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What is RS |
The RS is the ultimate factory Civic.
Dubbed Road Sailing, it was a more performance
oriented civic opposed to the standard economy-boxes we all know. It was released with an
1170cc EB1 motor pumping out 70hp compared to the 50hp of the standard model. Engine
modifications included twin Keihin carburetors, a freer flowing exhaust manifold, longer
duration cam (15 degrees), domed pistons (bumped compression up to 8.6:1), and
strengthened crank bearings. Handling was increased with a set of stiffer springs (30%),
shorter stiffer struts and 13" wheels wrapped in 155-80-13 tires. The wheels were
black with a polished lip and had a red "H" center cap- this is where the red
Honda "H" started. Besides the RS badge on the front grill other exterior
options included flared fenders, fender mounted rearview mirrors, and a slightly different
bumper assembly. The RS's were only released in warm red/orange paint schemes. The
predominantly black vinyl interior included a wooden steering wheel and shift knob, center
console, grab handles, a mechanical tachometer graded to 7k rpm, and a center auxiliary pod with
fuel/temp gauges and an air vent. The US gauge pods merely had the gauges for fuel and
temp.
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RS Owners
The RS head was also different from the standard EB1. The
combustion chamber was deeper, which allowed larger valves to be fitted.
The pistons where domed to make up for the increased combustion volume in
the head.
Along with larger valves, the head had larger ports. If you've every seen
the original Honda inlet & exhaust gaskets on the standard head, you would
have seen that the holes in the gaskets for the ports
where a few millimeters bigger than the ports on the standard head. This
is the port size on the RS & GL engines.
Which leads me to the EB1 engine in the GL model.
This basically the RS engine but with a down-draught carburetor. In this
case, it was a different inlet manifold to standard (larger diameter
runners to the ports) with a much larger down draught carburetor. This
carburetor was also used on Datsun 1600 engines, so parts were much easier
to find (back then) than for the side draught Kehin-Seki. The GL had
slightly less power than the RS, but still made for a very fun Civic.
Back to pistons, using the RS pistons with a standard EB1 head gave a
compression ratio around 11:1. I had an engine built like this, with a
head that had been ported and had larger valves, I believe, from a Coupe
9. What a blast that engine was, but it would ping horribly below 3000
rpm. Had done around 140,000 MILES before it died, piston cracked from too
much pinging
Any way, hope some of this history is useful.
Regards,
Murray. |
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Year/Model
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Motor
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CC
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Bore
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Stroke
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HP
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Torque
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Compression
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74-75 Civic RS
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SB1
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1169
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70mm
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76mm
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76
@ 6k
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10.3/4,000 (kg-m/rpm)
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8.6
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RS Camshaft Specs.
Source Archives
Valve timing
( Cam spec )
Intake open
ATDC 10
ATDC 10
ATDC 5
degrees @ 1mm lift
Intake close
ABDC 20
ABDC 30
ABDC 30
degrees @ 1mm lift
Exhaust open
BBDC 30
BBDC 40
BBDC 40
degrees @ 1mm lift
Exhaust close
BTDC 10
BTDC 10
BTDC 5
degrees @ 1mm lift
Max valve lift
8.4 mm
---------------------------------------------------------------------------------
Cam: stock height(IN-36.7mm, EX-36.6mm) and 15 degrees longer than
standard.
max. valve lift: 8.6mm
Honda cam spec is always defined at 1.0 mm valve lift
INTAKE- open: 5 ATDC
close: 30 ABDC
EXHAUST- open: 40 BBDC
close: 5 BTDC
The RS cam has the stock lift, and about 15 degrees more duration than
stock. You don't really need to pay much attention to specs unless you
really know a lot about camshafts. Depending on how they're measured,
different cams can seem comparable when in actuality, they're not. What
you need to find out is how the cams affect the engine. The RS cam is a
good performer from idle to about 6500 rpm. It has a smooth idle and picks
up well. The #68 cam is good for 3200-7000 rpm. It idles a little lumpy
but not too bad for the street. from 0 to 3200 it is not as quick as the
RS, but it makes up for it on the top end. With an adjustable pulley,
small diameter tires, and the 4.93 differential, you won't even notice the
short comings of the lower rpm.
