<VV> Turbo / 140 heads?

[The Robbins]

Ys Bill, he said that Early Turbos are better than Later Turbos.  :-(

AH of BBRT

-----Original Message-----
From: virtualvairs-bounces at corvair.org
[mailto:virtualvairs-bounces at corvair.org] On Behalf Of Tony Underwood
Sent: Sunday, March 21, 2010 11:45 PM
To: virtualvairs at corvair.org
Subject: Re: <VV> Turbo / 140 heads?

At 10:14 PM 3/21/2010, tconnolly wrote:
>I was wondering if there would be a performance gain to use 140 heads on a
>turbo engine.  Custom plumbing seems to be an easy fab job.  There must be
>reason for or against.  I would like to hear the pro & cons.





Pros:

More top end power but usually only top end.   For street use there's 
not that much difference between the stock turbo heads and the 140 
heads.   Really.    Unless you're racing there's actually not a lot 
of reason to do it.   The turbo makes up for a lot of that port size 
difference.


Cons:

Expect to spit out valve seats regularly if you stay on boost often, 
or unless you have deep seats installed.   The deep valve seat 
upgrade fixs that issue nicely... but it's not real cheap.   There 
will be a few plumbing issues as well but nothing insurmountable by 
any means.


End result:

A properly set up 140-head turbo engine can make serious power if 
pressed hard.   But, it takes knowledgeable prep to make it live and 
you can NOT run it to overheating on a constant basis.   It will wear 
out quickly.   Hell, a stock turbo engine will wear out quickly if 
you have your foot in it every time you leave the light.


My opinion:

Do not run 140 heads.   Use 95 hp heads with stock chambers.   Have 
someone who knows how, to clean up the exhaust ports, don't bother 
touching the intake ports because they're gonna flow plenty under 
boost.   Use GOOD exhaust valves in the 95 heads.  Do not skimp.   Go 
easy on valve springs... no battleship springs needed; you won't have 
to rev it over 6000 tops.    Use an early turbocharger which will 
spool up quicker than the later turbo or the aftermarket examples and 
still make enough top end boost to bust it if you don't watch 
it.   Use a respectable camshaft... try to find a '65 or '66 
turbo-only cam, or an Isky 280 cam available from vendors.   Yeah I 
know the venerable old Isky 280 is "obsolete" according to the 
computer generation but this is a turbo engine that doesn't have to 
bother with dual pattern lobes like naturally aspirated engines 
do.    A 280 cam in a late turbo engine with 95 hp heads done right 
is a vicious combo that will surprise the hell out of you.

Tweaked right, the combo can get you close to 250 hp at 5500 rpm and 
stay together doing it AS LONG AS YOU WATCH THE TEMP GAUGE.    Get a 
good quality aftermarket gauge.   DO NOT let the engine overheat 
while playing... and this combo will get hot quick when 
pressed.    Never use anything but premium grade fuel, do NOT run 
regular or midgrade.

You can NOT allow the engine to ping under boost.   You can't.   You 
just can't.   Pinging at high rpm under heavy boost can damage the 
engine in about 3 seconds.   Run high test always.  Always.   Hell, 
run race fuel if you can get it.   AvGas if you know somebody.   Now, 
in a pinch you can run regular if you drive like grandma but you can 
NOT push it into boost running regular unless you enjoy disassembly.

Use an aftermarket free flow muffler.   The factory turbo muffler is 
NOT that free flowing compared to modern hi-perf mufflers... and you 
want as little restriction in the exhaust as possible.   A chambered 
muffler (those ones you can see straight through) works nicely if you 
can stand the noise which might not be as bad as you may think... 
turbo will muffle a fair bit of noise by itself.   Remember, big 
inlet, big outlet, lowest possible restriction.

...you may need to play around with ignition curves...  you will NOT 
need to run 24 degrees initial advance with the 95 heads.   That 24 
degree advance figure was because of the MISERABLE bathtub chambers 
that afflict the turbo heads from the factory... to this day I wonder 
why GM didn't use the 95 head chambers instead of those bowls the 
factory 180hp heads used.


Forged pistons are gonna be necessary if you find that it gets good 
to you when the boost gauge walks to the right of center... and once 
it happens that first time you're gonna be doing it often.   Do not 
skimp on the hardware.   Make it out of guns, not butter.


Now-   this is all just me, how I'd do it.   Others with more bigger 
smarts and $ may have differing opinions.



tony..    
 _______________________________________________
This message was sent by the VirtualVairs mailing list, all copyrights are
the property
of the writer, please attribute properly. For help,
mailto:vv-help at corvair.org
This list sponsored by the Corvair Society of America,
http://www.corvair.org/
Post messages to: VirtualVairs at corvair.org
Change your options: http://www.vv.corvair.org/mailman/options/virtualvairs 
 _______________________________________________