Would be great to have some thoughts from you guys. Currently running mild 312 with 600 vc holley AOD trans (0.67) overdrive and a 3.0 to 1 9 inch final ratio. The car is running great...love the sound of that old Y. After a great weekend away in the Vicky I did some calcs... I ended up with about 13 miles per gallon! 60mph is currently calculated at 1545rpm I feel the car is too high geared. I am thinking of changing the diff ratio and also the carb. This car is used....I plan to drive it a lot.(Road use) My thoughts are that it should be turning over at 2000rpm or more at 60mph to get better gas mileage. By my calcs a 3.5 ratio will give me 1803rpm a 3.89 ratio will give me 2000prm a 4.11 ratio will give me 2117 rpm Perhaps a nice little 390 cfm holley would be better than the 600. My questions are as follows: What is the best mileage I can expect? What are your thoughts on getting slightly better mileage? Any other comments. Thanks in advance.
I would suggest a 3.50 gear, a Ford 4100 4V carb with 1.08 primary venture size, ( Mustang, some TBird's ) and a good check of your distributor curve to start.
The Ford/Motorcraft 4100 is a good Carb they have been out of production for some time and getting high priced,to have the features with upgrades of this Carb and being able to tune it with readily available Holley parts you may want to consider this:http://www.summitracing.com/parts/sum-m08600vs/overview/ In most cases 2-4 more MPG over a 600 Holley have been reported on several forums.If your '56 still has the stock rear a 1952-54 Ford 6 cyl with overdrive rear end will have the 4.10 gears and will bolt in.You probably went to a later distributor when swapped to the Holley,right? Those can be converted to electronic in 1957 and later distributors:http://www.summitracing.com/parts/acc-2020/applications/ having the curve set will help also give this a read:http://m571.com/yblock/distributortuning.htm
Are you running a stock cast iron intake? an hour with a dremmel will make a huge difference in the manifold. Then, for everyday street use, a 500 Edelbrock on a two inch four hole spacer will give far better fuel mileage than your current figure, and better low RPM throttle response.
Thanks guys keep the comments coming. Currently running a 1957 nine inch rear with 3.0 gears Also have a MSD full electronic dissy. Will check full advance but believe it is very close to optimum. Am running the stock cast iron four barrel manifold with heat riser. The setup runs very sweet, plugs the right colour, no flat spots. Just think it is labouring and too far (off cam) to run efficiently.
So how much advance do you reckon you have at your cruising road speed - combination of mechanical - and from manifold vacuum on the distributor can? Need a vacuum gauge plumbed up so you can read it at cruise. The mechanical won't be all in at 1500 rpm - and my guess is that the 600 cfm carb is killing your manifold vacuum at the very slightest twitch of your toe. You are having to keep the torque up by feeding the engine fuel from the accelerator pump.
Many thanks guys. Just checked the specs on the distributor (Mallory/unilite) not MSD. The units have 28 degrees of crankshaft advance at 3000 to 3200 in standard form. This unit is mechanical advance only. I will check total advance at 1500 rpm but am pretty sure it will be not enough adding to the in efficency. I see they do a kit http://www.summitracing.com/parts/maa-29014 to change the springs etc which looks like it might be useful. Keep the comments coming.
To build a road cruiser - you need some vacuum advance. Do you have an original distributor for the engine - or did it come with the Mallory when you got it? When converted to electronic trigger, and recurved - the original Ford distributors do a pretty good job. In the situation you have described - the full centrifugal set-up would never be able to match it for mileage.
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