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1956cc,
hp /
nm
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Basic ingredients:
- Stock AS41 engine case with two oil pressure valves.
- AA-piston's 90,5mm "B" stroker cylinder/piston
- CB's 76mm 4340 crankshaft
- Stock connecting rods "stroker-clearanced" from the bottom end
- Stock dualport 1600 heads with new stainless valves and single HD springs
- Engle W100 camshaft
- Stock 1,1:1 rockers, doghouse cooling etc.
- Small / basic equal-lenght exhaust header (not merged or any other fancier stuff). Stock heat exchangers.
- Self-built 2" exhaust with one glasspack and two bigger turbo-style mufflers in-line)
- Dual Dellorto DRLA 36's
- Aircoold.fi 043 breakerless ignition
- 30mm oil pump with spin-on filter
Machining made:
- Line-bored to 2mm / 20mm (should have been 1mm/21mm but machine shop made a mistake, oh well)
- Oil galley plugs opened and cleared, NPT threads made and plugs installed
- Heads bored to accept 90,5 cylinders
- Heads lowered a bit, not sure how much though
- Crankshaft and flywheel dynamically balanced
- Engine case's cylinder holes enlargened
- Case also milled down around holes: the ridge cut down and then cut into case for about 0,5mm. This was done so that I could use non-shortened barrels and still achieve the deck height I wanted.
- Case opened inside:
- Surprisingly large slots in the cylinder holes for connecting rod bolt clearance
- Slots also in the top of the case
- One camshaft bearing support cut a bit down
- ...this is why I don't usually use "HD cam bearings" as then I would have to had cut the bearing also as the thrust type bearing's wall may touch the con rod bolt
- Some aerodynamic mods done to bearing supports "under" the cylinder holes
- Stock alu pushrods shortened for 5mm. This was actually quite easy when enough heat was used.
- A total of four head bolts grinded down as they touched rocker shafts.
- Welded an steel AN10 bunge to oil filler and aluminium one to the air cleaner lid to make a sweet black breather hose. Biltema sold these quite cheap and they weren't thankfully the red/blue colored.
Head porting:
- Area around intake and exhaust valves opened from their sides to blend nicely into larger cylinder walls.
- Head volume 55cc after combustion chamber port work and lowering
- Steep corner on exhaust port rounded and the whole port opened up a bit
- Intake port cleaned and ported a bit
- Intake match then ported to manifolds (manifolds were bigger as stock)
Build notes:
- As I used "stroker" pistons with only 76mm stroke, it was natural that this engine would be narrower than stock. That made a few problems but nothing that couldn't be solved easily.
- Stock pushrod tubes were really a tight fit but they went OK
- Engine tin fit just about perfectly!
- As with earlier engine, cam thrust bearing slot was too tight for the bearing, had to grind the bearing a bit to fit into cam. Tested this time that the W100's slot was too tight with different bearings (silverline, kolbenschmidt, mahle)
- Deck height tuned via case machining to 1,5mm -> STATIC COMPRESSION RATIO = 8,6:1. Suggestions for W100 on the net are around 7,5 - 8,3.
- DRLA 36's specs, tuned with narrow-band lambda:
- 32 main venturies
- .2 emulsion tubes
- 54 idle jets (a bit over 20% smaller than "stock" 60's!)
- 135 main jets (4,2 x main vent diameter)
- 180 aux air jets
- X acc.pump jets, don't remember, "stock". These are too small for this engine and have to be changed.
- 60mm velocity stacks
Usage / riding notes:
- Same ignition and timing as with earlier 1641 engine, no pinging here also
- Steady idle from around 600rpm
- Pulls from 900rpm to around 5200rpm
- Way more grunt than in earlier 1641cc.
- Very easy to drive, very streetable
- Picks up easily 115-120 km/h speed
- Way better for T2 bay than the earlier engine
Got a 19,5s / 106km/h quartermile.
- Short burnouts can be done with second gear. Although my rear tires are 235/65 R 16's so pretty much contact area.
- I used a Kennedy stage 1 clutch with kush-lok disc this time. It's quite light and easy on T2.
- As this stroker is narrower than stock engine, this could fit fine also in older beetle's engine bays where usually it's a tight fit around head tins and heat exchangers.
- Oil temp sender installed on behind distributor: 1/4 NPT -> 1/8 NPT adapted ordered from ebay and cheap 1/8 NPT sender installed.
- On a pretty day, oil temps creeped up to 100c when driving more than 20km's and when speed was around 85-95 km/h. Then I took off the plywood plate I have over my doppelkabiner's engine room. Oil temps dropped 10-15c even if I then picked up speed onto 105 km/h steady. It really makes difference to have more air in the engine bay even if you don't have extra oil sump or any other than stock DH cooling.
- This engine has now been daily driven, for about 2500 km's now. Only problem I noticed was that one rocker shaft spring washer was broken when I adjusted valves, maybe I should upgrade to bolt shafts...