I have a 63 roadster I recently got as a restoration project. It has a 327, bored .060 over, 11.25 to 1, Edelbrock Performer Intake with a Holley 600 carb. I was told the cam has a 300* duration with .50" lift. I currently have the initial timing set at 14-16*, and I notice very little advance when I hook up the vacuum line. The engine pulls very well, but I feel it should have quicker throttle response than it does, given the setup. It has the original, tach-drive distributor with points, and I use an octane booster plus lead additive (per previous owner's advice). Am I expecting too much, or have I got this set up wrong? I live at an elevation of 4800 feet. (Note: car previously had a quadrajet carb which would cut out at high rpm, so I changed it as noted above.)

 

The vacuum advance bellows may be shot. At idle when you connect the vacuum line you shoul get ~10-12 degrees more advance. When you rev the engine past ~2,700 RPM there should be a 32-34 degrees. If not search the forum for Elgin (NAPA) and you will find the replacement vacuum unit, as far as mechanical advance the distributer must be torn down to do any troubleshooting.

 

How many inches of hg. idle vacume do you have now and at what rpm.

 

At warm idle, (850-900rpm) I have 5-6 inches of vacuum. At 2500 rpm, I get 15 inches. What does this mean? Seems like the vacuum advance unit is working, only at higher rpm's? Thank you for your help.

 

You may need a NAPA/Echlin VC-1810 vac can, it deploys (starts moving) at 8" hg. They are 5-10 bucks at your FLAPS. Several others are available that deploy at different levels of vacume.

You have the vac line hooked up to manifold vacume and not 'ported' (above the throttle blades) I hope.

Before you run out and get one check to see at what inches of vac your present vac can starts moving. Use a vac hand pump w/guage to see. It most likely won't move untill 12-14 in hg. What you need is one that goes all in at normal idle (550-900 rpm).

Thats a general waste of money and more 'snake oil' magic. You should be able to run a reasonable advance curve useing 93 octane unleaded. Your supposed 11.25 to 1 will be a problem.

 

You can't go wrong by going here: http://wiki.corvettefaq.com/index.php?title=Main_Page
This is the tech site that Lars of C3 forum fame maintains. Full of all sorts of good info.

 

Vacuum Advance Cans -

VC680 (stamped "B1") 0@8". 16@16" (283/220, 230, 245, 250, 275; 327/250, 300)

VC1765 (stamped "B20") 0@6", 16@12" (327/350, 396/425, 427/390, 400, 425, 435)

VC1810 (stamped "B28") 0@4", 16@8" (283/270, 290, 315; 327/340, 360, 365, 375, L-88/ZL-1)

IMO you need a VC1810 Vacuum can that will be full in at 8" of vacuum.
Connected to a full vacuum source, not ported. Your motor will be more responsive and will run much cooler....

There are tons of articles regarding this topic on this froum......

 

Thanks for all the pointers - I will do more research and keep trying to improve things. As I said, car doesn't run bad, but I think it can do better.

 

a cam such as you think is in the engine with 300 degrees of advertized duration (unknown duration at .050 valve lift which is what really matters) would want at least 18 degrees of initial advance at sae level and at your altitude it could maybe use more. 36 total degrees including the initial plus the vaccum advance timing is what i would recommend, i would not have the vacuum advance to manifold vacuum but use ported vacuum (even more so since it only has 6 inches of vaccum at idle). since you are at altitude i think you need a carb with 4 corner idle (such as a barry grant mighty demon) since the vaccum is so low at idle but that is a only my opinion, also the power valve should be a 4.5 so it is not open at idle. i would like to hear what Lars has to say on a subject engine such as this, since my tuning experiance at higher altitudes is much more limited than his. i work mainly at sea level and only had 1 race a year we had to tune to run at 6,200 feet and then we always had to richen the idle mixture to make up for the loss of vaccum with a cam that was in the .250 @ .050 lift range and the engine(s) liked about 2 to 4 more degrees total advance than when ran at sea level. the jet change for altitude formula that i have used is one jet size down for each 2,000 foot increase in density altitude (how much oxygen there is in the air the engine is breathing), again that is just my opinion. the higher the density altitude the less the need for octane so you should be fine without any additives in the fuel. good luck tuning

 

What's the source of vacuum for your gauge when you take that reading at idle? Carb base (where)? Fitting on the intake behind the carb? 6" Hg. is WAY low - even the radical "30-30" cam will generate 9"-10" Hg. at an 850-900 rpm idle.

 

The vacuum source I was using is at the base of the carb in the front. I just replaced the vacuum can after discovering the old one didn't even begin to open before about 15" of vacuum! Per your advice, I installed an 1810 can and what a difference! My original run had the car "loping" at cruising rpm, so I retarded the timing about 3-4* and it quit doing this. Idle seems to be much smoother now, even with the "lopiness" of the cam. You guys and this forum is great! I guess you can teach an old dog like me new tricks!!!!!!
Thanks again for all your help. The car now will set you back in the seat.