Optimised 2002 Ti exhaust manifold

[quant]

Dear all,

 

Having purchased a 1970 2002 Ti restoration project in Malaga red yesterday, I'm relatively new to the 'world of 02'.

 

I'm reading up on finding the right balance between originality and 'optimisation' for the restoration.

One of the things I'm wondering, is what an 'optimised M10 exhaust manifold' could be.

 

I'm looking to slightly improve the engine with a bit higher compression (e.g. forged pistons and conrods), some cam-tweaks (e.g. 292 cam) and perhaps a set of 40 or 45 Webers (looking more for low-end torque than high-end horsepower).

 

The other thing I'm considering is what the right exhaust manifold for this set-up could be - at least something with equal length pipes.

 

However, one of the things that keeps puzzling me is that all the M10 / 121 exhaust manifolds I've seen feature round ports. Whereas as the 121ti head has more somewhat rounded-square / oval exhaust valves. So such a 'step change' in exhaust diameter and shape, looks to me not to have 'optimal exhaust gas flow'.

 

See e.g. this (borrowed) photo:

 

As I'm sure this topic has already been engineered on many times before, by much smarter and more experienced minds than mine, I'm wondering what the experiences on this are - what exhaust manifold to consider for 'optimal exhaust gas flow'?

 

As a closing photo - my project car:

 

Edited February 28, 2021 by quant

[dp]

By optimised are you focused on flow? If you want flow with some appearance of stock, the late-model '02 manifold with the huge smog bung by #4 flows equal to Ti and Tii variations. But better than all those possibilities and less hassle is a basic tube header, you can get a new one that is well-built for about what people are demanding for a "Ti" or "Tii" manifold now. If you're looking for how to hog out the stock manifold (you hopefully got with your car) my advice is "don't" because I wouldn't.   

[Oldtimerfahrer]

From the threads, the ti/tii manifold is considered pretty good...headers wont bring much other than heat and noise unless you modify heavily and the engine needs to breath a lot more. A lot depends on what you put after it as well. I have a polished, ported and skimmed head with a 300 degree cam and 45 dcoes with the stock manifold and a free breathing exhaust behind it. I have no empirical evidence either way. If I had the ti manifold and heat shield, I would stick with it. As dp wrote, I wouldn't pay an arm or a leg for one either. Maybe someday one will show up for reasonable money if you search. Yours came exhaust free?

Edited March 3, 2021 by Oldtimerfahrer

[uai]

I would recommend the Alpina A4 Reproduction Y-Tube on a stock cast Header. It's a very good plug&play solution that flows as good as many aftermarket tri-y headers and is less intrusive and doesn't rattle or crack
https://marktplatz.bmw-02-club.de/index.php?page=item&id=2887

 

[quant]

Thanks for your recommendation

[Oldtimerfahrer]

What you can do is orient yourself on the Alpina A3 spec, just for the motor which would include the downpipe uai recommended. You can make your own downpipe sort of, by rewelding a stock item to move the join further away from the manifold. You will get good low end torque with the 40s, would probably need to raise CR quite a bit to retain driveability with 45's. I have 45s with stock ti pistons and its ok as far as Im concerned. I cant pull away cleanly from 1200 but after 1800 RPM it has enough go to get around the city. If you have the overdrive 5 speed, you will still need to downshift from 5th if you really want to go with either setup.