Mike's Cabrio Build

[greyV8pete]

Re: Mike's Cabrio Build

Hi Mike. Usually having the pipes projecting further away from the body is the most desirable as in theory it puts the exhaust gas into less turbulent air. Maybe there is a difference in the projection of the rear bumpers behind the cars as those will tend to scoop a lot of air about.

The noticable difference between your set up and mine is that you also have the "anti fuel leak shields" on top of your rear boxes. Maybe there needs to be a horizontal "splitter" above the whole area to force the under car airflow to exit cleanly. It would be really interesting to put "our" cars in a wind tunnel with some bits of white wool blue-tacked into place. Anyone work at Farnborough?? Peter.

[Mike]

Re: Mike's Cabrio Build

Hi Mike. Usually having the pipes projecting further away from the body is the most desirable as in theory it puts the exhaust gas into less turbulent air. Maybe there is a difference in the projection of the rear bumpers behind the cars as those will tend to scoop a lot of air about.

The noticable difference between your set up and mine is that you also have the "anti fuel leak shields" on top of your rear boxes. Maybe there needs to be a horizontal "splitter" above the whole area to force the under car airflow to exit cleanly. It would be really interesting to put "our" cars in a wind tunnel with some bits of white wool blue-tacked into place. Anyone work at Farnborough?? Peter.

Hi Peter

Do you have any photos of the position of your exhaust showing where it exits and how far back it is relative to your number plate face?

Its an interesting question you raise about the exhaust shields and bumpers?

To fit my new wider back boxes I will have to remove the current exhaust shields. I also have a set of Sportster bumpers which I was considering fitting on the rear of my Cabrio. These would probably alter the air flow around the rear, but what overall effect might be I have no idea?

The odd thing for me is that Alan Hogg's Cabrio, with standard bumpers, has a single centre rear exit exhaust and he has no problems. The only differences seems to be that I have a central sump on my fuel tank which could affect airflow, and his tail pipe finishes around 50mm before the number plate face.
Obviously I can not do much about the sump, but I will try cutting my tail pipes back to see if this will work for me - it has to be worth a try!

[greyV8pete]

Re: Mike's Cabrio Build

Hi Mike. I have attached the only photos that I have easily accessible on file. Your fuel tank sump may well disturb the airflow. Also my pipes are in line with the boot shut line. Are yours the same, or further in / out? Maybe shortening the tail pipes as you plan will alow any downdraught from the airflow off the boot to blow the exhaust downwards which will help? This would be similar to the effect that has been achieved with turn-down exhaust trims. Maybe make the back edge of the fuel guard turn down for the same effect? Oh for a wind tunnel!

Another thought, are the fumes being drawn in from inside, say around the edges of the boot floor / any gaps etc, rather than from outside? Are the fumes still a problem with the hood up? Peter.

[Mike]

Re: Mike's Cabrio Build

Peter

Thanks for the photos - the plot thickens.

There are similarities with our exhaust systems, but there are some potentially significant differences too.

Copy of Exhaust (6).JPG

Having read a little about air turbulence at the rear of cars, it could be that my seat lowering pans are part of my problem, along with my silencers finishing further back toward the rear of my car, and that I have a sizeable sump on my fuel tank too.

I have some ideas I want to test...........................

(I can feel another potato moment coming on!!)

[CompoSimmonite]

Re: Mike's Cabrio Build

Peter

Thanks for the photos - the plot thickens.

There are similarities with our exhaust systems, but there are some potentially significant differences too.

[ATTACH]5387[/ATTACH]

Having read a little about air turbulence at the rear of cars, it could be that my seat lowering pans are part of my problem, along with my silencers finishing further back toward the rear of my car, and that I have a sizeable sump on my fuel tank too.

I have some ideas I want to test...........................

(I can feel another potato moment coming on!!)

That is some neat alloy welding

[Mike]

Re: Mike's Cabrio Build

As a build thread I do not want to clutter this with news of days out, but within our family I think this one is a justifiable exception.

My Father in Law worked for Ford for almost 30 years, rising to the dizzy heights of Industrial Relations Manager for the Dagenham plant during the 70s and 80s - (when he was under huge pressure to manage Ford's production through very turbulent union led times) and he is like the proverbial stick of rock - he still has Ford written through him, 25 years after retriring!.

