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My Tunnel Ram

7446 Views 11 Replies 7 Participants Last post by  powrshftr
I made a tunnel ram that has strong low-end torque. I had the idea about five years ago and finally scraped together the money to make it. I have on on my 1971 El Camino.


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So tell us what you did here? It appear you took a stock Weiand and milled it down to drop both base and top lower? I'd like to know, 'cause we just spent a few hours yesterday trying to get a stock Weiand to fit Jeff's '56 gasser with no luck. A shorter version might be the answer!
I see the center section is gone, and maybe the bottom is milled lower? Looks like a divider installed down the middle lengthwise too. Can't tell for sure what all is done. Was this a new casting, or welded in and shaped?
The base is a standard Weiand part - unmodified. I made custom top castings that create four separate plenums instead of one big one. We also did a bunch of work to make the carburetors deal with the plenums. Each pair of cylinders connected to a plenum is uneven firing. One plenum has 5&7, which fire right next to each other in the firing order, for example.
The result is incredibly responsive from right off idle. Each cylinder draws from one side of one carburetor like in a dual plane.
The neck down in the tops seems very restrictive for top end flow. Or are you going for the responsiveness and forfieting the top end flow? OR is it flowing jsut as well in this configuratiion? What size are the carbs? I had a tunnel ram on a 377 small block (350 crank/400block-bore) in a '67 Nova. Twin 600 vacuum secondaries with secondary vacuum spring housing vacuum hose tied together. It was very responsive, 3.71 rear gears, and got 15-16 miles per gallon average all the time. That was one sweet little motor. Mark L
The convergent section flows the same amount of air as the two venturis in the carburetor. We experimented with different sizes, and this is optmized for trading off cylinder-to-cylinder mixture distribution versus airflow.

The carbs are 580CFM vacuum secondaries from Quick Fuel.

What kind of stall were you running with your setup?
It was one of those cheap GER converters that they used to sell years ago. I think it stalled about 3200. Could have used more but the Nova only weighed 2900 lbs without me in it. So it got by OK. Mark L
I made a tunnel ram .......
Hey FortFun.... I have enjoying what you have been sharing since you got here!!!!

Especially about the work you have been doing with your "unique" intake manifolds.

But...... I am really "scratching my head" about the "Offy CrossRam"????? I do remember "Offy" offering crossram.... similar to the Edelbrock I have (that hopefully I will be able to get on the Opel over the Winter).....

....... BUT NOT a Offy CrossRam with staggered carbs mounting at different heights??????

Is the "Offy" an off-the shelf-model or have you also re-designed it like what you did with your "Tunnel Ram" ??????

And again...... welcome to the forum.

I am also "new here" & have been really enjoying the "forum-chatter", interesting & informative topics & lots of GREAT pictures posted by a great bunch of fellow hot rodders who also "love" gassers like I do.
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Fortfun hows El Camino running? This is what I've been looking for. I have been playing with carb spacers and really don't want to run a tunnel ram. Let us know Thanks Gary
I love tunnel rams for the wow factor they have. Of course I'd really like a supercharger for more wow, but it's not in my budget. The crossram is also a cool intake, but in talking with a friend who's experimented with them he told me to steer clear of the crossrams that have large open plenums. He said the ones with runners work much better for lowend and street applications.
Can't remember which maker's crossram he showed me, but he said it worked so well he'd gladly pay $900 ea. for them used.
The Offenhauser cross-ram I have is not modified. I became a dealer for them in 2004 and must have sold 80-100 of them over the next four years, through an E-bay store. The Offy cross-ram is a close copy of the GM piece made for the Z28 cars in the Trans Am series. There are long runners underneath the lid. The performance characteristics are just like a vertical ram. I put it on the Vette because I was tired of my engine looking like all the other old Vettes. With my 4.11 gears, wide ratio Muncie, big cam, and headers, the whole thing works fine. I don't really need low-end torque with my gearing and a 3200-lb car. You can get the Offy for about $500 new still. I quit selling them when we had some medical stuff going on in the family and I didn't have time to mess with the side business for awhile. Then Summit started selling them and I figured there was no way to compete with them. My big advice is to use 390CFM carbs. This is key because it gives you the best possible venturi velocity. You still have plenty of airflow available through the carbs, since it is a giant single plane. The Z28s used 585CFM carbs, but I think Holley didn't have anything smaller available at the time. The 390CFM was developed for restricted carburetion in NASCAR at Daytona, not sure when. Mine are double pumpers, but I might switch over to the vacuum secondary versions, so it will be more responsive at low RPM if you punch the throttle.

From what I've read, the side-by-side cross-rams with two separate plenums are pretty quirky. You have an uneven-firing situation in each of the plenums, combined with a tough fuel distribution problem due to where the runners attach to the plenum relative to where the carb is. The cylinders on the ends tend to run lean. Offenhauser made this type as well as the Z28-style. If you are not worried about ultimate power you can probably get it to run OK though. I would use 390CFM Holleys, and an MSD multi-spark box, and a lot of initial timing.

The Elco is awesome. It is so eager and responsive. Really a joy to drive. Gotta get some pictures up!
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That is some fantastic creativity/craftsmanship! Wow. Great work.
FortFun,is there an Offy cross ram like that available for the 289/302 Ford?If so,I will take one!

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