Rallytwit, are you using a GX head? And what about carbs?

I am using a porter GX head with Keihin FCR 39mm Flatslide carbs. The Keinhin carbs flow more than the weber DCOE style carbs.

I'm bolting all the best bits I have on hand, lots of little bits like chrome moly push rods that are a whooping 50 grams lighter than stock. Under drive crank pulley that is 520 grams (stock ones are 650 I think) and the lowest out put alternator I have.

The tough part is my cam choices are less than optimal; I've put the GX cam in as my only other choice was one with .460 lift 286 duration 104 degree lobe separation. My spare GX head was milled 2mm and so the latter cam won't work with the flat top pistons. Additionally with that cam the motor revs out to 8600 rpm and that results in the rings wearing out after 8-10 weekends.

Over the summer I'll decide what to do with the shagged A15 motor. To further complicate things I just inherited an A12A short block that appears to have been rebuilt fairly recently.

what is the bore size of your engine atm RT?

are there any better rings you can use with thinner guages?
the original factory ones are very thick and take lots of boost
so the friction would not be ideal from thicker rings while
modern engines use very thin rings as an example the suzuki g13b
needs very few rebuilds compared to A series or K series corolla
pushrod engines which are also very thick ring engines.

RT....I am using a GX head as well and did the conversion from mm to thousandths..had my shop check the head and it has been shaved down 20 thousandths over the past 40 years which comes out to 0.50 mm. I have been concerned with piston to valve clearance with the stock "offset dish" A15 pistons. Don't think I need to be concerned?? My cam has been reconditioned by Isky. Specs are 260/.425. I still plan to do the clay test where you put clay on top of the piston, set a used head gasket and head on top of the block and turn the engine by hand and check the clearance. Hopefully no contact..... Unless you know of a better way to do this test.

I used a similar spec cam with the flat top pistons in my A15 without issue. It should be fine. Note the head I was using had never been milled.

The current GX head going on the A12, while professionally ported, has had 2mm milled off it. The combustion chambers are at 27cc. I've had to shim the rocker towers to get the rocker geometry right, I also did the clay test as well.

Interesting technique on "raising" the rocker assembly. By doing this the valves are not opening completely?

The height of the rocker towers has no effect on lift. Because the head was milled 2mm the push rods are now 2mm to long. Because of this you would have to back the adjuster screws out to far to get the lash correct. So the choices are shorter push rods or raise the rockers 2mm. A friend made up some shims several years back when I had a different cam fitted, he also milled one set of rocker towers down .75mm. All this was done so that the valve geometry would have a wide range of adjustability. This way it was possible to get the proper geometry as well as getting the wear pattern centered on the valve stem. Getting the two is not always possible.

Getting an a15 rebuilt currently, cant remember the specs of it off the top of my head but it will be a bloody screamer. 1608 cc when finished!!

RT surprised an American is using mm instead of inches, good to hear :)
also I missed it, what bore size are you running and valve sizes?

D as an Irish, English, Dutch, German, Polish, Afro-Cuban, with bits of Spanish and Italian thrown in American I have a bit of an International flair.

OK the truth is I was raised on Japanese motorcycles and so I started with metric.

The A15 was 76.5mm and the A12 is 73.5mm. Both the damaged head and the spare GX head use 37/30mm valves. The trashed head had SI valves; they use a necked down stem (7mm) that flows more.

I now have an A12A block; in an effort to make use of the forged 76.5mm pistons from the blown A15 I've toyed with the idea of putting an A14 crank into the A12A. It's either that or sell of the forged Pistons for someone else to use for the same set up. I could also bore out the spare A15 block and fit the pistons in that.

The obvious solution would be 78mm or 79mm pistons and 38/33mm valves but I haven't worked out how I'm going to keep the compression down so I can use the readily available 100 octane fuel (I can get it 24-7) The larger bore means 12.5 to 13-1 compression and that mean using 105 octane fuel. Getting the 105 octane fuel means making a special trip to either pick up 5 gallon jugs or storing large quantities of the stuff at the house. I try to keep my racing as hassle free as possible.

I finish assembling the A12 today so in the next week the car should be running again albeit with 10-15 less horsepower.

I think we can officially say we've highjacked Vixen's original thread.