I have a 1966 Oldsmobile Delta 88 that has a stock Ultra High 10.25 to 1 Compression Ratio Engine with an Edelbrock Performer Intake Manifold , Pertronix Flamethrower HEI Distributor , and a Newly Refurbished Rocheaster Quadrajet Carburetor which I had jetted for my Altitude. .I changed over from the stock two barrel setup. It seems to run well however I do not know where to set my initial timing at with using an HEI Distributor now ? I plugged the ported vacuum port above the idle mixture screw on the front driver side of carburetor after disconnecting the vacuum line from there and set my initial timing to about 11 or 12 degrees before top dead center while idling at 800 R.P.M. Should I be blocking or plugging any other lines or fittings when checking the initial timing at idle ? I also run Maverick gas station's Ethanol Free 88 octane Gas mixed with three or four gallons of 100 octane gasoline when filling tank. I live at an altitude of 4600 feet . I do not have a timing light with a built in advance option , I just have an old school Sun Timing Light.

 

With an HEI you should be about 18 to 20 degrees initial.

 

Welcome to the quadrajet team. These carbs are great. If you’re curious about rods, jets and other qjet tuning, I think I have some posts on mine around here. Fair warning: I’m no engine expert, just an interested hobbyist who’s been at as an amateur for about 40 years.

I have a couple of 455’s my 66 big cars with very similar setups: Performer intakes, HEI, qjets. I run 91 octane here in CA, but our gas here is part alcohol at all times, so I tune for that. I run my cars just a bit richer than typical to make up for the lower energy density in alcohol. Also I’m mostly at sea level near San Francisco.

There are many strong opinions about timing here from people who know a lot more than me, but I aim at 12-14° initial using manifold, not ported vacuum. This is just what I do, not authoritative.

Usually around 750-800 rpm, with the vacuum line off the HEI (and the line plugged - traditionally with a golf tee or screwdriver), I timed the HEI to around 8° initial or so. Then when you hook manifold vacuum back up, you’re in the 12-14° ballpark for initial. You’ll find the Olds big block really sings at 16° initial with vacuum hooked up, but it will also ping/knock like crazy at midrange and high RPMs unless you put high octane (like more than 91) gas in it.

If you’re not using the ported vacuum port, just plug it off. Use good quality vacuum plugs & check the condition of your vacuum plugs over the years. The heating & cooling cycle on rubber eventually cracks the rubber plugs which can cause vacuum leaks.

I recently switched to progression ignition HEI’s and like them. See my posts on that elsewhere. Here’s why I changed:

When I was using traditional vacuum can HEI’s, I was using Taylor brand HEI’s. My problem with those was I would have a terrific idle between 12 & 14° initial, but in the midrange and high RPMs the engines would knock. So I’d turn back the inital to 10-12 just to eliminate the upper RPM knock. But then they idled worse and didn’t feel as strong.

I tried several different vacuum advance cans along the way to retard mid-range timing - eventually landing on the Buick can Echlin 1838 (I think) as the best option. But when it wore out I couldn’t find another. The variable vacuum cans where you use an Allen wrench to advance/retard were almost always too advanced at midrange, but slightly better than the Taylor-suppled Olds spec’d cans.

If & when you get around to it, I like my Innova dial back timing light. It’s a real advance over the older models and the investment was worth it to me. I’ve only had my ‘66 Starfire over 5,000 feet once about 20 years ago at Lake Tahoe. Fun drive.

There are about a million threads here & everywhere on timing engines. Survey them and suit yourself.

Hope that helps, it may not be perfect, but it’s worked for me.
Chris

 

Never trust a dial back timing light…..no matter how much you paid for it.

 

Hi Chris , have you replaced the 425 engines in your cars ?

 

Why? Mine is a 45 year old Sears tested 100% accurate.

 

My 66’s both 455’s. I run both with late 170 series quadrajet because the center fuel inlet seems inherently safer to me than the original side inlet with the pressed in freeze plugs. My carbs are 800 vs 750 cfm, so that wakes up the engines a bit. Due to increasing emissions laws forcing carbs to get ever more precise, you can also tune those qjets with great precision. I use an oxygen sensor and wide array of parts in my tuning kit to aim at maximum power, not emissions.

My 98 convertible first got a 455 crank in 80’s when I was young and figured why not go for more displacement. So it’s a 425 block with 455 crank. My Dad was the original owner so I know the complete history of that engine. I deleted, but have kept the original California emissions equipment for decades, just in case CA ever decides to force me to put the stuff back on…

My Starfire had with a 1970 or so 455 in it when I bought it from the previous owner in 1997 or so. It worked, I had it rebuilt and whatever engine I put in it was not ever going to be original again so I’ve never worried too much about numbers matching or originality. If you looked at it, its the correct Oldsmobile ‘66 red, but the non-numbers matching thing is one of the reasons I had no great fear of piercing the inner fenders to add outside air induction scoops that Olds just didn’t put on the Starfire.

I don’t want to invoke a flame war, but why should we not trust dial back timing lights? I’m ignorant.

Good luck to OP on your timing & tuning project!
Chris

 

The initial timing depends upon how much mechanical advance the distributor has. Any idea how much your Pertronix unit has? It should be in the documentation.

Initial = Total - Mechanical

Many GM HEIs have around 14* mechanical so the initial needs to be around 20* per the above equation to achieve 34* total. My HEI has 18* mechanical so I set the initial to 16*.

I have a Moroso HEI Advance Curve Kit thats center bar and weights give 24* mechanical, which is the same as my original points distributor. I ran that for decades with 10* initial until a new cam needed more initial to idle smoothly, so the original HEI parts went back in.

As for vacuum advance, you can easily make (or buy) an adjustable stop. I did that with my factory HEI 24* can and limited it to 10*.

 

Ported vacuum was used to make cars run hotter for emissions reasons. You should use manifold vacuum. Chris gives you good advice above.