This is a short article from the late, great mark herbert reference engine building,
courtesy of the callook forums;
I
think building a large displacement VW engine has almost become an art
form. Bore, stroke, rod length, and compression can all be combined in
so many different ways that once you throw in the human factor you will
usually end up with a different and unique motor every time.
I
know when I build a new motor that I’m always thinking for a new angle.
With so many heads, carburetors, exhaust sizes and cams available you
can choose your “state of tune” or the RPM range that the motor will
operate at. Other engine marks don’t have this flexibility. Even the
famous smallblock Chevy that also has an entire aftermarket industry
behind it falls short of the aircooled VW in parts choice sometimes. So
many parts choices are a great thing but of coarse it can be confusing
sometimes.
The best thing I can tell you is look, listen and
learn. Sooner or later you will start to figure out who knows what they
are talking about and whose parts work the best. For those of you who
don’t want to wait that long I will list some proven motor combinations
later in this article.
There are basically two kinds of people
that want to build a more powerful VW motor. There is the person who
wants the fastest thing they can build and there is the person who
wants a reliable everlasting motor. I will try to bring these people a
little closer together. First of all the main goal is more power. So if
you’re going to build a more powerful motor there’s no sense in not
going far enough. It costs about the same amount of money to build an
1800cc stroker motor as a 2275cc stroker motor. And they will both last
if they are assembled correctly. With the same carbs, heads and exhaust
they will basically make the same horsepower but the 2275 motor will
make it at a lower RPM and be much more fun to drive. Also a motor that
turns 6000 RPM will out last a motor that turns 8000 RPM all the time.
So the point is bigger is better when done correctly.
There are
some basic levels of performance with a VW engine. Things like heater
boxes, boring and stroking determine how much performance you can
obtain at a certain level. The first decision you need to make is do
you really need your heater boxes? Are you going to be driving in cold
climate for long periods of time? I did, and it sucked with no heater
but at least my car was fast! :-) I eventually built an oil-cooled
heater and all was fine. But don’t kid yourself, it took me a long time
to build a custom heater and I froze my butt off until then. If you
choose to run heater boxes then I don’t recommend stroking your motor
or running it at sustained high speeds. The boxes are very restrictive
and cause heat to build up in the heads and will eventually crack them,
in some cases severely. Even a stock motor with cleaned up exhaust
ports and a competition header instead of heater boxes will run cooler
under extreme conditions.
The next step is boring the case for
bigger pistons. If you’re going to bore your case for 88s then why not
bore it for 94s? It costs the same amount. Just remember that you must
adjust your compression ratio as the motor gets bigger. If you just
slap stock heads on a 1900 it will have 9to1 compression and that’s too
much. I ran a 94×69(1914cc) 7to1 compr. with Kadrons in my bus for
years and it was a great motor as well as simple to build. Whether or
not you can go to the larger 94 pistons depends what year case you are
using. I don’t recommend using 94s with the early 10mm head stud cases.
The later cases as well as all new cases come with 8mm head studs and
can be bored for 94s safely. While I’m talking about head studs I use
chromoly 8mm head studs on all my motors. They can easily be torqued to
25lbs or more and do not come loose. The stock 8mm studs can be used
but they will only torque to 18lbs. and if you are buying after market
8mm studs they are usually substandard so just pay a little more and
get the chromoly ones. If your case comes with 10mm studs, the stock
ones are fine.
As far as big bore pistons are concerned the only
ones that need help are 92s. If you have a 10mm stud case, these are
the biggest pistons I would use. The tops of 92 cylinders are too thin
so if you want to use them I would have them sleeved up to 94 bore
size. A good VW machine shop will know how to do this. I will also
sleeve 94s up sometimes because it gives a better seating surface in
the head. When boring a case for larger cylinders its best to have it
cut for wide base cylinder shims. This also gives a better seating
surface. Sleeving the cylinder and using wide base shims keeps the
cylinder from eating into the case or head. I’ve taken apart daily
driver 2332 size motors after years of service and the heads were still
torqued to 30 lbs.
Next is stroke. The way I see it if your
going to stroke it then STROKE it! Buy at least a 78mm crank and I
prefer an 82. An 84 and larger crank should really have longer rods so
Ill get to that in a minute. A 74mm crank is better than a 69mm and if
you get one for free I would think about using it. The thing is if
you’re buying a crank it only costs a small amount more for an 82. An
82 crank with stock VW rods is an awesome combo! An 82 stroke with any
bore and some OK flowing heads will smoke the tires as far as you want!
It will also pull a bus and a trailer up any hill. The 82 crank
combined with a stock length rod creates a shorter rod ratio than a
stock 69 crank with the same rods. This short rod ratio causes the
piston to snap harder at top dead center and in turn makes the heads
breath harder. In short what you get is a high torque motor that pulls
hard and has excellent throttle response. This combination coupled with
some big pistons and a good set of heads and a medium size cam will
make a great street motor or even an excellent bus motor. If you go
with a big cam and heads you will have a real screamer capable of
quarter mile passes in the 12s The key to this whole combination
though, is a properly ported set of heads and the short rod ratio.
courtesy of the callook forums;
I
think building a large displacement VW engine has almost become an art
form. Bore, stroke, rod length, and compression can all be combined in
so many different ways that once you throw in the human factor you will
usually end up with a different and unique motor every time.
