BTB Exhaust installed - power loss!!!

Post Sun Sep 17, 2006 12:38 pm

Hi guys.
I just had the BTB manifolds installed on my car, and a brand new 2.5" single tail pipe installed - almost the same as what i used to have on the race car, except BTBs are much better manifolds than what i had before (just some home made jobbie).

After racing this weekend, the car is almost 1 second a lap SLOWER than it used to be - and this was a mixture of caning it and driving slowly.
The car FEELS nicer, a lot free-er and smoother on power delivery, but not quicker - seems i'm a lot slower than i used to be.

Just wondering if anyone could shed some light on this - whether the BTBs require some kind of preparation or run-in procedure for maximum gain - I don't want to feel like I paid over 1000 pounds (includes shipping and taxes) to go slower.

Just to identify what engine setup this is on:
-BMW 1988 325i, M20B25 (either 8.8 or 9.4 compression)
-Standard engine essentially
-'173' Bosch Motronic Control Unit
-UNICHIP piggy-back engine management system
-BBTB (64mm)
-BMC CDA on intake

The engine has been unchanged apart from the BTB exhausts.

Post Sun Sep 17, 2006 12:54 pm

i am DEFINITLEY no expert but does your ecu have to learn its got a new exhaust system?

Post Sun Sep 17, 2006 1:04 pm

This could take some explaining

I think a dyno is the best way to tell, before and after.

Perhaps you were having an off day

Post Sun Sep 17, 2006 2:31 pm

You might need to have the Unichip remapped to get full advantage of the manifold??

Post Sun Sep 17, 2006 8:16 pm

Yeah you need to have the fueling adjusted to make use of the new manifold.

I would also look at the exhuast for power loss not so much the manifold.

Andrew

Post Sun Sep 17, 2006 8:44 pm

I would get the Uni-Chip re-map'd after such a major part addition....

Post Mon Sep 18, 2006 2:39 am

Yeah that seems to be the consensus - on the note of me having an off-day; that's not the case. I was driving exactly the way i used to, but the car is slower in a straight line.

Post Mon Sep 18, 2006 1:56 pm

definately need to be getting it remapped with the new manifold n exhaust on!!

Post Mon Sep 18, 2006 3:41 pm

I'm also thinking that the UNICHIP may be overriding Motronic's ability to 'learn' or adapt to the bolt on additions; maybe its forcing it to run to a fuel/ignition map that benefited the older crud pipes, but hurts the motor's ability to perform with a well crafted manifold.

Oh, and the exhaust (downpipe back) is not restrictive, basically same as what i used to have, straight through 2.5" no cat tailpipe and straight through glass pack rear muffler.

Post Mon Sep 18, 2006 9:27 pm

The motronic system fitted to our cars cannot 'learn' or 'adapt' ever!

Andrew

Post Mon Sep 18, 2006 9:36 pm

Demlotcrew wrote:The motronic system fitted to our cars cannot 'learn' or 'adapt' ever!

Andrew

So that means that any aftermarket chip is useless then??

Well, in so much as that it's not gonna have an optimum map for any mods done.

Post Mon Sep 18, 2006 9:37 pm

Not always, as things have moved on and fuel technologies have changed so a chip will iron out any defects from factory settings.

It will never be as good as a live map.

Andrew

Post Tue Sep 19, 2006 7:25 am

When i said it has a 'learning' capability, it can adjust the system depending on the lambda values - my car no longer has a lambda sensor in it to measure air/fuel ratio after combustion. That could be the major drama.

Post Tue Sep 19, 2006 7:47 am

How did the exhaust cost you Ãƒ”šÃ‚£1000...can believe postage was Ãƒ”šÃ‚£300 as is half way round the world but must have been by air for that price!!!!

Post Tue Sep 19, 2006 11:27 am

Well the ECU doesnt take a reading from the Lambda sensor after 80% throttle and becuase on a track this is where the throttle stays most of its time the ECU wont learn anything.

