crappy gas milage: help me figure why

  • Thread starter Thread starter Anonymous
  • Start date Start date
so a heavier car would exert more pressure...so with our light mustangs, we are fine....
 
OK
Here's a way. I took the specs on my tires
1720 lbs @ 45lbs cold, divied it and it comes to 38.22 lbs. per lb of air.
the truck weights aprox. 4,000 lbs divied by 38.22 comes to 104.65 now I have 4 tires so divied that by 4 gives me 26.16 lbs of air per tire. Now I think that would only be right it the car weight the same on each corner, but a car with the front lower than the back would have more weight on the front tires and inturn need more air than the back.. Right?? You could take a race car scale and weigh all four coners and figger from there. What do you think..
tim
 
Damn...i think you guys have done as much analysis as possible on tire pressure...LOL.

If your missing almost 10MPG then tire pressure isn't going to fix it unless you have been driving on flats! You said most were over 30 and that's good. To much pressure and you will bald them in the center as that will be the only part of the tire acutally touching the ground.

Does your car coast ok? If it does then you probably can rule out something like a dragging brake. The other thing is after the drums and rotors (if you have disk) are cold drive it around the block and feel the roters or drums. If they are dragging they will be burning hot and a simple drive around the block with minimal brake use shouldn't generate to much heat. If that isn't the problem then the spark plugs should tell you the story. There isn't to much else it could be other then a gas leak of some kind.
 
Hmmm...

The only reason you would want lower your tire pressure would be to increase your handling - theoretically. Sure, you increase traction control but you are also increasing tire friction because of a greater patch surface area you are creating with lower tire pressure. This is not good for standard tires (non-performance rated tires). So, driving around with lower tire pressure is actually more harmful than helpful.

Most tire manufacturers recommend a few pounds less than the maximum allowable per tire. Not several pounds less than the maximum allowable pressure. Look at what happened a few years ago with Ford and Firestone.

Ford had recommended a tire inflation pressure for their SUVs of 26 psi (or something of that nature), which was less than the 30 psi inflation pressure recommended by Firestone (I think the max was 35 psi). After the recall Ford announced that it was informing its SUV owners to inflate their Firestone tires to 30 psi.

Something to thinkable.


-Chris
 
Well, that's not quite the whole story...but...

I increased my mileage by about 5 MPG by going from 27 psi to 42 psi. I'm just going off my experience. I've always run about 10% less then max cold (and I usually fill semi-hot so it is actually a little more the 10% when the temps even out). never had an issue with uneven wear, and get good mileage.

Slade
 
The tire spec regarding load of pounds at a given pressure is the load capacity. It is not to be used to back calculate an inflation pressure. Basically, if you have 4 tires with a 1400 lb load rating, you don't want to put them under a vehicle that can weigh 6000 lbs fully loaded. If your loaded vehicle is going to weigh 5600 lbs with those tires on it, then you better have them inflated to at least the maximum pressure or you risk severely over-loading them. Inflating at higher pressures will generate less heat which is typically what breaks down a tire. Under-inflated tires generate heat and may fail. Luckily, the Mustangs and Falcons usually do not come near the load capacity of the tires. But if you go tire shopping for a '65 Lincoln Convertible, you better read the lables, especially considering that the weight distribution is not 50/50 when you have a big block motor sitting over the front tires.
 
Blunt but basically, true.
If your missing almost 10MPG then tire pressure isn't going to fix it unless you have been driving on flats!
Click to expand...
Notwithstanding, Chaz, we have some other issues to consider. I point the finger at poor ring sealing (you had a re-ring by ol' walking death mechanic, didn't you?) and deck height, being both contributors. also, there's not enough peripheral info (cc's, dish, deck height, etc) to fully evaluate the situation yet.

Adam.
 
good point adam

very good point. I need to do a compression test and make sure everything is cool

funny thing is...thta even after all that engine work...I am still getting around the same 180 miles a tank (factor in the larger tires and I am guessing 210)

yikes thats 14mpg....

