At what RPM does your 350 SBC idle?

[Gregski]

Rather than staring WWW III asking more timing advance questions, let me just ask you this:

When your V8 350 cubic inch small block chevy is warmed up properly and purring like a kitten, what is your tachometer reading? What RPM is it happy at?

Since the manual splits the idle adjustments into Automatic and Manual, please let us now which one you got an auto or a stick, thank you very much.

[Axle]

in gear, auto, 900rpm. Any lower and I get dimming lights at stop signs/lights when the alternator ends up running too slow to keep up with the load.

[rich weyand]

Did somebody say timing advance?

350/TH350, 700 RPM in Park, 550 in Drive. The 350 has a Comp 12-300-4 cam, which is a torquey cam, and that's with 16* BTDC base timing and a stock HEI.

I don't have problems maintaining voltage at that RPM since I put in a 94-amp 12SI alternator in place of the 43-amp 10SI. 12SI and 10SI alternators are same size, same brackets, same wiring, just swap it in.

[Jake Wade]

650 in park with 12º initial

[csdineley]

700 rpm in neutral

[Tom]

My 79 with the vortec 350 idled about 600rpm in drive with the 200-4R. The 78 with the old 385 I had around 900rpm. The current 388 will probably be 1000 or so.

[bnoon]

Red Ryder stock 350 auto 800 in park about 650 in drive.

Green Jeans built 350 barely idles at 950 in park and 750-800 in drive with a 3200 stall.

[t5noel]

May I ask a somewhat related question? What would a high speed idle be with the choke engaged at cold start?

[Jake Wade]

Originally Posted by t5noel

May I ask a somewhat related question? What would a high speed idle be with the choke engaged at cold start?

1200-1500 rpm

[SkinnyG]

550rpm in drive, very stable, 10inHg.

Any lower in rpm and it's pretty "iffy."

350/TH350, 231°@.050/.470/108LSA, 10.9:1, doctored Rochester, 20° base, currently ported vacuum (was manifold; testing), 2500 stall converter, MSD box.

[rich weyand]

Originally Posted by t5noel

May I ask a somewhat related question? What would a high speed idle be with the choke engaged at cold start?

When it starts it will probably be near 700, but as it warms up, it will rise to 1200 or more. Then you pop the throttle and kick kit off fast idle. I think the recommended setting for fast idle is 1200 rpm on a warm engine.

[86c20]

as low as she will go and still charge lol. my 86 4sp is around 850-900 in winter do to no choke and summer it seems around 650ish

[motornut]

350 in the 78 with a Holley
starts ice cold,up to 15-1600
Ends up down 5-600 any lower,
it has issues

[Gregski]

thank you all I think I will split the difference of what the manual says and the feedback I have received 600 ~ 900 and set mine back to 750 where it was before I replaced the points distributor with the H.E.I.

[y5mgisi]

Should be about right.

[Your41Plague12]

700 in Park, 550 in gear (TH400). Ran and idled great that way.

[MikeB]

Originally Posted by rich weyand

I don't have problems maintaining voltage at that RPM since I put in a 94-amp 12SI alternator in place of the 43-amp 10SI. 12SI and 10SI alternators are same size, same brackets, same wiring, just swap it in.

Good advice. I've run 78 amp 12SI alternators (rebuilt by AC/Delco) in two vehicles over the years. One has been going strong since 2002. No dimming of the lights on either of the vehicles. Excellent info here: http://www.madelectrical.com/electri...elcoremy.shtml

Of course the dimming problem could also be caused by too much voltage drop in your wiring -- poor 12 volt and/or ground connections, or wire gauge too small.

[Axle]

A 12si is an easier conversion than a cs133. Never realized they where that much better at idle than a 10si.

Alex.

[rich weyand]

Originally Posted by Axle

A 12si is an easier conversion than a cs133. Never realized they where that much better at idle than a 10si.

Alex.

It's not a conversion at all, really, just a drop in. The reason they are so much better at idle is that you can get them at much higher amperages due to the better cooling. If at idle the alternator is running at only 30% capacity, 30% of 94 amps is a lot more than 30% of 43 amps!

[MikeB]

I see where new cars have as much as 140 amp alternators to handle the computers and all the power doo-dads that are now standard equipment.

But have any of you guys ever measured total current draw in an older vehicle with A/C, hi-beams, radio, brake lights, etc all energized? I did it a few years ago on a 55 Chevy. Using a DC clamp-on multimeter, the max I saw was around 35 amps! Of course the car had a basic radio, no electric radiator fans, no power windows or seats, and no computers. Engine was running and battery voltage was around 14.2 volts, as I recall.

But, hey, I still like the 12SI design, and the 2x safety margin of even 78 amps, at least for my non-power doo-dad applications.

[rich weyand]

It's not a 2x safety margin, because alternators do not put out their full rated amperes at idle rpm. I wouldn't expect more than a third of rated output at idle from any alternator.

[piecesparts]

383 stroker engine with a 700 R4 automatic behind as well as a Comp Cam roller setup. The idle is a little lopey, so had to put in a 2300 stall converter to allow for the tranny to not drag the engine down. I run a 700 RPM idle with the tranny in drive and around 900 RPM in park or neutral. My timing is set at 32 degrees total advance and the engine works great on the street, I also have changed my alternator to a Tuff Stuff unit that carries 80 amps at idle, so no flickering lights or stereo issues.

Prior to changing the converter, I could not keep the engine idling without setting the RPMs up to the point that the carb was no longer in the idle circuit.