Tunnel Ram tuning

[440Duster]

I’m sneaking up on this tunnel ram tune. It’s running extremely well. Idles good, cruises well, transition is much better that it has been. The latest tune has got me real happy. This is a 100% street car that does an occasional spirited backroad romp.
The car/engine specs:1971 Plymouth Duster with a straight axle “gasser inspired”
440 Dodge, 10.0 CR, iron 915 closed chamber heads with chambers cleaned up and mild porting. 231/237 @ .050 110 lobe separation 106 ICL, Weiand 1987 Hi-Ram Tunnel Ram w/2 ProForm 750 DP, 3000 stall and 3.23 gears. With this latest tune I’ve disconnected the secondaries to nail down the cruise and PV timing, and as stated before it’s running well. At this point I’m looking to address the pvcr and wot. The plugs show WOT lean. The question at this time is should I up the pvcr or connect the secondaries and tune wot?
The current tune:
P/S
.031 IFR .031
.070 IAB .070
.085 TSR .080
.046 PVR -
.036 MAB .036
74 main 80
10.5 PV
Emulsion stack from the top:
1) .028
2) blocked
3) .028
4) blocked
20* Idle timing 34* all in at 3200 and 14* of vacuum advance @ 15" of vac. vacuum can starts to add @ 6" of vacuum.
These pics are after 60 miles of in town cruising and a couple of wot runs on just the primaries.

[Bob Hollinshead]

If the idle and transition/part throttle fuel curve is good move on to the WOT tuning. Things are going to change quite a bit once the secondaries are opening so I'd hook them up now. Signal to the primary side is going to be reduced with all 8 opening now.

[In-Tech]

IMO, they all need 1:1 linkage. If it's too aggressive, fix it in other areas of the linkage and pedal.

[440Duster]

If the idle and transition/part throttle fuel curve is good move on to the WOT tuning. Things are going to change quite a bit once the secondaries are opening so I'd hook them up now. Signal to the primary side is going to be reduced with all 8 opening now.

Thanks for the reply, over the weekend I put some fresh plugs in and upped the PVR from .046 to .050 made a couple of romps and checked the plugs. Very little color, so I put in .054 and made another couple of romps still not a whole lot of color. I’ll hook up the secondaries and try again this weekend.

IMO, they all need 1:1 linkage. If it's too aggressive, fix it in other areas of the linkage and pedal.

I tried the 1:1 when I first started this journey. Couldn’t keep it from falling on its face under load. Crazy responsive in park with no load though.

[F-BIRD'88]

You need to get a AFR guage.
When you reconnect the secondaries you will need to revisit the primary side again.

WOT tuning you need to start plenty rich and tune towards lean best power by 1/4 mi mph while noteing AFR and plug colour between cylinders.
Do this with main jet changes only.
Then calc the area difference in cruise jet to wot jet and add to PVCR. Then fine tune main air bleeds.
The AFR guage is a yiu are too lean warning device as you tune WOT from plenty rich towards lean best power jetting @wot... MPH is your best indicator.
Again the AFR guage will clearly warn of a too lean condition @WOT when tuning rich towards lean best power.. It wants what it wants @WOT.

Plugs warn of overheated combustion, detonation, excessive timing, , plug heat range too.

When you dial in WOT jetting by the plenty Rich →→towards lean best power jetting method. even a simple (heated) narrow band AFR guage is all you need.
It clearly shows when things are getting too lean.

[F-BIRD'88]

Overall throttle responce, idle and cruise throttlle responce will probabily be best overall when the mechanical curve is locked out.
Especially if when the engine is cold and warming up.
With the tunnel ram...
Vaccuum advance rate in/out and max limit at high vaccuum (cruise, decelleration) is very important.

Do not allow the engine to idle slow when cold,. reguardless of how cool it sounds.. Keep the rpm up (1500-2000 rpm) during warm up or take it out and drive it to warm the engine..
The locked out mech timing helps a lot on this.
A manual fast idle throttle control cable is great for this.
So is a lil handy block of wood in the throttle linkage for during warm up.

[F-BIRD'88]

Your cam is tiny for getting (more) street power with a tunnel ram on a 440. It wants to eat.

