pick up even 1mpg extra it would be well worth it. Also I'd probably make it a little trick with a raised bowtie or flames in the center of it.

So if anyone has one or knows somebody that has one can you let me know if I'll see a big enough gain in mileage to warrant the time and money?

Wouldnt just opening the tailgate reduce wind resistance just as much? When he knows he gonna be doin like 50+ for a good amount of time, my friend just lets it hang

Nope.....numerous tests have shown that gator nets and leaving the tailgate open have negative effects on mileage.

did they say why it creates more resistence?

Yes....with the tailgate up a pocket of air forms in there to take up the space and most of the air goes right over this pocket. If you open the tailgate the pocket can't form and you get turbulence down there.

this is correct. picture a convertable with a soft top driving down the highway. the top is held rigid because the air inside the car is at a higher pressure than the air rushing over it. same concept with the air in the bed of a truck.

You can get a new tonneau cover off Ebay for $75-100 so you might be better off buying one and then put the bowtie in it. What year truck do you have? I have a brand new tonneau cover sitting in the box for 91 SS454 that might sell.

Mine's a 97 shortbed. They cheaper ones on ebay are probably soft right? If I make my own it will be hard with vinyl over it and cost me about $75 or so.

Yes, I'm talking about the soft tonneau covers. I personally don't like the hard covers because I've helped so many people move stuff that if the stuff sticks up, the hard cover has to come off. Heck, I fit my engine hoist in the back of my truck with the soft cover still on, I just had to unsnap the last couple of snaps to give it a little slack. But definitely put a cover on it. It helps keep stuff dry and helps with gas mileage.

Yeah gas mileage was my main goal....now with the whole raides pattern and such I'm looking for some style points.

I'm gonna do the cover, a K&N filter, 0-30 Synthetic oil, and maybe synthetic gear oil. I'm hoping for just a 1.5-2 mpg increase. This would give me an extra 30-45 miles per tank. This would be great since I only get about 11mpg right now. The lift kit and 35's don't exactly help though :wink:

What are you running for an ignition system? I put in the GMPP distributor, Hypertech coil and MSD wires and it made a huge difference. The truck runs a lot smoother and cleaner and picked up almost 1 mpg. I average 11 mpg with the 454.

Stock GM Ignition. All the ignition parts would take a long time to make up the price difference in gas mileage.

Get the Hypertech coil at least. It's so much hotter than stock it will literally clean out the combustion chambers by burning off the carbon buildup.

Not it won't.
Doing a coil upgrade won't help, going to a setup like CNP will. Even then it won't do any cleaning of the combustion chambers.

Those tires and the lift kit are the biggest problems with your truck. The cover will only make measurable results with highway speeds. Anything 50 and lower will take 10+ years to make up for the cost of the cover.
Try inflating the tires up a bunch, that should help too. Oh, and a grill cover made from sheet aluminum could also help. Just get it up as close to the back of the grill as possible.

A grill cover?? Won't that kill airflow to the radiator? Maybe I'm thinking of something different than you are??

It's rather cool out and if I'm not mistaken there should be at least a foot or more between the back bottom edge of your bumper and the radiator. You'll have plenty of air flow to the radiator without the grill opening. I wouldn't do it if you were towing in the summer... just an idea. I'd go with a cover first though and measure the results. I still think you'll gain a lot by bumping up the tire pressure a bunch.

Yeah but bumping up the tire pressure will cause uneven tire wear as well. I'm gonna do the cover and I just found some plans for a slick CAI that I'm gonna work on....should only cost about $25-$30 if I can get an K&N off Ebay cheap.

I'm hoping between the cover, CAI, synthetic oil at next change, and maybe synthetic gear oil I can pick up about 2mpg. Maybe wishful thinking though.

A hotter ignition will definitely help clean up the combustion chamber by burning off all the buildup. I've seen it personally on several vehicles and my boat. I've measured the performance/mileage increase on my SS454. I picked up a solid 1 mpg with the distributor/coil swap. I had already changed the plugs and wires and it didn't change my mileage. With a hotter ignition you can also increase the plug gap a little which also helps make it more efficient. The 35" tires hurt big time, I ran 32" tires on a 4 cyl turbo 4Runner and the best I could get was around 15 mpg corrected for the bigger tires. But in the end, I would be surprised if you can pick up more than a 1 mpg increase.

