Engine Tuning

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anthem75
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Engine Tuning

#1

Post by anthem75 » 10 Jan 2019, 18:54

Hello all...

So I have been relentlessly attempting to fine tune my freshly rebuilt 390 GT engine with my somewhat limited skill set. I'm currently at the point now where I would very much like to hear some opinions from those of you who are much more seasoned than I am in this respect. I will submit the following information for your consideration...

Engine...390 GT (.060 over...yes, .060 over)

Carburetor...period correct Holley 4150 (600 CFM)...professionally reconditioned with the factory metering blocks and altitude-adjusted jets (I'm in Calgary, Alberta)

Cam...Comp Cam 270H

Pertronix ignition (base model), sourced by a Rocketman pedapter unit sending 9V to the Flamethrower coil

Started with a baseline 1 1/2 turns out on the idle mixture screws. Connected my vacuum gauge and adjusted for max manifold vacuum. Final setting = 1 full turn out on both screws. Resulted in approx. 11"/Hg. (with slight fluctuations at idle)

12 BTDC initial timing...

800-850 rpm in Park with the lights on
600-650 rpm in Drive with brake depressed and lights on

Sounds good and idles well, but I would like to hear from others with more experience. I'm somewhat concerned about damaging the engine by running too lean, for example...

Thoughts..?

Classic Canadian Cougar
Standard '67 GT

"If you're the smartest person in the room, you're working with the wrong people".

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xr7g428
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Re: Engine Tuning

#2

Post by xr7g428 » 10 Jan 2019, 19:13

With that much cam I would bring the idle up by 100 RPM. Are you getting any pre-ignition? Then you need to look for lean surge at cruise. This is at maybe 45 to 50 mph on level ground. What you are looking for is any surge or hunting.
Bill Basore, Editor / Publisher
Legendary Cougar Magazine
Currently in the Cat House
'67 XR7 GT 390 4 speed, AC, AM FM, Lime Frost Green
'68 XR7-G 428CJ C6, Tilt-Away, AM, Black Cherry
'68 XR7-G 390 4 speed, Sunroof, Cardinal Red
'68 XR7 GT-E 427 C6 AM Cardinal Red
'68 XR7 resto mod 351W, soon to be AOD, Black Cherry

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anthem75
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Re: Engine Tuning

#3

Post by anthem75 » 10 Jan 2019, 19:29

xr7g428 wrote:
10 Jan 2019, 19:13
With that much cam I would bring the idle up by 100 RPM. Are you getting any pre-ignition? Then you need to look for lean surge at cruise. This is at maybe 45 to 50 mph on level ground. What you are looking for is any surge or hunting.
I should have been clear that these are not driving conditions. My Cat is confined to its Canadian den for the time being. All specs are idling in the garage.

Classic Canadian Cougar
Standard '67 GT

"If you're the smartest person in the room, you're working with the wrong people".

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Can68
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Re: Engine Tuning

#4

Post by Can68 » 11 Jan 2019, 00:33

Sound like a good staring point but are you running both an advance and retard Vacuum line to the distributor? The dual Vacuum advance/Retard might be a 68 addition for pollution control so your 67 might be just the single advance. I'd have to check (mines in the Garage for the winter as well) but I think I'm at 10 BTC to prevent any knocking and less than a turn out on the idle screws but I still have a slight lag out of the hole. Slightly less cam thsn yours but more than stock. Runs good on the highway and really pulls out of second.


390 XR7 G
302 XR7 G (Restoration I/P)
302 Coupe

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hanver
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Re: Engine Tuning

#5

Post by hanver » 11 Jan 2019, 05:21

Get the engine up to temp and then let it idle for a while (don't touch the throttle), then shut it off and check one or more sparkplugs.
If you fear the engine is running lean, the tips of the plugs would be white-ich/grey-ich.
Good color is a coffee brown.
That would ofc only tell you your running condition on idle, says nothing when you actually drive, then it could still run lean.

