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Old 08-07-2012, 06:10 PM
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Stall converter confusion

Hi folks, I'm building a '50 studebaker rat rod p/u. It came with a 350 chevy 30 over, flat tops, 2.02 heads and 600 holly hooked to a 350 turbo with approximately 373 gears. Here's the bad part the cam is one of those huffing and puffing wide duration cams but I have no idea what. I would guess from it's extreme rough idle it must be a 292 advertised or more. Problem is it also came with basically stock converter. At idle in gear,the engine just barely runs, loaping and wanting to take off. So I ordered a b&m 2400 stall. It came, i put it in and much to my surprise not much change. This was one of b&m's cheaper line. So this time I thought I would do a little more research. The engine idles at 1000 rpm's ( wouldn't get much lower), drop it in gear and it slows to 800 rpm's, power brake it and the wheels spin at around 1800. Now I'm trying to figure out what brand and size stall converter to go for. My confusion and ignorance comes in the area of what benefit in idle do you get as you increase the stall. It is the rough idle I'm trying to overcome without causing a problem with slippiing at normal driving. I'm considering around 2600 to 2800. Any help would be appreciated.
Thanks
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Old 08-07-2012, 07:06 PM
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Originally Posted by Bstalion View Post
Hi folks, I'm building a '50 studebaker rat rod p/u. It came with a 350 chevy 30 over, flat tops, 2.02 heads and 600 holly hooked to a 350 turbo with approximately 373 gears. Here's the bad part the cam is one of those huffing and puffing wide duration cams but I have no idea what. I would guess from it's extreme rough idle it must be a 292 advertised or more. Problem is it also came with basically stock converter. At idle in gear,the engine just barely runs, loaping and wanting to take off. So I ordered a b&m 2400 stall. It came, i put it in and much to my surprise not much change. This was one of b&m's cheaper line. So this time I thought I would do a little more research. The engine idles at 1000 rpm's ( wouldn't get much lower), drop it in gear and it slows to 800 rpm's, power brake it and the wheels spin at around 1800. Now I'm trying to figure out what brand and size stall converter to go for. My confusion and ignorance comes in the area of what benefit in idle do you get as you increase the stall. It is the rough idle I'm trying to overcome without causing a problem with slippiing at normal driving. I'm considering around 2600 to 2800. Any help would be appreciated.
Thanks
The ignition timing is at the root of it all. Basically you want a LOT of initial timing and a short mechanical advance. That allows the carb primary throttle blades to be closed where the transfer slot is exposed the right amount. If the throttle blades are open too far, the transfer slot becomes the main idle air/fuel mixture supply and this will cause a poor idle and off-idle transition.

There are many posts here on this subject if you want to do a search. Also you can read the info here and if you still have questions, just ask!

Holley primary idle transfer slot
The drawing below shows the primary idle transition slot as seen with the carb held upside down. The drawing on the Left shows an overexposed transition slot. Baseline the throttle blades to give a transfer slot that looks like the image below, Right:



Other carbs have similar transition circuits, and they need to have the throttle blades in the 'sweet spot' same as the Holley. If the throttle blades are open too far, a poor idle and off-idle transition can be the result.
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Old 08-08-2012, 03:42 PM
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Thanks fellows, I ordered the hei curve kit today and will follow your advice. thanks again.
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Old 08-10-2012, 06:49 AM
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When driving it,at what rpm does the engine come on cam,or worded another way,at what rpm can you start to feel the torque comming on.Mine started at 2800 rpms so I bought a 2700 stall converter.You dont really get any benefit at idle with the torque convertor,you want the t/q to kick in when you come on cam.What is your vac.reading at idle,if its low say around 10 to 8ins.then you have a big cam.Ive got a mid level cam and my vac.at idle is 14ins.

Last edited by dogwater; 08-10-2012 at 07:04 AM.
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Old 08-10-2012, 07:49 AM
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get a vigilante converter and never look back
3200 is the one i got and i love it
Precision Industries
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Old 08-10-2012, 07:59 AM
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a big cam like the 292H magnum needs as 10" 3500 stall converter.
It will show around 8"-9" manifold vacuum at idle 900-1000 rpm. no load/neutral
another way to approx the cam is to measure the lobe lift of the pushrod with a dial indicator.
(rocker arm removed)
between the idle manifold vacuum and lobe lift you should be able to nail down the cam.

Get the B&M hole shot 3600. Thats the converter you should have bought in the first place.
Distributor curve: Wiith a big cam you can simply lock out the advance curve and run locked timing
34-36deg bTDC. Then hook the vacuum advance to ported vacuum.

If the locked timing proves to be too much recurve the distributor for 26deg at idle and 34-36deg at max advance. (short limited 8 to 10deg advance curve) again use ported vacuum ...
get a 3.5" or 4.5" power valve. now reset the carb.

The 3600 stall will take about 2 weeks to get used to.
Ya it drives different but at hiway speeds the slipage is minimal when used with the right gears.
and it will now idle correctly and GLH.

The B&M 2400 stall is jsut a slightly modifed stock GM 12" 2100stall converter.
Not near enough for the big cam. Nore is the hole shot 3000.

You want the hole shot 3600... or change the cam to one that works with your converter.

The 2400 stall will work well with pretty much any cam with 218 to 226@.050" duration.
If you are a cruiser more than a racer you will probabily like the milder cam anyway.

you can get a good idea of the cam duration by reading the manifold vacuum at idle
and comparing to the Comp Cams extreme cams dyno and idle manifold vacuum/idle rpm charts.
http://www.compcams.com/Pages/401/dyno-sheets.aspx

You can see by the power/torque corves that a cam like the 292H cam (244@.050) don't get real busy till 3500 rpm
so you want a 3500+ stall with that one.

How to limit/or lockout the advance on a HEI


Be sure the OEM GM starter bracket brace is installed. If yours is missing get one.

Last edited by F-BIRD'88; 08-10-2012 at 08:22 AM.
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Old 08-10-2012, 08:33 AM
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A good cam for the 2400 stall would be a Crane Energizer 278H-10 pn 10013.
You will probabily like the car a lot better overall.
Crane Cams | Automotive Home Page
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