One day, the engine in your 911, Boxster or Cay­man might need a re­build. It’s a costly busi­ness, ad­mits Chris Hor­ton, but for per­haps an ad­di­tional £1500–£2000 you could also in­crease the cylin­der ca­pac­ity for a worth­while in­crease in power and cru­cially

911 Porsche World - - Contents - Pho­to­graphs by Antony Fraser

Power from torque, or power from revs? Hartech reckon that torque talks and we’ve tested its lat­est 3.7-litre and 3.9litre ‘over­sized’ engine con­ver­sions

There is, as we car en­thu­si­asts like to say, no sub­sti­tute for cu­bic inches. It’s a com­monly quoted au­to­mo­tive ‘proverb’, one of those hoary old apho­risms that we use with­out con­sid­er­ing their real mean­ing, but like most of its kind it is based upon eas­ily ob­serv­able fact.

Amer­i­can ‘mus­cle cars’ have for many years re­lied on the sheer size of their usu­ally V8 en­gines to gen­er­ate the power and specif­i­cally the torque needed to de­liver the per­for­mance for which they be­came fa­mous – al­beit usu­ally in a straight line only. And here in Europe, where smaller four-cylin­der mo­tors are the norm, both af­ter-market and DIY tuners long ago re­alised that of­ten the most ef­fec­tive way of sig­nif­i­cantly in­creas­ing a given unit’s out­put, its abil­ity to pro­pel the car sat­is­fy­ingly quickly and eas­ily from ‘A’ to ‘B’, is to in­crease its ca­pac­ity, or in more sci­en­tific terms the swept vol­ume of its cylin­ders.

This ca­pac­ity in­crease, all things be­ing equal, al­lows the engine to burn more fuel in the larger quan­tity of air which – if the in­duc­tion and ex­haust (and ig­ni­tion) sys­tems are up to the job – it can draw in to and then ex­pel from its larger com­bus­tion cham­bers. That pushes the pis­tons with greater force, which in turn turns the crankshaft with more of that same en­ergy. It’s much the same prin­ci­ple as throw­ing a stack of hefty logs on a sput­ter­ing camp­fire to cre­ate a bon­fire, and thus gen­er­ate more heat.

Porsche, too, has long been an en­thu­si­as­tic pro­po­nent of ‘over­siz­ing’ its en­gines for more power and torque; for up­scal­ing, per­haps, to use a mod­ern term. In stan­dard pro­duc­tion form the nat­u­rally as­pi­rated air-cooled 911 ex­panded from its orig­i­nal mod­est 2.0 litres to 2.2, 2.4, 2.7 and 3.0 litres, and then fi­nally to 3.2 and 3.6 litres. The wa­ter-cooled M96/M97 grew from 2.5 to 2.7, 3.2, 3.4 and 3.6 litres, and fi­nally to 3.8. (The sub­se­quent ‘shrink­age’ of the cur­rent gen 2 9A1 to 3.0 litres is an­other mat­ter, prompted by the need to re­duce over­all ex­haust emis­sions, but is ar­guably more than off­set by tur­bocharg­ing.)

Over­siz­ing is not nec­es­sar­ily a sim­ple process, though. At the very least it re­quires the engine to be stripped, and then the cylin­der block to be ma­chined to the size ne­ces­si­tated by the cho­sen larger-di­am­e­ter pis­tons. At­ten­tion must also be paid to smaller but no less im­por­tant de­tails such as the re­sult­ing com­pres­sion ra­tio (which will nat­u­rally in­crease), pis­ton-to-bore tol­er­ances, valve sizes, cylin­der-head gas­ket(s) and, for op­ti­mum re­sults, camshaft pro­files and tim­ing, ig­ni­tion set­tings, and not least the in­take and ex­haust sys­tems. And ob­vi­ously you need to make sure that the rest of the engine’s struc­ture is strong enough, too.

Ar­guably by far the sim­plest engine to mod­ify in this man­ner is the air-cooled 911, with in­di­vid­ual and eas­ily re­place­able cylin­der bar­rels sus­pended from the ex­ter­nal faces of a ver­ti­cally split crank­case by through-bolts, once you have re­moved the camshafts and the in­di­vid­ual cylin­der heads. (Like­wise the VW Beetle engine and its Porsche vari­ants, of course.) That’s the way Porsche gen­er­ally did it, and the rea­son why, even to­day, a good set of crankcases from even a 1965 2.0-litre can with the ap­pro­pri­ate bar­rels and pis­tons be­come the ba­sis of a no less than 4.0-litre mo­tor. There can’t be many other de­signs with that kind of ver­sa­til­ity.

