Thanks for all the information. I will pass this on to the machine shop to check the springs. He will also be repairing the end play on the crankshaft as well as checking the bearings. The H7240 head is still in the car at a salvage yard and the only way to make any port measurements is if I buy the engine, which I will pass up on. Talking with other MG owners, the only real desirable heads for the A series engine appears to be the H89 or GX. Will post follow up questions as they come up.

Any idea what the car will weigh with the A15?

Well checked some MG websites and the car is around 1600lb, the 1275cc engine is around 260lb and the transmission around 45lbs. Cant say for certain on the engine weight. It is all iron however, including the cylinder head. I would expect the A15 is heavier than the British 1275 motor. Also will be using a 60 series 5 speed transmission. It seems comparable to the MG transmission. Other MG owners that did the datsun engine conversion used heavier front coil springs and some did install larger front disk brake calipers. Also someone suggested to lighten the flywheel since the datsun B310 car is heavier than the Midget. I was going to ask this question at a later time to ddgonzal but maybe you can offer some suggestions on doing this. Does the flywheel have to be balanced with the crankshaft if it is lightened? Would a machine shop simply shave off some metal on one side of the flywheel? I haven't done this before. Thanks for any information.

60-series 5-speed is 70 pounds.

But the A15 is light at 205 pounds. It has a lightweight block casting plus aluminum head, so much lighter than the 1950's tech Austin.

So the datsun conversion may turn out to be a little lighter than the stock british engine/transmission?? Not sure why other MG owners installed heavier coil springs in the front. I can see the reason for better braking capability with the larger engine displacement and more HP. Will have to look into this a little more. Any thoughts on lightening the flywheel?

Datsun engines are internally balanced; the flywheel is not needed to balance it (unlike say a chevy). So you can lighten they flywheel as normal. See Flywheel.

Well these A series engines continue to amaze me. According to my application, the Flywheel link says that lightening is for racing applications. Would I benefit from doing this for street use? It does say that the flywheels are interchangeable. For my purpose, would you recommend putting the A12 flywheel on the A15 engine? It is 2.2 lbs lighter. I do recall the clutch and pressure plate are different diameters. So I would use the A15 clutch and pressure plate on the A12 flywheel?

Datsun has made it easy for clutches -- they are all the same diameter. The A15 pressure plate has a heavy duty spring so it is stiffer than the A12 pressure plate, although if you buy an aftermarket clutch they are all heavy-duty "generics". Genuine Nissan clutches are fine-tuned to the application.

Yes, a light flywheel can be a pain in stop-and-go traffic, but many like them even so. The flywheel, engine plate, transmission and release bearing sleeve are a matched set -- so if you change the flywheel type (A12 vs A15) you must compensate by changing the sleeve length or by removing/adding an engine plate. When fitting the thinner flywheel to A14, remove the Engine Plate to compensate. If there was no engine plate to begin with, fit the shorter release bearing sleeve.

the mini engine is an anchor of heavy cast iron while A15 with alloy head should be lighter even though box wont be.

At worst you can still run a mazda, ga16de or vauxhall head on an A series and see some big numbers.

A couple of things I will throw in:

First on the flywheel, you'll find a diagram here on the site for turning/lightening a flywheel which will take it down to 14lbs (7lbs lighter than stock) note that this is double the weight of a racing flywheel. As mentioned with a light car it will be totally streetable.

I have a 14lb for both an A15 & A12. I use the A12 flywheel because all of the throw out bearings and other parts I have are for an A12. Note I use this in the 1200 coupe I Vintage race and the car will chug along in the pits with no worries. Note I'd part with the A15 flywheel cheap.

On the GX cylinder head; the valve springs won't float till around 8200 rpms, I used GX springs (that I never bothered to check) for 10 seasons and only changed them because I went to a very aggressive cam. You should have no issues. Next on the ports check where the valve seats meet the port as the seats protrude 1mm into the port. If you do nothing else grind/sand/file this down so the seat matches up to the port as this will open the port up to 2mm. I used a dremel and flap wheel to clean this area up on my heads.

Also note you can order up thinner head gaskets than the standard Felpro ones. B-Projects in Japan sells .6 and .8 thick head gaskets at very reasonable prices. This will bring back the compression to near 10-1

You can order flat top pistons from JE or Arias they are $500 a set but as they are forged not preferred in a street car.

On the camshaft, the GX cam is very mild, Delta Cams in Tacoma can regrind the stock cam for something like $75 and they have done quite a few for A-series motors. I think something with around 260 duration and .375 lift will still be very mild.

Note a 60 series 4 speed is 54lbs and although the overdrive would be nice an A15 will rev to 6000 rpms all day long. The A15 in my car revs to 8500 rpms on the stock bottom end with no issues.

With all that said if you simply just reringed the motor and put iłt together with the parts you have you would easily reach the 85hp goal. If you cleaned up the head and upgraded the cam it would likely be around 95hp at the flywheel.

Tom