I have a 236/248 110° and having big problems with my idle. I'm trying to get the idle down to about 975 rpm but just can't get it to idle decent. With decent, I mean it just idles from 925—1025 rpm. Some say retard and others say advance the spark.
Can anyone tell me what idle speed and spark advance you are running with your big cam???
More engine info in my sig.

 

I'm running a SR 242i 248e in a 385 with the idle set to 950 and closed throttle spark advance set to 34. Aside from the lope, its idle is absolutely solid.
Scott

 

You need more spark advance to get a better idle. I have the GM847 cam and set the idle to about 900 rpms on my 383 for that nice choppy lope. If your motor is still a 350, I would set your idle to at least 1000 rpm since that cam is a bit hotter than mine.

 

Just for reference I have a 228/228 cam in my 355 and it idles quite nicely at 800rpm.

 

I have a 242/252 duration on 110* cam in my 383 and it idles fine at 950-975. How's your tune?

 

240/240 112 LSA - I run 28* advance at 950 rpm.

 

248 / 254 @ 0.050, on 112° CL with 0.670"+ SR in a 408, it idles with considerable lope at 925-950RPM. But I am using aftermarket tuning (FAST) which I believe allows more finese in adjusting the idle parameters.
Aaron

Edit: Mine is a solid roller

 

I had to crack open my throttle plates quite a bit, to have it idle at all. My MAP is at 70-75 Kpa with around 30° advance. IAC is open all the way to 160 counts.
My ECM $$DA2 doesn't have so many tables for adjusting idle. In case someone wants to see my Datamaster file, I'll be glad to mail it to you.
BTW, my previous cam 230/236 114° did idle quite good but this cam wouldn't even idle with the same VE and spark advance. So like I said, I cracked open the blades quite a bit to have it idle at all, and still my counts move up to 160 while idling.

Thanks
Arnold

 

I have a 252/260@050 on a 112 lobe sep in a 450, and mine idles around 1100rpm. I guess I like the idle smoothed out a little bit. But with the size of the cam, it doesn't sound like it's idling that high.

Edit: mine is a solid roller

 

Arnold,
I run a 236/242 @.050 on a 112LSA with a 108 LCA in my 396. It idles around 875 to 900 with 28 degrees timing.The previous cam at 230/236 @.050 on a 112LSA and 108LCA ran about 850 idle with 27 degrees.
RG

 

Don't forget mine is a hyd. roller cam. Some of you fellows did not mention if yours is also one or if it's a SR.

 

How much did it pick it up, and how different is the street manners of the bigger cam on a 396"?

 

Curveit,
Street manners are better than I thought or I would have left that cam in it after engine dyno instead of running the 230/236. Brakes are good with 13 inches of vacuum.Haven't taken it to the track yet to compare them until I run it on the chassis dyno again to check fuel and timing. Should run it in a couple of weeks just prior to the Corvette Challenge in May. I'll let you know then.
Rick

 

What type of throttle body are you running? WHat you need to do is try to give idle control back to the ecm with the IAC. Try removing the throttle body and enlarging the openings. WHat also might help is to drill small tiny holes in the throttle body and go larger if necessary. The stock IAC is designed to allow enough air in for a stock motor not for a stroker.

I heavily ported my IAC passages that allowed my ECM to use the IAC (and spark of course) to control the idle.

Try increasing spark until you can hear the motor trying to accelerate. You should then see your IAC try to close to compensate. Trick is to find a good medium. then lower the timing until the IAC counts are near where they should be so it can correct for a low idle or a high idle.

good luck

 

Before I sleep i thought I'd add in about the throttle body before i sleep so i dont wait for a response...

Depending on the throttle body, some are not designed like stock. The stock throttle body has a IAC port that connects to the IAC port on the manifold. Many throttle bodies, ASM, TPIS etc all bleed the iac port into the main plenum. There is a mod that involves adding a copper tube etc to these throttle bodies to make sure the air from the IAC goes into the iac plenum. It is designed to help stabilize idle when working as intended.

 

I did this mod with the AS&M throttle body, but I run the same type of cam before this new cam you have here. I can idle down to 800, with an auto with a 230/236 cam on a 114 LSA. But its not as good as 850-900 especially with vacuum for the brakes with my 396LT1.

 

Comp Cams Hydraulic roller and SR idles with some cool lumps at 900+/-. The chip is setup for 10 degrees advance, not the stock 6.

 

Here is a picture of my TB. It's a 58 mm Holley for LT1 use. What I did though was enlarge the hole from 0.18" to 0.23". Strange, everything was OK with the somewhat smaller 230/236 114° cam. It's snowing at the moment so I won't be able to do anything until the snow is gone.

Thanks so far for your comments!!
Arnold

 

The Holley is a good TB with a dedicated port for idle so You're good there. You were asking what spark advance you should use at idle. basically advance the timing until you see the motor begin to idle higher and want to accelerate. Trim it back down just a touch while watching the IAC counts. Try to pick an advance that has the IAC in the middle of its range so that it can close to slow the idle and open to bring it up if need.

it almost sounds like your iac is compensating too slow causing it to hunt for a steady idle. Double check your vaccum lines coming from the manifold for possible cracks. many of those hoses can be old and cracking on the bottom side because of the manifold heat.

This is generally How i set my idle on my gen 7 dfi I'm not sure what you can see or adjust with the tuning method that you have. If you can adjust how much timing is added or removed from the idle control it could be that the numbers are too large when the idle isn't at the target speed. For example instead of pulling 2-3 degrees when the idle is 1-200 rpm higher than target it's pulling 6-8 degrees. This can cause a sudden drop in idle which will then trigger it to add a large advance which will shoot it back up. Hope this isnt all confusing just trying to help

 

Enlarging my TB bore gave me my best idle so far. The engine doesn't die anymore when the fans go on and the MAP is down from 70-75 Kpa to 65-70 Kpa. Don't know if I should enlarge the bore even more, even though it seems to be the right thing to do at the moment.

I'm still running OL and hopefully can go back to CL as soon as I figure out why my right 02 sensor is stuck at about 850 mV. I will exchange the sensor and see what happens. I have my WB located on the left side but I'm not very happy with what I see. It stays under 200 mV (AFR 14.7) until the water temp. is about 140°F, after that the mV readings are OK.