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I'm thinking about getting a tunnel ram kit for my '56 chevy truck. I keep hearing about driveability issues. Lack of low end torque etc. The truck is running a 350, decent cam, late 60's vette heads and a B&M turbo 350 with a 2500 stall (about),valve body set on "whiplash". 3:73 gears in back. It runs great with the speed demon carb and performer RPM intake but I just like the visual impact the tunnel ram gives. Any thoughts? Thanks.
 

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1967 Chevrolet Biscayne 10-71 blown 433 Big Block Chevy, T400 & 12 bolt 3.73 rearend
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Stick with small carbs, 390-450 cfm and you will have a responsive and suprisingly drivable combination.

Barry
 

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Tunnel ram

Thanks for the input, Barry. Still have to figure out a couple of things but after checking out your photo album I want a BIG BLOCK. What a beautiful piece! :evil:
 

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Tunnel Ram

Thanks HG. jEGS sells a carb & intake kit for about $800. but the ad says 3500-7500 RPM. It'll most likely never see 7500 and 3500 seems a little high to get useable power on the street. Maybe I'm just turning into a wuss in my old age. God I hope not! Thanks again, Jim
 

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Find an Edelbrock street Ram. Don't see em advertiesed but mine runs great right off the bottom. Excellent throttle response. Check out this months Super Chevy, they do a tunnel ram comparo. Because of equal runners and proper cross section design, the ram pulls better over a wider range of RPM than a Victor.
383, 11.6:1, 226/489 at .050, aluminum vett fulies, 2x500CFM Edelbrock carbs with tiny Q-Jet style primaries. The key is the high compression and tiny primaries. I will state the engine is under cammed and the heads are just not up to the task. Soon to be remedied.
 

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Tunnel rams got a bad rap years ago because most people ran them on engines turning 7000+ and the engines were built for that, and obviously big carbs, big cams, and single plane intake sucked down at low rpms.

The long runners are great for the mid range street torque if the COMBINATION is built for streetable rpm ranges.

Modern FI intakes (are single plane) are just folded over tunnel rams and since the FI solves the fuel metering problems, the wide LSA cams make great torque.

When you are thinking street tunnel ram.... think smaller carbs well tuned, and wider LSA cam.
 

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Small carbs are important but the real killer in tunnel rams is the big plenum between the carbs and the runners. Once the air and fuel are mixed in the carb, the worst thing you can do is slow the mixture velocity down which allows the liquid fuel to drop out of the mixture and puddle, flow to one or two runners and not others, etc. The purpose of the tunnel design is to use the 'organ pipe' effect to super charge the cylinders at a narrow design RPM range and divorce the dynamics of weird pressure pulses thru a carb from the intake valve. Exactly the same technology of tuned exhaust headers. This design RPM is usually @ WOT at max power in a drag machine so low velocity isn't a problem. Try to idle one though and all bets are off.

If you want to run one of these things on the street and you want streetability, consider filling the majority of the plenum with something that will reduce the size to that equivalent to a standard hi-rise manifold. this will give you streetability and the power benefits of the longer runners. Devcon plastic steel is great as a filler 'cause it is inert to all chemicals and can stand a bunch of heat. I have used it in modifying intake runner shapes in cylinder heads with great success. The ideal situation would be get one of those tunnel manifolds with the removable top. Then form the filler inside the lower portion of the manifold, grind and sand it to the perfect shape and bolt the top back on. You could even make the insert removable by casting the epoxy paste in the manifold with some sort of release agent (tin foil liner B4 the epoxy would be great).

I did my senior project in college on intake and exhaust design and built a tunnel ram from sheet steel and exhaust tubing in about 1970. I think I was one of the first to make one, sure beat the commercial guys to the punch! Here is a picture of me in the process of making it circa '70. Note the hair!

 

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1967 Chevrolet Biscayne 10-71 blown 433 Big Block Chevy, T400 & 12 bolt 3.73 rearend
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What willys36 says about plenum volume is correct. Weiand tunnel rams generally have a smaller plenum volume than most other tunnels. The edelbrock street tunnel has a reduced plenum as well. I have used an old edelbrock pro ram manifold in a street application before and it worked well. The rpm range on that manifold was 6500-10,000. It was on a big inch sbc and it worked well. It had a very small plenum and large runners. Take willys36 advice.

Barry
 

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okay, I'm sorry, I know this is an old thread but I gotta ask...

Small carbs are important but the real killer in tunnel rams is the big plenum between the carbs and the runners. Once the air and fuel are mixed in the carb, the worst thing you can do is slow the mixture velocity down which allows the liquid fuel to drop out of the mixture and puddle, flow to one or two runners and not others, etc. The purpose of the tunnel design is to use the 'organ pipe' effect to super charge the cylinders at a narrow design RPM range and divorce the dynamics of weird pressure pulses thru a carb from the intake valve. Exactly the same technology of tuned exhaust headers. This design RPM is usually @ WOT at max power in a drag machine so low velocity isn't a problem. Try to idle one though and all bets are off.

