Frankie the Fink

My '63 split window ran great when I first got it and did some minor tweaks but over the past year it had gotten a little crazy to drive. If I floored it from a low RPM launch it would pull hard initially, then buck like a horse and then re-launch chirping the tires most times. Quite embarrassing. I chased various issues like accelerator pump, fuel pressure, dirty filters -- the usual villains. And after those didn't help I put a dial back timing light on the car. The book calls for 4* BTDC for the 250hp - I bumped it up to around 10* but noticed the advance was all over the place...freezing up on acceleration and then breaking loose and snapping in advance. Hence the bucking.

After exchanging several emails with Lars I sent off the distributor for a complete overhaul. He found several problems with the advance weights "stalling" before going over center, too much endplay and issues with the tach crossgear thrust area requiring machine work. Vacuum advance can was pulling a little but it was shot too. Wow - who knew ?

Got the rebuilt distributor back from Lars Friday morning (nicely packaged) and it looked factory-fresh. Decided to try Lars installation method for 'walking' the rotor around the firing order, pulling the oil pump drive along with it until it fully seated in the right location. Worked like a breeze -- much better than the old flashlight, mirror and long screwdriver in the hole method.

Set the timing at 16* BTDC per Lars instructions and the car idles smooth as silk and pulls hard to redline, cruising is effortless too.

If you need this sort of work at a reasonable cost, done by an expert Lars is the one you want. Sorry - was so pumped to get the dizzy back I didn't take any pictures of it! Very unusual for me.

rtruman

You know its nice to have it right ,I got lucky installed the top of the line electronic
pointless device .Mine runs strong to reline smooth . Everything hidden under shielding .
Don't anyone tell the NCRS police. Had a guy at the last car show say my spark plug wires weren't correct ,His car was a Cobra ,I asked him if it was a kit car ,he stumbled and said Carl Shelby said his car was the only one Carl approved off. He didn't admit it was a kit car.

Dave Tracy

Frank:
I'm surprised at the 16 degree advance. I'll try that is coming weekend. By the way, thank you again for the fuel pump info.
Dave

Bluestripe67

Lars is the distributor man! Dennis

MikeM

Unless your distributor has other non OEM alterations to the advance curve, I don't believe 16* intial will work very well on your engine if it's a base engine.

Powershift

Does this change your mind about points versus Petronix??

What advance curve did Lars build into the distributor?? With 16 degrees initial advance, he must have shortened up the centrifugal advance quite a bit…………as 38-40 degrees total (initial + centrifugal) is the generally accepted number. Assume the distributor still has its original vacuum can, or did Lars replace with a different unit/can??

Larry

lars

You can't just set initial at 16 without checking the total curve and setup: Total advance needs to be limited to 36. Your initial is a function of the total.

Lars

Frank's distributor had the stock, hi perf short advance slot in it, which resulted in a 16-degree initial spec to achieve 36 total. I could have machined the slot longer, but the 16 degree initial spec actually tends to work pretty well when combined with a 12-14 degree vacuum advance: This produces actual idle timing of about 30 degrees, which is about as perfect as you can get.

Yes, I replaced the vacuum advance control unit with a B26, limited to 13 degrees.

Lars

Frankie the Fink

Pertronix Ignitor III re-installed after I received the rebuilt distributor back.
Initial set at 16* EXACTLY.
All I can say is that the car is performing better than it has since I first acquired it.

In fact, the tach used to be shaky as all heck up to about 2,200 RPM.

It now bounces some at idle but on acceleration smooths out nicely all the way through the RPM band.

Powershift

Lars:

Thank you for the explanation. Hopefully it will also help others.

Larry

65tripleblack

For 1963 looks like all carbureted engines used the 1111024 distributor with a 24 degree advance slot. Is this correct?

For 1965, both the 250 and 300 HP engines used the same 1111076 distributor, with a 26 degree advance slot. In order to run more INITIAL advance than stock specs call for, the advance slot must be shortened by brazing, or an oversized oval bushing must be used in order to limit centrifugal advance.

For 1965, the 327/250 used 4 degrees initial with 26 degrees centrifugal, for a total @ 4100 RPM at WOT of ONLY 30 DEGREES. If you set initial to 16 degrees, you end up with 40 degrees WOT total!!!!!!!! No more than 36-38 degrees WOT advance is optimal for most SBC engines and more than this will kill power and result in bucking.

The 327/250 ran retarded timing according to factory specs. Must have been due to the small camshaft developing high cylinder pressure at low RPM (high torque), and customer complaints of detonation.

