So, once we have an understanding that there is a lot of marketing spiel, a lot of material and QC variances that you should look into to get the best, let's be more specific to VRT tuning!
Common destruction of engines;
I would say, in my experience, that there are two major factors in destroying engines and no matter how many times I tell people, this can also supersede any of the upgraded material specification aspects mentioned previously, it is what ultimately destroys engines the most in my opinion - age!
Engines are set up for certain tolerances, certain specifications like measurements, that can obviously change with time due to general wear and tear from the forces placed upon them! I did this little mod on a the wiki VR6 drawing but it simply shows how pressure is placed angularly on certain reciprocal parts...
G = Gravity, naturally pushing down on the offset angles of the reihenmotor - our baby's!
– in short, you've over 14lbs per square inch pressing down on you at any time, ambient pressure in most places, you times this by the parts moving x amount of times over the course of an engines life and.... simply put..... you get wear and tear that changes the engine from how it was designed to be!
Therefore, simple rule is – if you're looking to ensure longevity of your engine, do not think it is necessarily good “as is” just because it runs right! I have dealt with many that think that only to find their engine pop when the boost is turned up, usually due to all sorts from blocked oil pick ups to plugs not even being in properly! I will always maintain that the simple refreshing of an engine by an experience builder, will ensure far greater longevity than leaving it as it is and even some "forged engine builds"! If you can't fork out for forged parts, just refresh it all to oem should really help with longevity.
Reason for that again comes down not to the material in this respect on a used engine - as such material can often receive some form of heat treatment in it's usage over it's lifetime, but the tolerance aspects and additional strains it places upon your components if it is not running right - the shearing and tearing forces it is subjected to are increased relative to the design tolerance changes of stock.
Which moves us onto the tune.....
I assume most of you know that “a controlled burn” is what you always aim to achieve in terms of ecu tuning, the burning of fuel – as is required for correct operation. Detonation is an explosion rather than a controlled burn and this explosion, to cut a long story short, means a hell of a lot more stresses!
So the tune is a very, very, important part, personally I have seen many pro tunes with little component protection/knock control but they still work based on what work has actually been done in testing. So this explosion/knock, can destroy engines no matter how much you upgrade material spec, but the pressures alone could shear most materials, even hum dinger forged parts!
So that is another fundamentally important aspect to engine longevity in any build, especially FI ones! I could talk about the tune and it's effects in stresses and strains but that'd take a whole other thread – in short, skimping here causing detonation, can lead to severe product destruction and especially on old worn engines.
So we understand the basics on building if looking at upgrading and/or rebuilding with stock so let's focus on building an engine for FI and saving money!
In short, the more you do for an engine builder, the more you will save yourself!
Taking it out of the car, stripping it down and bagging up/tagging parts is a good start, it'll save you a lot so I would do that first of all to save you some pennies. There's plenty of info on the forum for that.
So you save some money by stripping a lot yourself, and you're now aware that you need to specify that the engine builder needs to look into checking oem angles/tolerances etc and will need new oem parts at least for basics like gaskets, rings, bearings etc. This is when you budget for your forged upgrades.
Although I am a firm believer in the fact an oem refreshment and/or simple rebuild in itself brings about a far greater chance of longevity, there are factors to consider when going FI on the 6 pots and as mentioned above - material spec can count for a lot!
First port of call is the compression ratio then, with stock 6 pots running 10-11.5:1 ratio's as standard it would take a lot of tuning to get it right so generally, for safety's sake and on a road car - compression ratio is lowered.
What ratio you use can vary, personally, I have dealt with many big turbo/big name owners that run very low compression ratio's (sorting out their big name tunes) and they seem happy, up to dealing with a 2.8 24v owner who ran 9:1 at nigh on 700hp on pump fuel! I would therefore recommend keeping that ratio at 9:1 at most but this can come down to the tune as well, as mentioned, detonation and tune can make a difference so factor that in to what you are doing as those stresses count for a lot if the tune's out! Get info on the tuners builds if you can (i.e. compression ratio, parts used, boost levels etc) - more research here should dictate your rebuild somewhat!
