i port matched my manifold ( air gap ) to my gaskets and heads. removed ALOT more material than i expected from such a great manifold. also i cut the gaskets right up to the silcone sealer that comes from the factory, and opened my ports to that size. got in there really good and shaped them too. not just on the ends. do you see me gaining anything? 2 hp

 

I did this a number of years ago with my brother in law. We started drinking beer and porting the intake. By the time we were done we gained about 500HP according to our guesstimate. Probaly more like 5 to 10 HP but after a few beers we were going 8 seconds with this car. The next morning we actually did a very good job porting it. It can't hurt performance so why not do it.

 

i know its not worth much, but i know its there

 

Sooooo........... instead of a "tube," you now have a "trumpet."

Probably isnt worth alot.

 

gasket matching the intake brings....... nothing!

The most imortant porting anybody can make is the "pocket porting".....

You have to check the shape of the port just under the valve seat and you have to smooth that transition area.
Even the guide boss can be shaped a bit..... leaving at least 0.1" of material to the bronze guide.

This is the job I have done on my Trick Flow Heads following this rules (coming from David Vizard).



The only work that is possibe to do in the ducts (being shure that you will don't hurt performance) is a general blending..... flattening any defect of the casting.

Like this:


Sorry for the quality of the pics...... but are done with the cell-phone!

 

I also did all of this to my engine (including pocket porting of the heads and port matching).

However..., BION, port matching the manifold can hurt performance (and hp) if the heads don't need the airflow due to reversion.

 

Actually not having a mis-match at the intake juction IS WORTH some power. There is power to be gained in a Air-Gap intake by radiusing the intake divider and working on the entry into the runners from the carb flange. There isn't a ton of HP to be gained but 5-10HP ACROSS THE POWER RANGE will get you down the strip faster than the guy who bolts on parts and runs them "out of the box". I loved it whan my LT-1 was running early 2.5in "Rams Horns" and guys would scratch their heads at a 12.6sec Vette running those "corks" at Vette Magic Drags (I ported the exhaust manifolds for over 16 hours and wasted $90 worth of extened shank carbide burrs on them removing the generator mounting bosses from the outer cylinders to the center dumps.)

 

tell me more.............

how much did you hog those suckers out?

 

my porting has to be worth something! the ports in the head and the gaskets no longer protrude in the path or flow of the gas/air charge. if i can gain hp with a manifold SWAP, then i can surely gain some by making that manifold better. you cant say ill get NOTHING.

 

You think??? Read the following:

Consider "standoff" or "pressure reversion" a phenomenon that shouldn't exist to the detriment of engine performance, but does in too many cases. Nearly everyone even remotely associated with high-performance engines is aware of the so-called "ram" effect as applied to engine induction and exhaust systems. This condition is generated by sonic pulses that continually rattle about in an engines induction system, exhaust system and at times, in the combustion chamber area, and a favourable ram effect will occur when these pulses become aligned in direction and magnitude to cause a larger-than-normal charge of air/fuel mixture to be pumped into the cylinder from the induction system. A similar alignment in direction and magnitude of pulses causes a larger-than normal volume of exhaust gases to be pumped from the cylinder through the exhaust system. In simplest terms, pressure reversion could be defined as diametrically opposite a favourable ram effect, a condition in which the air/fuel mixture is forced away from the cylinder, back up the induction system toward the atmosphere. A similar condition can exist on the exhaust side whereby exhaust gases can be forced back toward the cylinder from the exhaust system. It is quite reasonably felt by some experts in the field that the pressure reversion in the induction system is caused by a pressure reversion in the exhaust system, with the combustion chamber area as the connecting link between the two during the overlap period. However, later indications, are that pressure reversions in either system can occur independently of the other, although their magnitude seems considerably less than a combined induction-exhaust reversion.

Pressure reversion usually manifests itself visibly as liquid fuel or fuel stains on some surface at or near the upstream sides of the carburetors. Sometimes it doesn't get as far as the atmosphere, in such cases being visible as a sort of "ball of fog" extending from the intake manifold and perhaps into the carburetor while the engine is operating through its normal speed range, preferably at full throttle. Sometimes it may not be visible at all due to the intake manifold configuration, which would cause the reversion pulses to be damped and contained within the manifold. Happily, there are times when a pressure reversion condition does not exist at all within the normal engine speed range.

We sometimes like to think of the air/fuel mixture and exhaust gases as smoothly-flowing, but such is not the case. The sonic pulses, or pressure waves, as you prefer, which incidentally, occur in all engines, cause violent disturbances to the air/fuel mixture and exhaust gases within the cylinder and induction and exhaust systems. These pulses represent energy, quite a bit of energy, in fact, and when they can be made to work favourably for and with an engine, as they can in the correct application of the ram principle, engine performance comes to life. However, when they work against an engine, as in the case of reversion, engine performance tales a gigantic nose-dive. If these pulses were one-directional downstream pulses, that is, from the atmosphere, through the induction system and into the cylinder, then from the cylinder through the exhaust system to the atmosphere, things would be lovely. However, for every downstream pulse, there is a reflected upstream pulse of lesser magnitude and these are the ones that do the damage, particularly when they become so unsynchronised or out-of-phase as to cause a pressure reversion, a highly-undesirable, performance killing condition.

