Step 1: Engine Basics
Below is a description of what Tim Van Setten and many of his
fellow buggiers use in their rails. A turbo can be installed on any size motor
so don't let the following description scare you off. Be aware though that the
motor will only be as strong as the weakest link. For a play buggy that
only sees occasional abuse you may be able to get away with using your existing
motor. For the highest reliability and maximum HP you're going to have to spend
the money for the good stuff.
ALWAYS REMEMBER: You must
always use good gas, make sure the turbo always has a good supply of oil and do
not allow the motor to detonate. These rules cannot
There's a lot of people with different engine
configurations who just want the performance boost without having to build a new
motor from the ground up. The Fuel Injection can be tuned to work with all VW's,
4 and 6 cylinder engines. The turbo is a different story however.
Generally speaking, what engines aren't suitable to turbocharge?
|First thing for a VW to convert to fuel injection is you want
dual port heads. On a turbo motor, you WILL use Av-Gas, or some other very good
gas. If you don't, the detonation will take the ring lands right off the
pistons. You cannot cheat on good gas on a turbo motor, not even once! (There's
more about AV gas on the Fuel Systems page.)
Overlap is not your friend with a turbo because of the boost pressure and
exhaust back pressures of a turbo motor, keep it to a minimum. The cam still
sets the personality of the engine, whether it be a torque engine or high RPM.
As far as lift goes, unless your making a killer engine, the turbo will push it
in just fine.
Keep the compression ratio around 8.5 to 1. If you have a higher
compression ratio to start with, just don't run as much boost. This is why it's
best to build your engine for your application, street, or off road, turbo or
|Why is low compression better for a
|You make horsepower by how much air you move through the motor.
A high compression 10:1 engine is more efficient than a 7:1 engine, so the 10:1
engine gives you more bang for the buck. However, because the lower compression
is not as efficient, it will move more air through it. So, at 15 PSI of boost,
the 7:1 engine will have an effective compression ratio of 14:1, will not be
into detonation, and be moving more air, making more horsepower than the same
conditions for the 10:1 engine. That engine will be in self-destruct mode, have
detonation, and an effective compression ratio of 20:1!
This is why the racers only run 5:1 or even 6:1. All of this is great for a
drag car, but because the static compression is lower, you will not have much
bottom end torque either. So, since most of us don't drag race every place we
go, a good compromise would be 8:1 or 8.5:1 compression. This way you don't
loose too much bottom end for driveability, and if you don't run too much boost,
say 10 to 15 PSI, you stay away from the gray effective compression area of 15:1
Remember, that the shape of the combustion area, cam, type of fuel, etc. all
play a part of when the engine starts to detonate. It comes down to start with
low boost, and sneak it up from there until you run into problems.
|What should people keep in mind
when building an Engine for a Turbo?
The King of the Hill Motor:
will find that you will spend more money on your transmission than
on your engine. Transmissions with a turbo you'll find that the lower the
gear ratio, the better and faster the turbo comes on line. We all used to
run 4.37 ring and pinions and some 4.12's. With the turbo setups now, and
after cleaning all the teeth off of them, we now use the 3.88's just for strength!
Some use the fermic puck clutch disc, but my personal choice has been
to go to the "Double Disc" setup. To date, that has been the best
clutch I have ever had! You'll pay more to do it, but it will be
the last clutch you put in.
