Big Block Tunnel Ram 660s Questions

[71GSSDemon]

So I pulled the carbs off. I was able to confirm. There are 76 jets in the primaries, no power valves, and rear metering plates are #12. I found it strange that despite the 1000rpm idle, the transfer slots were covered by the throttle plates. The secondaries were closed. So, everything I have read says the transfer slots should be visible below the blade by about 0.050" or a "square" when looking at it. I adjusted the idle speed screw to get the throttle blade/ transfer slots set. Now I worry about the idle speed being much higher as I had to adjust the idle speed screw about 0.100" ish. Anyone thoughts as to how I had such a high idle (exactly what I wanted) with the transfer slots covered? Will this new set up make it richer also?

440 low compression short block
Hughes whiplash 440 cam
Shaved, ported iron heads
Weiand tunnel ram
Holley 4224 660 center squirters
2500 stall rmvb
3.91 SG

 

[Bewy]

Have you thought about where the air comes from for idling? A number of places:
- leakage around t/shafts
- PCV
- idle air bleed [ s ].
- gap around t/blades.

You now have 4 extra t/blades & two extra shafts for idle air, compared to a single 4 bbl carb.
I suspect that you have some leakage past the 'closed' secondary blades. Remove carbs & hold up to the light. If you see gaps, you may be able to re-set the sec blades to close more. If you any additional bypass air via drilled blades, then these need to closed/reduced.

 

[RustyRatRod]

What distributor do you have and how is it curved? Sometimes, some of the really light advance springs can pick up some mechanical advance at idle.

 

[ch1ll]

Are there holes drilled in any of the throttle plates?

 

[MomsDuster]

Not sure I’d get too caught up on the the small transfer slot exposure.
Mine idles at 950 in park with very little t-slot exposed. I would suspect air is coming from somewhere else, or as RRR mentioned timing.

 

[71GSSDemon]

What distributor do you have and how is it curved? Sometimes, some of the really light advance springs can pick up some mechanical advance at idle.

I am using a MSD pro billet ready to run. 18⁰ at idle and 38⁰ all in about 2000, 2300 IIRC. I am using vacuum advance and due to the 660 no having ported vacuum available, it is hooked to manifold vacuum.

 

[71GSSDemon]

Have you thought about where the air comes from for idling? A number of places:
- leakage around t/shafts
- PCV
- idle air bleed [ s ].
- gap around t/blades.

You now have 4 extra t/blades & two extra shafts for idle air, compared to a single 4 bbl carb.
I suspect that you have some leakage past the 'closed' secondary blades. Remove carbs & hold up to the light. If you see gaps, you may be able to re-set the sec blades to close more. If you any additional bypass air via drilled blades, then these need to closed/reduced.

I have the carbs off now. Just went thru them last night to make sure the jets and metering plates were correct. I can see if the secondary blades are closing. I removed the flat blade set screw for thr secondaries and replaced it with an Allen head cap screw to make that adjustment easier while they are on the car. Throttle blades are NOT drilled

 

[RustyRatRod]

I am using a MSD pro billet ready to run. 18⁰ at idle and 38⁰ all in about 2000, 2300 IIRC. I am using vacuum advance and due to the 660 no having ported vacuum available, it is hooked to manifold vacuum.

Is the vacuum advance adjustable? You may have one of the rare instances where ditching the vacuum advance is advisable.

 

[71GSSDemon]

Are there holes drilled in any of the throttle plates?

No, there are no holes drilled in any of thr blades

 

[71GSSDemon]

Is the vacuum advance adjustable? You may have one of the rare instances where ditching the vacuum advance is advisable.

I will need to look into the vacuum advance, I am honestly unsure if it is adjustable.

 

[71GSSDemon]

Not sure I’d get too caught up on the the small transfer slot exposure.
Mine idles at 950 in park with very little t-slot exposed. I would suspect air is coming from somewhere else, or as RRR mentioned timing.

Hey Mark. Yeah, mine idles about 1000 in park and 850 or so in gear. It all works well that way, I was just surprised to see no exposed transfer slots with that kind of idle speed

 

[Brooks James]

Every Holley 4 barrel I have rebuilt has had light escaping past the throttle blades. Loosen them slightly, as little as possible to keep the flattened end of the blade screw as intact as possible, so you won't have a screw come out.. I have on occasion taken a small flat punch to "reflatten" the tip of the screw. Once you have done that , you will have a good starting point for further adjustments elsewhere.

 

[MomsDuster]

Hey Mark. Yeah, mine idles about 1000 in park and 850 or so in gear. It all works well that way, I was just surprised to see no exposed transfer slots with that kind of idle speed

Yeah, I remember when I was setting mine up and was reading all that transfer slot info about .020-.040 exposures. It made mine idle way up there, especially with manifold vacuum on the advance.
I was talking with yellowrose back then and he told me that with the tunnel ram the most important thing was to make sure that both carbs flow the same at idle. Then whatever the transfer slots were, that’s what they are.

I made one of them tools with the UNI-sync (I think that’s what it’s called) to get the carbs to flow the same at idle. Neat little tool to have handy when working on a tunnel ram. Biggest key is to make sure that one of the carbs throttle links is disconnected at the carb when adjusting.

Bottom line is verify no leaks (air and fuel). Verify timing, and verify carbs are synced. 1000 rpm idle is not a bad thing.

 

[71GSSDemon]

Yeah, I remember when I was setting mine up and was reading all that transfer slot info about .020-.040 exposures. It made mine idle way up there, especially with manifold vacuum on the advance.
I was talking with yellowrose back then and he told me that with the tunnel ram the most important thing was to make sure that both carbs flow the same at idle. Then whatever the transfer slots were, that’s what they are.

