92PreludeSi
Oct-21st-03, 5:58 pm
I figured I should copy the free mods thread from the old board because it was really helpful for me, and it might be for someone else. So, here's the info NWAImports.com gave me. :ph34r:
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.
http://www.92lude.com/images/flapper.jpg
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?? ;)
http://www.92lude.com/images/flapper2.jpg
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 anal 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?
Courtesey of preludecrazy.com
EGR Mod
Exhaust gas re circulation is what is 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.
http://www.92lude.com/images/egr.jpg
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 ass 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.
http://www.92lude.com/images/fpr.jpg
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.
Ignition Timing Advance
Advancing your ignition timing is a trick that has been around for years and it's been proven to work on every car that has a distributor. Advancing ignition timing gives you better low end power, that's all there is to it.
http://www.92lude.com/images/timing.jpg
Step 1 - Find the distributor. Look in the picture and see where the distributor attaches to the cylinder head. You will need to make a mark that shows the stock timing setting(look in the purple square that says "Without timing mark"). Take a Sharpie marker, a screwdriver, a razor blade, whatever, and make a mark that goes across the distributor onto the cylinder head so when you move the distributor, the mark separates and you can measure the amount of movement from the distributor. Now that you have the mark made, it should look like the red outlined section, marked "With timing mark". Now to see how it works, look at the blue outlined section. You can see how the black mark on the right shows the stock setting and the mark on the left shows you how far you have advanced the timing.
Step 2 - Fill your car with 90-93(whatever they have in your area) octane gas. You should not advance your timing with low octane fuel because it will ping and that's bad.
Step 3 - Loosen the 3, 12mm bolts that hold the distributor in place. Don't remove them, just loosen them so you can rotate the distributor. Now, turn the distributor all the way towards the firewall, which is full advance. Tighten the 3 bolts and start the car. Drive the car down the street and make a full throttle pass(in any gear, doesn't matter what rpm or speed, just be at full throttle). If the car pings, immediately back off the throttle and pull the car over. When testing this, I always keep the tools in the car so I can adjust the timing without having to drive to the garage a zillion times. Now turn the distributor back towards the front of the car 1mm(1mm=~1degree). Tighten the bolts and do another full throttle pass. If the car pings, stop and move the distributor back another 1mm. Keep turning back the distributor 1mm at a time until the car stops pinging(doing a full throttle pass after each adjustment). Once the car stops pinging, you're done! You should be able to advance your timing 3-4 degrees(3-4mm) at least without having to worry about the car pinging.
Sway bar Mod
No, this isn't an engine mod. If you have lowered your car with lowering springs, remove the front sway bar. Honda puts a huge front sway bar on the cars to prevent over steer, so millions of old ladies with no idea of how to control a sideways car won't wreck and sue Honda. The sway bar dramatically stiffens up the front end which reduces front wheel traction(ie. steering). More front traction means more steering. If you have more steering you can go faster into corners and still have the ability to turn. SO basically, your car will handle a ton better. On a stock car this also helps reduce body roll, that why I recommend that you do it to a lowered car which has significantly less body roll than a stock height car. I removed the sway bar on a friend's stock height 94 Prelude and it had so much body roll it was scary at times. The car was a lot more unstable at high speeds also. However on my car(which had race springs) and Chris's 90Si(which has lowering springs/struts) the handling was improved a ton. So if you lowered your car, take the front sway bar and all the hardware off and throw it in a corner of your garage. Then take your car to an open track event or autocross and rail on it around a few corners and if you know how to drive, you will see a difference, big time. You have to push the car to it's limit to notice the difference. If you're a wuss and you don't push the car you won't notice anything. I took mine off and never put if back on. Around low speed sharp corners I've had my 92 totally sideways before, that's how much steering it has. To remove the sway bar you need to jack up the car, put it on jack stands and remove both front wheels. There are two 12mm bolts attaching the mounts to the car, then there are two 12mm nuts attaching the sway bar to the front suspension. There won't be any tension on the bar and it pulls out over the exhaust down pipe.
Dust shield Mod
1. Remove your front wheels.
2. Remove the front calipers and rotors.
3. There are a few phillips head screws holding the dust shields on, take out these screws. Now however you can(might take a dremel or a hacksaw), cut the dust shield so you can remove it.
4. Take the dust shields and throw them in the trash can.
With the wheel on, the dust shield not only shields dust away, but it also blocks off all the airflow to the brakes from inside the wheel and wheel well. Yes, it might be a good thing if you drive through sand(even most Pro Rally cars have the dust shields removed!) all day, dust shields are worthless. Try to stay out of puddles if they are heated to prevent warping. Get more air to those brakes, remove those dust shields!
Hope some of those helped you out, and remember, all of the above references are from, http://members.tripod.com/%7EPre_ludE/pmods.html, www.92lude.com, and www.preludecrazy.com
Quote from BrandonPool21-
Keep in mind guys, these mods are just that... mods.* Some are what we know for sure and some are from sites and other people.* Do NOT attempt to do these modifications if you are unsure of your abilities.* We will not be responsible for errors caused to your vehicle.* Just be safe and ask questions and everything is cool. 8-)
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.
http://www.92lude.com/images/flapper.jpg
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?? ;)
http://www.92lude.com/images/flapper2.jpg
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 anal 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?
