[Amc-list] 'Rear Mount' Turbos - cat scratch fever -

[Brien Tourville <hh7x@xxxxxxxxxxxxx>]

To work best, a rear mount turbo would have completely different turbine 
designs than a front mount type, to allow for the slower, and less 
energetic exhaust flow.  Simply bolting a normal front mount turbo to 
the end of your exhaust will have very poor efficiency.  I'm assuming
that the folks selling these kits have done their homework and are
sizing the turbines as best they can, given that the majority of "off
the shelf" components will be sub-optimal for their purpose.

The other problem that I see with a rear mount system, is the long lag
time that it will suffer, trying to pressurize the intake system volume.
Front mount systems all have some degree of lag, and with a rear mount,
you're adding 10+ feet of 2-3 inch piping volume into the equation.
That's a lot of volume to pressurize, and I suspect that these 
systems suffer a lot of lag....

of course, your mileage may vary!
Dave 




<>




The Toyota V8 car guys love the rear mount Turbo[s] 
[ 'Rear Mount' being 'Under the Floor' - not after
or even near the Convertor / Muffler ]

check the www.lextreme.com site - there are a few
great Installs documented with Photos there.

The main reasons they go for this is Space - 
there isn't any under the hood unless you
send the Exhaust forward - which takes
dedicated headers, etc.


The biggest problems with these under floor installs
is oil draining out of the Turbo[s]:

you need to 'valve' control restrict the oil entering the Turbo and
to design in enough of a 'drop' for the oil return
tube to allow the oil to get out of the housing -
elsewise you've a cloud of smoke coming from
oil backing up into the Turbo past the seals. 

Exhaust pipe I.D. AFTER the Turbo should be large -
like 2.5 to 3" - no back pressure on the Turbine
and use a big I.D. high flow Cat.

Mufflers on Turbo engines are usually omitted
since the Turbo quiets things down before the Cat.


The Exhaust Header to Turbo flange pipe I.D. is kept smallish -
like 1.75 to 2 inch to keep pressure up - 
and the run from Header Flange to Turbo
Flange is dictated by your available space - could be next
to nothing.

Placing the Turbos almost directly on
the Header Flange - is preferred as your best 
'under floor' space is the area almost 
in front of / beneath the Firewall.

>From the installs documented on Lextreme, they weren't
too picky on Turbo Sizing - something off a small 4cyl.
as the Toyota V8 is a 4.0 - making any MR2 Turbo 'fair game'.

Throttle Response from Testimonials is very good -
remember, these are street cars - not thinking in
thousandth or even tenths of a second lag.

Imagine your engine with 50 to 100 extra HP/ Torque -
and the type of Power Delivery with a Turbo is 'different'.

The 'normal' compression ratio hasn't been changed -
pistons are cast - so off idle engine response is
as it was - until the Turbos kick in around 2k RPM -
then the 'Grin Factor' gets Stupid.

The engine isn't 'winding up' pulling in fuel then generating
power - the fuel is 'stuffed' in -  the engine is being forced to make RPMs -
the sound of the power generation is 'reversed' -
it is 'weird and wonderful' - a totally different feel / experience
to acceleration - it's "Dirty Bird" ;)

There's some video on YouTube.com of these if you're
energetic enough to Google yourself.






-- 

                  Brien
            NEW YORK
     eagle registry #501 
eagle kammback registry

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