In a previous life I used to prepare a Mk2 Escort for circuit racing. I also used to build the engines and do the flow bench work on the heads, which is why I still have a Superflow 110 flow bench. I reckon that from a 2.1 litre Pinto you can see 210 to 215 bhp but that’s your lot. The example that came in for mapping was a track day car just converted with Jenvey throttle bodies. Back in the day my fast road engines used to make 165 bhp – measured on an engine dyno so that was real world figures so those were the sort of numbers I expected to see. After fully mapping the engine it proved to be a little down on power so I suggested we look at the cam timing. With any single cam engine you are fairly limited as to what you can do with it. I set my cam timing by measuring the lift on overlap at TDC. This is now an accepted method and one you see expounded by various experts on the net but I had a hard time convincing people that it was the way to go.
With the Pinto engine I use a rule of two thirds. That is to say that I advance the cam until the exhaust lift at TDC is two thirds that of the inlet valve. For example if the inlet valve is 90 then the exhaust would be 60. A calculator is handy because the numbers never come out in handy exact figures. This then is the most advance you will ever see and I retard from there until I get the best average power. We ended up with something like 150 bhp which isn’t bad for a road engine. Probably with some big valves and more head work it would get to 170bhp but when you think that you can buy a Zetec 2.0 that makes 170 bhp as stock for less than the cost of tuning the Pinto that’s really the way to go - unless you are into Historic events.
I have been doing Chris Palmer’s XJS racer for a few years now and Chris has had a fair bit of success with it. Trouble is the opposition are now really not playing the game. This year has seen a bit of a power struggle taking place and Chris is finding it very hard to get on the podium, let along win outright. For the 2011 season Chris has asked me to help him find some more power and suggested that new cams might be the answer.
But before you can order up a new camshaft you have to have some idea of what’s needed. I asked Chris to take the head off the car and let me flow bench test it. It helps to know how much lift you can usefully have before the port bottles up. Over-lifting a cam is a crime in my book as it adds a lot of mechanical strain for no performance gains at all. In order to flow any head you have to have a bore adapter. I scrounged around my next door engineering shop and came up with a large tube in almost the right diameter. It needs to replicate the bore of the engine. On the lathe I turned out the tube to 92mm and then set about making up some wooden platforms to support the head and locate the bore. That sounds easy but it took me a full day to achieve. Next you have to make up some sort of bracketry to hold a dial gauge and a screw to hold the valve open. You have to take flow readings in stages, I use every 0.050 inches because that’s how I started when I first bought the bench in 1987.
Having established where peak flow was we can now look at the camshaft. To be honest this is not the most powerful engine in the world. 300 bhp from 4.0 litres equates to 75 bhp/litre - which is pretty poor for a four-valve head. I spoke to Roger Bywater at AJ6 Engineering. Roger was on the design team for this engine when he worked at Jaguar. He said that the engine was never meant to rev and that the 3.6 actually gives better specific power in terms of bhp/litre. It seems we are destined to struggle with this one but I have a few ideas up my sleeve and I will let you know how it goes in due course.
Regular readers will know that I am not a big fan of turbo engines, even though I concede that they make big power. The big power in itself can cause problems and I don’t just mean the heat and thermal loadings. Fuel requirement is vast and you need a fuel pump and fuel lines that can keep up with engine demand.
This particular Nissan made very good power but there was a problem we could not pin-point. Inside the car we had a terrible smell of fuel as well as a pressure drop-off. We had a good hunt around but couldn’t find the source. After a while you start to convince yourself that there isn’t a problem, that it’s just one of those things; poor air circulation in the test cell or a badly sited breather. Off the car went and the owner later reported that he could not find any leak on the car but the smell of fuel is still there. The clue is probably in the fuel consumption: 5 mpg around town and 11 mpg on the motorway! I have been mapping a while now and nothing I have done has ever been left that rich – it has to be a leak. The problem appears to be finding it.
About four years ago we started to install a second-hand Superflow 901 engine dyno here in the workshop. A cell got built which was big enough to take a complete car, sound insulation went in and an extraction system was plumbed in. It was all looking tickety-boo until we tried to run the dyno. Basically it read 888 and not much else. The man from Superflow said we were suffering from “the crazy eights” and that the computer board needed to go back to the U.S.A.
It came back a month later and hey-presto! It worked for about 30 seconds and then…888 again. There were other problems like the load control unit not working and the load cell had been superseded, it just went on and on. Basically we gave up.
Now we have recently taken delivery of the latest Superflow 902, all digital kit and touch screens but we still can’t run it because the extraction is basically flawed. We need to extract air from the room, not blow it out from one corner as per our current arrangement. We are now organising the building around the new extraction system and have two fans coming that will pass 460 cubic metres per minute, or 11 Olympic swimming pools of volume per hour. That gives us 10 changes of air per minute; we don’t want the engine breathing in its own fumes. It is taking forever because we have to fit all this in between working for a living but it’s nearly, nearly there. If we ever get it all working it’s going to generate some interesting editorials here in PPC – a lifetime dream come true, I just hope I live long enough to get some use out of it!