Fuel Consumption

[rockman20]

Okay, I have a 82 Scottsdale with a 350 that has been bored 60 over with flat top pistons and an extreme offroad cam, edelbrock intake, Rochester carb, headers, dual exhaust (2.5") into flowmasters, and stock HEI distributer.

Why can I no longer get my 12-14 MPG on the interstate? I am at a loss at where my economy went. Truck runs great, just lost a lot of economy. I am down to basically 9 MPG no matter where I drive. In town, off road, or highway. Any suggestions on where to look?

[cdowns]

maybe you should have gotten a cam for mileage if that's what you were lookin for

[bigarmzz]

Originally Posted by rockman20

Okay, I have a 82 Scottsdale with a 350 that has been bored 60 over with flat top pistons and an extreme offroad cam, edelbrock intake, Rochester carb, headers, dual exhaust (2.5") into flowmasters, and stock HEI distributer.

Why can I no longer get my 12-14 MPG on the interstate? I am at a loss at where my economy went. Truck runs great, just lost a lot of economy. I am down to basically 9 MPG no matter where I drive. In town, off road, or highway. Any suggestions on where to look?

how big of an extreme energy cam did ya get?

whats the specs of it?

they make several, probably the lower the lift, the better the economy....

[Jason915]

The X-treame cams are ground for great low end torque profile, they are not designed for peak HP numbers so I wouldn't think the cam is the problem. I would check your A/F ratio and make sure your timming is right on. How do your plugs look? Also a .060 overbore is going to use more gas just because the pistons are bigger it's pumping in more air and fuel and its also heavier so more rotating mass. What cylinder heads are you using, stock or larger valve cylinder heads?

[bigarmzz]

Originally Posted by Jason915

The X-treame cams are ground for great low end torque profile, they are not designed for peak HP numbers so I wouldn't think the cam is the problem. I would check your A/F ratio and make sure your timming is right on. How do your plugs look? Also a .060 overbore is going to use more gas just because the pistons are bigger it's pumping in more air and fuel and its also heavier so more rotating mass. What cylinder heads are you using, stock or larger valve cylinder heads?

there's one of those xtrem 4x4 cams that has nearly 480 lift.....thats some fuel consumption

[Fred T]

Have you recurved your HEI timing? If not, get a set of weight and an adjustable vacuum module. Set your initial timing to around 10* and your total timing to around 36*. It should help your milage a few percent.

[72MARIO]

If it makes you feel any better my 84 runs like crap and gets 10mpg at the best.

I would guess the cam is the sucker.

[Beefcake]

keep your foot off it. Its amazing when you only drive 55mph on the freeway how much you have left in your tank.

I drive like a grandpa now.

[Jason915]

Originally Posted by bigarmzz

there's one of those xtrem 4x4 cams that has nearly 480 lift.....thats some fuel consumption

Not necessarily higher lift the worse the MPG, several other factors that determine poor mileage. A cam that has .480 lift but lower duration on the intake side and longer duration on the exhaust side will be a reasonably efficient option because the combustion chamber is getting a cleaner mixture. Lobe separation/lobe centerline and duration dictate efficiency more than lobe lift. A cam designed for great low end torque is typically inherently more efficient than other grinds because it will take advantage of the engines power potential at significantly lower RPM’s.

[rockman20]

Sorry, I was rushed when I did my post. I do not remember the specs on the cam right off hand, but I will see if I can find my sheet somewhere.

The dang thing use to get around 12MPG when I put the fresh engine in. It ran like that for about 2 months and then went down hill. I have put new plugs, wires, even went with a different distributer. I have a Mallory distributer now that I have an adjustable vacuum on. I have my timing set around 6* initial with a total of 32* I could run 10* initial and that will get me to 36* total. I may go ahead and try that.

I haven't pulled the plugs for about a month or two now. I can pull them and see if they are black or white or tan or shot.

I had originally suspected an intake leak so I had redid my intake gasket. But no matter how I drive, I am right around that 9 mark.

I just found it odd that a fresh engine got better mileage then one that is now broke in.

[MylilBowTie]

I would run a compression test or have a leak down test done, the leak down test is the best. That will tell what's going on in the engine.

[cdowns]

just wondering/ is this a competition cams extreme series camshaft that you have?? if so on all thier extreme camshafts they provide warnings about using any stock components I.E. lifters rockers springs retainers locks with the cams. did you change all the stuff too or just the cam??
why did you choose that cam ?? was it for the name,or for some other undetermined reason??did you ask any questions on the teck line B-4 getting it or did billie-bob just tell you it was a kick-ass way to go
poor cam and component selection i believe is your problem, you should be able to get alot better gas milage with a better cam choice . i suggest you call a tech line or 2 from different cam companies and tell them what you're looking for and see what they suggest. i'd bet with proper cam and components you could double your mileage and still have a nice power curve

[Jason915]

Why would you blame the cam when he just said that when the engine was fresh he would get about 12MPG, and now its broke in his milage has reduced?

Rockman20, is this truck an auto or std trans? If it's an auto maybe it's not locking up. If you say that your engine is running just fine as far as power output and you can determine that it's not running pig rich after a plug inspection maybe something else is going on.

[cdowns]

Originally Posted by Jason915

Why would you blame the cam when he just said that when the engine was fresh he would get about 12MPG, and now its broke in his milage has reduced?

Rockman20, is this truck an auto or std trans? If it's an auto maybe it's not locking up. If you say that your engine is running just fine as far as power output and you can determine that it's not running pig rich after a plug inspection maybe something else is going on.

well if you read my comments about MATCHING of the components you might understand

[Jason915]

Ok tell me what is mis matched now that wasn't when the engine was new. He was getting 12 mpg before and now that has been compromised for some reason. I don't understand why you blame cam selection when you don't even know the cam specs it's just not the logical part to put the blame for the resent MPG decrease. It would be different if he said that he swapped cams and now his MPG has gone to hell

[cdowns]

there's a reason why comp cams warns about NOT using stock components with ALL of thier extreme cams!! stock stuff fails!!! the springs are probablly loosing tempering and closing slowly, and it wouldn't be a big surprise for them to finally snap dropping a valve in turn trashing block and rotating assy
this is all based on the assumption that stock components were retained

[rockman20]

Go ahead and bash me on this one, but I honestly didn't pay much attention to what happened to the engine when it was built.

Mine had gone to crap and it was winter and I needed an engine. I called up a shop about 100 miles away and explained to them what I needed for my truck. I told them that I tow with this vehicle so I will need something with some low range torque. They suggested the cam and told me that is what they usually go with on a tow vehicle. My assumption would be that they would be nice enough to change the other components as well, but honestly I am not sure.

This is the first engine that I have ever had built by someone else and it will be the last. I really do not like not knowing what happened to my engine during assembly.

I will have to take some time to run some tests on this engine now and see what has happened. Live and learn. I was in a rush to get my truck back out on the snowy roads and just did not have the time nor the heated garage to assemble an engine.

Thanks for all the pointers. It gives me some areas to turn to. I am getting a little worried about the cam discussion now though. I will have to see what I can find out.

[ratfreak888]

maybe try ported vac. vs manifold vac. to the distributor. don't know w/o trying but they do have their diff's.

[71_Street_Rod]

u say that ur truck does well to get 9 to 12 or so i just wish that my 71 would get that much it gets about 6 to 8 and thats without my foot in it

[FLAGG]

My 85 Silverado was doing anywhere from 11 to 14 back when I was calculating it out, and that's a 305 with 3.42 gears and a 700R4.