Interesting Thing About Intake Manifold/ Port Design.....

[JSIR]

While I had my intake manifold removed I noticed something different about this engine's intake ports compared to the intake manifold. The opening at the end of the intake manifold ends is actually larger than the opening to the intake ports at the head mating surface. The intake ports on the head are a good 4mm smaller in width (measured left to right), the height of the ports seem perfect, but the width measurement is a good bit smaller. In past Hondas it was always the other way around, the ports were usually larger than the intake manifold openings so you had a step down not a step up at the mating surface. I find it strange as the step at the mating surface would be at least 2mm on each side of each port. I wonder if this is just caused by Honda using the larger manifold from the RSX-S which is not totally designed for our heads. The RSX-S uses larger ports so it probably fits that head better.

I took a chance and shaved off a bit of material on both sides of each of the 4 intake ports to get a smoother union with the manifold giving it a venturi shape. Hoping this may help the top end a bit. Shouldn't really hurt the bottom end any as I'm not changing the entire port, just the opening. We'll see how she works when I get it all back together in the near future. Crossing my fingers on this one, its worth the gamble. :confused:

[SiR Medic]

You are a braver man than I!



Let us know how it works out!

[bioevolve]

If that is the case our intake flow is not at full potential, the uneven (port match) would cause air bubbles on both sides of the intake runners at the head, causing a restriction.
ITR runners are wider than the ours and type-s.

So what you're doing should free up some power :D

[JSIR]

Originally posted by bioevolve
If that is the case our intake flow is not at full potential, the uneven (port match) would cause air bubbles on both sides of the intake runners at the head, causing a restriction.
ITR runners are wider than the ours and type-s.

So what you're doing should free up so power :D

thanks for the confidence, that was my thinking as well. The inside diameter of our runners are just over 51mm (width), not sure what the ITR's run. Our ports are about 47mm wide. I think Honda threw on this manifold to make the Si more distinctive from the base RSX , even though our ports were made for the base RSX intake manifold. I will definitely keep you posted, I have some pics as well. I've done some other crazy things to the ports but will leave that discussion for another day.

[spoon3168]

hmmm.. we should ask the rsx base and s owner to measure for us too.... so we would know if there is any differences

[Tekdemon]

well from what I understand our flow is still better than the base RSX because we actually have less torque(due to less backpressure or something) but a higher HP peak...according to the RSX people anyway.

Still if you make it match better you should obtain a better HP peak...of course I'm almost sure you'll lose more torque from this, but do post results =P

[JSIR]

I know RSX-S guys that port matched their intake manifolds to their head openings by widening the intake manifold. So that tells us that their head intakes are larger than their intake manifold runners at the mating surface. The opposite of our setup.

I'm guessing that torque won't be hurt with what I'm doing. I should just get more air flowing into the stock sized ports (leading to the valves) which should increse air velocities, or so I'm hoping. Wont know until I run it though. I may have it up and running by the weekend.

:angel:

[JSIR]

One other observation, I think Honda gave us some upgraded intake valves as well. From the looks of it, our intake valve stems have been back-cut, such that they are thinner where they enter the port, much like the old ITR intake valves. They look like they are pretty good quality valves. Lighter intake valves may explain why we can rev our engines to 7800+ rpms with single valvesprings without experiencing float. Just some info.

[fishboy]

thanks for the heads up on this. i will keep my eye out for this when i do any mod that involve taking the im off for a bit. i have a question though, how did you widen the intake ports? what did you use and were you worried about shavings going into the engine? if so, how did you make sure nothing got into the engine, or did you take the head completely off the car? sorry for the barrage.:)

[JSIR]

I used a dremmel like tool, and I have one of those wand attachments which you hold like a pencil, with a couple different cutter bits. I just widened the two ends of each intake port, didn't touch the floor or roof of the port. Took the material off in small amounts and made sure it was all smoothed into the wall areas, looks really good actually. I covered the engine with garbage bags above and below the ports, to keep shavings from flying everywhere but you still get some.

