Is this too much initial timing for my 302? - Vintage Mustang Forums
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post #1 of 12 (permalink) Old 08-19-2019, 04:57 AM Thread Starter
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Is this too much initial timing for my 302?

My 302 in my 69 Fastback was built by me a long time ago but has not done much mileage as the rest of the car and other problems took a long time to get it on the road. It has only done about 1000 miles now.

From the Edelbrock Performer RPM range, it has cylinder heads, Airgap inlet manifold and cam. Edelbrock 9635 625 CFM carburettor and an Edelbrock timing chain. JBA shorty headers, 2.5" exhaust system and Magnaflow silencers. I am also running a Duraspark 2 distributor with a GM ignition module and a mid 1990's Mustang square ignition coil.

The other day I decided to recheck and maybe improve the carburettor and timing settings. I am no tuning expert but I know the basics of what I am doing.

I checked the timing with the vacuum pipe unplugged from the distributor and plugged. I am using the manifold vacuum port on the carburettor. I also had a vacuum gauge on the carburettors large manifold vacuum port.

My harmonic balancer is the original 69 one, but it has not slipped as I checked it with a homemade spark plug piston stop, and the zero was spot on. And the Edelbrock timing chain only has about 1000 miles on it, so it should be fine with no stretch.

The instructions for the Edelbrock cam say to have between 10 - 14 degrees initial timing and 32 to 34 degrees total timing which is in by 3000 - 3500 RPM.

My main question is that the engine seemed to really like lots of initial timing. As above, the instructions say 10 - 14 degrees. But the engine idle was even smoother when I went above this. Even getting close to 20 degrees, it was running so smoothly. And with this extra timing, the vacuum gauge was improving.

I have changed the springs in the distributor and the total timing is fully in at 3000 RPM. And I have modified the plate to limit the total timing to no more than 35 degrees.

So is it okay to run this amount of initial timing if the engine does not ping under load like going up a hill?

Can this make the engine run hotter at idle? At the moment I never have a problem with cooling. I have an Edelbrock water pump and a 24" aluminium horizontal radiator. The temperature gauge seems to behave itself and never gets too high in traffic.

I have tried to research this and I found quite a few people saying their engine loved lots of initial timing.

Any thoughts or comments on this?

Jeremy.
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post #2 of 12 (permalink) Old 08-19-2019, 07:46 AM
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Mine was doing the same thing after I swapped to a 4 barrel manifold. Turned out to be a vacuum leak.

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post #3 of 12 (permalink) Old 08-23-2019, 11:00 PM
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My 363 stroker likes 20 degrees initial and 32 total. I would say put it on a dyno and see what it likes tuning wise.

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post #4 of 12 (permalink) Old 08-24-2019, 12:41 AM
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My 331 with aluminum heads liked 19-20 initial and 34 all in. Not uncommon!
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post #5 of 12 (permalink) Old 08-24-2019, 04:21 AM Thread Starter
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Thanks for all the replies.
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post #6 of 12 (permalink) Old 08-24-2019, 06:57 AM
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Interesting. Iím definitely no tuning expert either and obviously there are many variables, but I thought most 302-based motors liked 12-14 initial timing, and all-in by about 3000-3500 as you mention above. Just curious if you have put a vacuum gauge on it, and what rpms are you idling at?

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post #7 of 12 (permalink) Old 08-25-2019, 12:54 PM
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Might check out your local track for test n tune or fun run nights. Easy to tune between runs at my track and a lot cheaper than dyno. And though more variables might sneak in to mix, its the seat of pants you want anyhow, right. My older setup with RPM setup (Dart heads) in a 351 (which is a hotter cam if I recall than 302) actually performed best at nearly 24 initial with mechanically all in at 36 degrees (no vacuum). On pump gas, annular discharge 750dp, 9:1, long tube headers, TKO and 3.50 gears. This was verified on 1/8th mile and I was able to run pretty lean like this too getting just under 20mpg.

Are you doing 20 with or without vacuum hooked up? Does Edel assume 14 physical before vacuum and then your getting 20 with vacuum? I had deleted the vacuum from prior EFI use.

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post #8 of 12 (permalink) Old 08-25-2019, 05:17 PM Thread Starter
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Quote:
Originally Posted by Lukesportsman View Post
Might check out your local track for test n tune or fun run nights. Easy to tune between runs at my track and a lot cheaper than dyno. And though more variables might sneak in to mix, its the seat of pants you want anyhow, right. My older setup with RPM setup (Dart heads) in a 351 (which is a hotter cam if I recall than 302) actually performed best at nearly 24 initial with mechanically all in at 36 degrees (no vacuum). On pump gas, annular discharge 750dp, 9:1, long tube headers, TKO and 3.50 gears. This was verified on 1/8th mile and I was able to run pretty lean like this too getting just under 20mpg.

Are you doing 20 with or without vacuum hooked up? Does Edel assume 14 physical before vacuum and then your getting 20 with vacuum? I had deleted the vacuum from prior EFI use.
I am running about 18 degrees with the vacuum disconnected and plugged and then reconnected afterwards. Edelbrock's recommendation is also with the vacuum disconnected. I still want to play around with this and see if things can be made better or not.

