SSC

Mine is still fuzzy from exhuast fumes.
I'm bouncing around here trying to figure this out..........

With my new setup new to my bird anyway Ive got a bit more flexability as far as carbs go, no more tv cable to worry about.

Right now I'm using a Holley 600vs. I like holleys more then any other carb but.....
Anyway with the cam in here now close to a 270H's numbers (factory LT1 replacment) Ive got fairly low vacuum, best I can work with is 13in at idle not terribly bad. When in an everyday driving situation stop go my vacuum drops to 0-2 when taking off from a stop, granted in some situations this is fine but it doesent help economy any. HYW cruising, consistant highway driving holding her at 75 vacuum is 10-11in I barley tip in to keep speed and it kicks the secondaries open. Tried secondary spings to see if I could work it out a bit better but I run into flat spots. I cant seem to find a happy medium.

My fubard thinking is If I swap over to a mechanical secondary carb like another AFB or edelcrap where vacuum isnt really going to be as critical in the fuel enrichment circuts I'll gain better economy and probably better drivability.

Do I got somthing here or just more wishfull thinking?

five7kid

iTrader: (14)

What PV do you have in it?

The nature of VS's is that the velocity through the primaries is what opens the secondaries. If they are opening just by giving it a little more gas from a highway cruise speed, that probably means the carb is on the fringe of being too small.

SSC

I think theres a 2.5 in it now cant remember for sure. The ideal choise with this setup should be 4.5 or 5.0. Ive tried quite a few PV's In fact Ive got every single PV made including the plug.
The carb does border on the fringe of being too small but its one of those issues of drive today race tonight, still waiting for my insurance to decrase LOL.

five7kid

iTrader: (14)

With the vacuum numbers you quoted, you need a PV more like 7.5 (10 minus 2 = 8, rounded to next number down = 7.5).

SSC

I started out with a 7.5 But it would dip into the PV too early, The second the clutch starts to catch and move the car it would go into a slight stumble dropping PV size reduced the stumble.
When I first put this setup in the car I started out with a 750 but that dogged the engine too much on the low end. I think I am going to try another edelcrap my friend has a spare it cant hurt to try.

Auggie

What are the cam spec's? It seem's to me that you should have more vacuum then that at idle and at steady hwy speeds. How does your power brakes work? My cam spec's are as follows:

Int = 278*
Exh = 278*
Int = 222*
Exh = 222*
L/S = 110*
Lift = .467" int & exh
Eng. = 355ci

My eng. idles at 14.5" of vacuum. You may have something else wrong.

Auggie

SSC

Its a Melling 22210. Vacuum is slightly effected by altitude somewhat. Brakes are actually fine seeing how you let off the gas and it raises vacuum enough to stop decent.


Had to DL PDF cant find cam card.

http://www.melling.com/products/melling_catalog.pdf

@.50, 224. 224.
ADV 291. 287.
IVL. IN .450 EXH.461
DLC IN. 114 EXH. 114

Auggie

You are right about alt. affecting vacuum readings. Example:
A/Pressure at 1000 ft = 14.1 psi and vaccuum would = 18.5". A/P at 6000 ft = 11.5 psi and vacuum would = 13.5". If your at 6000 ft your vac. reading of 13" would be right on. If thats the case you should have your carb setup by one of them hi-alt guys. Anyhow here are your cam spec's:

Int Dur = 291* @ .050 = 224*
Exh Dur = 288* @ .050 = 224*
Int lobe C/L = 114*
Exh lobe C/L = 114*
L/S 114*
Cam Adv = -0-
Overlap = 61.0*

I/O = 32*
I/C = 80*

E/O = 78
E/C = 30*

Cam Intenisty = Int/67* Exh/64* Pretty high.

When you installed this cam did you raise the comp. ratio? If not do a comp. test. It should be low! If you don't want to go through the trouble of raising your C/R then I would adv. the cam 6* and adv the ign. timing until it started to ping. If you do these you should see a few inches more of vac. Just my .02 .

Auggie

SSC

Hmm post dident stick last night.

I set timing the edj'uma'cated' hill billy way with a vacuum guage then varify it with a light. This way seems to work well considering all the watered down camel wiss we get. I do it this way also to get the maximum amount of vacuum at idle as possible. I actually reduced compression some what on this engine by swapping 58cc heads for a set of dart 64cc, compression is still high but less tendancy for detonation now. Initail advance is 15* with a total of 32* @2200 RPM.

Actually picked up the edecrock last night, my frined was running it on a tunnel ram with no airfilter!!!!!! So right now it sits in the carb tank at work.