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Old 25 Feb 2009
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More power on a slightly larger engine.

Hi all,
During my upsizing considerations I keep falling back to the very readily available 12 tonne 170 hp Magirus and Mercedes 4x4 trucks that the german army are currently disposing of. They’re available cheap with low mileage and some are in good condition.
But I’ve had feedback that the Mercedes 170 hp is not really grunty enough, and I’m guessing the Magirus might have the same problem.
If I go by the output of my Daily from about the same year, (1990, 2.5 l for 100 hp untweaked and no intercooler) the 6 litre 6 cyl inline engines should be perfectly capable of producing 240 hp with a normal mechanical injection pump. If I add an intercooler from a scrapyard this figure should be even easier to obtain.
My question:
Does anyone know of a diesel mechanic who tunes larger engines?
I’m not averse to installing an injection pump from a more powerful engine, so which 6 litre 6 cyl engines are there out there with an output over 200 hp that I could scrounge the pump from?
In this day and age of chipping to get more power I wonder if there are any mechanical injection tuning specialists left?

I know that I’m not the only one interested in a power boost, so lots of ideas please.
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Old 26 Feb 2009
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With a bottomless wallet anything is possible!

The risk with over tweaking an engine is that a whole host of other parts need to be beefed up for reliability - clutch, gearbox, brakes, diffs, radiator.

If you do a weblookup on the Bosch injection pump, you'll find plenty of info on giving them a bit of a boost for horse power by increasing the fuel charge. You may lose torque rise as you increase HP by getting higher revs.

Value for money you probably would do better getting the inlet system polished to improve air flow, and then the exhaust system to let it breathe a bit easier.

I'm not a big fan of trying to get 30% or more increase in power out of an engine - especially Merc whose engineers would have done that in the first place if they could have made it reliable and economic.
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Old 26 Feb 2009
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Don't, it will give you a lot of problems. Only tweak the fuel pump a bit. Bring it away to a bosch dealer and have themset it so it gives a bit more fuel to the injectors (5-10%). Also bring your injectors, have them checked and maybe set the opening pressure a bit higher (most are around 175-200bar).

If you want to get more power than 180-190bhp out of the engine you will have the risk of a blown haed gasket, broken pisstons and all that comes behind the engine and it is probably cheaper to buy a newer more powerfull truck.

This said, in a truck bhp is not everything torque is what matters. The bigger the engine the more torque. If you want your truck to have great off road capabilities keep it light, low centre of gravity. for example a magirus with 170bhp air cooled deutz engine fully loaded 8-9ton, they are very capable offroad and still are quite fuel efficient (4km/L). Remember the more you tune the enginge the more fuel it uses (if fuel consumtion doesn't matter go for a MAN KAT1). See for a great example Die Pistenkuh – das Expeditionsfahrzeug von Sabine und Burkhard Koch (it's in german)
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Old 26 Feb 2009
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Thanks for the replies, more are always welcome.
It’s quite clear I intend to keep the truck as light as possible (and make up the difference in fuel tanks = temporary weight), and CS’s report of his MAN adventures show that once you’re on 20 inch wheels the power/weight considerations of little cars like the LR/TLC are quickly forgotten.
All the LR mod stories show that with cars, power increases are risky, with the trucks, there’s a lot more margin for manoeuvre. The Merc 1017 and the 1222 share the same drive train, and I’m trying to confirm the same thing for the Iveco Mags, this means that setting the power output at 170hp was more a commercial decision and that power increase won’t be too dangerous for the drive train. Besides, if a 30 % power increase diminishes the life of a 500kkm drivetrain by 30%, I’ve still got 350kkm available before having to worry, and that’s more than adequate (and more than most if not all cars).

Remember, cars are designed to fail, otherwise manufacturers wouldn’t sell more. Trucks are designed not to fail, if they do the buyers go elsewhere.

