Stock American Austin claimed they had 12 hp. My coupe is a pretty good runner but it is lacking a little in the performance area. If you look at the difference between Austin and early Bantam there are only a few changes made in the engine to increase it from 12 to 18-20hp. The changes they made were in the cam, compression ratio, carburetor venture and main jet size. On the later Bantam 65 they increased the bore from 2.20" to 2.260" and a little longer stroke (3.125"), and also increased the intake valve size from 1.020" to 1.125".
On this engine I changed the following:
I changed the cam profile and lift from .243" lift (including lash) to .259" lift (including lash) and the duration from 220-240 to 263-263. Integral Cams did a great job on reworking what little there is on an Austin cam.
I went from the radius-faced lifter to a flat-face lifter (a modified Model A lifter see picture below). This does a few things: I can use new lifters instead of old worn resurfaced ones, the flat-face lifter opens and closes faster because of geometry, and it's a little easier on the cam because there is rotation of the lifter instead of a constant bearing on the cam at the same place. You can see in the picture below the new lifter bushings I made and the new lifter configuration.
I increased the intake valve size from 1.00" to 1.125" and machined for valve guides for the use of seals (Honda). I also had custom stainless steel valves made from Ferrea Racing. I ported and polished the intake and exhaust ports and increased the compression ratio to 6.3:1.
The motor was balanced to within .2 grams. J & M Machine did most of the major machine work, boring, babbitting, balancing, etc.
I also machined and installed modern seals wherever I could in the engine, transmission and differential, etc.
Change out the rod bolts to ARP rod bolts. If you don't do anything please change the rod bolts!!!! I have said this to a lot of people "I wouldn't run stock Austin or Bantam rod bolts in my lawn mower". You can find the ARP rod bolts on the internet: APR stock number 208-6001 Click here for more on rod bolts
I have tested the engine and it runs extremely well. It sounds healthy, doesn't leak or smoke and revs up pretty good. I bought a water brake for a dyno to test the engine to see what the final hp increase is so that will be another page in my projects. The last pictures on this page shows the engine on its stand. The distributor is not finished and there are a few other details yet to be done.
More picture added 07/05/06
A couple of bigger photos
As of this date I now have 525 miles on the engine. It runs really good (I mean really good), a notable increase in horse power, torque and RPM's It is a very smooth running engine with a very slight lope at an idle. I have had the car up to 58 MPH, that's about 4,200 rpm with no problems. It loves to cruise between 40 - 45 mph, 40 mph is 2,500 rpm and 45 is 3,000 rpm. I have done some driving through hills and steep sections, the increase in performance is really noticeable, it just keeps on going without slowing down like the stock engine. I believe the cam (for the Austin) and porting allows this engine to breath a little thus giving it the capability to increase the rpm's. By having the engine balanced and using the ARP rod bolts (and a few other things) the increase in rpm's is not a real concern. If you plan on running a stock Austin or Bantam at these rpm's without changing the rod bolts or balancing your going to launch something inside.