<VV> Re: 95 vs turbo heads

[Tony Underwood]

At 10:57 hours 07/21/2004 +0000, djtcz@comcast.net wrote:
>Message: 4
>From: "Sam & Marissa Andolino" <mandolin@rochester.rr.com>
>To: "Virtualvairs" <virtualvairs@corvair.org>
>Date: Wed, 21 Jul 2004 15:56:16 -0400
>Subject: <VV> 95 Head conversion (zero compression update 2)
>
>Hi Everyone,
>What are the pros and cons on converting a 95 hp to a 180 turbo.  The head
>on the car and the spare one both are cracked and need to be welded.  The
>shop that is doing  the heads is a well known Corvair shop  suggested that I
>have them covert a 95 head.  I know that the compression on both 95 and 180
>are both low but will the two heads  work together on the same block and
>give good performance? Has anyone done this,  and can they give me their
>take on this conversion?  


Using 95hp heads on a 180 turbo engine is one of the best things you can do
to it and yes I've done it more than once.   Works well.   



>The last question is there an issue with the
>valves and valves guilds on the different heads can they use the same
ones?   

Purists would insist that bronze guides be installed in the 95 heads but I
used the stock iron guides in the last one I did and never had any trouble
with them.    I did use turbo exhaust valves... mainly because I had a set
on hand.   I'd bet that stock exhaust valves would likely work as well if
you didn't flog the engine often.   Then again, high tech exhaust valves
aren't that expensive, cheap insurance.   



>One  turbo head has a big oil drain tube for the turbo.  I brazed fittings
on my 140 head rocker cover for a drain.  


I found it easier to drill a hole in the head valve cover boss in the same
location as the stock oil return drain fitting.   Tap it with NPT and
screwed in a brass nipple of the correct size and ran the turbo oil drain
to it, all was well.    


>The turbo valves' better material is important.  

It certainly is if you intend to exploit the engines output.   

>The 140 guides held up OK in my flogged on Corsa, at least as far as
outright seizing goes. Don't the 95 and 180 go about getting lower
compression with much different chamber shapes? Like wedge vs open chamber?  

Yep.   The 180 head has a "bathtub" chamber like a bowl... terrible for
flame front control and combustion propagation.  The 95 head uses a deeper
more confined chamber with a "step" squish area which requires considerably
less ignition advance in order to burn the entire charge quick enough to
take advantage of its total energy.   This means that the stock turbo
distributor is NOT going to work correctly with the 95 heads.   I'd start
out (and did) with a 110hp distributor and experiment with springs and
weights to get it where it needs to be... or find a shop which has done
this and already has dyno data.     Be sure to use the pressure retard.   

I think you'll find that the +24 degrees advance as per stock 180 will not
be necessary... more like ~12-14 degrees as a starting point and work from
there, depending on how much centrifugal advance is in the distributor...
avoid more than around +34 total unless you're running some GOOOOD gas.
 YMMV, no pun.      

These are all ballpark figures.   Each individual engine will "like"
different adjustments.     



>Can the thermistor be installed in the 95 head? I'd hate to lose that cyl
head temp gage.



Yep.    You can buy the adaptors from the vendors... or do like I did and
cheat...  

I simply took the jackleg route.  It involves the additional drilling of a
1/4" hole down through the bottom of the thermistor mounting hole to allow
the thermistor sensing element to fit into the head.    Drill absolutely NO
farther than necessary to allow the thermistor to fit into the head.   If
you drill too far you'll  likely bore into a combustion chamber.   "Measure
twice, drill once."   Once the hole was drilled (being careful NOT to scuff
the existing 3/8X16 threads) I simply ran a 3/8X24 tap through the existing
threads...  I know, crude and sorry-assed engineering but it worked fine,
thermistor screwed in and stayed there both times I did this.    But that's
me.    

I *did* try this trick on a junk head first, before I wrecked a good 95
head.    That's also how I learned that if you drill too far you can end up
with a hole in a combustion chamber.    

Any doubts, use the adaptor which avoids any potential hassles.    Don't
take a chance in relying upon my jacklegness.   


After all is said and done, I think you'll find that the 180 w/95 heads
will run stronger and actually ping less and to sweeten the pot still run
on relatively cheap fuel if necessary, as long as you keep your foot out of
it.    I took mine on road trips running cheap-ass regular gas and never
had the first ping on the Interstate unless I pushed the boost gauge to the
right of center.    


To this day I still wonder why GM didn't use 95 type heads on the 180
engine since they avoid several issues that plague turbocharged Corvair
engines.  
  

tony..