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?
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.
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.
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.