I need someone who has an in depth knowledg of the H23 motor to answer some questions about mods that I found on a web site. They seem a little out of the ordinary.

I can e-mail the list of mods to anyone that wants to see them. But I really need some one to look at them and tell me what they think.


[Modified by PreludeSi, 4:10 AM 2/1/2002]

 

why not post them on the board? thats what its here for...

 

Here it is:

Engine Mods
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Have you ever wondered what you can do to your stock engine to make it faster? Due to the amount of factory emissions equipment, your stock engine is severly restricted in many ways. Fortunately there are a few minor things you can do to free up some extra hp, which involves modifying the emissions equipment. But, since everyone who reads this page only races their car on race tracks and never drives on the street, it's ok. I don't warranty any of these mods so if you screw something up cuz you don't know what you're doing, then that is your fault and you are 100% responsible, not me. What are the chances of screwing something up? About one in 200 million, but I had to say that cuz sooner or later some idiot will remove the timing belt instead of the power steering belt which will bend all the valves and $2000 later his angry redneck dad will be at my doorstep with a chainsaw threatening me. But I did all these mods to my 92 and 50,000 RACING miles later everything was fine. Enough of the bullpoo poo, have fun!

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 rpms, 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 diaphram that controls the opening and closing. The diapram has a vacuum line running to it and at 4800 where there is enough vacuum pressure, the diaphram 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 diaphram 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 diaphram. Now the flapper valves will always be open at all rpms. 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(attatched 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 recirculation 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 conntected to the engine) and recirculated 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 suppoed 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. Bacically the EGR has a plug, a vacuum tube, and two bolts holding it down. Unbolt the EGR and unplug everything attatched.
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 airbox removed - 17.4@80mph
With airbox removed and fpr mod - 17.0@80.5mph
Stock 95 Del Sol Si(SOHC VTEC, 125hp)
Airbox removed, timing advanced, adjusted tire pressure - 16.0@87mph
Airbox 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 diaphram. Don't mistake with the flapper valve diaphram, the fuel pressure regulator is the smaller gold diaphram 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.

Step 1 - Find the distributor. Look in the picture and see where the distributor attatches 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 razort blade, whatever, and make a mark that goes across the distributor onto the cylinder head so when you move the distributor, the mark seperates 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 withouth having to worry about the car pinging.
Coolant Bypass Mod
Just about every stock car has a feature called the cold start valve. The cold start valve is located on the bottom of the throttle body and it has two lines that run into it, one in and one out. The lines transfer coolant which in a cold start situation, helps warm up the engine faster by warming up the air in the throttle body via-coolant. In a cold climate(one that has regular temps below freezing) it has a purpose, but in summer months or a climate that doesn't have a winter of freezing temps, the cold start valve hurts hp because hot air is bad air. So you have two lines to modify:
1. The coolant line coming out of the block into the cold start valve, and
2. The coolant line coming out of the cold start valve and back into the block.
The mod is simple: Bypass the valve by running line #1 where line #2 connects back into the block. Now you have coolant going out of the block and back into the block, which is essentially what it did before, but it doesn't go through the throttle body which drstically reduces air temps in the intake manifold. This whole cold start valve is just for warming up a very cold car, but it's not needed in a hot climate. V8 guys have been doing this for years in F-Bodies and Mustangs with all kinds of success. The idle may change, but again, that's life. People have reported up to 8hp at the wheels with this mod alone.

