Which gets better mileage? 305, or 350?

[SUX2BU99]

My truck has an air dam that I think was used on the later Suburbans and Blazers. It looks good but it's also getting beat up from anything that has a slope to it when I pull in (like my driveway) and it does block air from going up into the rad. If you are going to block off the nose to improve aerodynamics, then you are wise to get the air deflector that installs below the rad and do NOT get the air dam. Those F-bodies need the underbody deflector to direct air up to the rad.

If you really want to get serious about cleaning up the drag coefficient then the front of the vehicle has to be as flush as possible. All the gaps have to be filled or as tight fitting and flush to each other as possible. Recesses create drag. Think of the Charger 500 and Talledega Fords. Put headlight covers (clear if you like) on, tuck the bumper, tighten the hood clearance, etc.

[Skunksmash]

I have to disagree with synthetic oil not helping MPG. In my experience, several times i have seen it work. Now, i'll give it to you that this was not on one of these trucks. I have not tried it on one yet but i intend to. I had a 95 GT mustang where you could literally feel the difference between the two types of oils. It got anywhere from 1-3 MPG better with synthetic oil. Same goes for my honda Civic. There was no noticeable change in the way it ran, but i would closely monitor MPG in that car (and i still do) and it leaped up from 26 MPG to 31 MPG with the only change being the change to synthetic oil. Also noticed this on an Oldsmobile i used to have.

One other thing that seems like it would help out MPG might be the switch to an electric fan, instead of that factory belt driven one. Also, an electric water pump might help out, but i have no idea i have never had an electric water pump. It just stands to reason that if the engine does not have to work as hard, it can save a little bit more gas.

[Captkaos]

You would be disagreeing with reality and facts, because I tested it on my 73 w/454/4speed  when I switch and I also tested it on my 87 305TBI/700R4 when I switched.  The Crew Cab is up for a switch soon and right now it gets 13/17.
Comparing it to a Honda 4 cylinder wouldn't be a good comparison IMHO

[eventhorizon66]

I've heard that synthetics aren't good for flat-tappet cams anyways.  Apparently they lubricate so well that the lifters don't have enough friction to rotate properly in their bores which accelerate cam/lifter wear.  I switched to full sythetic in my mother's Acura TL-S and my sister's Toyota Avalon; neither saw an increase in mpg.  I just did it to extend the change interval and reduce sludge buildup.  A 5 mpg gain in a Civic seems bogus.  Something else must have changed.

Electric fans will increase fuel efficiency only if they stay off most of the time.  If you do mostly city driving, which would cause them to remain on most of the time they will not improve mpg due to the increased load (drag) at the alternator.  An electric water pump absolutely would not help out, they are only good for dynos and extended low speed (and rpm) cruising situations.

[VileZambonie]

hmm my reply has vanished.  Oh well....

Blocking off the radiator is not a good idea. F bodies use the air dam to direct air flow through the cooling system. Without it they overheat.

As far as synthetics go every company marketing their oils says the same thing, longer life, better mileage etc but the bottom line is the difference you spend in $ on the synthetics equates to the $.01 pennies you save in fuel mileage. Lower viscosity will produce less windage. To change to synthetic and expect noticeable increases is not very realistic. You will typical notice a difference after an oil change especially if the oil is broken down and contaminated.

A 350 can produce more power and less fuel consumption than a 305 if the 305 is working harder. The engine should match the vehicles intended useage.

[Captkaos]

At $6 a quart compared to $2 a quart Vile is correct.

Vile, Where did it go?  It wasn't removed based on the admin logs...

[VileZambonie]

No idea. It just vanished  Oh well

[Lt.Del]

Bermuda ThreadAngle

[Stewart G Griffin]

When i switched to Mobil 1 synth 10W-30 about 2 months ago, i got a 1.5mpg increase.  But my latest figures are now close to the same as my orignal figures----15.8 mpg.  So i'm thinking it may have been because the previous oil was really broken down---it was the same oil as when i bought the truck about 2 yrs ago.

Right now i would prefer to state that mpg increases due to switching to synthetics are inconclusive at this time.

