Torque Cars chat forums - View Single Post - General engine tuning tips (VERY General)

HDi fun · 07-10-2006, 06:57 PM

Yes, I've driven a current 330d and also a 535d. Both are disgustingly rapid from the factory. These engines can still be made to deliver more torque, but you have to question if it's really necessary given the ease with which they both fling themselves foward in response to a gentle squeezing of the right toes

I do think that manufacturers modestly undertune the current crop of performance diesels in order to create a place in the market for their petrol powered models. For some folks, only petrol will do. Curiously, in my estimation these are of the older generation who will not even test drive a diesel car because 'they're slow and nosiy, aren't they?'. Just look how many current model Micras are being driven around with Nissan's excellent but spineless small cpacity 4 cylinder petrol units. Try the dCi 82, for example. It handles like a go-kart (Nissan is bloody good at track-like steering in road cars) and accelerates absolutely beautifully. It would suit my Dad perfectly.

As for internal Modifications for sophisticated diesel engines, I think that the rewards obey the law of diminishing returns. With forced induction there's only so far you can go with cam/valve lift and air (gas) flow. Especially with a diesel engine, given the limited rev range there's not that much reward from tuning a head in the traditional way. Diesel burns very slowly (hence the 4000rpm peak BHP most achieve, even if they will spin to over 5000rpm).

Getting the flame front inside the combustion chamber to accelerate faster than the piston crown is the only real option, and this is to some degree achieved by allow small amount of fuel to be injected during the expansion phase of the engine's cycle. Too much of this and you get smoke and soot, and burn a load of fuel. Increasing the BMEP (brake mean effective pressure) by means such as increased boost can assist. This, too, is a double edged sword as the biggest fraction of the atmosphere is nitrogen, which, although good for cooling, is still incombustible. That's where nitrous comes in, in the same way it does in a petrol powered vehicle. The gains achieved in this way can be absolutely silly, but given the cost and legal position with regard to road usage it's a bit of a white elephant.

Increasing the cetane rating of diesel fuel is quite effective in increasing the release of 'free' power. With a diesel engine, the key is getting the fuel to burn more rapidly, as opposed to a petrol engine where octane number is God. Higher octane petrol fuels burn more slowly and resist pre-ignition better than low octane fuels.

Good results can be obtained with cetane improvers. Sadly, these can prove expensive and should not be used in engines that are Euro Iv (2004) compliant. Strangely, the 2.2HDi I use (which is a 2001 model) is 2004 compliant. The particle filter (subject in itself) can become blocked or excessively obstructed by use of such products.

I will post more very soon on this topic, but I'm being hounded by my kids to cart 'em up the road and fetch 'em back a decent Indian takeaway - they've got style too

Cheers to all,
Regards,

Paul Anderson.

07-10-2006, 06:57 PM	#6 (permalink)
HDi fun Moderator The Torque Meister Join Date: Apr 2006 Location: SOUTH EAST Posts: 1,416	Yes, I've driven a current 330d and also a 535d. Both are disgustingly rapid from the factory. These engines can still be made to deliver more torque, but you have to question if it's really necessary given the ease with which they both fling themselves foward in response to a gentle squeezing of the right toes I do think that manufacturers modestly undertune the current crop of performance diesels in order to create a place in the market for their petrol powered models. For some folks, only petrol will do. Curiously, in my estimation these are of the older generation who will not even test drive a diesel car because 'they're slow and nosiy, aren't they?'. Just look how many current model Micras are being driven around with Nissan's excellent but spineless small cpacity 4 cylinder petrol units. Try the dCi 82, for example. It handles like a go-kart (Nissan is bloody good at track-like steering in road cars) and accelerates absolutely beautifully. It would suit my Dad perfectly. As for internal Modifications for sophisticated diesel engines, I think that the rewards obey the law of diminishing returns. With forced induction there's only so far you can go with cam/valve lift and air (gas) flow. Especially with a diesel engine, given the limited rev range there's not that much reward from tuning a head in the traditional way. Diesel burns very slowly (hence the 4000rpm peak BHP most achieve, even if they will spin to over 5000rpm). Getting the flame front inside the combustion chamber to accelerate faster than the piston crown is the only real option, and this is to some degree achieved by allow small amount of fuel to be injected during the expansion phase of the engine's cycle. Too much of this and you get smoke and soot, and burn a load of fuel. Increasing the BMEP (brake mean effective pressure) by means such as increased boost can assist. This, too, is a double edged sword as the biggest fraction of the atmosphere is nitrogen, which, although good for cooling, is still incombustible. That's where nitrous comes in, in the same way it does in a petrol powered vehicle. The gains achieved in this way can be absolutely silly, but given the cost and legal position with regard to road usage it's a bit of a white elephant. Increasing the cetane rating of diesel fuel is quite effective in increasing the release of 'free' power. With a diesel engine, the key is getting the fuel to burn more rapidly, as opposed to a petrol engine where octane number is God. Higher octane petrol fuels burn more slowly and resist pre-ignition better than low octane fuels. Good results can be obtained with cetane improvers. Sadly, these can prove expensive and should not be used in engines that are Euro Iv (2004) compliant. Strangely, the 2.2HDi I use (which is a 2001 model) is 2004 compliant. The particle filter (subject in itself) can become blocked or excessively obstructed by use of such products. I will post more very soon on this topic, but I'm being hounded by my kids to cart 'em up the road and fetch 'em back a decent Indian takeaway - they've got style too Cheers to all, Regards, Paul Anderson.