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Old 06-24-2009, 11:46 PM
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Need help picking a dual carbs for my tunnel ram (sbc 383)

So currently I have the Weiand Tunnel from summit (it came on the car when I got it) http://www.summitracing.com/parts/CMB-03-0177/

This has two 4160 450cfm chokeless carbs with mechanical secondaries on them. I have been trying to get this tuned and just can't get it correct. I have been told to go to vac. secondary carbs w/ choke and things will run better. I was curious what you would recommend.

Details:
383
Wieland high tunnel ram
Cam: Duration 308/318, Lift .488/.510 (http://www.summitracing.com/parts/EDL-7102/)
64cc aluminum heads

I know that I could go with a different intake but I only drive this car every so often and it is more or less for cruising around town or up and down the valley and my Wife and I love the look of the ram :-) If you are curious the car is a 1930 Model A chopped and channeled. I would embed the image but my server isn't up right now. Thanks for any recommendations

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Old 06-25-2009, 09:27 AM
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Just get a pair of 390cfm VS Holleys #8007. May cost a lot, but they do work very well for the street.
BTW: replace the top cover of the vacuum sec. diaphram housing with the cover that you connect a vacuum line between the two covers. This will give uniform secondary operation. It's not nessary to use both electric choke just use the rear choke for easy start-up. Leave the front choke wide open.

Last edited by lg1969; 06-25-2009 at 09:34 AM.
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Old 06-25-2009, 10:58 AM
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I've got a 50 Chev. with a 350, 480/230 cam, and Weiand tunnel ram, Edelbrock 500 cfm carbs. I know it's over carbed but it's what I had around. 411 gears and as much timing as i can put into it. Runs great on the street. Just my 2 cents worth
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Old 06-25-2009, 11:19 AM
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Holley

What can't you get them to do these should work fine if the are synced and adjusted properly,timing right no vacuum leaks. How about more info
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Old 06-25-2009, 11:27 AM
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Those Holley 660 is designed for tunnel ram
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Old 06-25-2009, 11:29 AM
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Its mostly a matter of knowing how to tune the carbs.
This big duration cam+ manifold will not work with a stock stall torque converter.
You need a 3500 stall converter (10"). The engine wants to rev, needs gear.
3.55 or higher.
The spark advance curve (mechanical advance) needs to be modified, optimized for the big cam and manifold.
What is the spark timing at idle? Needs to be 24deg base timing at idle or more. More is better. You want 24 to 26deg at idle and 34 to 36deg at max advance 3000-3200rpm. You cannot achieve this by swapping just the weights and springs. You must physically limit the mech advance travel stop limit to around 10-12deg. (20 to 24 is typical stock, too much travel for this motor). This mod allows the nessessary increased base idle timing without overadvanced timing at max advance. Some people just lock out the timing advance (eliminate the advance weights and springs and set the idle timing at 34-36deg. (No mechanical advance)

Vacuum advance is a separate issue. Once you have the mechanical advance modified, you can run 10-15deg (limit) of vacuum advance for efficient cruising. The vac adv rate in and out (diapharm spring tension) needs to be optimized by trial and error.
Remove both carbs, flip them over and look at the bottom and reset the throttle blade opening /idle fuel transfer slot exposure (.020-.030") on all 8 barrels (idle throttle opening position). reinstall the carbs with new 3.5 or 4.5" rated power valves.

You must allow the tunnel ram manifold to "warm up" a bit before expecting good throttle response. Let it warm up a good bit before final carb idle mixture adjustment. The heat in the warmed up manifold aides throttle responce and fuel vapourization. Liquid fuel will not burn, but does a great job of fouling plugs. once the carb throttles are re-set properly, avoid changing this as the throttles/idle transfer slot exposure must be in this narrow "sweet spot" for best idle quality and throttle responce. The increased base idle timing will allow this. (24 to 26deg right up to locked out (34-36deg at idle if nessessary)
Don't forget to hook up the PCV to the base of one of the carbs or the manifold plenum and be sure to vent the other valve cover.
Should idle rough but rock steady and clean at 900rpm and will only idle correctly while in gear with the correct high stall torque converter ("3500")

This engine wants to cruise on the highway at 60mph at around 2800 to 3200 rpm. If its not within this rpm zone at 60mph cruise , you have the wrong rear gear ratio. Change the cam or change the gear.

