Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - Vacuum Advance Canister question
View Single Post
  #12 (permalink)  
Old 04-16-2008, 12:29 AM
oldbogie oldbogie is offline
Registered User
 
Last photo:
Join Date: Apr 2007
Location: Seattle, Wa
Posts: 7,095
Wiki Edits: 0

Thanks: 4
Thanked 541 Times in 457 Posts
Quote:
Originally Posted by strokey
Techron - I'd love to have the link, Ive been reading old posts for hours trying to diagnose.

I think I've finally narrowed the problem.

I spent time blaming my sour performance on the stock stall converter and stock highway gears, then the swap meet 650 holley double pumper with a kit in it.

I bought a brand new box stock holley 670 and noticed much crisper throttle response in park, yet the same completely no idle/stall when in drive.

I'm running a 388 ci sbc with a comp xe284h. The car makes 6-7 hg" of vacuum in gear at 800 rpm's.

Ive been blaming the drive train/running gear for the high idle it needs in park in order to sustain a sufficient idle when placed in gear. Here is what I think my problem is.

The car has a real sweet attitude idling at 1300 in park. This is probably at the point where it is producing a good ammount of manifold vacuum.

When the car is placed in gear the rpm's drop and it immediately falls on its face and stalls.

I think this is because of the non adjustable factory style advance canister. It is providing no advance in drive ( at 600-800 rpm's, again making 6-7 hg" of vacuum).

In a nutshell to even have the car driveable I was running at 1300 rpm's in park. I have now realized that at this point (in park) the vacuum advance is running at full clip providing an additional 15 or so degrees of timing, thus a total of around 27. Then when you switch to drive and the rpm's drop (as well as manifold vacuum levels) you are back to the base timing of around 12 degrees (because the canister is providing little or no advance at this point with such a low ammount of vacuum).

Simply there is no happy medium with this cam and this advance canister with this configuration.

I need an adjustable can badly.

I may be preaching to the quire.

But someone please let me know if I am on the right page.
I'm going to quibble with your thinking a little. Although for an XE-284 1300 is a bit fast while 800 is probably too slow, so the engine is easy to stall when it's dropped into gear and wants to creep against the brakes when-ever stopped. You also probably are getting a hard engagement when dropping it into gear, these can and will bust inner tranny parts.

For a stock converter you're probably right up against the stall, although stall speeds are kind of mushy things to describe.

With a hot cam when driven on the street you're looking for something a little different in a high stall converter than a drag car. for the street you don't want such a hard engagement, but unless you're going on Pinks, you don't need a loose converter that doesn't hookup till the torque peak on the cam. All you need is something high enough to keep from knocking your teeth out when you put the tranny in gear or pulling you through an intersection with the brakes set.

My recommendation is that you talk to Comp and some converter folks, as well as lay your hands on a Summit catalog, they always include a little tech article regarding converter stall against cam timing. It's kind of generic, but it's a decent data point and you'll get plenty of those, decent and otherwise.

Bogie
Reply With Quote