BMW 3.5 T project

Road-race engines and ancillaries - general discussion
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Hexer
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BMW 3.5 T project

Post by Hexer » May 6th, 2010, 9:58 pm

Hello everyone, I'm now working on a BMW m30b35 turbo engine and hoping to go over 550 hp.
Yet I have some questions about how and why most of the builders fail with this engine, at least their engines are unreliable, the engine I'm working on is one of thees unreliable ones, the owner came to me for solving the problem.

The problem is quit simple, the had cracks under the camshaft very ease if you push to hard without overheating or any other symptom.

On the photo you can see where the head is cracking, he had one head crack at the 2. piston, the other between 5-6.
One of the tings I think could cause this is cavitation and the shock wave weakens and finally cracks the head, ore a gas pocket.

I spoke with a few people, and they say the cause is local overheating because the exhaust is very close and the engine wasn't heated properly before going on the track. The last 2 heads failed on well heated engines, on was NA the other turbo, so this theory fails here...

How can I saw the problem?


3 tings I can do to stop cavitation if thats the case:
-make bigger pressure in the water lines
-better heat conducting stuff, thinking on water watter
-bigger flow, only with an external electric water pump
-the thermostat is of 80 degree, so its ok

I found a suitable electric pomp, Meziere Enterprises WP116SHD, 40 gpm free flow...(the same as the V8 one just in a universal mounting case)
My doubt is that the pump consumes 6-7 amps witch is around 100 Watt, in all of my books it reads that the mechanical bell driven pump consume ~1 kW (~1,3 hp) witch is a lot more than this electric one...how can this manage better results then the original?
Have someone tried pumps like this?
Attachments
Cylinderhead.jpg
The red line indicates where the heads prompt to crack
Cylinderhead.jpg (40.58 KiB) Viewed 5004 times
mez-wp116shd_w.jpg
The pump
mez-wp116shd_w.jpg (14 KiB) Viewed 5004 times

pastaroni34
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Re: BMW 3.5 T project

Post by pastaroni34 » May 7th, 2010, 6:17 am

I can't offer any advice as to your head cracking problem but I have used Meziere pumps before with great results on a BMW S14 motor before. The great thing about them is they use a constant amount of power and always run at optimum flow so we don't overheat at idle or caviate at high rpm.
-Jason Miller
Miller's Mule Machine and Design Inc.
Houston, Texas - USA

Guy Croft
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Re: BMW 3.5 T project

Post by Guy Croft » May 7th, 2010, 8:14 am

If the heads are prone to cracking I'd find a different engine. They should be able to survive anything, including cavitation, detonation etc without doing that. Must be a stress concentration there that is aggravated by vibration from one of those causes.

GC

4v6
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Re: BMW 3.5 T project

Post by 4v6 » May 7th, 2010, 8:40 am

Could it also be a material/construction issue?
Tony Warren. GC #96.

Hexer
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Re: BMW 3.5 T project

Post by Hexer » May 7th, 2010, 9:07 am

First of all thanks for the fast reply.

So I understand that you didn't use a controller for regulat pomp speed based on coolant temperature.
I was wandering if there is no controller I could over-cool the engine, or the coolant temperature fluctuates during road use, as at low power, low rpm the cooling would bee to efficient and the thermostat would open and close.

What if I leave the original pump and install the electric before that, it will serves like a of flow regulator, in this way at low speed the flow would bee smaller, yet when the rpm goes up the pump can do its best...


There ware many racing engines made of this M30, ex. 633csi, had no problem producing 400 hp in race condition. When it sees a turbo it goes nuts, so most probably the extra heat makes the head crack or make the stress point to show up.
In this case longer collectors, the heather made of stainless for low heat conductivity and better ventilation near the turbo end header could also help... because the exhaust gas temperature is around the same as on an aspirated, ~900 degree.

1NRO
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Re: BMW 3.5 T project

Post by 1NRO » May 7th, 2010, 9:12 am

Can you access the area for welded repair/reinforcement? maybe it has already been tried?

What about a tiny outlet in the area? maybe just not possible.

Nik
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Guy Croft
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Re: BMW 3.5 T project

Post by Guy Croft » May 7th, 2010, 1:38 pm

Whoa!

I hear about these XXXbhp projects every day and they all end in failure. Either this head has an inherent weakness that restricts how much you can tune it or it doesn't and it's the units exhibiting cracking simply being very badly set up. I'm trying to put the finishing touches to a book over over 350 pages wherein I talk about many of the probable causes.

