The Superboxer, a new heart for the Silver Bullet

[silverbullet]

Well now I've got the transaxle back from Aidan, not too much for the bin this time

Herr Getriebemeister reports that he's rarely seen one so early (it's an '82 DW with some peculiar internal details) and had been previously repaired by a competent individual with no proper tools, so was set-up a bit on the tight side but otherwise had a good gearset:

4.86 diff with a taller 5th making it near enough the same as AAP ratios, but a bit quicker off the mark which suits the revvy Subaru quite well!

Upgraded to a 4-pin diff (damaged planet wheels in the 2-pinion possibly as a result of too much wheel-spinning fun by the previous owners), oiling plates, later welded selector forks. And a replacement 4/5 syncho hub that was 33% deficient in it's driving capacity...

So not an SA one at all, but rather what was available at the time it was converted. Need to find/negotiate some time to get that fitted now

[toomanytoys]

DW.. same as in my very early 'velle.. which Aidan is going to give a freshen up..

[silverbullet]

As long as I don't go honking it in 4/5 (not easy with the revvy rice fryer in the back) it'll be OK.

Long-term, the blown motor may have to get an Auto but I don't really fancy one. Recon 915's are heavy money and I'd have to convert the clutch to hydraulic, but they do bolt straight on and have a sensible diff ratio for a bus i.e. not too tall at around 31/8 or 3.875. Still a pretty big gear to pull though!

'84 on they have an oil pump for the 3.2 which makes them good for up to 280 lb.ft

But...the G50 came along on '87 and although it has a lower torque rating at 220 lb.ft it is supposed to be easier to live with. Diff is a bit too tall at 31/9 or 3.44 unless this engine turns out to be really strong

[silverbullet]

Still gathering parts...bought this used VW Speedshop exhaust from one of the Brickies as they are hard to get:



NOTE! The silencer hanging point on these silencers is completely crap, far too small and causes the can to crack (reason for sale) so I made a shaped s/s 4" pad and saddle to cover the repairs and more importantly, spread the stresses! Got it welded by my favourite meister, using a combination of TIG and MIG:



A little polish (now the spatter is off) and it'll be lovely again!

[ELVIS]

Is that Tony(booted) old exhaust? good bloke him

[silverbullet]

Yep. Figured it was a good buy as they are on back-order at Speedshop.

Didn't meet Tony on the day, but his lad made a good cuppa

[silverbullet]

Looks like I may have stumbled upon a good core to get this build started, after a fashion.

Having sold the DG from the syncro to bail out a mate who was in dire straits (it had popped a head stud under the inlet manifold), I took his dead motor in p/x to see what I could salvage.
Heads off (barrels stuck on as per) but no dramas, nothing else broke and it appears to be a genuine 160k-odd unmolested engine. Just for a try, I put my little 3/8 drive strud extractor on the broken one with a ratchet handle and to my amazement it unscrewed Three more studs had just started to show signs of distress, so I tried them and they came out too



All the rest are perfect:





At least I've got this lot to put it right (shiney ones are old-stock Lemforders so it might get four genuine ones instead)



Sump plug stripped but no helicoil, water pump face rather eroded due to a failed pump in the past (sealant on the O-ring )



Might get this TIG'd over and re-faced or maybe a plate to blank off the void. Need to check best design practice for pumps to avoid the risk of cavitation, unless I decide to go electric....

The only bugger was that one of the pushrod guard bolts sheared off at the first show of the spanner

[silverbullet]

I'm starting to lean towards building this as a 1.9 a bit like the original Polo Sprint engine which inspired this project

Why? Well for a start the 69mm crank has something like 50% overlap between the journals, making it a lot stiffer than the 2.1's 76mm item. This is good for bearing longevity. Secondly, to get the required compression ratio of around 9:1 the 2.1 commands a very deep piston bowl (like the MV one with it's peculiar bulge in the middle to clear the little end of the rod) which increases it's surface area and consequently increases the heat transfer/loss to the piston. Not good.

The 1.9 piston has a shallow bowl that's nothing like as deep in comparison and also has more metal between the rings as a result of it's #3mm greater compression height. The rings are also wider which will aid heat transfer to the cylinder walls and prevent the rings from overheating under full load conditions. This is all good news for reliability and ring life.

I reckon a custom forged piston set with bowls matched to the heads, valve cut-outs handed for the flat 4 (unlike the OEM "universal" piston) and also with offset gudgeon pins for reduced thrust losses should complete the picture.

This engine is never going to be short of torque, so the shorter stroke seems to be the obvious choice for reliability and making the most of the Opcon's efficiency over a wide rpm range. I can see the engine rpm limit getting revised upwards

Might just help the transaxle to have a slightly easier time of it too...

[Mickyfin]

Result getting that sheered rod out. Off to eGay to look for a Britool 3/8 drive strud extractor

[Fin]

I'm starting to lean towards building this as a 1.9 a bit like the original Polo Sprint engine which inspired this project

Why? Well for a start the 69mm crank has something like 50% overlap between the journals, making it a lot stiffer than the 2.1's 76mm item. This is good for bearing longevity. Secondly, to get the required compression ratio of around 9:1 the 2.1 commands a very deep piston bowl (like the MV one with it's peculiar bulge in the middle to clear the little end of the rod) which increases it's surface area and consequently increases the heat transfer/loss to the piston. Not good.

The 1.9 piston has a shallow bowl that's nothing like as deep in comparison and also has more metal between the rings as a result of it's #3mm greater compression height. The rings are also wider which will aid heat transfer to the cylinder walls and prevent the rings from overheating under full load conditions. This is all good news for reliability and ring life.

I reckon a custom forged piston set with bowls matched to the heads, valve cut-outs handed for the flat 4 (unlike the OEM "universal" piston) and also with offset gudgeon pins for reduced thrust losses should complete the picture.

This engine is never going to be short of torque, so the shorter stroke seems to be the obvious choice for reliability and making the most of the Opcon's efficiency over a wide rpm range. I can see the engine rpm limit getting revised upwards

Might just help the transaxle to have a slightly easier time of it too...

You lost me right there, but it's cool too see how you are getting on
Aiden is a top bloke - picked up my box a couple of week back, which we changed on his workshop drive and thrashed back to Bath in the Bus, baiting big Audi's and stuff on the way, I was clear off the clock on a couple of occasions, it's funny seeing the look on peoples faces when they have to shuffle over for a T25
Love it

[silverbullet]

Journal overlap is the amount that the big end "eclipses" the main bearing, when viewed end-on. With the wbx's relatively small dia. main brg. diameters, the shorter stroke crank means more overlap. It basically means there's more metal joining the crank pins together over a shorter distance!

[Fin]

Aahhh cool... so in theory stronger then

[silverbullet]

Well I revved one off the end of the tacho two winters back when the throttle cable froze and it was fine

[toomanytoys]

1.9....

[silverbullet]

I was originally hoping that a 2.1 would give the optimum rod ratio of 1.8; 76mm stroke x 1.8 = 136.8 or ~ 5.4", standard rods are 138mm(?)

The 69mm crank with the same rods has a 2:1 rod ratio but that's probably what makes them so smooth, a bit like the later VW inline 4's with their taller blocks and longer rods, which are more refined than their predecessors.

Can't have everything then. Shorter rods = heavier pistons with tall compression heights, to get 1.8 ratio the rods would have to be only 124mm long! I'll go with the stronger crank and smoother running, even if it means reigning in the performance a bit!