We are in a quandry about the correct exaust manifold for our GEN 3.
We read the stock ones crack, the stainless ones crack, the iron ones are
heavy... which way to go?
What works, what lasts and what about performance?
...Chrissi
I assume this is for a turbo version of the gen 3.
Did Greg Richter say his off the shelf after market HKS TO4 turbo
manifold cracked?
The 1989-92 stock Mazda cast iron turbo manifold does not crack in
automotive
service, it will fit the gen 3 and it is not that heavy as I recall
because it is small. See the picture below.
If you can afford it Inconel is the ultimate way to go.
Performance does not seem to be that big of an issue. The turbo
is capable of generating way more power than the turbo and the engine
can tolerate for long periods of time. People have got 800 HP out
of a 13B for drag racing with a simple turbo exhaust manifold.
The big question we have now is; how much boost can you run
continuously
and for how long? Greg is our guinea pig.
We discussed this for years off and on and it is all on the CD.
Paul Lamar
In a recent email with Greg, I posed this very question. I am sure he
won't mind my sharing with you.
Greg Richter wrote:
Hi Dale,
The manifold is an HKS unit that the rotary racers like. Heavy, but
bulletproof. You may want to checkout www.rotaryaviation.com
...etc.
snips
On further investigation, I have found at least one source of these at
http://www.rx7store.net/turbomanifolds.htm , but they are pretty pricey at
$600 ... I still have hopes
of maybe getting one used, but I like "bulletproof" and may sacrifice
the weight and "bite the bullet" and shell out if I have to.
I see this as a "critical failure" part, failure of which is not an
option if it can possibly be avoided. I am still not clear on the engines'
ability to run in the event of
turbo failure? Reduced power, I would assume, if it runs ... but how
much?
Dale Smith
The HKS works with the Garrett TO4 so the bolt pattern is different
than the stock turbo bolt pattern I think. Perhaps an adapter can be made.
As a quick check the TO4 bolt pattern is 2.750 by 3.250 inches. My 91 turbo
is up at the hangar so I can't check at the moment. I know the 87-88 won't
fit the TO4 pattern.
If you go the HKS TO4 route you are looking at another $1000 for the TO4.
Here is Greg's HKS showing the blocked off waste gate port. Apparently Greg
is getting along with out a waste gate.
Paul Lamar
Couple of issues here.
1. Stock manifold cracking: The stock (I'm talking 89-91 T2 manifold) can
and will *eventually* crack, however it is not a structural failure it is
more of a gasket sealing failure. It would wither leave soot streaks where
exhaust was leaking around the gaskets (easy to spot on preflight) or it
won't show until you disassemble the motor. Remember, mine was like that at
160K miles, which is honestly past the design service life of a car. No
problems making boost, and I probably wouldn't have noticed if the water
Oring groove failure hadn't forced me to remove the engine. In other words,
if it cracks it doesn't mean the engine fails.
2. Stock turbo housing cracking: This one worries me. My exhaust housing had
several thinner areas of the scroll cracked out, IE missing. Wheel was OK
though. Usually turbos fail at the bearing, IE they spit oil everywhere into
the exhaust stream (smoke) and intake stream (oil in IC).
3. Replacements: The HKS unit has a very good reputation. Stainless tubular
manifolds, either custom or from a Japanese tuner, will set you back a fat
wad of cash but are also well nigh indestructable. The only problem is that
they are all made for a T4 turbo. I think you may be able to size this for
aircraft applications, but in auto use they use the full T4 to generate
about 20 PSI of boost, which in a rotary with proper fuel is a LOT of power
with correspondingly short lifespan. We're talking in the 500 HP range on a
2-rotor here.
To summarize: I'd use the OE manifold and a rebuilt or new OE turbo, and
just remember to magnaflux at your TBO overhaul. With a TBO of 2000 or so
there should never be any problems. For that matter, I am not entirely
convinced that the reason they begin to fail isn't due to equipment
failures: The stock catalytic converters increasing heat and backpressure as
they deteriorate, and the stock FI system running the motor leaner and
hotter as sensors fail or go off cal, wiring embrittles and resistance
increases, deposits build up in the injectors, etc.
Mike Harrington
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