GROUP BUY BTB tubular manifold

I will find this out from BTB and get back to you.

2. I would like to see steel tubing with *no seams*. for a prototype
this is ok and quick to make a header, but for the final product,
I dont like to see any seam running the length of the tubing. if it
makes the product more expensive, I will pay more to get the better
tubing.

Agreed.

3. how the Y-merges are done is important for performance.
you could also take measurements from the merge to the
exhaust flange at the secondary. and from the merge to the
exhaust input flange (primary). compare these lengths with the
standard noncat header (320is).

We wanted to get a better look at it off the car but because installation is quite difficult, we didn't get a chance. I;m sure BTB will have these measurements though. I will ask and get back to you.

4. Nick, that you are doing a dyno run is great. Im willing to do
a before and after on my exhaust system too. Since you are
running an airbox and alpha N, I would like to point out that if
the exhaust makes a significant difference you will need  2
alpha N maps!  each one optimized for the particular exhaust.
Only then can you compare dyno runs of standard header
vs. this new header. I also advise optimize the AN map as your engine *might* be in danger otherwise.

Good to hear you're doing a dyno run. The dyno run we did was before the Alpha N and airbox was fitted. So basically we got a dyno result of the Supersprint Race and standard cat-manifold (even though our Ewok was supposed to come with a non-cat manifold!) which was in our last issue... and a dyno result of the Supersprint Race and BTB manifold.

Our Alpha N is still running on a base map until we decide whether to go for 284 cams or not (which will be decided by our tiny budget - we cant get them for free or for little money sadly). At the moment it's purposely runnning very rich all the way through the rev range to keep it safe until we get it properly set up.

Obviously, ideally I'd put on all the modifications at once and then tune it, but we are doing things bit by bit to see how everything affects the engine output and drivability.

just a general observation since Ive played with exhaust a bit:
On my engine I have a map for the stock exhaust and one for
my DTM style exhaust, in both cases the header is the same.
but the AN maps (each optimized for the particular exhaust) are
much different! if I run th stock exhaust map but use the DTM
type exhaust, the engine doesnt run right and is very lean
(AFR in the 16s )

obviously the size of the exhaust cam also plays a role in how
sensitive it responds to exhaust changes. I dont know which
cams you are running, but it might not make such a big difference
on stock cams. Which brings us to another point:  on a stock setup
you may see little difference with the header, perhaps even
a loss is possible, whereas on a
wilder engine you could see very significant performance gains.

Totally agree and as already stated, this manifold is designed to work best on tuned engines that need the benefits at high rpm at the potential loss of low-end power. Even on a stock engine we saw gains at the top end and losses at the bottom end... as predicted. Hopefully with airbox, cams and good tuning, it could be a good powerband.

I saw this this weekend on Kevins (barefoots) car. Im sure the
single exhaust setup is great for most poeple, but on his engine
with motorsport cams, he is giving up power/torque
in the 5k-8K rpm band using that setup. But where his exhaust
performs better compared to my exhaust is that around 3000 rpm
I have a torque dip which is larger than the dip that Kevin has.
This dip seems to get larger the larger the diameter of the pipes
of the exhaust system as whole.

I have his new AN map, I will try to post his map vs. my map this
weekend, then you can see there is a significant difference
in the fueling.

anyway, just throwing that out there to be aware of:
you can play a lot with
exhaust systems especially when the cams become more extreme.
on stock setups, the stock system is hard to beat overall.

Again, totally agree - on the dyno run of the standard car, it produced a very good power/torque output. Of course NA engines are never as easy to make power from of as turbo ones, especially ones as well tuned from the factory as the M3!

John