It is, un­sur­pris­ingly, a dif­fer­ent story for the wa­ter-cooled flat-sixes, de­signed for the eas­i­est and cheap­est pos­si­ble ini­tial assem­bly pro­cesses, and in ef­fect as sealed-for-life units prob­a­bly in­tended, like most masspro­duced mod­ern en­gines, to be dis­carded when they wear out or go wrong. Few, if any, en­thu­si­asts, then, would in this case rou­tinely em­bark upon a tun­ing pro­gramme based first and fore­most on ca­pac­ity. A remap and an af­ter-market ex­haust sys­tem will de­liver a

cost-ef­fec­tive im­prove­ment quite suf­fi­cient for most, and ul­ti­mately it is cheaper and eas­ier to fit a larger sec­ond-hand unit – or per­haps just to buy an­other car.

But the times they are a-chang­ing. His­tory has shown many of the wa­ter-cooled en­gines to be dis­ap­point­ingly frag­ile (al­though some do man­age to notch up im­pres­sive mileages; we know of sev­eral 2.5s that have hap­pily ex­ceeded 200,000), and a sig­nif­i­cant subindus­try has sprung up to cater to the needs of en­thu­si­asts who, un­der­stand­ably, don’t wish to con­sign to the scrap-heap a high­value and cer­tainly highly de­sir­able sports car that they jus­ti­fi­ably cher­ish.

Pre-em­i­nent among those spe­cial­ists here in the UK is Barry Hart, since 1985 the tire­less en­gi­neer­ing ta­lent be­hind Bolton, Lan­cashire­based Hartech, and in terms of the molec­u­lar­level met­al­lurgy and ther­mo­dy­nam­ics of Porsche’s wa­ter-cooled flat-sixes prob­a­bly the most knowl­edge­able – and cer­tainly the most boldly and painstak­ingly in­no­va­tive – man out­side the fac­tory it­self. His long ca­reer in the au­to­mo­tive in­dus­try be­gan way back in the late 1960s, and in­cludes both the de­sign­ing and man­u­fac­tur­ing from scratch of a num­ber of race-win­ning mo­tor­cy­cle en­gines and gear­boxes. A be­gin­ner he is not.

Barry’s first re­work­ing of the then con­tem­po­rary M96 was as long ago as 2002, when it was be­com­ing painfully ap­par­ent that the stan­dard of­fer­ing wasn’t quite as ro­bust as we had all hoped, and since then he has gone on to de­velop so­lu­tions cov­er­ing just about ev­ery as­pect of the units. One of his ear­lier up­grades was to fit a pur­posedesigned brac­ing col­lar be­tween the top of each cylin­der and the sur­round­ing coolant jacket, to pre­vent the for­mer dis­tort­ing and crack­ing, and it was surely no co­in­ci­dence that Porsche it­self later adopted this so-called closed-deck con­struc­tion.

Thus far Hartech has in one way or an­other re­claimed at least 2000 of these power units for own­ers right around the world (there is at least one Hartech engine in Iran), and even now, with the po­ten­tially af­fected mod­els rapidly age­ing, and be­ing re­placed by more mod­ern and al­most cer­tainly more re­li­able ver­sions, there is no sign of the steady flow through the com­pany’s busy ma­chine shop di­min­ish­ing. Like any gen­uine en­thu­si­ast, how­ever, Barry couldn’t help think­ing that for all its flaws – en­tirely fix­able, thanks to those re­pair tech­niques and mod­i­fi­ca­tions – this was a de­sign that had still more to give.

With time on his hands, then, now that the day-to-day run­ning of the busi­ness is ably han­dled by his step­son, Grant Pritchard, and with a team of long-serv­ing tech­ni­cians and ma­chin­ists be­hind him, Barry has spent the last three years de­vis­ing a pro­gramme of ca­pac­ity in­creases ap­pli­ca­ble to pretty much the en­tire range of M96 and M97 en­gines (but not the MA1/9A1 from the gen 2 997 and the gen 1 991). All are de­signed around the holy grail of the eas­ily ac­ces­si­ble and en­joy­able per­for­mance that comes not just from their head­line-grab­bing power out­put, but pri­mar­ily from the in­creased torque avail­able. (See pages 84–87 for an ex­pla­na­tion of the cru­cial dif­fer­ences be­tween power and torque.)

