The mk3 1.9L TD power-quest

[Logzy]

Nice write up and an interesting read.
Look forward to hearing more.

[gldgti]

I would have thought there may be possible gains to be had from better gas flow by modding intake, valves, cams, compression ratio, intake air temp (eg more efficient intercooler), turbo capacity/efficiency or exhaust ? I didn't realize diesels were THAT different to petrol engines (except for being not very amenable to tuning for more power at higher revs)

ahh - sorry about the misunderstanding -

All aspects of the engines performance in terms of engine management (i.e. air and fuel intake) are goverened by the injector pump and turbine wastegate.

this is not the same as saying that other improvements such as bigger valves, reducing flow losses and optimising mechanical efficiencies do not have the ablility to increase the power output - merely that these things are not part of the engine management...

Indeed, adding larger valves would be desireable - if it were possible! but alas, there is no more room for larger valves, and in fact there is no real need in terms of max horsepower that is likely - the turbocharger more than makes up for that. likewise, there not a lot of improvement possible with the cam timing (for IDI diesels) either.

however, portmatching and polishing does work well for diesels, as well as ceramic coating of the piston crowns, and exhaust valve faces.

now, there are gains to be had in the areas of compression - lowering the compression from the stock 22.5:1 down to about 18.5:1 would likely be optimal - however this has implications for cold starting behavior etc etc - and is far beyond what i want to do with my daily driver!

when i come to modify my 1.6TD for the mk1 hillclimb/rally/whoknowswhat car, then i will certainly look at these things... but under 150hp, i would be wasting my own time and money bothering on some of the more serious modifications for the 1.9L AAZ in my daily driver.

And, please note that I have already mentioned about modifying the exhaust on the car in the first post...

[gregozedobe]

As the old saying goes, "How fast can you afford ? "

I agree that what is possible should never be confused with what is practical, desirable, satisfying, justifiable, sensible or just plain economically rational. And everyone has a differing definition for when the line is crossed, and where their priorities lie.

From what I can see, if a tuner gets too ambitious with hotting up diesels you can end up with lots of torque and power, but over a very narrow rev range, thus making the car difficult to drive and not much fun at all in everyday driving.

I find the low rev torque of a good diesel is much of the fun of driving one ( I love the kick that I get from the 400Nm my transporter has at 1800rpm, no waiting for revs to buld up, just put your foot down and go, even in 6th gear). And this has the added advantage that you can enjoy this fun without constantly risking your licence - I will have to be a lot more careful when I take delivery of my new Octavia RS wagon (2.0 TFSI motor which likes to rev much more than the diesels).

I hope you have a long and enjoyable relationship with your newly peppy beastie.

[gldgti]

From what I can see, if a tuner gets too ambitious with hotting up diesels you can end up with lots of torque and power, but over a very narrow rev range, thus making the car difficult to drive and not much fun at all in everyday driving.

this is not really true, but i can understand why this might be the general understanding...

typical diesels don't like to rev, i'll agree - especially direct injection engines like the TDI's.

Indirect injection has the advantage of allowing very early injection so that high rpm can be reached.

people will go on about stress on the engine and blah -di blah blah blah, but none of this is really an obstacle - its entirely achieveable to have 3-4000rpm of good driveable power in a diesel engine - and that is just as good as any performance petrol engine;

the fact that a diesels range of rpm might be restricted to say, for me, 5000 rpm, leaves me with everything under that to make as much power as i can. the stock engine pulls well from about 1600rpm, and thanks to the rpm governor the Injector pump starts cutting the fuel at about 3200rpm, so at the moment, i have about 1500rpm worth of real power - not a lot.

however, if i dive into the injector pump with a couple of shims, and install some clever boost control (which i plan to do) theres no reason i cant make good power all the way to 5000rpm quite safely - then i get 3400rpm of good drivable power.

now i know from driving other cars that 3400rpm of good power is very reasonable - a vtec honda might get you 3000rpm above 4500rpm, and a LS1 5.7l v8 doesnt really get up and boogy until its over 3500revs either -

so the argument about a narrow power band doesnt really apply - it is more of a phsycological boundary.

i guess the proof will be in the dyno charts, hehe

theres a lot of guys with modified 1.6TD's in the states reving out to 6500rpm - and full 25-30psi of boost from 3000rpm means big power figures - 200hp is possible. but peak power being just a selling point, im rather more concerned with the fact these engines have a flat torque curve, and hence great driving feel.

if i can achieve good feel and a strong pulling engine all the way to 5000rpm, i don't think anyone would hop in the car and think it was difficult to drive.

the other nice thing about diesels is this - the only thing that controls the power output of the engine is your foot. regardless of rpm, a highly modified extremely powerful diesel engine will react just the same as a boring dawdler as long as you keep your foot off the floor. unlike a grumpy petrol engine with camshaft modifications, large valves and big bore throttle bodies...

