What do you think of my MPG?

[fstfwrd]

A quick easy start would be to disable the lockup feature of the torque converter. You will still have overdrive for going down the road, but you will gain 200 to 400 or so rpm going down the road at highway speed. If you decide to do this, I would make sure you have an external tranny cooler, or even a tranny temp gauge.

I don't think having the converter NOT lock up is going to produce enough heat to murder the tranny, but any way you can cool essential fluids it would be wise to do so.

leftybass209, I've sold Edelbrock carburetors for several years to guys that have leaky Holley carbs on their old farm truck that is lucky to see a thousand miles in one year. We have a shop and perform repair work as well. While they are relatively easy to work with, you get an old C60 truck with a tall deck 366 or 427 big block Chevy, and they will not run for ****. It's nothing to tune it so it idles fine, but then you have to deal with the actual driveability aspect of the carb.

We stuck a 204/214 cam in a 1968 Chevy 307 V8, then mated it to a lockup turbo 350 trans and installed it in a 66 C10 pickup. 3.42 axle ratio, when the converter locked up at highway speed the aftermarket tach would read 2700 rpm. Obviously not a mile per gallon highway cruiser. But that particular carb had warm start issues, my buddy was always fighting high idle issues (nice feature up here in chilly North Dakota). In the end, I installed a Quadrajet with a few minor tweaks in place of the 1406 Edelbrock. The 307 idled better, the idle surge was 100% eliminated, fast-idle worked great on cold mornings, and he ended up getting better mileage on his 30 mile round trip to work everyday.

I wasn't trying to start a heated debate, I've just dealt with these carbs and figured I could share my experience in using one and modifying if needed. The 600cfm seems a little awkward on a mid 70's tall deck 427. Adjust and tune to your hearts content, but there is a HUGE tradeoff between just getting the damn thing to idle, or driving down essentially lugging the engine with a full load on the tandem axle truck. Not that it matters in this conversation, but the factory C60 etc trucks had a Holley carb set up for use with the PTO to run the hydraulic pump to lift the box. The customer complained several times, and after several adjustments, we finished the job by putting a kit in the stock Holley. Again, driveability was better, it idled about as well as any worn out big block Chevy, and the customer claims the fuel mileage went up some.

[fstfwrd]

Originally Posted by 71enthusiast

Here is the thing I am currently faced with:
My truck is a 71 sporting a 350 with an RV cam.
I have a 700R4 tranny with a 3.08 rear.
On the interstate the best mileage I can get is somewhere in the 10-11 range at 2000 revs. From what I have read from other posts is I should be getting better economy than this.

My question is does this seem right to you?

Chime away!

Other potentially useful info:
500 cfm Edelbrock carb.
28" tall wheels.
2.5" duals running from headers

Where do you have BASE timing set to? Is your vacuum advance set up to the proper port (not trying to get into the timed vs ported vacuum ideology)? If the timing is set wrong (I know of A LOT of guys that mess with cars and will "time" the engine by turning the distributor until it sounds good). Get a good timing light, verify you are at or near ZERO on the balancer and timing mark on the front cover. Get a WHITE or HAZARD ORANGE paint pen to mark the groove in the balancer. The paint stands out with the timing light and its easier to get it all right.

How do the plugs look? Black and sooty, maybe a little oily? Or are they kind of a crusty white-ish color? If you haven't pulled one or more of the plugs, I would check either a random plug, or pull them all out. Also, verify plug gap. Assuming you have an HEI ignition (ANYTHING other than points ignition), go ahead and set the gap to 40 or 45. Just a few easy tips that might help you make some mileage with that beast.

Feel free to ask any questions, and I'll do my best to reply asap if I'm not out in the shop.

Brendan

[71enthusiast]

I apologize for not responding in a while I've been rather busy.
I am running an HEI dist and the torque converter was wired to lock up by the guy I had build it.

I do not have a timing light, however if I get the chance I will see if someone at a parts store can help me out with that. Also I plan on doing a compression test and checking my plugs possibly tomorrow if I get rained out of work.