Not for a mo­ment is Barry sug­gest­ing that any­one in their right mind will spend the best part of £10,000 on an engine re­build purely for the sake of a ca­pac­ity in­crease some­where be­tween 200cc and 500cc, and in­creases in power and torque of around 15 per cent at the very most. His pro­gramme is based on the per­fectly rea­son­able as­sump­tion that any engine re­ceiv­ing such an up­grade re­quires re­con­di­tion­ing any­way, ei­ther be­cause of a fail­ure, or be­cause its owner wishes to avoid one. In which case, for the sake of per­haps just £1500–£2000 plus VAT out of that £10K bill, why would you not go the ex­tra mile? Or in this case, per­haps, the ex­tra cu­bic cen­time­tre?

Cen­tral to each over­size con­ver­sion is a set of six Nikasil cylin­der in­serts and match­ing pis­tons, de­signed by Barry him­self and man­u­fac­tured un­der li­cence by Capricorn in Hamp­shire, and in prin­ci­ple no dif­fer­ent to

those used in all of the com­pany’s engine recla­ma­tion jobs. Thor­oughly tried and tested, in other words – and things of un­de­ni­able beauty if you should be lucky enough to hold them in your own hands. Sig­nif­i­cantly, all have a nom­i­nal work­ing di­am­e­ter of 100.0mm, fin­ished ca­pac­i­ties (see chart be­low right) de­ter­mined by the stroke of the crankshaft.

The orig­i­nal Porsche cylin­ders are ma­chined out and the new ones pressed in, and cru­cially with a sup­port­ing ring not just at the top of each bore, but now also at the bot­tom. These are them­selves drilled (see photo above), partly for light­ness, but pri­mar­ily in or­der to fa­cil­i­tate oil drainage back into the sump. There is an ad­di­tional sup­port­ing in­ter­fer­ence fit be­tween the block and roughly the mid-sec­tion of each cylin­der; and the up­per area of the tube, in­side the coolant jacket, is ribbed to give ad­di­tional sur­face area and thus more ef­fi­cient heat trans­fer.

Cool­ing is fur­ther as­sisted by the open­ing up of the coolant path­ways be­tween the top of each block and the cylin­der head – an­other proven Hartech mod­i­fi­ca­tion to aid cylin­der­bore longevity. That said, Nikasil cylin­ders are in­her­ently re­sis­tant to scor­ing, be­cause the cylin­der sur­face does not con­sist of hard sil­i­con par­ti­cles trapped in an alu­minium ma­trix that grad­u­ally comes loose and scratches at the pis­ton sur­face, but in­stead a ho­mo­ge­neous elec­tro­plated sur­face that re­mains per­ma­nently fully bonded, like a com­plete thin tube within the alu­minium.

It would for sim­i­lar rea­sons be the brave owner of an ear­lier engine who turned down the op­tion of an in­ter­me­di­ate shaft mod­i­fied to take the later larger-di­am­e­ter IMS bear­ing. This can be in­stalled in ei­ther the ear­li­est sprocket- or the slightly later gear-type shaft – and that first shaft is it­self ‘up­date­able’ to the sub­se­quent gear-style item if re­quired, al­though nat­u­rally that re­quires the match­ing chain, and var­i­ous other parts. Fa­mously, that fi­nal it­er­a­tion of the IMS bear­ing can­not later be re­placed with­out split­ting the crankcases again, but such ap­pears to be its dra­mat­i­cally im­proved re­li­a­bil­ity and longevity that this should hardly be an is­sue.

It would be un­der­stand­able if at this point you are imag­in­ing all sorts of ex­cit­ing pos­si­bil­i­ties – turn­ing your Boxster 2.5 into a 3.9, for in­stance; and re­mark­ably ev­ery sin­gle one of these Porsche en­gines has the same over­all ex­ter­nal mea­sure­ments – but not sur­pris­ingly there is a prac­ti­cal limit to what is pos­si­ble, and Barry has no less sen­si­bly set out just five op­tions. (And, based upon the sim­ple but of­ten over­looked fact that to­day the 2.5 and 2.7 rarely, if ever fail, nei­ther of those units is con­sid­ered to be a vi­able ba­sis for con­ver­sion.)

