If it seems too good to be true, it probably is. But it can still be pretty darned good.
I first heard about Hans Pedersen's blower kits, years ago and would periodically go to his website http://www.hi-flow.com and wish and dream about getting one. I had heard such wonderful things as "it only took four hours to install", "it nearly doubled the power", and "if I keep my foot out of it, my mileage actually improved by nearly 30%. The first two are likely true for a Rubber Bumper MGB (though that would leave the problem of passing smog tests with a non-certified carburetion system on post 1973 cars in California).
In retrospect, I'd summarize the project as "for about the price of a used Miata, you can make your MGB accelerate about like a used Miata". In raw performace numbers, a Rubber Bumper B puts about 50 hp to the ground. A typical Chrome Bumper B will put about 65 hp to the ground, the previous incarnation of my motor put about 75 hp to the ground and with the blower, it puts about 100hp to the ground, and it seems to be limited on streetgas primarily by predetonation.
Translating this to laptimes, at Thunderhill, running the three mile course on the naturally aspirated motor, I would turn very close to a 2:30 running either the "cyclone" or the bypass. On my first visit back to the track, after not having driven on a race course for nearly a year and a half, I turned a little better than a 2:23 running the bypass.
When the does settles, it probably costs about as much from "ground zero" to buy an MGB and fit it with a supercharger as it does to buy a used Miata and build it into a Spec Miata. The Spec Miata will be faster, and will be competitive in it's race class. On the other hand, complete strangers will come up to the owner of the MG to talk about what cool cars they are. And even if the blower didn't increase the power of the engine at all, motorheads would still be impressed by it just on the coolness factor.
BEFORE YOU BEGIN:
It is possible to take the kit, and just bolt it on to your motor. If you have a late model (Rubber Bumper) MGB, this should take about an afternoon. On the other hand, you are dramatically increasing the power output of the motor, and it is probably worth thinking about what other things you will want to do to the car in the process.
Not only will the engine develop more torque, adding stress to the motor, but chances are that if you are the sort of person to throw nearly the value (or possibly more than the value of the car) of a car into increasing it's horsepower, not only will you have more power, but you'll use more of it more often. Trust me, a 130hp MGB is a lot of fun to drive. Especially if your commute to work is on twisty roads through the Santa Cruz Mountains or if you find yourself on a racetrack, no longer having the Miatas just walk away from you down the straights.
The first class of modifications are those inside the motor. You will want the motor to be able to handle the extra power without developing a case of "light seeking rods". One benefit of getting power via supercharging is that you get the power at by 6000 RPM rather than having to wind the motor out to 8000. I'm hoping that this will help alleviate the stresses from a thirty percent gain in torque.
Articles, actually books, could be written on just the subject of building a motor for strength. Hans actually reccomends building the motor for reliability, rather than trying to get the last few horsepower out of the motor. There are many things that can, and should be done; balancing, nitriding, line boring, surfacing and so forth. You want to make sure that your oil supply is good, you may want to consider a baffled oil pan and/or an Accusump. You may want to spend a little bit extra on ARP bolts for holding all the stressed parts together. I discovered that Venolia forged pistons did not cost much more than a lot of the cast pistons.
You will also want to make sure that your motor is built in such a way as to prevent predetonation. I have had a couple of expensive lessons over the years in how much damage predetonation can do to a motor, and adding a blower will push you close to the edges of the envelope. First of all, you will want to run lower compression pistons (probably about 8.0:1), though I've heard of folks getting away with as high as 8.4:1 on street gas. One major mistake that I made was not measuring the volume of the combustion chamber in my cylinder head. I foolishly figured "it's stock, I don't have to worry", but I've later learned that the volume on the stock heads varied quite a bit from year to year. Likewise, the choice of the cam profile can make a big difference. The cam grind I have works great on a naturally aspirated motor and is optimized for the 3000-4000 RPM range. Guess where I've been having most of my problems with predetonation?
