Head temp ranges for Type IVs

[Dave_Darling]

Hi, all!

Do you guys have any data for what the "normal" range of head temps is for the Type IVs? A "redline", as in "pull over and turn the car off"?

These would be measured at the spark plug, by the standard ring-type thermocouple.

I have a friend who asked Porsche about the 914 motor. They said "Go ask VW, it's their motor". VW said they didn't have any numbers, because they never thought it would be an issue.

Thanks for any input!

--DD

[tmk]

Hi Dave. See you have found this site from the pelican BBS. Lot's of good info at this site. I asked this some time back and this is what come up: http://shoptalkforums.com/bbs/NonCGI/Fo ... 00150.html
If you can not get to this do a search for head temp.

TMK
73 914S 2.1L

[Joseph]

Dave,
Seems neither Porsche or VW has ever let
out numbers re head temps. Their not knowing
is like Porsche manufacturing a car without
R&D. Both the Type 1 and 4 seem to yield
close to the same temp range. The max seems
to hover at the 400F range. Getting to that
level and going back to a lower temps like
325-375F does'nt seem to have any nasty effect on the engine.
In order to determine the "point of no return" temp, a recording device on each
cylinder plug would be installed, overload
the engine, and then check the spike on the
failed cylinder. This won't tell you the
failure temp of the piston.
Maybe someone on this NG knows or is an
engineer with a company like Alcoa or
Reynolds aluminum with access to strength
of materials tables with a factor of heat
included. I know many aluminums melt in the
900F range and lose their strengt well before
that temp level.
In the meanwhile, I'll stick to the 400F
number under the plug and play it safe.
Joe
Oregon Performance Products http://www.siretech.com/~opshroud

[kokanee]

The yield strength won't change with a change in temperature as a plastic would until you get really close to the melting temperature. But what does effect the strength is long term application of heat, or short durations of high heat.

If you submit aluminum to heat (over 250F) It begins to harden (strengthen) by dropping precipitates (Magnesium-Silicide) out of the aluminum solution. The problem occurs when you over-age the head. This is when the precipitates build up and cause the mat'l to weaken as well as become more brittle. After a minute at 400F your head begins to weaken by this abundance of precipitates. but at 350F the strengthening rate is rather slow, which allows the heads to age and become stronger but not to over-age.

I'm not saying that 400F is some magic number, in fact the further you stat away from it the better, just don't let the needle sit too close too long.

does anyone know the particular alloy # for our heads? I assume that it is #356 but it would be nice to know exactly what it is.

k-
(4th year Materials Engineering student)

------------------
Less Rice...
More Kraut.

[This message has been edited by kokanee (edited 11-05-2000).]

[Joseph]

Kokanee,
That was an excellent post re the "mystery"
type of aluminum in the heads. I thought that
after paying all those taxes you would have
a nice spectroscope at school so you could
"burn" a little bit of cylinder fin
The "other" Type 4 heads made by other than
VW could possible be made out of yet another
alloy. (Poor castings, though.)
Also, you stated that the long duration of
heat would weaken the metal. Are you talking
about heat and cooling cycles? If so, the
older heads like the 1700 would make poor
candidates for modification.
The instructor's manual lists the heads on
the Type 4 only as "aluminum alloy" with sintered metal (Arrrrrgh) valve seats.
If you can find the exact alloy of the head
we could establish more accurate op temps
instead of relying on hearsay by the experts or the fact that the VDO Cly head temp gauge has 350F straight up on the face of the gauge.
Joe
Oregon Performance Products http://www.spiretech.com/~opshroud

[kokanee]

Cycling does play a role in the loss of head strength, but it is not as significant (or rapid) as the precipitate problem. All solid metals have a fatigue limit (except lead which recrystallizes at room temp.), so given enough cycles the aluminum will eventually wear out. But aluminum is such a ductile material that it's fatigue limit is higher than most others.

One thing I forgot to mention if it wasn't clear: this precipitation is irreversable, the more times you run in that heat range, the more damage your heads will take... but its the dwelling at high temps that really takes a toll quickly.

you could run a water cooling system and wasser heads to control the excess heat, but then you get into corrosion problems... wasn't somebody working on that?

K-

------------------
Less Rice...
More Kraut.

[[email protected]]

I am thinking about H2O cooled heads but I wouldn't call it working on it. The bore spacing is different from the T4 so they can't just slip on even though the stud pattern is way close. Cutting the head down the middle is the only way.

If you have an old JayCee catalog you can see his watercooled Autocraft 910 head which gives lots of ideas. I just need more welding skill with the TIG.
Steve

[kokanee]

What about boring the heads for oversized cylinders? While doing it, grind off-center to put the centers the right distance apart. That way valves would function ok, studs would line up and some of the geometry would be preserved.

as well, use the wasser crank to line rods and such up. what does that do to pushrod alignment?

K-

------------------
Less Rice...
More Kraut.

[This message has been edited by kokanee (edited 11-12-2000).]