It’s hard to believe but some people still call me up asking for advice on using carbs or throttle bodies. Some “old school” engine builders are still insisting that carbs are the way to go and that you don’t need the complication of fuel injection. Look, nobody sees carbs more affectionately than I do, but even through my rose tinted spectacles I can see their limitations. The more power you try to squeeze from an engine the more the carb’s limitations show up. You have a conflict of interests; small chokes to get a good signal over the main jet, big chokes to pass the air required for maximum power. If you think about this long enough you will come up with the S.U. carburettor. With a throttle body you can have a massive choke and it almost doesn’t matter. You just squirt in the amount of fuel that's required and it finds its way into the engine.
A classic example was a Seven we had in fitted with a Raceline Zetec engine. On carbs it had made 175 bhp and Raceline were expecting more power on the bodies, possibly 190 bhp. To cut a long story short the engine made 200 bhp and with good manners to match. The carbs had been too small at 40DCOE with 34 mm chokes but I hope you get the point.
First Injection experience
A friend of mine recently showed me a prized possession, something called a Wal Phillips Fuel Injector. Oh wow, no need for rose tinted glasses, here was a piece of my youth, still vivid in my memory. Wal Phillips had invented his “injector” for use on motorcycles. His workshop was less than half a mile from my house so many years I went along to investigate. To a 16 year old clueless apprentice it was a thing of wonder. “Forget all you know about carburettors” said Mr Phillips. This was easy since I knew bugger all about anything at the time.
I look at it now and I see a tap, linked to a butterfly. It could not be any cruder but at the time I thought it was awesome and I soon parted with my £7 16 s 6d for a unit to fit to my Dad’s two-stroke 250 Ariel Arrow. Within a couple of months I had melted several sets of pistons and then destroyed the crankshaft. I could not be sure if the crank failure was due to the mixture constantly being out or if it was down to the “super wonder” two stroke oil that I started using.
The super oil maker’s claim was that you could run it at half the normal mixture ratio thus leaving more room for petrol – which must then give more power. God I was thick. I believed everything that my perceived betters told me, a salesman’s dream. Just think of how much trouble I could have gotten into if the internet had existed then! Thanks Ivan, if you ever want to sell that Wal Phillips fuel injector...I have cash waiting.
Variable cam timing.
Just about every engine now has some sort of cam control on it, from cam profile switching like the Honda Vtec to actual variable pulleys or a combination of both. The Toyota 2ZZ in the Elise has a cam switch to a second profile and a cam timing wheel that can vary the timing of the cam. I ran one of these engines up when they first replaced the K Series. On paper there is no comparison, 190 bhp against 118 bhp but when you compare the curves it starts to get interesting.
Up to 6000rpm the two engines deliver almost identical torque, then the cam switches over on the Toyota and you get a big “bump” up to 190 bhp. Having installed a couple of ECUs and re-mapped the engines I was pleased to see a small gain over the stock ECU but I was following the original cam control strategy from Lotus. Then I heard (bloody internet again) that if you varied the cam timing wheel from the original positions there were big power gains to be had.
On the Lotus it just moves the wheel from one end of the range to the other. The range can go from zero to 47 degrees so keeping away from the stops we had it at 5 degrees on one end and 45 degrees at the other. To cut a long story short with some new firmware we had the camshaft timing following our target map within a couple of degrees and no matter where we put it, the original Lotus setting was best. Back off the timing at higher rpm and you can see the power drop away exactly in tune with the timing. Internet bullshit yet again and since the information came from America I should have known better.
No month would be complete here if we didn’t have a few problems. This time is was linkages that gave us the headaches. The Rover V8 had a twin plenum intake which, I am told, is pretty rare. The problem was that it had a flat spot off idle that mapping would not sort out. Been here before, look at the throttle pot numbers and see how they do not alter with initial butterfly opening. In this case the twin intakes had a carb type linkage between them with the cable pulling from one end and the pot on the other. The spring tension had to be taken up before the pot moved with initial opening of the throttle from the cable end. I just screwed the adjuster up tight and the problem went away.
The second one was more complicated even though it was a straight forward GBS kit car with a stock Zetec 170 engine on bodies. The idle was lumpy as hell and since a quick look at the mixture didn’t help it was obvious that the bodies were out of balance. No problem, the Jenvey linkage is pretty straight forward and I have some bent up Allen keys to get at what I need to. Now take a look at the pictures. Somebody (no the people with the car) had gone to great lengths to cock it up royally! The linkage had somehow been fitted to one end of the bodies (the wrong end) and a bridging piece had been fabricated and pinned between the two main shafts. The original, correct, linkage had to be dismantled to do this! The only word I can find to sum this up is: “insane”. It could not be mapped as it was and we couldn’t find the right linkages in stock. The car had to go away for sorting out and come back some days later for mapping. 173 bhp: pretty good for a brand new, tight, engine.
I have seen this car before but not with the newly built turbo Cosworth with eight injectors. Unlike most applications where you have upper and lower injectors, these ones are fitted side by side. Both injectors are the same flow rate so the idea is to use four for light throttle running and then eight when you need the fuel flow to make the power. And that’s exactly how it worked out. If you are looking for some custom made carbon panels contact NUR Motorsport on 0118 9594 866 and speak to Noel.