The way that a car makes power is by burning gasoline, or petrol if you prefer. By forcing more air into the motor the blower allows the car to burn more gasoline. Burning gasoline produces heat, if you burn more, you make more heat. Do you see where I'm going? If you do something to get your car to produce more power, it's going to produce more heat. Cooling systems usually work fine up until the point that they suddenly can't keep up anymore. That is why a car might run nice and cool up to an ambient temperature of 90F, but when it hits 95F all of a sudden you have lots of problems with overheating. Invest money in upgrading your radiator as much as you can get away with. I'm running four rows in mine, and they are closer spaced than the original. Even on the track (granted at ambient temperatures in the sixties) the highest temperature I've seen was 210F, I'd usually see about 200F during the middle of the session. With the 190F thermostat the temperature normally varies between 180 and 200 anyways.
In order to run the blower, you will need to get the pipe for the lower hose repositioned. It's not too expensive, and while you are there, I highly reccomend getting a valve added to the bottom of your radiotor so that you can drain your coolant into a tub rather than just disconnecting the lower hose and making a mess all over the floor.
The kit also requires that you use the shorter (later) of the two
types of water pumps found on MGBs. If you have an early motor, you may
want to check on that.
Then there is the question of everything from the flywheel on back. Do you have a good clutch that will handle 30-50% more power? Are your u-joints in good condition? Your differential? On my last track weekend I stripped the splines out of one of the hubs that connects the halfshaft to the brakedrum and the wheel.
A car is more than just the engine, it is a complex system. There is a lot more to performance than how much power is produced at the flywheel. In addition to making sure that the whole driveline can handle the stress of more power, there is the question of getting the power to the ground. If you are running stock size tires you might start exploring wheelspin like a teenager in a musclecar. If you have wire wheels, they might not hold up well to the added stress that you find yourself putting on them. If you drive at the track, you might find a limited slip differential (the motorhead's LSD) much higher on your wishlist.
Then there is the question of once the car is much better at going forward, making it turn and stop. I run the Porterfield LD48-R4S pads on the street and have a set of the LD48-R4 for the track. I've also cut nine inch sections out of my front valence to improve airflow to the brakes.
The only suspension modifications I've made so far are a Ron Hopkinson swaybar kit (which does a fantastic job of making the car handle neutrally), and 30 wt forkoil in the shocks. I'm starting to shop around for heavier springs, tube shocks and various other, even more expensive toys, to make the car handle better.
After you've installed the supercharger, you will have the opportunity to learn tremendous amounts about the theory and practice of internal combustion engines if you decide to "dial it in" yourself to get the most power. You may want to invest in various guages and instruments such as Exhaust Gas Temperature guages and Oxygen sensors. More on this later, but to get the most out of each of them will require significant research and learning on your part.
INSTALLATION:
Before you begin your installation, read the directions. Then photocopy them and read them again. Make sure that you completely understand everything in them. Make notes on your photocopy. Try to make sure that you understand how the parts fit together. Then read the instructions again.
During the whole process of installing and dialing in the supercharger, I systematically made every mistake in the book. Some of these mistakes were caused by my being too clever, some of them were caused by my being too stupid, and many of them were caused by my misreading, or not correctly following the instructions.
Rather than repeating everything in the installation manual, I'll concentrate on the places where I had difficulty, or difficulty understanding it.
PREPARING THE MOTOR AND ENGINE COMPARTMENT:
For the purposes of this article, I will assume that the motor is in place. I pulled the motor to freshen the bearings, and was actually able to get the motor into place, with the steering rack in position, but it required an impressive amount of incremental adjustments on the hoist, using the leveler. I also installed a set of the extremely low restriction headers that HP sells, and found that mine would not fit between the engine and the frame, with the engine in position.
installing the blower
Adding timing marks to the motor
Making stepped washers for bolting on header and manifold
Mounting intake manifold and blower
In case you need to pull the unit off
Attaching the carb to the blower
Using a pin spanner to change the blower pulley
filling the blower lubricant resevoir
Rubbing on underside of the bonnet
I'm at that stage where I know just enough about what I'm doing to be dangerous. Most people buy the kit, bolt it on, and it just works. If I hadn't put so much thought into trying to fix the problems that I caused, I would not have had nearly so many problems. This project seems to be the one where I systematically make every stupid mistake in the book, learning all sorts of important lessons in the process. I'll chronicle some of the mistakes here that cost me time so that you don't have to make them. Mistakes that I made:
Mistake #1
Having heard that it only took a few hours to install the blower, I figured that I'd be able to run it with the blower most of the time, but if I wanted to enter a race, I'd revert back to the carbs. Don't even think of switching back and forth, it's not worth it.
