Looked at Miata website on the different heads available for the mazda twin cams and found that some dont flow near as much as a a-series so please be careful who ever it was that was thinking of a tc head cause there are so many different varieties and some are much better than others
Sadly the mx5 sucks but the fe3 from 626 and other cars flows heaps more.
http://members.aol.com/solomiata/MX5Engine.html

Look at port differences!!!!
http://members.aol.com/solomiata2/BPHeadCompare.jpg

and the alloy 2.3 monster twin cam hybrid
http://members.aol.com/solomiata/FE3.html

I wonder if the ca18 can be taken to 2.3 with a ka24 crank?

I say ca cause the sr is much heavier and in a zoom article there was an fj24 turbo stroker from japan.

on the topic of the fj24, i think it was a factory pre made item from japan. i believe some of the old tourers used them. i think it was a purely racing thing. my old boss told me he knew a guy in new zealand who had a few and was running t35s on them or something like that, or that he got the t53s from old touring cars, ahhhhh i dont know ill shut up now.

One of our members Tsillay has a FJ 24 it comes standard in his Group B Nissan 240RS rally car..they were factory but extremely rare. There were probably less than 50 acually built from the required 200 for homologation..

The early MX5 was rated at 116HP standard, doesn't seem too bad to me, plus the plan is to use the 323 turbo and pistons.

The only prob with the KA 24 crank is the ridiculous stroke. You just cant rev 'em....The FJ24 was a factory special, just for the GpB cars.

There's some internal shots of the FJ24 at www.geocities.com/tsillay/240.html
Works out at 2370cc with a 0.5mm overbore.

Unfortunately 116 is nothing if you look that in 1972 the 2tg toyota 2 valve 1600 produced 126 hp NA and no injection. The famous "R" 1600 pushrod engine on fairlady 1600 produced 96hp on twin sus and factory u20 2ltr sohc fairlady engines 150hp from factory at 6000rpm!!! with perfect torque and power curves now thats a super beautiful engine with complete drivability!. The secret is in the 89 bore with 92mm overbore I think (most engines under 80mm specially mazda 1600) that accomodated huge inlet valves high port design and shorter stroke. They are 2 valve setups as opposed to 4!!!. So Im afraid the mazda tc head is a waste of time unless you can fit a tc design like late toyotas 3sg lexus design were the ports are higher better angle and square rounded corner inlets.
Its better to get an "R" engine or the u20 soch witht the factory 150 hp found in the 2ltr fairlady rebuild one and turbo it. I say this because you can get these engines from a growing amount of newer owners of these old cars who are making conversions to import turbo sr20s cause they dont want to rebuild them. Youll stay all nissan too with no major mods.
The thread I posted explains why the fs3 mazda engine kills even the latest bp 1.8ltr mx5 engine in head cfm flow figures and overall hp. So unless you can fit a honda or other head on an a-series its a lost cause unless you think you can get more than 250hp from the setup. The e15 bathurst turbo exa got 250 in pole sprint setup. You have alot of work to do only to attain what you can with an a-series pushrod. Plus you dont know how reliable your setup will be with the possible hot spots bringing the curtains down on your engine cause the oil gallery and water setup doesnt do its job properly as it was originally designed to do.
Theres alot of jargon about twin cams as only a few 1600 non vvt or vtec Twin Cams produce big numbers and those are not by mazda pisstons. So a 1990s mazda twin cam 116hp is a bees dick compared to 40 year old Nissan factory ohv and soch tech.
Matt, seriously add up your plusses and minusses for the conversion research cfm figures for everything I mentioned, youll see that there are better solutions from our friend nissan.

You fail to see the point of the excersize, it is not just all about horsepower, a large part of it is the enjoyment of solving the problems encountered in building it!

If it were merely about HP I'd chuck an SR20DET at it.

How many twin cam, turbo, injected A15's have you seen?

The head I am using is a BG!
Both cut-away heads in your previous post are 1.8L (BP)

I have done a lot of research on this and think a moderate amount of boost will make a considerable difference.

I have also already solved nearly all of the adaption problems such as oil, water galleries etc

If it works for you fantastic.
The reason I never thought youd go for power or an sr is because I thought you are trying to upgrade the a-series by keeping the block which will make it pollution type with no probs on catalyc convertor and the such of later engines.
In theory the things youve solved, are yet to be tested and yes I would love for you to succeed dont get me wrong. Its just that the BP is an improvement over the b 1600 and thats cause of better ports as shown in pics and higher port design. Its just a shame that since you are going through so much trouble you arent using whats even better.
Good luck with gasket hot spots, setting up a chain or cam belt, modding or making the cam gear, running 3 cams like the early 1600 ford lotus engine, getting the timing right, and all the money youll need for getting it to run the needed extras. Unless you have cash to burn or engineering buddies to help you, youll need all the luck you can get.

The BP head is physically longer to accomodate the larger bores to achieve 1800cc and therefore not able to be used.

3 cams? Not in my engine! I can see it is time I invested in digital camera!

Cash to burn, I WISH!!!, No i am doing most of the work myself.

Cheers.

Hey Matt , I am following your progress with interest. The idea of bolt on injection or turbo manifolds appeals to me. Now you said you are not using the 3rd cam..what stops the oil from the cam bearing spraying around have you fitted drilled plugs?? The KAD twin cam head for Minis is pretty close to what you are doing have you had a look at one of them? Keep us posted and plenty of pics please...If you need any machining done for it let me know I be happy to do it for nothing just to see it work, let me know...