[Mischa]

i cant wait to see how your car turns out (if you ever stop modding it ) would i be able to leech a quick ride in it next time im in gosford? id be happy to take you for a spin in my gt

[gldgti]

i cant wait to see how your car turns out (if you ever stop modding it ) would i be able to leech a quick ride in it next time im in gosford? id be happy to take you for a spin in my gt

anytime mate.. i'm in hornsby every working day too!

[gldgti]

the saga continues -

saturday was spent with my good mate and work colleague Mark, as we put a full day into the construction of the mk3's fully replaced exhaust system.

total and complete 2.5" mandrel bent fabbed system from the turbo to the tailpipe - and what a difference its made!

we spent the morning making the downpipe, and the afternoon doing the rest.

the results are amazing, and i'm quite surprised at how well its all turned out - i now have the best of both worlds! the car is actually quieter while cruising, i think because of the lower exhaust pressure in the system- despite being one muffler short now. and when you get on the boost and theres more fuel, a pleasing growl erupts from the bowls of the engine and a rush of torque to boot! i actually achieved some clutch slip in 3rd gear today because of the extra torque...

acceleration everywhere is improved, but the best is the increased revability of the engine, now happy to rev past 4000 whereas before it didnt sound happy at all, now its willing!

and a comment from a work neighbor upon hearing me drive up the road during the first test - "it doesn't bloody sound like a diesel!"

some pics for good measure.... fabbing the downpipe - we made a jig to get it just right and re-used the brackets to ensure its all solid and not putting any pressure on the turbo



making sure it fits nicely....



the finished downpipe - aint it pretty?



the old downpipe and new side by side



Tacking up some of the rest....


big thanks to mark for helping me make the diesel even better!

[Jarred]

cool fun. nice bit of custom work there.

If i ever find one of these for sale....

[gregozedobe]

the finished downpipe - aint it pretty?

i actually achieved some clutch slip in 3rd gear today because of the extra torque...

It sure do look purty ............ (and more efficient too)

I note that you are starting to edge into the area of "consequential" mods (needed because of all the extra power). So are any (or all) of the following now on your wish list ?

Stronger clutch
Better tyres
EGT (pyrometer)
More engine cooling
More efficient intercooler
Improved brakes
Better suspension
LSD (..... and so the list goes on )


As far as diesel engines not having a significantly narrower power band than petrols, you still have a long way to go to convince me, plus I do like to stir a bit too .

Rather than choosing specific "no low rev torque" petrol engines for comparisons with highly modded diesels, how about looking at unmodified engines within the VAG family to see a shining example of what I'm talking about - the latest 1.8 TFSI petrol engine that is going in current Octavias and Audis. Maximum torque from 1,500 - 4,200 rpm, and good power continues through to 6,500 rpm from a stock standard motor (more available with mods, and reflashes are already on the market). And it even gets good economy (not as good as a diesel though). When they release the 2.0 version of this motor it should be a bottler. The 1.9 TDI motor just doesn't compare, and both versions of the 2.0 TDI still have a much narrower torque/power band.

I agree that you do nearly all "normal" driving on torque rather than power, but don't forget that the higher gearing that usually comes with diesels does somewhat reduce the torque advantage of diesels. It is also more important to be in the correct gear to accelarate in a diesel (although the off boost, low-rev feeling of nothing, nothing, nothing, something, WHACK ! can be amusing as long as you don't need to go instantly).

Have fun with your mini-monster, sounds like it will keep you amused for some time to come

[gldgti]

gregozedobe,

you are right ofcourse about the 1.8T engine, and a lot of other VAG engines... but thats not really the point i was trying to make.. i was really trying to demonstrate that theres no reason you can't have a very driveable car with a "narrow" power band.

as to other modifications, i've already put VR6 brakes in it, and i'm not totally happy with the intercooler set up either.

and EGT guage is needed but i wont be doing that until i have a good reason to pull of the exhaust manifold.

i dont think i need a bigger clutch, theres a good chance mine is original and the car's at 160,000km but its not slippy normally, so its probably just getting close to worn. i would say that a new clutch will fix that problem (which hasnt yet reoccurred... yet) and i have one in a box downstairs.

the car already runs on 205/45 16's and i dont think that it needs any more tyre than that - just some better quality ones for my next set.

i will probably change out the current k14 for a newer and larger K04 in time, which i feel will be better matched to this engine going on the turbine efficiency maps i've looked at and the way the boost drops off at higher revs with the k14 now.