The Sierra was in productiion when he left, and he has often asked when I would be able to drive my "Recyled Ford" over to his home in Derbyshire.

It was a true pleasure, at long last, to deliver on that long promised day.


Ron Webster, aged 91, outside his Slaley Farm home, with a "Recycled Ford"
...........though he was not too happy that I had shunned a Ford engine for a BMW!


Copy of IMG_6916.JPG



Copy of IMG_6912.JPG

[Mike]

Re: Mike's Cabrio Build

IMG_6919.JPG


When tested for IVA my exhaust, with the 2 smaller rear oval silencers, recorded 96db - well inside the 99db limit.
(as I undertand it, each 3db drop represents a halving of the noise pressure level).

However, although acceptable to IVA, it was thoroughly unpleasant on a long journey due to a loud BWAAAAAAAAAAAAAHHH under any load, and at steady 50-60mph.

Fitting the 90mm diameter single straight through centre silencer certainly helped reducing the noise considerably to 91.7db (effectively more than halving the noise from the original IVA value).

This made it drivable on long journeys, though still louder under load than I want.


The two new rear boxes I've made up have twice the internal volume and reverse flow perforated tubing, as well as adding resonant expansion chambers each end, to improve sound deadening.

When fitted these lowered the noise to 90.1db without tail pipes, which although halving the noise once again, was not as big a change as I might have anticipated/wished.

I took my car out for a short test drive with no tailpipes fitted to the new boxes but I still noted a slight smell of fumes rolling back into the cabin, so I have taken the reluctant decision to add bent tail pipes taking the exhaust out to the rear wheels, which I know works for other Cabrios.

IMG_6922.JPG

(The blue tape is only temporary - holding cut pieces of stainless bends and straights together whilst trialling angles and lengths, before committing to welding).

I feel it is a shame, as it has spoilt the rear end aesthetics of the original design:

Exhaust 2.JPG


But, I'm not totally beaten yet .............. (only for the moment!).


Research suggests that a rear splitter might help reduce the swirling of the airflow behind the boot, and may allow me to fit centre rear exit tailpipes without fumes rolling back into the cabin: but whether this is achievable with my seat recesses, - lowering the ground clearance and accelerating the air under the car, then trailing radius arms, fuel tank sump, larger oval back boxes below the boot, and a large wheel mounted on the boot, and finally the Cabrio bumpers positioned away from the boot, all messing up the airflow - I really do not know.
Without an air tunnel, I may never find out either, so this arrangement will have to do for now.

Given time, I may experiment with a simple splitter and try straight tailpipes just to see what happens, as I would really like my straight ones back again.

Later, when I finally transfer my M54B30 engine into my Cabrio, I'll retain the inbuilt CATs on the Exhaust manifold which should help reduce the noise significantly, so that I can go back to the smaller oval rears as well................. all good fun....... but I know what I like, and I'm prepared to work hard and persevere to get it!

[greyV8pete]

Re: Mike's Cabrio Build

Mike. Another idea for you to consider. Using your original set up, how about sleeving the rear exhaust pipes with say 2 1/2" dia stainless tube. The front would be open to scoop air from under the car so the exhaust gases would be surrounded with fast moving air which would help eject it clear of the body turbulence.

It could also help with noise reduction as per fan jet technology on the airline engines.

If you do end up with your latest configuration, flash a bit of hi temp matt black paint over the rear pipes like I did as it makes them less noticeable.

Peter.

[cameronfurnival]

Re: Mike's Cabrio Build

Ive been following this thread with some interest, having studied fluid dynamics at uni way back in the 80s I know that without some proper tests we are only guessing as to the flowstreams over a cabrio. Im guessing that since the distance over the top is greater that that underneath the air will move faster on top causing lift. I also guess that running boards will add to the lift and must be near enough close to an aerofoil stall. Thus the turbulence at the rear will be enormous at anything over walking speed. (still guessing). the air under the car will be moving slower and have higher pressure (ok so far?) when the under-car air recombines with the over car air its going to be a real mess. trying to get the fumes away from the car then would suggest angling pipes upwards into the faster lower pressure air. What do the engineers think?
BUt...please be kind, I have not had to use my brain in a good long while

[greyV8pete]

Re: Mike's Cabrio Build

It would be really interesting if we (Cabrio owners) could all attach some bits of white wool with blue tack to the rear of our cars and then get someone to video them from a following car when we are doing 30mph or whatever speed at which the fumes occur. That should show up any differences between airflow on the fumy and non-fumy cars. Any takers? Peter.

