Tunnel ram: single v/s dual top ?

[PETEROC]

I just picked up an Offenhauser tunnel ram for a 460 Ford. It came with both tops. One carb top and another for two carbs (both standard flange). Besides looks and costs, what are the performance pros and cons for the single or dual carb set up? It will be on a 18' jet boat.

[SmokinLowriderSS]

The single top makes a nice coffe-table conversation piece, or a trivet in the kitchen. Lots of folks on here will tell you of the near impossibility of getting the 4 end cylinders to feed a decent mixtureway out on the ends.
The TR is a high-rpm design intake, works great in the vicinity of 6,000 RPM, seldom worth a damn lower down.
Pros,
High-bling factor.
Higher bling factor if polished.
performance gains IF you have one seriously wicked bichin monster motor
Cons,
buy a seccond carb (another $400)
Linkages to buy, tune, adjust to sequence properly, swear at all the while
I have seen a FEW people on here deny the greater fuel consumption, but MANY who admit to it. "Burn LOTS more gas"
hell of a time getting idle and lower midrange to run well, as it is not designed to run in that RPM range for long.
Often performance gains on most motors (see exception about seriously wicked bichin monster motors) switching to a proper size single 4-barrel and a good single plane or high-perf dual-plane (like the Performer RPM Air Gap) manifold, especially if RPM max is UNDER 5500.

[FASTRAT]

"very" well put Smoke ...i have run a sgl TR on my BBC & after further review, i have switched to a RPM air-gap...alot less trouble & works great...u would be way ahead of the game if u go with a sgl/dual plane manif & 750/850cfm carb...TR's look great, but as stated, if u dont have a killer motor, they are IMO a waste of time!...just my .02 cents
fastrat

[rrrr]

I had a friend who ran a '69 Mustang at the drags back in the day. He bought an badass engine from a guy to go FASTER..... :rollside:
It had a TR and two 4bbl carbs. Uh, and 302 cubic inches.....
After screwing around with it for weeks, I convinced him to switch to a 4bbl and a single plane manifold. Picked up .4 seconds......
Kinda like Superdave's Summit catalog shopper...... :crossx:

[SmokinLowriderSS]

But rrrr .......... it LOOKED so much faster going slow. :cry:

[SmokinLowriderSS]

"very" well put Smoke ...i have run a sgl TR on my BBC & after further review, i have switched to a RPM air-gap...alot less trouble & works great...u would be way ahead of the game if u go with a sgl/dual plane manif & 750/850cfm carb...TR's look great, but as stated, if u dont have a killer motor, they are IMO a waste of time!...just my .02 cents
fastrat
I really think that RPM Air Gap is the best thing available for MOST of the boat engines out there. It breathes even better if you put an open-plenum spacer under the carb. (course, my spacer has N2O plumbed to it.) :crossx:

[FASTRAT]

I really think that RPM Air Gap is the best thing available for MOST of the boat engines out there. It breathes even better if you put an open-plenum spacer under the carb. (course, my spacer has N2O plumbed to it.) :crossx:
Smoke...
how thick on the spacer?...1" or 2"?...what about a spacer with the divider in the middle to match up to the manif?
fastrat

[LakesOnly]

Discard the Offy single top, sell it on Ebay, etc. They have distribution problems on the outer corners. (There are newer single-four top designs coming out today that offer much more even distribution, but that does not apply here.)
In regards T/R's being a "top end only improvement," I disagree and when placed atop an appropriate combo, they can offer improved mid-range torque on up. The rpm range where the improvement occurs is very dependent on the overall engine combination. rrrr gives an excellent example of a major mismatch where a 302 had 2-fours on it and swapping to the single four improved performance measurably. But the opposite may have been true on a different engine and combination.
Ford 460's, by virtue of their intake port architecture, love tunnel rams. Whether or not you will see a worthwhile improvement with the 2-fours is dependent on your combination. But ditch the single-four top for sure.
LO

[beerjet]

I must be the exception to the rule.

[SmokinLowriderSS]

Smoke...
how thick on the spacer?...1" or 2"?...what about a spacer with the divider in the middle to match up to the manif?
fastrat
My spacer is 1" thick.
I would not use a divided spacer. The cut-out "notch" in the "RPM manifold is supposed to let the manifold draw slightly from the other side of the carb/manifold when RPM's get high enough that the division starts cramping the breathing ability on 1-side (2 venturi) alone. True single plane manifolds allow all cylinders to "pull" from a comon plenum at all times, which usually helps higher-rpm cylinder filling while hurting lower rpm filling (which is helped by higher runner velocity in cross-H manifolds). The "cutout" is supposed to try to mix both worlds somewhat. IMO, an open spacer can help this desired effect, a divided spacer will not. I know the open spacer has not caused me any troubles, but I cannot compare with/without, it has always been there, even on top of the orriginal cast iron dual-plane.