As part of the scheme of switching back and forth, I kept my own custom cam. A grind by Dema Elgin that keeps the stock duration and lift, but steepens the ramps. What some might call a "cheater" cam as on nominal inspection it looks stock, but actually improves the breathing. The cam grind changes the breathing patterns of the engine, and therefore the jetting required. I get more charge in the cylinder in the midrange than a stock cam, which is good for naturally aspirated, but it pushes me closer to predetonation with the blower. I'm also now in "uncharted territory" on needle profiles. If I were doing it all over, I'd get one of Hans' cams that has been optimized for the application.
Mistake #2
I was hit by a combination of bad luck and utter stupidity on my part. I had finished getting the car running very late at night. Since there was no exhuast system aft of the header, I didn't run it much at that point as even living in a somewhat rural neighborhood I have too many neighbors within earshot of an MG running straightpipes to appreciate the sound at 2AM. I woke up early the next morning to take it to the muffler shop to get the rest of my exhaust system before driving to work. I did notice a very minor coolant leak where the lower radiator hose attached to the radiator, so I packed extra water and kept an eye on the temperature guage.
We had no problems on the drive down highway 9 from Felton to the muffler shop in Santa Cruz, though there was one person who obviously did not "share my taste in music". Nor did I have any problems on the drive home from the muffler shop. I kept an eye on the temperature guage and it always read well within the normal range. A little bit cool actually.
I decided to drive the car to work in Redwood City. Over the next few miles it was acting very strangely, like it was quite hot, despite the temperature guage reading at the low end of normal. It took a while, and several blown headgaskets to figure out all of the ramifications, but my tmeperature guage which had always read much lower than the previous one, was broken. I seriously overheated the motor and cracked the head.
Mistake #3
In the process of trying to get everything dialed in, I apparently ran the jet adjustment past the point where the adjusting screw meshed with the adjusting lever and popped the lever off the screw. Once they were no longer attached, turning the screw did not effect any change in the jet position.
Mistake #4
When fixing the carb after mistake #2, I did not keep everything absolutely sanitarily clean and got some dirt between the jet and the sleeve. The jet got jammed into position so that turning the mixture screw had no effect on the jet position.
Mistake #5
When trying to track down why I was blowing head gaskets, I bought a solid copper headgasket rather than using the Payen gasket. It flat out did not work. The car did not even come up to temperature before it blew.
Mistake #6
One evening after replacing a head gasket, I was having an incredibly difficult time getting the car to start. I just assumed that it had something to do with the carb or the headgasket and it took me way too long before I actually checked for condensation inside the distributor cap.
Mistake #7
When I prepped the car for the track, I ran a hose from the carb
breather to a catch tank shared with the carb vent and the crankcase
breather. Eventually enough oil and gunk accumulated to cover the end of
the carb vent hose. At which point the carb would not be able to suck
any gas from the float until the needle valve opened. The symptoms came
on gradually with the car leaning out in some weird low and mid power
situations, then suddenly coming back to life. It culminated with the
car dying as I pulled into a parking lot one night. When I tried to
leave, the car would fire up, run for a few second then die. I swapped
the fuel filter, allowing the float to vent, and the car ran fine for
20 or 30 seconds before it died. I figured it died because it was cold,
buttoned everything up and tried to drive off. It wasn't until the
next morning when I came back and cut a hole in the vent line near the
top of the catch tank that the car would actually run.
Mistake #8
In my installation, I could not install the header with the engine
in place, I had to loosen up the motor mounts and shift the motor to
the distibutor side to have enough room to install the header. Hans
says that this is not typical.
Tuning the car:
I will start with the caveat that as I write this, I still don't
have the car completely dialed in. I am also finding that the setup
that I'm ending up with is going to be very close to the setup that the
kit came with. However, as with any sojourn where you return to home,
it's not so much where you end up, but what you learn along the way.
Possibly the most important thing that I've learned is how much the
guys that do this professionally really know, and how little I do.