I stuffed the ports with those blue mechanics type paper towels that you get at any auto supply store. I cut the towels in half and stuffed them into the ports behind each valve fairly tight, and then kept adding to them building it up until I got close to the front of the port, keeping enough room to get my cutter in without grabbing the towels. I used about 2-3 sheets per port, ending up with about 5-6 ball like towels stuffed into them. The very first towel inserted behind the valve I wet down with simple green to keep it moist and attract any shavings that made it past the other towels balls. After I finished doing all the grinding I used a vacuum to suck up all the loose shavings in each port, that got rid of about 99% of the crud. Then I pulled out the towel balls one at a time and wiped down the port after each one was pulled out with needle nose pliers. They come out in little ball like shapes. By the time I got to the last towel ball (the moistened one behind the valve) there wasn't any remnants of metal shavings left. I've wiped down the ports many times and stuck my fingers in all the way down and didn't find any shavings, so none made it past the first one or two towel balls. You are only grinding the first 1/4 -1/2 inch depth of the port so you dont enter too deep, thus the shavings come out easily without working their way downwards. I'll try to get some pics if they show up clearly.

You grind a bit at a time on each side, left and then right and back and forth to try and get an even shape. I would grind some material away then measure the port with my digital caliper until I got close to the size of the intake manifold openings which is 51mm. It's a slow process to get everything shaped right and smooth. You don't have to polish the finish though, just smooth so there aren't any ridges anywhere, the finish left by the cutter bit is good enough as you want an "eddy" or "velvet" finish to induce air-fuel mixing, not totally shiny smooth finish.

hth


Joey

[BlasTech]

Nice writeup JSIR.

I've never done any porting, but when I use my dremel tool to grind something (usually plastic or metal), I use some masking tape rolled up in a ball (sticky-side out) to pick up bits and shavings from the carpet or corners in the car. That might help someone somewhere down the road, and it sure beats getting the vaccuum out.

[JSIR]

sticky tape would work once you get down to the smaller amounts after the vacuum cleaner is used. The shear volume of filings would require lots of tape. Its amazing how quick a good vacuum sucks up the filings since they are so light weight.

Keep in mind anyone that reads this, what I've done seems to make sense in terms of air flow characteristics, but until I actually get the car running and do some informal testing its hard to say what difference it makes. Like many other mods it could do nothing. I'm just the type who is willing to spend some time with DIY small mods like this that cost basically nothing, even if they might not have any significant effect. It's worth the effort for me, but I don't want anyone to think that this is the next hot ticket for our engines and have everyone trying it out expecting gains. More of an experiment if anything.

[BlasTech]

Originally posted by JSIR
I'm just the type who is willing to spend some time with DIY small mods like this that cost basically nothing, even if they might not have any significant effect. It's worth the effort for me, but I don't want anyone to think that this is the next hot ticket for our engines and have everyone trying it out expecting gains.

Someday, you'll be the one who makes the killer hack for EP's! Keep us posted! :)

[JSIR]

Originally posted by BlasTech


Someday, you'll be the one who makes the killer hack for EP's! Keep us posted! :)

ha, ha, lol, hack-job may be more like it.

Although I just got through painting my stock plastic spark plug cover, and I must say I impressed myself even more, hidden talents are coming out in droves. :)

[fishboy]

thanks for taking time to do the writeup. it was very helpful. keep us updated.:)

[JSIR]

well I got to dyno test the car today after the changes. Firstly I should mention the differences in testing today compared to my last dyno run. The results are on a fully warmed up engine compared to a fairly cold engine last time I dyno'd. Today I basically got off the highway (which was about one hour drive at 70 mph and about 5 minutes of city driving) and hooked right up to the dyno as I wasn't able to wait until the car cooled down. The dyno run which I compare to last time had the car fully cooled down for an hour before hitting the dyno on a much colder day.

The gains were up and down, rather roller coaster like, but that is what happens when you change intake shapes and sizes. There was a decent gain on the bottom end right up to 3800 rpms of about 5 ft lbs, which you can feel quite noticeably and corresponds to improved fuel mileage on the highway today. That was followed by a small loss from about 4200 to 5000 rpms of about 2-3 ft lbs. Then a small gain on the top end all the way to redline of about 1-2 whp. Not a huge difference overall, but the bottom end gains really felt good and were decent. If I had a better intake it probably would make more of a difference I think.


Joey