bweaver999

I have known for a while my stock distributor has not been what it should be. The car currently has 350CI, 60 over, 10:1 motor with Edelbrock Performer aluminum heads and Performer RPM cam. Have an Edelbrock 600CFM Performer on it as well. Planning to install new distributor, wanted to check a few things first and developed a few questions. I decided on a Mallory Unilite as it is new, breaker less, and costs about the same as a rebuild.

Distributor and parts I purchased from Jegs for this:
650-3864501 Mallory Unilite for Corvette Distributor
650-29216 Chrome Coil For Breakerless Systems
650-700 Ballast Resistor, 0.7-1.5 OHM
650-29351 Active Power Filter

Specs on cam: http://www.bjpgj.com/MyEdelbrockPerformer.pdf (figured pdf was only way to get it to display correctly).

Checked timing and vacuum before replacement. The distributor appears to be in correct location, timing appears to be 12 degrees at idle with vacuum disconnected. This is based on a pencil mark on balancer from previous owner. The odd thing is, it is opposite the “mark” on the balancer, which is highlighted in white.

Vacuum:
RPM “Hg.
900 7
1500 13
2000 19

Seems to max out at 19/20 further up the range. At least I believe I do not have a vacuum issue other than it’s a bit low at idle which sounds like the cam overlap. It has a great sounding idle and runs pretty well so I like the cam.

Questions:
What is up with the timing mark?

Does vacuum sound okay? I know it’s a bit low for a stock cam, but believe I should be able to set it up okay.

Thinking of setting initial timing at 12 degrees (vacuum disconnected) and 36 degrees total (vacuum attached at 2000RPM). From threads I have read, that sounds like it should be pretty close. Any perspective would be appreciated.

Thanks!!!

Kensmith

You are right on the money with that setup. Shoud run good. Should be 36 at 3000 rpm though.

AZDoug

Your timing mark is 180 off.

Sounds like you need to:

1) verify the rotor is pointing at approx the right rear inside valve cover hold down bolt at TDC with the balancer (white) mark at the zero on the indicator tab, and

2) verify that your plug wires are correctly postioned on the cap.

#1 plug wire should be at the position the rotor is.

#1 plug wire is the frontmost left hand side cylinder.

Doug

Sky65

Sent you a PM.

Kensmith

If you think the timing mark on the balancer is wrong or the degree indicator, you can buy a tool that you screw into #1 plug hole and rotate the crank after removing all spark plugs and the tool has an indicator the will show you when the piston on #1 is at top dead center. Then you can check the line on the balancer against the degree marker. That only works if you installed the timing chain properly (dot to dot) on cam and chain wheel when swapping cams.

Injected Stingray

Hello, Sometimes the Inertia ring will slip on the damper causing a false reading on a timing light. With the mark on the opposite side I think u may have that problem. Pull the# 1 plug and the driver side valve cover. Pull the COIL wire so the car wont start.Have a someone bump the engine over with your finger in the spark plug hole on the # 1 cylinder. When both valves close on #1 and you feel pressure on your finger your timing mark should be close to or approching TDC. If the factory mark is on the other side and the painted one is close you should replace the damper. hope this helps. chris PS If the Mark is off 180 exactly the cams in 180 off.

bweaver999

Doouu!!!! Helps to check the correct wire, I know where the #1 plug is, thought I knew where the wire was on distributor. Actually checked #7 wire. Found an Interesting site on the C3 forum:

http://boxwrench.net/specs/chevy_sb.htm

Shows firing order and torque specs for Chevy small block. Poached a picture of the distributor and wiring from BarryK's site, edited it to show cylinder numbers:
http://www.bjpgj.com/IgnWiresFull.JPG

Plan to re-check timing before replacing distributor, hopefully tomorrow.

JohnZ

"Total timing" (36*) is set with the vacuum advance disconnected and plugged; "total timing" is initial + centrifugal only - vacuum advance is not part of that equation. If the vacuum advance unit is the correct one and is connected to full manifold vacuum as it was originally, it will add about 15* to the "initial" setting once connected (12* + 15* = 27* in your case, which is "total idle timing").

bweaver999

Wahoooo!!!!! Holy cat fish batman!!!!!!

Put the new distributor in today, first confirmed the timing was correct on the #1 cylinder with old unit. She fired right up. I had read some info on Mallory distributors and thought it had vacuum advance, turns out the Corvette distributor is pure mechanical. Buttoned everything up and went for a spin. What a difference. She does not light the tires up just nailing it in any gear, but they are close to breaking free.

Some advice, if you know it has never been or don't know if it ever was re-built, have your distributor re-built by a reputable source and insure the curve is working correctly. I am sure my mechanical advance was not working properly, not sure of vacuum but suspect it was also not up to snuff. Either that or replace your current with the Mallory. The part numbers above are about $500 from Jegs and replace everything in the line and the Power Filter provides protection from spikes, which Mallory claims is the number one killer of electronic ignitions. It fits nicely in place of the old unit and once the covers are on, few will no it’s not original. Figure a proper re-build would cost about the same. Yes you can re-build it yourself but how to you know it’s working correctly when done? Perhaps if you attended a Lars TFB session, otherwise seems something best left to someone that knows what they are doing.

Once I discovered there was no vacuum advance on the new unit, I decided to split the difference and set timing to 18 degrees at idle. Did a quick check, looks like mechanical takes it to 36 degrees in the 2000 RPM range. Took her for a spin and boy, it’s a different car!!! Just trying to figure out where to set things for this. I think there is some adjustment on the mechanical advance I could play with, but for now she is running great.

Question, sounds like with a properly working system, at idle you should see have 25 degrees. Is that correct?

At 3000 RPM, timing should be 36 degrees?

JohnZ

If 25* is your base timing and you're sure it's fully-advanced at 3000, the distributor is only adding 11*; 25* is fine with a vacuum advance distributor, as initial with that arrangement is set at about 12*. Base timing of 25* may result in hard starting.

Mallory also makes that Unilite distributor with vacuum advance - it would have been a much better choice than the centrifugal-only version.

bweaver999

Thanks John!!!

Just read Lars recommendations, sounds like where I have it (18* at idle, and 36* at 2800) is a good starting point. The car is running better than it has in the year I have had it. I did not realize this distributor did not have vacuum advance until I pulled it out of the box. It is made specifically for Corvette, has the mechanical tach drive which is the main reason I purchased it. Took her out again this morning to see how it behaved cold (yesterday she warmed up in the garage while checking things out). Ran better than before.

Lar's tip:
http://forums.corvetteforum.com/show...71&postcount=1