There are a couple of aspects of the carb that aren't immediately
obvious. First of all, the HIF does indeed have a lifting pin, for
checking mixture. It's near the airfilter on the intake manifold side
of the carb, where it's hard to get at. But don't worry, you probably
won't really use it that much anyways.
The other thing that is hard to find, is the screw for adjusting the
idle mixture. It is underneath the fuel inlet, and is hidden very
nicely by the inlet hose. You will need a small flat blade screwdriver
to adjust it.
In case you feel you need to know exactly where on the needle the jet is, I took some measurements on position versus number of turns of the adjustment screw. My measurements aren't perfectly accurate, and the action is not quite linear (there's some trigonometry involved when you push on one side of a lever and something else moves at right angles, but it works out to roughly 0.042" per turn:
turns dist
0.0 .000
0.5 .034
1.0 .048
1.5 .066
2.0 .089
2.5 .113
3.0 .124
3.5 .143
4.0 .159
Quantitative measurements:
The combination of a dynomometer and a gas analyzer is invaluable.
There is no better way to learn about a lot of the things that happen
with your motor, than being able to measure both the power output of
the motor, and the exhaust gases. The percentages of O2 and CO in the
exhaust will tell you what fuel air ratio you are running. The
amount of NO, can tell you if your car is predetonating. The
dynomometer will tell you if the change you made actually improved the
power output, or reduced it. Chasis, or rolling road, dynos don't even
require you to take the engine out of the car, and can also help you
check the accuracy of your speedometer, and the real ratio of MPH to
RPM in various gears. The only problem with a dyno, is that rental of
one costs $100 and hour and up. If you don't have experience with one,
you will need the assistance of someone who is an expert at tuning cars
on a dyno. Trust me on this, it's actually cheaper in the long run.
Whether or not you will have the assistance of a trained
professional when you do your dyno runs, I strongly reccomend that you
read the manual for the dyno. Not only will you better understand what
is going on, but you will learn more in the process, which you will be
able to use in other aspects of tuning.
Instrumenting your car:
Not only can spending time tuning your car on the dyno become
prohibitively expensive, but there are various conditions in day to day
driving that either are hard to duplicate on the dyno, or you don't
even realize are an issue unless you see them happening at the moment.
Traditionally, the way to see if your car, or any cylinder, is
running rich or lean is by measuring the Exhaust Gas Temperature, and
it can even sometimes tell you if the engine is predetonating. I have
not yet installed EGT probes on my car, so I cannot speak with much
authority on the subject. I have noticed that the air injection ports
on my cylinder head go almost directly to the exhaust valve, and for a
future project would like to set up some probes using these ports. My
preliminary research also points to "Aircraft Spruce"
http://www.aircraftspruce.com/ as having a good selection and
reasonable prices. They have even just recently come out with a catalog
for race cars.
Many years ago, Heathkit sold a CO meter kit, the CI-1080. As the
Heathkit that we all knew and loved is no more, the kits are no longer
available new. However there are still a few available at garage sales,
swap meets etc. They can be an inexpensive way to get some good data
about your engines performance.
I installed a Nordskog M7009 air/fuel guage and the S8942 sensor
http://www.nordskogperformance.net/m7009.html which I purchased from
Summit Racing http://www.summitracing.com/ . At first glance, it
would seem that this marvelous tool would simply tell you what your
air/fuel ratio is. It turns out that Oxygen Sensors are extremely non
linear with most of the voltage change within a very narrow range of
air/fuel ratios (close to stoichiometric). This prompted the Do It
Yourself Wide Band Oxygen Sensor project, which can be found at:
http://www.diy-wb.com/02info.htm
I have not yet built a wideband sensor, but I found a Digital Multi
Meter from Radio Shack, for $60 which has RS-232 serial output, and
datalogging software that will run on a laptop computer running
Windows. If you have a Macintosh there is some software for reading it
which was written by Jeff Luszcz available at www.polar-orbit.com.
There isn't yet software for reading it with a Linux box, that I know
of, but writing some is on my ever growing todo list. I
have found that just having the O2 meter on the dashboard while I drive
is very instructional. I can see at any given moment whether the car is
running rich, or lean. I've been able to tell when the engine leans out
on "tip-in", i.e. when I hit the gas from a low load condition. I've
learned what a huge difference mixture makes on gas mileage. Even with
the nonlinearities, the inexpensive sensor and guage is very useful.