What most of the buggy group has done (that let's me hang out with) has
ended up building their engines like this. First they use a good case or after
market one, that has dual oil relief's, and 10mm studs that do not have
case savers on them. The case is drilled and tapped to accept the full flow oil
mod. They also cut the cases to accept the 94 Cima cylinders while moving the
studs out, and installing the case savers so that maybe just the tip of the
threads show. Next use a welded-up 82mm stroker crank (2276) from your
favorite supplier, and have the case clearanced. Some go with after market rods
so they can slip in a 84mm crank (2332). Assemble the bottom end, and using
Super Flow heads, or to keep within a budget, CB 044 heads with the 40mm
intakes, and 37mm exhaust valves works fine and keep the compression ratio to
8.5 or less. If you really want, a little porting and polishing and cleaning
up the ports works great also with these heads. Setting the compression ratio to
about 8.5 to one is the best of both worlds. The flywheel should be converted to
the 8 dowel pins. Always use a chrome moly gland nut! Some use the stock ratio
rockers, and others have used the 1.25 roller rockers. This is a personal choice
because the cam mfg. specifies how much valve lift and when it will occur with
what type ratio rockers. That's about it for the magic in the engine.
Valves: One interesting thing about heads
we found with the turbo engines is that some people have taken and made both
valves the same size. Rumor has it that they are different sizes to keep the
vacuum signal high to keep the carb happy. Anyway, the one's that have made both
valves 40mm are very fast and an interesting side effect is they say it takes
longer to heat up the motor. They seem to run cooler.
Cam: On naturally aspirated engines that
run high RPMs, usually there is a lot of overlap because the air doesn't start
moving instantly. By opening both valves at the same time, it gives the intake a
head start and helps to flush out the cylinder of the exhaust. The exhaust by
now is a column of air that is already headed out the pipe and helps pull in the
intake charge. On turbo cars, this valve overlap will allow the increased
cylinder and exhaust pressure to flow backward into the intake.
|Much has been written on Camshaft theory.
Unfortunately most of the published research is done for non-turbo or carbureted
engines. When you have a pressurized intake system and exhaust back pressure
from the turbo, much of the existing theory goes out the window. The following
links may give you some insight into normally aspirated camshaft theory.
Basic Camshaft Science
Some turbo cam grinds also wait with opening the intake valve until the
piston is already headed down. This is because on a boosted engine the exhaust
back pressure can be as high as 30 PSI. The intake pressure under boost is only
15 PSI and will be blown backward. By waiting until the piston has started
downward, the cylinder pressure drops and the trick is to open the intake valve
just as the cylinder pressure is crossing 15 PSI (in this example).
Good high performance cams for naturally aspirated engines will have a intake
and exhaust duration of say 270, 280, or 288, 298 etc. Notice the exhaust event
is longer than the intake. On turbo grinds, it is always shorter, say 270, 260
(intake, exhaust), or 275, 255.
On turbo VW's, reports are coming in that the Engle 110 turbo grind has
better bottom end than the Engle 120 turbo grind. The turbo grind 120 loses
bottom end but trades it for top end RPMs. This is all "Seat of the
pants" scientific evaluations. Hopefully somebody out there has done some
"Turbo" cam comparisons. I have used a regular Engle 120 and have had
very good success although I would recommend a turbo grind if you are building a
new turbo motor.
Engle Turbo Cams Part Numbers:
Engle 110: TCS-10 284 deg advertised .430 lift(in) 112 lobe center 276 deg
advertised .420 lift(ex) 112 lobe
Turbo cam street/strip good idle-low compression.
Engle 120: TCS-20 294 deg advertised .435 lift(in) 112 lobe center 284 deg
advertised .430 lift(ex) 112 lobe
Turbo Drag race only/large cc-low com
Rod Length: What's the difference
in the length of the rods and what effect does it have on an engine? After
doing a lot of research, here's what I found. First, a stock length rod will
make good bottom end torque because of the thrust angle relationship to the
crank. The piston speed is much faster for a given RPM compared to a longer rod.
The long rod motor has 3 things going for it. First, the piston speed is slower
because the thrust angles are less. Second, because the thrust angles are less,
it can spin the crank faster. And third, the reason a long rod engine makes more
horsepower than a short rod is because the piston is at the top of the cylinder
longer, so the combustion pressures have more time to push on it. Just things to
consider when building up an engine. Short rod = Good bottom end torque and mid
range. Long rod = Good mid range, excellent high RPMs.
|Full flowing the case
is recommended with turbo engines. To full flow a VW case you
plug the oil exit hole in the case where the pump pushed the oil into.