Your car needs its fueling set again.

Andrew

Post Tue Sep 19, 2006 12:04 pm

Can you tell us a bit more about your exhaust please. Go into as much detail as possible.

Sal

Post Tue Sep 19, 2006 4:30 pm

Postage was by air, but then had to pay stamp duty and GST (similar to VAT) to get it out of customs - essentially 150 quid for shipping, then the same amount for customs clearance BS.

The BTB manifolds are hooked into the BTB 2-1 downpipe, which is mounted to a single 2.5" straight through downpipe to a straight through glass pack muffler. Essentially the only restriction in the system is the slightly larger diameter resonator or 'hot dog' in the centre where a catalytic convertor would be, it's there to dull the noise down to 95dBA on a 30m drive past.

Post Thu Sep 21, 2006 5:06 pm

2 major points made, and will be looked at:

1. Will be wrapping manifolds up in thermal wrap, or maybe ceramic coating at a later date.
2. Will be getting UNICHIP retuned on dyno in the next week or so - bring on 20 bhp!!!

Post Thu Sep 21, 2006 5:11 pm

Just a thought,

when is the last time you did a time lapped before you fitted the BTB?

Since then has the weather changed? Is it hotter? If so then this could possibly explain things as intake air temp would have gone up.

Sal

Post Fri Sep 22, 2006 2:23 am

No difference, everyone else was doing laps just as fast as they used to, if not faster.
The car is noticably slower in a straightline compared to the other cars - slower than it used to and they haven't changed anything on their cars.

Post Fri Sep 22, 2006 8:28 am

Hi djs325,

my guess is that the exhaust caused the engine to lose some mid-range torque at the expense of top end power. Now when you're track racing you need mid-range torque to accelerate out of a corner and if your slow out of a corner you will be slow on the straight - even if you have slightly more power in the top of your rpm range, your not likely to catch up what you lost.

IMO, get a new camshaft that works well with this BTB exhaust (check your average rpm coming out of corners and aim at good torque there) or simply put your home-made exhaust back.

Post Fri Sep 22, 2006 8:53 am

I dont know much about exhaust design except the pipes not allow to be too small, or too big - so here's an uneducated thought:

Is the pipe the right size? I know that single 3" is used by several E30 M3 owners from a few articles I've read on the net. They aught to be chucking out the same amount of exhaust gasses as a 6 cyl. 2.5?

Post Fri Sep 22, 2006 2:27 pm

Andreas: The Racing class i'm in does not allow for different camshaft.

JazzMan: The pipe is the size that BTB themselves told me to use (2.5" all the way back)

Post Fri Sep 22, 2006 4:36 pm

Did you run the system in first ?
An exhaust can take 500-100 miles before it is at its best as the carbon seals the joints.

Post Tue Sep 26, 2006 11:38 am

Didn't get a chance - will have done at least 300miles worth on the weekend, as basically all at full-tilt.

Post Tue Sep 26, 2006 2:45 pm

I'd say re-map on the rollers mine is in need of this big time with all the toys on her shame she is coming off the road at the end of next month

Post Mon Oct 02, 2006 4:41 am

Yeah, I'm just waiting to hear back from the guy I was going to get to tune the UNICHIP, as they are getting new software soon, but maybe not in time for the next round - will have to look elsewhere to get it done.

Post Mon Oct 16, 2006 10:07 am

Unichip retuned - air fuel was way off; was just about perfect until about 4000rpm, then really leaned out. Have richened it up a bit, gained about 6 hp, but is also a flat power delivery from 5-6k rpm, and torque is only a small decline from 4000rpm onwards downward - gains across the whole rev range over last tune. But it only works out as 133bhp at the rear wheels - means about 180bhp @ flywheel, which is not much, though the engine probably needs a rebuild (rings and bearings) to be properly quick again. Should also probably look at a new clutch soon.