1959-60 tri-power owners ~ ? about idle vacuum

[woodillac]

Folks who are running factory tri-power '58 through '60 (or other years), what does your idle vacuum seem to be. Recently installed a '59 tri-power set up, everything  redone, on my '55 331. I am using an Isky 262 deg cam, headers, and '57 365 heads. I have checked the usual suspects but the engine does not generate more than 15" at about 800 rpm. Does some air sneak past the end carbs no matter what?

[Jeff Rosansky CLC #28373]

I don't have an answer to your question. However have you removed the vac pump from the equation?  If it is failing or weak you could lose vacuum if that check valve is stuck.
Jeff

[woodillac]

Sorry, I should have said that I am not using the factory vacuum switch/set up or a vacuum tank. I am using mechanical linkage.

[David Greenburg]

I don’t think mine gets much more vacuum than that.  Where did you get your mechanical linkage?  I’ve been thinking of going that route.

[Dave Shepherd]

With the stepped up cam your idle vacuum is going to be lower than stock.  Also make sure the end carbs are seated, not slightly cracked.

[fishnjim]

The cam maker may be a better source to answer this.
Distributor should be cammed to match the advance curve and adding a race cam changes from stock timing.   There's machines to do that, but the know how is getting scarcer.   I'd convert it to electronic in the long term.   More importantly is, if you're using the vacuum and stock timing advance?
These are not your modern electronic, change the program cars.   The old hot rodders knew most of this, and how to handle, but no so anymore since the '80s.
Also, what carbs are on it?  Some idle on vacuum, some don't.   
I'd suspect you're not going to do much better without the pump, but disconnect everything vacuum and run the vac gauge direct to the manifold and check it there.  If it falls on it's face when you hit throttle, then you got problems, if it idles and revs, probably OK.   I don't know where you'd need to time it at idle, depends if they degreed it in or not.   Stock is probably not right.   
I think the best my '58 4 bbl did before the overhaul was 19" with pump, but motor was weak at that point.   Vacuum is one of those things you don't worry about until you have to.   We did not check the vacuum during the dyno with the tripower, and ran w/ no advance.  Stock 365 cam and internals.   I should have it on the road "soon" whatever that means - measured in years?

[woodillac]

Thanks everyone. I should say that the engine idles ok when warm. I am using a manual choke, which I personally think is better to control the cold/fast idle. The engine revs freely and the vacuum does bounce up to 20" so that is reassuring. I am aware that increasing cam timing with the aftermarket cam affects vacuum, I have the initial timing set at about 12 deg. advance and distributor has been upgraded to electronic. I did check vacuum at the manifold with both a portable vacuum gauge and the gauge in the car, both are the same = 15+ ". I am mostly just curious about what others are experiencing.

["Cadillac Kid" Greg Surfas 15364]

FWIW, and just comparing the cam timing to vacuum.  My 9.5:1 500 inch motor with a Comp  "262 degree" cam having the a (approx) 220 degrees at 0.050 lift idles at 525 RPM and pulls 18 inches.  My suggestion is that you look for a vacuum leak SOMEWHERE.
Greg Surfas

[woodillac]

I don’t think mine gets much more vacuum than that.  Where did you get your mechanical linkage?  I’ve been thinking of going that route.

I used parts I had around the shop, a few rods with an adjustable end, and a slightly modified link/bracket on the center carb.

[Caddyrag67]

go with vintage speed secondary aluminum throttle bodies there the best and do not leak. also there ball bearing progressive linkage is the best

[woodillac]

go with vintage speed secondary aluminum throttle bodies there the best and do not leak. also there ball bearing progressive linkage is the best

I went with another brand, new cast base, throttles etc. They seem to seal pretty well.

[Scott Halver]

Hello, It's been a year or so since I checked but know I had at least 18 inches of vacuum at idle, maybe closer to 20 inches and then 20 to 22 inches of vacuum just off idle ……. engine rebuilt very tight.   I have so much vacuum that I "sucked the door locks out of the car" ……… stressed the diaphragm in the door lock switches-   since replaced with salvage yard switches.   My tri-power is all original with the tri-power vacuum switch, works very good-   1 second for opening front and rear carbs, about the time you want for the transmission to downshift.   I had a bad vacuum leak at the "ac idle speed-up switch", which is mounted on the center carburetor …….   might be your vacuum leak.  SHalver