290H Cam vacuum

Just curious for those of you running the TA 290 H cam, what manifold vacuum ##s are you getting?
Cam: .525"-238'/.525"-238',112

Thanks!
Bob C.

 

I'm running the 290H in my 470 Regal. While setting up the carb we got between 12-14 on the vacuum gage from the carburetor at idle in park which is 1200 rpm. In gear it idles at 850 rpm very nicely and the brakes work perfect at all speeds. Never had a problem with stopping even after several hard stops in a row. Roger

On The Eighth Day God Created Buick

 

Thanks Roger,
That's what I though i should be getting....I'm at about 8.5" @ a 950 idle. No vacuum leaks, but i think I'm sacrificing vacuum with the QJet throttle placement...an already heavily modified carb, it is having fits with the idle on this cam.

 

Yup...the advance is as good as I can get it and have normal starting. I have very little control with the idle system on the carb though.
Interesting about the start retard....never heard of that. Is that a simple addition?

 

With only 14* overlap and 112* lobe center I would hesitate to lock out the timing due to the higher cylinder pressure. Even though a start/retard is a good idea, that may be asking for detonation under heavy load in lower RPM range. Its really not that big of a cam. Roger's vacuum numbers are right on the money. What is that cam dialed in at? What compression ratio?

Larry

 

Also check to see how far open the primaries are at idle, and if the throttle shafts need to be bushed. If you have access to another carburetor it may be worth the time to try it.

Larry

 

Great info!

One related note.... I'm intrigued with the idea of locking out the timing and using the start retard. Are there any disadvantages to doing this on a street driven car?

 

Yes, detonation. There's a balance to static compression, the intake closing point, air density (altitude) and machining specs (things like quench distance and area from dish shape).
A GM HEI module is available that can be wired for a slight retard.
Also, if you have a stable idle speed and a good smooth-working mechanical advance, another strategy is to use direct vacuum to bring the initial timing total up...once it starts.

 

This is the method I use. I have the Crane adjustable vacuum advance set at 10* and my initial timing at 12* for a total at idle of 22*. The car will idle down to below 600 RPM although I usually set it at about 750 in neutral. And, it runs a lot cooler than when timing was only at 12*.

 

As posted in #6. Locking timing is better off left to track cars only. As an example hard acceleration from a stop is a recipe for detonation in a normal weight street car with timing locked full.

 

Actual converter flash speed would have major influence on the feasibility of locked timing.
If your's flashes a bit higher than the rpm the ignition curve maxes out (mostly) at then it wouldn't hurt.
An ignition cut-out or kill switch would also allow you to crank with spark dead and then flick it on when it spins real good.

 

I stole that idea from a Ford guy I know p I'm not generally an advocate of locking out timing. I lock my distributors out because I let the fuel injection computer control timing and it doesn't need any mechanical or vacuum help. The alternative is to go to minimum advance setting and either wire tie or zip tie it, then just turn the distributor to raise the advance.

 

Larry,
When you installed the 290H, did you install it straight up, or advanced to any degree?

 

My cam was installed at 108* ICL , 34 degrees total advance using a standard Delco points distributor set up with the single wire Limited Lectric eletronic ingnition conversion and 10.5 to 1 compression all set up by Jim Weise and I
have never had a problem with starting. 850 DP Holley worked beautiful right out of the box with proper adjustment. So my experience says this cam can work great with a simple ignition system and carb set up. Throttle response is instantanious, idles great and pulls like a freight train the whole quarter mile. Roger

On The Eighth Day God Created Buick

 

No 290H here either guy's,..............He's "The Wizard", I'm "The Doctor". All we need now is more Larrys.

Larry

 

Here's a few questions that might help get you on the right track. I'm surprised that no one asked these yet.

What is your initial timing at idle? Manifold, ported or no vacuum advance?