tunnel ram update

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aaronk785

aaronk785

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I installed my tunnel ram this winter on my 340. Engine is 9.8 to 1 comp. Ported 2.02 heads, hughes solid 237 242 at .050 and .537 .542 lift. Intake is eddy street tunnel ram with to stock 69 340 avs. Got to take it out today. Its a little cold blooded but once warm runs and idles really well. WOT it screems to 7000 rpm easily but I shift at 6600. Problem is on the shift at the bottom of the next gear it lays down just a bit for a second or so then recovers just fine. Any advise to solve this would be greatly appreciated.
 
What does the rpm drop down too?
Does it do this no matter how high or low the shift is?

Tell us about what stall the converter is and what the gear and tire combo is.
This could be a factor.
 
Stall is 2400. Tires 26in. 3.55 gears. rpm drops to about 4000 rpm when shift at 6600. I have a 4000 stall I'm going to try when I have time this should help with the rpm drop on the gear change. In my race car I have a 5000 stall and shift at 6500 and tach never gets below 5400 on the shift. Does this sound like this should help?
 
Yea it does but I’m going to be honest up front and say I don’t know what it could be. I’m asking questions for clues that may POP up and say something to me.

So far, the way I would have done it would have been more gear. This may or may not be a part of the problem but IMO not the single soul guilty party.

You also have a lot of carb on top. The 340 AVS carb is rated at 630 cfm by Carter. So that be 1260 cfm. And that’s a lot of gobble gobble! LOL!

IMO, it is also more cam than I would have used for the combo and a 4bbl. (Except a manual trans car.)

I’m wondering if the slightly low gear coupled with a ton of W.O.T. cfm is creating a momentary stop of airflow (metering issue with the OE carb) and your having trouble getting everything moving again. This would have the carb go rich lean rich lean rich lean until the engine can injest it all.

I do think that this thing (via your description) runs like crazy with long legs. It’s gotta be pretty good on the street!
 
Is this the intake?

image.jpg
 
Watch the manifold vacuum and see what it is before and after you shift, if it doesn't drop enough when you shift you will need to change the springs in the power pistons to get more fuel.

What I'm trying to say is you need more fuel to compensate the air, 2 4bbls wide open will need a lot of fuel when the engine slows down and the air going through the carbs slows down and doesn't pull as much fuel.

I had the same problem it ran great with 4.88 gears then put 3.91 and ran it on the street I had to reset the carbs because it had a lean bog because it had more load for a longer time.
 
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Thanks everyone. I will try some carb tuning to start with. It does feel like a lean bog. I would love to get some 500 eddys or 390 holleys later but I used what I had. Yes Rumble that is my intake. Car really doesn't feel like it lost much if any low end torque and idles just as good as the duel plane and holley. Will eddy springs work in the avs? What about jets and metering rods?
 
brian6pac said:
Watch the manifold vacuum and see what it is before and after you shift, if it doesn't drop enough when you shift you will need to change the springs in the power pistons to get more fuel.

What I'm trying to say is you need more fuel to compensate the air, 2 4bbls wide open will need a lot of fuel when the engine slows down and the air going through the carbs slows down and doesn't pull as much fuel.

I had the same problem it ran great with 4.88 gears then put 3.91 and ran it on the street I had to reset the carbs because it had a lean bog because it had more load for a longer time.
Click to expand...

This.
What carbs?
 
shifting at 6600 is a bit high for that cam. more rear gear would help by more torque multiplication. a 4000 stall conv. will not help-it will still drop to 4000, a 5000 stall would help. how much ignition advance at 4000? eddy springs and secondary jets will work. adjust primary with metering rods. carbs are 2 1969 625 cfm 340 avs=good
 
The AVS carb is slightly different in that it uses taller rod covers.

If you decide to use AFB metering rods/springs/jets in an AVS carb, then make sure it is all 3 items listed and not just one or two of them. You will also need the AFB rod covers.
 
If you tighten the spring the air valve, it shuts when there's not enough air to hold it open, like a choke it sucks more fuel.
 
AJ/FormS said:
AVS
Air Valve Secondaries
I thought the air valves were adjustable by bending the little tangs. Maybe you can turn the "630"s into 600s,580s,or 550s,lol.
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Ahhhhhh, no... that would be a TQ as the AVS is a positive stop on the upper body IIRC. The spring loaded secondary door can be wound really tight, but ......
Dang! It’s been a while since I owned one. Love the AVS!
brian6pac said:
If you tighten the spring the air valve, it shuts when there's not enough air to hold it open, like a choke it sucks more fuel.
Click to expand...
I don’t know if the spring is capable of holding the door closed at high rpm. Middle rpm... maybe. It is a good thought though. I didn’t think of that.
At least in that way the secondary system totally shuts down until a higher rpm comes back into play.
 
brian6pac said:
If you tighten the spring the air valve, it shuts when there's not enough air to hold it open, like a choke it sucks more fuel.
Click to expand...
No that's not what I meant. The TQs have a tang that you can bend to limit the air door opening. I thought I remembered the AVSs also being so adjustable.

Oh sorry Brian, I bet you weren't talking to me.
 
1260 cfm! LOL
The motor is only going to use what it needs. Try what Triple-R said. It's free and it's a simple tuning problem. Have fun. Any pictures of the quads?
 
He can get all the barrels open ez enough since there mechanical and the secondary spring can be unwound. What the engine gobbles up is different!





Spelling fix
 
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To give you a baseline, the factory setting for the secondary air door spring is one full turn after the air door just closes all the way. This way, if that's not what it is, you can return it to ground zero.
 
Weather finally warmed up so I worked on the t-ram some more. Tried to adjust secondary door but had no real affect on the bog, just when it happened. So I changed jets. stock where 89 front and 98 rear. I went to 92 front and 107 rear. Man what a difference. Car runs even stronger and no more flat spot on the shift either. Still have a tiny bog if I stab it from an idle so I will adjust the air door again and see. Drives just as good as the rpm and preform 750 that was on it just way stronger from 4500 up. I am very pleased with the way it runs with as little tuning as ive done and it looks damn cool.
 
aaronk785 said:
Weather finally warmed up so I worked on the t-ram some more. Tried to adjust secondary door but had no real affect on the bog, just when it happened. So I changed jets. stock where 89 front and 98 rear. I went to 92 front and 107 rear. Man what a difference. Car runs even stronger and no more flat spot on the shift either. Still have a tiny bog if I stab it from an idle so I will adjust the air door again and see. Drives just as good as the rpm and preform 750 that was on it just way stronger from 4500 up. I am very pleased with the way it runs with as little tuning as ive done and it looks damn cool.
Click to expand...


I'd bet you need bigger squirters. IIRC, Carter only had three sizes. Small, medium and large and I'd bet you have the small shooter. A medium squirter would clean all that stumble off idle right up.
 
If your having trouble with the tune and secondary tip in, focus on the primary tune until excellent. If need be, disconnect the secondary side. This allows focus on the primary sides. Once that’s in like I should be, hook up the secondary side and adjust the tip in point and then the jetting.

Love those early OE AVS carbs. 630 cfm rating.
 
Yes YR my next step was to drill out the squirters. I have drill bits form .020 to .o50 so I can go up till bog is gone. Tuning the primaries to the max sounds like the way to go. I never get done tuning.
 
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