The yellow line(it's black on a stock car) is the line that goes into the throttle body. Now find the line that goes out of the throttle body(it's kinda under the Tbody, sorry i don't have a better picture) and remove it entirely. Be sure to do this when the car is cold!! A little bit of coolant will pour out and if the car is hot there will be a lot of built up pressure and you'll get hot coolant everywhere(probably in your face). Disconnect line #1 from the throttle body and connect it into the block, where line #2 used to connect to the block. Now you're done!
Injector Mod
A while back when I first got my car, I was fiddling around trying to find all the stock parts I could modify for little or no money. I took out my injectors to see if there was a way to modify them and indeed there was. I was looking for something internal, but I found something a little easier. There is a small filter located in the top of the injector that's supposed to filter out any last little particles that could get inside the engine. Well I wanted an extra edge so I removed the filters to get a few extra cc's of fuel. The filter is an orange cylinder with three "sides", each side having a small screen which acts as a filter. So take the cylinder filter out of the injector(just lifts out) and get a razor and cut out the small screens. It sounds complicated, but once you remove the injector you will see how it works and what the screen looks like. But isn't this a stupid idea?? Sure, it sounds like one. However, I removed the injectors when my car has 65,000 miles and there were NO particles or any kind of debris in the injector filters. I figured that I will take the chance because the car went so long and the filters were still brand new and if something did happen(the worst thing that can happen is a small particle getting into the injector and partially clogging the flow, if that. gasoline will dissapate just about anything), I could use it as an excuse to get the injectors blueprinted. Well I drove the car for another 50,000 miles with no problems at all. I ran a bottle of injector cleaner through the tank every few months which might have helped, but it was more of a superstitious thing. I then sent the injectors out to RC Engineering to get blueprinted(something I had planned on doing anyways) and they said the injectors were clean as a whistle. So if you want some extra fuel, remove the injector filters. I did it and had no problems whatsoever. To remove the injectors you will have to remove the 3, 10mm nuts holding down the fuel rail. Lift up the fuel rail and you'll see the injectors and the orange filters located on top of them. The filters lift out and you can begin modification. As it turns out, several of the major Honda tuners in the Phoenix area have been doing this mod with turbocharged cars to get extra fuel flow. I know of 4-5 cars that have done this and no problems have been reported.
Airbox mod
The stock airbox is a mess of crap that's designed to be quiet. Who want's quiet?? The stock intake system consists of an airbox and a resonator inside the right front wheel well. Here are a few simple steps to make your stock airbox a little better(ie. add more horspower to your airbox!).
1. Remove the airbox(held in my 10mm screws) and set it on the ground.
2. Remove your right front wheel and right front plastic fender liner. Remove the right side turn signal light also(on the bumper).
3. Remove the square black plastic resonator inside the wheel well. It's held in by a few 10mm bolts. I think one of them is accessible through the turn signal hole, that's why you remove the turn signal light. I'm not positive, but that's what I heard(I removed mine when I had the bumper off).
4. There is a vacuum line connected to a butterfly valve. Disconnect it and plug it with a golf tee. You can also pull the line through from inside the engine bay and follow it all the way to where it connects to the intake manifold. If I had a choice, I'd disconnect the line from the manifold cuz you remove 3 feet of useless tubing. Get a vacuum tube cap and cap off the outlet on the manifold(you can buy the caps at any parts store).
5. Take your airbox and remove the filter. Get a hacksaw and cut the entire bottom off the airbox. Make sure you don't cut it too high so the filter doesn't fit in, but cut as much off the bottom as you can so the filter gets as much air as possible. Now you have two choices: 1. Put the stock filter back in, or 2. Get a K&N replacement filter. I don't know the part number so don't ask. K&N has a website and I'm sure it's listed on there.
6. Now assemble everything and you're set! The hole where the resonator went will allow 10 times more air into the filter and since you have a huge hole in the airbox, you'll get way more air into the intake.
Crankcase Filter Mod

Ignore the blue circle in the picture. Notice how there is a filter on the valve cover and a filter on the intake pipe? From the factory there is a tube that connects the valve cover to the intake manifold. Again, hot air is bad air. Remove the line connecting the pipe to the valve cover. You have to put a filter on the valve cover side, as shown in the picture. As for the intake side, you can either put a filter on it or cap it off.
Swaybar Mod
No, this isn't an engine mod. If you have lowered your car with lowering springs, remove the front swaybar. Honda puts a huge front swaybar on the cars to prevent oversteer, 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 reccomend 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 swaybar you need to jack up the car, put it on jackstands and remove both front wheels. There are two 12mm bolts attatching the mounts to the car, then there are two 12mm nuts attatching the swaybar to the front suspension. There won't be any tension on the bar and it pulls out over the exhaust downpipe.
Dustshield 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 dustshield so you can remove it.
4. Take the dustshields and throw them in the trash can.
With the wheel on, the dustshield 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 dustshields removed!) all day, dustshields are worthless. Get more air to those brakes, remove those dustshields!

Please post serious comments.


[Modified by PreludeSi, 4:40 AM 2/1/2002]

 

Yeah, the only one I think is worthwhile is removing the resononator box and remounting the flapper valve that controls the intake runners.

 

the FPR one isnt worth it?

 

I have already removed the resonator box and I have tried the flapper valve before but I lost too much bottom end power so I changed it back.

I was thinking that the FRP mod would hurt more than help.

 

end up running way to rich?