Ok guys, I have an a15 I picked up, with no cam shaft, I've been considering buying a tomei cam for it as I build it, but obviously that's expensive.
My q is this, I have 2 A12s sitting in the garage, could I regrind and fit one of these and use it in my a15? Is it possible or costly to have it ground similar in spec to a tomei, I've been considering?
I've red the tech section and I'm aware fitting the right can is possible, but it does confuse me a tad.
Normally I'd ask my mech mate for advice, but he's currently incommunicado for some reason

If the A12s are 1974 or newer, yes. Earlier A12 cams cannot be used in newer engines.

So how do you tell which a12 is which

if distributer if towards front of engine its an early a12
if distributer if towards back of engine its a late a12

lol.. cool. I have both..lol

so they question still lies, about grinding the cam shaft. Whats the cost, and because the camshaft was originally ground to suit a A12, will it suit the uses of an A15

A12 can suits an A15 as-is will pull hard to 5000 rpm.

Sweet ty

one bit of advice I'd give _any_ first time cam swapper, is to deliberately go a bit conservative on the cam specs. Without a doubt as many as half the engine builds out there, even by guys with some experience, run a cam with too much duration and overlap and end up losing out on the mid range _big time_ and although the 'cam' will work at higher rpm, the rest of the combination, including the gearbox ratios that pull the rpms down lower than they realise and down and out of the powerband, just isn't suited to quite as much rpm and so instead of getting half the gains of the bigger cam, you get all of the low-mid rpm losses, and then because the rest of the combo is milder, you lose 'all' of the higher rpm potential of the big cam too.

Generally the wilder you go with a cam, aside from the rpm range going higher (if the rest of the engine spec will support it!) it also leads to a NARROWER powerband. This is the enemy of any street driven car, and frankly it's the enemy of a LOT of competition cars. Rallying is a good example of that. hillclimb to a lesser extent.

It's tough to know precisely what you are aiming at, but I'd make a strong case for the idea of not going for anything that needs to see the high side of 6000rpm for a streeter, and most of us here could make a good case for a lower limit too. Don't get me wrong, the engine itself will actually handle these sort of rpms if it's rebuilt properly, with new rod bolts (and nothing much more exotic beyond that) and all that, but it's not (at this stage) about whether or not you will break it but rather what the overall package will do for the car.

Another thing generally is that the wilder the cam, and the higher the rpm range, even 'with' a closer ratio gearbox, you'll still need to go with lower diff gears (higher numerical ratio) to get the thing to really perform. If the car isn't a true streeter and you aren't doing big trips on the highway that may just barely be liveable, but you tend to get sick (even if the motor will handle it) of a big 4cyl running pretty high rpms at cruise.

What you might consider doing in conjunction with this is locate a 5 speed gearbox, and running _slightly_ lower diff gears. For example if you are running 3.9s now, you could consider 4.11s and with a 5 speed the freeway rpm is still lower overall than 3.9s and a 4 speed, you could even go to 4.3s and the same would still (just) be true. That can help things potentially. Then again, the a15 has a fair bit more torque than an a12, so relatively you don't have to go quite as deep with the diff gearing anyway.

I don't know nearly enough about your engine to make any sort of an educated guess, but based on it being a streeter, possibly unported oval port head, and nfi what carburetion or exhaust, it'd generally be hard to suggest looking beyond around 250-255 degrees advertised duration.

It's also pretty important to know the cam specs before you machine the head surface at all. The thing is, there are compression ratios that are too high for any given pump fuel, and some that are ok. but it also depends on other factors. Being an alloy head, it'll tolerate more than a cast iron head safely, all else being equal. Being moderate bore size, also tends to help. If you could hypothetically run a head with a closed chamber, and a piston with a dish that matched the chamber 'bathtub' shape, that would tolerate more static comp ratio than an open chamber head and a flat top piston. And lastly, and of relevance to this thread, when the intake valve closes, also affects how much compression it'll safely tolerate. In general the 'bigger' the cam, the later the intake valve closure, and the more compression it can safely run. BUT it also 'needs' more compression to work well with a big cam, and you can get to a point where you just can't run enough compression safely to 'make' the cam work harmoniously. So with a basic plan of the overal combo worked out, you close in on the cam specs, and based on that, you can see how much you may be able to skim the head to bump up the compression ratio. It may actually be the case that you can't raise the comp much at all, due to a smaller cam, and (potentially) higher compression coming about fromt eh fact the head has been previously skimmed (as most used ones have by this point in time!) and or the deck of the block has been skimmed too. Even boring the engine oversize increases the comp ratio, because the engine capacity is larger but you're squeezing that larger volume into the same chamber space at TDC.

I know this sounds like a truck load of info to absorb, but I assure you, picking a suitable cam and balancing the comp ratio to suit it (and re-curving the distributor to run the sort of advance curve such an engine will 'like') and you end up with a rock solid combination of parts that work very well together. Get one or more of these factors 'out of step' with the rest of the combination, and it can be a frustrating result.

The GX grind is a good compromise and conservative enough to work well for the street in an A15, will have more bottom end than an a12gx due to capacity increase in engine but will rev very well up top unlike most A15 stock grinds. Then you can do as mentioned above but higher compression is a must along with a lightened flywheel will allow the gx grind to come on song sooner and punchier. Some quad 38mm bike carbs on a custom manifold and some well designed headers will be like night and day in response, sound and performance. If you want more after that then you are in for big $$$ as its easy for the first 20-30hp but beyond that is an art and science few are able to succeed.

