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 Modificaitions for an SOHC engine

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Number of posts : 125
Registration date : 2006-10-17

PostSubject: Modificaitions for an SOHC engine   Sat Nov 24 2007, 13:39

From a website

Intake: First things first. Enabling the engine to breath; after all,
engines are nothing but big air pumps. To start off, we look at the
filter and piping. Cold Air Intakes (CAI) although some assume just
relocate the air filter into the front bumper, are actually
acoustically tuned to the engines they are made for and allow for a
rather comfortable bump in the mid-range horsepower. K20s (RSX-S for
this example) have been dynometer (dyno for short) proven at +20 whp
(wheel horsepower) with a CAI as apposed to the 5 whp with a "short
ram" design. There have been dyno sheets that show a 3" piping makes
great power (more air flow), the Integra Type R (ITR) CAI will fit on
Civics and is 3" unlike the EX CAI, which is 2.25".

Following the air flow we come to the throttle body. This is more
of a throttle response upgrade than a horsepower upgrade. UNLESS the
stock throttle body is too small to allow all the air the piston
chambers can pull in at wide open. Basically, adding a larger throttle
body allows you to be a "full throttle" faster because of the larger
volume of air. Any throttle body for an H series B series or D series
are interchangeable, with one catch; you need to pay attention to where
your IACV (idle air control valve) is. For example, the D16Y8 (96-00
EX) has different mounting points and uses a 2 wire IACV. On the
automatic, the IACV (which is a 3-wire) is mounted on the throttle body
and the manual has the IACV mounted on the back of the intake manifold.
The later model VTEC B series and B20 (CRV) throttle bodies are all
60mm in size. Except for the ITR, this is 62mm. The H22 is also a 60mm
throttle body, while the Civic gets a puny 56mm. Make sure when you add
the larger throttle body that you port match (make the holes the same
size) the opening of the intake manifold.

Next in line is the intake manifold. For those of you who want OEM,
you want the D16Y8, often referred to as the Type R manifold for the D
series. It has short, fat runners and a large chamber to allow the air
to distribute to each cylinder properly. The Y8 IM has the common
horizontal throttle body, which will allow you to use the larger CAIs.
Here is a link Courtesy of VTC_CiViC with a complete how-to:
NOTE: This will not work for the D17's. Honda had the bright idea to
make it a return-less fuel system. Recent research has developed
aftermarket IMs for the N/A SOHC. Edelbrock is at the top of the list
on this one. Not only does it fit better than the Skunk2. You do not
have to raise the fuel pressure to get more power on the Edelbrock IM
like you do have to with the Skunk2 IM. Lastly, there has been a recent
interest in taking motorcycle Individual Throttle Bodies and attaching
them to an OEM intake manifold cut at the runners. Find an example at

In my personal experiences, I had a AEM short ram intake when I was
asked by Edelbrock to test out their Intake Manifold. So I needed a
before dyno. With a AEM short ram, DC 4-2-1 header and a 2.5" Cat-back:
The D16Y8 put down 116whp. Once we had the Edelbrock Intake Manifold
installed, peak horsepower jumped to 121whp, with the only loss in
power being 2whp just before VTEC crossover. Once that was completed,
the car was loaned to AEM for design and fitment of a CAI. After a week
of research, the CAI was designed and not only did it add 10whp with
the "AEM HUMP" (a term used for the mid-range increase in HP) but added
another 5whp overall! This brought the total to 126whp! To put this
into perspective, a stock Civic EX puts down 109whp.

Exhaust: Lets start off with the exhaust manifold (header). There
is no OEM exhaust manifold out there that doesn't need work. But, for
those of you who want to stay naturally aspirated (or don't have the
money for a turbo) a used aftermarket manifold for the EX is where you
want to go. There are a lot of people out there who by the time they
can swap have already put a header on there D series and now need to
sell it. You will have to relocate your catalytic converter under the
car to use this header configuration (which happens to be illegal in
some states). There are two different designs for a header. The 4-2-1
(or Tri-Y) and the 4-1. It is said that the 4-1 costs you low-end
torque to give you more power up top. However, if you follow this link http://www.automotiveperforman....html
you will see that some 4-1's have better low and mid then the 4-2-1.
Header designs on stock engines are so good that this is more a
preference thing until you start building. One advantage of the
two-piece 4-2-1 is that you can remove the lower half when you need to
pull the oil pan, instead of pulling the entire header. There are some
new designs for the SOHC headers as well, they are all well designed
but also tested and designed for built engines. I suggest speaking to
each company and seeing what the recommend before deciding. Bisimoto is
one of these designs. Available through
The HF (all Civics other than the EX and SI) exhaust manifold can be
modified to add a turbo. Then you don"t need to spend the extra money
on a turbo manifold. See for more information.

