anybody tried tweeking 1y manifolds for a few extra bhp???

[oldiguana]

yo dudes just wondering if theres any advantage to fettling the roughness out inside the cast manifolds on 1y engines or similar...used to do it on minis/escorts and the like years ago...or would a tubular exhaust manifold aid combustion at all....just a thought thats been buzzing around in my head for a while

[Simon Baxter]

You need turbulence to mix the air with the fuel.
You can do it, but the the little gain you see i don't think the effort will be worth it.
If it was 300hp then maybe you could tell some difference, but not on a 1Y.

[HarryMann]

or would a tubular exhaust manifold aid combustion at all...

Might aid cylinder filling if designed properly, not combustion. Branch lengths would have to be longer than for typical petrols... unless one arrrives outa da blue gratis, I wouldn't bother, turbo is the way to go, then most of that inlet/exh tuning is much less important.

As for porting and polishing, Simon's advice is good...

The Importance of the Valve Seat
And speaking of hard and fast rules, there is one part of porting that is generally downplayed but is in fact more important than any other part. That is the simple valve job. When making changes to various parts of the port, it will be noticed that the most immediate and gratifying gains will result from careful work on the valve seat. This means narrowing the seat, and raising it toward the edge of the valve. It also means carefully blending the seat's angles. This blending is the purpose behind the so-called "five-angle" valve job. The five-angle valve job is really just the standard three angles with careful blending between them (which adds two angles). You can have most of the benefits of porting simply by doing the standard valve job meticulously, something that takes fewer special tools and much less skill.

Polishing
Finally, we get to the subject of polishing. Polishing is, if possible, a myth within a myth. It is one of those traditional yet ineffective techniques which has somehow survived in the dank swamp of motorcycle mythology. However, the industry is more to blame than the unwitting public. The truth is, port polishing in a practical sense serves merely to "sell" expensive porting jobs. It's "eye candy." The customer has been conditioned to be more easily impressed by the unreality of what he sees than the reality of what he can't see. Sort of like the detail work done on your car during its 10,000 mile inspection. As just explained, most of the magic in port work is almost invisible -- fully 90% of effective porting takes place within an inch of the valve seat. The parts of the port that are usually polished are far from this area. The polish gives the customer something to look at.

Furthermore, polish is not only unnecessary, it's actually harmful, in two ways. The first concerns the airflow itself. The experience of countless engine builders, plus research by Superflow, Boeing, and various members of the Society of Automotive Engineers, indicate that a smooth surface is not necessarily the slipperiest where air is concerned. Ever notice that an airplane's wings are not shiny smooth, but rough? The rough surface reduces air drag, and the wing glides through the air easier. Olympic bobsled teams stick sandpaper-like skateboard grip tape to the sides of the sled and the tops of their helmets for the same reason. Air tends to get lazy on a smooth surface. It's called the "boundary layer effect," and it refers to the fact that an ultra-smooth surface accumulates air pressure next to it. This pressure is really stagnant air, and it effectively obstructs airflow. A slightly roughened surface eliminates this boundary layer and increases airflow. The second way polish is bad concerns combustion. Intake tracts don't just flow air, remember. They flow an air/fuel mixture, whose behaviour is quite different from plain air. The same lazy air boundaries that constrict a polished port's airflow also make fuel "drop out" of suspension in that air. The mixture then enters the cylinder less thoroughly mixed, and poor combustion and reduced power result. For this reason, most builders glass-bead the port walls instead of polishing them. The slight roughness creates tiny eddy currects which keep fuel droplets suspended in the port airstream. Good combustion is thus ensured.

The Bottom Line
Traditional porting is effective. But far from the glamorous thing it's made out to be, it is difficult work requiring excruciating patience. It's not taking out large amounts of what presumably foolish manufacturers left in there. Often it is more filling than grinding. The experienced engine builder knows that velocity is just as important as total flow, and that port shape is the means of gaining both, not just simple cross-section. Increasing cross-section will get you only the flow, with resulting losses in velocity that will actually reduce power at middle rpm. The professional also saves the polish for the valve covers. It's a waste of time and money in the port, and will usually reduce rideability. Finally, if you have porting done on your cylinder head, insist on flowbench charts documenting the gains. This should include references to port velocity as well as total airflow. If those charts are not available, have the work done someplace where they are. No matter how experienced a builder is, porting without a flowbench is akin to luck; the practitioner doesn't know what is really going to happen. In other words, blue sky, "watered" Florida real estate. But now you know. Oh, and please pass the ketchup...

===

Ever notice that an airplane's wings are not shiny smooth, but rough?

A misleading exagerration and a port is not an aeroplane wing, so a bad analogy, so trying to make a point.. the golf-ball analogy is better

Full text of that article can be found here

[caveman]

Hey oldiguana, do you have that setup already in your truck? I'm trying to get as much info about using that manifold before shoving a 1Y into my t25 and it seems there is some metal cutting/banging involved.