Datsun 240 Z

Datsun 240 ZMore development...6 cyl on TB's


Steve Kiddell is no stranger here at the rolling road; his Datsun 240 Z is a stunning piece of kit, over-bored engine, 45mm throttle bodies, head and cam work – it’s got the lot. It also has a new inlet manifold from John Mangoletsi – a name that will be familiar to more mature readers.  John has come out of retirement into semi-retirement and is producing new/old manifolds for cars like the E Type Jaguar and the Datsuns.  You can check out his web site for the latest offerings:

Idle problems

Damaged idle stopRequired a little make it useable again


It is not exactly unusual to get engine problems here at Emerald and sometimes you can follow the trail like a detective novel. This MGTF had a slow idle problem which I could not fix by opening the idle air control valve (IACV). A quick look at the throttle body told the story. The head of the adjusting screw had been sheared off flush with the body. This is a screwdriver slot job and normally has an anti-tamper cover over it.
The screw had been tightened right up and when the engine still would not idle; the last gasp turn of the driver had sheared it off.  The “mechanic” had then pulled off a breather pipe to allow enough air bleed for the engine to idle, but now too quickly. His/her answer was then to bend the throttle stop back until it no longer made contact with the screw. The engine now idled – sort of.
I had to remove the body from the car, drill out and re-tap the thread and fit a new idle screw, then bend back the tab to make proper contact.  I set the tick-over to 950 rpm with the IACV valve at 50 per cent of its opening. Now I had enough adjustment on the valve to get the cold and hot idle right just by using the valve.  Bloody amateurs!

GBS Zetec

Smokey Zetec!

I see a fair few Zetec engines in Great British Sportscars' kit cars. These engines are often used, lifted from the breaker’s yard without being stripped or checked. This example had a problem with starting which took a few minutes to sort out and in doing so we routinely checked for full throttle. It was making less than half throttle with the pedal to the floor! The owner/builder had adjusted his stops to get the pedals level but hadn’t checked the opening range. We had to bodge the pedal travel to get full throttle and I was driving with my right knee almost under my chin.
Initially it all looked gloom and doom; the exhaust was smoking really badly. I set about doing some light throttle mapping so that the car could at least be moved about under its own power. Magically, and very unusually, the smoke cleared and the engine performed faultlessly. We are seldom that lucky.

5000 RPM Fast idle

The Clio Williams had a highly modified engine that I had previously started mapping which then ran out of injector. Now it was back with larger injectors and a note from the engine builder saying that it was idling at 5000 rpm.  I have no idea why people think this is an ECU problem. Engines run on air and you cannot get air down a wire. If the idle is too fast then it has to be an air leak.
Sure enough, a quick look (and I do mean quick) revealed the problem. The new injectors had a much smaller seal than the originals and were literally floating about inside the head. I pulled them out, replaced the injector seals with the original injector seals and then mapped the engine. There is no excuse for this; any professional should have spotted that when installing the injectors and swapped the seals at the time. If it happens here I fix all these problems free of charge but if you were on a truly commercial rolling road you would be paying someone £100 an hour to do basic spanner work.

Thruxton GT 200

Classic lines

Actually this kit car looks more like an Austin Healey on steroids. This pre-production car was running a K1800 Turbo engine in box stock form and should make somewhere near 200 bhp – hence the name; GT 200. It mapped up on the money at 200 bhp and I was invited to take it for a test drive. I never drive customer’s cars on the road. It only takes someone to drive into the back of me at the traffic lights and I have all the insurance aggro to go through. In any case, I learn nothing that I haven’t already discovered on the rollers - but in this case I made an exception.
The car is very quiet in town but still attracted a lot of attention. A gaggle of schoolboys were pointing and I heard one of them say:”look it’s a seventies Thruxton GT200”. I was really impressed, not that he got the look of the car right so much as he could actually read. I thought most kids these days could only spell text-message style: Innit?
Once I got on the open road it was a pleasure to drive. I am not a big turbo fan but the response of the stock engine combined with not a lot of weight made for instant response – I loved it.

Booker Prize

Roger's Book

I have recently finished reading one of the best books on engines that I have ever come across. It will never win a Booker prize or make the best seller list because those awards are based on volume of sales. But for me it was a page turner that I could not put down.

Roger Bywater has worked in the automotive engineering business for a lifetime, specialising in engine design and development with a long spell at Jaguar working on the V12 engine. His recently published book draws mainly on personal experience, not information gleaned from the internet!

There are 11 chapters in total covering just about every aspect of engine design, from camshaft and valve operation to pressure charging, inlet systems and exhaust design, all written with a view to explaining pretty much in layman’s terms how it all works. I really learned from this book but then I have known Roger for over 20 years and I always learn something when I talk to him. Let me give you an example.

I have always wanted to know why so many motorcycles run megaphone exhausts when you never see them on cars. Roger explains that the best way to get a reverse pulse in a pipe is by having an extreme section change; like an open-ended pipe.  That’s exactly what the early racers used. Then a rule change specified a minimum exhaust length. The megaphone started to appear just after that rule change as a way of getting a shorter pipe length while meeting the overall length rule. With a tapered megaphone shape, inlet or exhaust, the engine sees it as an uncertain length and the pressure wave usually reflects before it reaches atmosphere, part way up the pipe.

Roger goes on to explain how 4-1, 4-2-1 and six and eight cylinder exhausts work by interaction.  If you are an internet expert and already “know it all” then this book is not for you. If you want to learn how it all really works then I suggest you invest £60 in this soft-back book from AJ6 Engineering. Contact Roger on 01625 573556.