Following the exhaust stream out, we come to the Catalytic converter.
Unless yours is old, don't worry about it. For those of you who can
afford to upgrade the cat, tests have shown that a 3" free flowing cat
has almost flown as much air as a 3" test pipe. In fact some people
were shocked at how well a free flowing cat works (and it's legal but
only on OBDI vehicles). Or go with the $10.00 test pipe from Home Depot
(NOTE: Test pipes are not smog legal and you face a $3,000 fine).
That's right, people have even made there own test pipes with minimalMini Fahrertraining
Ready for MINI? Mitmachen und
gewinnen! effort.

After the catalytic converter, is the Cat-back. Most people recommend
using a 2.25" sized exhaust for the little 1.6L. And a lot of the
aftermarket exhausts are 60mm or 2.3 inches. I believe that you should
actually use no less than 2.5 inch. My dyno results proved that it adds
more power than the 2.25 and I gained another 1 whp throughout the
power band when I removed the silencer from the muffler. But, you also
want to make sure you get mandrel bent piping and straight through
designs on both the resonator (if you have one) and the muffler. If you
don't get the straight through designs, you will loose power, it's that
simple. However, with straight through designs also comes sound volume.
A good compromise has is an exhaust that comes with a silencer. You can
remove them for track days and leave them in for daily driving, as
stated before, only losing about 1whp on a stock engine.

Transmission/Flywheel/Clutch: Remember this, the shorter the gears the
better. It is easier for the engine to push/pull the car. MistaBone's
link: MistaBone's trannies The VTEC engines have always had the
shortest gears and it is a "bolt on" part. The 96-00 transmissions will
bolt on a 92-95 Civic. One small thing to consider is that the 96-00
transmissions have steel shifter forks instead of the aluminum forks
that are in the 92-95 transmissions. For you cable transmission guys,
there are the Hasport kits that convert your Cable to Hydro. And, SSR
offers a 4.7 and 4.9 Final drive for the D series Hydro transmissions.
HX/VX/CX owners, upgrading the transmission should be the first thing
you do, this is a HUGE difference. Once you get the shorter geared
transmission or already have one, a limited slip differential is the
second biggest thing to have on a D series. The performance improvement
is profound. I recommend Quaife because it has gears, not a clutch and
it comes with an unlimited lifetime warranty. A lighter flywheel is
also a recommendation. Not only do they increase throttle response,
they "free up" horsepower by decreasing rotational mass. (Just like the
whole argument of reducing wheel weight that goes around on H-T
constantly) The aftermarket offers weights varying from 8.5 to 15 lbs.
You can shave your existing flywheel to no less than 13 lbs. However,
this is a controversial issue and if you search will discover how
everyone feels about it and the dangers that can come with it. The
clutch, although capable of handling up the 12psi of boost, should be
replaced if you are considering more than 125whp. Many people have
suggested that a Clutchmasters or ACT clutch is the way to go.

Engine: Well, where the hell do we start? The motor mounts all have
gaps in them. has inexpensive polyurethane mounts. And the
mounts that they don"t make you can go to and get the rest.
Okay, now that you got that sucker still, lets increase some power. On
a naturally aspirated engine there are # things you can do.
1. Increase the compression

2. Increase the displacement by bore (size of pistons) or stroke (crank)

3. Add more aggressive cams or cam for the SOHC.

One way to up the compression is to mill the head. It is very important
for you to not remove more than .03. If you do, you risk timing issues
because the timing belt is going to have slack and you will risk
jumping teeth on either the cam gear or the crank and your timing will
get screwed up. You can also get thinner head gaskets, the Y8 is cheap
and is the thinnest metal OEM head gasket that you can get. Now that we
have covered some inexpensive increases, let us move on to pistons. The
1988-1989 D16A1 Engine came with some really high dome pistons, they
will increase your compression ratio as follows:

d16a1 pistons (stock bore) in the following with a y8/z6 metal head gasket (no mill):