I am betting mechanic used a thicker head gasket, decreasing my compression
 
One thing to check is your choke adjustment. Closed when the engine is cold, of course, but make sure the choke is fully open when the tempurature needle comes up towards operating temp.
Vacuum advance signal from the carb, not manifold.
As for tires, I run at 38psi.
Rick(wrench)
 
Check for vacuum leeks in and around the carb and if your running bigger tires and haven't corrected the speedo gear you’re probably getting bad odometer readings which are throwing off your calculations.
 
addo":3ry6l509 said:
Blunt but basically, true.
If your missing almost 10MPG then tire pressure isn't going to fix it unless you have been driving on flats!
Click to expand...
Notwithstanding, Chaz, we have some other issues to consider. I point the finger at poor ring sealing (you had a re-ring by ol' walking death mechanic, didn't you?) and deck height, being both contributors. also, there's not enough peripheral info (cc's, dish, deck height, etc) to fully evaluate the situation yet.

Adam.
Click to expand...

If the ring job by Ol' Walking Death hasn't seated yet, do the ol' BonAmi treatment. Of course, that won't help low compression RATIO, poor air/fuel mixture, etc. I would verify the ignition advance at cruise speeds also.
Joe
 
myhead is spinning


actually, I started by throwing in some carb cleaner and my choke, which seemed to not work on my cold engine, now works

I had already inflated tires to 42psi each

this weekend I am checking for gas leaks...

then I am going to try a compression test and get that damn timing light...

I already see a difference that is seems smoother...I mean it rolls better...I think the tires had a lot to do with it so far...
I will keep tyring things
 
how do I verify ignition advance at crusing speeds..?

I better break out my repair manual
 
rag had a good point about the odometer. if you increased tire size you need to correct your mileage when calculating. this could be worth a couple mpg unless you changed the speedo gear already.
frankie
 
Chaz, at cruising speed, you have to infer what the timing is. It will be some combination of your initial, centrifugal, and vacuum advance. The initial is what you set and will remain constant. To see what the centrifugal is, you will need to plug the vacuum line to the distributor, and rev the engine. Typically you might do it in 1000 or 500 rpm increments. It is usually going to be fully advanced by 3000 rpm. You will either have to mark your dampener with a bunch of additional marks or use a dial back timing light. These reading represent the sum of the intial and the centrifugal and would represent the total timing under wide open throttle conditions, where engine vacuum is low. Subtracting off the initial timing lets you see how much centrifugal advance is contributing at each of the reading.

Total advance at cruising will vary with throttle position, load and engine rpm. But to get an idea of the maximum, read the timing with the vacuum hose connected at idle. Assuming you are connected to manifold vacuum, then this will be the highest vacuum advance achieved. This number is the sum of the initial and the vacuum. Adding in the centrifugal at a particular rpm. would give you an idea of the maximum advance that you could see at cruising speed.
Clear as mud?
Doug
 
funny but the mechanic will do the same thing for me without the math...he gives me one number...price

just being a wiseass but that is wayyyy over my shadetree head....

I just learned how to turn the distributor...

thanks fo rthe help though.. I MIGHT try these things sometime...I am actually afraid....

chaz
 
BE AFRAID CHAZ VERY AFRAID lol :lol: :lol:
A timming light is very important for performance, milage, Idle and such. If you have just been timming it by ear then thats were your milage is I would think...
tim
 
You must log in or register to reply here.

Similar threads

JoeCrozier
All Small Six Fuel line routing from pump to carb
Replies
3
Views
303
JoeCrozier
JoeCrozier
GreasyNRusty
All Small Six Effective 170 Exhaust System-What Should It Be?
Replies
10
Views
676
DON
DON
D
All Small Six 65 Mustang 200 Need Help
Replies
17
Views
4K
Dshak65
D
6
All Small Six Distributor guidance ideas
Replies
10
Views
1K
wsa111
wsa111
R
All Small Six New guy with Comet dying leaving a stop
2
Replies
37
Views
2K
DON
DON
Back
Top