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September 2018
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  #1 (permalink)  
Old 02-02-2018, 05:12 PM
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Default Tuning question

I am working with a customers freshly built 427FE, known specs are as follows;
Mech cam, .528" lift, 272deg adv, 232deg duration @.050, lobe center 112.
Single Holley 4160 750cfm, factory aluminum intake, factory iron heads

Issue I have is that it won't idle under 1000 rpm, manifold vacuum at 1000 rpm is 10" hg. Primary throttle blades set correctly with transition slot barely exposed.
Needs 30 deg of combined vacuum and base ignition advance with the above settings.

Carb gone through, (it is new). No apparent vacuum leaks from above. Does have PCV valve.

Questions I have;
I assume 10" vacuum is too low for this cam?
How common are intake manifold gasket leaks on FE's?
Is valve train ticking normally audible on FE's with solid lifters? I hear nothing from the valve train.
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  #2 (permalink)  
Old 02-02-2018, 05:49 PM
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I assume flat tappet mechanical lifters. I have very similar cam specs in a SB only it is hydraulic roller lifters. I can idle it down to 800, but I have EFI. If memory serves it idles about 11"Hg. I would expect more vacuum out of the larger displacement.

From everything you have said, I think it would be worth checking the valve lash.

Take everything I say with a grain of salt. I'm just an armchair enthusiast that owned a 390 FE in 1975. In short, I don't know much.
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Old 02-02-2018, 05:53 PM
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I'm running a similar setup and can tell you that the engine should idle just fine with 10 inches of vacuum. I would check the rocker arm adjustment to make sure you are within range that the manufacturer has recommended. I can also state that on my motor you can definitely hear that it is a solid lifter camshaft. I also set my idle around 950 rpms as low rpm idle setting can be very hard on solid lifer camshafts. There is a lot of load on the camshaft lobe as the lifter begins to ramp up the cam lobe.
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Old 02-02-2018, 10:55 PM
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A cam of that profile should quite happily idle under 1000.

Can you not get to run slower than 1000, or does it stall at slower than this?

Should run at 850 at 16 degrees.

I would check the valve lash is set to the recommended lash.

The carb is probably on the lean side and needs some idle feed restriction tuning.

Gary
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Old 02-03-2018, 11:34 AM
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What is your dist. advance at idle without the vacuum?
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Old 02-03-2018, 12:30 PM
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Thanks for the replies, will be checking valve lash first thing.

Gaz64, at 1000 rpm it will remain idling, I can lower it to 950 and it will run there for a minute or so but then eventually die. The carb is a pedestrian 750, good idea about the idle feed restriction.

vector1, unknown what the base timing is, I do know total advance without vacuum is around 32-34BTDC

Are you guys saying 10" vacuum at idle with this cam is normal?
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Old 02-03-2018, 01:07 PM
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10" Hg is probably about normal for a cam like that.

I think it will improve when you sort the carburettor.

My last engine at idled at 5 inches Hg at 850.

Gary
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Old 02-05-2018, 06:14 PM
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you have an intake leak, vacuum leak.
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Old 02-05-2018, 10:53 PM
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Do you have fuel dripping down the carb at idle?
Then your power valve may be incorrect, or the fuel level high. This will cause the engine to die.

You may find that the motor runs with air cleaner off, but dies when you put it back.

This does not explain the high idle, but rather the need for it.
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Old 02-09-2018, 02:55 PM
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^ No fuel dripping from the boosters at idle.

Measured the valve lash, found intakes at .014" and exhaust at .018". I do not have a cam card that specs out the valve lash for this cam. Internet specs for valve lash are all over the place. So I opened up lash to .020" on both intake and exhaust.
Immediately on restart vacuum fell to 15"hg at 1100 rpm. Now able to idle down to 800 rpm at 10"hg vacuum.