d16a6= 11.0: 1 compression

d16z6= 12.0: 1 compression

d16y8= 12.6: 1 compression

Obviously high compression and you 91 octane folks should consider
a thicker head gasket. However, 12.5:1 can be driven daily on 92
octane. Since you have decided to open that sucker and upgrade the
pistons you should also consider upgrading your rods. Whether you
decide to shot-peen your stock rods or upgrade to some LS rods, it's up
to you.
The LS rods can fit a D series piston simple by removing a little
material from the inside of the piston. When upgrading these, you
should consider new OEM bearings and ARP rod bolts. Strength is always
a comfort, right? The head is what traps all of the power in any
engine. Be it naturally aspirated (N/A), nitrous injected,
supercharged, turbocharged or all three. It has the valves that allow
the air in and out of the combustion chamber and the cam that opens and
closes the valves. Porting is the process of removing material to make
the holes for the valves larger to allow more air even if you use the
stock cam. But, within the head you have all of these moving parts that
rub against each other, even with oil there is friction. To reduce
friction, you can get bronze valve guides, coated valves, and rollerSCOOTER CENTER Onlineshop
Roller - Tuning - Teile
rockers. Roller rockers are cam followers that have wheels instead of a
contact point. They greatly reduce friction and, the D16Y5 (HX) has
them! Unfortunately, it only has a 2-lobe cam instead of a 3-lobe cam.
Again another crazy topic that has been discussed a few times. Still
with a custom cam, This VTEC-E head could theoretically produce more
power than the D16Y8 VTEC head ever could. Since the rollers would
allow for a cam lobe so aggressive that the regular followers would
fail. Adjusting the cam with a cam gear can also change your power band
to what best suits your driving, some drive easy, some drive hard every
now and then, and some visit 6800 with every stop light and every
shift. Well, almost. Remember, an engine is an air pump, the more air
it moves the stronger it is. And the best way to move air is to open
the valves really high (lift) for a long time (duration). A good
quality camshaft maker is Crower, my personal choice. There is also,
Zex (comp cams), Crane, and Skunk2. Some companies that make regrinds
are Hondasaver and Gude. I personally don't like regrinds. They were
stock cams that had material added then reground off.

If you decide that you want to build a monster engine, the D16Z6 head
has the best design for port flow. The ports are straight and easy to
work on. The only draw back to the Z6 head is the combustion chamber,
but there is a solution. You can have material welded into the chamber
to not only increase resistance to detonation but also increase your
compression ratio by decreasing cylinder head volume. Again, refer to for combustion chamber work.

Cooling: Hey, in case you didn't know, heat kills. Keeping your engine
cool is not just the radiators job though. The water pump, thermostat,
your coolant/water mix, and even the radiator cap affect your ability
to cool the engine. If you change one you affect the whole system.
Radiator caps pressurize the coolant to raise the boiling point (good)
but, if you over-pressurize; the radiator could fail because of the
plastic tanks on the sides.

There are two radiators that you can use for the Civic; there is
the Del Sol, which is a dual core. Or it has two cooling cores, one in
front of the other. And the other is the Integra. You have to make
custom mounts but you will have your needed cooling for sure. Or you
can purchase an aluminum aftermarket radiator that is a very efficient.

For you track guys, since antifreeze isn't allowed, there is a product
called water wetter. You mix this and water, no coolant. It is
discussed in the racing forum if you haven't been over there. DON'T use
this on the street. Antifreeze does exactly that, when water freezes,
it expands and will crack your block, radiator and head. You've been

Fuel/Spark/ECU: Fuel isn't as easy as we all would wish; a fuel
pressure regulator (FPR) isn't necessarily a good thing. Too much fuel
can cost power, and forcing your injectors to flow more than what they
were made for can hurt them as well. I personally believe that you
should upgrade the system as a whole, injectors, fuel pump and
regulator. The stock Civic (other than 99-00SI) and Integra LS fuel
pumps only flow 79lph and the SI, GSR, Type R flow 135lph. In fuel tuningD&W Tuning
Europas größter Online-Shop für
sportliches Autozubehör.,
the DOHC ECUs, can feed more fuel than needed as well. The best way to
figure the needed fuel out is to tune on a dyno that also has the
capability of reading your air to fuel ratio. Whether you're using a
FPR or a fuel controller. Apexi makes a VAFC or VTEC Air Fuel
Controller. This allows you to adjust your fuel amounts in the RPM
range. These are good but there is something better, Hondata. That's
right, Honda is in Hondata, and they are making great amounts of power
on the SOHCs. Supplying fuel is just one part though. You have to
ignite it. Fortunately, Honda made a great ignition system right out of
the box. And Erik's Racing proved this by using an OEM ignition in
their 10,000RPM 9 second Civic.
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