[Mike]

Re: Mike's Cabrio Build

Found this last night while surfing.............a BMW 328i back box cut open. Without knowing it, I appear to have arrived at a loosely similar arrangement. It has a bigger internal volume, an additional central baffle plate, and holes through the baffle plates themselves, but lacks wire wool/glass packing?





At first I thought it seemed to be remarkably carbon free inside, until I saw the next shot....









It also has two small expansion chambers just before exiting through the tips - like little Cherry bombs?

[Mike]

Re: Mike's Cabrio Build

10 years ago when I was researching engines, I concluded the BMW M50 2.5TU was the most advanced engine I would have the ability to successfully install: it had well proven electronic fuel injection and 24 valve variable valve timing, and was a well known swap among the BMW community: later engines were more refined/powerful, but were being fitted with evermore complex engine management systems (ECUs) and anti theft software (EWS) which no one seemed able to by-pass.

Now that I have my Cabrio on the road, and 190HP at full chat, which is nice, it lacks low down grunt by comparison to its top end, and I couldn't help feeling there must be something better around these days that wouldn't break the bank.

To cut a long (18 months) story short, my research led me to choose the BMW M54 3.0 engine. It was made between 2000 - 2006, and appeared on the Ward List of 10 Best Engines in 2002 & 2003. Its close to the current state of the art petrol engines for power and economy, but is becoming commonly available in breakers yards, having been fitted in almost all BMW models.

The M54B30 enjoyed some significant upgrades over the older M50 engine, notably infinitely variable Dual Vanos (variable Outlet as well as Inlet timing), with 20 degrees of advance (cf 12degree in the M50) and DISA (Variable Inlet runner length), significantly improving power at low rpms, without detriment to power at the top end. Lightened pistons made from new alloys reduced internal friction and so fuel consumption, to create a more powerful engine with a wider power band, yet just as eceonomical as earlier smaller engines. Win, win, win.

For comparison:

Engine .................... M50TUB25................... M54B30

Torque(ft.lbs) .......... 184 @ 4200rpm ............ 221@ 3500rpm

HP ......................... 189 @ 5900rpm ............. 229 @ 5900rpm

Peak torque occurs at only 3500rpm, and through the use of DISA these high levels of torque are available as low as 2000rpm: The M54 offers just the sort of performance characteristics I am looking for.

The one problem holding me back, and many others who've recognised its potential, from swapping one into my Cabrio was the fiendishly complex engine management system - The MS43 ECU. 18 months of research jnto how to defeat the software revealed nothing more than lots of false dawns, and no reliable solution.

But always one for a challenge I kept chasing my Holy Grail engine, and I'm pleased to say I believe I have now found it. Ergen Motorsport have reprogrammed my MS43 ECU which will run my M54B30 engine in my Cabrio chassis. They have also prepared a modified wiring loom which will be 'Plug and Play' with the M50 wiring connector, called an X20, I installed for the M50.

This week I went down to see Adem Ergen, and his M54B30 engine running outside an E46 chassis, and have returned with a loom which will allow the transfer of my M54B30 into my Cabrio, with hopefully not too much additional work required.

15428924579_3e8f29071c_o.jpg

The top half is totally standard M54 wiring loom, having all the connectors to attach to the engine.

M54 Wiring Loom Engine Connections.jpg

The bottom section is the new and revised business end - having the modified MS43 ECU, a new (M50) X20 connector to plug straight into my existing M50 X20 connector inside my Cabrio, along with the BMW Key/Antenna to allow it all to keep the rolling code changes, and a Drive by Wire throttle. Interestingly Adem has maintained the EWS (anti theft) unit, which most people believe is the cause of this swap being so difficult. I also get a Drive by Wire accelerator, doing away with the throttle cable.