In or­der of orig­i­nal size, then, the range com­mences with the 3.2-litre Boxster ‘S’, which with those 100.0mm pis­tons in place of the orig­i­nal 93.0mm items gives a nom­i­nal 3.7 litres. The 3.4-litre 996 (96.0mm bore, again raised to 100.0mm) be­comes a 3.7, and with the ad­di­tional fit­ment of the ap­pro­pri­ate longer-stroke crankshaft the 3.4-litre Cay­man ‘S’ can be stretched to 3.9. The 3.6-litre engine (96.0mm) is an­other good can­di­date for the 3.9-litre up­grade, not least be­cause it al­ready has the same free­breath­ing cylin­der heads as the 3.8, and like­wise the 3.8 it­self can eas­ily be given those ex­tra 100ccs, al­though ob­vi­ously by this stage any ben­e­fits are be­gin­ning to be out­weighed by the costs.

Pre­cise in­creases in both power and torque de­pend on a num­ber of fac­tors, but gen­er­ally, as we’ve said, amount to some 15 per cent, and with a no less use­ful low­er­ing of the revs at which they are achieved. Both the 3.6 to 3.9 and the 3.4 to 3.7 will run with the orig­i­nal engine man­age­ment sys­tem, we un­der­stand, al­though per­haps un­sur­pris­ingly the 3.4 to 3.9 will ben­e­fit from a remap – as, of course, will those smaller ver­sions. There should also be an im­prove­ment in the engine’s over­all ef­fi­ciency and thus its fuel con­sump­tion, al­though since you would have to be as ab­stemious as a Fran­cis­can friar not to use the ad­di­tional per­for­mance at ev­ery avail­able op­por­tu­nity, that is un­likely to fig­ure in any cal­cu­la­tions. It is cer­tainly not some­thing that Barry Hart is cham­pi­oning.

For him – and, as you will see else­where in this story, for us, too – it is all about the torque, and the re­sult­ing im­prove­ments in not just the cars’ 0–62mph times, but also in realworld, mid-range ac­cel­er­a­tion. The abil­ity not just to main­tain a re­laxed mo­tor­way cruis­ing speed, but also to over­take swiftly and safely when needed. Sounds ideal to us. PW

In­creases in both power and torque de­pend on a num­ber of fac­tors

One of Hartech’s most sig­nif­i­cant up­grades to M96 and M97 en­gines is to fit a sup­port­ing col­lar be­tween the top of each cylin­der ‘bar­rel’ and the in­side of the sur­round­ing coolant jacket, to pre­vent dis­tor­tion of the bore and even crack­ing. Porsche it­self even­tu­ally adopted this so-called closed­deck con­struc­tion. Note, too, the sub­tly cut-back ar­eas where coolant passes be­tween the block and the head

From left to right: Hartech di­rec­tor and ser­vice man­ager To­bias Hig­gins; com­pany founder Barry Hart; and Grant Pritchard – Barry’s step­son, and now MD. Barry be­gan his ca­reer de­sign­ing and man­u­fac­tur­ing race-win­ning mo­tor­cy­cle en­gines and gear­boxes, in­clud­ing one for the late Barry Sheene, al­though sadly he never com­peted with it. Barry (Hart) also de­signed the in­no­va­tive square­four mo­tor for the Phoenix 4 bike that featured in the 1980 Bri­tish movie Sil­ver Dream Racer, star­ring David Es­sex

Belt and braces: it’s not just the mid­dle and the top of each cylin­der that is firmly braced against the crank­case. Lat­est Hartech in­no­va­tion is to add these drilled rings at the base of each tube – holes are partly for light­ness, but pri­mar­ily to aid oil drainage. Pis­tons and cylin­ders (top) de­signed by Barry, and man­u­fac­tured un­der li­cence here in the UK by Capricorn. Both first- and sec­ond-gen­er­a­tion in­ter­me­di­ate shafts, with small-di­am­e­ter bear­ing, can be mod­i­fied for the larger-di­am­e­ter third-gen­er­a­tion job (above, left of pic), and which has proved it­self vir­tu­ally un­break­able. Chart be­low gives a good over­view of var­i­ous ca­pac­ity op­tions

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