C2 67 427 Overheating at idle

[Alex K.]

I have an aftermarket cam in my 435 hp. 67,which is more radical than the stock 435 cam.The one speck I am positive about the cam is it has 7" of vacuum at idle.All cooling items,radiator,waterpump,fan clutch, are new.The car runs at 180 degrees on the road.I think the 435 advance can is not working with just 7" of vacuum,causing overheating at idle.Does anyone know how much vacuum the 435 needs at idle? What vacuum advance can should I try to solve this problem?

Thanks Al

[Joe L.]

Re: C2 67 427 Overheating at idle

Al------

The only one that I think MIGHT work would be the GM #1115355 or, possibly, the 1116163, although there might be others. Unfortunately, the 1115355 is long-since discontinued, but the 1116163 is still available (although it's not the same as the original 1116163 either in configuration or performance specs).

The Standard Motor Products #VC-24A is approximately the same as the above-referenced. You might want to try that.

One other thing: you wouldn't catch me running a street engine that produced 7" of vacuum at idle. If I had one, I'd change the cam. The standard cam for an L-78, 72, or 71 is MORE than radical enough for street operations.

[Alex K.]

Re: C2 67 427 Overheating at idle

I agree Joe,the company I got the cam from said this would give me more top end and still have enough vacuum at idle to operate power brakes etc.They were wrong,until I change it out this fall,Iwant to make the best of it for now.Do you know the specs on how much vacuum the 435 cam pulls?

Thanks Al

[Joe L.]

Re: C2 67 427 Overheating at idle

Al-----

Yes, the distributor used with the 1967 L-71 used a vacuum control which required 8" of vacuum to start the plunger and produced 16 crankshaft degrees of advance at 15" of vacuum. So, if that control is currently installed on your distributor, then it is, essentially, "non-functional" and you have, essentially, no vacuum advance, at all.

That's not to say, though, that this is the sole cause of your idle cooling problems. It's probably a major contributing cause, but it's not necessarily the sole cause.

[Alex K.]

Re: C2 67 427 Overheating at idle

Joe,
Do you have any other thoughts about what the problem is? I have a new Dewitts radiator,flowkooler water pump,shaw thermestat,seven blade fan
,fan clutch rebuilt by Fred Olivia,seven blade fan,50/50 mix coolant.Any advice would be greatly appreciated.

Thanks Al

[Mark #28455]

what duration is your cam at .050 lift

What duration is the cam, what is your idle speed, what is your timing set at (both idle and max and what RPM)? Are you running headers or a stock manifold and exhaust? Need more info!

I have successfully run racing cams with over 245 degrees duration and 108 degree lobe centers on the street with a lot more vacuum than you're making. Of course, it took about a 1000-1200 RPM idle speed and about 16 degrees of mechanical advance at idle with 36 degrees max advance at 3000 RPM (and it still produced 12 mmHg vacuum at idle).

Tell me what you have,
Mark

[Mark #28455]

I bet it's running really rich too

If the power valve in your carb is stock, it's probably open at idle. The power valve needs to be at least 2 mmHg less than your idle vacuum - or maybe you have a ruptured power valve that's making things worse.
Mark

[Joe R.]

Re: C2 67 427 Overheating at idle

I suggest that you fix the vacuum advance problem first and then see if you still have an overheating problem. Retarded timing is a known factor that can cause an engine to run hot. Others on this board can probably suggest the appropriate part number for a vacuum can that provides full advance in the range of 8 inches, but if necessary I think I have the info on file somewhere.

[Alex K.]

Re: what duration is your cam at .050 lift

Mark,
Cam duration is 240 degrees and 104 lobe centers. Idle speed is 1000 rpm.Have stock manifolds with sidepipes,using a stock 435 trans. ign. system 12 degrees of mechanical advance at idle with 36 degrees max at 3000 rpm.Hope this info helps for some advice about my overheating problem.

Frustrated,Thanks Al

[Alex K.]

Re: I bet it's running really rich too

Mark,
Thanks for the carb info I will check for that when I do the vacuum can change.

[Alex K.]

Re: C2 67 427 Overheating at idle

Joe,
Thanks for the response,if you have the part number handy Iwill give it a try along with the one I have from Joe Lucia.

Regards Al

[Mark #28455]

way too much overlap

A cam with 104 degree lobe centers and 240 degrees duration will idle very poorly with a stock exhaust as it will allow a lot of the intake charge to be diluted with exhaust at idle (as you already know). I think it was Duke who noted below that the manifold vacuum (not ported) for the advance can is the only way to go. In addition, you may still need to increase your idle speed to about 1200 RPM.

When you go to a higher than stock idle speed, you can get into other problems, especially if your mechanical advance curve is starting to kick in at or near idle speed. The only way to get a stable idle is if the mechanical advance doesn't kick in for at least 200 RPM above the idle speed.

Hope this helps,
Mark

[Michael H.]

Re: C2 67 427 Overheating at idle

Al,

Just curious. You didn't mention how hot or how long the car ran at idle before the problem occured. If, after reaching 180, it idles for an additional ten minutes and stays around 210-220, I wouldn't consider that over heating. My 66 425 HP always warms up to 220 in traffic or when standing/idling for a while and I've tried just about every different combination of everything over the last 23 years, including timing/vacuum adv units etc etc. I never saw any dramatic change no matter how I had it set up.

[Duke W.]

Re: C2 67 427 Overheating at idle

I'm so disappointed that the posts in this thread show such a lack of knowledge of vacuum advance and how to select a proper vacuum can.

How many times does this have to be explained?!

First and foremost, the L-71 has "ported" vacuum advance, so there is no vacuum advance at ide.. The first thing to do is convert to full time vacuum advance by routing the vacuum can signal line to the choke vacuum break (use a tee) or other convenient FULL TIME manifold vacuum source. Then install a vacuum can that is properly matched to the idle vacuum characteristics.

For the one millionth time, the vacuum can should provide FULL ADVANCE at no less than two inches less than idle vacuum!

The most aggressive off-the-shelf vacuum can (NAPA/Echlin VC1810 or equivalent) provides 16*@8", but with full time vacuum advance at idle, the idle vacuum should increase a couple of inches, or increase the idle speed until you get at least 9-10".

And my advice to everyone else is DON'T EVER install some bogus aftermarket cam with a 104* LSA in a SHP big block. It's just idiotic! The OE cam is just right.

I'm done with this thread!

Duke

[Alex K.]

Re: C2 67 427 Overheating at idle

Michael,
The car runs at 180,then after 5 to 10 minutes at idle goes to 210-220 after that it will peg the guage.

Any thoughts, thanks Al