The consensus is that these sonic pulses are initially generated by the opening and closing of the valves, although when either or both valves are open, the piston crown cannot be ignored as a possible secondary source of pulse generation. It could also be that the piston is a primary source of pulse generation within the combustion space when both valves are closed. The latest data corroborates earlier findings in that the pulses are basically sonic in velocity. But sonic velocity varies with the density, temperature and pressure of the working fluid; therefore the actual pulse velocity in the induction system will vary greatly from that in the exhaust system, with the combustion space serving as a transition between the two extremes. In addition, there is a thought that downstream pulse velocity should be added to downstream gas velocity, while upstream pulse velocity should have downstream gas velocity subtracted from it. With all this downstream/upstream gas/pulse thrashing about going on simultaneously, there is little wonder that some disagreement exists between experts in the field, but the biggest wonder is that the engine runs at all.

Pressure or pulse reversion exists most prevalently to a performance-damaging degree in engines equipped with individual runner (IR) induction systems where each cylinder has its own isolated carburetor throat and intake manifold runner and there are no interconnections between carburetor throats or manifold runners.

The reversion problem shows up at its worst when the induction and exhaust systems appear to be "clean"; that is, when the carburetor throats, manifold runners, cylinder head ports, exhaust header pipes are all nicely matched and blended to their mating pieces. It may be clean in fact as well as appearance, but unfortunately, it is clean in both directions, so reversion pulses have and easy time of it.

Four separate and distinct areas require possible reworking to minimise the effects of pressure reversion, if not eliminate them completely. First, the exhaust system flange and primary pipe should be about 1/8-inch larger on all sides than the port opening in the cylinder head. Second, the intake port face in the cylinder head should be about 1/8-inch (1/4-inch on the diameter) larger than the intake manifold runner, then the port should be funneled down to more normal dimensions as it approaches the intake valve. Third, the intake manifold runner should be about ¼-inch larger in diameter than the carburetor throttle bores, and the runners funneled down to a smaller dimension at the manifold mounting face.

The idea is to make deliberate mismatches at these three points. The reasoning behind this is that there is pretty conclusive evidence that the downstream pulses (the good guys) take the shortest distance to get where they're going, while the reversion pulses (the bad guys) stay close to the walls of the carburetor, intake manifold runner, intake port, exhaust port and exhaust pipe. The deliberate mismatches make abrupt changes in cross-sectional area, which are highly beneficial in damping the unwanted reversion pulses. In addition, the air/fuel mixture traveling downstream is pumped into areas of lower-than-normal pressure, which in itself, helps induce a larger volume of mixture into the cylinder, and the same is true on the exhaust side. Edelbrock Equipment Company has made a couple of prototype manifolds incorporating the mismatch concept for the L-16, L-18 engines with encouraging results for a first attempt in damping reversion pulses.

The fourth are that may require a change is valve timing. By itself, valve timing can have rather dramatic effects upon the presence or absence of pressure reversion.

If a reversion problem exists, the changes should be made one at a time and in the order shown until the problem disappears completely or is at least helped considerably. At the points of mismatches, leave the edges square and sharp. DO NOT ROUND OFF THE SHARP EDGES! Perhaps strangely, there are highly modified L-series engines with no reversion problems at all within the normal operating speed range.

 

this is the exact opposite of everything ive ever known,read, or seen

 

I'm not saying that you've lost, (or gained) power. In some cases port matching can be of benefit whereas in others, a detrement. Every unlike situation is different. You'll find similar information in many high performance publications. Do some research and educate yourself.

 

Interesting discussion I'm definitely in agreement that an "anti reversion" dam is required on the exhaust - that the header opening should be larger than the head opening - at least at the bottom.

I'm not as confident on the intake side; I don't have anything to back up my data here other than what I've seen on pro-built racing engines that match these very carefully. I have heard some performance street engine builders (with a higher skill level than I) note that the intake/head intake "interface" is not as important as people think unless the engine will be turning constant high RPM for racing.

 

This is quite true!

In addition, having the manifold runner smaller that the head is beneficial in wet flow systems as any fuel that puddles and drops out of air/fuel flow suspension is reintroduced to the air/fuel flow as it leaves the smaller runner.

 

you assume alot. while im no engine master, ive built about 25 all together. i raced dirt track with my brothers for 8 yrs. and i read ALOT. while i understand that port matching is not the holy grail, it can almost always be beneficial. it is not an exact science and new ideas come along all the time. also be wary of what YOU read. i can find a hundred articles on the supreme capabilities of the TORNADO, GAS LINE MAGNETS, and the like. but im sure your aware that their claims are bogus

 

What is the rest of your engine build ? You will not know for sure if you hurt it or helped it until you go run it.

 

I've assumed nothing.

I only mention it because you said EVERYTHING you've read or seen is contrary to reversion philosophy. Obviously then, you've not read and seen nearly everything that's out there.

 

Could you provide the reference info for this? Thanks!

 

This specific section is included at the following link. But if you do a search of the 'net, you'll find other articles that also back this up.

http://www.datsport.com/Chapter_Seventeen.html

 

This is kinda telling from the article...

"Pressure or pulse reversion exists most prevalently to a performance-damaging degree in engines equipped with individual runner (IR) induction systems where each cylinder has its own isolated carburetor throat and intake manifold runner and there are no interconnections between carburetor throats or manifold runners".

I also wonder if this is significantly applicable on a street engine making < 1.4 HP/CID or so. It's an interesting academic discussion but I don't see it as anything that's keeping me up nights.

The safe bet might be to leave a small lip around the edge of the manifold intake port - most of the aftermarket manifolds are pretty close to the gasket size these days as are the heads - I'd just take a look and not try to "venturi" them in (round off the corners into the port to match). As noted, every header manufacturer has been very clear that an anti-reversion dam is built into the header port shape with an intentional mis-match at the bottom of the port with the head exhaust port.