Courtesey of preludecrazy.com
EGR Mod
Exhaust gas re circulation is what is 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.
http://www.92lude.com/images/egr.jpg
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 ass 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.
http://www.92lude.com/images/fpr.jpg
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.
Ignition Timing Advance
Advancing your ignition timing is a trick that has been around for years and it's been proven to work on every car that has a distributor. Advancing ignition timing gives you better low end power, that's all there is to it.
http://www.92lude.com/images/timing.jpg
Step 1 - Find the distributor. Look in the picture and see where the distributor attaches to the cylinder head. You will need to make a mark that shows the stock timing setting(look in the purple square that says "Without timing mark"). Take a Sharpie marker, a screwdriver, a razor blade, whatever, and make a mark that goes across the distributor onto the cylinder head so when you move the distributor, the mark separates and you can measure the amount of movement from the distributor. Now that you have the mark made, it should look like the red outlined section, marked "With timing mark". Now to see how it works, look at the blue outlined section. You can see how the black mark on the right shows the stock setting and the mark on the left shows you how far you have advanced the timing.
Step 2 - Fill your car with 90-93(whatever they have in your area) octane gas. You should not advance your timing with low octane fuel because it will ping and that's bad.
Step 3 - Loosen the 3, 12mm bolts that hold the distributor in place. Don't remove them, just loosen them so you can rotate the distributor. Now, turn the distributor all the way towards the firewall, which is full advance. Tighten the 3 bolts and start the car. Drive the car down the street and make a full throttle pass(in any gear, doesn't matter what rpm or speed, just be at full throttle). If the car pings, immediately back off the throttle and pull the car over. When testing this, I always keep the tools in the car so I can adjust the timing without having to drive to the garage a zillion times. Now turn the distributor back towards the front of the car 1mm(1mm=~1degree). Tighten the bolts and do another full throttle pass. If the car pings, stop and move the distributor back another 1mm. Keep turning back the distributor 1mm at a time until the car stops pinging(doing a full throttle pass after each adjustment). Once the car stops pinging, you're done! You should be able to advance your timing 3-4 degrees(3-4mm) at least without having to worry about the car pinging.
Sway bar Mod
No, this isn't an engine mod. If you have lowered your car with lowering springs, remove the front sway bar. Honda puts a huge front sway bar on the cars to prevent over steer, so millions of old ladies with no idea of how to control a sideways car won't wreck and sue Honda. The sway bar dramatically stiffens up the front end which reduces front wheel traction(ie. steering). More front traction means more steering. If you have more steering you can go faster into corners and still have the ability to turn. SO basically, your car will handle a ton better. On a stock car this also helps reduce body roll, that why I recommend that you do it to a lowered car which has significantly less body roll than a stock height car. I removed the sway bar on a friend's stock height 94 Prelude and it had so much body roll it was scary at times. The car was a lot more unstable at high speeds also. However on my car(which had race springs) and Chris's 90Si(which has lowering springs/struts) the handling was improved a ton. So if you lowered your car, take the front sway bar and all the hardware off and throw it in a corner of your garage. Then take your car to an open track event or autocross and rail on it around a few corners and if you know how to drive, you will see a difference, big time. You have to push the car to it's limit to notice the difference. If you're a wuss and you don't push the car you won't notice anything. I took mine off and never put if back on. Around low speed sharp corners I've had my 92 totally sideways before, that's how much steering it has. To remove the sway bar you need to jack up the car, put it on jack stands and remove both front wheels. There are two 12mm bolts attaching the mounts to the car, then there are two 12mm nuts attaching the sway bar to the front suspension. There won't be any tension on the bar and it pulls out over the exhaust down pipe.
Dust shield Mod
1. Remove your front wheels.
2. Remove the front calipers and rotors.
3. There are a few phillips head screws holding the dust shields on, take out these screws. Now however you can(might take a dremel or a hacksaw), cut the dust shield so you can remove it.
4. Take the dust shields and throw them in the trash can.
With the wheel on, the dust shield not only shields dust away, but it also blocks off all the airflow to the brakes from inside the wheel and wheel well. Yes, it might be a good thing if you drive through sand(even most Pro Rally cars have the dust shields removed!) all day, dust shields are worthless. Try to stay out of puddles if they are heated to prevent warping. Get more air to those brakes, remove those dust shields!
Hope some of those helped you out, and remember, all of the above references are from, http://members.tripod.com/%7EPre_ludE/pmods.html, www.92lude.com, and www.preludecrazy.com
Quote from BrandonPool21-
Keep in mind guys, these mods are just that... mods.* Some are what we know for sure and some are from sites and other people.* Do NOT attempt to do these modifications if you are unsure of your abilities.* We will not be responsible for errors caused to your vehicle.* Just be safe and ask questions and everything is cool. 8-)