To BTB or not to BTB

[Captain_Birdseye]

BTB say they can make me a manifold for the 318is, problem is they recon the cost will be between £1,900 and £2,400 before VAT. Anybody got experience with BTB manifolds and think the benefits of fitting one matches the price tag?

[ross_jsy]

Isn't this the iS you spent 8 bags on? I would leave it as close to how it left the factory if I were you.

The standard m42 manifold is pretty good, it's not going to have the performance gains of the BTB on an m20

[Captain_Birdseye]

Correct, and thanks for advice. I will call them and see if they did any conversions on the M42 E30 and have any graphs of before and after. Yeah, why not, no harm in that if I add a pinch of salt to the answer.

[DanThe]

I hope its going to give extra clearance for an E46 rack!

[Captain_Birdseye]

I hope its going to give extra clearance for an E46 rack!

Good point!

[jmc330i]

What are your reasons for wanting a BTB manifold?

I bought one for my S50 conversion (many years ago, when no others were available) and they are very good, but I'm not sure they are £2k good, especially on an M42 when (as Ross says) the standard manifold is pretty good as is.

[DHFiS]

I have never heard of anyone getting significant power gains by modifying the exhaust on an iS.

Just out of curiosity I think you should do it.

[DanThe]

£2000 would buy you much more power in the form of 6 cylinders...

[Captain_Birdseye]

My reasons were wanting a bit more oomf, when I started down the BTB avenue I was assuming there was as much gain to be had from the M42 as from the M20, which it now appears there isn't, thanks to your advice. I was also hoping they may be easy to source, which they're not, probably due to there not being a need for them in the 1st place (at least not for my model).

I will still ask them what they think it might achieve, if they are clueless then 2000 is a lot for an experiment when experienced people here know it's not a great idea, and, when tried and tested methods -engine swap- can be had.

It's nice having the smaller engine for lighter weight and fuel expenditure so will have to have a think.

It woulf be nice to keep it close to original, but as I've heard others say - you can always put it back to standard if you keep the old stuff.

[Kedge]

Wasting your money, the iS already has a tubular manifold. I can only see there being negligible gains, if any. If you want to keep the M42 look at capacity increases and weight loss on the flywheel, a JBR aluminium flywheel transformed my 318iS.

One thing I've always wanted to see the results of being fitted is a Metric Mechanic Pulse intake manifold (if the company still exists), give it a Google.

[DanThe]

To be honest ive never seen anybody post results of a tubular manifold that has been made for power on an M42, yes the standard is tubular but it doesn't mean there is no extra power to be made, some tubular manifolds make no power over cast manifolds so I wouldn't say its a waste of time or it cant be done.

[Kedge]

Has anyone ever had one made before?

Fair point about some tubular manifold not making more power than the cast version, but they tend to be the cheap Chinese copies, and even those have made gains in other areas of the rev range, if not peak figures, only speaking from what I've seen regarding M20s. Surely a BMW tubular manifold will be better than those, but I guess there could be more optimal diameters, and from what I remember the BMW manifold isn't particularity leightweight.

But £2000 for a 4cyl manifold!?! What are they charging for M20 ones nowadays?

[Captain_Birdseye]

Hmm, I don't know but it nay be possible they still have the moulds or whatever kicking about for the M20? The quote is for a bespoke one for me.

[kieran325]

I had the full system and manifold on my 325 several years ago. I then decided to get the M3 done and enquired about the manifold on the S14 but Joe didn't think it was worth any gains in doing so. I had a full system on the M3 coupled with the stock manifold.

[Jon_Bmw]

£2000 on a "basic" 4 cylinder manifold is what i'd quote to get rid of a job I didn't want to do!

[Captain_Birdseye]

If you want to keep the M42 look at capacity increases and weight loss on the flywheel, a JBR aluminium flywheel transformed my 318iS.

One thing I've always wanted to see the results of being fitted is a Metric Mechanic Pulse intake manifold (if the company still exists), give it a Google.

And thanks, this should keep me entertained for a while.

[Blitz]

All sounds like a waste of money. Leave it alone and buy something faster.

[Captain_Birdseye]

All sounds like a waste of money. Leave it alone and buy something faster.

I think I'd get more enjoyment out of spending money on some interesting mods.

[reggid]

To be honest ive never seen anybody post results of a tubular manifold that has been made for power on an M42, yes the standard is tubular but it doesn't mean there is no extra power to be made, some tubular manifolds make no power over cast manifolds so I wouldn't say its a waste of time or it cant be done.

by looking at the standard jobbie, there looks like there could be some nice midrange torque gains with longer primaries and secondaries. BFYB is never going to be there when youre paying this much for a manifold

[steve_k]

£2k for a 4 branch manifold?? I was quoted that to copy a RD 6 branch by a place in Chesterfield & that includes having my car there so it fits perfectly & the price included down pipes & vat.

