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Discussion Starter · #1 ·
im building a ghetto 20VT using an NG bottom end from an 88 audi 90 and the head off of my AAN engine. i've already read that i should have valve relief's machined into the piston tops which i have covered. what im wondering is if which rod would be stronger for this setup, the AAN or the NG? i realize i have to drill out the hole for the oil return in the block, make the notch in the bell housing end for the crank sensor, install my AAN oil pump, drill and tap a few holes for the AAN timing belt tensioner and thats about all i foresee. anyone else know of anything im missing?

The NG bottom end and rods/pistons.


the rods and pistons all numbered and ready to go with my brother to the machine shop.


The ANN installed in the car. the AAN spun a rod bearing and chewed up the crank.




My 4000 quattro. trying like hell to get it back up and running for winter.
 

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i never machined the pistons on mine, and i ran it quite a lot and hit (and sat on) the rev limiter countless times. The rods are the exact same I believe. I would just run the NG slugs with the rods that are already attached. Mine was still running great until new owner ran 91 octane fuel in it and exploded a rod.
 

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im pretty sure rods are the same too, id run the NG rods as they've prob had a much easier life than the AAN stuff
 

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Discussion Starter · #5 ·
looking at the rods side by side the AAN rod's have an oil passage that runs down the middle of the and the NG pistons dont. that's why im up in the air with which to choose. the AAN's with the oil passage would obviously oil the rod bearings better but i feel would be weaker as they have a hole through the middle of them and i feel the NG rod would be stronger because their lacking the hollow center but also they dont have the oiling for the rod bearing that the AAN rod does.

my2000apb said:
which cylinder spun?
Cylinder 4 spun.

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death 4kqt said:
i never machined the pistons on mine, and i ran it quite a lot and hit (and sat on) the rev limiter countless times. The rods are the exact same I believe. I would just run the NG slugs with the rods that are already attached. Mine was still running great until new owner ran 91 octane fuel in it and exploded a rod.
What im fearing is the engine exploding, i've had nothing but bad luck with I5's ever since i got into them honestly. it puzzles me because i have a buddy who beats the ever living crap out of his C4 S4 and it only breaks all 4 tires loose. seems like every time i want to go out and have some fun in my swapped car its shitting an engine and its getting old.

my2000apb said:
im pretty sure rods are the same too, id run the NG rods as they've prob had a much easier life than the AAN stuff
The AAN engine didnt really live too rough of a life when it comes to abuse but when it came to maintaince it lacked there. i got my donor car from the original owner who was a older lady and she babied the car but didnt take care of it for crap. the engine has a fairly new dealer installed head because she never took it for servicing and it junked the timing belt. she took the car to crappy oil change places who used crappy oil filters and oil etc. i guess thats a give and take situation lol.
 

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vwnut8392 said:
What im fearing is the engine exploding, i've had nothing but bad luck with I5's ever since i got into them honestly. it puzzles me because i have a buddy who beats the ever living crap out of his C4 S4 and it only breaks all 4 tires loose. seems like every time i want to go out and have some fun in my swapped car its shitting an engine and its getting old.
well mine exploded because it was running 30 psi on a holset and tuned on 93 octane fuel, and he put 91 in the tank and boom. Could you tune be causing death of engines? I have found 5 bangers to be extremely resilient to abuse at moderately high power levels. Stock they seem like they can live on the rev limiter forever.
 

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Discussion Starter · #7 ·
the AAN was pretty much stock. only mods where 3in downpipe and exhaust, external dumped wastegate, chip tune, intake and 7A cams as i had them laying around so i tossed them in while i was assembling the car. i would venture to say it was probably the tune, i was experimenting a little with it. i only had it around 15psi though. im honestly fed up with the stock management and im considering installing MS3X on it while i have it apart this time. DIY autotune has all the goods i need to build a PNP jumper harness to the factory ECU connector. me and my brother machined the crank pulley to have a 60-2 trigger wheel on it like what 034 motorsport sells and made up a bracket to house a crank sensor. i planned on making an extension harness from one of the 2 crank sensors to reach out front to the new crank sensor and that should be all she wrote for getting it to run on megasquirt.

im going to take a few pics of an NG rod i have and an AAN rod out of my engine just so you guys can see what im talking about.
 