Finding an RS cam will be hard. It is basically
a stock lift cam with more duration. Made 68 hp on the stock RS. It has
power from idle to about 6500-7000 rpm. The Mugen R1 can be bought from
Racecraft. (www.users.bigpond.com/Racecraft) I think they weld up and
regrind your cam. I have never used this cam but it is supposed to be a
really good grind. No idea about power. The Webcam can be bought from
Webcaminc.com. They can provide a new cam or can regrind yours (makes the
base circle smaller requiring lash caps). Power starts at about 3500 and
pulls strongly to about 7000. Mine makes about 90-95 HP. Very lumpy idle.
I recently found Elgin cams has about 6 grinds available for 8 valve
Hondas. Never tried them, but it might be worth a look.
Todd |
RS Cams and Springs
Here’s some more cam specs from Tsuyoshi Hasshan. I'm not
sure of his source or how accurate they are.
Valve timing at 1mm lift (net)
Mugen R1( we call MS-1) : btdc 10 - abdc 40 / bbdc 40 - atdc 10
Yoshimura: btdc 15 - abdc 45 / bbdc 45 - atdc 15
(Mugen MS-2: btdc 25 - abdc 55 degrees with more lift.)
It’s sort of funny talking Web Camshafts (http://www.webcamshafts.com/pages/honda-auto.html#1)
and Mugen cam grinds.... as Web basically copied what Mugen was doing at
that time, with slight lobe changes and those grinds haven't changed since
the 70's. I have an original Mugen MS1 Camshaft and the power is pretty
much in the same range that Todd described for the Web Grind with the same
results. RaceCraft is no longer and wasn't the source anyway.
Colt Cams Is also a good choice.
http://www.coltcams.com/ I have used them, and while some of their 1.2
cams are old standbys -they will grind custom stuff too. He does have a
grind that's almost spec for spec for a RS grind (using an early prelude
cam lobe design I seem to remember) that idles fairly smooth and kicks HP
up in the 6500 range too.
With D. Elgin cams you will get a much more personalized service if you
fill out the cam forms and their cam designs seem to have kept up with the
times better.
http://elgincams.com/ A few members here have had cams ground
including myself (not Honda for me though) and been very happy with the
results. There may be HP to be gained in a custom cam design over the
older ones, especially for competition use.
Web Camshafts has no new cam blanks last time I checked. Blanks or a hard
welded stock cam are required on some really big cam grinds, probably not
something you would want to run on a hot street Civic anyway. The
aftermarket blanks are sometimes made of softer metal and like to eat the
oil pump gear if used for lots of miles. (Two cam grinders have told me
this; I have not experienced it myself)
Some mild regrinds can get by with stock springs if they are in good
shape. RD Springs in Ca. Used to carry good springs for the 1.2 -BUT The
last time I checked they must have some new people, they Suck now and can
seem to find the correct springs for a 1.2, but want to sell you some
cruddy things. Isky Cams also list springs but if you look at how many
shims are required.... can you say Mickey Mouse.
I did find what ended up working very well for me.
http://www.schneidercams.com/parts/springs.htm
Schneider Racing Cams # 68018 Fits the early Eb1-2, "S" head, standard
valve spring retainers perfectly and the pressure was what I was looking
for. They are V-tec springs. Now I did not get them directly from
Schneider so check the measurements very carefully and consult your engine
machinist and measure everything related if in doubt.
Don |
RS Civic close ratio gearbox
First gear 3.00 Teeth 39 - 13
Second gear 1.79 34 - 19
Third gear 1.18 26 - 22
Fourth gear .85 22 - 26
Fifth gear .71 20 - 28
Diff 4.73 71 - 15
Close ratio gearboxes use different combinations of gears to keep the
engine within its power band throughout the racing. With a close ratio
gearbox, when you shift from 2nd to 3rd your engine doesn't drop down to
such a low RPM. By keeping the engine turning within its power band, you
can maintain constant acceleration throughout the course of the race.
Drawbacks of close ratio gear box? Since your close ratio gearbox reduces
the amount of RPM drop between gears, it also reduces the overall span of
speed you can ride in the same RPM range. Depending on the final drive
ratio, you may find that you can't cruise at 60 anymore, or that you can't
take off as easily from a dead stop. Such are the trade-offs. You wanted
to race, didn't you? Or did you want to cruise? One set of gears can be a
compromise between both worlds, but no set can give you the best
performance on the track and on the street. |
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