B310GX
Thanks for the tip. If i can find the book, i will buy it as i am a strong aviation buff. Beukeleow's book barn is not far away, so i will check it out.

By the way, if you have any leads on stuff for a Boomerang fighter, we would be glad to hear of it as a friend is attempting a full resto on A46-158, a CA13 fighter. Much of the airframe is now complete.
Chris

1200RC

Good question, & if i come up with an answer, i will let everyone know, but there must be a way of "sizing" carbs. I wonder if some of the carb manufacturers have websites with the means to answer these questions?

My GX is strictly street & it is currently about .140" oversize [76.5mm] but it's now worn out again, so i will hit it at 77mm.
I keep the revs down a bit so that it will live long enough for me to be able to drive it home & i'm too old to be a highway hero anymore. My cam is of an unremembered grind, but it was described as a "light sports profile" & my engine idles quite ok at about 900rpm. It pulls smoothly from down low & this is also a benefit of the variable venturi carb design [SU's]
I also got more than 50mpg one day when i drove for economy when i went to Holbrook for the Ultralight Fly In weekend.

I also managed an AVERAGE speed of just over 70mph while turning 42mpg [screw metrics] late one night between Albury & Bendigo. I figured that i had to be happy with that.
If i were to go seriously racing i would do some things diferently, but i can't afford it, so i tailor everything for maximum street pleasure & that doesn't impress the wankers. Not my problem.
Chris

I know i'm a nit picky bastard, but according to Bill Gunston in his book "Aero Engines" [second edition 1986 & '89, page 142]

"In 1945, special Merlins were giving up to 2,780hp at 36lb of boost, running on fuel with monomethane aniline added"

At wars end, Mustangs were running Merlins with much closer to 2,200hp It's all academic really, but no production Merlin produced 3,000hp.....ever.

Yeah yeah, i know, pickey pickey pickey.
Chris

FM1200, you get my YAY for the day. A voice of sanity in the great carb debate.
You are ABSOLUTELY right.

The only thing that i would care to add is that when one calculates the max air consumption, one must remember that this is a theoretical maximum based on a volumetric efficiency at max revs, of 100% which few engines of our type can approach. I think that The Chrysler hemi's come reasonably close, but the're legendary, & i'm biased, so we won't count them.

To get the true volume of air, the formula must be adjusted by figuring in the percentage of volumetric efficiency.
For stockers this figure can be about 80% with souped up examples on the street running at something like 85% & the real hotties looking at about 90% AT FULL SPEED.
Lets see, a 1200 is 71.5 cubic inches. Now my formuls is diferent, but gives the same result. It is CFM = RPM x CID/3456 divided by VE

So our example is a 1200 at 6000rpm Thats 6000 x 71.5 = 429000, divided by 3456 =124cfm. Now divide this by,... lets say 85% [VE] for a street engine like my GX, & we get about 105cfm. That's a realistic carb size, or maximum airflow for THIS EXAMPLE.
Now we can round this number up or down a little to fit in with a carb[s] capacity that we can buy & feel confidant that we are not short changing ourselves & not reducing performance due to overcarbureting. I could cope with an increase of 5% to 10% on this number, but it will not really yield any noticeable improvements.

Lets be realistic blokes, how many RPM does YOUR street engine see for 95% of it's running life. Mine is red lined at 5,500rpm, i run stock GX carbs, & i still have the same engine 23 years later.

FM1200,.. you the man.
Chris

Nicholas
You just gotta do something with that avatar of yours. It's hypnotic, & since i live alone, so it has other effects. Ohmygawd she's cute.

As for the head gasket, see if you can get a used A12 one as a sample. Place it over the A14 head & line up all the holes. See if the combustion chamber overlaps the gasket. If it does, then use the A14 one, if the combustion chamber is completely within the gasket opening, then use the A12 one.

I have never done this before, so i can not say from experience which one to use.
Perhaps someone else can help here.
Chris

These bolts seem to shear as a by-product of harmonic vibration & flywheel bolts that are not as tight as they should be in this application. [Or just plain loose bolts] Our "A" series engines do not have a harmonic ballancer & i will be investigating the possibility of adapting something for mine.

One of our local blokes has sheared of the bolts a number of times in his B110 Coupe racer & the fitting of a severely modified Falcon [i think] ballancer seems to have overcome the problem.
He was able to re-use the crank too, so get the busted bolts out & have a good look. Your crank might just be OK, & thats gotta be good in the $$$ department.
Chris

The mechanical pump is a true GX one & these run at a slightly higher pressure than a stock 1200 one. The carbs would see the pressure of whichever pump put out the higher pressure as the mechanical one has two simple one way valves & if the electric one was higher [which i seriously doubt] the fuel would simply flow straight in & out of these two valves.

The electric pump was fitted so as to push some liquid fuel into the mechanical one in the event that it got hot enough to form a vapour pocket inside the pump, & this is what stops the pump from pumping. When this happens, the carbs run out of fuel, but the electric pump just pushes the fuel straight through.
I was in luck that day as just enough liquid fuel got in & it pumped again, & with the high fuel usage at full throttle, the pump became "fuel cooled"

Simply put, i raised enough energy to fit the electric one, but was too damn lazy to remove the mechanical one. I did not have a blanking off plate & could not be bothered to make one. It worked fine.
Chris

You do not mention which model of A12 engine that you have. If it is a 1200 engine then the following will apply, but if it is the one with the altenator on the distributor side, then it is a straight bolt on.

I fitted a 120Y GX head to a 1200 & the same problems apply.
Simply study both heads very carefully & figure out how the two designs differ in the supply of oil to the rockers, then copy the 1200 one. From memory, it needed two small passages to be drilled. The size can be determined by simply placing a drill bit into the 1200 head to check that you have the right size

There is no need to weld anything if you have access to a comprehensive tap set. Just tap the newly drilled transverse hole with a 1/8" gas thread, or it's metric equivalent, & fit a suitable plug. Thats what i did back in about '86 & it's still on the road.

Even without porting, if you want to keep it low buck, the A14 head will yeild better flow figures as the ports & valves are bigger than the A12. Just compare the combustion chamber sizes & measure them if necessary, as any increase in volume means a reduction in compression ratio & there are a couple of diferent A14 heads.
Chris

Hey Bullit
I LIKE THAT. The tyre size calculator should solve a lot of problems both quickly & easily.
Thanks for that & it's now in my favorites list
Chris

When i ran an electric pump. i left the mechanical one in place. The fuel passed through both of them. I added the electric one when i had a small vapour lock problem one hot summers day in my 1000 sedan [with 1200GX] There was 4 of us in the sedan, towing a boat, which was loaded with all our camping gear & the outboard motor, as i was about to pull out to pass this slacker in a Commodore while coming up a steepish pinch on the Clyde mountain. The engine died for a second or so, then got with the programme. Those 5 speed option 1 boxes are magic.
The electric pump helped out with this problem & it never happened again.
Chris