I'm going to have to (within a very narrow range of use) disagree with going to a mega light flywheel.

Here's the why. Being lighter there is less mass to accelerate (in neutral with the engine free revving) so a lighter flywheel WILL improve throttle response in neutral. Once the car is in gear and the clutch is out, you have the weight of the gears in the gearbox, the tailshaft and the diff gears to spin/accelerate (and to overcome the resistance of the car (at several hundred kg) to accelerating. Meaning that in practice, the change in flywheel mass is only _very_ small in terms of the overall picture of what there is to accelerate.

If we look at it back to front, in first gear (obviously the lowest gearing, highest numerical ratio) it increases the torque applied to teh wheels, the diff ratio also increases it. You could almost compare it the other way round, if torque is being multiplied by the gearbox and diff gearing, then the 'resistance' to the car being accelerated away is 'reduced'. so if the first gear is 3.2:1 and the diff gears are 4.11:1 then the torque multiplication overall is just over 13:1 and so the engine will perform (in contrast to how well it would in 4th gear) as if the car is only 1/13th of its actual weight. Since the mass of the car (as far as the engine knows) is reduced to 1/13th, then dropping a kg or two off the flywheel _will_ actually increase the acceleration (albeit mildly) in first gear. It'll do it less so in 2nd gear, and by the time you get to 3rd or 4th gear, the difference in flywheel weight is practically negligible and has no impact on acceleration. So basically 'at best' it'll improve acceleration in first gear a little bit, and less and less as you move through the gears.

But having a really light flywheel has drawbacks. That slightly heavier flywheel has more inertia, and so it actually helps to smooth out the idle quality (since the force from the pistons on the crank is one at a time, 4 'shunts' evey 2 full rotations, meaning with no flywheel weight the idle rpm can effectively go up a fraction with each combustion stroke, then die off a fraction until the next cylider fires and so on. The heavier flywheel will help to keep momentum up and smooth out each pulse. This can have a good effect on idle smoothness (including just how low you can get it to idle without stalling). In practice, esp for street driving, that light flywheel will also allow the engine to rev up quickly, and this can make for more 'attention' every time you take off from a set of traffic lights, as it'll rev higher. You could 'feather' the throttle and only let it lift the revs a tiny amount before lifting off the clutch, but with less flywheel weight, it's easier for the engine to bog down, and be a 'pig' to get off from the standing start at said traffic lights, so it's sometimes a case of either having to feather the clutch across some % of the intersection, or having to lift the rpms higher and take off like that.

It ends up being a pain (potentially) for a streeter. Some tractors and other equipment often have particularly heavy flywheels, so that the motors can run at lower rpm, and if caught in terrain where the engine will bog down (potentially) this heavier flywheel and its inertia helps prevent it stalling even at quite low rpms.

Don't get me wrong, if you are racing, esp with diff gearing that produces a very low overall gear ratio with the gearbox in 1st, it's certainly the way to go (and don't forget that within reason, you don't have to constantly get the car off the start line, you do that once, and so even if it was less than optimal at lower rpm, in competition the engine never or rarely sees those rpms/conditions. So certainly good for those applications.

To further clarify, certainly I think that going to an a12 flywheel is worthwhile, I'd be reluctant to take that a12 flywheel and drastically lighten it if it's a streeter. The a12 flywheel is heavy enough to avoid the negatives (for a streeter) but light enough to improve throttle response. Lightening (if done at all) has to be done 'right' and done right, the result is actually a safer flywheel at higher rpm, but done wrong (and that can be a result of it not being properly centred, or the tool and angle/direction of the tool to machine it away) and it is actually far more likely to come apart at higher rpm.

The bike carbs are a doable option for sure, but just be sure to take on board that custom making an intake manifold is straightforward enough BUT it's after that that the real work begins. It'll take a while to optimise the carb a/f curve for all driving conditions (and the flow/rpm rates for an a-series are dramatically different to any big motorbike engnie). You could do it on a dyno, which is good for finding peak output, but be well aware it can take a _long_ time to get the fuelling good for full power at high throttle openings, amd for part throttle cruising/idle etc. You can do that on a dyno, but the amount of time involved, you'd want to be good friends with the dyno operator, or that process will cost a fortune. Another option (and one I'd recommend) is getting one of the wideband ego sensor/reader/logger kits. There's a few brands and I haven't heard anything bad about the wbO2 and innovate (spelling) one. Using one of these you can find a quiet enough factory area or whatever and set it up, logging the a/f mixture and slowly cruising around through all throttle positions (obviously if it starts going lean at higher rpms stop before it can do any harm, and alter the settings (possibly jet, possibly air corrector, or in teh case of motorbike carbs jet/needle profile/needle height setting) and continue. Driving around and logging like that will allow you to get right in on the ideal settings, and whilst the wideband kits aren't dirt cheap, in the long run they wil actually end up saving you money, since you don't need anywhere near as much time on a dyno, within reason you won't spend as much time/cost of parts, because you have a more accurate picture of the a/f curve with any particular setting and know which to change and by how much, and then ongoing savings because you are also able to tune the part throttle fuelling for reasonable economy.