There are three main options nowadays to do that; spacer plate, pistons and rods;
Spacer plates can vary in thickness which brings about various compression ratios, so there are options there - roughly 7-10:1 I think on the market nowadays. Main thing as boost rises using plates would be squish, which is why head and block studs would be a good upgrade, although you're talking nigh on forged piston money now!
Forged rods we've mentioned above, 4032 will expand less than 2618 which what they all seem to be, various options on skirt mods to negate this, various compression ratio's etc
Another option fairly new to the market is low compression rods, I've dealt with some big name tuners testing these out in Europe and they seem to be happy, it negates the need for a spacer plate and add's strength in design and material, as they are a few mm shorter as you can see;
Material can count for a lot in terms of psi resilience;
Low compression rods have the benefit of adding material strength in these areas as well as lowering compression for detonation purposes, negating the need for pistons and/or a spacer plate!
*** I'll get around to working out the equations when I have time hopefully, but I'll likely just ask the tuners how their 600hp+ builds are holding up with these rods and ratio's etc - some maths if you want to do that though;
Ebay rods v Big name
There was an interesting thread on another forum about Chinese rods and I think they came to the conclusion that the rod bolts were the weak point. I put a thread up ages ago to see if I could drum up numbers for some custom x beams (not enough interest though) and in dealing with the manufacturers and suppliers I saw test data of 210,000+psi on the bolts if I remember right, surprised to read that then on that forum thread! Again, this can come down to the manufacturers used and variances in that respect - so I am skeptical about their statements somewhat being a reference to any "Chinese rods" if you will. Of course the big names all put up some data and talk about the development in-house and we all know they tend to hold up - as mentioned in the thread though, there are many factors to consider.
When I was dealing with manufacturers I think it came to in-between a 3rd and half the cost of a part manufactured in the UK (buying/filing patent, moulds and initial product) to outsource it abroad unfortunately, which is why many big name companies have done similar with parts, but the quality specified was still top notch (International QC standards/material spec etc) and the part would have been just as good if I had got the numbers. So, cheaper doesn't necessarily mean any less of a product and the blasé statements about such parts should really be looked into more in depth!
So you have a few options, generally;
Rod bolts (stressed area) - Low compression plate (various ratio's, need't go crazy but match to tune)
Possibly head studs/main studs/bolts - squish and alignments etc plus strength
Low compression pistons - better v cost
Rod's - low comp or stock, various material/costs etc
But....... give it a good refresh first, budget that then changes mentioned above for longevity depending on your budget and that's why some relatively stock engines can reach big power!
The head can set you back a lot.... a hell of a lot really! Not always necessary as this vid shows;
The head can take a lot of money to upgrade but, aside from checking oem tolerances and refreshing as mentioned for the bottom end, you could keep this fairly simple.
Valve guides are often the bane of VAG vehicles with high mileage, just general parts refreshing things, I can't really emphasise that enough as I have seen people try and take short cuts time and time again and it always ends up costing them more!
Valve float can be a problem on older engines, especially if you are upping rpm limit's like many tunes do, so heavy duty valve springs is a good idea to stop this.
Whilst you are stripping your engine for the engine builder or your own DIY you can do some little things yourself, it's what I did years ago, just bought some simple dremel tools, files etc and had a go! You can do things like gasket match your manifold gaskets to your ports, you can chamfer oil and water passages, even have a go at porting and polishing. This work can end up costing lot's of money, you are better with things like flow benches obviously but you can do some clean up and lot's of measurements and if you're going to have a go at DIY building then why not, just do your homework!
Cams can help get a lot more power/torque when going NA to FI as many will know, again this should come down to the tune and changes in your set up/your goals - all of this head work should really be specified to your ecu tune and it can take up huge amounts of budget - usually pro engine builders will have their own parts they use and a lot of this is worked out with them - in terms of DIY - well, that's what the forums for, plenty of info online!
So, just a brief overview, I wanted to mention the manufacturing and material side rather than the usual conversations as some incorrect presumptions/information is often bandied about.