Some people may prefer to spend a bit more and get the m9200, which
reads in voltage, http://www.nordskogperformance.net/m9200.html but
I've been happy with the bargraph, and hooking up my DMM when I need
more resolution.
If the engine goes lean on tip-in, predetonation can occur, and that
can cause bad, expensive, things to happen. Dealing with this problem
leads you to a situation where two experts have distinctly different
ideas. Hans Pedersen suggests just using a very heavy oil in the
carburettor dashpot. Joe Curto,http://joecurtoinc.com/ who some
consider one of the United States biggest experts on SUs suggests
plugging one of the dashpot vacuum ports in the bottom of the piston,
and closing the other one down to 1/8". My current setup is to
plug off the holes as Joe Curto reccomends, run 85/140 diff fluid in
the dashpot and a green (12 oz) spring on the piston.
Modifying the needle:
You may decide that no commercially available carb needle is exactly
right. One nice thing of there only being one carb on the car, is that
you can modify the needle and not have to worry about two pistons being
out of sync with the other two at various points. If you do start
modifying the needle, yourself, you will want to be able to sand and
measure them at specific spots, probably those corresponding the the
measurements in the book. Since the needles are profiled in increments
of 1/8", I took the ruler from a tri-square, which has a handy groove
that is just about the right width to hold an SU needle, and scribed
lines every 1/8". I use an extra fine point sharpie to mark the needles
at those points.
Profiling the carburettor needle
Hans suggests a Fuel/Air ratio of about 15:1 at idle or low
load, and 12.5:1 under heavy load. One possibility is to just buy a lot
of needles at $10 each, another is to buy some rather lean needles such
as the BBA and reprofile them to your desired measurments.
Perhaps the trickiest thing to learn, is what position on the carb needle is active (how much piston lift there is) in any given situation. This is not something that I've solved. By using a ruler, a mirror and a chassis dyno, I discovered that under freeway cruise conditions (5-10 inches Hg vacuum at 3000-4000 RPM) my car is about 5 positions down on the needle. I also discovered that at almost any RPM, at full throttle, the piston will be fully open, and the SU will effectively be working as a fixed choke / fixed jet carburettor.
It took me all weekend to do it, but I finally made a widget that will tell me where the carb piston is, while I'm driving. I don't know if it is peculiar to my setup with the blower, but if I take the damper cap off the dashpot, the car won't even start, so I need a way to measure the piston position, with the dashpot cap on.
I'll spare you the details of all the things I tried that didn't work and just cut to the chase.
You'll need:
some 1/16" brass rod (several inches)
some brass tubing with a 1/16" ID (less than an inch)
a 1/16" drill
a 3/32" (or whatever the OD of the tubing is) drill.
a propane torch, preferably with a fine flame
various hammers, punches, pliers etc.
The goal is to attach the brass rod to the sheet metal hat thingy that fits inside the top of the damper tube on the piston. The problem that I had was that I kept trying to fasten it in ways that didn't let the "hat" move in relation to the rod.
The purpose of the tubing is just to act as a sleeve for the rod going through the cap. You may be able to get by without it.
Pull the metal shaft with the brass valve out of the plastic cap.
Remove the "hat" from the shaft.
Drill a hole in one of the ears of the hat, just big enough for the brass rod. If the rod won't fit through the hole you can file it down a bit so that it does.
Drill a matching hole in the cap. Make sure that the hat is centered on the stub that the shaft mounts into. You can either make this hole the diameter of the rod, or if you use a sleeve, the diameter of the tubing.
If you use tubing, cut a short section, make sure that it slides easily on the rod and insert it into the hole in the cap. It should not extend past the plastic on the inside of the cap.
At this point, you may want to mark the rod every 1/8". I used a triangular file, then used sandpaper to smooth everything down so that the rod would slide well. The other option is to mark something that the rod would move in relation to. In retrospect, I would have taken a flat piece of metal and drilled 1/8" dia holes, 1/8" apart then cut down the center to get nice arrows that would show up in sillohuette.