I intend on getting to the bottom of this however long it may take. If I can remember, I will keep this forum updated for the whoever may need this help as well.

[sawman]

guys your talking about a 350 here did they ever get far on a gallon of fuel,it depends if he has the good heads and cam too 71 350s were bad on fuel,big valves

[MAC71]

I have a 71 with a 350, world products sr toquer heads, a tpi cam and Holley 600 carb. At first I had a th350 and 3.07 gears and got about 12 mpg. Went to a 700r4 but locked up at 70 it turned such low rpms I got Only 9 mpg. Un locked rpms were around 1800 and was back up to 12 or so mpg. Changed to a 3.73 gear and locked up at 2100 rpm at 70 it gets 17 mpg. There are a lot of things that will effect fuel mileage but first you have to get it in the right rpm range. I know newer vehicles run low rpms but they have fuel injection. A carburetor has to have a certain amount of are moving threw it to run correctly.

[MAC71]

Originally Posted by MAC71

I have a 71 with a 350, world products sr toquer heads, a tpi cam and Holley 600 carb. At first I had a th350 and 3.07 gears and got about 12 mpg. Went to a 700r4 but locked up at 70 it turned such low rpms I got Only 9 mpg. Un locked rpms were around 1800 and was back up to 12 or so mpg. Changed to a 3.73 gear and locked up at 2100 rpm at 70 it gets 17 mpg. There are a lot of things that will effect fuel mileage but first you have to get it in the right rpm range. I know newer vehicles run low rpms but they have fuel injection. A carburetor has to have a certain amount of are moving threw it to run correctly.

Something else was that in overdrive and the 3.07 gears the engine vacuum was so low at that load that it was in its power mode so full rich.

[71enthusiast]

It has been a good long while. Longer than I had anticipated, however I have some results.
I have not messed with timing nor have I changed any plugs. I did inspect a few and saw no reason to do such.

Here is what I DID do:
Main jet change from 1428 (.100) to 1427 (.098)
Metering rod swap from 1451(070x047) to 1456 (073x047)
And also I swapped the Step-Up spring from Orange to Yellow

With doing this ALONE, I now get and additional 5 miles to the gallon which brings me to 15mpg.
There is no loss of power what so ever it is as if nothing changed.
I am also looking at switching the Step-up spring back just to see how it effects mileage.

[clemsonteg]

Originally Posted by 71enthusiast

It has been a good long while. Longer than I had anticipated, however I have some results.
I have not messed with timing nor have I changed any plugs. I did inspect a few and saw no reason to do such.

Here is what I DID do:
Main jet change from 1428 (.100) to 1427 (.098)
Metering rod swap from 1451(070x047) to 1456 (073x047)
And also I swapped the Step-Up spring from Orange to Yellow

With doing this ALONE, I now get and additional 5 miles to the gallon which brings me to 15mpg.
There is no loss of power what so ever it is as if nothing changed.
I am also looking at switching the Step-up spring back just to see how it effects mileage.

How do the plugs look after the rod/jet change? Can you tell the mixture has leaned out some?

[Taibo]

Originally Posted by 71enthusiast

Here is the thing I am currently faced with:
My truck is a 71 sporting a 350 with an RV cam.
I have a 700R4 tranny with a 3.08 rear.
On the interstate the best mileage I can get is somewhere in the 10-11 range at 2000 revs. From what I have read from other posts is I should be getting better economy than this.

My question is does this seem right to you?

Chime away!

Other potentially useful info:
500 cfm Edelbrock carb.
28" tall wheels.
2.5" duals running from headers

I get 12 with this and it's a tad more fun than a 350!

[MARKDTN]

Originally Posted by 71enthusiast

SS Tim
I have been looking into 3.42 gears. Are they still too (numerically) low?

3.42 is a great all-around gear. That is what is stock in my '83 K20. With stock 350/Q-jet/700R4 I used to get 14 around town. Now I swapped to Tuned-Port fuel injection and I am over 17 in town.