172/182 Exhaust Manifold Question

[skinner]

I was scrabbling about under my 172 the other week (putting the plastic sump bit back as it was left hanging off after a service!), and thought the exhaust manifold was a 4-1 design, followed by a parallel pair of cats.

Looking at the picture in the other thread of the trophy, it looks like the 182 has a 4-2-1 manifold and a single (but bigger) cat.

I always thought that a 4-1 manifold was the way to go to achieve more power, so why have Renault done the opposite?

Obviously you can tune an engine with a 4-2-1 manifold and get more power than one that has not been developed as much but has a 4-1 manifold, but can anyone explain the change?

 

[Fred@BTM]

yep all mk1/mk2 172s have a 4-1 manifold which is crap, massive heat build up due to the design

the 182 has a 4-2-1, which is amazing, we took it too our exhaust builder and he said that it cant really be improved anymore, and thats a std part built by renault!!!!

j3ned can supply new ones for around £250

 

[BenR]

correct, the 4-1 at the time was quite the peice of kit in terms of std fitment to a car.

However, the collector on it is short and stubby, it has poor neat flow properties and pulse tuning properties, the manifold pressures are high and holds up EGTs. The 182 manifold is good, much better in terms of pulse tuning and neat flow.

However, it can be bettered because it is a production item and there are many inefficiencies because of that.

Fred, i dont understand why you guys ground down the flange on the 182 manifold, its more beneficial being there than not.