I
know when I build a new motor that I’m always thinking for a new angle.
With so many heads, carburetors, exhaust sizes and cams available you
can choose your “state of tune” or the RPM range that the motor will
operate at. Other engine marks don’t have this flexibility. Even the
famous smallblock Chevy that also has an entire aftermarket industry
behind it falls short of the aircooled VW in parts choice sometimes. So
many parts choices are a great thing but of coarse it can be confusing
sometimes.
The best thing I can tell you is look, listen and
learn. Sooner or later you will start to figure out who knows what they
are talking about and whose parts work the best. For those of you who
don’t want to wait that long I will list some proven motor combinations
later in this article.
There are basically two kinds of people
that want to build a more powerful VW motor. There is the person who
wants the fastest thing they can build and there is the person who
wants a reliable everlasting motor. I will try to bring these people a
little closer together. First of all the main goal is more power. So if
you’re going to build a more powerful motor there’s no sense in not
going far enough. It costs about the same amount of money to build an
1800cc stroker motor as a 2275cc stroker motor. And they will both last
if they are assembled correctly. With the same carbs, heads and exhaust
they will basically make the same horsepower but the 2275 motor will
make it at a lower RPM and be much more fun to drive. Also a motor that
turns 6000 RPM will out last a motor that turns 8000 RPM all the time.
So the point is bigger is better when done correctly.
There are
some basic levels of performance with a VW engine. Things like heater
boxes, boring and stroking determine how much performance you can
obtain at a certain level. The first decision you need to make is do
you really need your heater boxes? Are you going to be driving in cold
climate for long periods of time? I did, and it sucked with no heater
but at least my car was fast! :-) I eventually built an oil-cooled
heater and all was fine. But don’t kid yourself, it took me a long time
to build a custom heater and I froze my butt off until then. If you
choose to run heater boxes then I don’t recommend stroking your motor
or running it at sustained high speeds. The boxes are very restrictive
and cause heat to build up in the heads and will eventually crack them,
in some cases severely. Even a stock motor with cleaned up exhaust
ports and a competition header instead of heater boxes will run cooler
under extreme conditions.
The next step is boring the case for
bigger pistons. If you’re going to bore your case for 88s then why not
bore it for 94s? It costs the same amount. Just remember that you must
adjust your compression ratio as the motor gets bigger. If you just
slap stock heads on a 1900 it will have 9to1 compression and that’s too
much. I ran a 94×69(1914cc) 7to1 compr. with Kadrons in my bus for
years and it was a great motor as well as simple to build. Whether or
not you can go to the larger 94 pistons depends what year case you are
using. I don’t recommend using 94s with the early 10mm head stud cases.
The later cases as well as all new cases come with 8mm head studs and
can be bored for 94s safely. While I’m talking about head studs I use
chromoly 8mm head studs on all my motors. They can easily be torqued to
25lbs or more and do not come loose. The stock 8mm studs can be used
but they will only torque to 18lbs. and if you are buying after market
8mm studs they are usually substandard so just pay a little more and
get the chromoly ones. If your case comes with 10mm studs, the stock
ones are fine.
As far as big bore pistons are concerned the only
ones that need help are 92s. If you have a 10mm stud case, these are
the biggest pistons I would use. The tops of 92 cylinders are too thin
so if you want to use them I would have them sleeved up to 94 bore
size. A good VW machine shop will know how to do this. I will also
sleeve 94s up sometimes because it gives a better seating surface in
the head. When boring a case for larger cylinders its best to have it
cut for wide base cylinder shims. This also gives a better seating
surface. Sleeving the cylinder and using wide base shims keeps the
cylinder from eating into the case or head. I’ve taken apart daily
driver 2332 size motors after years of service and the heads were still
torqued to 30 lbs.
Next is stroke. The way I see it if your
going to stroke it then STROKE it! Buy at least a 78mm crank and I
prefer an 82. An 84 and larger crank should really have longer rods so
Ill get to that in a minute. A 74mm crank is better than a 69mm and if
you get one for free I would think about using it. The thing is if
you’re buying a crank it only costs a small amount more for an 82. An
82 crank with stock VW rods is an awesome combo! An 82 stroke with any
bore and some OK flowing heads will smoke the tires as far as you want!
It will also pull a bus and a trailer up any hill. The 82 crank
combined with a stock length rod creates a shorter rod ratio than a
stock 69 crank with the same rods. This short rod ratio causes the
piston to snap harder at top dead center and in turn makes the heads
breath harder. In short what you get is a high torque motor that pulls
hard and has excellent throttle response. This combination coupled with
some big pistons and a good set of heads and a medium size cam will
make a great street motor or even an excellent bus motor. If you go
with a big cam and heads you will have a real screamer capable of
quarter mile passes in the 12s The key to this whole combination
though, is a properly ported set of heads and the short rod ratio.