'66 427/425 update

[R N.]

[Craig S.]

Re: '66 427/425 update

Kurt - this is GREAT to hear! I have been following your posts, and everyone's advice, and copying into a file for my records. I have a 66 L72 also I am in the process of building back to factory origninal specs, and I have the NAPA/Ecklin VC 1810 already purchased. I will set it up identical to yours, is sounds like a much better set up than the original. I do have the original distributor as well, but my springs have been tampered with, so I will have to play with the mechanical advance. Thx to you and everyone else for the great posts!...Craig

[Duke W.]

Re: '66 427/425 update

Excellent news, Kurt! I've been anxiously awaiting someone to implement this configuration and hear the results, but one thing has me perplexed. You report 20-22 of degrees of vacuum advance. The spec on the VC1810 should be a maximum of 16 degrees at 8" or above, so either the vacuum can is out of spec or you are getting some centrifugal at idle.

I'd suggest wrapping up the centrifugal with a strong rubber band and rechecking your idle advance. It should be initial plus full vacuum or 12 + 16 = 28. You might also want to check the can against spec with a timing light and vacuum pump. The plunger should start to pull at about 4" and be fully pulled at about 8" with about 16 degrees and no more regardless of vacuum.

It was a real revelation to me that the L-72 has ported vacuum advance. Similar overheating issues are experienced by L-71 owners, and I believe the same issue may apply - the engine may have a ported vacuum advance signal line, and from the specs, I believe that the vacuum can is too lazy with full advance at 15.5", so the 8" VC1810 connected to full manifold vacuum should insure that full vacuum advance is applied at idle.

Another thing you might want to try, Kurt, is drop the idle speed. My rule of thumb on idle speed is to set it as low as possible commensurate with acceptable idle quality, so you might actually find that it idles okay at 750 and a little less manifold vacuum.

I don't know if you record fuel consumption very closely, but if you do you should notice better fuel mileage in normal driving, that is, if you can keep your foot out of it.

Duke

[John Lokay]

Re: '66 427/425 update

Very interesting post. I have been working on my 1966 425hp coupe which also runs hot at idle. With great advice and much assistance provided by Everett Ogilvie and the wealth of information provided by Duke Williams on the DB, I'm on my way. As a first step, I just indexed the wires in my cap to factory specs (the wires were off by one position) and re-installed the distributor to better center the vacuum can. I plan to fire up the engine this weekend, set timing and see how she runs. Then I'll look into the possibility of changing to the Echlin vacuum can (I now have the orginal 360 can) Just a few questions for Keith:
1) At what RPM level did you set your initial timing?; 2) What shape is your radiator in, is it the original or a replacement model?; 3) You stated that at idle your temperature did not exceed 210 degrees. What idle temperatures were you experiencing prior to your new set-up? I assume that your temperature sending unit is accurate?

[Everett Ogilvie]

L72, For the record

Glad to hear that your car is running well Kurt.

Just for the record, I would like to say a few things about the L72. I own two L72 cars, and I have recently completed going through both - confirming factory configuration, or correcting it where items were found improperly configured, installed, or adjusted. I agree with Duke that full vacuum coming in early will help some parameters and this post is in no way saying that making changes is not the right thing to do with some cars.

My input is that if you aren't having problems with other parts of the car (old radiator, bad fan clutch, improperly installed distributor, badly adjusted carb, etc.), - the L72 can idle smoothly, and not overheat even when set up to factory configuration. Both my L72's idle so well and run so well that I don't feel the need to redesign and reconfigure the system. They can warm up a bit at extended idle on the hottest days, but the temperature comes right back down at the start of cruise. Neither pukes coolant (once the radiator self-determines the volume it likes).

Every 093 distributor I have tested (4) has centrifugal advance coming in between 900 and 1000 rpm. To verify, slow the idle down to 600 (yes, both my cars will run even at 550 rpm) and check the initial with your light. Increase the idle 100 rpm at a time and see if the timing advances. The distributors I have tested have at least 2 or 3 degrees coming in between 900 and 950 rpm.

To check your total mech. advance without having to rev the engine to 5500 rpm, remove the springs and run it at about 2000 rpm - it will all be in, and you can dial in the distributor to give you the total mech advance you want. Then let the initial fall where it may.

Right now, my cars are set up with 12 or 14 true initial advance (at 600 rpm), which gives about 15 to 17 at 900 rpm (there is also a small vacuum contribution, even with the ported signal). I admit that this initial timing may be giving too much total - I have about 46 - 48 total. I may dial the initial back to 8 or 10 (at 600 rpm, which would be about 12 or 13 at 950 rpm), which should give about 42-44 total.

My point is not to discourage owners from testing altered/improved setups on the L72, or the L71 for that matter, but rather that the L72 can be smooth, stable and pleasant when set up to factory configuration if all parts of the system are performing correctly.

[R N.]

Answers for John

John:

I'll try to answer your question about the rpm the intial timing was set.

1) I believe my mechanic first reduced the idle rpm and then set the carb first which brought the rpm up somewhat (I think around 700-750 rpm) and then set the intial timing.

2) The rad in my car is using the original end tanks with a new copper core.

3) You asked what my idle temps were prior to the fix. Before the fix the temp gauge would read min. 210 after a twenty minute drive, after that it would easily go 220-230. If I could keep out of traffic or at a steady 50 mph of so, if would never go below 210. I did replace the original clutch fan with the current GM service replacement (while I have the original rebuilt) which made a big difference to the amount of air coming through the rad, this alone keep the temp at the 210 mark or slightly less.

I also installed a 160* thermostat just prior to the fix, since the fix I've had the car out a few times for long drives (city & hwy)and the temp gauge reads between the first hatch line and the 210 mark.

I am assuming my temp gauge is accurate just based on the reading of the gauge and some other simple tests I did. Later this weekend I will be testing the temp reading of the thermostat housing with a I.F. temp sensor to compare the reading on my gauge should the weather clear.

One other thing you should note is that I live in southern Ontario and since I did the fix the outdoor temp has dropped into the 50-65* range, so I will not know the true effect until next summer.