If you want to run one of these things on the street and you want streetability, consider filling the majority of the plenum with something that will reduce the size to that equivalent to a standard hi-rise manifold. /QUOTE]

now I kinda understand the theory here, but if this holds true, why does edelbrock recommend using a 2" spacer on their victor intakes? or doesn't a spacer increase the plenum? I just measured the runner length on a victor for a pontiac and it's within 1/2" of a wenzler tunnel ram. doesn't that make it more similar to a tunnel ram than a regular intake? seems tunnel rams are getting alot of bad press, but from what I can see the victor intake is using the same priciples as a tunnel ram, and it doesn't fit under my hood either, with or without the 2" spacer.
 

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you will loose vac with a tunnel ram, as there is more area to draw a - preassure in, therefor, in the bottom end, it may not run good, as it cannot suck the fuel in ( and coming from such a long distance does not help ). this is where the drivability issues come in, but also in the fact of the correct CFM carbs, Holley/ wieand will direct you to the Holley 450 CFM tunnel ram carbs, when that's 900 CFM, a healthy 350 might need 750 CFM if it's turning a few RPM's.
 

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wyomingoutlaw said:
okay, I'm sorry, I know this is an old thread but I gotta ask...

Small carbs are important but the real killer in tunnel rams is the big plenum between the carbs and the runners. Once the air and fuel are mixed in the carb, the worst thing you can do is slow the mixture velocity down which allows the liquid fuel to drop out of the mixture and puddle, flow to one or two runners and not others, etc. The purpose of the tunnel design is to use the 'organ pipe' effect to super charge the cylinders at a narrow design RPM range and divorce the dynamics of weird pressure pulses thru a carb from the intake valve. Exactly the same technology of tuned exhaust headers. This design RPM is usually @ WOT at max power in a drag machine so low velocity isn't a problem. Try to idle one though and all bets are off.

If you want to run one of these things on the street and you want streetability, consider filling the majority of the plenum with something that will reduce the size to that equivalent to a standard hi-rise manifold. /QUOTE]

now I kinda understand the theory here, but if this holds true, why does edelbrock recommend using a 2" spacer on their victor intakes? or doesn't a spacer increase the plenum? I just measured the runner length on a victor for a pontiac and it's within 1/2" of a wenzler tunnel ram. doesn't that make it more similar to a tunnel ram than a regular intake? seems tunnel rams are getting alot of bad press, but from what I can see the victor intake is using the same priciples as a tunnel ram, and it doesn't fit under my hood either, with or without the 2" spacer.
If I understand your question, the 2" spacer you refer to is acting as an intake runner extender more than a bigger plenum. As long as the area of the added passage doesn't increase substantially it adds to the length of the duct from the carb to the intake valve which changes the tuned rpm range of the system. The longer the intake runner, the lower rpm the engine power band kicks in. Tunnel rams are intended to shorten the intake runner length so the engine has a higher rpm power band. The problem is that the tunnel increase the area as well as the length. The area is so big, it effectively eliminates the distance from the point the intake runners enter the plenum to the carb. The organ pipe pressure waves operate only in the relatively short intake runners. Great for high speed tuning and performance but deadly to low speed performance.
 

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wyomingoutlaw said:
okay, I'm sorry, I know this is an old thread but I gotta ask...



Tunnel rams are intended to shorten the intake runner length so the engine has a higher rpm power band. The problem is that the tunnel increase the area as well as the length. The area is so big, it effectively eliminates the distance from the point the intake runners enter the plenum to the carb. The organ pipe pressure waves operate only in the relatively short intake runners. Great for high speed tuning and performance but deadly to low speed performance.

HUH?
Proper tunnel rams increase the power across the board.

You have been dealing with waaaay overcammed engines= bad combinations. cam not matched to induction system.

4 days ago we just put a brand new set up with 500s (bought as a set) on a 360 Mopar.
 

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That's news to me!! If that's the case, why doesn't Detroit put tunnels on all production cars? Why do Edelbrock and Weind, et al, produce dual plane manifolds? Guess my physics books are all wrong.
 

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That's news to me!! If that's the case, why doesn't Detroit put tunnels on all production cars? Why do Edelbrock and Weind, et al, produce dual plane manifolds? Guess my physics books are all wrong.

Single-plane and dual-plane intakes operate differently, as you know.

All new SFI cars ARE long single-plane tunnel-rams with small plenums, layed over sideways because they are dry flow, so they can lay them over. That is also why they require such large LSA cam angles to idle.

