[gary29]

I have pulled and restored the exterior of my 65 GTO 389 tri-carb engine. Did not due a total rebuild as the cylinder compressions were good. I could list the many many things I have done, but it is a work of art now! It does have the original GTO heads and cam. So it is supposed to have a compression ratio of 10.75:1 !

Last to do is to install my new MSD Bullet Distributor.

1) Cylinder 1 is at TDC on the compression stoke.
2) Balancer is pointing to the TDC line.
3) Dialed in the oil pump slot to put my number 1 wire connecting to the rear center left distributor terminal. This was only 2 wires (2 & 3) will cross under the distributor.

I am not an expert my any means. So please chime in if I am doing something wrong.

Now I need help setting the initial curve of my new distributor. Can someone please help me. Here are my options:

Amount of advance in degrees (18, 19, 21, 23, 25, 28)?
Rate of advance in RPM's (1400-5500, 1300-4700, 1300-4500, 1200-3600, 800-2300)?

* Actually it looks a little more complicated. The degrees limited above by bump stops also limits the top RPM for each spring rate. See attached. Again pleas HELP!

From MSD the distributor is set at 21 degrees advance and 1400-5500 RPM rate.

Also, can someone tell what the red line should be for my 65 389 tri-carb?

Also, I plan on starting with an initial timing at idle of 2 degrees. Does this sound like a good place to start?

[steve25]

The MSD is a Billet type, not Bullet.

Two things here I need to ask.
Does this distributor have vacuum advance, because that’s mandatory for even a street strip no less a street only car.

You’re asking about a safe red line and that hinges on if the valve springs are still the original ones from 59 years ago?

Bottom end wise and with a 60 psi oil pump a trip power motor with the 068 cam should get you 5400 rpm easy, and 5400 is where the 068 cam is fully done making power in a 389 and especially with 389 heads.

Please go into your photo section and hit the 2nd icon from the bottom left and rotate your picture the right way and re-post it please.

[gary29]

Sorry about the misspelling! It is Pontiac V8 350-455 Pro-Billet Distributor

Fits 326, 350, 389, 400, 421, 428, and 455 Pontiac. Must be used with an MSD 6, 7 or 8-series ignition.

I am running an MSD Digital 6AL Ignition Control

The engine was rebuilt at some point, but not sure when! So I will keep in mind that the valve springs may be ageing. Thank you!

The distributor does not have a vacuum advance. It will only be a street car. You say a vacuum advance is required? Can you let me know who requires is on a street car? The Colorado Department of Transportation? I will call MSD now.

I'll try to figure out out how to flip my attachment. I am fairly new to forums!

Can someone please help me setting my distributor timing curve? Thank you!

[steve25]

The car came with vacuum advance as all factory production cars did from all American auto makers because it helps with .
Throttle response .

Fuel mileage big time!

And helping the engine run cool at part throttle highway cruse speeds.

Seeing as you have a true 10.25 ( not 10.75 ) compression if your motor is in good shape I would set it up for the 1300 to 4500 curve for now, and then you can try the curve that starts at 1200 and see if the motor pings or knocks.

If the motor reused the original cast pistons those are very prone to cracking out the ring lands if the motor knocks, so you want to stay far away from that even if it cost you 4 or 5 hp, ask me how I know this!

The chance of ping and knock is also tied into how hot the motor runs so this is another reason for running vacuum advance.

Here’s the typical advance curve for a 4 bbl or Tripower motor from the 60s when we had good fuel, today you will have to back this down somewhat.
If you had vacuum advance you would only want to start with about 8 degree's and work your way up until the motor pinged at part throttle .

[gary29]

Thank you Steve. Yes I understand what I vacuum advance does. I do not care about fuel mileage and I will address the cooling issue a hwy cruising speeds, but frankly I am not going to be do much if any hwy cruising. It is being build for a fun in town street car for a retired couple to have fun cruising around in. I will work hard at getting a good timing and inner carburetor fuel mixture to also address cooling. I am also plan on running a 160 thermostat is necessary.

P.S. My Tri-Carbs were restored and tuned by Tom Wright at PontiacTriPower. I highly recommend!

I went with an MSD Digital Ignition Control box to get hotter sparks, multiple sparks and longer sparks for better performance. The Pontiac V8 350-455 Pro-Billet Distributor was my only option, unless I wanted to run the Pontiac V8 Ready-to-Run Distributor that does have a vacuum advance, but was not specially designed to go with an MSD Digital Ignition Control box , as it has its own built in ignition control. I am happy with my MSD choices and I understand the no vacuum advance issues. But thank you Steve!

Can you help with setting my timing curve? Thank you

P.S. I cannot figure out how to flip my attached image. It is not sideways in my photo library. Can you please be more specific if possible on how to rotate posted images? Thank you and sorry. I am a new-be.

[gary29]

Thank you Steve for you curving suggestions! I did not see at first.

[gary29]

Ok, I have read your comments and looked at your attachment. I will start with your curve recommendation baring any other input. Thanks again. What centrifuge advance do you recommend? I will talk to MSD about running the other distributor with a vacuum advance with and MSD Digital Ignition Control box.

