Tunnel Ram Tune

[GTO Geoff]

What is the timing at idle? Are you using vac adv? Man or ported?

[440Duster]

22* base
12* mechanical advance all in at 3200 rpm
14* vacuum advance @ 15” of vac
34* at idle with vacuum advance connected to manifold vac.

[440Duster]

Think I’ll try a larger IAB first rather than Reducing TSR. Seems like that would probably be the most logical next step.

[GTO Geoff]

I would reduce the size of the idle jets. At cruise, you have a LOT of air going past the t/blades, so I do not think that an IAB change will make much of a change percentage wise in the overall air flow. A larger IAB will stop the idle cct at a lower rpm, but if it is cruising in the middle of the T slot, would expect minimal effect. It is T-ram, correct? All the more reason for maybe too much idle fuel.

[rgalajda]

MPH RPM AFR  
35 1500 14
45 1900 15.5
55 2250 16.5-17
65 2800 15
70 3050 14.5 
It runs and feels good in the 14-15 afr cruise range. 

.031 IFR .031
.072 IAB .072
.085 TSR .080
.046 PVRC ---
.036 MAB .036
#74 MainJet #80
================================================
First Change Smaller IAB
.031 IFR .031
.070 IAB .070 ____________
.085 TSR .080
.046 PVR -
.036 MAB .036
74 main 80
10.5 PV

20* Idle timing 34* all in at 2300rpm and 14* of vacuum advance @ 15" of vac. vacuum can starts to add @ 6" of vacuum.
The results:

MPH RPM AFR VAC
35 1500 14 15"
45 1850 15 16"
55 2250 15.5 16"
65 2800 15 16"
70 3000 15 15.5"
====================================================
Timing Curve updated
.031 IFR .031
.072 IAB .072 ___________Back to .072?
.085 TSlot .080
10.5 PV ---
.046 PVR ---
.036 MAB .036
#74 Main #80


AFR Vac Rpm
12.5-13 14 950 in park
13.0 12 850in gear
12.0 14 1100 @ 20 mph
12.0 15 1300 @ 30 mph
13.5 14 1700 @ 40 mph
14.7 16 2100 @ 50 mph
14.7 15 2600 @ 60 mph 
14.1 15 3100 @ 70 mph  
12.0 0 WOT 

Did you try .070" IAB and then go back to .072"
When you make changes are you readjusting mixture screws? If so this will skew the results. You can change AFR readings simply by adjusting the Mixture Screws

[rgalajda]

I should have added that Idle mixture screws will mostly effect low speed AFR. I have seen changes in AFR at cruise speed by simply adjusting idle mixture screws. Of course this will effect idle quality.

I try to leave idle mixture screws as is for most changes to see the effect.

Geoff may be right about reducing idle jet. Maybe you don't need .031" IFR for a good Idle. You will need to readjust Idle mixture screws for best idle then.

[440Duster]

First off let me say thanks for the replies.

GTO Geoff, I have tried reducing the idle jets in the past without any positive results, but that was with the faster timing ramp so it's now on the list of things to experiment with.

rgalajda, I did try the 70 IAB's and I did readjust the idle mixture without any noticeable difference. I obviously wasn't thinking clearly on that. I went back to the 72's when i slowed the timing ramp thinking i'd be testing the original tune on the carbs with the timing change.

We're supposed to have some better (cooler) weather this weekend so i should get get some quality time to play with it.

Thinking my 2 options on my plan of attack:

(A) Adjust idle mixture, and test again. Curious, how do you folks approach it? I have adjusted for highest smoothest vacuum, the mixture screws are very sensitive when there are 8 of them lol

If there is a noticeable and improvement i may leave it alone, if its better but not quite there maybe increase the IAB and retest (without readjusting mixture)!

If there is no improvement then i'll reduce the IFR's, readjust and test again.

or

(B) Just say screw it and go for the IFR change first and go from there.

If/when I try smaller IFR's would going from .031 to .028 be too much? Would it make any sense just to change the primary side?

Thoughts?

[rgalajda]

Out of curiosity , how far out are the idle mixture screws? 3/4 turns ?

[440Duster]

I would guestimate somewhere between 1/2 and 3/4

[rgalajda]

On dual quad tunnel ram setups do they usually use the idle circuit on the secondary carb? Do you have the secondary throttle plates closed on these carbs?