Okay I just got done with the new mill. Cam is a 239/247@.050 on a 112. Overlap is the same as a comp 262cam. Something like 35-40deg.

I can't get this thing to idle well. We are just going to deal with warm open loop right now. It wont hit my target idle of 750. It stays around 500-600 and eventually dies.

O2 says about .45MV

I've got a nice flatspot for my timing and right now it's at 28deg which is where I got the old cam to idle stably.

IAC startup is 160. WARM iac park steps i've tried from the 5 it was before to 20 and it only seemed to get worse.


So can you have too much timing at idle? Any ideas?

 

While Harolds cams are small on the advertied duration, they idle like any other cam based on the .050 Duration. Think of it as a 230 at .050 hyd and it might make things easier on you.

Also, my cam is a little bigger than yours and at 110 lsa and idles fine at 14 *, 650 rpm in gear, tight converter. (carb btw) well not fine, but it will idle till it loads up. Your idle problem is probably fuel related. Since you tried more air and spark and it didn't get better. Try fuel. Also, from what Grumpy has posted, you should have your iac steps real low and let the TB set the idle. There was a post a while back about it.

 

My steps are pretty low, the screw in holding the blades open more.

Thing is it smells a little bit fat at idle. When I drop a few PSI (checking before burning a chip) it made the idle worse. Of course with out a cat this could just be the smell of the exhaust with a big cam.

I'll try adding more fuel and dropping the timing. I've noticed you can get a good idle out of a carb with low timing, but it seems as though I've usually had to add more for my FI setups.


Well, I've got it to do a nice flareup now... but then it just falls back down to 500rpm hangs then dies.

 

You didn't mention what kind of ign. system you are running! 28* initial sounds kind of high, it's a wonder it even cranks up at that setting. You sure you didn't get the dist. a tooth off on install?

 

No such thing as a tooh off. You put the spark plug wires on the cap where they need to be in relation to the rotor and TDC. This is fuel injected. It's timed at 6deeg before the computer takes over. MSD coil, MSD 6AL box, stock dizzy.


Added some more IAC steps, gave it a hair more fuel, lowered the o2 swing values, put it at 22degrees and it idles good at 700 in gear. Kaplutika~

 

So what your saying is, 28* is the reading after you connect the spark control link on the firewall? As far as getting it a tooth off, there's people out there that do that! Believe me!

 

28degs advance is what the car was seeing.

and as I said there really is no such thing as being a tooth off. You rotate the engine so that #1 is TDC. Put the distributor in however you like. See where the rotor points? Put #1 plug wire there.

End.

 

Correct! I agree! BUT! GM (if you look in the manual) shows a position for the #1 spark plug wire in relation to the engine (front to back view) I'm not saying it has to go there and I understand what your saying BUT, some people have pulled the dist. and re-installed it without removing the spark plug wires from the cap and have installed the dist. 1 tooth off. That puts it out of time with the cam. DON'T tell me it can't be done, because I've seen it happen. If you want to pull the dist. and re-install it in the same position AND, align the oil pump slot without changing the spark plug wires on the cap, you need to mark the position the rotor is pointing at TDC on the edge of the dist. body so it drops in at the same location. If you want it at the same timing * you mark the dist. flange (where the hold down clamp is) with a mark on the manifold. Do you understand what I'm saying now? I'm not saying your doing it wrong, Where you want #1 wire at is your decision, but , some dummies have never figured that out! and loose power by installing the dist. one tooth adv. or retarded from TDC. If you don't believe me ask the moderator of this forum.

 

That's where the factory put it, that's all. I left the plug wires on my dizzy, just turned the dist to where it needed to be where #1 was.

You can always turn the oil pump with a screw driver. And it's been my experiance that one tooth wont engage the oil pump the next will and the one after wont.

I see what you're saying, and I'm glad you see what I'm saying. I just don't want to be thrown in that catagory of a tooth of. I'm not that much of an amatuer.

 

Never stated that you were! I'm just saying that it can be done!
You never know who or what your dealing with on here. I just asked. Good luck with your engine, Hope everything run's good for you!

 

So cold startup/cold idle....

Big cam. Big cam wants more air or more fuel?

 

28*degrees at idle with the spark control link hooked up is fine. Mine idles best at 30* Adjust it, check the map, and readjust. Try to get the most vacuum at idle.

Charlie

 

Engines with big cams have trouble pulling air at cranking speeds. A greater IAC step count for cranking can help. On a TPI/MPFI engine fuel is injected at the port so it needs the air flow to move it into the chamber.

RBob.

 

How did you adjust the swing values on the o2?

Is that done by narrowing INT and BLM boundaries?

What are the benifits to doing that?

Thanks

 

Big cams tend to self EGR at idle from all the overlap.

EGR means more timing, and richer, to get a decent idle.

And yes you can have too much timing at idle.