SHARP ARTICLE FROM SPORTS
CAR, APRIL 1965
THERE HAVE been many 'sleepers' written about in the past. Here is a real possum. The Datsun, having played dead since its introduction in this country, has begun to wake up. We feel very confident that this is the year when the Datsun's strength and potential will be realized.
After a problem-solving sorting-out period the SPL-310 became a 1964 threat to every other marque in G Production. During the last half of the year the Datsun was driven to third place in North-east Division. Beside the Datsun's racing achievements it has been gaining enthusiasm among sports car fans. It is one of the better values per dollar in the sports car field.
In preparing the Datsun for competition, keep one basic theory in mind - be conservative. The stock car is very rugged and has a strong "torquey" engine. Beginning with the engine, the cylinder head should be polished and manifold alignments checked. It is unnecessary to remove much metal, just smooth everything out. Don't forget the conbustion chambers, which should have equal volumes to within 1/10th of a cc if you are really serious.
One of the few basic decisions which will have to be made is how much to mill off the head. In other words, what compression do you want to run? Several factors should be taken into consideration: first and most important, optimum performance as a function of your maintenance budget! wildness of camshaft (which depends on the types of courses you will be driving); and so forth.
The vital thing here is that depending on the amount milled off the head, the valves may hit the pistons and, in the Datsun's case, the block. Therefore, it is a must to use the modeling clay technique in the combustion chambers to determine the clearances and whether or not pistons and block will have to be notched. Also, the head may have to be re-contoured where there is interference with the domed (stock) pistons. These possibilities can be checked by mounting the head without a gasket and rotating the engine by hand (use old valves). Camshafts are available from several west coast grinders and it is best to use their specified valve springs. Standard factory .040-over pistons are advised.
The lower end of the engine is very rugged and, coupled with the shorter stroke, makes for an excellent, broad power band. Use the factory heavy-duty oil pump, large sump, and oil cooler, and check the hardness of the crank, which by factory specification should be at least 50 Rockwell C.
Balance for Insurance
Naturally, have the engine balanced and it is wise to have every stressed part magnafluxed or zygloed. These operations provide the most reasonable engine insurance you can buy. Because rev limits of the engine are somewhat determined by breathing, we have found that a cam which gives a power peak of around 5800-6000 rpm leads to a solid power band from 4000-6800.
Clearances should be a loose stock fit in the bearing department and about double stock when it comes to piston to cylinder wall clearance. There are two basic theories which are often forgotten: cleanliness during assembly (equal to an operating room); and a gradual, running break-in of at least four hours. All steel or iron parts should be scrubbed in soapy water until you are willing to eat from them, then heavily oiled before assembling. The same goes for soft alloys such as pistons and bearings; however, use care not to scratch these surfaces.
So much for the engine. Let's move on to the clutch and drive train. The flywheel should be conservatively lightened on a lathe, keeping in mind that the most valuable weight to remove is from the outer portions. The clutch should be beefed up with 200lb. springs and a competition lining used on the disc, which should be both riveted and bonded.
Drive Train, Tires and Wheels
The '65 SCCA option list allows a set of close ratio gears which definitely should be used. Another helpful addition for the serious competitor is a limited slip differential. Goodyear T-7 tires in conjunction with a mag wheel (5x13) should be an excellent combination. The standard wheels are fine for the road but the magnesium racing wheels should be considered a must for serious competition.
The car's braking performance can be improved by liberal drilling of the backing plates and installing air scoops on the front. Mintex competition linings have worked well.
The only modifications necessary in the excellent suspension department are: a set of heavy duty shocks all around; and a very beefy front sway bar. We have found no need to change the standard springs.
Two other helpful additions are an electric tachometer and a large radiator.
We have made no attempt to suggest spark plug heat ranges, ignition timing or carb needles (SU's will fit) as there is such a wide range of tuning called for depending on the type of course to be encountered.
Several general rules to keep in mind: Use the coldest plug without fouling; when in doubt start rich and gradually lean it out; don't get carried away with ignition advance; keep the entire state of tune on the conservative side and concentrate on engine flexibility rather than high revs and you will find the Datsun SPL-310 durable and competitive. With the entire race set-up the car is still flexible enough to run down to the local grocery store.
These pages, unless otherwise stated, are copyright ©1999 & 2000, Rob Beddington & The Classic Fairlady Roadster Register. Do not redistribute in any form without the prior permission of the owner.