hey guys,i was looking around,and then the stupid question came to my head.i am just interested,what would happen if i would take stock 2.5 TDI block with all internals,and would put 20v head.and run gas ,not diesel.sorry for question,i am just curious
You will want to change out the pistons atleast to match the 20v head. I am doing a Eurovan 2.5L block with a 20v head. The cylinder head studs are 1m larger in diameter, and you need to drill the head to accomidate these larger head bolts/studs. Also, there is an extra oil drain in the block that needs to be pluged. Check out this thread. It is very detailed about the conversion:
The main differences are:
-Need a longer timing belt. ABF 16v spec will work
-12mm*1.75 head studs needed
-cylinder head bolt holes need to be enlarged to 12.5mm
-block needs extra oil return plugged
Have you ever held a TDI piston? They weight so much more then standard gas pistons to be durable in the diesel. I'm not sure which model year of the tdi bottom end you are considering using, but the tdi that I'm experienced with came in the 2000 beetle. They have cast iron piston crowns I agree they may be very strong, but that bottom end wasn't designed to rev to 7k like 20v will want to.
I think you would be better off swapping them out for a set of s2 pistons, and suitable con rods, or bore out to 83mm? On the tdi piston, I think the lip at the edge of the 'hole' would become a hot spot and cause detonation..
You guys probably know this Jonus fellow, the first I saw of him was when he was at our local track. When I asked him about the engine he said that it was a stock diesel bottom end with diesel internals. I asked him if he was joking and he said that he wasn't, I asked him if he was lying and he said that he wasn't. But I still get a feeling that it's not the whole truth.
Jonus's 2,5'er has (as far as i know) only the tdi block and crank from the tdi bottom-end. Rods and pistons are custom.
I just took apart a 2,5 tdi block (making a 2,5 with AAN setup), and the pistons have (as mentioned) a depresion. But in that there is a dome. This dome is there for helping the diesel-spray in the chamber, as the spray is directed against this dome.
Also (as mentioned), the weight of rods and pistons are considerable higher than the 20VT oem internals. The X-pin is 26mm, and almost 2x the weight of oem 20VT x-pin.
All this makes it not very rpm-friendly, as the loads on bearings and crank will be nasty at 7000+......
And then the CR, i dunno the exact cr on the 2,5 tdi. But say it is 16:1. It is a considerable amount of milling on piston to lower this to, say 9. If not impossible!
And if all the above mentioned was possible, the dome in piston still had to be removed. As this would definately corrupt the combustion, pluss be a very likely hot-spot.
I asume that all the mods/machining that had to be done, would cost moore than a set of used aan,aby,adu,3b pistons and a set of custom rods.
PS!, Maybe some of you have heard the news, but Jonus has just dynoed his new-built 2,5 20VT. He made 740 hp @2,1bar on 98 gas with The motronic. And 1065 Hp/1016Nm @ 2,8 bar on race fuel and Autronic.