thoughts on superchargers vs. turbochargers

I'm in search of some information so i can make a rather important milestone like decision for my motor. This is for a 13B rotary engine and being used in the CHCA hill climbs.

My options are running a Camden supercharger or a T4 type turbo.

What i am curious to is the following:

1. which one would yield the best response? (thinking supercharger...)
2. How does each effect the cooling system and oil temperature.
3. longevity of both

etc

i have my thoughts and theories but i would like to hear from those you have first hand experience.

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~A.M.S.

"Some people are afraid of heights, not me. I'm afraid of widths"

We put the factory GM supercharger kit on my sons Cavalier Ecotec. It feels like a healthy big v-6 all the time. No lag, no wierd power band,no heating issues, just smooth power right from a dead stop. 12 psi, 10:1 compression, no overheat and it's been on for nearly a year now. The car regularly slaughters Sti and M3s at trackdays. He beats the snot out of it on trackdays too. Lost about 1 mpg overall, not bad for about a 70 hp gain.

The Camden is shit. The Eaton style blowers have near turbo like efficiency but the Camden is the same old radial-in radial-out lobe blower that is lucky to get up to 50% efficiency. It beats the air and heats it a LOT. IN worst case scenarios the efficiency can go negative - the boost pressure is entirely due to added heat and the actual mass going into the engine is the same as naturally aspirated (only you can still detonate the shit out of the engine)

It looks beefy though.

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Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.

I had a Camden supercharger on my Toyota pickup truck (22R) in the late 1980's. While I'm quite sure a turbo would have been a lot more efficient, it did make a snotload more power and torque than stock. Felt like a big N/A V6, I could shift it at 2500 rpms and pull away from traffic with ease. Used to give 5.0 Mustangs fits up to about 120 mph.

Sure, when it got hot after sustained use you could feel a loss of power, but a pre-blower water/methanol injection system pretty much cured than issue. I beat the heck out of it for 50,000 miles and actually just dug the blower out of my barn a few months ago and tore it apart. Looks fine inside, no unusual wear. Gonna stick it on my Opel wagon next.

---

Opel is a 4-letter word...
http://www.flickr.com/photos/10498579@N07/sets/

Pete Wrote:
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> The Camden is shit. The Eaton style blowers have
> near turbo like efficiency but the Camden is the
> same old radial-in radial-out lobe blower that is
> lucky to get up to 50% efficiency. It beats the
> air and heats it a LOT. IN worst case scenarios
> the efficiency can go negative - the boost
> pressure is entirely due to added heat and the
> actual mass going into the engine is the same as
> naturally aspirated (only you can still detonate
> the shit out of the engine)
>
> It looks beefy though.

Hey Pete, since I think we agree the rotary is really somewhere around 3. something liters I know peeps are always saying T4 Farrett size..

And then they talk abooot lag.

There ARE some pretty big T3 turbine sides and reasonable compressor sides, you ever seen anybody use a T3 derived turbo on one of these thangs?

I reckon with enough wastegate capacity one could select parts to make the turbo work at relatively low rpm. Goota have LOTSof wastegate capacity cause if you spoolit early AND rev it there will be a BIG volume of gas that needs to be gotten rid of to control turbine shaft speed.

Right?
>
> Pete Remner
> Cleveland, Ohio
>
> 1984 RX-7 reshell
> 1978

---

John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

i dont believe there is much aftermarket for these in a T3. I wonder how small a T4 i could go though...

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~A.M.S.

"Some people are afraid of heights, not me. I'm afraid of widths"

i can get a t4 undivided down into a .61 a/r

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~A.M.S.

"Some people are afraid of heights, not me. I'm afraid of widths"

The stock turbo is about the size of a Grand National's turbo. basically tyhe biggest T3 they make.

Lag actually goes down with a more efficient exhaust side. There's voodoo in turbo sizing for rotaries and I won't profess to know a thing about it, other than knowing who to ask.

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Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.

the other thing is the low the turbo comes on the worse efficiency i can expect up top. I may follow in your foot step's Pete and limit my redlining.

---

~A.M.S.

"Some people are afraid of heights, not me. I'm afraid of widths"

john vanlandingham Wrote:
-------------------------------------------------------
>
> I reckon with enough wastegate capacity one could
> select parts to make the turbo work at relatively
> low rpm. Goota have LOTSof wastegate capacity
> cause if you spoolit early AND rev it there will
> be a BIG volume of gas that needs to be gotten rid
> of to control turbine shaft speed.
>
> Right?

Right. The TO4E we put on Hintz's car had a smaller exhaust turbine and a larger compressor. The inlet was 57mm (thank gawd for no restrictors in G5!) but I can't remember any other specs. The lag wasn't any worse than the stock twin scroll turbo with the flapper door in the exhaust manifold. You're right about the wastegate capacity. The HKS manifold incorporated a flange for a nice poppet valve wastegate but the standard size HKS wastegate wasn't really big enough. Keeping the boost level down to a safe level was a challenge with that turbo.

Whipple makes some great superchargers. Twin screw design. Instant response just the sort of thing that a rotary engine lacks.

In a lab they can produce 20psi boost pressure and only raise the ambient air temps by 25degrees.

I think a small whipple charger would be sweet on a 13b

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Michael LeCompte

john vanlandingham Wrote:
> Hey Pete, since I think we agree the rotary is
> really somewhere around 3. something liters I know
> peeps are always saying T4 Farrett size..
>
> And then they talk abooot lag.
>
> There ARE some pretty big T3 turbine sides and
> reasonable compressor sides, you ever seen anybody
> use a T3 derived turbo on one of these thangs?
>
> I reckon with enough wastegate capacity one could
> select parts to make the turbo work at relatively
> low rpm. Goota have LOTSof wastegate capacity
> cause if you spoolit early AND rev it there will
> be a BIG volume of gas that needs to be gotten rid
> of to control turbine shaft speed.
>
> Right?

Close. A 13B is a 2.6-liter if you're comparing to a 4-stroke (and who isn't?) It has a tremendous amount of exhaust energy (wasted energy) though, which will allow it to spool even larger turbos if you capture that energy effectively. The right way to do it is a large twin-scroll turbo, since rotaries are also very sensitive to backpressure at the exhaust ports, and the twin scroll keeps each exhaust path independent all the way into the turbine.

Bad news is that I don't know of any appropriate turbo. I know of one such turbo, but it was custom made by an ex-Garret engineer and you'd have to buy the whole RX-7 if you wanted the turbo...

-Dave