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-   -   Street Tunnel Ram (http://www.hotrodders.com/forum/street-tunnel-ram-101694.html)

BOWTIE JIM 11-03-2006 04:42 PM

Street Tunnel Ram
 
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.

topfuel 11-03-2006 05:12 PM

Stick with small carbs, 390-450 cfm and you will have a responsive and suprisingly drivable combination.

Barry

BOWTIE JIM II 11-03-2006 07:41 PM

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:

HemmiGremmie 11-03-2006 08:04 PM

I think the biggest mistake in street tunnal ram setups is over carbing.
Like Barry said, stick with smaller carbs and you will be ok. HG

BOWTIE JIM II 11-03-2006 08:27 PM

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

techinspector1 11-03-2006 09:07 PM

"Any thoughts?"

Yeah, get over it. :nono:

Elevinpointsixtoone 11-03-2006 11:50 PM

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.

xntrik 11-06-2006 01:19 PM

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.

willys36@aol.com 11-06-2006 08:25 PM

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!

http://hotrodders.com/images/projects/001/willys1.jpg

topfuel 11-06-2006 09:01 PM

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

wyomingoutlaw 02-02-2007 03:10 PM

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

[QUOTE=willys36@aol.com]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.

matt167 02-02-2007 05:04 PM

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.

willys36@aol.com 02-02-2007 08:35 PM

[QUOTE=wyomingoutlaw]okay, I'm sorry, I know this is an old thread but I gotta ask...

Quote:

Originally Posted by willys36@aol.com
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.

xntrik 02-03-2007 12:35 PM

[QUOTE=willys36@aol.com]
Quote:

Originally Posted by wyomingoutlaw
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.

willys36@aol.com 02-03-2007 02:16 PM

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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