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Discussion Starter #1
Guys since i have addressed this issue last year i purchased a new 600 cfm carb from summit and Boy I sure like that smoothness and having a choke.I have no run on issues or carb issues at all.

However i still have some engine pinging while the engine is lugging and also at throttle tip in.I think I know what might be a major cause of this and wanted to run it bu you guys.

I was told buy a local retired ford guy this morning not to run full vaccuum at idle which i am doing now.So i think that is my problem.
I have been adjusting the set screw inside the vac advance cannister in and out and it does make a little different but the pinging cannot be dialed out however i think i might be wasting my time because as my friend says i should NOT be running off the carb port running full vacuum.

He also said try the timing at 10 initial and all in a 36* around 3500rpm but it's been a while seen he has messed with one so do not quote him on the max rpm.He is a great guy.
 

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2V or 4V heads? Actually open or closed chamber?
 

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What kind of distributor are you running and has it been curved by a knowledgeable distributor service? If so, please share the mechanical AND vacuum advance curves so we have something to work with. Manifold vacuum works great if (and only if) the vacuum and mechanical advance curves are tailored to the engine and the distributor is "healthy" in all respects.
 

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Discussion Starter #7
The dist is a duraspark II and i am using a msd box with blaster 2 coil .Tonight i switched from manifold to ported vacuum and raised the curb idle.
The distributor has never had the mechanical curve set.
The distributor has never had the vacuum advance curve set.There is nobody around here that does it.

I tried a various combination of dist springs last year but I think i was trying it on full vacuum.

I will try a test drive in the next couple days and report back.

Is there anyway to ID the heads while on the motor ?
 

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The 4V Cleveland heads should have a "4" cast into each end that is visible with the valve cover installed.
'70 & '71 heads were closed chambers and '72 & '73 were open chambers. Look for a D0 or D1 casting number but I don't recall where it is located.
More info at mustangtek. Scroll way down for 351C heads:

Heads
 

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I'd run as much initial spark advance as the motor likes and full manifold vacuum for the vacuum advance. If you have spark knock, under load, then you want to dial back the centrifugal advance. If it starts at low rpm but is fine at higher rpm then you want to go with a slightly heavier spring(s) on the weights. If it starts at a higher rpm then go with a limiter cap to limit the total advance.

If you get spark knock at "tip in" that goes away with more throttle, then your vacuum advance is too aggressive. You should be able to dial it back.
 

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When I had open chamber 2v heads they liked 36* mech adv all in by 3000 rpm. I had no vacuum advance on my MSD distro. Closed chamber should be less than that...
 

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Very good advice in this thread already. The question I have is also concerning the closed chamber vs open chamber. As others have said, you will find the "4" on the top of the head in the corner. You need to look at that and see if there is a dot beside the 4. the vast majority of the 4 barrel heads with the dot are closed chamber.

With that being said, what kind of pistons do you have? I am trying to get an idea of your compression ratio. It could be as simple as needing to run a higher octane fuel.

The ported vs full vacuum is an old debated topic. I have always used ported vacuum. But a good MSD distributor is easier to mess with because there is no vacuum advance, The vast majority of my experience has been with the MSD units.

To help you more I need to know about the pistons and head details.
 

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Discussion Starter #13
Sorry for not having the info you guys need .I never expected this issue and am inexperienced at much of this engine stuff.I bought the engine used .It looked really good inside and not worn or anything.In hindsight I should have take notes and pics and removed the cam and took measurements etc so i would know what i have.I will tell you what i know
Yesterday, I spoke to the guy I bought the engine from and he told me the block was out of a 71 ford and it was the CLOSED chamber heads.I just went to check and I see a DOT to the left of the 4 that is stamped on the heads above the valve cover.
The engine is bored .040 and i do not know cams specs nor did the PO.
I remember the pistons being dished out as opposed to being somewhat flat like the ones in my original engine.
The PO thought it had around 9.5: comp ratio.
I did a compression test last summer after i warmed the engine and let it cool enough to get my hands in around the header without getting burned.I forgot to open the throttle and hold it open while cranking(rookie)and I got cylinder values that ranged from 167-175 if i remember correctly however those notes are at work and I am at home.

I checked my duraspark dizzy last night with the hose of the vac advance and plugged.I "think" my curve is to slow and comming in too late from what i read.Last summer i was trying to get the ping out and using manifold vacuum and playing with springs and then test driving and got frustrated and gave up.This summer i would really like to figure it out and get past it.
He are my timing marks and rpm from last evening with one of the springs(heavy i believe that came in the remaned dist) and one of the gold (which I know came from the mr gasket recurve kit.I have the remaining springs from the mre gasket kit as well as another kit containing two black springs only which i see mentioned on several recurve tutorials which BTW do not tell you which springs to use to get a desired curve .
So i am hoping to find that here.
So
10-750rpm
11-1500
12-2000
16-2500
21-3000
24-3500
26-4000

All i read indicates that that curve is too slow and too late.
If i give it quick shot above 4K say 5K it will go to what looks like 34* which should be about the limit as i have my 16L slot jb welded and then filed down to limit my full mechanical to 12 or 24 total as was suggested last summer.I have the basic understanding of some of the timing stuff but not all.

My plug gap is around 43-44 and they are autolite 25
Msd box and blaster II coil
Duraspark Dist I do not know the weight of the weights in the dist I bought it remaned at o'rilies for a ford big block(this was suggested on one of the duraspark tuning sites) hoping to get the smaller slots in the reluctor plates which i ended up modding one side and using that modded side.

I hope this helps you guys understand my dilema and someone can suggest which springs to use and if it matters which one goes on which post on the plate.I have it apart and have not experimented with other springs however i know the current setup is stiff .

Thank you very much
Terry
 

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The Dot next to the 4 means that the heads are open chamber...no Dot means closed chamber heads and higher compression. Carbon build up can cause detonation in the chamber too. Also make sure your harmonic bal timing marks are correct. Did builder use a new balancer?
 
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There are many variables that cause detonation or preignition. The result is the same, but the cure is different. trying o figure which one you have is difficult. If you have open chamber heads, whereas the compression ratio is low, especially if you have dished pistons, yikes . . . . you have a really inefficient combustion chamber. Dished pistons would actually be making it worse. You need the flame to burn and move across the piston quickly, or at least before enough compression is generated for abnormal combustion. A lot of initial advance will help.
 

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Discussion Starter #16
Will getting my curve to come ins faster and all in sooner help at all.
Should i experiment with the springs i have to do so ?

How much initial would you suggest ?
 

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Discussion Starter #17
I changed the springs in the dist and checked the reluctor with the micrometer and it should have given me 13x2=26 however it is actually15x2=30 plus my initial of 12 for 42 total all in at 2900.
I still get ping with advance unhooked and hose plugged while test driving it but it is the least amount of ping to date.
I tried the vac advance in it's strongest position and it still pinged.

Should i limit the total using something over the stud as a first step and check my full mechanical ?
What do you guys think of this curve ?
12-1200
16-1400
20-1700
24-1700
30-2000
34-2200
36-2500
38-2700
42-2900

I was thinking it would fine if i ended up at 36 at 2900 ?12 initial and 24 mechanical ?
I added a can of sea foam gas additive to see if that might help.

HELP
 
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That curve is s tarting point. It's going to be tricky I believe. You have some opposing problems.
 

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Unfortunately those open chamber heads that you have are a poor street design. They were big detonators back in the '70's. Poor design that Ford used to meet emissions restrictions. I don't believe there is much you can do other that get the closed chamber heads or the Australian heads.
 
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