Also would be made from 316 or higher grade stainless steel.

Not bad for a one off.

[jmc330i]

To be honest ive never seen anybody post results of a tubular manifold that has been made for power on an M42, yes the standard is tubular but it doesn't mean there is no extra power to be made, some tubular manifolds make no power over cast manifolds so I wouldn't say its a waste of time or it cant be done.

by looking at the standard jobbie, there looks like there could be some nice midrange torque gains with longer primaries and secondaries. BFYB is never going to be there when youre paying this much for a manifold

My M44 conversion has used an E30 M42 manifold for the last couple years. Compared to my friends standard M42, mine had better pull at low revs (mainly due to the M44 DISA I guess) and his would pull a bit better at higher revs.

I recently changed mine to the E36 M44 manifold, so it's now running as a standard M44. There was a very noticeable gain in midrange torque and a definite change after around 5.5k rpm - it feels less lively. While I might of lost some top end, as road car I don't tend to spend much time near the red line, so the extra low down torque is more useful.

Not my pic, but top is M42 bottom M44...

[matt86]

You could fit a big bore throttle body, lightened flywheel and cold air intake. These are reasonably cheaps mods and would give you around 15bhp or so extra. You could also add a ecu chip for an additional 5-8 bhp and will smooth out any flat spots.

[reggid]

To be honest ive never seen anybody post results of a tubular manifold that has been made for power on an M42, yes the standard is tubular but it doesn't mean there is no extra power to be made, some tubular manifolds make no power over cast manifolds so I wouldn't say its a waste of time or it cant be done.

by looking at the standard jobbie, there looks like there could be some nice midrange torque gains with longer primaries and secondaries. BFYB is never going to be there when youre paying this much for a manifold

My M44 conversion has used an E30 M42 manifold for the last couple years. Compared to my friends standard M42, mine had better pull at low revs (mainly due to the M44 DISA I guess) and his would pull a bit better at higher revs.

I recently changed mine to the E36 M44 manifold, so it's now running as a standard M44. There was a very noticeable gain in midrange torque and a definite change after around 5.5k rpm - it feels less lively. While I might of lost some top end, as road car I don't tend to spend much time near the red line, so the extra low down torque is more useful.

Not my pic, but top is M42 bottom M44...

that looks like step in the right direction.....

exhaust changes need a retune though if you want to reap most benefit though more modern ecus can usually adapt to get the fueling part pretty good, the ignition timing probably is not going to adapt.

its amazing how much the exhaust influences the characteristics of an engine you can totally kill an engine bottom end and mid range with the wrong exhaust especially with any sort of performance cam.

[rix313]

lightened flywheel

This certainly makes a huge difference to the way the engine feels.

cold air intake

This I don't get. Have you seen the standard airbox? Air intake directly behind the front grille? No restriction inside and straight to the engine? Only thing I have done to either of mine is fit a serviceable air filter.

[Kedge]

cold air intake

This I don't get. Have you seen the standard airbox? Air intake directly behind the front grille? No restriction inside and straight to the engine? Only thing I have done to either of mine is fit a serviceable air filter.

Back in the day there was some dunk graph kicking about of back to back runs with various filter setups on a 318iS, standard came out on top.

[Brianmoooore]

You could fit a big bore throttle body, lightened flywheel and cold air intake. These are reasonably cheaps mods and would give you around 15bhp or so extra.

I think the decimal point has been missed out between the 1 and 5.
Lightened flywheel won't add a fraction of a HP., although it will have an effect on how effectively the HP you already have is delivered.

[Gert_8]

My thoughts/advice on the BTB for £2k is would it make my £8k a £10k car?.....I don't think so. In fact I think it would make your £8k car a £5k car.

[kieran325]

In fact I think it would make your £8k car a £5k car.

Why's that ?

[Gert_8]

Messed around with the original specification.

Does it make it a £10k car?

[ross_jsy]

All of the modifications mentioned so far will decrease the value/saleability of the car. Most modifications will

[Rav335uk]

£2k for a 4 branch manifold?? I was quoted that to copy a RD 6 branch by a place in Chesterfield & that includes having my car there so it fits perfectly & the price included down pipes & vat.

Also would be made from 316 or higher grade stainless steel.

Not bad for a one off.

I bet you didn't have it though

[steve_k]

£2k for a 4 branch manifold?? I was quoted that to copy a RD 6 branch by a place in Chesterfield & that includes having my car there so it fits perfectly & the price included down pipes & vat.

Also would be made from 316 or higher grade stainless steel.

Not bad for a one off.

I bet you didn't have it though

Not at the time a big bill came in, but I know the offer is still there though ;)

[Rav335uk]

Was that for a dustpan and brush Steve?

[kieran325]

Easy to put back to normal and retain its original part and plus you get the resale of the BTB.

[steve_k]

Was that for a dustpan and brush Steve?

Nah, I can't be trusted with those, I might sell them ;)