Is this engine worth modifying.

I'm about to rebuild the head from a 1988 bmw 730i.
(The oil rail bolt loosened, causing the oil feed to fail at the front of the cam, this quickly removed the cam lobes on number 1 and
2 inlets).
What modifications are worth doing to this type of engine.
A piper cam will add 12 bhp .... which in a 1600kg car would be unnoticeable.
(Where the 85bhp-128bhp modification in my 680kg citroen axgt was very noticeable).
Would i be better off with a standard camshaft and concentrate on fuel injection modifications, 6 > 2 custom manifold and maybe a performance front box (tuned expansion box).
The car is mint .... i've put 2 stonechips on the front over the 8000 miles since i've bought it. The single owner before me put 3 on the front. (Over 108k!!)
I intend to keep this as my main car for another 3-4 years before moving on .... i nearly bought a 68k v8 car until i noticed how loose the doors were, then how worn the pedal rubbers were, seat belt webbings worn,etc ..... clocked methinks. (And the bonnet had been resprayed over rust dots ... very strange). All other v8's i've looked at are a pile of shite ... the only good one i've seen was over 7k. (I'd rather spend 7k on a porsche 944).
What say you guys.
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Check to see if BMW did a more powerful version of this engine, and if so get the parts from that. Modifying injection engines and getting them to run *properly* afterwards ain't easy.
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Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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and
You want to boost torque with this engine- its a heavy car. Enquire what the piper cam does lower down the rev range. If its like a "tow" cam (a la pinto yrs ago) then it might well be worth it.
I wouldnt mess with the fuel injection, however I'd consider a decent 6-2-1 tubular exhaust manifold- i'd hazard a guess BMW did one themselves and fitted it to perhaps the 3.5 engine or M series unit?
Tim..
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Altering the valve timing will mean altering the ignition and fuelling maps, if it's to be of any real benefit. And this is costly or near impossible on many EFI engines.
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Dave Plowman snipped-for-privacy@argonet.co.uk London SW 12
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the
pinto
6-2-1
I'll start looking ..... the 24 valve M series engine might not have the same manifold as the 12 valve m30 engine .... also the "tuning" of the thing might be wrong for my engine. (Tuning as in efficient exhaust gas-pulse extraction, not boy racer sound).
I don't think much can improved on the air induction system on bmw's, its all cool fresh air from the front ..... the only modifications are to increase the diameter on everything.
Then theres the length/diameter of the inlet manifold ports .... is it narrow, long ports for low end torque and wide,short for high end bhp??
The cams i've checked so far have a power range of 1500-6500 (kent and piper). They are supposed to be designed to match the existing fuel injection system. I suspect with one of these cams, my car will be even slower off the mark, and won't benifit from the additional bhp until its past 3000 rpm, by then everyone in a nova would have left it standing.
I suppose the obvious modification would be a diff change .... i have a 4.1:1 on my old 525eta, which is slightly humiliating to golf diesels off the lights, but only matches the acceleration of modern saloons above 90mph.
Thanks for the pointers guys.
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Steve



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SDD wrote:

Fuel injection mods ?
What would that achieve ?
You need to get more AIR into the engine - all the fuelling system does, is inject the appropriate amount of fuel under any given condition. If you mess with this, then it will no longer be injecting the appropriate amount of fuel.
If you genuinely want more power, you need to look at simplifying the breathing system (air intake, and exhaust), and then cams and head work (porting, polishing, bigger valves, etc. etc.) - getting a reasonable power increase from an NA engine, is non-trivial !
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is
mess
power
Cams don't do much alone other than bugger things up usually... Cheap sensible option instead... Skim about 1.5mm off the head, reseat all the valves with a proper careful care and make all the seats the correcrt width. This is a DIY job if you are careful.
Then you will need super unleaded and have maybe 10 percent more power right across the range. Cheaply. Then go here www.nitrous.info (I dare you!)
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right
Never thought of that ... upping the compression!!! Wouldn't hacking 1.5 mm off the head retard the camshaft timing quite a bit and shift the power band even higher up the rev range??
.... Maybe i should put my spare eta engine in the 7??
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Steve



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careful
As well as the existing engine...
;)
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Dan



