I'm running a custom grind comp cam similar to a comp 278H. I got the engine running, but I have to idle it pretty high or it will stumble and stop.

This is most likely to due with the fact that I'm running a single plane intake with a decent cam. So a couple of quick questions.

I'm hard of hearing, so I can't really hear pinging. I have 93 octane in the tank and the initial timing at 8 degrees Before TDC (roughly).

Given this setup, what is the lowest reasonable rpm to set the initial timing at?

This is my first big block. Any recommendations on initial timing? Every BBC spec sheet I've seen has different settings than SBC's. I planned on following Lar's doc on setting the total advance, but I need to get the damn thing running reasonably first.


I'm hearing what sounds like tappet noise as I speed the thing up past 2K rpm. It has harland sharp roller rockers. I didn't hear this when I first got it going. Is it possible I need to readjust the rockers or could this just be pinging and I'm hearing residual noise from it.

I'm concerned. I shut it down and am letting it cool off. In the meantime, I'll check the plugs carb, etc to get a feeling of where I'm at.

I'd appreciate any advice. I could use a second set of trained ears to come listen. I always had my dad and brother back home to tell me what was going on, but my wife and neigbors here can't tell me what they're hearing.

Anyone that lives in the Northern VA/MD area is welcome to come help. Beer is on me.

Thanks

 

Anyone?

 

Steve, are you running vacuum advance? if so plug the line and set initial to 12 to 14 degrees. this might help it idle better for you and the fact that the vacuum is plugged it will curb the total advance when you gas it and might help stop the pinging..if that is what yur hearing.

as far as what idle speed to set initial timing: It just needs to be low enough to insure that the distributor weights are not swinging out and adding advance. you can check this by adjusting the idle speed up and down while looking at the mark with a timing light. Hope this helps you get it sustained...at least to begin with.

 

I would suspect that the 278 cam will not want to idle very good anywhere below 1000rpm. You may need to add stronger dist advance springs to hold the advance closed at idle.

 

Isnt' 14 degrees a bit high for a big block? I recall big blocks having their initial advance set lower than a small block.

I have the medium advance springs from the mr. gasket kit installed. Lars seemed to recommend those.

I'll give it another go tonight.

 

I have to agree with bumping the initial timing up to around 12-14 with the advance disconnected and plugged. Also, take some care in setting up the jetting on the carb. If you have not re-jetted, then you are probably very lean with your setup. I don't know what carb you are running, but you may have trouble getting the idle jets set correctly without some modification to (enlarging) the ports. Even with that cam, there is no reason why you can't idle at or below 1000.

 

I can not find a 278h in the Comp catalouge. If it is between the 274 and 284 (which I assume it is) it is a pretty mild cam for a 468 in. motor. :chevy

 

This cam doesn't feel Mild. Maybe I have my numbers are off. I just sent email to my engine builder. He can give me the exact cam specs. It's a custom grind that their shop uses.

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Steve

 

Ok, another stupid question while I'm at it. This thing get's hot *REALLY* quickly. Is that a trait of it having aluminum heads or something? It almost feels like it's running to lean, but it's running rich, I can smell it.

I've never been this confused with an engine in my life. I'm normally really good at this.

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Steve

 

Even if it is a small cam the motor is still a 468 with a very good set of heads and a 4 speed. I am sure the car will be fast. I would be curious as to the cam specs and the intake you are using.

 

The intake is an Edelbrock Victor Jr 2-R (single plane) with a milled down flange and ported intake runners. It's the older style manifold with the twisted carb flange.

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Steve

 

I just saw the other thread, 620 hp, with a hydraulic flat tapet cam? I know you have very good heads and a good intake, but that kind of power usually requires a solid roller or a very aggresive solid flat tapet. I remeber seeing the engine build before, mind printing it again. Did you have work done to the heads also. What are the flow numbers?

 

The heads are the Canfield's with the 350cc intake runners. The heads have been ported, polished, matched to the intake etc. On the dyno run they used a different intake and carb setup, so that may have had a little to do with the numbers as well. I'm so pissed, I can't find any of my engine paperwork in my office. I don't know what the hell I did with it. I'm scared because I was enron'ing old bills in here a few weeks ago...:eek:.

I emailed the builder and he's going to snail-mail me all of the specs. I'll post them as soon as I get them