Team Chevelle banner
Cancel
Create thread New Garage Forums

How much does stall speed affect idle quality?

Jump to Latest
1 - 20 of 22 Posts
D

Dan Orgill

· Premium Member
Joined
·
5,054 Posts
Discussion starter · #1 ·
This is my current set-up:

496
Hyd Roller: Adv. 288/294, 235/241 @ .050 .618/.618 on a 110 LSA
Pro Systems carb
TH400 w. 2400 B&M Holeshot

I've been trying to get the idle where I want it to no avail. I'd like it to idle at 750 in gear, but when I get it there it's always around 1000 in park, where I'd like a 100-200 rpm difference at the most ( 900 in park would be nice ).

I need to get my distributor vacuum can changed as well, but it was suggested to me that a 2800 stall speed may help out as well.

Any thoughts?
 
#2 ·
i recently got a torq converter spec'ed for my combo by Pete@Hughes
i moved from a 2500stall hughes unit to a custom unit for my cars spec's
and it's WOW, what a difference, very happy i took the advice to do this...
it does idle much nicer now in & out of gear.
 
#3 ·
The 2400 stall converters are for guys with non stock engines. Perf engines are inappropriate for tight stock converters. More stall/2400 is to prevent creeping at the stop light. There should not be a problem here with the converter... you should be able to tune your idle system (distributor curve, timing and carb's idle mix, air bleeds, and idle speed screw) to have a very solid idle at 800 in gear. That cam is mild for a 496.

My own 454/461 has approximately the same cam, I can idle in park or neutral 750-800rpm and neutral/park 900
I laughed at my neighbor several months back. He was complaining that the L79 327 cam I sold him would not idle at 600 rpm. I told him that was PIE IN THE SKY. I told him to check the service books for idle speed, etc. After some tweeks we got 800 in neutral and 700 in gear, solid, without a hint of it dying.

No vacuum leaks
more initial timing
less total timing
used a vacuum gauge to set the idle mixes
 
Save
Reply Quote Like Like
#4 ·
It sounds like the throttle is open too far to idle properly. What carb and what are your timing specs?
 
Save
Reply Quote Like Like
#5 ·
How much does stall speed affect idle quality?
Click to expand...
In my case, it affected idle quality tremendously.

I did everything that everyone ever suggested with no real solid improvement.

I did the t-slot squaring thing, no better, actually worse
changed air bleeds, no better
adjusted a/f for best idle, no better
adjusted for best vacuum, no better
had IFR/emulsion circuit modified, helped a bit, but still never 100% "fixed"
tried full manifold vacuum, nothing
ported vacuum, nope...
different power valves...
Heck, even a different carb....not quite
Base timing at everywhere from 18* with 20* mechanical, to locked out at 38*...still never quite right.

No vacuum leaks, no fouled plugs, no bad wires, no nothing that I could find...

Had to idle at 1000 in Park, in order to idle at 750 in gear, and even then it was a little inconsistent.

Swapped in a converter that was designed for my combo about 2 weeks ago.... car now idles at 850 in Park, 750-ish to 800 in gear...no more raw gas smell, and idles rock steady
 
#6 ·
I agree with the converter suggestions. The only other thing I can think of is you might have a vacuum leak. You mentioned wanting to replace the can - Is the distr vac adv plugged at the carb? More initial timing might also help.
 
#7 ·
rel3rd said:
In my case, it affected idle quality tremendously.

I did everything that everyone ever suggested with no real solid improvement.

I did the t-slot squaring thing, no better, actually worse
changed air bleeds, no better //snip!!!//// No vacuum leaks, no fouled plugs, no bad wires, no nothing that I could find...

Had to idle at 1000 in Park, in order to idle at 750 in gear, and even then it was a little inconsistent.

Swapped in a converter that was designed for my combo about 2 weeks ago.... car now idles at 850 in Park, 750-ish to 800 in gear...no more raw gas smell, and idles rock steady
Click to expand...

Tell me what you previous converter was?
 
Save
Reply Quote Like Like
#8 ·
Fuel needs are load dependent, so a lower stall will load the engine harder and need more fuel. A/C adds a load when the compressor is energized, so more load there. And add performance cams that drop idle vacuum you don't vaporize fuel as well, so mere fuel is needed or more heat or energy applied to the fuel is needed. And usually more initial timing. And the bigger the cam, the lower vacuum is at idle, and then everything becomes more sensitive to the amoount and quality of fuel delivery at idle. then you add different fuels that have different vaporization properties...
 
#10 ·
I had a b&m converter once and it was crap. Mine was the opposite... too loose. I recommend a custom converter like Hughes for anyone. It's like a custom cam... it probably is better because it's made for your car
 
#11 ·
kettbo said:
Tell me what you previous converter was?
Click to expand...
It was "supposedly" a 10" B&M, but ended up being a 12" No Name converter that footbraked to about 1400 and flashed to 3000 with the new engine...maybe 2600 with the old 402. New Freakshow converter footbrakes to 2700 and flashes to 4600 :eek: Whole different animal now...:yes:

With carb, distributor and everything else double, triple, and quadruple checked...and then checked again, it idles consistent and tame like a stocker now...just sounds a lot meaner. ;)
 
#12 ·
I agree, a custom spec'd converter would most likely solve your problem. Freakshow sells a decent custom spec'd converter for $320. Not sure if Bob got that particular one or not. Everyone seems to rave about them.
 
#15 ·
Dan pbly a combo of convertor and tuning .........yes a real loose convertor can cure it but then you have a real loose convertor ........ so as Mark posted get your carb as close as possible with as much initial as you can then think convertor ........my .02
 
Discussion starter · #16 ·
CDN SS said:
Dan pbly a combo of convertor and tuning .........yes a real loose convertor can cure it but then you have a real loose convertor ........ so as Mark posted get your carb as close as possible with as much initial as you can then think convertor ........my .02
Click to expand...
I'd like to solve this with tuning and not touch the convertor...much cheaper. Once the weather warms up I'm going to pull the distributor and install the new B28 vacuum can. I'm looking for someone who will re-curve it for me.
 
#19 ·
Dan, I had the 2400 B&m holeshot converter.
Zz502 with 242/252 110lsa cam
Prosystems carb.
Idled solid down to 600rpm and could idle a 500 in gear IF I wanted to.
Idle would jump up and down about 50rpm.

With the idle screws 1 1/4 out, it would idle at 650 in gear and 800 park. When very hot, after 45min + it was idling around 800in gear and 1000park.

Timing at idle around 34degrees inclduing vaccum.
I don't like setting idle mixture screws with vacumm, always made for a too lean in gear idle. I set it where it has the least drop between gear and park.
 
#20 ·
Suggest you start with finding out how much initial timing you have now ........timing tape and a std timing light is all you need to do that ............then once you know where your at you can start to tune Also how much vacuum does motor make at say 800 rpm in gear with VA disconnected ....... that will tell you what vacuum can you need and tell you whether you can tune dist / carb to get better idle before you move to a losser convertor .......IMO if it really stalls at 2400 you should be able to get a steady idle with no more than 200rpm drop
 
1 - 20 of 22 Posts
About this Discussion
21 Replies
13 Participants
Last post:
1968 hot rod
Team Chevelle
posts
5.3M
members
131K
Since
1998
A forum community dedicated to Chevrolet Chevelle owners and enthusiasts. Come join the discussion about restorations, builds, performance, modifications, classifieds, troubleshooting, maintenance, and more!
Full Forum Listing
Explore Our Forums
Bench Racing Performance Engine Chevelle Tech Body Shop