...Or you could polish the intake(s) since they are aluminum.

 

I have a ported upper that I started to polish. Polishing is a major PITA. I decided to quit before it was finished. If it provides a power increase I'll finish polishing it. If it doesn't, polshing is too much work for a garage ornament.

If everything goes well this week I'll go to the dyno to get a new baseline next weekend. Ordinarily I wouldn't worry about it, but with 266k miles on the clock it's needed to ensure accuracy. Then I'll swap out the rockers and go back to the dyno the following weekend to test the rockers with the stock intake. I'll also take the ported upper and a 302 throttle body if I can get one and swap them out between pulls to see what works and what's junk.

I am planning to take notes on all my stuff and tabulate it into a (hopefully) useful document that others can benefit from. The only problem with that is I'm a terrible procrastinator and it will take forever for me to get around to it.

 

Any update silver streak?

 

The rocker pedestals are at the machine shop as we speak. They've actually been there for a few weeks, but when I get stuff done for free I try not to ride them too much about the time.

I haven't done anything else on the intake. We've been busy at work, so there hasn't been any time to mess with it.

 

Sounds fun, any news?

 

Silver Streak i'd just like to thank you again for all the help you give us fellow 300ci guys.

By dyno testing and proving your results you're providing not only a good platform of reliable upgrades, but also a great basis of performance and theoretical discussion.

I've been away from my truck for about 3 weeks, which is a sad, sad thing, but i'll be picking her up this weekend so i can make some cash after classes and on the weekends. With what isn't spent on beer, errrr books, i'd like to start slowly fixin up the truck again. Better to do preventative maintenance and keep her running well than to have to buy a new motor all at once!

 

also, the M5OD gets a real lot of bashing. I believe most of this is due to the tranny leaking fluid and burning up. The first gear could be a bit lower, and this probably leads to synchros burning out a little sooner than they should on the numerically-low rear end trucks. I would think it would handle 320ft-lbs alright.

SS- i thought for better air flow a slighlty porous, or "bumpy" rather, surface was optimal..? The high polishing was reserved for exhausts to keep carbon from sticking as easily. I can see how air would slip by a highly polished surface, but i thought the theory behind the rough surface was to create a sort of "film" of air on the material that the intake charge will go by easier.

please, teach!

 

Still waiting on the machinist......this is a recording. It's times like this that I wish I still had a key to the machine shop at OSU. It was really nice to be able to go in any time of day or night and make what I needed. I just called and left him a message, hopefully he'll call back and say their done.

I actually wish the 1st gear in my m5od was a bit taller. I've got 3.08 gears and 1st is pretty much useless, but 2nd is too tall to drive off in all the time. If I had 3.36 or 3.55 gears second would be OK for normal driving, but wouldn't get off the line at the track. I'd also be out of motor at the end of the track and have to shift to 5th.

The proper surface for airflow is open to a lot of debate. Logic would say that the smoother the surface is the better flow would be and thus the better the power would be, but this isn't always the case. Here's a few topics that must be considered when talking about intake surfaces. BTW, I was talking about polishing the outside of the intake for improved appearance.

Back in the carb days, a polished internal surface caused fuel to fall out of suspension and puddle on the inside of the manifold creating mixture control problems. This is called a wet flow intake because fuel is carried in the air in the intake. With EFI this is not a problem as the fuel is not introduced to the air stream until it's almost to the valve. With a carb it is generally believed that the finish left by an 80 grit sanding drum is sufficiently rough to keep the fuel in suspension.

In a dry flow intake, there is no fuel to keep in suspension, so smoother would be better, right? Not necessarily. Scientists who study fluid dynamics use a concept called "no slip at the wall" to describe fluid flow. What this means is that the velocity of any fluid flowing in a pipe is zero at the microscopic point where the fluid is touching the pipe. Conversely, the velocity exactly in the middle of a pipe would be at the maximum. The speed of the fluid between the two varies parabolically in relation to the distance from the wall. This applies to fluids that are in what is called fully developed flow. Fully developed flow can only occur in special circumstances that are set by the temp., surface finish, size of flow channel, fluid Reynolds number (don't ask, just nod and say OK), and other factors. If you crunch all the math you will find that fully developed flow typically occurs after travelling through a pipe for a distance equal to 10 times the pipe diameter; so a fluid in a 2" pipe would achieve fully developed flow after about 20" of pipe length. Once a fluid has reached a state of fully developed flow, it's average velocity can drop. This is remedied by "tripping" the flow with a surface imperfection creating a slightly thicker boundary layer at the wall and allowing the fluid near the wall, but not touching it, to move faster. This results in an overall fluid flow that is faster than fully developed flow. The intake runners in the 4.9 will never see fully developed flow. They have a sufficient length to diameter ratio, but they also have bends in them that will prevent fully developed flow from happening. It is still possible that small areas of insufficient turbulence can occur, so a slightly rough surface might be needed to help things out at part throttle.

Another thing to consider is that deposits don't form as easily on a smooth surface. The first time I pulled the upper off of my engine there was a 1/4" thick layer of carbon on the inside of the intake. Yuk. And it hurts flow.

In the quest for ultimate airflow, there are many steps taken to get to the destination. Some of the steps make a huge difference, some make hardly any. Polishing a surface is one of the steps that gains hardly any. The difference between a mirror finish and a finish obtained with an 80 grit sanding drum is probably less than 2% on a 4.9.

Have you noticed that 80 grit sanding drum keeps coming up over and over? This is the finish I would use on a street engine. There isn't enough gain from fully polishing to make it worthwhile and there are possible downfalls. Rougher than this will cause noticable reductions in flow.

Extrude honing is another option, but I've seen it leave a finish anywhere between rough as a cob to nearly mirror. That probably has to do with how much was done. A moderate EH finish would also work fine.