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Old 10-19-2008, 02:02 PM   #1
Mercury Kid
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Default Tunnel ram carb theory

I bought my first tunnel ram today and I'm excited as hell to get it on an saw a hole in my hood, but first I need carbs. I've been doing some searching and as far as I can tell there are two schools of thought as far as tunnel rams are concerned.

School 1- Two small carbs- This school says that two 390 or 450 holleys will work best becuase of the combined flow. This school also tends to say that vacuum secondaries are best because the motor will only use as much fuel and air as it needs.

School 2- Two big carbs- This school says that if it runs good with a single 600-750 carb, then it will run good with two. They say that it will make more power without any sacrifice in throttle responce. Some of them also say that mechanical secondaries work fine because it will give the motor as much fuel and air as it can take.

The engine in my Comet is a stock bottom end 289, but the ultimate goal is a forged 331 stroker. Currently I've got a 600 edelbrock mechanical secondary carb on it. It has Edelbrock heads with 1.9/1.6 valves and the cam is 224/234 @.050, .496/.520 lift. It's backed by a T-5 and 4.11 gears turning 235/60-15 tires. It's set up as a street gasser and is stripped down quite a bit. I figure 2850 lbs with me in it. It is a street car and I drive it a lot.

What are your thoughts? Would love to hear from the guys running a ram on the street.
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Old 10-19-2008, 02:22 PM   #2
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Default Re: Tunnel ram carb theory

I run one carb on my 302 tunnel ram in the Ranchero .If you plan to drive it much i wouldnt over carb it for sure,and i mean drive it.I dont mean backing on and off trailers.Im talking about sitting in traffic ,driving in 20 degree weather.All of which i do with mine.The carb thing isnt what kills low end ,its the size of the plenum or volume under the carb .I used the same carb on mine with the torker intake ,and all i did was switch to a tunnel ram .It lost its balls of an idle for sure ,but more than made up for it above 4000 by going to the tunnel ram.I am running a 4 spd and 4.57 gears now so it seems to be srong of an idle. I think with the 4.11's and stick shift you wont notice it as much as you would with highway gears and an auto .It all depends on what your gunna be doing with the car .Race only (2 carbs for sure and big ones),race 95 percent of the time but a tiny bit of street driving (2 small carbs or one biggun) ,driving it daily in any and all conditions (use the same carb you have or maybe a 650 with a bigger shooter and 50cc pump ,and maybe jet it up in the primaries a bit to help smooth out the stumble ,then drive the crap out of it).You have to decide what rpm range its gunna be used in most of the time to decide what carb / carbs is best .Running two 750's on the street with that little 289 is gunna be worse that if you had a 600 on it.Thats why tunnel rams got a bad rap on the street is because people simply get carried away with too many cfms .Just my opinion here .Some people tell me that a tunnel ram doesnt look right with only one carb.These are usually the guys that store their cars during the winter months and only drive their car on and off a trailer.Meanwhile im cranking my tunnel ramed car at 5:30 am in 20 degrees weather in Janurary and driving to work .I dont like to change fouled plugs all the time ,so i dont run too much carb .If it was a race only car i would run 2 carbs for sure...
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Last edited by The Shocker; 10-19-2008 at 02:29 PM.
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Old 10-19-2008, 02:51 PM   #3
pitman
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Default Re: Tunnel ram carb theory

Probably the best thing you can do, is to size the cfm rating for the 289-302-331, and carbs accordingly. Too much will wash oil off the cylinder walls, give poor throttle response, and generally loook grand. All depends if you are building for show, or for go...a real driver. I now size them for the intended driving and engine's disp.
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Old 10-19-2008, 02:57 PM   #4
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Default Re: Tunnel ram carb theory

Its a driver. I'm out there cranking it and waking up the neighbors at 6:30 on my way to work. I deleted the heat and they salt the roads here so it's a summer driver but still a driver. I'm sticking with duals, cause I love the way they look.

Shocker, your car is awesome, I gladly listen to someone who drives something like that.

All the advice is appreciated. Exactly what I'm looking for.
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Old 10-19-2008, 03:09 PM   #5
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Default Re: Tunnel ram carb theory

Quote:
Originally Posted by Mercury Kid View Post
Its a driver. I'm out there cranking it and waking up the neighbors at 6:30 on my way to work. I deleted the heat and they salt the roads here so it's a summer driver but still a driver. I'm sticking with duals, cause I love the way they look.