Last edited by wolf k; 02-09-2018 at 03:19 PM..
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Old 02-09-2018, 07:28 PM
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Check your spark plugs and plug wires. This doesn't sound like a fuel problem or a timing problem.
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Old 02-09-2018, 10:13 PM
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By opening the valve lash you practically reduced the duration of your cam, making it less "radical". This would explain the gain in vacuum.
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Old 02-10-2018, 02:19 AM
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I have recently experienced similar problems. I changed fuel pump, rebuilt crab, checked my lash (.015/.018 solid lifter cam very close to yours).
Finally, I changed the two fuel filters when examined had small black specks (lead) from when I run race gas and the pump gas had broken down the lead while setting for relative long periods without driving (several weeks).
My timing is set at 38 degrees and runs quite well now on race gas. My idle is a lumpy idle at 900 rpm.
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Old 02-10-2018, 01:54 PM
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Quote:
Originally Posted by wolf k View Post
Mech cam, .528" lift, 272deg adv, 232deg duration @.050, lobe center 112.
We have these details, but no card, and don't know the manufacturer?

The carb is the reason for the stalling.

At least you are closer now with some looser lash.

Gary

Last edited by Gaz64; 02-10-2018 at 08:05 PM..
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Old 02-11-2018, 05:12 AM
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^ We only have contact with the owner, who had the car built by someone else, who had the engine built by someone else. I will try again to get the cam card.

What is a good test that I can perform to determine for sure if the idle restrictions are too small, other than o2 sensors? The plugs are not dark but they are not glazed white either.

Otherwise the car runs excellent as is, no off idle stumble, no light cruise surging.

Last edited by wolf k; 02-11-2018 at 05:15 AM..
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Old 02-11-2018, 05:54 AM
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Quote:
Originally Posted by vector1 View Post
What is your dist. advance at idle without the vacuum?
If you don't have enough base advance it is not going to idle. The mechanical hasn't advanced and not enough vacuum to pull the canister.
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Old 02-11-2018, 02:45 PM
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Quote:
Originally Posted by vector1 View Post
What is your dist. advance at idle without the vacuum?
Quote:
Originally Posted by wolf k View Post
Thanks for the replies, will be checking valve lash first thing.

Gaz64, at 1000 rpm it will remain idling, I can lower it to 950 and it will run there for a minute or so but then eventually die. The carb is a pedestrian 750, good idea about the idle feed restriction.

vector1, unknown what the base timing is, I do know total advance without vacuum is around 32-34BTDC

Are you guys saying 10" vacuum at idle with this cam is normal?
Ok, you set the maximum at 32-34 with a timing light, but we don't know the next critical parameter as in timing at idle??

I see no mention of how much at idle you have.

I would hope it has at least 15.

Gary
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Old 02-11-2018, 04:19 PM
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^ Initially, I had to set combined base and vacuum advance at idle to 30 deg BTDC (vacuum advance is manifold sourced not ported) just to allow the engine to idle with the throttle set with the transition slots correctly exposed.
After increasing the valve lash from .014 to .020 on the intake valves and .018 to .020 on the exhaust valves I can now idle down the engine to 800 with the same distributor settings. I am now able to disconnect vacuum advance at idle to see what the base timing is and it is around 6 BTDC.
However, I will most likely leave vacuum advance manifold sourced, as it runs well off idle the way it is. I have to deduce that the engine builder has lightened the vacuum canister spring as much as possible to get that much vacuum advance at idle.

Last edited by wolf k; 02-11-2018 at 04:28 PM..
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Old 02-11-2018, 04:34 PM
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Ok, sounds like you are close to a happy medium.

How much mileage has the engine done now?

Has it seen some load as part of running-in procedure?

I would have the distributor mechanical advance limited to provide more at idle, to keep total where it is now.

So about 12 at idle, 32 at 2500 rpm.

Gary

Last edited by Gaz64; 02-11-2018 at 04:37 PM..
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Old 02-16-2018, 04:31 PM
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Runs really well now with limited running we have been able to do, has very little mileage on the engine, maybe a 100 or so. Have no info about running-in load. Perhaps we will able to talk the owner into dyno tuning.
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