Why no tunnel rams?
 

OK, probably going to reveal my mechanical ignorance here, but why don't you see more tunnel ram / dual carb setups on boats? Seems to me that these type of setups are pretty prevelant in the hot rod world as an alternative to blowers. I realize that it is apples and oranges between cars and boats, but.....

They do use them alot in the jet boat world and it is mainly for looks because I don't think they help with the low rpms we spin on the water.

They do use them alot in the jet boat world and it is mainly for looks because I don't think they help with the low rpms we spin on the water.

I use one, with EFI and 2 1000cfm air valves. Had to have a sheet metal intake made to fit my block and heads. Seems to work ok, havent broken any world records yet, but I dont have any low rpm issues.

Dick

Tunnel Rams although they look good are long outdated. The IR (individual runner) sheet metal intake that is custom tuned for a particular engine combo is unbeatable. Tunnel Rams were mass-produced by the You Name It Performance Company. They were available for either big or small block engines. That was as fine tuned as they got. As you know there are many different displacements of small & big block engines. Marine engines rely heavily on torque and tunnel rams were known for anything but. I know that every car I had ridden that had one always left a lot to be desired in the horsepower dept.

Have a good weekend
Roby

A properly carbed tunnel ram will make gobs of torque.
A few years back Car Craft did a dyno shoot out on manifolds. The tunnel ram won TQ and HP with two small carbs.
I've driven a 440 Chrysler that had a tunnel ram with two small Holleys and that thing ran like stink down low.
Most street guys will stick two 850 double pumpers on a big manifold and wonder where all the get up and go went!
I almost forgot my 320 horse efi Mercury Hi Performance
5.7's have tunnel rams, too.

In my case the tunnel ram seems to be hurting performance. The carbs will flow so much air, I don't even have to use the secondaries. Maybe their more useful on a drag car turning 8500 rpm. They do look cool though.

They do use them, just look at this months Powerboat. That 100+ MPH Cig with the N/A 750hp motors looks to have sheetmetal intakes.

Ran tunnel rams for years, were worth about 50 HP at 6200 RPM over the best single at the time (late 80's). however the engines were 540 CI, mechanical roller / Brodix heads. In a back to back test, stock 750's compared to out of the box Dominators the small carbs were worth 20 HP or so, probably 30 Ft lbs. After much tweaking, finally made 850 HP or so.


A little soggy under 2500 RPM or so, but once on plane they were pretty good.

No idea how today's single 4 would compare.

If you think of a tunnel ram as a single plane intake manifold, only with perfect length runners and no need for turning the air/fuel mixture (a straight shot into the port). Then you will like a tunnel ram.

Reducing the plenum volume to that of a four barrel single plane intake manifold would create the "ultimate" single plain intake manifold for low speed torque. Each carburetor barrel directly over each intake port is an unbeatable combo.

If a person thinks about intake manifold designs instead of listening to the old wives tails, a person would begin to understand that the advantages of eight smaller barrels on a single plane manifold would give superb air/fuel mixture distribution over four larger barrels on a V8 engine.

If the plenum volume is similar between the manifolds, the single plane tunnel ram will run away and hide from a single plane four barrel manifold at low engine speeds. Equalizing the plenum volume to a single plain four barrel is not hard considering that most single four barrel manifolds make more horsepower with a spacer anyway.

Sincerely
Dennis Moore