Shocker, your car is awesome, I gladly listen to someone who drives something like that.

All the advice is appreciated. Exactly what I'm looking for.
No problem ,and i agree 2 fours look coolest ,but i've been there and done that on a street car that i drove daily.Maybe you will have better luck than i did .BTW i like your Comet too...
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Old 10-19-2008, 03:20 PM   #6
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Default Re: Tunnel ram carb theory

What kind of T ram did you get ? You can always buy another top and switch back and fourth from dual 4's at shows and races to a single the rest of the time.You can change the top in about 15 minutes ...
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Old 10-19-2008, 03:45 PM   #7
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Default Re: Tunnel ram carb theory

I just got back from a little road trip with my hot rod. The motor is a ZZ4 crate motor with a ZZ430 hot cam kit, Dart pro 1 heads with 200cc runners, 3.73 posi, 700R4 over drive tranny, tunnel ram with twin 450 Holley carbs. I changed the power valves to 4.5 and still need to put 50cc squirters to help with the slight off idle stumble.

I do have to brag about the fuel mileage on the highway. I got 18.5 MPG. That's better than my daily driver. But I also have to say that the fuel mileage in town realy sucks.

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Old 10-19-2008, 05:02 PM   #8
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Default Re: Tunnel ram carb theory

Didn't Edelbrock make a device that went in the plenum and called it a Turtle?

Since tunnel rams give a weak vacuum signal to the carb, I wonder if it would help to install a device in the plenum that didn't interfere with flow, but would cut the plenum volume down for low-speed street use.

The right size triangular shape would be easy to do for most.

The medium riser manifold with dual quads on my late Buick engine worked well winter and summer as well as idled at 600 rpm with a fairly big cam.

Aided by the large 462" engine and MSD ignition no doubt.

And maybe running a tunnel ram on it would be easier than it is on smaller engines, but I do think an avenue to pursue is the smaller plenum volume for street use.
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Old 10-19-2008, 05:32 PM   #9
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Default Re: Tunnel ram carb theory

although a differant animal, I run 2 500 cfm edelbrocks on a tunnelram on my sbc with decent street manners. It is cold blooded without chokes hooked up but still manageable even in 20 degree weather. At a steady rpm of around 25-2600 in 4th gear it makes 17 mpg with 4:11 rears and 29 inch tires.I use a pertronix igntion with a accel 42000 volt coil that seems to do a good job.Biggest thing to get used to is the lack of bottom end power til it hits 2500 rpms or so. They are alittle hard to get used to but you will get used to it and probably love it.Mine is on to stay as long as it has the sbc in there.
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Old 10-19-2008, 05:43 PM   #10
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Default Re: Tunnel ram carb theory

It's an old weiand intake. I don't really have the money to have two tops and three different carbs. I'm going to have to hit the swap meets for some carbs as it is. I think I'm going to run holleys because they make them smaller than 500 cfm and because tuning help will probably be easier to get.

BinderRod, thanks for the tuning tips. I have heard about the 50cc pumps before and it seems to be the setup.

Keep it coming.
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Old 10-19-2008, 06:03 PM   #11
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Default Re: Tunnel ram carb theory

mine is an old Team G Super Ram for competition only but works well on the street. I do know my sbc runs and works fine with the Edelbrocks but it took alot of tweaking to get it there. If I remember right you'll have to mount the Holley carbs sideways right? I do know a guy here that has 2 450 Holleys new in the boxes that he'll probably never use. PM me if interested and I'll find out for you
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Old 10-19-2008, 06:19 PM   #12
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Default Re: Tunnel ram carb theory

Any carb setup you choose with take some tuning but it will be worth it in the end ,because you will freaking love the way a tunnel ram pulls at 3000 to 6000 ,especailly with those 4.11's and light weight .My Falcon accelerates from 3000 to 6000 in first gear so fast that its a blur on the tach when you floor it.Of course the 4.57 gears help also.Once you get all that velocity moving its on baby.I wouldnt use a box to take up velocity in the plenum but i have heard of it.It defeats the purpose of the T ram .Despite looking cool they have there advantages performance wise.I dont know what ign. system you are running ,but it better be a hot with 2 four's in traffic ,or you better keep plenty of spare spark plugs in the trunk.I am running a Mallory procoil ,and MSD 6 AL and i havent fouled a plug yet on my setup .You and i have and i have about the same car mechanically weight,heads,cam ,close to the same cubes.Keep me informed on how the two carb deal works .I may buy another top for my tunnel ram and try it with 2 as well ,but i will proly use the single top like im using on the street and save the two top for the track ...
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Old 10-19-2008, 06:21 PM   #13
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Default Re: Tunnel ram carb theory

