Hello. I have recently purchased a car with a 406 (supposedly), Edelbrock heads, a tunnel ram with two 600 CFM Holleys and full tube headers. The seller knew nothing about the engine. The engine runs well (no stumble off idle, good partial mid-range) until it I attempt to floor it at mid-throttle, then it bogs and won't accelerate further. I checked the oil and it had fuel in it. So, I stopped running it. Do I need to change power valves, vacuum secondary springs, jets, throttle pump cam? Off of the distributor, the vacuum advance hose is running to the rear carb. Will I have to re-curve the distributor? It's my first tunnel ram and I'm ready to tinker with it this summer. Where do I start? Thanks.
1,200CFM capacity on an engine that probably needs 780CFM is a problem. That 780 is at wide open throttle, at the redline. Your current total venturi cross section is too large. When there is insufficient velocity through the venturis, proper fuel metering is impossible. Try drinking a soda with a 2-inch pipe, instead of a straw. Find the list numbers on your carburetors, and post them. It should be on the choke air horns.
I would start by changing oil, then check the timing curve with the vacuum advance plugged, check to see if you need to install an advance recurve kit with lighter springs, if this engine is installed in a light car with manual transmission or a high stall converter, I try to have full advance all in with light springs by 2500 rpm. Then on to the carburetors. I've had best results not running power valves on top of tunnel rams, by blocking off plugs and increasing the primary jet sizes by 5-8 numbers from stock number, the vacuum secondaries shouldn't open unless your engine requires the airflow
I would suggest cracking the carbs open to see what power valves and jets are in them, also look at the shooter to see what it is. I would also suggest buying the quick change vacuum pod kits that tie the two carbs together, the nature of how vacuum secondaries work will allow the 600 cfm carbs to work just fine.
Op , Your are going to need to know close to what you have , 406 will only turn about, Like 5,800 6,200 before rods will window your block . Unless $$$ (crank /rods piston, vavle train ) 406 will like a Tunnel but , Tunnel Good working around 4,000ish to Well pass North of 7k It takes some mid budget parts to Average a 406 to 6,400 rpm's . Initial Timing 18 - high 20's 33-38 total WOT , testing required, Note Book .. Weight of vehicle ? Witch T-Ram ? Holley S D ,Victor R. Two best before custom's . Stick or Auto ? Heads ? witch Edelbrock,& specs Pistons ? Fuel 87 , 91-94 ? Or higher ? Cam ? Solid , Hyd , Roller ? Rockers ? Header size ? Full , short ? Exhaust ? There more ,
An off-the-shelf 1850-2 has a 65 power valve. Fuel enrichment comes in when the vacuum drops to 6.5in-Hg. vacuum. That is pretty standard for a SINGLE carburetor application. You have two. My customary practice is to run power valves that are the stock value, divided by the number of carburetors. So 6.5/2. Since no 3.25in-Hg. valve exists, maybe a 3, or just plug them, and increase the main jet sizes. I never do this sort of thing without using a wideband Oxygen sensor. Modern fuels make reading plugs less accurate.
In red above... NOT a fully true / correct statement ! You just need to know "what" you are looking at ! But, this does NOT preclude an A/F gauge for more proper air fuel ratio, AND at, from idle to a fully open carburetor, preferably on a dyno. Mike
The 1850-2 should have come with the stiffest spring (late/high RPM). You need to verify that is what is in there, and if not, put those in. If I recall correctly, they are colored black.
True, but if one looks at the page in a Chiltons manual, or similar, they are likely to not get it right. I have seen almond-colored porcelain on engines burning way too much fuel.
There's a tunnel ram guy on you tube, Andy Wood, he's affiliated with Unity Motorsports Garage. The guy knows how to make tunnel rams work on the street and perform. It can be done, but it will likely take some experimentation. and despite the old wive's tales, the thing will fire up and run acceptably somewhere well below 10 million RPM.
I drive my tunnel rams on the street in stop and go city traffic without issues, one to one on linkage, no chokes etc etc Once you get them tuned they are a blast to drive, you just have to figure out what the carbs need and it does take some experimentation, there's no magic formula off the internet. Once you do have them right you get to have the pride that you did it yourself and then you can chuckle at all the old wives tales about how they don't work on the street.
My last 3 cars all had tunnel rams, and all used either 600 cfm, or in the case of my 468 BBC I had 650 cfm carbs, and all ran excellent on the street with very little tuning needed. I did have issues with the 650 cfm carbs on my BBC as it turned out the factory jetting was way too small for a tunnel ram with two 650's. I changed out the jets from the factory 64's to 78's and plugs went from white to tan, and the engine ran much cooler. It also lost the low speed surge it had at around 2500-3000 rpms. It was surging because of the lean condition, and that lean condition also caused the overheating issues. Tunnel rams almost always need and run well with larger carbs than you'd use for single carb or dual carb intakes that are much lower. The big plenum size just needs more cfm carbs to work nicely.
You didn’t mention which tunnel ram but if it is the original Edelbrock TR-1 those had an issue with fuel at low RPM constant speeds falling out of suspension and collecting at the bottom of the plenum. The design had individual ports raised an inch or so above the plenum floor and Edelbrock offered a filler to eliminate that issue. I guess a couple pints of gas on the plenum floor and a backfire could get exciting.
T-Ram work on street if you take time to Tune , My self Many miles & low 6 sec Sbc 1/8 Race Rod . I use the S -D & V -R , 1.1 carbs & a custom made T -Top for Dominator , Single D more harder to tune for Street driven Even witch a 3 Circuit
The key here for me, at-least, has always been using vacuum secondary carburetors, which you have, and restricting the secondary operation very tightly. You don't want the secondaries open when the should not be, nor do you want them open any more than the engine demands. That, along with the always necessary proper jetting, it key.
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