Converting a 9a gasser shortblock to diesel???

[Jetmugg]

I'm going to start a thread, and attempt to document this process.

I'll be picking up a 9a (2.0L, flat-top pistons) this evening, with the goal of building a hybrid gasser/diesel engine, probably with an AAZ head.

Wish me luck.

Steve.

[R.O.R-2.0]

Been done, the pistons are NOT NEARLY tough enough..

the last one i saw, was a 1.8L gasser, diesel head, and it lived all of 300 miles..

[Jetmugg]

If this one lives 100 miles, I'll be happy.

Did the 300 miler melt down a piston, or break it?

Thinking about thermal coating the top of the pistons.

Steve

[vanbcguy]

What's the bore/stroke on the 9A?  Actual diesel pistons are a near necessity.  If you can find a set of diesel pistons you can somehow cram in to the block you might be able to do something.  Remember, all the VW diesel pistons actually protrude from the block a small amount to fill up the area of the head gasket.  Most gasser pistons are the opposite.  All the IDI pistons also have an area cast in to them to direct the flame out of the prechamber too.  TDI pistons of course are completely different as they have the combustion chamber in the piston itself.

The other one we saw on here a while back had dropped its compression down to around 130 PSI, not enough to light diesel anymore.

[Jetmugg]

Bore and stroke of 9a are 82.5mm and 92.8mm respectively.

The 9a pistons are essentially flat-topped, and protrude from the block a small amount, albeit not as much as diesel pistons.  The values I've seen are in the range of 0.016" of protrusion.

Modifying some other pistons is definitely a possibility, as is "decking" the block a bit.  I'll have to do some calculations to figure compression ratio.

My 1.5L / AAZ "Franken" engine has somewhere in the range of 17.5:1 compression.  While it's certainly smoky on a cold startup, it is making good power on 30psi boost.

[R.O.R-2.0]

If this one lives 100 miles, I'll be happy.

Did the 300 miler melt down a piston, or break it?

Thinking about thermal coating the top of the pistons.

Steve

Broke the ringlands and rings..

Gasser pistons dont have much "meat" between the ringlands, and they dont have the stainless steel insert in the top ringland either..

diesel pistons are MUCH beefier than gasser units, and have over twice as much material between the top, and second ring..

you HAVE TO use diesel pistons, and they dont make one in the 2.0L bore size AFAIK..

if you want a 2.0 diesel, then bore out an AAZ...

[8v-of-fury]

This is CRSMP5's back woods home-brew idea of a cheap stout way to build a fire breather.

I think you'd be 20 steps ahead to START with an ALH block and rotating assembly and upgrade from there.

[MJF]

Yeah, find a diesel bottom end. Gasser is waste of time and money.

[8v-of-fury]

Thank-you/

[CRSMP5]

 1.8 is not flat top... has a V milled into it and makes a weak spot...

they make forged 9a pistons.... $$$$ yes.. but if it pulls good #s on the stock ones... why not then invest? pre testing fun...

it is cheap experiment.. 9a value very little vs a aaz bottom end.. hell cheaper then worn out 1.6 diesel ones...

i think will last a few thousand... i think 5-30 with stock 11mm tty headbolts and 30psi... im going to try to greanade mine with nos/propain mix though before that... i want to see what is the weak part..

[ffgb]

Could you find a used set of diesel pistons and get the cylinders machined for inexpensive sleeves???

[Jetmugg]

The conventional wisdom may be correct, that this is not a worthwhile adventure, but it still doesn't cost anything to dream.

I'm poring over lists of commercially available pistons, rods, etc, trying to come up with a combination that's worth trying.

Those Ford 1.8TD pistons look reasonable.  Finding a set of connecting rods suitable for that application is a different matter.

For now, the fun is in the search.

Steve.

[RabbitJockey]

The conventional wisdom may be correct, that this is not a worthwhile adventure, but it still doesn't cost anything to dream.

I'm poring over lists of commercially available pistons, rods, etc, trying to come up with a combination that's worth trying.

Those Ford 1.8TD pistons look reasonable.  Finding a set of connecting rods suitable for that application is a different matter.

For now, the fun is in the search.

Steve.

there was someone who put a set of these in an aaz a while back.

[CRSMP5]

he is doing speed passes on salt flats.. 100 miles = 10 years of life...

i am the idiot who plans to dd one... and i am not worried on the pistons...

knowing how a 8v piston is.. for a 9a style block.. audi engine.. if that material is in the piston.. aka they have dish.. i see no reason a flat top piston will have a issue..

to diesel the pistons = different rods of custom make.. rember this block short like a 1.6.. not tall like a aaz/tdi...

audi short block 2.0 revs better then same set up with a 2.0 tall block.. but the torque on the shorty is less then the tall one.. ive built both on cis with no knock sensor.. why they went to the taller block..

for the at the wheels #s of his 1.5 set up.. which is impressive.. i think him just changing bottom ends will be much like when the gas crowd went from 1.6 to 2.0 modded bottom ends back in the early 80s by people at tt and such.. they had the 1.5/1.6 mastered.. but worked the bottom end up to 2.0... had crank failures and such... with a real 2.0 bottom end.. those weaknesses resolved..

the 1.8s i know were tested had issues of blowing fiber head gaskets by the areas of the piston V cut..  this predated metal aaz gaskets.. then aaz born.. so no one went down 2.0 that i know of... but 2.0 resolved the v cut piston...

its a giggles test.. very cheap to try.. 9a 1/4 price of aaz needinf a rebore... he would imo be foolish to not swap oil pump, im shafts and add the vac pump.. bolt his current goodies to it and give it a test to see how it runs.. then decide if he wants to chase it and throw $ at it..

i would be very suprised if it did not work... question is how well.. sad part is if it works very well... and vs gold dipped diesel crap be nice to have a cheap option.. you all shpould incurage him... he will do way more # proving then i will.. im going with drive it to break it aspect... not going to dyno mine... unless i cannot blow its head off... then i will to see where nos and propain take the numbers... while still tryimg to blow the head off... that will be vid day as till blown ill feel as if i failed..

his #s with the what did it take for me to break it = win.. mine will not be rebuilt... stock rings and all.. mine was running bottom end...  

[RabbitJockey]

http://www.vwdiesel.net/forum/index.php?topic=19163.0