Then you change the pump cover to one that has an oil exit fitting. Now ALL the
oil for the motor will flow through this fitting, through an external oil filter
(and maybe a cooler if needed) and then back to the case right at the main oil
galley. You drill and tap a return fitting at the case plug just to the left of
the crank and just above the oil pump.
Above picture shows line from pump on bottom, and case return
Warmup Reminder: You're
now going to have more pressure in the filter and oil lines so it's even more
important to use the right viscosity oil and to let the engine reach operating
temperature before driving.
Oil Filter: Use a high
pressure full flow filter such as the FRAM HP1. The typical automotive oil
filter has an oil pressure bypass inside. If you want 100% of the oil filtered
you need to use a full flow oil filter.
Pressure Sender: An
interesting idea stolen from the off road circuit is that the oil pressure
sensors seem to fail more often when mounted on the engine. The extra vibrations
seem to do them in. They mount the pressure sensor on the remote oil filter
where it does not see the engine vibrations.
Oil: At full throttle, the turbo can spin
at speeds upwards of 100,000 RPMs. At these speeds it's going to need a constant
supply of oil to lubricate and cool the bearings. It will have a small supply
line going into the top (1/8" pipe thread) and a larger return line
coming out the bottom (1/2" or 5/8"). You can supply the turbo with
oil by adding a "T" fitting at the oil pressure sending unit on the
engine (next to the distributor.)
Why the bigger return line? After the oil goes
through the turbo bearings, it's going to get whipped into a frothy
lather. It's important that this large return line be allowed to gravity
drain back into the case at a point above the oil level. This will allow some
time for the oil and air to separate. You can return the oil into a valve cover,
or into the old fuel pump hole. It never-ever "T"s back into the oil
Oil Pressure: Wire the oil pressure sender to a
loud horn. Something that's loud enough to overcome the noise of your eyeballs
rattling at the top of that monster hill. With the higher RPMs, full flow, and
bigger oil pump it is possible you could run out of oil at the top of a hill.
Depending on your application, it may be necessary to increase your engines oil
capacity through the use of a deep sump or dry sump. That decision is something
you have to make yourself. I can say this though, your engine will run without
oil for a certain period of time. (Don't test this though!) Because of the high
rotational speeds of a turbo under boost, it will fail quicker than your
co-pilot can say "What was that noise?" so keep it oiled.
Oil Type: The science of oil and oil types is
enough to fill a book so don't expect this paragraph to answer all questions for
every engine application. You want to use an oil with an SE or SF
classification. This classification has antiscuffing agents that turbochargers
like. Watch out with multi-viscosity oils. The polymer additives in these oils
do not like the heat of the turbo bearing very well. In a street car with a
really hot turbo, these viscosity additives can aid in oil "coking"
which means that after you shutdown the engine, the oil will bake itself into
charred clumps in the turbo's bearing housing. In a buggy, the turbo will
typically be exposed to open air so it will tend to stay cooler than it would be
in a closed engine compartment so oil coking is not as much of a problem.
Whenever possible avoid these multi-viscosity additives and use the proper
straight grade oil (SAE 30, etc.) If your climate requires you to use a
multi-viscosity oil, then use the smallest range of viscosity necessary. One
more thing: It should go without saying that you should change your oil often.
FAQ on Motor Oils
Speed-O-Motive Service 1 - Quench Depth and Detonation
What it is and how to check it
Rod Length article
Ignition and Combustion Tech Faq
A Quick Look At My Engine Ideas - intake & exhaust runner, cam
Standard Abrasives - DIY Cylinder Head Porting Guide
Inc. - Deciding to Build a Type 1 Performance Engine
of Internal Engine Knock, and How to Eliminate it. By Ray T. Bohacz
Intelligent Engine Mods