I run a single 600 cfm with electric choke on my 55 chevy,(355,480 lift 292duration 7 degree lobe center cam, 9.5/1 comp. 882 heads with 202/194 valves and a home port job.hooker supercomps 1 7/8" primary into a 3" collecter, 3" pipes all the way back to a set of flowmasters. 350 turbo trans. 3000 stall/soon to be 4 speed, 9" ford with 4:11 gears) seems to work good. I had two 450 cfm on a basicly stock 350 back in high school. It was ok, but the throttle respose was a littly soggy of idle.

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excuse the pic. it was from when she was first going together.
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Old 10-19-2008, 06:35 PM   #14
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Default Re: Tunnel ram carb theory

Personally I think Holleys are probably best. I've seen people run 2 600 double pumpers on smallish engines. I think the accelerator pump is the key, maybe not for economy, but for throttle response. For a daily driven car theory number one is probably best...
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Old 10-19-2008, 06:39 PM   #15
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Default Re: Tunnel ram carb theory

Glassthamesdoug here on the HAMB is running a tunnel ram on his small cubic inch (283,302,327)Chevy small blocks. He is running (2) Holley 6425 carbs (600cfm 2bbl) the engine runs great and looks good as well.
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Old 10-19-2008, 07:08 PM   #16
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Default Re: Tunnel ram carb theory

Quote:
Originally Posted by Mercury Kid View Post
It's an old weiand intake. I don't really have the money to have two tops and three different carbs. I'm going to have to hit the swap meets for some carbs as it is. I think I'm going to run holleys because they make them smaller than 500 cfm and because tuning help will probably be easier to get.

BinderRod, thanks for the tuning tips. I have heard about the 50cc pumps before and it seems to be the setup.

Keep it coming.

Make sure you have the correct power valves also. They are a must when coming off of the idle circuit. There will be people that say to plug them and bump up the jet sizes 5 to 10 sizes. I tried and it didn't work for me. I called Holley and they said to hook a vac gauge to the manifold, have the engine warmed up and in gear. Take the reading and divide by 2 and that will be the correct power valve to use. It sure helped my set up.
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Old 10-19-2008, 09:25 PM   #17
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Default Re: Tunnel ram carb theory

Go get yourself the December issue of Car Craft, they do a complete tunnel ram tuning guide. Oddly enough they run two 1850 series 600 cfm Holleys because they are vaccume secondaries and have no problems once tuned. They put the system on the dyno and compare it to 660 center squirters and tell all.
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Old 10-19-2008, 09:35 PM   #18
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Default Re: Tunnel ram carb theory

Mercury Kid, are the tops machined from flat aluminum stock?

If so, making your own from a piece of say, 1/2" - 1" aluminum plate is a fairly easy project.

You can probably use your present top as a template.
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Old 10-20-2008, 08:14 AM   #19
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Default Re: Tunnel ram carb theory

Tunnel rams actually have a very stong carb signal . In fact so strong that is is easy to over jet the carbs. Usually what comes in a carb stock is more than enough where as with a single plane usually 2 to 4 sizes increase is necessary generaly speaking two of what would be normal for a single carb set up works best. The power valve advice from the chevy guy is excellant. Sometimes they can be a bit cold heated for starting . Need a lot of fuel or pumping to light them off. Normal flow calculations do not apply . Similar to IR system in that respect . because of how they work they can handle a lot more than a standard singe 4 manifold. 289 302 ? I would use a pair of 600s
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Old 10-20-2008, 09:02 AM   #20
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Default Re: Tunnel ram carb theory

Based on your engine and use, I'd listen to school #1 - small carbs, vac secondaries, and non-progressive linkage. On the street, off idle response will be your biggest drivability issue. The smaller carbs will have a faster air stream and a better metering signal. You'll most likely have to play with the vac secondary spring, power valves, and acc pumps.
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