Once you have made all this changes you'll find the tunnel ram very street friendly. A AFR meter/O2 sensor will allow you to really dial in the carb jetting and airbleeds. You'll find even a cheap narrow band AFR gauge very usefull in dialing in the carbs.

Last edited by F-BIRD'88; 06-25-2009 at 11:49 AM.
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Old 06-25-2009, 02:39 PM
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IMO: 450 and 660 cfm Holley are worthless carbs to use on the street. They will load up at idle. Your Gas mileage will suffer. It will backfire. It will be difficult to start when the motor is cold. Who is going to sit in the car feathering the gas pedal to warm the car? The cam and heads you have are fine. Just do me a little favor just get the Holley 390 and you will be fine. Your 383 will only see around 600 cfm at 6000 RPM. You do not need 900 or 1200 cfm on the motor unless your planning to shoot for 10,000 RPM.

Last edited by lg1969; 06-25-2009 at 03:03 PM.
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Old 06-25-2009, 06:59 PM
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Thanks for all the advice :-)

I have a TH350 with a 3500 stall right now with 355/373 gears I would have to double check.

I have the timing at 18 right now since I wasn't sure how much higher to go, 12 is about as low as it goes before it stalls.

The biggest frustration for me has been trying to dial it in to respond when I punch it. It seems to go fine with very light throttle but if I gas it at all (specially with vac advance on) it just stumbles then finally picks up and goes. Originally the first owner had the pink holley pump cams and those seemed to cause an over rich condition so I changed to the orange cams and gave that a try and now I can drive w/o stalling from idle but still not "balls" when you go. As far as available vacuum those carbs I have don't have any hookup other than ported. The previous owner tapped the intake for a vac. connection to the TH350 but other than that I have nowhere to hookup PCV (also which is leading me to want new carbs). The blow by w/ no hood leaves a nice fine mist after a long drive.

I think this weekend I will take some advice from F-BIRD'88 and see what I can get. In the meantime I will look at some of the 390cfm carbs recommended and see if I Can scrounge up the 700 for the carbs. I think the biggest reason for wanting the choke is upsetting all the neighbors trying to get the car warmed up :-) It doesn't get that warm up here in Seattle most of the time so I have to sit out there with it >1000 rpm for a few minutes and with more or less straight side pipes on it...
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Old 06-25-2009, 08:06 PM
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carbs

This is a big cam , it need gears ,what compression does it have?,what heads are on it, too little info.
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Old 06-25-2009, 08:12 PM
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It is running 10.1:1 compression as far as the make of the heads I would need to check with the previous owner. He had just finished building it when he lost his job and sold the car to make mortgage payments.

I attached a few pictures of the heads although I suppose it would be hard to tell without removing them.
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Old 06-25-2009, 11:57 PM
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I just got home from work and e-mailed the previous owner to double check which brand the heads are (not really sure why I hadn't asked before). Based on visual inspection and knowing he got all the parts from Summit (he still had all the boxes in the garage when I bought the car) they are these:
http://www.summitracing.com/parts/SUM-162111/
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Old 06-26-2009, 01:23 AM
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Quote:
Originally Posted by lg1969
IMO: 450 and 660 cfm Holley are worthless carbs to use on the street. They will load up at idle. Your Gas mileage will suffer. It will backfire. It will be difficult to start when the motor is cold. Who is going to sit in the car feathering the gas pedal to warm the car? The cam and heads you have are fine. Just do me a little favor just get the Holley 390 and you will be fine. Your 383 will only see around 600 cfm at 6000 RPM. You do not need 900 or 1200 cfm on the motor unless your planning to shoot for 10,000 RPM.
Talk to this guy.. He does really know what he is talking about with the 390 carbs!!!! he has helped me out greatly on some info for a tunnel ram... two 390's is only 780 totall cfm, Not much more than what some guy's run with a single plane one carb setup... 390 IMO are the better setup for street use.
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Old 06-26-2009, 08:56 AM
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Thanks again for all the advice :-) I will take this and play with the car some more this weekend and shop around (Summit and Jegs I suppose) for the 390cfm carbs.

Also I checked with the previous owner and he can't get the make of the heads since the paper work is at home and he is on vacation but he said the block + heads came from Cylinder Head Specialties in Portland.
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