<VV> 3-Speed Corsa and Spyder

[jvhroberts at aol.com]

The purpose of the blow off valve is to avoid compressor stall. On a draw through, the vacuum at the compressor inlet makes such a stall not much of a problem. 

I've heard of people using PGs with turbos with good result. I think GM didn't offer it simply because of having a 2 speed auto on their finest sporting powerplant just didn't make sense. 
Clearly the tranny would be fine, as would the engine. 
 

John Roberts
 

 

-----Original Message-----
From: Jay Maechtlen via VirtualVairs <virtualvairs at corvair.org>
To: virtualvairs <virtualvairs at corvair.org>
Sent: Sat, Nov 15, 2014 7:30 pm
Subject: Re: <VV> 3-Speed Corsa and Spyder


Since stock Corvairs use a suck through system, I guess a blow off valve 
would be bad - you'd be dumping a perfect air fuel mix.
If you used a blow-through carb, a blow-off valve might take care of the 
issue.

Or- a throttling arrangement to restrict air to the turbo at shift, to 
let the turbine wind back down.
Maybe set it up to limit boost as a function of RPM?

(not a trivial project, of course.)

regards
Jay

On 11/15/2014 6:27 AM, djtcz--- via VirtualVairs wrote:

> http://www.vv.corvair.org/Library/benzinger.htm
>
> Benzinger said this -
>
> "We wanted rather desperately to match up a turbocharger with an automatic 
transmission. It has some pretty attractive aspects about it. But we just could 
never make it go. The thing that you run into - and maybe some of you have even 
experimented yourself with this combination - is that when you wind up the 
engine in low gear, get the turbine wound up to full boost and then make the 
upshift, it suddenly pulls the engine RPM down with the boost still up where it 
belongs for a couple of thousand RPM higher. With the low engine speed and the 
blower still wound up, it gets into combustion difficulties that makes wild 
detonation look pale. There was just nothing we could do to get the engine thru 
this rough spot. Once the malcombustion starts, you can't just shut it off 
again. Perhaps the availability of a three speed automatic or maybe a four speed 
would have done it by getting the gear steps tighter. But with Powerglide being 
a two speed set up we could never find anyway arou
 nd
>    it."
>
> I take that to mean the issue was maintaining bigboost airflow when the engine 
rpm changed almost instantly , not the large rpm drop per se.
>
> powerglide ratio 1.8, softened a bit by the torque converter.
> Early 4 speed drop on the 1-2 shift 1.55, with direct rpm change, but with a 
noticeable period of closed or reduce throttle between shifts.
> My recollection is the boost has to build back up between even my quickest 
shifts.
>
> Long ago A New England racer used a Turbo PG combo in a dune buggy (Meyers 
Manx maybe) in some form of oval track or circuit racing pretty successfully.
> At one point he claimed he was using one of the factoery hot cams and did not 
feel the need for "more,"
> I do not recall him mentioning special tuning or driving during the 1-2 shift 
back in those non-digital days.
>
> Dan T
>
> ======================
>
> From: RoboMan91324 at aol.com
> Subject: <VV> 3-Speed Corsa and Spyder as rare as MONO "Sgt Pepper"
> LP?
>
> Beside the undesirability factor, I imagine that another reason for a 3
> speed being rare is that it would cause similar problems (but maybe not quite
> as severe) paired with a turbo as a 2 speed automatic would have caused.
> Specifically, too much RPM drop between gears. I understand that no
> factory turbo motors were paired with 2 speed automatics for this reason. I
> suppose the 3 speed would work OK with the 140 Corsa but were any 3 speed
> Spyders or turbo Corsas available from the factory? If so, any feedback as to
> performance? Was the 3 speed tranny/turbo combination one of the
> "standards" that GM disallowed at the factory whether you wanted it or not?
>
> Doc
> ~~~~~~~~~~~~~~~~~~~~~~~
>
> I
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-- 
Jay Maechtlen SoCal '61 2-dr modified w/fiberglass skin, transverse 3.8 
Buick V6 TH440T4 trans


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