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anthem75
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Re: Engine Tuning

#6

Post by anthem75 » 11 Jan 2019, 10:42

Can68 wrote:
11 Jan 2019, 00:33
Sound like a good staring point but are you running both an advance and retard Vacuum line to the distributor? The dual Vacuum advance/Retard might be a 68 addition for pollution control so your 67 might be just the single advance. I'd have to check (mines in the Garage for the winter as well) but I think I'm at 10 BTC to prevent any knocking and less than a turn out on the idle screws but I still have a slight lag out of the hole. Slightly less cam thsn yours but more than stock. Runs good on the highway and really pulls out of second.
I have just the single advance on my dizzy. I dialled in the base timing to 12 only because that's the manual spec. I have not set the advance timing yet. I'll drop the initial to 10 before I take it out again just to see how it likes that. I will also raise the idle by 100 points or so as Bill has suggested.

I set the idle screws to get max vacuum. The highest reading I got was a fluctuating 11Hg (close to 12 at times) with the screws at 3/4 turns out. I turned them out another 1/4 to put it back at an even 1 turn, for fear of maybe running too lean and damaging something. I take it from your response that you are comfortable with less than one turn out.

I'm not a racer or anything like that. I just want enough performance to have a little fun and an engine that doesn't burn 1/4 tank of gas going down to the beer store.

Thanks for your comments. They are much appreciated.

Classic Canadian Cougar
Standard '67 GT

"If you're the smartest person in the room, you're working with the wrong people".

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anthem75
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Re: Engine Tuning

#7

Post by anthem75 » 11 Jan 2019, 10:43

hanver wrote:
11 Jan 2019, 05:21
Get the engine up to temp and then let it idle for a while (don't touch the throttle), then shut it off and check one or more sparkplugs.
If you fear the engine is running lean, the tips of the plugs would be white-ich/grey-ich.
Good color is a coffee brown.
That would ofc only tell you your running condition on idle, says nothing when you actually drive, then it could still run lean.
I will do as you have suggested...thank you.

Classic Canadian Cougar
Standard '67 GT

"If you're the smartest person in the room, you're working with the wrong people".

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xr7g428
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Re: Engine Tuning

#8

Post by xr7g428 » 11 Jan 2019, 11:36

Being stuck in the garage puts some big limits on tuning. The only other thing you can do is to verify the mechanical advance curve. You can measure this with your timing light. I would start by making sure mechanical advance is all in by around 2000 RPM. Here is a link to and old thread that can shed some light on this. Keep in mind that once you change the cam factory specs are really not relevant, you will need to sort this out based on the way your engine is built.
viewtopic.php?t=7921
Bill Basore, Editor / Publisher
Legendary Cougar Magazine
Currently in the Cat House
'67 XR7 GT 390 4 speed, AC, AM FM, Lime Frost Green
'68 XR7-G 428CJ C6, Tilt-Away, AM, Black Cherry
'68 XR7-G 390 4 speed, Sunroof, Cardinal Red
'68 XR7 GT-E 427 C6 AM Cardinal Red
'68 XR7 resto mod 351W, soon to be AOD, Black Cherry

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mfc133
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Re: Engine Tuning

#9

Post by mfc133 » 11 Jan 2019, 15:38

Surprised it will actually idle at 650 RPM with that cam. If you have power steering, might want to also try working the steering back and forth while in gear to see if putting load on the P/S pump drags the idle down at all.
-Mike

1968 Cougar Standard, 302 4V, auto, Madras Blue

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anthem75
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Re: Engine Tuning

#10

Post by anthem75 » 11 Jan 2019, 16:17

mfc133 wrote:
11 Jan 2019, 15:38
Surprised it will actually idle at 650 RPM with that cam. If you have power steering, might want to also try working the steering back and forth while in gear to see if putting load on the P/S pump drags the idle down at all.
I made some adjustments today based on the good advice that I've received here on the subject. I dialled the initial timing down to 10 BTDC, and reset the mixture screws to achieve a full (and very steady) 12 Hg at 900 RPM (curb w/lights on). Both screws now sit at 1 full turn out. It rumbles at around 700 now in drive (brake depressed & lights on). To your point, the power steering is not engaged at this time (long story), but it sure seems to run very well with no leaks or overt fuel smell. I am still quite keen however to have any dissenting opinions out there presented for more further consideration.

With thanks....

Classic Canadian Cougar
Standard '67 GT

"If you're the smartest person in the room, you're working with the wrong people".

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