Tricky decision as there is no absolute answer on this one, but plenty of theory, dwell time of piston etc (I think the drawing is on this thread?). Cams may end up getting changed if your are altering compression. Interestingly the 440cc injectors strike me as v. v. large for n/a output. Not a typo?
Yea left my edit a bit late. For some reason I have always wanted to keep it completely ABF but a mate suggested a 9a block today and got me thinking.
Chris I think the injectors aren't being used on full duty, I'll be pretty happy with 215-230bhp it's 208bhp now, rev'in to just over 8.2k this is why I want the bottom end worked. Since this 9a block as been suggested I'm stuck to want to do!! Can't see much of a difference as there seems to be pro's & con's to both
I reckon you could get both to perform well. So why not go with the lighter short block and possibly lighter 144mm rods, compared to the longer 159mm rods. Gudgeon pin size is 1mm smaller at 20mm on the 144mm rods too, that could be the weight saving clincher. Actually got the same thoughts going on myself but with an 8v build at the moment. Short block wins for me. If there is not going to be any pukka competition regulations to adhere too then you are free in that regard.
Lightness of the 9A versus apparent torquiness of the ABF? Could boil down to that. We see power/torque more easily off ABFs on the rollers, but then people tend to go for those anyway, so there are more of them.
How much of a weight difference we looking at?? It's seems the summary of this thread over comparing these blocks are ABF = more torque, 9A = more power and less weight?? I thought this was going to be a easy choice but it's not looking that way lol
It really isn't easy. Rod length, rod angle, revvabilty - all played out via the Golf 3 kitcar (ABF) and Ibiza kitcar (ADL - shortblock) back in the day. KR vs ABF blocks are 4kgs apart. There's more meat on a 9A than a KR, so 2-3kgs, plus the fractions of different rod lengths.
In addition to what has already been said and posted, the ABF base short engine is designed to have less pumping loss. The TDC dwell is increased due to running a longer rod. This good for maintaining cylinder pressure for a particular set of circumstances (CR, load, fuel mixture and spark timing, revs). This cylinder pressure is required for maximum acceleration of the crank pin when the rod is at a CA just after TDC or some say 10-14. Internal friction is reduced on the piston/rings as a result of the rod length and the maximum angle of it travels when the crank sweeps throw TDC to 90 to BDC. The ABF pistons also has thinner rings and a smaller skirt which further helps to reduce friction over a 9A engine. What I saying is if both engines make say 100 indicated hp, then frictional losses, based on different bottom ends could mean one would achieve say 80 clutch hp and the other say 70 clutch hp. This analogy means, increased fuel consumption for the 9A to achieve 80 clutch hp. Your graph for the current engine says 208bhp@????rpm. You also have a redline of 8200rpm. Studying this graph would be useful to predict how the engine would achieve 215bhp@????, what type of WOT torque will be delivered and ultimately what components can be efficiently added. I cannot see why your current engine would have a problem, pending good component selection and mapping.
The bit I *never* understand is why Seat did not re-homologate their rally F2 Kitcars from: the short block 84mm overbored / destroked 1.8 ADL to: a destroked 84mm ABF .. if the block height, rod length and power characteristics were a hinderance. The ADL had the 373 D head anyway? Admittedly both engine types in F2 format had longer 149mm/160mm rods, huge compression, every bell and whistle going so the overall configurations are not comparable with production engines, but the principle of block height / rod length must clearly not have bothered Seat. They were not short of budget and a re-homologation of a later production ABF engine should not have been any issue at all. This lack of outward decision-making therefore represents one of the following: Avoidance of increased weight Reluctance to reverse out of an R&D alley into another one (but the engine was available from Lehmann anyway for the Golf...) Administrative hurdles Engine height packaging Indifference between the two Views on the above? Edit: I would say this infers the short block is better But that does not correspond with the road tuning outputs we see. Meanwhile the Mk3 Golf was stuck with the ABF because it was only ever produced with them from the factory - and they used the aforementioned 160mm rods.
My next bottom end will be 9A, mainly because as a standard block it has no internal trigger wheel, the weight saving is important as it will also have a lower centre of gravity. The ABF in standard form has proven to be great but in Daves case if you are changing pistons and rods I would think the ABF would have very little gain over the 9A for power, let alone the weight and packaging issues.
I will add my 2p. Have you considered kr block. If you going for oversized pistons that would make it ~1.9. Plus kr has got 86.4 mm crank which allows you to rev engine to 8700 rpm and stay within safe piston speed region.
Chris, Some race / rally ABF blocks were heavy skimmed ( gave cracking issues) F2 > 90 mm stroke and a 2 ring piston with 18 mm pin then you need a rod about 165 mm long in a 236 mm block
They're homologated at 160mm though Hugo, which forces a height of sorts, depending on high up the piston they can get the pin. From the actual evidence I have seen, F2 Ibiza ADL 84mm pistons were 3-ring, unlike the touring car 2 ring set ups, and the pin was right up against the 3rd ring. Either way, Seat had access to both engines if they wanted them and stuck with the short block
Think on a full build engine there will be not much between low and high blocks.... even VAG decided to go further mainly on the 220 mm block route...except TDI and very few others
I think the Golfs sounded very different back in the day to the Ibiza - the Ibizas revved like mad, very noisy and very distinctive. Rod angle and dwell, with a torque cost for the short block?
Indeed F2 Ibiza short block engines revved skyhigh and that`s always at the cost off TQ But in the end its a compromise between rod weight and strenght , rod ratio/ dwell and friction Rod ratio`s Audi STW = 1,73 (152,5/88.1) Seat Ibiza F2 = `1,65 ( 149/90) Seat S2000 = 1,71 ( 151/88,1 ) ABF = 1,71 9A = 1,55 dwell is about cilinder pressures and that can be tweaked by C.R and cam timing , etc
