9a....ABF..... Which is easiest to swap into a bare mk2 bay (originally 8v digifant?) and does the rod ratio affect any of the engine's characteristics other than smoothness? any issues running either on normal 95 ron unleaded?
The rod ratio effects the torque and power delivery - the ABF makes peak figures higher in the rev scale than a 9a generally. There was a thread a while back on putting an ABF into a digi 8v mk2 - you can probably dig it up in the search
thanks guy; unfortunately for me in some respects a 9a would be easier, if there's not much difference in performance (see my KR V-belts onto ABF thread).
between the ABF and the KR heads, are there alot of diferences!? the ABF, is suposed to be better, right?! both gas-flowed, will be almost the same result?
So does the tall block have smaller pistons and a longer stroke as opposed to the short block. would the tall block produce more torque than a similar spec short block and would a short block rev more freely than a tall block??? Many thanks Adam
I'm under the impression (well...told by the late Bill Blydenstein) that the ABF head has a vastly improved exhaust side, compared to the KR. I know from playing about with mine, that my ABF just doesn't like a bigger exhaust cam than inlet cam, as is common on cammed KRs. I thought it was the Digi 3.2 management... But a swap to Megasquirt proved the same... On Megasquirt, I gained 5 BHP peak over my Blydenstein ABF head with Schrick 268 in / std ex combo, by adding the matching Schrick 268 ex cam...and lost 15-20 lb-ft of torque midrange. Back to the Std ex cam...all the midrange back and only a loss of 4-5 BHP to contend with. To me, this suggests the ABF exhaust side is pretty good...OK, mine has been breathed on by Bill B...but enhanced rather than re-engineered! I've not compared KR to ABF heads on the same block...but it seems thay DO respond differently when gas-flowed. I've no flow numbers...only my experiences to go by.
Bore and stroke are the same. The taller block is to accomodate longer rods. There's no difference between the revving or power potential of the bottom end. However, the taller block might be a little stronger, due to the reduced rod angles. The ABF head is a bit better. My view on this is that it's because the KR/9A head suffers from shrouding on the exhaust valves (28mm valve, 27mm seat) compared to the ABF which has 27mm valves and seats. Of course, you could have 28mm inserts put in the KR head and sort that out...cost a couple of hundred quid though. Incidentally the KR/9A has sodium cooled valves. The ABF doesn't.
And to add to what Mike said, the late 051 castings had thiner valve stems and almost none protruding valve guides.
Didn't know that bit... I thought all KR/9A used the same valves? If the guides don't protrude, doesn't that mean there's more meat on the casting. A certain man in a shed once told me there's a difference in the water jacket in the later heads, which changes the shape of the ports (more cooling round the ports allows the engines to run a bit leaner, but means you can remove less when porting.) I can't remember now if he was talking ABF type heads or the later KR/9A
pretty sure it's the KR/9A heads, I've certainly seen pics showing cut-aways before and the additional waterways on a 2L(9A) head, mind you ABF/ACE heads are probably different again.
Oh, and the ABF does fit under the bonnet of a mk1 running k-jet. Use a Supersprint manifold and all is well. Gurds
ive run the 6a, 9a and the abf but my personal favourate at the moment is the abf mated to a o27 head , not to fussed on the abf head though,
Just a quick point to the differences in the heads the ABF head has a raised combustion chamber in the head but the KR heads be it O51 or 027 are flat My point better squish.. more squish... more power less spent gas faster flow.. And the ABF uses doubled Colet valves The ABF head is the best for turbo charging
To add something else to this thread i fitted a 9A head to a KR block and it made more torque and felt a faster , everything else was the same. I only had to use it as my old 2.0 expired so went back to the parts i had left over . My mate now runs this setup in his Mk2 and its sweet. A unexpected find :-)