M54 Wiring Loom - ECU EWS Key Antenna X20 In Car.JPG

My plan is to stand the M54 alongside my Cabrio in a temporary frame, plug the X20 into my Cabrio's X20, take Live and Earth plus fuel across to the new engine, and it should start from my Cabrios ignition switch - quite literally "Plug and Play".

Hopefully there should be a video before Christmas!...................watch this space.

[Michael Turpin]

Re: Mike's Cabrio Build

Mike, I really like your take on power steering and I am keen to give it a go, however, mine is a LWB YKC roadster will it still fit?
I will have to have a look, but I would be interested if you know of the differences of space between a Cabrio and a Roadster.
And yes I can see a few on E Bay available for £25

[Mike]

Re: Mike's Cabrio Build

Mike, I really like your take on power steering and I am keen to give it a go, however, mine is a LWB YKC roadster will it still fit?
I will have to have a look, but I would be interested if you know of the differences of space between a Cabrio and a Roadster.
And yes I can see a few on E Bay available for £25

Sorry Mike, I have no knowledge of the YKC. Having said that, I am guessing it uses a standard Sierra steering column?

If it does then, based on the conversion I made up the only physical issue is the size and location of the electric motor.
In the Cabrio it is very marginal for space in the footwell, and again I am guessing it would be tighter/more difficult in the YKC?

However, this is based on the Corsa C column.
It may be worth investigating the Corsa D column, possibly a Mk2, as it is possible the motor is more compact than the Corsa C columns?
- please do not take this as fact, it is merely an observation from the photos I've seen on ebay.

It is on my list of "Want to investigate further............?", but will have to wait until the more pressing jobs, like finishing off an exhaust which does not cause fumes to roll back into the cabin when the hood is down, and fixing screen frame latches to hold my new hood down.

If you do get the opportunity to compare a Corsa D against the C I'd appreciate your feedback.

Mike

[Mike]

Re: Mike's Cabrio Build

Oh dear.........It's obviously been a while since I made my last post on my diary - not on the list, so couldn't find my diary!


Once I started to drive my Cabrio there were 3 key things I wanted to adjust:

1. The exhaust was too noisey on long journeys
2. Fumes rolled back into the cabin, making driving unpleasant
3. The ride was too hard

I have now "almost" dealt with all three...................but not quite fully with any of them!

My mark 2 exhausts are now almost complete - I just want to weld on my rolled tips to the ends of the exhaust tailpipes, (purely for aesthetic reasons) : hopefully the bigger back boxes will quieten the noise down, and the tail pipes out to the rear wheels will now stop the fumes rolling back in to the cabin.

Today I finally managed to fit my new Gaz adjustable shock absorbers - hopefully to soften the ride - they've been on a shelf in my garage for the past 4 months!
Peter Licence posted details of his adjustable Gaz shock absorbers, which were a great success, so I ordered the same items from Rally Design, expecting them to be a direct swap : they were nearly..........but not quite!

IMG_7159.JPG

Top fixing sleeve has a 10mm I/D fixing hole: but the lower hole is 12mm I/D

It transpires Peter's Gaz adjustable rear shocks, part no. GT5-2066, were for the Cosworth/Granada rear trailing arms which have 12mm holes for the shock absorber fixing as standard - mine, being standard Sierra, were only 10mm fixings.

Oh bu**er.

Rather than waste more time sending them back, or requesteing new 10mm sleeves, I have drilled my trailing arm fixing holes out to 12mm, and found new bolts to attach the Shocks.

So why is it not complete? - I broke the drill bit on the last hole - a 12mm drill bit for goodness sake - that must take some doing! nevermind, with a new bit tomorrow, I should see the job done.

I still want to take the opportunity to swap diffs back again while the chassis is up on its stands. The 3.14 makes for very relaxed cruising, but my car is so over geared, 5th only really becomes necessary over 70MPH, which lets be honest, is a waste in a Marlin!

I will go back to my 3.38 diff, although a 3.62 would make for a whole lot more fun on acceleration! But as the medium term plan is to refurbish the M54B30 engine, which has bags more low down grunt at low rpm, the 3.38 should combine to offer pretty sharp acceleration AND relaxed low revving cruising.