63 Red Stake Bed (12/10/2008)
I have a .060 over 292,
E-4 straight up w/silent chain, 57 intake, 600 Edelbrock, pcv to carb, c1te heads ported & pollished w/1.78 intakes, & 1.6:1 roller rockers, headers & duals.
I still only pull 13" vac @ Idle. Not sure if that's normal for a setup like this on a Y.
When you say the cam is installed straight up, did you infer that the camshaft is degreed in and installed at 108° intake lobe centerline or simply installed in the zero position on a multi-slotted crankshaft gear? I like 4° advance with the E4 camshaft or installed at 104° intake lobe centerline. Simply installing the gears so that they are twelve pins apart is not the same as degreeing in the camshaft. I ask because this makes a difference when trying to troubleshoot. What’s the cranking compression look like?
AZ28 (12/11/2008)
None of the new style carbs have the venturi vacuum feature (as far as I can tell) - just the "on/off" with the throttle balde as Tim said. Ted has mentioned modifying a modern carb to supply venturi vacuum before - but I don't know how you would go about it.
This is a mod that’s only performed on a ’57 and later style of carb when attempting to run the early (pre ’57) Load-O-Matic distributors. And the only distributor worth doing this for is the ’55-’56 T-Bird units when a ’57 T-Bird distributor is unattainable and still wanting to run a modern style of carb. Much of this modification is trial and error as each engine combination ultimately has different requirements and the modification itself varies depending if being performed on a Ford, Holley, Demon, or Carter (Edelbrock) carburetor. Likewise, I’ve modified the Holley 4000 4 bbls (Teapots) so they could be used with the ’57 and up distributors. This is a much easier mod as it simply requires the blocking off of the venturi vacuum which tees into the ported vacuum circuit. But life can be made simple by lieu of simply using ’57 and up distributors with ’57 and up carbs. Some adjustments may need to be made to get the curve right, but the basics are there without having to re-engineer the whole shooting match.
But in regards to the use of ported vacuum for the distributor, I have found it necessary to relocate the ported vacuum holes in some of the Demon carbs as the hole has been too high above the blades and was providing insufficient vacuum for the distributor. This ends up limiting the amount of ignition advance available in cruise situations. Lowering the hole and/or resizing it larger increases the amount of vaccum to the distributor and thereby allows for additional cruise ignition advance.
57Fordluvr (12/11/2008)
Hmmn, I hope I'm not missing something here but is that vacuum advance actually a worth while benefit? And what is this 'gas mileage' of which you speak? 20 gallons usually lasts me a whole day, no problem..
Gas mileage is the fuel economy as stated in miles per gallon or mpg. This value can vary depending upon how the vehicle is driven, whether it's town or highway driving, and the fuel quality among other factors. Improved fuel economy is the recipient of a correctly working advance chamber which is why so much effort goes into getting it right but the ported vacuum part of the signal allows the engine to idle and take off without the surging or quirkiness associated with running the distributor vacuum directly off of the intake or a vacuum port located under the carburetors throttle blades. A properly tuned vacuum advance will net an additional 3-4 mpg while maintaining a basic tuneup that will not clatter or detonate under heavy loads. It’s not unusual to go even leaner on primary fuel jetting when the vacuum advance portion of the system is up to speed. This is a subject that could be devoted to a whole book in itself so it’s difficult to expound on it in any detail in a paragraph or two.
As always, this is fuel for thought so feel free to pick it apart.