IMO the cast hole above the centre main present on many A series blocks is not the problem Vizard makes out.
Racers here in Oz routinely use A series blocks for group Nb racing because apart from the 1275S it's all we got sold here.
Some of these motors are giving well over 160HP at the crank now in race trim.

A+ blocks have a reputation for porosity behind the liners commonly fitted, and their water jacket cores misaligned to the bores.
If building a big motor, race builders here reckon an A series block bores out better than an A+ does.

There are so, so many factors to keep a high HP mini engine alive but from my experience it's the rev's not the ultimate HP that kills them.  High rev's, 3 mains, crappy dampeners, overhung weight... =  death. And it doesn't make a rats ass A or A+.  If the engines where being designed today all the analysis would be done by the computer and you could get a number.  I am not aware of anyone reverse engineering to get these numbers and trusting this or that person because of a small or one time sample probably would not pass my desk.

Case in point.  Our #88 used a THIN FLANGE block from the early 70's to about 5 years ago.  Sometimes we would go 10 or 11 race weekends on a build.  And the thin flanges are considered poison by mini engine builders and racers.  Why did it last for a gazilion years?  Hell, I don't know and we have been doing this for, well, alot of years...

My opinion of why nearly all competitive racers now use the A+ and the rod change is that parts are more available and perhaps cheaper.  I also believe that the guys making the new hot parts are now geared to the A+ with a rod change and have been steering away from the A and remote as the market is shrinking. 

Kerm

I know that A blocks and A boxes can hold together on race coarses with 150 hp. I used four different machine shops to build my K motor. It is alot of work.

This is all good informaton. For clarification, the Hp number is arbitratry and included for reference. I am not afraid of the cost, as I have had a few quotes done up from SC and am comfortable with the prices, but I am debating on building the engine in house instead of paying SC. This may change. The spec'd engines were running EFI with theTyphoon setup.

The question I have is in the strength of the casting of the two generations of engine housings. As far as i ahve gathered, the AA transmission is sronger than the A, but the blocks are of equal strength, the former being made of a better grade of material and the later being more ridgid from cast ribbing. The question lies in if the A is strong enough and only requires the correct selection of gears for high level of power or are we going to see some catastrophic failure of the housing. Same with the block.

What is the power limit of each, respectivly? Do the A engines tend to fail at high horsepower or are they fairly equal under <200p?

Image Gallery

Chase down Mad Matt Read in Queensland.  He has built a BMW bike headed A Series and can tell you how it went.

Matt is also a very lucky man...he had a heart attack while surfing at Byron Bay...that day another surfer was out there...and someone was on the overlooking cliff and could make a phone call...Matt died 3 times that day...and lived!

Matt will give you the goods.

PHOTOS: in/about Matt Read's shop in Brisbane November 2011

My 1380 16v K head motor started its life as a MG midget motor. The gearbox is also a A box and is remote. I run carbs and something like 130hp. It is a huge job,and I would not want to go for more power as I fine it hard to drive with traffic that is going so slowly.

The spec you're proposing with a rinky-dink lil ol' turbo would probably see you pushing 300+ nanas...

N/A and you'll be under half that I reckon.

Forget about it!   $25,000 later, still THREE main bearings!!!!   Still absurdly long stroke!  Still a gearbox initially designed for 20HP!  Still a big BOOM!  Or indifferent silence....

IMHO, a car like mine making nearly 100 HP at the wheels is barely streetable,  at the edge of reliability.  I'm not comfortable taking it very far from the car trailer!   Furthermore, IMHO, about 80 HP is about all you can expect if you want a shred of reliability (we're not talking about Honda, but those have a whole lotta different problems!).  Now be careful... we all define reliability a little differently!  If you want to spend cubic money on the absolute best components... and I mean billet cranks, Carrillo Rods, 4 bolt mains... it might last a bit longer, but not that much!  Those mega dollar race engines only run for half an hour at a time.

I have not bought one in awhile and would not be surprised if they like everything else have gone up. Steve (CTR)

A competitive Appendix-K motor will set you back £25,000 !
$25,000 seems like a bargain...

As far as blocks go the AA has a slightly different front plate for timing cover and the dizzy drive is different. You may want to check the center mian web for a hole above the main bearing. Some have the casting hole while others don't and this is thought to be a weak point. Considering the money you will be spending I'd buy an A+ block. As for trannys most AAs have a remote tranny. The later rod change trannys DAM5626 have a larger main shaft spud and larger idler gear bearings. If you could find a turbo clutch housing they have larger first motion support bearing. You may want to consider SC/CR gears and S/C drops and a cross pin diff. The kind of numbers you are talking about break things. While robust the crank rods and pistons will be put to the test as well. Racers spend in the area of $25,000. for power units complete with trannys making 150 HP. They are only driven on weekends and they break from time to time. Steve (CTR) 

I think 170 NA nanas on pump gas is a tad optimistic, even with the K-head.
I'm not saying it can't be done, just that it will be horrifically expensive to make an A-series turn in excess of 10,000rpm regularly.

The A block has a higher grade of cast iron than the A+, but the A+ is allegedly stiffer due to the ribs.

Majourlittle there's a regular here, Craig Dewey who is I think 3 years into his.  It is gorgeous and purrs like a new toyota.  But my understanding is it's been a lot of work and the HP gain wasn't quite what he expected.  And he's a Lockheed engineer.

"..With the remembered displacement, increased compression ratio and now having the more correct fuel/air map in the ECU, I think it might get somewhere between 80 and 100 HP at the wheels. Specialists makes over 120 with a 1380cc engine; mine is 1310cc."

Craig if you're here please correct me if I'm wrong.

I am getting ready to dig into the engine on my car and I am debating if I should find a replacement A+ 1275 and start fresh or just build from the engine I have wich is an austin america A bored to 1310 (apparently)

The question I have is that I plan on doing a BMW head swap and am shooting for a lofty goal of 170hp NA. Would I gain anything from spending the money to find an A+ engine or would the A engine I already ahve be capable of handling the assoicated power. What are the power constraints of the two blocks? What about thier respective transmissions?

Input would be appreciated.