The question I have, is why the 327/300, which was essentially the same engine, ran an additional 4 degrees................for a total of 34 at WOT, which is closer to optimal? Bigger chambers in the 327/300 due to different heads? That would explain it.

lars

The slot in the distributor I received from Frank (and all indications are that it is original) allowed a total centrifugal advance curve of 20 degrees. Not 26. The slot had not been welded or brazed - it was original. A 20-degree slot requires the initial timing to be set at 16 to achieve 36 total at WOT. I run all distributors on my SUN machine for setup and verification.

Lars

65tripleblack

Lars,
See edited post # 10 above.
Some questions for you.
Thanks.

PS: my 1111069 distributor now runs 20 degrees initial with 16 degrees centrifugal after I shortened the slot from 26 to 16 degrees.

rtruman

The fact that Frankie says it runs great is enough for me .Maybe my new I phone
has an APP I can dial into the Petronix Ignitor III and see what's going on.

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Pertronix Ignitor III

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Pertronix Ignitor III

lars

Many of these decisions were made to limit warranty claims: A person buying the 250-horse entry-level Vette is probably more likely to fill it with regular rather than premium, whereas the customer buying the "performance engine" is more likely to use the correct fuel. From a performance standpoint, there is no reason to run the retarded setting: I've never seen a set of stock small block heads that did not need at least 36 degrees of total timing. Many perform best in the 38-range. Getting the timing advanced from 30 to 36 makes a significant difference in power, but will get a 10:1 engine into detonation if premium gas is not used.


That probably gets you some excellent off-idle throttle response, and if you have a big cam, will certainly help your idle quality. I'm running a big solid roller in my '64 407 car, and I run 20 initial with 34 total (good aluminum heads). This setup puts out 500 horse, and the car will idle in traffic on a hot day all day long without ever breaking 200 degrees.

Lars

Frankie the Fink

Ha! - there are no more "entry-level" split window coupes !

Part of why the distributor got sent off was because I couldn't get anywhere near the 36* "all-in" total with the initial at anything close to the 4*...so I tried 8*, then 10*. That's when my sticky advance really made itself known. I tried lots of options including the advance limiter bushing in and then back out. A dial-back timing light is not a SUN machine so I got tired of filling the garage with gas fumes and revving the snot out of the engine for trial and error testing.

Now, the car runs out strong (it IS a lil ole 250hp after all) with no issues. No detonation, no 'trailer-hitching' at cruise, etc... I detected no signs that the distributor had been modified and it had stock weights and springs..did NOT have the advance limiter bushing at all initially. Those were prone to disappear over time anyway.

lars

Yeah, no kidding... I was referring to the cars when they were new and under warranty: The "entry-level" Vette would be the 250-horse, and GM sold quite a few of the them.

Glad to hear the setup is working well for you. The way the curve finally came out, it should provide a very smooth and strong level of performance under all throttle conditions. Good job on the installation and timing!

Lars

65tripleblack

Sounds like a stout, well thought-out build!!

I'm running a solid roller of around 250/250 .050" duration with high ratio rockers for valve lift of around .600+/.600+. With angle plug aluminum heads with (somewhat) compact heart-shaped (modern) chambers, 34-36 WOT (all-in by 2300 RPM) advance works best. This cam would not tolerate the stock 236 vac can, and an adjustable Accel can was fitted, which I limited to 14 degrees vacuum advance by making a limiter block for the link arm. This .030 over 327 (331) makes 414 RWHP on a DynoJet........something around 460-480 NET flywheel depending on your generosity with drivetrain losses. The roller cam gives the engine 300 ft-lbs @ 2500, which is plenty torquey for this type build. Because of other mods that I have done, as well as the addition of an oil cooler and a 160 thermostat (which keeps the Z28 dual plane nice and cool), this engine runs pegged at 160 degrees at all times. Just like a modern car, ambient temperature has no bearing on coolant temp, it is strictly governed by the t-stat because the cooling system has tons of "margin". With the 5 speed, it's a joy to drive on the highway. The closed-system which I inconspicuously fitted makes checking coolant level unnecessary.

65tripleblack

It was not a "limiter" bushing at all. It was present on all distributors, and again, GM in it's infinite wisdom farked-up. A bronze bushing should have been used to avoid those millions of rubber bushings that only lasted a few thousand miles. Probably saved a good .04 cents per car.

A LIMITER bushing is oval shaped, which, in effect, shortens the travel of the autocam without having to braze the slot to shorten it.

BANG11

Like to hear more about this method, I've got to install mine this evening.

Frankie the Fink

Here its described in detail....starts on second page.