I made one of them tools with the UNI-sync (I think that’s what it’s called) to get the carbs to flow the same at idle. Neat little tool to have handy when working on a tunnel ram. Biggest key is to make sure that one of the carbs throttle links is disconnected at the carb when adjusting.

Bottom line is verify no leaks (air and fuel). Verify timing, and verify carbs are synced. 1000 rpm idle is not a bad thing.

View attachment 1716020414

I made one of those also. I am not worried about the idle speed, just wondering about the transfer slots being covered at that speed. Curiosity mostly. If I turn the idle screw to get them square, it assuredly will idle much faster. I know you been tuning on yours a bunch too. I have reached out to a few senior car/tuning members that have helped many people and I trust what they have to say, but no luck yet. I can definitely just set the idle speed to what it needs to be and not worry about the slots. Sync the carbs and go with it. I have a stumble from part throttle to WOT I am chasing. Idle to WOT also. Been trying some things but the covered slots made me wonder about fuel present. I hear these run so rich, etc, but mine runs well and gets good mileage, so something must be wrong..

 

[MomsDuster]

I’ll admit I have zero experience with the 660’s. Are power valves an option? I was able to get rid of a tip in stumble on mine by getting the power valve circuit to open sooner. I’m sure the carb guru’s will have something to say. I’ll be watching this thread for sure!

 

[71GSSDemon]

I’ll admit I have zero experience with the 660’s. Are power valves an option? I was able to get rid of a tip in stumble on mine by getting the power valve circuit to open sooner. I’m sure the carb guru’s will have something to say. I’ll be watching this thread for sure!

I can swap the from metering blocks for ones with power valves. I also could add rear blocks to have replaceable jets in the back. I have not done either. These historically run very rich, but these don't seem to do that. I question if the secondary plates aren't sealing. The adjusting screw for the secondaries is not holding them open

 

[mbaird]

if you are using a stock distributor try adjusting the VA can so that it starts at a point higher than your idle vacuum.
As it sits it may be advancing at idle.

 

[71GSSDemon]

if you are using a stock distributor try adjusting the VA can so that it starts at a point higher than your idle vacuum.
As it sits it may be advancing at idle.

As stated above, I am using a MSD pro billet ready to run. 18⁰ at idle and 38⁰ all in about 2000, 2300 IIRC. I am using vacuum advance and due to the 660 no having ported vacuum available, it is hooked to manifold vacuum. I am sure it is pulling advance at idle, idle speed increases when hooking it back up.

 

[mbaird]

As stated above, I am using a MSD pro billet ready to run. 18⁰ at idle and 38⁰ all in about 2000, 2300 IIRC. I am using vacuum advance and due to the 660 no having ported vacuum available, it is hooked to manifold vacuum. I am sure it is pulling advance at idle, idle speed increases when hooking it back up.

Sorry I missed that . And IIRC the MSD unit is adjustable for total amount of advance but not when it starts . In which case you could lower your initial timing and recurve the distributor to compensate .

 

[71GSSDemon]

Sorry I missed that . And IIRC the MSD unit is adjustable for total amount of advance but not when it starts . In which case you could lower your initial timing and recurve the distributor to compensate .

I have the bushings for 20⁰ mechanical and the springs set to bring it in about 2200. With initial timing of 18⁰. Maybe it should be dialed back to reduce idle speed, but I thought you should use as much as the engine wanted without ping or detonation.

 

[71GSSDemon]

If the exposed transfer slot is not important unless too much is uncovered, then what I had isn't an issue, just need to sort out the stumble. I was thinking with the transfer covered yet, maybe I am lean and then in the transfer slot longer than typical. Which could explain the good mileage too

 

[MomsDuster]

I hear these run so rich, etc, but mine runs well and gets good mileage,

Leads me to question I've pondered since i started my tunnel ram journey: Does lower compression affect intake air speed? Not wanting to hijack this thread but, I've read and been told that I would need to reduce my idle feed restrictors from .033 to .028 or so. I found by doing that it would go stupid lean (17+ AFR) in the transition slot area. Curious if that is due to the lower compression, in my case being exactly unknown but in no circumstance more than 10:1 causing lower air speed thus causing a lean condition. Where as when using a larger IFR compensates for the lack of air speed with more fuel being available. Am i making any sense at all?

 

[71GSSDemon]

I have wondered much of the same. Mine worked much better with the small air cleaners. I have wondered if I have lazy air and reduced signal on the carbs. Not enough motor?? I have velocity stacks only at the moment and wonder if I need the motor to pull harder on the boosters. I picked up 2 of the 4 hole spacers for under the carbs which should help signal. I also added 0.010" wire in the main air bleeds to make them come in sooner, but can't drive the car....winter in WI. When I slowly advance the throttle 2700-3000 the fuel is lazy thru the booster and that is the stumble. I can watch it happen

 

[MomsDuster]

It all makes perfect sense in my noggin! Mine is very similar in that fashion with the boosters. Really curious what mine will do with the annular booster main bodies.

 

[Dubob]

I also added 0.010" wire in the main air bleeds to make them come in sooner,

With a typical Holley, restricting the main air bleeds typically will delay the mains starting. It also doesn’t take big changes on the bleeds to make big differences. A .010” wire is a big jump and should shift the mains starting higher in rpm. I’ve spent a lot of time at racing fuel systems website reading to get my Holley where I want it. Here’s a graph I found that really has helped me understand what’s doing what and when.
Also stumbling at low throttle while in the transfer slot very well could be not having enough transfer slot exposure. My thought there is the transition circuit may not have flow established and that has to occur before feeding mixture to the engine causing an off idle stumble.