[lowriderbowtie]

I tested sythnetic oil in my 2007 kawasaki ninja zx-6r..i was getting a constant 35.6mpg with dinasaur oil, and i switched to amsoil 10-40 and my milage has gone to 37.9 on my last fuel up.  oil temp dropped quite a bit also

i dont think i would waste money running synthetic in my old junker truck..but it does great in the quad and bike

[VileZambonie]

I run synthetics in my toys too but my Jeep has 300K original miles on nothin but cheap oil. I just did my oil change on it the other day and used synthetic because one of my vendors gave me a few free cases so I ran it. There was no fuel mileage increase.

[78 Chevyrado]

In my 87 I had a 700r4 tranny.  With that said, I got better mileage out of the 400 I put in it that I did with the 305 that came out of it.  Where i was driving was a bit hilly, and the 400 had enough power that the trans never downshifted and rarely unlocked the converter, whereas the 305 had to drop down to 3rd on almost every hill.  With a 3 speed auto though, smaller size probably = better mileage.  If you live where it's mostly flat ground, te smaller engine would do just fine since there's no hills to climb.  I also had a tall rear end with a 2.80 to 2.90 something ratio and 32 inch tires so at 70MPH the engine was only turning like 1600RPM.

[eventhorizon66]

A Honda Civic now a Kawasaki Ninja seeing gains of 5 mpg and 3 mpg respectively.  I find that hard to believe.  I'm not saying that you're lying about your mileage, but rather that something else must have changed, like the driving style or route taken, maybe different tires (lower frictional losses, maybe lighter), etc.  The only thing a synthetic can do is reduce windage (very slightly) and reduce the friction on bearing surfaces (very slightly) and the engines in these two machines are already built for very high efficiency.  Maybe you might see gains in something like a 1790 cubic inch V12 engine out of a Patton tank where the bearing surfaces are large and many, just not in one these tiny efficient modern engines.  In fact if a civic were getting as poor as 26 mpg (my mother's mid-size 3.2 V6 averages 25-26 BTW) it was either doing alot of idling in traffic or being driven very aggressively; same to the ninja (flying down the highway, weaving in and out of traffic, at triple-digit speeds much?) wouldn't that thing get closer to 45 mpg if driven normally?  My stepdad's 850 lb Harley can get 35 mpg.

BTW: Try not to get irritated by anything I said here.  I'm no expert and I could be wrong, but I'm just voicing what I think is logical on the subject.

[Dragon]

When i switched to Mobil 1 synth 10W-30 about 2 months ago, i got a 1.5mpg increase.  But my latest figures are now close to the same as my orignal figures----15.8 mpg.  So i'm thinking it may have been because the previous oil was really broken down---it was the same oil as when i bought the truck about 2 yrs ago.

Right now i would prefer to state that mpg increases due to switching to synthetics are inconclusive at this time.

That statement might be true of any Car/Truck/Van made after 1986(If not Newer), but not so with anything under that timeline......  Newer Cars/Trucks/Vans are able to handle Synthetics alot easier, and yes can even see Mileage increase due to less friction....  Older Cars/Trucks/Vans are more likely to see no benefits at all, but you are more likely to see a Nice Large Expensive Synthetic Oil Slick in your parking space/driveway(Thinner Synthetics will find the Cracks,Pin Holes,Flaws that are common in the older engines, and it will make an escape path quicker than the thicker Conventional Oil will).....    

[Skunksmash]

Well, i can say this. My mom has an 07 trailblazer, and my granny has one of those small Lincoln suv's. Whats it called? MKX? MXK? I dont know but i do know that both of those engines call for syntetic oil only. The trailblazer even says that you may void your warranty if you dont use the oil. The lincoln will not even run right on the old kind. I once had to have the manager re-change the oil in Granny's 05 Lincoln LS (a 4 door sedan) because when i drove it up to the quick lube, it ran fine. I told them only sythetic oil. When i tried to leave, i got a few miles down the road and it ran like hammered crap. I realized the only thing that had changed was the oil, and so i went back and asked what oil and he said they had put in, and it was some cheap crap regular. They changed it back, and what do you know, the car ran just fine. Now i know this does not prove anything, but it does tell us that the automakers are switching to run sythetics more than the old stuff. If so little was to be gained by using synthetics, then why would they even mess with it? Not saying our old trucks will see any noticeable difference.