Another option is to take a hotmelt glue stick, apply some flame to one end to soften of the glue and attach it to the top of the cap. Then use a sharpie to mark it every 1/8"
Heat up the brass rod to soften it near one tip. Use a chisel, punch, pliers or whatever to flatten out a small section of the rod near the tip. You want the deformed section to be as short as possible, and wide enough to prevent the "hat" from sliding up the rod.
Put the rod through the hole in the "ear" of the hat. Make sure that the dome of the hat faces away from the rod. Heat of the tip of the rod and flatten it out so that the hat won't fall off. This way, when the piston drops, it'll pull the rod down with it. You must make the metal extending through the "ear" as short as possible as there is not a lot of clearance.
Put the hat back on the damper shaft, and reinsert the shaft into the cap.
I finally realized that it is easiest to remove the dome. Screw the cap into the dome, then put the whole assembly on the piston and carb body and screw the dome down to the carb body. You will want to remove the air filter and make sure that the piston rises and falls freely, and that the rod tracks the movement of the piston.
I removed the bonnet from my car, attached my camcorder to the rollcage so that it could see the carb (manual focus, manual exposre) and went for a drive narrating what was happening during the process. Ideally, I would have been able to mount my DMM attached to my O2 sensor in view of the camera as well, but at least I now have a feel for where on the needle I am under what conditions.
Ignition Timing:
Ignition timing will have a dramatic effect on power. Going from 4
degrees BTDC at idle to 12 degrees can increase peak horsepower at the
wheels from 80 to over 100. The downside is that the more advance you
run, the more likely you are to have predetonation. Keep an eye on your
NO and your exhaust gas temperatures.
Valve Lash:
When I mentioned the difficulties I was having with predetonation to
Dema Elgin, he reccomended that I close the valve lash on my intake
valves from .015" to .012", which would increase overlap and bleed off
some of the extra charge. This did seem to help the problem.
I had been doing various tests at a very conservative ignition
timing, about 4 degrees at idle. I wanted to be certain that if I was
running a lean needle, I wouldn't accidentally cause predetonation,
which can lead to a case of "light seeking rods". I ran the car
until the gas was nearly empty. I actually started to run out, then put
in another half gallon of 91 octane unleaded. When I had the
information I was looking for, I dumped in two gallons of 110 octane
leaded, and the power from my engine dropped dramatically, until I
bumped the timing up to 14 degrees at idle. There seem to be
several things going on here. First of all, race gas will run at a
different fuel/air ratio than street gas. To grossly oversimplify,
heavier gasoline molecules need more air to burn, but have a lower
octane. The higher octane molecues also have a lower specific energy
per unit of volume. What this boils down to is that if you change
the fuel that you use, you may lose power rather than gain it,
and you will almost certainly screw up your carefully calibrated
air/fuel mixtures.
Also, be aware that in many places it is illegal to use either
racegas, or aviation gas in cars being driven on the road. They don't
pay road taxes on those fuels, and therefore they aren't supposed to be
used on the road. Also, avgas is formulated for very different
conditions than automotive gasoline. Most cars don't often change
altitude by 5-10,000 feet in less than an hour, and as such the fuel in
them doesn't need various additives that help airplanes run well under
a wide range of atmospheric conditions.
List of things you will need to get extra:
maybe a water pump
oil for lubing the blower synthetic 15/40 or 25/60
thread locking compound
gasket compund
modifying the radiator
maybe tappet cover
split level washers
Conclusion:
Bolting on a supercharger from HP can breathe new life into an
engine design that was not particularly good, even fifty years ago.
There is probably no cheaper way to get 130 horsepower out of an MG
motor running on street gas. Most people can complete the job in an
afternoon, leave the system alone and enjoy years of trouble free
horsepower. There is, however, always the possibility of trouble,
especially for those of us who are "too clever for our own good", or
"know just enough to be dangerous". The benefits can be very
rewarding. While you will not end up with a car that will be a star at
the Saturday night drag races, you will end up with a very tractable
car, with nearly modern levels of power, and classic styling. You, may
however, find yourself suddenly needing to spend a lot of money
improving your suspension so that it works as well as the new engine.
=====
drive belt tension: says to check but doesn't specify how
distributor headers specs of car pistons cam
build for reliability rather than every last bit of power
More breathing in a naturally aspirated motor translates to more breathing in a blown motor, but it can compensated for by more boost.