[tom s]

My 421 SD engine has the factory 421 SD dizzy that does not have a vac advance.I have been driving on the street for 27 years now.I might be giving up some gas mileage but never cared.My engine is a true 9.5 CR iron head engine.I run 12 degrees initial and 36 total all in at 2000.Maybe start yours at 12 initial with 34 total and pay close attention for detonation.I only run our CA 91 piss gas and have not needed more.I run a Hi6 box.FWIW,Tom

[gary29]

Thanks Tom. Steve's document says initial timing at 10. You suggest 12. Great you both are close. Funny though, I had heard pursuing other forum posts initial timing as to be 2. Before I pulled my engine, and knew far less than I do know now, it seemed to like to be around 10. I will start at 11. Thanks guys.

So taking in both of your suggestions I am thinking I will start all in at 3200. it is the second lowest I can go with starting the timing increase below 1000. And its in between both of your suggestions.

As for total timing I am thinking total all in at 36. Initial at 11, centrifugal at 25.

Any comments? Thanks again guys? Yes, I will be very away of pinging and detonation.

[gary29]

Thanks again Steve and Tom. This curving sutff is new to me. Just a heads up, to learn as much as I can I am going to post my curving question again on the gtoforum.

Looking at my options of springs and bushings, I cannot dial it in exactly as either of you are suggesting. So I am still a bit nervous. I don't want to have to rebuild my engine internals. From what I was told it could take up to 1.5 years to have a shop dismantle, send off to be machined and reassemble. And from what I here as well, mechanics and machine shops are not as good at working on these old engines any more. I have heard of a lot of cautionary tales. So, yes Steve, I may have tired old iron pistons! I was just wanting to upgrade my ignition system to something I can maintain.

Steve question.... You say my compression ratio is 10.25:1. Everything I read it says its 10.75:1. You sound like you have been around awhile. So was the compression ratio over rated along. Just curious.

Tom question.... What is an Hi6 Box. Sorry for my ignorance. I am still becoming familiar with the different setups.

Steve and Tom... I am correct in assuming that you both are not running electronic ignitions? Stupid question... Is curving always done with the changing of springs and bushings?

Thanks guys!

[tom s]

Hi6 is a electronic box.I have been run SD dizzy for most of my life so I’m comfortable with it.My other cars use a Pertronix breaker less unit.Only the first gen module built in the US.I have my dizzy setupby a pro.I don’t do carbs of dizzy.Tom

[Tim Corcoran]

Not sure why you chose an MSD Billet distributer for a street car as it does not have vacuum advance. All street driven cars should have vacuum advance unless you have fuel injection and computer control timing.

[Kenth]

A friendly advice, get 1966 Pontiac/Tempest Shop Manual, in this you´ll find the "how and why" answers.

To throw a pile of aftermarket bling/crap on the engine is "backwards engineering" as i guess most of us is guilty of in our younger days.

FWIW

[Bill Hanlon]

Originally Posted by steve25

Please go into your photo section and hit the 2nd icon from the bottom left and rotate your picture the right way and re-post it please.

Per your request Steve. It got fuzzy if I tried to make it bigger.

[scott70]

21 degree bushing,, springs for all in by 3000-3100 rpms. 13 degree initial for a 34 degree total. No need to push it any farther than that. You have to pay attention and actually dial in your vac advance numbers. I’ve run vac hooked and unhooked and am fine with either way.

[gary29]

Thank you Scott.

I have to admit this all a bit overwhelming. Conceptually it is understandable. When I decided to upgrade my GTO (what I think is a stock 65 tri-cab 389) to a newer electronic ignition I did not know what I was in for. After reading and ready forum posts from very hard-care car guys it began to make my head spin. I played with cars back in the 70's, but after a career in IT, I thought I would pickup a old hobby. Again, reading the posts from so many gear heads makes my head spin.

As I stated before I purchased a MSD Pro-Billet dizzy with a CD box. Again the dizzy has no vacuum advance. I hear you concerns about no vacuum advance. As I have to vacuum advance I cannot dial it in. Did I make a mistake? I read that having a vacuum advance as many benefits! But talking to MSD they make it sound like its no big deal.

Thank you for your bushing, springs and initial settings. I will take your advice, even though it is temping to put in light springs

I do not want to trash my engine, as I do not know more about the internals other than it has 150 compression all the way around and it does not smoke. I wish I could have had it rebuilt to sure, but everyone local says it would have taken up to 1.5 years total. I did replace all the external parts, repaint, and PontiacTriCarb restore my cabs.

I appreciate any help I can get.

[scott70]

Originally Posted by gary29

Thank you Scott.

I have to admit this all a bit overwhelming. Conceptually it is understandable. When I decided to upgrade my GTO (what I think is a stock 65 tri-cab 389) to a newer electronic ignition I did not know what I was in for. After reading and ready forum posts from very hard-care car guys it began to make my head spin. I played with cars back in the 70's, but after a career in IT, I thought I would pickup a old hobby. Again, reading the posts from so many gear heads makes my head spin.

