port match on tunnel ram

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prairiehotrodder
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port match on tunnel ram

Post by prairiehotrodder » Mon Nov 06, 2017 11:21 am

so i noticed on the used BBC tunnel ram that i purchased that the ports got opened up where they meet the head. The intake port is lower than the port on the head. So now there is a 1/8" step up to the head. I have to take the t-ram back off to fix the end seals where the ultra-black did not seal. Will use "right stuff" this time. Should i epoxy the bottom of the intake ports to get better alignment ? To get rid of the step ? If so what and where do i get this epoxy?
Brian
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Frankshaft
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Re: port match on tunnel ram

Post by Frankshaft » Mon Nov 06, 2017 12:07 pm

How about this. Run it both ways. And then report back how it didn't make any difference. I will supply you free intake gaskets.

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Re: port match on tunnel ram

Post by mag2555 » Mon Nov 06, 2017 12:11 pm

If anything you could live with the Manifold ports smaller by a hair, but centered on the head.
If you can correct the mismatch with like 2 hours of rework I would go for it!

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Re: port match on tunnel ram

Post by F-BIRD'88 » Mon Nov 06, 2017 7:31 pm

I was going to ask you what the runner cross section area is.
To see of the runners are big enough for that motor.
Some one smart will tell you what Epoxy putty is best.

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Re: port match on tunnel ram

Post by F-BIRD'88 » Mon Nov 06, 2017 7:39 pm

If you use thicker er intake manifold gaskets the whole intake sits higher
and the port alignment will be raised up at the roof and floor of the runner.

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Re: port match on tunnel ram

Post by Old School » Mon Nov 06, 2017 8:22 pm

F-BIRD'88 wrote:
Mon Nov 06, 2017 7:39 pm
If you use thicker er intake manifold gaskets the whole intake sits higher
and the port alignment will be raised up at the roof and floor of the runner.
Mr. Gasket makes an intake gasket roughly twice the thickness of a regular gasket. The thicker gasket will raise the intake. You will have to double check the oil pump shaft engagement and the cam gear/distributor gear mesh if you raise the intake up much.

Is both sides the same mismatch? Usually one side is worse than the other. I know that it should be the same but they're not.

I have corrected such mismatches and could not tell any difference in et or mph. It would be more critical if the ports were too small for the engine. Made me feel better though.

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Re: port match on tunnel ram

Post by Tuner » Mon Nov 06, 2017 10:18 pm

prairiehotrodder wrote:
Mon Nov 06, 2017 11:21 am
so i noticed on the used BBC tunnel ram that i purchased that the ports got opened up where they meet the head. The intake port is lower than the port on the head. So now there is a 1/8" step up to the head. I have to take the t-ram back off to fix the end seals where the ultra-black did not seal. Will use "right stuff" this time. Should i epoxy the bottom of the intake ports to get better alignment ? To get rid of the step ? If so what and where do i get this epoxy?
Brian
With the port floor in the head higher than in the intake manifold, I would leave it.

There are more than a few examples of a step facing into the flow that indicate it can be beneficial, particularly a mismatch at the floor.

For starters, it is well known that, in spite of flying in the face of “conventional wisdom - common sense - it just doesn’t look right”, a square-port intake on an oval-port BBC head runs great, gets mileage and makes good power, better power than some supposed to be correct oval-port intakes.

Anybody who was paying attention and is old enough to have played with the engines when they were new has seen it.

I had an experience with a 225 V-6 Buick in a Jeep that had a near 1/8” step from the stock intake manifold floor to the head; the head floor was higher than the manifold. The manifold was off to do a valve grind so porting the floor to match the heads seemed the thing to do.

This engine had a small Isky hyd. cam, headers and a 500 Holley 2bbl that had been tuned and fiddled with so it would 4-WD good at crazy angles and climb steep hills without stalling, it got 25+ MPG.

After the valve grind and porting job, which included a bowl job in the heads and matching the heads and manifold to the intake gasket, the formerly snappy engine with a good torque and tractor-like low speed lugging abilities and the aforementioned good mileage was sluggish junk and did not respond to carb or ignition tuning attempts to return it to its former good performance.

Efforts to tune outside the engine were obviously getting nowhere, and having had a previous experience with a step facing into the flow on a 289 Ford carb spacer that was extremely beneficial (is an understatement), we pulled the intake and ported the floor down to mimic the original mismatch and the original performance was restored.

Go figure.

The ’66 220 HP 289 has a sharp step in the carb spacer bores at the casting parting line, the lower half is smaller than the upper half with an irregular 1/16”-3/32” step. On a carb overhaul/tune-up, removing the step on a ’66 Mustang that got 25 MPG and ran 9:50’s in the eighth caused it to fall to 15 MPG and 10:70’s. After much anguish and fiddling with the carb and timing, etc, replacing the spacer with the ugliest one we could find in the wrecking yard put it right back to its original performance.

Go figure.

Those two incidents are the scariest thing about carb tuning I know.

Another example is a dyno test done by Joe Mondello back in the late '70s with the 460 Ford marine engine. One of magazines, Power Boat I think, had numerous Joe Mondello tech articles about modifications of the 455 Olds and 460 Ford jet boat engines. The high performance 460 that was married to Berkeley pumps in the popular little jet boats had standard small port heads with a large port Cobra Jet intake. The intake mismatch is about 1/4" all around the port, about half as "bad" as the BBC oval port head with a square port intake. One of the tests Mondello did was to port the head to match the CJ intake. Eliminating that step mismatch at the gasket flange killed the power bad, 40-50 HP as I recall,

I think the most important areas to match are the port roof and outside radius wall.

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Re: port match on tunnel ram

Post by Mike Kalbfeld » Tue Nov 07, 2017 4:07 am

Tuner - Those are interesting observations that are definitely contrary to all conventional wisdom. I don’t doubt you but I (and probably others) am having trouble understanding what what is going that causes a step facing into flow to be beneficial. I was thinking that the mismatch maybe causing turbulence that has two beneficial effects. First, the turbulence along the port floor may help the flow to stay attached to the short side radius. Similar to vortex generators commonly used on airplanes. Second, this turbulence may also help reintroduce fuel into the airstream that was running along the port floor.

What are your thoughts?

prairiehotrodder
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Re: port match on tunnel ram

Post by prairiehotrodder » Tue Nov 07, 2017 10:52 am

thanks guys, i ordered a mr.gasket #5819 intake gasket and will see if it helps. I didn't really want to do the epoxy because i know i couldn't sleep at night wondering if it would break loose and get sucked into my motor. The new gasket is .120 thick and my current one is .060 so that should make a difference. Job needs to be done anyways to fix the leaky ultra black silicone on the ends. Don't know why that started leaking. I've used ultra black for years. It did seem to me that the intake sat down lower than normal. Perhaps its been milled. I need to stop buying used parts!
Brian
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www.therocketshop.blogspot.com

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