<VV> LM turbos and no lower shrouds

[Carlton Smith]

Hi Eric,

Thanks for your opinion. I am seeking those with experience and you have
shared yours.

I have owned my particular 1965 turbo Corsa since 2007. The previous owner
had rebuilt the engine in 2000. It was totally stock with the exception of a
Clark's 260 cam. On the highway in the Midwest if I went over 65MPH for any
length of time  on a 75-80 degree day the head temp would reach 425-450
degrees (the gage is accurate as I have a infrared temp gun). The engine
always had a couple of (loud) clacky valves that were lifter/cam oriented. I
decided to have the engine rebuilt last winter by a professional Corvair
mechanic. The engine was totally rebuilt stock, head veins cleared as much
as possible, correct valve geometry restored, etc. We discovered the bad
Clarks cam grind on 2 lobes is what was causing the 2 clacky valves and
replaced it with an Isky cam of the same 260 spec. (I checked with others
and found they also had problems (on occasion) with this particular Clarks
cam). Anyway I now have normal quiet engine now. However, with the shrouds
on I still would go to 425-450 degrees on long distance highway traveling.
So I decided to try the shrouds off option and it usually travels at 300-325
degrees and on a hot day might go to 350. I am told by may turbo owners and
the folks at Clarks that the shrouds on temperatures are absolutely normal
for a turbo. Also that those temperatures will eventually shorten the life
of the engine as compared to a standard engine. I drive the car every day in
the summer and garage it in the winter. I drive it as long as I can every
year so that does involve fall and spring days in the upper 30s and 40s. I
can still get heat in the cab from the upper shroud hose so that is ok with
me. However, I don't like having the bottom of the engine exposed all of the
time to possible road debris (rocks, etc.). I am a little worried about the
start up/warm up factor although it seems it warms up fairly quickly. So you
can see I am already at the point of making a possible mod decision. I am
interested to know what John Roberts is suggesting.

 Thanks for your input Eric!

 Regards, 
 Carlton Smith      



-----Original Message-----
From: virtualvairs-bounces at corvair.org
[mailto:virtualvairs-bounces at corvair.org] On Behalf Of Eric S. Eberhard
Sent: Sunday, October 23, 2011 2:29 AM
To: virtualvairs at corvair.org
Subject: <VV> LM turbos and no lower shrouds



I am always puzzled by this discussion which comes up every so 
often.  The car was designed well from the factory.  If you have 
everything correct -- all the shrouds as well as seals and so forth, 
there is no better system.  I am in AZ, totally bone-stock, at 
altitude (3500-8000 feet), summer temps of 110 ... and I NEVER have 
even gotten remotely close to overheating.  Our speed limit is 75 and 
I can go up a 6% grade at 80, no over heating.  From my 3500 to 7500 
feet happens in 6 miles, no overheat even at 80.

I believe that those that overheat and think they need to 
remove/modify shrouds simply have other problem they are compensating 
for.  Mine is a 62 EM and perhaps it is different, but I have had to 
EM turbos as well and neither ever had a heating problem.
And we get 20 degrees in the winter, so having those shrouds on then 
is crucial and I don't need the hassle of swapping them on and off.

One writer pointed out the correct heat is required for quick 
boost.  Correct.  Some people even wrap their exhaust to push temp 
even higher, for that reason.  Some people mistakenly use a "free 
flowing" muffler which actually reduces boost and is bad.  I used an 
NOS turbo muffler.

Keep it stock and it will be absolutely reliable (my only mods are 
electronic ignition and related upgrades).

If you have heating problems -- are your plugs too hot?  I use Nology 
Silverstone plugs and they perform very well with a 38 gap and hot 
ignition, no overheating.  They are made for vintage cars.  They are 
expensive, but I have over 30k on them and they are clean as a whistle.

BTW -- opinions are like belly buttons and so I have one.  I respect 
others, as other people have done neat things.  I am not a good 
enough amateur mechanic to re-engineer things.  But I believe a 
properly set up stock system -- not all that hard to achieve -- is 
going to be reliable.  Doing the ignition and putting a Judson on one 
of my cars is sort of the limit of my explorations.  However, my 
Spyder always has instant boost (no lag), boosts at 2000 rpm in 4th, 
pulls to redline, and I can't overheat it.

So if you are in the mood, you might try making it factory spec 
first, seeing how that goes, and then modify.  Otherwise, you might 
mask a problem that later gets ugly.

Eric 

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