Tech Stuff Archive

Listed below are some previous questions that Gordon Dobie has answered. If you would like to ask Gordon a question, click here .

Ralt RT4, Sandown round of the Australian Drivers Championship

Hi Stace.

To set up the cam to the standard timing marks. First get the engine on top dead centre on number one cylinder ( Rotor button pointing to number one terminal on the distributor cap ).

The camshaft end float plate on the front of the front cam tower has a small oval slot at twelve o'clock. You will find three V shaped slots around the hub on the back of the cam gear. The cam gear also has three dowel holes marked 1,2 and 3. Place the gear on the cam using the dowel hole which allows one of the slots in the gear to line up with the slot in the end float plate. The valves on number four cylinder will both be opened slightly. It is best if the inlet valve is opened .020" more than the exhaust at TDC.


Opposition's view of the 2-Litre Datsun- engined Asp

>SIR i hope this mail finds you well...ive contacted you previously in regards to my carbs,thankyou for your promt response...i now have a problem with my air/fuel ratio. Ive dynoed the car tonight and they go from 14.6 @2000rpm to 16.6 at 5000rpm which is VERY lean.i think the the carbs are stock 240z hitachi-s/u"s..when ive dynoed the car on previous occassions it had a L24E cam and std air cleaner assy......... it now has a 260z cam (248in-248ex) and 2 finer filter socks over the stock trumpets....the air/fuel ratios on previous occassions were 14.4@2000 to 12.9@5000....
>The motor is fresh and has flat top L24e pistons and a e88 efi head on a L26 bottom you think the mods are enough to strain the stock carbs?how can i get the mixture richer?will the lean mixtures be why my torque has dropped off all through the range but hp has increased?how can i find a needel/seat combination that will suit my motor?will turning the adjusting nut under the carb richen the mixture through the rev range or only at idle?any answers are greatly appreciated......................

Adjust your SU carburettor mixture at idle via the adjusting nut which raises the jet to lean the mixture. All SU needles are the same diameter at the top therefore the idle mixture with the jet wound right up is fixed. The mixture is enriched by lowering the jet (due to the tapered needle and lowering the jet in relation to the float level).

To vary the mixure at particular rev or load conditions on the dyno' hold the revs and load where the mixture reading is incorect and measure the distance between the top of the jet and the bottom of the piston (this will vary with the air speed through the carbie throat).
Having measured the piston height you can remove the needle and measure the needle diameter where it enters the jet. If the mixture is to lean find a needle which is smaller in diameter at this point. Needles are available with diameter variations every 1/8" down their length. If you can't find a needle to suit you may modify the ones you have by reducing their diameter at the point where the mixture is lean.

 1969 Datsun 240Z chassis No 149 fitted with DPC fuel injection producing 250 BHP.

>Am thinking about a Group N 1600, do I have to use the origonal 4 speed?
>If so where can I buy a close ratio gearset?  I saw your DPC set in the
>tech archive, what does that fit?
>Thanks...Rob T.
Hi Rob

The gear box question is a contraversial one. The Datsun Racing Team, of which I was Chief Mechanic at the time, ran an imported P510 SSS factory race car which had a 5 speed gear box as fitted at the factory. This car was driven by both Doug Whiteford and John Roxburgh between 1968 and 1970 as an improved production touring car. The car was identical to the ones raced in the East Africa Safari and the London Sydney Ralley. As far as I am aware CAMS have not recognised this as fact but if you read the CAMS manual and do a bit of homework you should be able to get approval for the 5 speed.

The C/R set on our website is an A series but we also supply sets to suit the L series 4 and 5 speed boxes.

Best of luck with your project


Howdy my names Brendan,
  Have just worked up a L28, and need some help acheiving more horses. The heads have been mildly ported, 50thou of the exhaust ports, 30 thou outta the cylinders, have had custom fitted extractors leading to a 2 and 1/4 inch system. The cranks been lightened and polished, cant remeber the exact spec for the cam but can remeber 72 degrees mentioned. Have converted carbies to triple 44mm mikunis (havn't got this cold air box thing that your mentioning on the net)
 The ignition is still standard, lectric fuel pump, and a 240k box, all this and I only get 194 horses at the wheels. Am also getting the pops is this a bad thing??? Got it tuned at the dynos which didnt really help although he got 4 more horses whith the jets he installed.
  Im thinking I need a limi slip diff, is there a R200 limi thatll fit the 260z.
 Am a serious fan of the z and need a good place in brisbane thatll help me with 260Z

Hi Brendan

Thanks for the email. 194 BHP at the wheels translates to around 235 at the flywheel. This is about average for the mods you mention. If the 'popping' is occuring at a light throttle setting it's most likely the result of a lean mixture. Check the 'f' hole size in the idle circuit, it may be to big.
Is your car a race car or road car? The 44mm carbs are a bit big for a road car and a bit small for a race car. Does it have a flat spot below 2500rpm? We get excellent results with 40mm dellorto's ( 235BHP no flat spots or popping 0 to 100 Km in 7 seconds and 30 mpg fuel ecomomy ).
An LSD from the Jap' import Skyline will fit the Z. Try one of your local importers.

Your distributor should be recurved. Is it Electronic? What is the compression ratio? Do you have flat top pistons?  What fuel are you using?