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i can picture the hole you are talking about, ill look at my coat rack when i get home (made from AAN rods). Honestly I think you can use which ever rod you choose for what ever reason. Either will work just the same IMO.
 

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Discussion Starter · #9 ·
Here's the difference's i noticed in the rods right off the bat. not sure which would would be a better choice.





 

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NG looks like it could be marginally stronger...but honestly I dont think it matters. Choose what you like best and run it.
 

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Discussion Starter · #11 ·
i think i'll stick with the NG rod. another thing i noticed is the size of the wrist pin too, the AAN's wrist pin looks alot thicker than the NG's.

 

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theoretically rods and wrist pin choice doesn't matter since the pistons are the weak point anyway, but thats not how mine went out. You can use the AAN wrist pins in the NG slug right?
 

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I honestly think the best ghetto 20vt bottom end is a nice, healthy factory assembled NG block with the 7a head slapped right on. Factory assembled is always a plus in my mind. (thats not how I did mine, but thats how i would do it again)
 

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Discussion Starter · #14 ·
i totally agree on the stock engine point of view. i've had my battles with building 10V turbos and the most bullet proof one i had was a JT engine from an automatic coupe GT. all i did was put a 3 layer metal head gasket, an ARP head stud kit and an MC2 turbo cam. that engine took 18-20psi on the rev limiter all day long. i never touched the bottom end at all. everyone told me that turboing a JT engine was stupid because their weak. i had mine on EFI instead of CIS-E. the mechanical fuel system is the downfall to make boom with a 10V turbo. hell the bone stock JT that was in my 4000 with 5000 turbo parts just bolted to it took 15 PSI before the fiber head gasket popped and that lasted for a year and a half before that happened.
 

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vwnut8392 said:
Here's the difference's i noticed in the rods right off the bat. not sure which would would be a better choice.





really that oil hole is not where a rod gets its strength. It is an "I" beam. the center has the least to do with how strong it is compared to any other part. Also, let us not forget that the hole has material around it. notice the bulged out area? looks like Audi replaced the material they took away with the hole and added some oiling. can not be bad.
Noramally, I would suspect a turbo rod is stronger but not sure on this one.
 

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death 4kqt said:
I honestly think the best ghetto 20vt bottom end is a nice, healthy factory assembled NG block with the 7a head slapped right on. Factory assembled is always a plus in my mind. (thats not how I did mine, but thats how i would do it again)
This. You risk more issues "refreshing" a motor than you do running it bone stock.
 

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Discussion Starter · #19 ·
i just took the rods and pistons out to have the pistons machined for the valve relief. i have new rings and rod bearings even though there is nothing wrong with the stuff that came out. when i pulled the rods i kept all the bearings in the rods they belong to and for the the rings they came off the piston they the was installed and i taped them together and numbered. the rods, pistons and rod caps are all numbered and i also marked the bearing shells to which rod they belong and weather their top or bottom. i never ever mix anything up in an engine. now the question is weather if i want to use the original stuff or install the new stuff.

Here's all the old and new parts i have ready.
 

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Discussion Starter · #20 ·
well as i've been tearing down my AAN and trying to switch parts over to the new engine im realizing that the NG block is lacking ALOT of the provisions to mount most AAN related parts. no holes for the timing belt tensioner, missing a hole to mount the power steering pump, no holes to mount the AAN front snubber mount, and no holes for the AAN crank sensor. in my mind this NG block is going to take far too much modification for my application so i guess its time to bite the bullet and go searching for a good AAN/3B bottom end or save up money and send mine to the machine shop to have it repaired.
 
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