Now: turbine inlet temperatures of 900 deg. I hope you mean Fahrenheit because if you mean Centigrade the ex valves are going last one race before they bend under the influence of heat and pressure whatever they're made of. If the TI temp is that high the cylinder temp at valve open is way higher. Sure there are turbos Like new generation Honeywell that, with special cooling systems and materials, can just about cope with 1050 deg C (for how long is anyone's guess) but 825 deg C is more the norm but 21-4n stainless valves can only cope with 800 deg C cylinder temperature before they start to deform and nim 80A will only last a short while longer.

A great deal depends on the ex cam timing. The earlier the valve is opened - for max pressure to the turbine - so the less power you're going to get in the firing stroke and the hotter the valve is going to get. Remember the valves only get a chance to cool down when they are shut. Early EVO means less cooling to the ex valve on overlap - even assuming the incoming pressure is high enough to overcome the ex header back pressure. If you open the ex late the inlet valves are going to be exposed to higher temperatures on the overlap than with early EVO because the even is longer. You have to be real careful choosing cams and timing. They must have minimal overlap and start/end and middle of valve event are utterly critical. They have to be designed by a, well... real expert.

And the big killer is exhaust back-pressure. Poppet valve systems are ill-suited to high back pressure. But obviously a certain amount is needed or there won't be enough energy to drive the wheel. First point is that if you aren't considering a tubular system with big diameter generous bends and long runners (which they will have to be to achieve that) - and a turbocharger with turbine housing especially designed for your exhaust conditions - you should be. The higher the back pressure means more heat trapped in the header and ports than should be. It causes detonation and sends cylinder temps skyrocketing. And the effects are totally random, so much so that it can render ecu calibration meaningless.

There are some examples of good header design here:

http://www.google.co.uk/images?hl=en&lr ... CD8QsAQwAw

But with one or two exceptions, eg: F1 Renault Gordini, how anyone imagines anything so capacious and effective can be 'shoehorned' into production car architecture escapes me. Figuring this out - as I repeatedly say to Project XXXbhp folk, should be your very first priority.

GC

Hexer
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Re: BMW 3.5 T project

Post by Hexer » May 7th, 2010, 4:41 pm

I think ~160 bhp / litre isn't that exaggerated from a turbo engine, with proper cooling and good management, yet I'm aware that I have to take actions not to destroy the engine.

I'm using Garrett or Turbonetics, they withstand 900 deg Celsius for longer periods without problem. The exhaust valves are the problem, I'm using stainless EV8 (21-4N), but the car goes on drag strip so it should be ok considering full throttle for ~12s.
The cam profile is attached, isn't the final, I'm planing to advance it a little as the exhaust open at TDC 0,7-0,9mm, it depends on the back pressure, I don't want to burn the valves wit opening them to early.

Hope to achieve bigger intake pressure than back pressure until the engine goes over 5500 rpm at full throttle and max 30% over the intake pressure at rev limit, around 7000 rpm.
Big turbine (GT40 A/R 0,83 or HP72 with ~1,xx A/R), I have boughs, will see which is better.

Exhaust is a big problem because the BMW engine tilts toward the exhaust so the place is very limited for nice big curves long pipes, but I'm trying to do my best.

Regarding the cooling I thought on 2 possibility:
-leaving the original do its job, and put the electric one to feed directly the back of the head
-leaving the original do its job, and put the electric one to feed through the last freeze plug on the engine (between the 5-6 cylinder)
In bought way redesigning the head gasket water holes.
Attachments
TurboCamM30.jpg
This is the actual cam profile, measured with worn rocker arms but 95% its ok
TurboCamM30.jpg (126.04 KiB) Viewed 4937 times

Guy Croft
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Re: BMW 3.5 T project

Post by Guy Croft » May 7th, 2010, 5:18 pm

It would not be unreasonable, no, 160 bhp except that you are in the unique position of knowing the heads crack! What you don't know is why, so altering the cooling system is guesswork. You can't afford to do that at 560bhp. Remember that whilst each cylinder may 'only' be producing 160bhp that's equivalent to a 640bhp on 4 cylinder unit - and that I do know about - and that is a colossal amount of heat stuck in the header trying to get out.