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careful
It would theoretically but it will not lose any low end power as the compression change will more than make up for that. Just be sure that the tensioner is enough! And that nothing will hit...
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Get the plasticine out- I think this engine uses a 10.5:1 CR as stock and a very small piston / valve clearance, so u might have them kissing it you're not careful..
Tim..
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power
a
you're
1.5mm should be OK though?
Whatever! You may need a grinder to be really sure...
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My modified citroen axgt has a verified 128bhp and weighs 680kg = 188bhp per tonne. The beemer needs 300bhp hauling its lardy assed 1600kg, just to match that. A sports cam x performance chip x inlet and exhaust modifications = to many variables for my liking as a home diy mechanic.
Max power magazine would hype on about "bunging these in and it works instantly"
**************************************************************** To quote from the excellant gmc motorsport website: (Modified vts).
This vehicle was tested in Max Power magazine as being a rocket ship, which naturally took our interest. I contacted the company marketing it, pretending to be a private individual and asked what they did to the engine to make it so much better. The answer was very hazy and very uninspiring for sales patter to get someone to buy one. It went like this. Oh! Well we polish the head a bit alter the ECU and a few other bits and pieces, which would cost about 1000 to do on your car. I could not believe that by such minor alteration such an increase in power was possible and remained very skeptical. As luck would have it the owner of the car tested in Max Power contacted ourselves and told us how disappointed he was in the cars performance in comparison to his friends standard Saxo VTS and asked for us to do a dyno test on it. *****************************************************************
Carburator + adjustable timing via distributor + sports camshaft = easy for home diy mechanic. Old style motronic engine management (non-learning) + sports camshaft + performance chip home diy mechanic pulling hair out!!!
http://www.gmcmotorsport.co.uk/ Is worth a look .... read the bit under rolling road.
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Regards
Steve



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What does it actually produce at the wheels? If that's the flywheel figure then I'd expect somewhere around a 20-25 BHp loss in the box/drivetrain, unless it's straight-cut or unless you're running on thin oil and rebuilding every 2k miles... Also, I assume 680 kg is the kerb weight? So with a 70kg you and half a tank of fuel, the actual weight might be closer to 770kg.
A realistic actual power:weight would then be something around 140 BHp/ton, which isn't bad - about the same as the actual figure for the 600Ti, so I'd expect it to be somewhere around 7 secs to 60. Much above 60 and wind resistance is going to have a big impact, so the 0-100 and the quarter mile times will be worse than for the Ti.

It actually needs something like 224 Bhp at the wheels, i.e. something like 265BHp at the crank.
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figure
Just over 90bhp at the wheels, where it used to be 58bhp.

Sounds about right.

BHp/ton,
I'd
mile
7 seconds is about right, every 0-62mph trial i've done is different, the average figure is 6.9. It will keep with a standard Ti to 100mph (104 on the citroens speedo, when checked with a gps). 0-100mph in 18 seconds.

like
On the old E28 bmws there was nearer 35% loss through rear wheel drive, so 265bhp at the crank would reduce to 172bhp at the wheels.....265bhp from a modified 535i 12 valver, 286bhp from a straight 535i 24 valver.
Just out of interest and to confuse the power to weight issue. My "next project car" has 125bhp at the flywheel, 1280kg chassis weight giving it a power to weight of 97.6 bhp per tonne .... yet does 0-60mph (65 on the speedo allowing for gps correction) in 8.7 seconds ..... all due to torque. 140lb/ft @ 550rpm (below idle speed) and a maximum of 170 lb/ft at about 3300rpm, then much lower geared than it was from the factory. ..... Its not a diesel either.
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Regards
Steve



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What is it? Something turbocharged? Small V6 (Mx3 1.8 V6?) ? Something else?
I do like cars with an even spread of torque from idle all the way through the rev range (or even from below idle). That's what appealed to me about the VAG W12 engine from looking at the torque/revs graph in the little glass display they had it sitting in at the motor show at the NEC a couple of years ago.
Peter
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I'm guessing it might be the 525e.
BTW, with a perfect CVT gearbox, a car with 100 BHP/ton should be able to get from 0-60 in 5 seconds, ignoring wind-resistance etc.
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Spot on ... bmw's diesel engine which runs on petrol. What an absolute hoot to drive .... the thing has power where other beemers don't.
My 730i has always felt less powerful, until you get it above 4000rpm, then the normal bmw "urgency" kicks in.
Side by side, the eta would leap ahead, but i think by the time the 525e got to 70mph, the 730i would also be at 70mph, then the 730i would gain on it.
Thats why i like using the e around town and the i for weekends!!
B.t.w ... i once chased a 1990 7 series alpina, and kept with it all the way to 100mph. In the french car of course!!
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Steve




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SDD wrote:

lot of alpina badges dont mean shit.
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You forget that AX can keep up with an Audi S4....
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Dan



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