As I stated before I purchased a MSD Pro-Billet dizzy with a CD box. Again the dizzy has no vacuum advance. I hear you concerns about no vacuum advance. As I have to vacuum advance I cannot dial it in. Did I make a mistake? I read that having a vacuum advance as many benefits! But talking to MSD they make it sound like its no big deal.

Thank you for your bushing, springs and initial settings. I will take your advice, even though it is temping to put in light springs

I do not want to trash my engine, as I do not know more about the internals other than it has 150 compression all the way around and it does not smoke. I wish I could have had it rebuilt to sure, but everyone local says it would have taken up to 1.5 years total. I did replace all the external parts, repaint, and PontiacTriCarb restore my cabs.

I appreciate any help I can get.

I believe the numbers I gave you are safe numbers without leaving anything really on the table. When I set up my RTR MSD dist I noticed the springs seemed stiff compared to older recurve kits but the numbers on the chart dont lie. Ive tried 2400 to 3000 rpm all in and didnt see any difference at the track. I use a black 18 bushing 33 total and 15 intial. 175 cylinder pressure . Never starts hard even hot. The numbers I suggested should be safe and give you good power. I ordered my dist with vac and do use it but honestly I dont see much of a difference without vac. My throttle response feels the same and gas mileage isnt a big deal to me. My vac adds 10 degrees at part throttle if i remember right so like 43-44 degrees. But yes if I personally was buying a new Dist, I would order one with vac so you have the option but youll be fine if you want to stick with yours.

[AG]

Originally Posted by scott70

I believe the numbers I gave you are safe numbers without leaving anything really on the table. When I set up my RTR MSD dist I noticed the springs seemed stiff compared to older recurve kits but the numbers on the chart dont lie. Ive tried 2400 to 3000 rpm all in and didnt see any difference at the track. I use a black 18 bushing 33 total and 15 intial. 175 cylinder pressure . Never starts hard even hot. The numbers I suggested should be safe and give you good power. I ordered my dist with vac and do use it but honestly I dont see much of a difference without vac. My throttle response feels the same and gas mileage isnt a big deal to me. My vac adds 10 degrees at part throttle if i remember right so like 43-44 degrees. But yes if I personally was buying a new Dist, I would order one with vac so you have the option but youll be fine if you want to stick with yours.

This is a typical curve I use with an MSD RTR, biggest bushing and adjust the initial to get the desired total.

[Cliff R]

Without VA you are MISSING a lot of timing at light engine load. This REQUIRES more fuel and throttle angle plus a richer A/F mixture in that load/speed range.

Adding a distributor with a quick timing curve does NOT make up for missing timing from the VA. Typically timing requirements for these engines are around 8-12 initial, about 10-11 from the mechanical advance (20-22 at the crank), and 12-15 degrees VA.

If you add up those numbers the distributor is providing upwards of 42-49 degrees timing at light engine load. This improves engine efficiency, throttle response, and power in the "normal" driving range.

Last time I looked it was 2025, not 1969. The days of running bug-zapping distributors w/o VA should be LONG over, but sadly they still sell and promote those parts for these engines and poorly educated guru's, owners and tuners buy into all that thinking that somehow it's an "upgrade" over the stock parts.

I love stories so here goes one DIRECTLY related to this topic. For many years I rebuilt and restored factory carburetors for well over 10,000 customers. There is one business in the deal here that is solely dedicated to Pontiac engines, parts, etc. Every single time I prepared a carb for one of their engines and it ended up on the dyno I'd get a call that "the carb you built is WAY too lean, please send me much larger jets and smaller metering rods". So I did. Problem solved for the dyno runs, however, once the engine made it in service the customer was NOT happy with the fuel economy, although their engine ran OK in the "normal" driving range. Some just dealt with it, but overall for most it was not a good experience for them. Good thing that at least 95 percent of the customer base here don't put but a few hundred miles a year on these engines, so minor issues like 10-11 MPG's vs 14-15 or so isn't a big deal breaker for them.

This problem went on for quite some time, then one day I asked the dyno operator some questions about the engines they were building trying to figure out why carburetors that were dead-nuts on the money for calibration showed up WAY too lean on his dyno.. I wasn't overly fond of their cam choices as they LOVE that fast-ramp "tight" LSA crap which adds to the issues but we eventually got around to talking about the distributor and timing. When I asked how much timing they were adding with the VA I got this response:

"We don't use Vacuum Advance".

Hum, problem discovered and there was absolutely NO WAY I was going to educated those folks as to why the had to run such rich mixtures on their engines, or the benefits of VA as it was absolutely and for sure going to fall on deaf ears.

So I stopped doing any carburetor work for customers they were building engines for.........problem SOLVED on my end........FWIW.......

[steve25]

The second paragraph in Cliffs above post needs to be carved on big a stone tablet and mounted on some folks dash board !

Just to reinforce what he said lean part throttle mixers are needed also to extend engine life.
Lean mixtures take more time to burn fully and this requires more timing that vacuum advance provides.


If you don’t care that your richer then needed part throttle non vacuum advance timing is waring out your rings and cylinders at a increased rate then as some do on this board then go right ahead and do not use any vacuum advance timing.

Oh, and I should also mention that the richer part throttle mixtures run without vacuum advance contaminate the oil faster also.