The same goes for engine life, I’ll happily accept a small reduction in lifespan for a bit more oomph. Head gaskets can be conserved with higher pre-load on the bolts, pistons can be cooled with a bigger oil cooler, and pistons and heads can be cooled by a cooler air charge intake (intercooler where there wasn’t one before)

I know vaguely what’s possible, I’m a mechanical engineer who has served time in the motor industry (powertrain, chassis & suspension design-no engines) so structural and load considerations are already taken into consideration.

As for the equation more power = more fuel: yes if driven at max all the time. The guys at Top Gear disproved this with a comparison BMW/Prius recently. There is also an argument that a gutless engine consumes more because it’s always at max, whereas with a bit of power in reserve you’re able to be much more light footed. I’ll only use the extra power occasionally, but would very much like to have some in reserve.

So, higher injection pressure for the same pump is the main recommendation. Anything need doing on the timing?

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Old 26 Feb 2009
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"Remember, cars are designed to fail, otherwise manufacturers wouldn’t sell more. Trucks are designed not to fail, if they do the buyers go elsewhere."

Sorry but I have to disagree to a large extent here. As recent customers of quite a large number (14) of Renault Kerax 'Extreme' we are totally surprised by cheap and shoddy designs resulting in premature failures, examples being (all at less than 50,000 kms)
- cracked airfilter housings
- split induction hoses through vibration
- Chassis cracks (luckily not major)
- burst a/c hoses due to poor routing and chaffing.
- poorly designed axle breathers sucking dirt
- snapped half shafts
- broken leaf springs
- chassis and suspension bolts not torqued during manufacture
- Oil leaks from timing cover gasket
- Rear chassis cross members twisting under towing loads
- engine mounting failures
- engine rebuild due to dust ingress from induction pipe failures...

Oh, and we bought the Renault as we were not happy with either MB or MAN previous fleets (including a huge warranty issue with major chassis cracks on the MANs ..... All the above mentioned failures were warranty claims.

Over the same period of owning the 14 MB, then 14 MAN, then 8 MB then 14 Renaults we have owned:
2 x 75 Series LC
8 x 80 Series LC
3 x 79 Series LC
8 x Hilux
9 x 105 Series LC
1 x 120 Series Prado

And to be honest we had not one warranty issue or a premature failure which we could attribute to poor design. The 3 x 79 series all suffered gearbox failures fairly early, but largely due to extreme abuse, although I do have to admit the gearbox is not 'extreme duty' - but that is the ONLY design issue we could say we are not happy with.

IMHO the Toyota Landcruiser is largely better engineered to do it's job than most of the trucks we have tried.

Back to the topic:

If you are convinced that the engine can take it - or you are going to strengthen head gaskets, increase oil cooling, reduce charge temperatures as well as play with fuel delivery then why not go the whole hog and add:
- Propane injection
- Water/methanol injection
- forced (or more forced!) induction

Sorry for the rant - I don't want to come across too strong, but truck failures have caused us endless sleepless nights and a lot of financial losses and frankly some of the engineering on the Renaults is a joke. Don't even ask me about the Kraz (Ukrainian truck) that we bought to evaluate.... What a piece of ****!
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Old 26 Feb 2009
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Hello Luke,

I have to disagree with you on the head gasket, I know of 4 separate cases of a blow head gasket ( 2 in a DAF 615DT, 1 in a mercedes and 1 in a Deutz). The problem is combustion temperature and pressure are higher in a tuned engine. This couses an old type head gasket to harden and evenually crack. This can be solved if you make (yourself) a copper head gasket.

If the had gasket holds or if you make a new copper one then your valves and pistond must be able to withstand higher temperatures, your pistonrods have to cope with higher forces etc.

In short I have seen nothing but misery from more than slightly tuning your engine, but you might be right about the drive train, at least on my DAF Ya4440 it is probably capable to withstand 250bhp.

Hope this helpes,

Henk Jan
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