BLACK_DEL_SOL

sorry about the whoring just posting some helpful stuff trying to make up for earlier .heres some stuff i found just trying to help out fellow lude ownerns out there


Flapper Valve Mod
All Si and VTEC Preludes have a dual stage intake manifold, similar to what twin cam B16 and B18 motors have. Why the H23 Prelude motor has it is beyond me cuz the two stage manifold is usually part of the VTEC system. A normal manifold has 4 runners, one for each cylinder(on a 4cyl). The dual stage manifolds have 8 runners in the top two sections. At low rpm's, only 4 of the 8 runners are "open" and at a certain rpm, a set of flapper valves opens up to allow more airflow which results in more hp. Why don't they just have all 8 runners open full time? Simple, too much air will result in a low end power loss. So until ~4800rpm
you have 4 runners open, then at 4800 a set of flapper valves opens and you have 8 runners all the way to redline. The runners have a diaphragm that controls the opening and closing. The diaphragm has a vacuum line running to it and at 4800 where there is enough vacuum pressure, the diaphragm opens the runners. Ever notice how your Si at around 4800 drastically changes sound and it sounds like the car is going to explode? Well that changeover in sound is the manifold opening up.




This is what the middle section of the manifold looks like with the flapper valves. The silver diaphragm on the left side is what controls them. Until 4800 they are closed, but after 4800 they open up as shown in the picture. All the small piping and fittings are for Nitrous so don't look at those. So what's the mod? Simple, if you want more power sooner, unplug the vacuum line that connects to the diaphragm. Now the flapper valves will always be open at all rpm's. Yes, you will lose a little bit of low end power, but you will gain power sooner(above 3700) as a result of them being open. 4800 is a good rpm, but it's possible to take advantage of the 8 runner design before 4800 and by unplugging the vacuum tube, that's what you're doing. Since racing always takes place above 3000 or so rpm, you won't have to worry about losing low end power. After all, why else would you want your car to be faster if you're not racing it??


This is where the flapper valve is located on the engine. You can see it's between the brake master cylinder and the left side of the upper intake manifold(attached to the manifold actually). There is a line connected to the top of it, just unplug it so it hangs or cap it off. I have ---- retentive people asking me all the time if stuff will get into the vacuum tube if it isn't capped off. Let's be realistic, the opening is smaller than 1/8" wide, do you think that with the hood shut, something will bounce around in the engine bay and land inside the tube which is tucked under the manifold?? Hell no. Unless your car sinks to the bottom of a deep lake, you're not going to get any water or dirt in there. Besides, that tube BLOWS are out when the engine is running, how is something going to get sucked inside there if there's 40lbs of air pressure blowing out of it constantly?

EGR MOD

Exhaust gas re-circulation is what it stands for. Of course there's probably some other technical term for it but basically, it does what the name says. Exhaust gasses are sucked into the EGR(via hole in the bottom of the EGR which is connected to the engine) and re circulated back into the intake manifold. I don't know about you, but wouldn't hot exhaust gasses be BAD for the air intake, which is supposed to be as cold and oxygen filled as possible? The engine's byproduct is carbon monoxide(or dioxide?)... would feeding an engine it's own byproduct be good for it?? Do you eat your own byproduct I sure hope not! So what do you do? Remove the EGR and cover the hole so exhaust gasses aren't sent back into the engine.






It's hard to see in the picture, but look inside the circle between the two Nitrous lines and there is a black valve sitting there with a yellow line hooked up to it. It's easier to see on an engine that's not all cluttered with NOS plumbing everywhere. Basically the EGR has a plug, a vacuum tube, and two bolts holding it down. Unbolt the EGR and unplug everything attached. 1. Cap off the vacuum tube. Either get some tubing caps at a parts store or plug it with a golf tee. 2. Leave the plug alone. Zip tie it out of the way. 3. You can see that you have a hole left over where the EGR went. Get a thin sheet of metal and some tin snips. Set the metal on a table and put the EGR on top of it. Trace the bottom of the EGR on the metal and cut the shape out with the tin snips. This is your cover for the hole where the EGR went. Drill two holes that correspond with the holes in the EGR. Now, get the EGR bolts and bolt the plate down over the hole where the EGR went. Now you won't have exhaust gasses being shot out of your engine nor back into the engine via EGR. Your car might trip a check code but that's life. The check engine light is designed to detect errors in the emissions equipment and since you're removing some of the emissions equipment, it might trip a code.

Fuel Pressure Mod

After installing an intake, header and exhaust the car will have a ton more airflow which is good, but it can be bad if you don't have some extra fuel to balance it out. Many people like to install adjustable fuel pressure regulators but they're a pain in the *** because they have to be tuned constantly and the correct way to do it is on a dyno. Not many of us have a dyno handy all the time and even when there is one in town, it costs a lot to use. The stock fuel regulator gets its pressure by vacuum pressure, which is usually constant. If you want more fuel pressure, unplug the line connecting the fuel regulator with the intake manifold. Now the regulator can suck in as much air as it wants as it's no longer limited to the vacuum tube pressure. So find the line that goes from the regulator to the manifold and remove it. Cap off the opening from the manifold where the vacuum line went. However, DO NOT cap off the regulator! If you cap off the regulator it defeats the whole purpose cuz you will be stopping all airflow to the regulator. I saw someone put a K&N breather on the regulator. this is pointless. Nothing is going to fly into the 1/16" hole. Your idle may change a little due to the change in vacuum pressure, but that's something you'll have to get used to. Several people have done this and been very pleased, and I have had some excellent results as well on many cars.

Stock 95 Civic DX(Automatic)
With air box removed - 17.4@80mph
With air box removed and fpr mod - 17.0@80.5mph

Stock 95 Del Sol Si(SOHC VTEC, 125hp)
Air box removed, timing advanced, adjusted tire pressure - 16.0@87mph
Air box removed, timing advanced, tire pressure, fpr mod - 15.8@88mph

92 Prelude Si(my car)
All mods listed including SX adjustable regulator - 14.6@94mph
All mods with fpr mod(SX disconnected) - 14.5@94.6mph

Yes, I got a better time with the fpr mod over the adjustable SX regulator



This is where the regulator vacuum line connects to the intake manifold. On a stock car it's not a yellow line, but look in this area for a line connected to a gold diaphragm. Don't mistake with the flapper valve diaphragm, the fuel pressure regulator is the smaller gold diaphragm located on the fuel rail.

Spenser

Don't listen to that, it's retarded.

HondaTuner

I didn't even bother to read it. :P

Spenser

the only thing i would bother doing would be the EGR mod,

the guy is a moron and doesn't understand what the
"flapper things" are for, or the FPR. or how engine vacume works, black delsol, tell that stupid ---- to come here so we can give him ----.

BLACK_DEL_SOL

hey im being serious and give back to the community i have taken so much from

Doofnoil

like the jyard sign says: useless ---- goes around back.

HondaTuner

lol, black_del_sol.. doesnt look like you're getting anywhere, bud.

quadnie

This is about the only part of the thread I actually read. I hear H-T has a great prelude section, and clubsi should fulfill all your bullshit needs.

Spenser

the valves close of one of the 2 runners leading to the inktake port, increasing air velocity, resulting in better fuel atomization which is key for better emissions, fuel economy and power. it does plenty, basicly accomplishes what VTEC does but on a lesser level. unless i see dyno sheets proving it doesn't do ----, i'd leave it, unhooking it is a stupid idea, if your gona mess with it, remove it entirely.