hsmidy

as for the casting differences in the housings, i have two housings like one ones showen and both and an older style housings from an rx4, just to confuse things even more

heretic

All housings I have seen were like that. I don't know about contracting out to other factories, but Mazda paid royalties to NSU for MANY years. If I'm not mistaken, NSU was maintained as a company within Audi strictly for the purpose of collecting royalties.

Kyrasis6

This type of exhaust porting is going to have significant impacts on an engine phase called "blowdown" which is not often talked about. Blowdown is the period of time from when the exhaust valve or port starts to open until the piston or rotor reaches BDC. Once BDC is reached the actual exhaust stroke begines. The blowdown phase is very important because it HIGHLY effects pumping losses in the engine, it also has effects on thermal efficiency and exhaust noise. Because the exhaust opening is very small during blowdown, the "cylinder" pressure extremely high as well as extremely hot, and the temperature and pressure inside the exhaust pipe are very close to outside atmospheric engines the exhaust gases exit the small exhaust opening at sonic velocity. As the pressure blasts it's way past the exhaust opening and enters the exhaust pipe both the temperature and pressure inside the exhaust pipe rise and sonic velocity of the gasses deminishes quickly. The gases also loose velocity quickly as they enter the much larger area of the exhaust pipe.



Why is this so important? If the blowdown phase is incomplete by the time the rotor (or piston) reaches BDC the remaining pressure inside the cylinder area must now be pushed out by the rotor (or piston) and higher pumping losses occur. To maximize blowdown the open surface area of the exhaust port (valve, etc) must be as large as you can get it in the first few degrees of opening. Speaking strictly of rotaries now the best way to do this is for the floor of the exhaust port opening to be wide and flat. This will yield the most surface area in the shortest amount of time allowing the most blowdown gases to be expelled. Doing this will also increase exhaust noise and will reduce thermal efficiency since a lot of heat will be ejected into the exhaust system.



A more rounded exhaust port floor will open more gradually and decrease how well the blowdown phase can do it's job but the more gradual opening will yield a quieter motor (you get a poof not a bang) and better thermal efficiency.



So the good things about the port shown above is that the engine will probably be pretty quiet and be more thermally efficient. The cons will be a constipated engine which can't get it's exhaust gases expelled properly, it will rely HEAVILLY on proper scavenging from the exhaust system to help pull the exhaust from the cylinder which will be difficult because there is little velocity available from the small surface area bleeding pressure over a long period of time before the rotor reaches top dead center. The engine will also run hotter from the increased amount of heat lost through the water jackets, rotor, and engine oil squirted inside the rotor. It is possable a port designed like this might make the engine prone to detonation, and you could forget about making descent power out of a turbo.

Old Grey

The housing on the left is a S5, the right one with a flat on the bottom knee is a Cosmo, S6, 20B style housing

Stanello

I have seen S5 housings with both variations of the bottom foot part. NA and T2



FD housings have a groove in the legs for RTV. FCs and Cosmos (I think) are smooth.

Stanello

Also ALL FD housings have the lower foot area like the one on the LEFT.



I think I may root around and try and make a housing Identification list so we can get to the bottom of this

RX200013B

The housing on the left is a S5, the right one with a flat on the bottom knee is a Cosmo, S6, 20B style housing

"qoute"





I have 3 s4 n/a blocks and one block has the flat spot around the 13b, the other has the 13b that stands out from housing

is there any way to find casting #s to see where the block was originally?