Ok excuse the dopey title, I'll think up something cooler at some point.

This is a car I bought near Boulder, spent its life in the mountains, its a bit of a mess but has a solid body (notchback). I put a motor and transmission from an '88 900 turbo in it a couple of years ago, along with the later model 900 axle and steering knuckles, and brakes from a 9000. It overheated it at some point and lost compression, presumably the head got warped. I ended up parking it and have been driving an A4 since (needed something good in the snow, actually not a bad car).

So fast forward a few years, two moves, a few more vehicles, and now I finally live at a place with a shop and getting the itch to get it back on the road, plus I'm sick of looking like a broke yuppie in my (battered) compact executive car. It'll be my daily driver and I fantasize about taking it out for the occasional track day and step one is rebuilding a motor for it.

I'm going to start out with this block from another 88, new seals, bearings, and rings and hopefully a T7 head, I've collected the fuel injector block / injectors / rail and an intake from a 2.1 and couple of heads - hopefully I've got one that is in good shape and needs nothing.

So anyways, I'd like to just re-ring this guy, but I'm thinking the pistons may be too scuffed, they don't grab your fingernail but look kinda crappy. I know more or less nothing about how messed up things are allowed to look inside an engine, so hopefully someone has an opinion about whether its worth the expense of new ones:





The block seems to be in good shape, I've opened up ones that have a little ridge at the top of the bore, this one is smooth. I'm leaving it at the machine shop today for hot tank and inspection, I'll ask them to check to bores for roundness and taper. There is a little bit of scuffing and a little rust but its still even, no pitting at all - the picture certainly makes it looks worse:




The current pile of engine related bits:



I'll take some pictures of the car and put them up soon, there is a list of other issues to be sorted, the main one being the front suspension.

Zac

First, I really like 'Sven Block,' but I am also into bad puns.

If the marks on the piston skirt don't grab a fingernail you can reuse them, but if you're going to go bonkers trying to get more power out of it you may just crack the stock ones anyway.

I've re-used worse looking ones than that, but if you're building up a reliable DD / sometimes-track-car now would be the time to spend a little extra money and do it right.

NOS stock pistons are getting really hard to find anyway.

Yeah that's good advice, I was kinda wandering away from new pistons because I was having a hard time finding them, but one more search yielded a 90.5mm set on ebay for $220 shipped. I did look at your thread Drew about 9-3 and 9-5 reciprocating assembly - maybe next time around, don't have the energy to spend an afternoon in the junkyard right now, but I love the mix n match game.


EDIT: Hmm now I'm thinking these are non-turbo pistons - what does that mean? I done bought 'em already, might see if they'll keep them instead.

part number 75.20.836 in 90.50mm oversize (1st oversize) from Vintage Imports.

So those are 8V pistons. They will fit in your block and everything, I just don't know what the compression ratio change will be.

The dishes on the 16V turbo pistons are much larger diameter and deeper than that photo, if that's actually a picture of what you're getting.

If you're going to do the more efficient T7 head and T5 injection that's meant for 9:1 or 9.3:1 compression you shouldn't have any issues tho.

Can't wait to see it run! I'm a fan of 16V 99s!

What axles did you use for the 88> hub conversion? I'm getting all the parts together to do that to my 78.

John

I honestly cannot remember what axles went where, one of the reasons I started this thread is to aggregate everything I've done/doing to this car in one spot! I'll try to figure it out, I didn't have to machine any new circlip grooves or anything and fairly sure the tripod bearings sit correctly in the inner drivers, but that may be wrong. I'll investigate when I pull the motor out in the next few weeks. I can say that the 9000 brakes are well worth the hassle, the 88+900 spare did not clear them so grab one of those when you get calipers, and braided lines are fantastic, I had mine made up here in town - could probably be a half inch or so longer but they seem to be fine.

Looks like I've got 8 valve turbo pistons on the way, sources say that the NA pistons have flat tops, meaning 7:1 compression (turbo), any one confirm this? See picture in my post above.

the 8v N/A pistons are not flat top. I think they are somewhere around 9:1 compression. There were "emissions" n/a motors too with deeper dishes, but most are 9

My green '79 EMS has the B20 "CA" N/A engine, which is like 8.3:1 compression and had a catalytic converter, and has deeper dishes than those. The other N/A B20 engines were 9.0:1.

The turbo 8V engines had two different compression ratios (actually I think 3 different ratios if you count B20's from 99's and early 900's.) The early non-APC H engines were like 7.2:1 and the H APC engines were like 8.5:1? Something like that.

You'll have to see what actually shows up and take some measurements. Good price on those though, you kind of can't go wrong.

Yeah I figured it was worth the gamble, we'll see what shows up in the mail...

The 85 T16 used the same pistons as the 84 T8.

The head had the hemispherical ports. 86 saw a redesigned head, and different pistons.

I'm using 91mm 8.5 (BSI201) pistons in Frank. I know that drops my cr a bit w/ the B212 head, but I'm very happy w/ the results.
Thanks for the info on the axles. I'll measure my axles when I tear them out and go from there.

John

So my new pistons will definitely be upping the C/R some, I'll make some unscientific measurements to get a ballpark number. I'm gonna take them down to the machine shop tomorrow and have the bores bored, any recommendations for clearance?

You have a 90.5 mm piston. On the top it is stamped SP 0.03. And 90.47. This indicates .03mm of clearance. So the piston is actualy 90.47mm in diameter but when placed in a block bored to 90.5mm you will have .03mm of cleaeance.

Ok so that's .0012" or so, is that right for the turbo application? Seems like turbo motors frequently get something in the .003" range, don't have my Bently handy but somewhere on the internets it is claimed that it recommends .0008-.0025".

Gonna drop pistons off at the machine shop this afternoon.

swmeatball wrote:Ok so that's .0012" or so, is that right for the turbo application? Seems like turbo motors frequently get something in the .003" range, don't have my Bently handy but somewhere on the internets it is claimed that it recommends .0008-.0025".

Gonna drop pistons off at the machine shop this afternoon.

you could ask the machine shop or give the piston supplier a call and see what they think. I know that cast pistons and forge pistons require a different clearance.