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Tunnel Rams although they look good are long outdated.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

Ok, lets take this a step further. What about the EFI setup that Merc has with individual throttles for each cylinder. With no plenum will that kill the low end? I have only seen this setup on race boats, so I make the assumption that it would be a high rpm friendly deal??
My next set of heads will cause me to throw my pretty sheet metal intake in the trash. I hate the thought of paying for a new one. But besides a slice and dice on the present one to make it fit a new one will be needed. Just want to know my options..

Thanks

Dick

The reason why plenum volume is so critical with carburetors is because you are using engine vacuum to pull fuel out of the carburetor. The larger the plenum, the less vacuum the carburetor will see (from the engine) and the weaker the air will pull on the carburetor (this is particularly harmful to low speed performance).
With fuel injection, engine vacuum is much less important because the fuel is being forced into the engine under fuel pressure. It is really comparing apples and oranges.
Dennis Moore

You’re absolutely right Dennis. The problem with getting a tunnel ram to work right was the user. Although each ram was still a little large to feed 4 cylinders they would still sacrifice torque when compared to a good dual plane manifold. Everyone seemed to compare them to a single plane but those are not known for torque either. The reason why they were so hard to get power out of is that everyone would run dual 600-CFM or larger carbs on them. Sonic30ss says he saw a dyno shootout on the tunnel ram and it won out HP & torque over other manifolds. I saw a comparison (don’t know if it was the same one) and the tunnel ram was impressive but it had two 390 CFM 4150 Holley’s. However it was Edelbrock’s Performer RPM manifold that kicked all of their butts to 6500-RPM and still made good power to 7200 RPM. It was tested on a Small block Chevy 355 cu-in. It was the clear winner overall and only fell short of the tunnel ram by 11 measly HP at 7200 RPM. Up to 6500 RPM not a single manifold was within 60-HP of the Performer RPMs maximum.

Now based on what I have read from this list I haven’t seen many marine engines spinning over 6000 RPM. I’m sure you guys are out there but I’m talking close to stock Magnum Mercurisers. If you are normally aspirated and staying less than 6000 RPM then there is really no need for a Tunnel Ram.

Remember the formula for the correct carb size is:

cubic-inch times maximum RPM divided by 3456 = CFM.

And that is running at 100% VE. You normally aspirated guys can deduct at least 10% off those CFM results. Do the math on your engines and tell me if a couple of 750 Holley’s on your tunnel ram is too much or too little.

Later
Roby

Gadgets/

I ran the Merc/Kinsler EFI race system for one year with 14 degree Big Chief heads and a solid roller as a pleasure boat. The intake had 8 -2.10" throttle plates. System was fantastic above 1500 rpm or so. The throttle plates are so large they make idling sometimes tough. But, with that particular cylinder head and the EFI, you make some pretty respectable hp at 6500+!

Thanks Bob,
that was what I was looking for. I guess I am looking at what type of manifold I can build the easiest. A sheet metal one is a work of art, but if I could bolt on a bunch of air valves and fill in the hole in the middle.. well I am thinking.
Thanks

Dick

I've run a tunnel ram w/ 750's on my 540 for several years with no problems.No problems with idle,comes strong on plane,good mid range,excellent top end.

I run a Dart tunnel ram with 2X775 Race Demons on my 632" BBC. CR is 10.5:1; Dart 360 fully ported heads; 280/288 @.050 .730" 115CL solid roller. Idle is 900, 650 in gear. Motor never loads up hesitates or stumbles ANYWHERE in the rpm range. The key is to making a TR work is to have your cam and carbs correctly matched. A correctly set up TR will always make more TQ in the mid range and always make more power up top. LONG RUNNERS with little restriction. Usually a single carb will be better down low. 900 HP @6500 on 93 Octane, 845HP @5800. TQ is 820 @5000.

SMALL CARBS is the key to making a TR work. 1050 Dominators would probably make another 25hp up top, but low end and idle quality would go away. Now if you were going to turn 8000 you would need some monsters to keep the motor fed.

JDNCA1,
You need 1 more or those 632's for your 28!!!:D

I Know!!;) :D Its cheaper to put on whipples though..:rolleyes: Plus the whipples are stealthier, you know the 632's are nasty when they're idleing..:D :D

I had an L-88 427 chev in a 21 ft jet a few years ago. It was topped with 2 660CFM center squirter carbs. Full-time four barrels, with 1 50CC accelerator pump if I remember right. The accelerator had 1 nozzle in the center that shot all 4 barrels at the same time. The TR was a Weiand Hi ram which has a small plenum compared to the Edelbrock. The engine had torque everywhere.

Once when I was running it on the trailer I noticed that the manifold had condensation on it. I often wonder if the plenum/long runner system allows for some expansion of the wet fuel & air mix, and cooling itself like in a refrigerant cycle????

Bulldog

Cool thread! Thanks for asking Rocker!

tunnel ram
 

Mine works great. 565ci. 750hp efi hydraulic roller cam 92 gas. A tad over 90 in my 92 27 fountain. Two miles per gallon.

