Well let me start this off by saying I'm in no way an engineer or anything related to book smarts.

Well I've been thinking over the past few days, reading about the turbocharged 6 ports. I've spoke to some people, and after a while I was convinced that when I want to go turbo, to actually go with a turbo block and everything else involved. But then I started thinking -

The turbo motors rotors are a lower compression than n/a. Turbo and N/A motors get ported to allow more air in to the compression cycle, right?

So, theoretically (well, what it seems to me anyway), if internal seals and gaskets were identical in both motors, and you compare a 6 port with stock ports to a turbo block with porting work done, would it not be pushing similar amounts of air into the compression cycle, and be identical (or close) in reliability?

Maybe I'm clueless on all of this, I've never owned a turbo car. I just figured this logic almost makes sense. Now I'll allow the smart guys to chime in.

 

the problem is the bigger your porting, the less low-end torque you have. if you ported a TII block to have similar port area to an n/a block i would think it would have no torque down low.

Im no expert, but I would think 6 port turbo setup with working 6-port actuators would actually have a better power curve than a TII block, due to the fact you can turn off the aux ports in low rpm

 

I am by no means an expert on rotaries but i do see your point. The optimal set up to me would seem to be a ported n/a motor with a turbo added. high compression turbo's aren't good for durability, but id imagine it would be awesome for power. With a great tune, i think a 6 port turbo could be the best set up..I wouldn't run a 6 port turbo without a tunable form of engine mgt or atleast a wideband to monitor afr's...u do have to consider how far u can push the limits of boost tho

 

So the way I see it - lets say a n/a motor compresses in about 2000cc of air per compression cycle, the turbo motor has about 1400cc of air per compression cycle (before turbo spool). Almost everybody that gets a rebuild gets their turbo block ported. So maybe after porting, it allows about 2000cc of air in per compression cycle now.

You see what I'm getting at? I feel like you could be able to use the more easy to find n/a block parts to run a turbo motor, and not have to dish out all kinds of dough for porting and such.

Now this is all assuming the housings and such are not reinforced or something on a turbo block.

 

I think you are looking at it slightly wrong. The NA has higher compression ratio.


Benefits:


You will have better off-boost horsepower.

You should have higher port velocity at low rpm, thus off-boost you should have better chamber filling compared to a 4-port, (let alone a street-ported 4-port) yielding better economy and throttle response off-boost.

You should have a lower rpm transition to boost with 6-port than 4-port, but the 4-port (especially if street-ported) will 'hit harder' when boost does come on (I personally don't think this is a desirable trait).

You will make more hp per PSI of boost with the higher compression rotors. This is not a 6-port/4-port thing, this is compression ratio.

Difficulties:

Your 6 port, high compression ratio will be much easier to blow up-all those little mistakes that one can make- too lean AFR, poor spark timing control, boost creep etc etc will be magnified.

The road is narrow and the ditches are deep. Good Luck, you are going to need it!

 

ok, aren't you essentially increasing the compression in a 4 port by porting the motor to allow in more air?

I did state above that I was convinced not to do this, I won't be.

On a side note, a guy here in town turbocharged his 6 port and was beating on it for 3 years before it blew. On a used motor.

 

No, you are not increasing the compression. Think of it in terms of a camshaft change in a piston engine. You are increasing the overlap (think valve timing) and port area (think valve lift).

As the rpm's rise, the time for the intake (and exhaust) event is reduced and physics is working against you.

You are increasing the rate that fuel and air that is inducted/exhausted with each cycle- The increased overlap and port area allows the chamber to more completely fill/empty at higher rpms.

Due to the overlap some of the air/fuel mix actually blows on through into the exhaust manifold.

I didn't say the 6-port turbo was a Bad Idea, just that it is riskier by nature.

 

Yes, NA end irons are like massively ported 4 port irons. However, while that does mean a lot of flow, it also means a torque hit down low.

If the NA engine is turbocharged and the aux ports left open, then you will certainly notice the lack of low end grunt at partial and lighter throttle. It will just take more pedal to accomplish the same thing versus a working 6 port or 4 port setup.

But at WOT with far more port area and higher compression the result is more power for obvious reasons. The higher compression engine also spools the turbo at an impressive rate. On several 6 port turbos I have done using the HT-18, it is hard to keep it out of boost on the highway.