Automobiles Forum banner
1 - 20 of 21 Posts

·
Registered
Joined
·
145 Posts
Discussion Starter · #1 ·
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 :)
 

·
Registered
Joined
·
1,138 Posts
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

http://www.s2forum.com/forum/showthread.php?t=6797

Regards,
Justin
 

·
Registered
Joined
·
1,138 Posts
No, you definitely need to modify the head bolt holes to even bolt it on.

I doubt the diesel pistons will work right with the 20v head.

Justin
 

·
Registered
Joined
·
223 Posts
I have not seen one, but I'm under the impression, that the tdi piston has a 'cone shaped depression' in the piston crown. Also there will not be any pockets for the inlet valves.
 

·
Registered
Joined
·
2,882 Posts
I doubt anyone in the US would have done this as no 2.5 tdi's made it to the states. I think the questions you have can only be answered by your own investigation. We ambitiously await your findings.
 

·
Registered
Joined
·
1,138 Posts
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 :p I agree they may be very strong, but that bottom end wasn't designed to rev to 7k like 20v will want to.

Justin
 

·
Registered
Joined
·
145 Posts
Discussion Starter · #11 ·
the engine would be like stroker with 5 k revs .but when i think about these diesel pistons...they should hold tons of boost with high compresion ratio.how do you think?
 

·
Registered
Joined
·
223 Posts
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..
 

·
Registered
Joined
·
2,425 Posts
doncez said:
...they should hold tons of boost with high compresion ratio.how do you think?
This is great.... FOR DIESEL.

Since the well-thought-out and fully explained responses are not getting the job done let me just say this in the most simple way:

No, it won't work.
 

·
Registered
Joined
·
145 Posts
Discussion Starter · #17 ·
what if shaving off some mm from the top of the piston,so valves wouldnt hit piston? :frustrated: kill me for stupid question,but i am still interested :D
 

·
Registered
Joined
·
1,012 Posts
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.
 

·
Registered
Joined
·
17 Posts
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.
-Rune
 
1 - 20 of 21 Posts
Top