Hi all, I've been through the site here quite a lot but not seen a thread on all the things people do to uprate the A12GX.

I've done custom high energy ignition and a big bore exhaust and real SU's on the standard GX manifold. Oh.. I've also replaced cooling fan with electric one.

Is anyone willing to chip in here and give their thoughts / advice on what to do to the motor and in what order? It would be great to show predicted or measured BHP increases for each mod anyone's done.

Is anyone proud enough to state their results and how much they've spent?

i was under the impression that the hitachi carbs(SU copies) were better than the english SU's

I am a British car owner myself, and I run the same things you do on my A series (except I use Dellortos)and I mean no offence here, but your question regarding what to do to a 1200 motor and in what order, and what HP to expect, theres not a simple answer.

There are at least 10,000 posts on this site directly relating to this topic, its really the basis of what the whole site is about.

Personally I would chuck the SUs away and replace them with some 40mm Webers, and a more agressive cam, that should do the trick.

Indeed - there's more to be had by getting rid of the SU's - but the flexibilty and ease of tuning appeals to me at present.

Now - a warmer cam. Yes - has anyone got a favourite grind for fast road use i.e. still street-able.??

From my experience with brit cars I'd say that seeing as the head's pretty good and there's double valve springs we should be in good shape to do some higher RPM stuff with a bumpier cam.

Do people go for roller rockers or is that just overkill on such a small motor?

My motor has no doubt been rebuilt before I got it but I doubt it was fully balanced. I'm still in the process of getting my car ready for street and have not yet had it on the road.

Are there any harmonic points in the rev range that need to be avoided? I plan to strip and rebuild the motor and uprate after I've got it going suitably in this body.

I know there's been debate about the GX manifold v's a good pair of extractors and that some say they're pretty closely matched. In my british car experience the header design has had to be fairly well matched to the cam profile so the most was made of torque or outright power.

I know there's no simple answer - I guess I was just hoping to spark some preferences and experience discussions.

Thanks.

There are a couple of members here using roller rockers , they are expensive and would be more "wish list" stuff than top of the list "must do" stuff.

I'll try and ask the question in a different way.

Usually, in my limited experience thus far, with any motor from the 60's/70's there was always a bottleneck or two that is always first on the list to fix in this modern age.

i.e. on my 6cy triumph every exhaust header was rubbish, and because of the limited number of crank bearings a full rotating assembly balance is rewarding...

So with the A12GX what is fundamentally a weak point with it? If there is one....

Weak point? A series Datsun engines? Surely a contradiction in terms.

These are an amazingly robust design & can take a lot of hard use without complaint. If your base is a GX engine, then you already have a good head & any problems will depend on the intended use, & the level of outright abuse.
The GX manifold/header is still factory recomended for use in rally engines with dual Hitachi [SU type] carbs, but a tube header was recomended for all out racing, so I presume that the GX manifold/header flows pretty good up to about 6.000 to 7.000 rpm.

Several people have reported flywheels coming loose after a missed shift at racing speeds where RPM rose to frightening levels, so if you think that there is a chance that your engine will see anything like a five digit number on the tach, then doweling the flywheel to the crank is a good idea.
There is also a school of thought that says that a custom made harmonic balancer will help a great deal in this area as well, & one Datsun racer near here seems to be having quite some success with one on his engine, but again, this is prety much justified as a race-only item
Balancing is always a good thing in any hot engine.

Roller rockers are nice, & I have them for my street engine, but I am just stroking my ego with these as they are simply not justified either operationally or in price for road use. I justified their purchase to myself on some flimsy engineering pretext, &, well, because I could.
If your engine will see sustained RPM up near the red line, then these will be a good thing.

Other than that, I don't think that there are any real weak points in the design itself & the usual mantra of carefull component selection, & carefull assembly will see a strong & reliable engine in your chassis.

More [Datsun] power to you.

Thanks Dodgeman,

The spitfire has a condensed cardboard transmission tunnel so I guess a shield for the drivers ankles would be a good idea.

Without wanting to get off topic, I've had to use a remote oil filter due to clearance problems. I've also got a modified sump (reduced in capacity slightly right near the front. So in the interest of sticking with A12 Performance as the topic...... Has anyone enlarged their sump, baffled their sump, or used a remote oil filter?

Are there any oil feed issues to any parts? The hole for getting oil up into the rocker gear on the GX worried me a bit!

PiGDOG - I went for genuine SU's as they're commonly available - have loads of parts available and plenty of needle profiles. On that matter -- I'm still to identify anyone that can tell me a suitable SU needle profile for 1 1/2" SU's on an A12GX.

A cardboard transmission tunnel? Some of us have a less than ideal view of British cars, & this little fact isn't going to improve that view very much.

There seem to be no real issues with the oil supply to the rockers, unless you use the later [1974 & on] cylinder head on the earlier [front distributor] block. Even then, a small mod is all that is required.

While many of us regard the Hitachi carbs as being better made than the SU's, the simple fact is that there is a very limited supply of replacement needles for tuning purposes, while the supply of different needles for the SU's seems almost limitless. The SU carb is simply much more tuneable.

Remote filter mounting is not all that uncommon in race cars & baffled sumps would be regarded as standard for those who are serious about performance on the track. Enlarged sumps similarly, would be regarded as standard by those who race to win.

There are some factory recomended mods to the crank that involve enlarging the crank drillings, but I don't believe that there are many who do this & I also believe that as long as there is oil in the sump, you will be very hard pressed to kill an A series bottom end.

i have a remote filter and oil cooler. I have a check valve right at the oil pump output to the filter so there isn't any drain back into the sump, all the oil goes into the engine until the pressure bleeds off. That seemed to be the easiest way to prevent excessively dry starts. When i used to have the oil pressure gauge on the high pressure side of the check valve it had oil pressure for a while after I turned the engine off. I wish I had a high volume ( not high pressure ) oil pump, since all that tubing and coolers is much more than the original system had to feed, but it may stay primed better than the oem filter system.

as far as enlarging the sump, why not use one of those accusump systems that holds up to 3 liters of oil in a pressure cylinder to keep the oil pressure constant. also pressurizes the oil system before starting. It's about $500, but a nismo sump is more and doesn't do anything for dry starts.