GC

Hexer
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Re: BMW 3.5 T project

Post by Hexer » May 8th, 2010, 12:05 am

Hope to sort out the head problem with proper cooling, this is my first objective because the rest is ok, it is good until over 600 bhp.
I have spare heads for 80 pound, machining and stuff another 100 pound...so for 200 is no problem if one cracks under test, this is why many of the builders and racers won't pay much attention to this...just saying that over 450 bhp its a common thing changing heads monthly.
But I won't build an engine knowing that its condemn to distortion and accept money for it, rather I'll blow a few until I get to the result.


The other thing, BMW makes there valve seats at 45 degree and the valves the same, I been thinking on doing the seats to 45.5 degree and 2mm (maybe 2.4mm on ex) for bought in end ex. It has cast seats and 21-4N valves.

Hexer
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Re: BMW 3.5 T project

Post by Hexer » May 19th, 2010, 12:39 am

In the meantime I had some problem with an BMW M5 engine in the valve-seat region, so I decided to order some Trojan from Columbia Metals for the bought of them, my only problem is what tolerance should I give?

Under normal circumstance on a 30-40mm ring I do 0.09-0.12 mm tolerance depending on material.
The M5 (s38b36) and the m30b46 engine is assembled with 0.11-0.15 mm tolerance (more or less the beamers do this).


In the past I saw BeCu rings fitted with threads or crimped in the head on high output high revving engines, bought are costly, time consuming and the threaded version quite complicated to make.

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Re: BMW 3.5 T project

Post by Guy Croft » May 19th, 2010, 8:25 am

0.09-0.12mm is right, but you have to heat the head to 120 deg C and chill the inserts in liquid nitrogen,

G

Hexer
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Re: BMW 3.5 T project

Post by Hexer » May 19th, 2010, 8:44 am

I asked my workshop and they heat the head to ~250 deg C in an oven and the insert at room temperature because they don't have liquid nitrogen or other cooling substance lice aerosol.

Maybe I could try with dry ice, its cheep and easy to buy, and still cools is to -70 deg C.

gazzol

Re: BMW 3.5 T project

Post by gazzol » October 8th, 2010, 8:02 pm

Do we have an update on this issue?
What year is the engine block you are using? also what year(s) are the cylinder head castings? If you are unsure the year marker on the cylinder head is cast above and between number 1 and 2 inlet ports. The engine code you gave (M30B35) denotes that this is an early engine and would have started out as 3453cc as opposed to the later 3.5 ltr (M30B34) engine which was 3430cc.
Traditionally the problem that you have experienced came from too much heat but was mostly confined to earlier head castings i.e. pre 1981 which is also when the B35 suffix engines stopped being produced, these early cylinder heads had badly designed waterways. I have also read that the problem with the earlier heads was exasperated by poor maintenance with reference to the anti freeze not being changed often enough allowing electrolytic corrosion to weaken the head further still but that is only hearsay.
By far the strongest M30 head castings which BMW produced are the ones used in the E32 7 series and E34 5 series (1990 onwards are supposed to be the best) these also came with 47mm inlet valves instead of 46mm also the inlet ports were made much bigger in an attempt to recoup some of the power lost by the reduction in compression ratio which was implemented to comply with emissions regulations at the time. An advantage of using this head (If you aren't all ready) is that it lowers the compression ratio by approximately 1: if used on a earlier engine but the downside is that the inlet port gas velocity is too low and some of the low end torque is lost but since this is a race engine forum we won't be too concerned with that here. There was also another head casting produced by a Spanish company called AMC which was reputedly the strongest head casting of them all, the easiest way to spot one of these (they are very rare) is that the exterior cast surface is slightly rougher than BMWs and there are no numbers cast into the head above but in between number 5 and 6 inlet ports where all BMW heads have a casting number.
I hope this helps in some way.
I am very interested to know how this project is progressing.
Regards gazzol
Last edited by gazzol on October 9th, 2010, 12:28 am, edited 1 time in total.

Hexer
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Re: BMW 3.5 T project

Post by Hexer » October 9th, 2010, 12:10 am

Interesting things you write there, the old head was from '88, the new was casted in '92.
In the end I found out what killed the head, it was the bad turbo water cooling, it was between the vent hole of the radiator ant the expansion bottle, here is where the sisem vents itself...no wonder the head cracked, the turbo made steam ant the block never vented. Despite the relatively low coolant temperature the head was full with steam.

I had some progress in the last months, not to much but hope it will help me reach my goal.
Some pictures:

Image

Image

Image

Image

This is how the car will look like whens done:

Image

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