You won't get a hotter ignition from a coil swap like you recommended. Also I don't know what you're trying to say about combustion chamber cleaning but no ignition will "help clean up the combustion chamber by burning off all the buildup." Buildup as in carbon is created during the combustion event. Combustion comes after ignition so how could a hotter ignition be cleaning a combustion chamber? The only way to clean a combustion chamber is to wash the cylinder with water (steam cleaning), mechanically scrubing, or a really rich fuel mixture. As for a CDI ignition, that's a good starting point since it'll give you better gas milage at anything below 2000rpm. Above 2000 the CDI setups are sparking multiple times.
About the tires, running high pressure isn't going to cause funny tread wear unless you go out of spec or have them mounted on an incorrectly sized rim. They're radials right? That's the advantage of radials... flat contact patch all the time if kept within spec tire pressure. The increased pressure decreases the rolling resistance of the tire and stiffens up the sidewalls when you corner, both yeilding lower rolling friction and increased milage.

i think he migth be talking about carbon build up on the valves, not in the cylinders. although i dont think an ignition would clean the valves either. i ran Run-Rite through my old 86 iroc. did a good job gettin al the build up off the valves.

Carbon buildup is the result of incomplete fuel/air combustion partly due to a weak spark/flame situation. Using a longer/hotter spark will allow complete combustion of existing air/fuel and will also promote burning off the buildup. Stock ignition systems are pathetically weak. Manufacturers don't run high energy ignitions due to warranty/longevity concerns. I ran the JAcobs Omni-Pak on one of my old 69 Camaros with a POS 307 motor. I finally decided to do a cam/head upgrade for more power and when I pulled the heads off, the heads and pistons were incredibly clean. I did a head swap on the Yamaha 650 jetski motor in my boat and I had been running the MSD coil/wires on it and the head and pistons were spotless and that's a 2 stroke with oil/gas premix. And I saw the deposits burning off on my SS454 right after I put the distributor and Hypertech coil on it. The exhaust had some smoke coming out for about 10 miles of driving. It has never smoked since then, but it's a low mileage motor so it couldn't have had too bad of deposit buildup. If you're getting any kind of pinging from the motor, then you probably have some buildup in the combustion chamber or on the valves.

I'd agree with you that in 69 the ignition setups were pathetically weak. Once emissions was a concern ignition systems from OEM have stepped up rather nicely. The CNP on today's gen 3 chevy motors are excelent setups that will surpass any CDI or DIS (wasted spark) setups that aftermarket companies are still offering. The stock GM HEI setups of the 80's are awesome setups in there own right. The only problem with them is there single coil secondary voltage troubles at high engine speeds. Everything else is rather excelent.
I also disagree that a complete burn decreases build-up. Build-up of deposits in the combustion chamber are the result of completely burned mixtures. The buildup that's left behind is formed from complete combustion of all the impurities in the gas, oil, and air. Dyno juice from the PCV and ring blow-by is the main source of build-up. No amount of ignition upgrading will chean the chambers and if anything it'll promote the burning of ALL impurities creating more build-up.
A clean chamber has everything to do with your oil, ring condition, PCV, and detergents in the gas you burn.

Stock HEI setups are notoriously weak. They are better than the 60's ignitions(except the transistorized ignition) but they were only created to allow the motors to run bigger gaps and leaner carb mixtures so they would pass new emissions tests. Then GM stuck with the carb style HEI setup on it's trucks for years even though they were EFI. The Grand National ignition and LS1 ignitions are awesome, but the HEI is very weak. The examples I gave above of my own vehicles is pretty solid proof a strong ignition will clean out buildup. I've never had the top end of a vehicle cleaned or had it run through injector service. So either someone snuck into my garage and poured top end cleaner into my engine while I was sleeping, or the hotter ignitions helped clean out the chambers. Obviously a hot ignition won't clean off valve deposits but it will keep the back side of the valves clean. He's looking for ways to increase gas mileage and a better ignition system is probably the best bang for the buck. Tonneau cover, properly inflated tires, free flowing exhaust, free flowing intake, bigger plug gap with hotter ignition. Oh, and don't forget the Z-Max engine treatment with Linkite and the Tornado! :roll:

Hahahah the infamous tornado. As far as free flowing intake and exhaust I've got that half covered. My exhaust consists of stock exhaust manifolds, new cats, two straight pipes out the back. I also found a plan for a good looking cold air intake that I'm planning on building.

I suggest we go back the discussion of tonneau covers. I got my truck a little while ago and the gas mileage sucks for a V6. Granted it has the aerodynamics of a parachute, I want better gas mileage.