Best of luck


Hi Jim & Kim

My records indicate that the N47 head is off a '77-'80, 280Z. This makes it an EFI head so it should have four extra 10mm  mounting studs for the inlet manifold and semicircular slots in the top of the inlet ports in line with the injector nozzles. If not it can be modified to suit your engine. The combustion chamber size is the same as your original head.

The variation in head gasket design is along the manifold (left hand) side of the head. The edge of the gasket is not straight but follows the contour of the head stud and water holes. If the wrong gasket is used the water holes in the block or head will line up with the space fromed by the contour of the gasket, allowing water to escape between the head and the block. Brand of gasket is not important.

The P79 head is intended to be used with flat top pistons due to it's large combustion chamber volume (53.6cc).

The 30/70 cam refered to is a 72 degree Nissan Factory grind the nominal timing of which is:
inlet open, 30 degrees,  inlet closes 70 degrees  / exhaust open 70 degrees, exhaust closes 30 degrees and about .480'' lift at the valve.  This cam is ok for road or track

The next stage up would be a 74 degree grind , with the following timing:
in' open 43,  in' close 73 / ex' open 78,  ex' closes 38 and 505 lift at the valve.
You should be able to find a local shop who can provide a suitable grind.   'This one is not suitable for the road'.

The 240SX 60mm TB should be ok. the 63mm TB is off our Australian production local 4.2 litre Ford Falcon.

The Bosch injectors should be available from your local Bosch agent. You may find them by going into 'Google' and doing a search for ''Bosch fuel injectors''.

Due to the fact that we are on the other side of the world it may be easier for you to find the parts you require in the U.S. If you have any difficulty we will be happy to help.


Hi Gordon,

Just been checking out your web site and it looks like you could be the man who could answer a few question about getting some horsepower out of an L24 z engine.  I have been searching the internet for a while now and have seen a lot of modified zeds out their, but few give any details of the performance figures they have achieved with all this work.  This is where I hope you may be able to help?  I am looking for around the 200-220 bhp mark and similar torque out of zed motor, without it being a tempremantal beast to drive daily.  Possibly an idealistic dream but here are my plans so far.

L24 block with an E31 head.
40 dcoe 151 weber carbies with air box.
Mild Cam.
De-burred block and internal paint finished sump.
Electronic fuel pump.
Aluminium radiator.

Do you think this combination will give me the power outputs I'm looking for?  Or do you have any suggestions to achieve them?

Hope you can help.

Hi Simon

The mods you suggest will produce good horse power but it will be a bit short on torque. To obtain the performance you are looking for using the 240Z E31 head I would suggest boring the block and fit standard (86mm) 280ZX pistons and an L26 crank and rods. These mods convert your 240 to 280 specs with 10 to 1 comp'. You will be able to run on LRP or premium unleaded fuel ( We recomend Mobil Synergy premium unleaded ). I suggest fitting 44mm (280ZX) inlet valves. and 3 x 40mm dcoe Webers or Dellorto DHLA carburettors with 32mm chokes and a 30/70 cam grind.

The above mod's will produce around 230BHP with good drivability and fuel economy without breaking the bank.

If you wish to discuss this further give me a ring on 03 9553 5309 or 0409 02 8181

Best of luck



 DPC Close ratio gear set


I need help. I desperately need a wiring diagram for a FJ20DE out of an RS Skyline. I'm putting the motor into a Datsun 1600. I am an apprentice Auto sparky so knowledge isn't a problem, just lack of resources in New Zealand. Can you help?

Daniel Palmer


Dear Daniel

Yours is a familiar story. The FJ20 Skyline was not sold in Australia or N.Z. so info is hard to get. Send me your postal address and I will send an FJ20 wiringdiagram. I hope this is of some help.

If you are modifying the FJ20 for more power I would suggest replacing the analogue computer with a digital unit such as the Motec.


The air box draws cold air from in front of the radiator.


I am putting together a really wild L20B for my Datto bored and stroked to 2.2 litres and want a cam to give really big horsepower what can you suggest?



Dear John

We can supply a cam to suit your engine. What maximum revs do you intend using? (The long stroke engine works best if the revs are limited to around 6500 rpm).

What type and size carburettors? Or: Type of fuel injection and throttle body size. Please supply this information, as it will help us choose the best cam for the job.


EFI multi throttle body setup.

Without a cold air box this engine is breathing hot air from inside the engine bay.

Dear Shannon

Thanks for the Email. Turbo charged engines using carburettors are prone to be unreliable. Due to the large range of parameters i.e., rev range, throttle opening, ignition requirements, load conditions etc, it is not possible to properly control the boost, mixture and ignition requirements through the whole rev range under all conditions using a carburettor and conventional ignition system. This can lead to lean a mixture and to much ignition under particular circumstances resulting in a destroyed engine.

In order to get satisfactory results from a turbocharged engine it is necessary to use a good EFI management system. This can be achieved by:

A. Purchase an EFI engine such as the Z18 turbo, FJ20 turbo or SR 20 turbo. These will all fit into the 1600. (They all require an Engineers Certificate).

B. Fit a turbo and aftermarket EFI system such as the Motec to you 1600 or an L20B engine. Each of these options will cost six or seven thousand dollars. The simplest would be A.

C. Another option is to fit an L20B with big port head, flat top pistons, cam and 40mm Webers or Dellorto carb's. This combination will give 0 to 100km in around 7 seconds and excellent reliability and fuel economy for less than half the cost of a turbo engine.

I hope this answers you questions.


A cold air box
gives better power
due to higher air density.