[prairiehotrodder]

Were your carbs designed from factory for 2 x 4 application ? If not, is that .031 IFR what they came with ? I have a pair of holley 750 track warriors on a t-ram and putting in a smaller IFR really helped correct the idle and cruise AFR. There are a few T-ram guys on here and hopefully you will get some good advice. F-bird knows what he is talking about.

I am a believer in not straying to far from the factory calibration. To me thats a sign of a problem if the carbs seem to want major changes. In David Vizards book he says that a T-ram carb will want a smaller IFR and slightly bigger IAB. I think that is true. I also believe what f-bird says about using a AFR gage. My car is a race car and i do data logging with my AFR gage and i try to keep the AFR curve flat by tuning the HSAB. My carbs seem to like the factory main jetting.


Brian

[skinny z]

You need to get a AFR guage.

An invaluable tool.
An in cabin vacuum gauge is also useful. I found it helped a great deal with power valve tuning.

[440Duster]

Thanks for all the input. I do have an AFR meter and a vacuum gauge installed in the car. I’m in total agreement that they are invaluable to nailing down the tune. I’ve also learned not to tune to a particular AFR but rather to see the results of changes made especially when they weren’t necessarily obvious. Hope to get a few hours this weekend to move forward. Thanks again, I’ll post results as I have them.

[ClassAct]

Ignore the post about locking out the advance. That is just dead wrong.

[F-BIRD'88]

Some that think this way may bauc at fixed mech advance + vacuum advance on Street driven tunnel ram induction engines but short of fully mapable computer ignition timing control that this works very well for overall operation.. The engine loves the increased idle- low speed spark timing. Especially when cold.
It works.

[In-Tech]

I agree Fbird, Those rear end gears are not favorable either, maybe why he has to run some mech advance. Those cam numbers shouldn't mind a locked dizzy with a start retard and full time(not ported) vac advance would be even better.

Personally I would start those carbs with 1:1 linkage, .065" power valve restriction hole front and rear with your 10.5 PV's front AND rear, blue cams, .037" leg squirters with the better HV screw, .035 hsab(you might end up as high as .050"), .045 IAB, 74-76 jets square assuming double down leg(annular 12 or 16 hole would be better and will get signal faster requiring less pump squirter size and maybe less than the blue cam but I would keep the blue till the end, and more hsab).

[mopardave]

I have a 511 with 12.5:1 compression and a 270/276@50 sft. I use an Indy cast tunnel ram with twin BLP 650’s that flow about 750, they were built by Thumpercarbs. I played with the power valve set up a whole summer. 4 power valves. I had it doing everything quite well, but after trying square jetted their is no going back. It does everything perfect. It idles at 14.0, cruises 14.0 and wot is 12.8 with a .030hsb and 13.2 with a .032hsb. Jetting is 83 square using BLP jets, Holley jet would be 78. Squirted are 35. I think it’s a bit smoother cruising and transition is awesome. Being squared it comes on faster and harder when flat footed than it did when using PV’s. Using .031ifr and .70ib

[RW TECH]

Thanks for all the input. I do have an AFR meter and a vacuum gauge installed in the car. I’m in total agreement that they are invaluable to nailing down the tune. I’ve also learned not to tune to a particular AFR but rather to see the results of changes made especially when they weren’t necessarily obvious. Hope to get a few hours this weekend to move forward. Thanks again, I’ll post results as I have them.

Where is the O2 sensor positioned in the exhaust? If it's in the collector (with sealed exhaust system) it is likely to read 0.3-0.5 leaner than actual, as measured nearer to the cylinder head in the header primaries.

Tuning to a specific AFR isn't a great idea, but generally speaking you want it to idle as consistently as possible. Sometimes that means idle AFR at 13.0:1 - 13.5:1 to avoid plug fouling from misfires that occur when mixture is too lean for bigger overlap camshafts. Cruise can typically be leaner than 14.0:1, and sometimes will be best up to 15.2:1 in some cases. WOT at 12.8 is safe but you may find out your combination would rather be at 12.5, or richer yet near peak TQ. All of this assumes calibrated sensor(s) near the cylinder head.

Mileage may vary.........