Ah, it's only 90 mm bore spacing on the later engines. I suppose that they did this to stick them in the transverse engined cars? Or, to save tuppence on the block, head, manifolds and crankshaft? Shame they did not keep the 95 mm centres!
Still can't really understand why VAG produced two almost identical engines, with different rod lengths? Bit like, I don't understand why they fitted a back-to-front clutch, in the early Gtis, when a conventional clutch would have fitted easily?
They produced the engines at different times though, one as a development of the other. I'm sure I heard the explanation once. Was it to do with emissions?
As with all things modern. They have to make them crud. So by adding the heavier tallblock to the lardy mk3 16v gti they could just about make it understeer as well as the vr6!
I'm guessing the 9A/6A was the first production 2.0l valver block, which is simply an evolution of the 1.8 block. Perhaps the engineers decided on the next round of designing (or next evolutionary step) to increase the deck height, to afford longer rods, and all the advantages associated with it. Out of curiosity, what deck height & rod length do later blocks have, say for the 20v and FSI engines?? If they stuck with the longer rod length then it suggests that it was an evolutionary step, rather than an engineers whim.
There were big delays IIRC before the Mk3 GTI ABF 16v came out. I think the engineers were told to come back with 150 brake. Somewhere in the mix is the evolution of the 6A block from late '80s to ACE. Late 6As had crank sensor castings (not drilled) and wide block skirts, like the ACE.
9A-ABF Block comparison Relative to the above discussion, the American site "panic Tech Papers" includes an article entitled "Connecting Rod vs. Stroke Analysis" at http://victorylibrary.com/mopar/rod-tech-c.htm Likewise, header manufacturer Jere Stahl and associates post their conclusions under "Rod Length Relationships" at www.stahlheaders.com/Lit_Rod Length.htm John C Erb, former chief engineer of oem piston manufacturer United Engine and Machine, and associates have authored a series of technical articles on combustion chamber shape, piston design, and squish, the latter titled "Magnificent Quench" at http://kb-silvolite.com/article.php?action=read&A_id=39 LeftcoastTigger
Bit pi**ed off now, I did not need to spend hours doing the sums. I sent this to danster yesterday, and I am dead chuffed that my theory appears to be correct! I did point out that all other things had to be equal, for what I posted to be a definative comparison. There is a lot more to it than my simple approach. But, it does show that rod length can make a difference to how an engine might perform. I am of the opinion, and always have been, that oversquare short rod engines produce more power because the piston accelerates away from TDC so rapidly that the speed of the mixture is so high that the momentum in the mass of mixture keeps it rushing in, even when the piston is slowing down. It can't brake so quickly. So it fills better. What do you recon.?
just to add another couple in the mix, an engine which is almost identical to the 9a/abf in dimensions, Technical overview of the Clio RenaultSport 197 Engine Induction capacity 1,998cc Bore x stroke 82.7mm x 93mm 4 in-line cylinders with 16 valves Compression ratio 11.5:1 Max. power kW EEC (hp DIN) 145 (197) Max. power 7,250 rpm Specific power output 100hp/litre Max. engine speed 7,500 rpm Max. torque Nm EEC (m.kg) 215 (21.9) Max. torque (rpm) 5,550 Specific torque 108Nm/litre Injection - Multipoint Con rod details Engine Type: F4R Rod length C/C: 144.00mm Small End: 21.00mm Big End: 51.60mm Engine - 2.0L Duratec ST - 173PS * Displacement (cc): 1988 * Bore: 84.8mm * Stroke: 88.0mm * Fuel type: Unleaded petrol, 95 (RON) * Max power: 127kW * Max power: 173PS * At engine speed: 7000rpm * Max torque: 196Nm * Max BMEP: 12.2bar * At engine speed: 5500rpm * Compression ratio: 10.2:1 139mm con rod
So, it appears that good power can be obtained from an undersquare/short rod engine. Read somewhere, probably on here, that, when VW brought out the 16v engine, engine tuners said that getting big power out of them would be a problem due to the poor shape of the inlet tracts, or was in the exhaust tracts? So, anyone got cross sections of the heads on all these engines?
FWIW, another update: Code: [B]Engine Bore Stroke Rod length Compress Deck height* Comp height BHP NM Characteristics[/B] 9A 82.5 92.8 144mm 10.8:1 220mm 302mm 134 186 More power ABF 82.5 92.8 159mm 10.5:1 236mm ???mm 150 180 More torque Type-R 87 84.4 153mm 11.7:1 223.9mm ???mm 246 217 "No torque!" Clio 82.7 93.0 144mm 11.5:1 ???mm ???mm 197 215 French! Duratec 84.8 88.0 139mm 10.2:1 ???mm ???mm 173 196 F*rd! Civic 86.0 86.0 ???mm 11.0:1 ???mm ???mm 197 188 306 GTi6 86.0 86.0 ???mm 10.8:1 ???mm ???mm 167 193 * Crank centre line to deck
Peugeot 306 GTi-6/Rallye added above, at a square 86 x 86. These engines and the 150/155bhp predecessor engine both lack low down torque, though the 6-speed first gear doesn't help.
The short rod in the earlier 2.0's 9A blocks tend to put more pressure on the wall, ABF with the 159 supported a reliable long life motor than the 9A and the KR
I understand about the side pressure reduction, I mentioned it in post #46. Below is not 16v I know, but still the long vs short rod theme at VAG: What I was getting at, was that Audi first produced the 3A 8v engine with 144 rods, and used it for five years from 1988 to 1992. (The 3A led to the 16v 6A and then 16v ACE) For 3 years, from 1990 to 1992 they also built the AAD 8v engine with 159 rods. From 1993 on all 2.0 L 8v used 159 rods. So, for three years, they were building two identical engines, except for rod length. All other major parts were identical: Heads, cam, valves, injection, etc. The only difference was the exhaust manifold! And, the AAD only had a catalyst, but the 3A was available with or without. I think Chris Eyre's mention of emissions may be the right track as to why? (As a side line: I was looking at the reverse clutch system on Mk2 Gtis. Looks like VW are not to blame. I recon it came with the engine when they bought Audi from Merc? So, we can blame Merc for that!)
Toyota has released two versions of their 1.8 litre I4, see http://www.sandsmuseum.com/cars/elise/thecar/engine/toyota.html for basic information, viz A 1ZZ 1794cc model with 79.0 x 91.5 bore/stroke and 146.65 rod, quoted as producing 145bhp @ 6400, 125lb/ft @ 4200 with 10.0:1 compression And the 2ZZ 1796cc version with 82.0 x 85.0 bore/stroke and 140.15 rod producing 190bhp @ 7600, 133lb/ft @ 6800 with 11.5:1 Assuming identical deck heights, at 1.60:1 and 1.65:1 respectively their rod length to stroke ratios appear pre ordained by the piston compression height, deck height, and stroke dimensions rather than desired torque characteristics The latter appears principally due to completely different cylinder head designs, compression ratios, camshaft events, manifolding, and mapping Perhaps VAG originally intended raising hp, torque, and rpm to emphasise performance, believed the rod length/stroke ratio change advantageous, then aborted the programme due to promising 5 valve results Lastly and relative to engine architecture, does any member have access to the engine reconditioning data sheets available through established National reconditioning groups, for instance the American Engine Rebuilder Association's AERA RRO-SIS database? These databases contain virtually every conceivable dimension required to identify and machine all basic components, describe updates and prudent "in house" modifications, and may include both oe casting and part numbers