1.8L VS 2.0L T4 exhaust systems Options

[technicalninja]

I've wondered why Porsche built different exhaust systems for the T4.

It appears that any year complete exhaust system can be installed on any year T4.

And yet the systems are so different that even the mount at the transmission needs to match the exhaust.

Why?

It seems the systems have the same size pipes.

The 1.8/1.7 have a short "S" kick up at the back that doesn't look like it will affect flow very much.

What am I missing?

Are the 2.0L mufflers higher flow?

Was it just a sound difference?

I didn't "see" an obvious flow difference when I bought a pair of used 1.8L SSI exchangers and the Bursh muffler that fit them.

Was I wrong?

[wonkipop]

@technicalninja

the answer to your question is relatively simple if you take a chronological view of history and place yourself back in time.

the first three years of 914s, as type 4s (ie the four cylinder cars) is solely as 1.7 engines.
and importantly - if you take yourself out of the american context and put yourself in the native european/german context - its the VW version that is sold in VW dealerships - as a budget sports car by VW and Porsche using as many VW parts as possible.

the mufflers were standard VW 411 mufflers. absolutely as fitted to VW type 4 sedans.
only the heat exchangers and exhaust manifolds were special. had to be anyway - mid engined location.

the other one - the six - used a porsche 911 muffler. more or less. again with its own heat exchangers due to mid engine location.

after the first three years you basically still had the same scenario.
because.........a 2.0 is in many ways a porsche engine despite being based on and using many components from the VW type 4. porsche engineer it to be the replacement for the more expensive 6. and in euro tune form it nearly is a replacement since it generated 100hp and had a lot more low down torque than the 6.
and like the 6 it got the porsche treatment. a porsche designed muffler that was in many ways a scaled down 911 muffler. same higher flow design.

the 1.8s repeated the formula of the 1.7. they used as many components from the later 412 engine. including the muffler. and slightly bigger diamerer tailpipes.

the way to think of the 2.0 is to always regard it as the development of the 6.
development does not necessarily entail ever more powerful engines and going faster.
sometimes its about getting a better compromise between showroom cost, manufacture cost and acceptable performance. thats what the 2.0 was. a very very successful replacement for the 6 with a unique porsche designed (re designed) T4 engine and accessories.

the 2.0 muffler is higher flow. but quiet enough to pass TUV regulations (German noise regs). the VW mufflers on the smaller engines are more restricted. primarly designed to keep the short exhaust system on the standard VW sedans as quiet as possible to pass TUV test certification. the problem VW always had was that the engines being in the rear (and being naturally very clattery) were also close to the exhaust outlet.
so all the noise was in one concentrated spot when it passed by the microphone used in the certification tests by TUV. the 914 small engine simply inherited this very conservative muffler despite having a less concentrated zone for the microphone to pick up on it.

as to bursh and other aftermarket mufflers. none of them were ever part of this initial german design regulation certification and testing. they were US aftermarket systems.
never really subject to noise certfification etc. so they could have a much freer hand.

(IMG:style_emoticons/default/beerchug.gif)

[JamesM]

@technicalninja

the mufflers were standard VW 411 mufflers. absolutely as fitted to VW type 4 sedans.
only the heat exchangers and exhaust manifolds were special. had to be anyway - mid engined location.

(IMG:style_emoticons/default/agree.gif) THAT^^^

My educated guess would be along the exact same line.

Im an odd duck that finds the PET to be an interesting read, and it can also help infer a lot of information. Specifically that the 1.7 muffler was one of the many 914 parts taken from a 411. I would assume the 1.7 heat exchangers were designed to fit the existing parts bin muffler and nothing more. Then to optimize the 2.0 they needed to go larger diameter pipes necessitating a new muffler/heat exchangers and it made sense from a cost and/or weight distribution perspective to not bend the pipes up and mount the muffler lower.

Progression of part numbers in the 914 PET tell a story of sorts. Really interesting stuff.

The one thing I don't have a theory on though is why the 72s used a 911 heater lever where all other years got a 914 part. (IMG:style_emoticons/default/confused24.gif)



On thing i have been getting some first hand data on lately are the various heat exchanger and exhaust systems impact on performance, at least when used with performance motors. The 75 style 1.8/20 exhaust setup absolutely kills performance and is pretty much at its limit in the stock application. When running SSIs the 1.7 isnt much different than the 2.0 as the pipes are the same. I haven't had reason to install factory 1.7 exchangers on a performance motor so cant speak to those but I would expect they would be less given the smaller ID. Everything I have been doing lately is with PMBs built 2.3s with aftermarket EFI and ITBs. (150+ crank HP motors) Factory 2.0 mufflers are ok, better when opened up with a 2nd exit. Busch so far have felt the best but haven't thrown that one on the dyno yet. Going to be putting a Monza on one shortly as that is what the customer has, but just from looking at it I suspect its going to cripple the power on it quite a bit, the pipes on the Monza are tiny. that one is going to be run back to back with a 1.7 bursch I am using to setup the tune so ill have a good comparison.