Get­ting more out of an en­gine

Motor Equipment News - - PERFORMANCE FEATURE -

Per­for­mance tun­ing, ac­cord­ing to Wikipedia, is gen­er­ally re­stricted to cars re­quired for mo­tor­sport, although the web­site also points out that many of these ve­hi­cles never hit the track, or are even driven “in anger” – and you’ll see lots of cars just like this if you visit the CRC Speed­show in July.

We’re con­stantly amazed when we go to the Speed­show to see how much love, at­ten­tion, and money goes into these “show ponies”, and es­pe­cially the high de­gree of en­gi­neer­ing ex­per­tise.

The choice of mod­i­fi­ca­tion de­pends greatly on the de­gree of per­for­mance en­hance­ment de­sired, bud­get, and the char­ac­ter­is­tics of the en­gine to be mod­i­fied.

In­take, ex­haust, and chip up­grades are usu­ally among the first mod­i­fi­ca­tions made as they are the cheap­est, and make rea­son­ably gen­eral im­prove­ments, whereas a dif­fer­ent camshaft, for in­stance, re­quires trad­ing off smooth­ness at low en­gine speeds for im­prove­ments at high en­gine speeds.

In the mo­tor­sport con­text power out­put, torque, and re­spon­sive­ness of the en­gine are of pre­mium im­por­tance, to­gether with re­li­a­bil­ity and fuel ef­fi­ciency, but for the “show ponies” re­spon­sive­ness, re­li­a­bil­ity and fuel econ­omy are of­ten not rel­e­vant as the en­gines will rarely be taken to their max­i­mum for the ex­tended pe­ri­ods re­quired in racing, ral­ly­ing or other forms of mo­tor­sport.

One thing that’s some­times for­got­ten when a client wants more power from an en­gine is that pro­duc­ing more power usu­ally puts ad­di­tional stress on other parts of the car, such as the trans­mis­sion, drive­shaft and any other load-trans­mit­ting pow­er­train com­po­nents, and these will most likely need to be mod­i­fied to with­stand the load from the in­creased power.

Many well-tried and tested tech­niques have been de­vised to achieve more power, but all es­sen­tially op­er­ate to in­crease the rate (and to a lesser ex­tent ef­fi­ciency) of com­bus­tion in a given en­gine.

This is achieved by putting more air/ fuel mix­ture into the en­gine, in­creas­ing com­pres­sion ra­tio (re­quires higher oc­tane petrol) burn­ing it more rapidly, and get­ting rid of the waste prod­ucts more rapidly. Since get­ting more power – and us­ing it – will mean more fuel is used, this also has to be fac­tored into the equa­tion as ex­tra fuel may need to be car­ried, which will in­crease the weight of the ve­hi­cle and thus re­duce its power to weight ra­tio.

In other words, the per­for­mance tun­ing of an en­gine should take place in the con­text of the de­vel­op­ment of the over­all ve­hi­cle.

Now let’s have a closer look at ways to in­crease power. These in­clude in­creas­ing the en­gine dis­place­ment by one or both of two meth­ods: “bor­ing” – in­creas­ing the di­am­e­ter of the cylin­ders and pis­tons, or by “stroking” – us­ing a crank­shaft with a greater throw.

On older en­gines, us­ing larger or mul­ti­ple car­bu­ret­tors cre­ates a more con­trol­lable air/fuel mix­ture to burn, and to get it into the en­gine more smoothly. In mod­ern en­gines, fuel in­jec­tion is more of­ten used, and may be mod­i­fied in a sim­i­lar man­ner.

In­creas­ing the size of the pop­pet valves in the en­gine, and thus de­creas­ing the re­stric­tion in the path of the fuel-air mix­ture en­ter­ing, and the ex­haust gases leav­ing the cylin­der, also pro­duces good re­sults, while us­ing mul­ti­ple valves per cylin­der re­sults in the same effect, although it is of­ten more dif­fi­cult to fit sev­eral small valves than to have larger sin­gle valves due to the valve gear re­quired.

Us­ing larger bored, smoother, less con­torted in­let man­i­fold and ex­haust man­i­folds helps main­tain the ve­loc­ity of gases. Sim­i­larly, the ports in the cylin­der head can be en­larged and smoothed to match.

This is termed cylin­der head port­ing,

A mas­sive su­per­charger on a 5.2-litre Ford Shelby 350GT V8.

Newspapers in English

Newspapers from New Zealand

© PressReader. All rights reserved.