The primary purpose of a tunnel ram is not to shorten the runner, but to give the air a straight shot into the intake valve, which improves fuel atomization because the fuel does not get slung out by centrifugal force and run down the port walls. (New cars with SFI eliminates the fuel distribution problems.)

The true tunnel rams can be short, or long. Plenum big or small.

Look at the new Weiands for good tunnel rams. Lots of things have changed over the years, including tunnel rams. I just put a new one together last week.

Properly done tunnel rams will make more torque and power across the board, except at the very lowest rpms where all single plane intakes suck, literally, figuratively, and poorly, pulling exhaust into the intake manifold.

You are probably like most of us. We have always seen big carbs on big plenums on overcammed engines with crappy ancient heads running for 7500 rpm. Ya, they really suck, in every sense of the word.
 

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this is interesting,Intrix how about the Wieland tunnel ram, on an 383 stroker engine cammed dur @ .050 246 degree .515 gross lift intake and exhaust
stall is 3400 rear gear 343, with what size carbs
 

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pepi said:
this is interesting,Intrix how about the Wieland tunnel ram, on an 383 stroker engine cammed dur @ .050 246 degree .515 gross lift intake and exhaust
stall is 3400 rear gear 343, with what size carbs
Our set came with dual 500 Holley small body mechanicals. :sweat: They are very rich.

I believe that dual vacuum secondaries would be mucho bettero without overcarbing at low rpms. 500-600 OK... Lots more than you need, that's where vac secondaries or Carter/Edelbrock air valves would be better. Holleys would probably need to go sideways, Edel I don't know, didn't measure.

Whats your LSA overlap on that cam?
 

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LSA? are you talking Lobe separation if so then it is 108 degrees. Rich.. I see that ( slurp, slurp), was also considering 2x4s and now I have seen the in line 4 by BG so this is more bench racing and information gathering at the moment. But there is for sure an intake change in the wind. The intake I am running is the Weiand Team G intake.
 

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xntrik said:
Single-plane and dual-plane intakes operate differently, as you know.

All new SFI cars ARE long single-plane tunnel-rams with small plenums, layed over sideways because they are dry flow, so they can lay them over. That is also why they require such large LSA cam angles to idle.

The primary purpose of a tunnel ram is not to shorten the runner, but to give the air a straight shot into the intake valve, which improves fuel atomization because the fuel does not get slung out by centrifugal force and run down the port walls. (New cars with SFI eliminates the fuel distribution problems.)

The true tunnel rams can be short, or long. Plenum big or small.

Look at the new Weiands for good tunnel rams. Lots of things have changed over the years, including tunnel rams. I just put a new one together last week.

Properly done tunnel rams will make more torque and power across the board, except at the very lowest rpms where all single plane intakes suck, literally, figuratively, and poorly, pulling exhaust into the intake manifold.

You are probably like most of us. We have always seen big carbs on big plenums on overcammed engines with crappy ancient heads running for 7500 rpm. Ya, they really suck, in every sense of the word.
I was using the single plane comment sarcastically. TPIs can use long inlet runners to take advantage of organ pipe theory and get a tuned boost without the danger of liquid dropout since the gas is injected near the intake valve. Detroit TPIs have the x-over long tubes on production cars since they are designed for low to mid range speed boost. The lower the design boost speed the longer the tubes need to be.
Tunnel rams are designed for organ pipe boost at the tuned length (short runners @ high rpm). There is no way to get the uniform short length in a dual plane or single plane manifold, that is what they designed the tunnel in the first place. What you gain in high speed organ pipe boost you lose in low speed loss of velocity in the relatively huge plenum. Tunnels as opposed to TPIs are hampered by the fact that the fuel is introduced at the inlet not the outlet. Once atomized gasoline ends up condensing and puddling resulting in bad distribution in a tunnel at low speed. It is unavoidable, regardless of the size of the carb. And the number of turns has zero impact on organ pipe boost, the only critical parameters are flow area and runner length. Think of a tunnel as injector stacks (tuned for high speed organ pipe boost) with a carb on top instead of injectors at the base.

Tunnels are great for drag racing for which they are intended and for looking mean on the street. However, if used in the latter application they will perform poorly at the rpms encountered 99.999% of the time.

Here is a photo if me in mid construction of the tunnel I built circa 1968 when I was in college. I used it as a physics project as well as a cool looking street manifold. This was before commercial tunnels had hit the market. I designed the runners for 3000rpm primary boost and as you know there is a harmonic secondary boost @ 1/2 design rpm or 1500rpm in my case. Worked great when I put my foot in it but regardless of the size carb I used (I tried several including a Rochester 400cfm 4-jet clear up to my current Holley 950cfm 3-bbl) it was terrible at normal driving speeds. These things just are not intended for the street.

 
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