Engine Porting

[Siddharth Mandal]

Is porting the intake and exhaust of the f4i
advisable

[Siddharth Mandal]

Is porting the intake and exhaust of the f4i
advisable

[Mike Claffey]

yes and no.

I didn't have time to expand on this before, but I sort of can't sleep right now, here I go http://fsae.com/groupee_common/emoticons/icon_smile.gif You should think about time spent vs gain. Have a read through Big Birds threads, he goes into this quite often. I would say the time spent porting heads, back to back testing them, or instead doing this theoretically would be better spent developing a dry sump, improving your dyno/tuning abilities or better yet optimising your suspension package.

A stock f4i head will still give you over 90hp restricted - porting will improve that marginally but getting science into your tuning process is where the biggest gains are to be had.

If your really keen on dicking with the ports, read up on the Uni of Queenslands turbo project. The guy on that was doing some very interesting work decreasing the port diameters, if you stop and think, it makes alot of sense.

Regards,

Mike

[Maverik]

Start at the restrictor, figure out your volumes and use some good ole' fluid dynamics to figure out whether it'd be smart to port or not... or just go the easy way and compare unported vs ported head WITH the restriction. Just an opinion, but figure out what's roughly going to happen before you do something irreversible.

[Bill Kunst]

Maverik,
This is good advice.

Siddarth
The only problem is if you use a flowbench for your second suggestion may give bad data. Sure it may flow more (cfm), but it may not make as much torque/power through certain rpms. What happens when a valve stays open constantly and when it opens and closes is very different. This means that you will have to compare this with software, equations, or hardware(dyno).

[Michael Palaszynski]

well of course testing data is not REAL data. but all heads are flowed this way. i can't think of an effective way of flow benching a head with opening and closing valves....

[raska]

At shows and gatherings there are always guys asking about what porting, polishing, bluprinting, and roller rocker kits for our engine.

[57JoeFoMoPar]

The topic of porting has come up several times in our engine discussions. Now before I continue, please keep in mind that I am NOT an engineer, but I have lots of engine building experience. My knowledge is more practical than theoretical.

In the restricted application, porting may actually hurt overall performance. Here's an example; take a straw and a paper towel tube. take a deep breath and blow through each. you've moved the same volume of air, just at different velocities. Low RPM operation requires less air, so the smaller runner increases air velocity and improves low end power. AS RPM increases, air demand increases and runner size needs to increase as well. Since intake runner size is a static factor, the intake/intake port should be designed in a manner that is a good comprimise to work well in most conditions. Since the normal operating range for an SAE car in competition is in the mid to high RPM band, the set up should be optimized to meet that requirement.

The port size of the stock head works well for the unrestricted engine, but the restrictor changes all of that. By making the runners smaller, I think there is lots of power to be had in the mid range and in the higher RPMs. Maybe huge intake ports will produce a big peak number, which is fine if you're into a HP pissing match, but the power band would likely be much flatter and usable with the smaller ports.

My experience has also shown that polished intake runners don't really contribute to performance gains. In fact a less smooth intake runner/port might "rough" up air flow and help atomize fuel/air mixture for more power. On the exhaust side, the name of the game is just getting that stuff out of there, so a big exhaust port as smooth as posible is the hot ticket, with a tuned header.

my $.02

[Maverik]

Kinda on the right track, as an engineer though nothing is ever straightforward. If you don't mind, you're analogy of the straw and paper towel tube is good for proving the point you want, but you aren't looking at losses. I guarantee that the "blower" in this case is physically exerting more power to get the same volume of air through the straw in the same amount of time. To tie that over to the engine being the blower, obviously more power used in moving the air is less to the ground. Like everything, design is compromises... how much are you willing to give up for higher air velocity and is it worth it?

[absolutepressure]

I think that not polishing the ports is the better way to go, especially if you're using smaller diameter runners. In our case, I don't think that smaller runners would be advantageous either, so I'm choosing not to go with them.
My reasoning is this. The ports are usually fairly long. 3.707in from the rubber connector to the back of the valve for a 92 F2, and 5.06in for the 2002 R6. If you decrease the runner diameter, but not the port diameter (which is really difficult, I'd suspect) your air is going to slow down when it hits the port. If it slows down, the fuel will have a harder time staying atomized, but the turbulance created by the stock port should help that (I don't want to say counter that, per say). I'm just using the same diameter as the connector.

[57JoeFoMoPar]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Maverik:
Kinda on the right track, as an engineer though nothing is ever straightforward. If you don't mind, you're analogy of the straw and paper towel tube is good for proving the point you want, but you aren't looking at losses. I guarantee that the "blower" in this case is physically exerting more power to get the same volume of air through the straw in the same amount of time. To tie that over to the engine being the blower, obviously more power used in moving the air is less to the ground. Like everything, design is compromises... how much are you willing to give up for higher air velocity and is it worth it? </div></BLOCKQUOTE>

You are absolutely correct, and I am well aware of this.

For arguement's sake, lets call the "straw" motor your typical street engine, and the "Paper towel tube" motor an all out race motor. The street engine's main purpose is to deliver smooth performance in non-demanding environments, smooth idle and low end power. The race motor has one purpose and one purpose only, full throttle, high rpm HP where idle and manners don't matter. Yes, the straw will take more effort to blow through, but that is because for that breath, the straw is restrictive, which means it's time to step up the runner size. The paper towel tube may be too free flowing, and not enough air velocity exists at mid range rpms...time to step down runner size. I think ideally there is a comprimise between the two to acheive a good balance. An SAE engine that can only make a huge peak number will most likely get stomped by a motor with less peak power but with a broader powerband. A car with power only at the top end will be a nightmare to drive in the autox and enduro. Think of the motor screaming at it's redline for the entire course, which leads to excessive engine wear, overheating issues, and excessive fuel consumption. Compare it to motor with a flatter curve that has broad torque to pull through gears, much easier to drive, and smoothness equals better lap times.

The true problem exists in applying this idea. It's easy to make a smaller intake, just make the runners out of smaller diameter tubing or carbon fiber. The tricky part is making the intake port smaller to match. I've seen guys use epoxys to fill the port then smooth it out by hand. time consuming and very tedious work. Also, the heads will need to be put on a flow bench afterwards to make sure the hand ported heads will flow the same cfm

[murpia]

Just a thought, has anyone ever tried running one of the five-valve (3 intake, 2 exhaust) Yamaha heads as a 4-valve?
Might be a good way to get the port velocity up.
Regards, Ian