This is a very interesting thread!
The original question was why aren't more of these set ups used in boats. My take onit is that blower motors are easier to build, make more horsepower (and of course torque, which is KING) at lower RPM's. They also have the benefit of longer life due to lower operating RPM's.
Having said that, there is a TON of power to be had in a proper "tunnel ram" manifold and carb set up. Look at NHRA Pro Stock cars. 500 cubic inches, two carbs, gasoline (120 octane +/-) and 1300 horsepower. Problem is, it makes peak torque at 6300 rpm and peak power at 9500 RPM:eek: :eek:
I don't know anyone that would want that kind of rpm's in their boat!
When running Comp Eliminator, we ran a Sonny Leonard 437 cubic inch motor with carbs, and switched to a Motec EFI system. While we lost 5-10 horsepower on the top end, the torque numbers increased all across the RPM. Bottom line was that the first time out with the car, we ran a full one TENTH of a second under the national record at the time!!!
The point is that with dyno time perfecting runner length (the critical issue in a "tunnel ram") and the benefit of individually adjusting the fuel AND timing PER CYLINDER, you have an incredibly efficient fuel system. The only other problem with boats is the wet exhaust system. It makes it tough to place EGT probes and O2 sensors to get the maximum performance and tunability from the motor. We ran our car on "open loop" a couple of times testing in order for it to automatically adjust the fuel to the perfect level (again per cylinder) within the guidlelines we specified (10% max adjustment), saved the fuel map and ran after that "closed loop" with no other issues. Can't do that in a marine system with no O2 sensors.
Sorry for the long post, but this is cool stuff.:D :D

Here is a 565 cubic inch, 8-71 blown BDS fuel injection system on a Pro Street motor I just sold. It made 900 + hp on pump gas.
It was brutal for torque numbers!

Slick piece that was going in a 1965 GTO, but I ran out of time to mess with it. Still have the car though.;)

Here are some pics of my TR set-up. 900HP NA PUMP GAS.

on dyno at freshen.....

I can't talk about the technical aspects of it, but here is a picture of mine.

I just seen two 750HP Tunnel rams at Tyler Crockett's yesterday. He was just completeing them. They dynoed over 750. They are going in a Nortech Cat.

I watched my engine builder dyno his 3yr old NHRA pro stock motor that was down on power. it made 1280HP @9400. The pulls started at 7500. VERY VERY impressive to say the least. I couldn't believe the fuel that thing consumed compared to mine. Of course 1250 Dominators like fuel esp at those RPM. He had to change valve springs every 2 pulls. On the last pull, power fell off by like 65hp and they thought they lost a couple of valve springs....it was the vacuum pump...65HP from pulling 30 inches of vacuum. Unbelievable. The heads actually had aluminum lines that ran to jackets around the exhaust valve seats...I said what in the hell are those for. "It cools the seats and its worth 7hp". Everything counts to those boys.

By the way, top teams in NHRA are making around 1380HP today.......

That exactly right on the dyno figures, depending on who you talk to, and which dyno they use:rolleyes: :rolleyes: :D .
They are an inpressive piece. The interesting thing is that once you get the valvetrain geometry correct, springs are no longer an issue! We could run all weekend and never change a spring. On a previous motor though, it ate at least one spring every run.
Titanium springs weren't any better. In fact, they would break instead of become weak. Very bad thing at 9500 RPM:eek:

I hear you on the dyno comment. He had better luck wirh the comp springs than the manleys because the comps would sag where the manleys would snap....a very bad thing indeed. A drag racing friend of mine has experienced the same thing with his 10,500 rpm small block ford.

Cool Thread
 

Not to change the subject but how come there isn't vacuum pumps used on boat motors? I saw 40hp go away on Pat Musi's dyno because of the crankcase vacuum sucked the pan gasket in due to a POS oil pan.

I think because most boaters don't turn enough rpms to really see the benefit. Plus its just more stuff to maintain. That's why I chose not to go that route anyway.

454 jet boat with single carb would switching to tunnel ram and dual carbs make much
 

I have a jet boat with a 454 single carb with me switching to a tunnel ram with a dual carb set up make much of a difference? Please help I may be purchasing today should I not waste my money he wants $1000 for the set up

An old thread but that’s what their for. Much of it depends on your tune/combo. If I had to guess in a boat app with all optimum components you’d probably gain 50 hp + - at 6,200-6,600 over a good SP intake carb/efi set up. Equate that to speed 3-4 mph + -

What heads, intake, carb currently and what TR you looking at? I’d only consider dart.

Actually thanks for bringing up an old, entertaining thread! Lots of names from the past. Can't answer your question though.

Been running 8-71's and 10-71's on Darts for 10 years or so. Motors seem to really like the port flow above 3800. You pick up a cooling effect from surface area of aluminum in TR. They do very well mid range and up on a dyno compared to a typical blower intake and even compared to an intercooler unless you are really cranking up the boost. KE can get you the adapters.


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