I would like to go to a dyno, but there are not many around my way and they cost quite a bit of money which I do not have spare at the moment. A local track might be the best bet. My seat of the pants meter is quite accurate :-)
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post #9 of 12 (permalink) Old 08-25-2019, 05:27 PM Thread Starter
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Quote:
Originally Posted by 68Ghost View Post
Interesting. Iím definitely no tuning expert either and obviously there are many variables, but I thought most 302-based motors liked 12-14 initial timing, and all-in by about 3000-3500 as you mention above. Just curious if you have put a vacuum gauge on it, and what rpms are you idling at?
I have had a vacuum gauge on it and am getting about 11" of vacuum. And according to the Edelbrock instructions, this is about right. My idle is about 700 - 750 RPM. I am wondering if this is a little slow and the jury is still out on whether I raise this slightly to around 800 - 850 RPM.
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post #10 of 12 (permalink) Old 08-25-2019, 09:25 PM
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Mine cools better at 850-900 rpm idle.

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post #11 of 12 (permalink) Old 08-25-2019, 10:13 PM
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Jeremy, what you're talking about is very consistent with ported vacuum instead of manifold vacuum. Edelbrock suggests you use ported vacuum, which might be appropriate if you have a really hairy cam. Unless you have a really surging idle though, using manifold vacuum makes more sense.

Here are a few basic points to help you figure this out.

1) At idle, and even at cruise, your engine needs a LOT of timing in order to make peak pressure at the right time, because the thin mix (high manifold vacuum) takes a long time to light. Having a total of around 24 degrees with vac advance for idle is pretty common.

2) With the throttle wide open, running near atmospheric pressure instead of vacuum, you need a lot less timing to avoid ping/detonation. (14 could be all right, but it's towards the high end)

3) Your final timing is most important, because it is more likely that your engine will blow itself apart with detonation while making max power, instead of at idle.

You're using vac advance, which is good, but you're using ported vacuum, which means when the throttle plates close, you have no vac advance. Using manifold vacuum makes more sense, because you have full vac advance at idle, allowing for a smoother idle and less unburnt fuel in the exhaust. You get more advance when your engine needs it (high vacuum) and less when you don't (no vacuum). You'll have smoother off-idle response when you step on the gas too.

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Last edited by Grimbrand; 08-25-2019 at 10:16 PM.
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post #12 of 12 (permalink) Old 08-27-2019, 04:11 PM Thread Starter
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Originally Posted by Grimbrand View Post
Jeremy, what you're talking about is very consistent with ported vacuum instead of manifold vacuum. Edelbrock suggests you use ported vacuum, which might be appropriate if you have a really hairy cam. Unless you have a really surging idle though, using manifold vacuum makes more sense.

Here are a few basic points to help you figure this out.

1) At idle, and even at cruise, your engine needs a LOT of timing in order to make peak pressure at the right time, because the thin mix (high manifold vacuum) takes a long time to light. Having a total of around 24 degrees with vac advance for idle is pretty common.

2) With the throttle wide open, running near atmospheric pressure instead of vacuum, you need a lot less timing to avoid ping/detonation. (14 could be all right, but it's towards the high end)

3) Your final timing is most important, because it is more likely that your engine will blow itself apart with detonation while making max power, instead of at idle.

You're using vac advance, which is good, but you're using ported vacuum, which means when the throttle plates close, you have no vac advance. Using manifold vacuum makes more sense, because you have full vac advance at idle, allowing for a smoother idle and less unburnt fuel in the exhaust. You get more advance when your engine needs it (high vacuum) and less when you don't (no vacuum). You'll have smoother off-idle response when you step on the gas too.
After reading your reply to my question I had a dig into my carburettor and found a problem. You said that what I am experiencing is consistent with running the distributor off of the ported vacuum connector and not the manifold vacuum connector. Well, I actually have it running off of the manifold vacuum connector.

I found that the small manifold vacuum connector had a partial blockage inside the carburettor body and it was acting like the ported vacuum and had no vacuum at idle and only gave a vacuum when coming off the idle. When I blew through it, it felt restricted. So I decided to strip the carburettor down and clean it with carb cleaner everywhere. After the cleaning, I could now blow through the manifold vacuum connector easily.

I set the idle speed such that the transfer slots were only showing a little square of the rectangle which seems to be the recommendation. And the idle mixture screws were set to 2 turns out from seated. Once the engine was up to temperature I set the initial timing to 12 degrees with the vacuum disconnected and plugged. I could feel a vacuum on the manifold vacuum connector at idle which I could not before, so it looks like this is now working as it should.

I set the idle mixture screws and got a vacuum reading of 10 inches and an idle speed of about 750 RPM. I reset the plate in the distributor to ensure the total timing did not go above 34 degrees. And the springs stayed the same which brings in total timing by about 3000 RPM. With all of this work, the idle is very smooth and I now have things set up in line with Edelbrock's recommendations, which makes me happier.

When driving the car, fast acceleration and wide open throttle seemed about the same as before, but there is a big improvement when driving slowly in different gears. Before, if I slowed down too much in 2nd, 3rd, 4th or 5th, it did not like it at all. Now I can slow right down in 3rd and just pressing the accelerator it wants to pick up speed easily. And 2nd gear can easily go down to a near enough standstill and not complain. I can even pull away from a standstill in 2nd with ease. So it looks like I have gained some low down drivability and this ties in with the manifold vacuum connector now working correctly.

So thanks for your reply which has enabled me to home in on my issue. I would like to take the car to a dyno, but as I mentioned in another reply above, there are not many around my way and I cannot really afford it anyway. I have no complaints about how it drives now. Also, another problem with dyno's these days is finding one that knows about carburettors.
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Last edited by JRFox; 08-27-2019 at 04:14 PM.
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