Tun­ing: the new-school

Evo India - - MAKING POWER -

Iain Litch­field has been ex­tract­ing com­edy amounts of horse­power from en­gines for 20 years – most fa­mously those of Nis­san GT-Rs.

‘It’s about air­flow,’ he says. ‘With tur­bocharged cars, it’s quite sim­ple in the­ory: you fit a big­ger tur­bocharger that will flow more air. Un­for­tu­nately, it’s not quite as sim­ple as that, par­tic­u­larly if you’re af­ter big in­creases in horse­power. The big­ger the turbo the more lag you’re go­ing to get, not just be­cause of the mass of the tur­bine and com­pres­sor but be­cause of aero­dy­namic drag on the big­ger blades. To help solve the prob­lem you can go up in en­gine dis­place­ment, which is what we do on the re­ally pow­er­ful GT-Rs. It’s why McLaren has made the 720S’s en­gine larger.

‘Even­tu­ally you need larger in­jec­tors that can flow more fuel, big­ger fuel lines and high­er­ca­pac­ity fuel pumps. Then there are in­ter­cool­ers that have to be made larger to cool the ex­tra air. Man­u­fac­tur­ers are turn­ing to charge-cool­ers be­cause they re­move heat so quickly. The snag is that that heat goes into the cool­ing sys­tem, which on a cir­cuit with hard use is a prob­lem.’

Tun­ing mod­ern, nat­u­rally as­pi­rated en­gines presents other prob­lems. Mainly be­cause they’re just so good out of the fac­tory.

‘The power gains tend to be very small,’ says Litch­field. ‘We can fit a new ex­haust sys­tem to a Nis­san 370Z and remap the ig­ni­tion, fu­elling and even valve tim­ing, but still only get a gain of 15bhp. The next step is to fit new in­take sys­tems and camshafts and up the com­pres­sion, but even then the gains aren’t huge.’

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