NZ Performance Car - - Contents -

If you thought we were at the peak of devel­op­ment with the Mazda Ro­tary en­gine, es­pe­cially in nat­u­rally as­pi­rated form, you’d be dead wrong. The rise in pop­u­lar­ity of bil­let al­loy means that we are en­ter­ing an ex­cit­ing phase of devel­op­ment, one that Mazda it­self never had the op­por­tu­nity to take ad­van­tage of, un­crack­ing a whole new level of per­for­mance and re­li­a­bil­ity in high-power ap­pli­ca­tions.

Long-time ro­tary rally driver and en­gine builder by trade Wade Hen­shaw, of Hen­shaw Race En­gines in Christchurch, has de­voted the past three years to de­vel­op­ing his own after his ex­pe­ri­ences us­ing bil­let in pis­ton en­gines drove him to pur­chase some off-the-shelf plates to try in his 13B pe­riph­eral-port (PP). How­ever, the qual­ity was not what he’d ex­pected, and, after a lengthy process of wreck­ing parts, mod­i­fy­ing the parts, and then wreck­ing more parts, he de­cided to cut his losses and de­sign and pro­duce his own bil­let parts from scratch.

With rally his fo­cus, Wade has en­gi­neered his plates to be OEM re­place­ment with in­te­grated en­gine mount bosses for all RX-7 models, along with sig­nif­i­cant im­prove­ments in the block sta­bil­ity, strength, wear, fric­tion, cool­ing, and also the abil­ity to im­prove oil scav­eng­ing from the ro­tors. The devel­op­ment started with his ex­ist­ing 13B PP on the en­gine dyno. “I did a lot of dyno test­ing and I lost count after about 25 strip-downs with the pur­chased plates. I put 15 EGT (Ex­haust Gas Tem­per­a­ture) sen­sors and some pres­sure sen­sors on the mo­tor and then sat it at 9,000rpm to see where the temps would climb,” he ex­plains.

From there, new bil­let plates were de­signed in CAD to be con­sid­er­ably lighter than the OEM iron type, fea­tur­ing 20–30 per cent more cool­ing ca­pac­ity with pri­or­ity cool­ing pas­sages to feed the spark plugs in the hous­ings. They also fea­ture new re­place­able, hard­ened duc­tile iron-wear sur­face lin­ers, which have 20 per cent more sur­face area on the back­side of the wear sur­faces to fur­ther aid heat trans­fer. Although Wade also has Nikasil seal-coated al­loy inserts ready for test­ing.

The 13B runs CLR Mo­tor­sport pe­riph­eral ported hous­ings; although, with a stack of orig­i­nal Mazda Fac­tory Rac­ing (MFR) hous­ings sit­ting there, his next plan is to de­sign a process to re­fur­bish us­ing Nikasil seals, just as Mazda used from its fac­tory.

A replica MFR dry-sump cover has also de­vel­oped in bil­let, and he has gone one step bet­ter by in­stalling a float­ing bear­ing in the front cover to sup­port the crank­shaft pul­ley at big RPMs. The in­ter­nals in­clude a Su­per Fin­ished RX8 crank, MFR ro­tor bear­ings. MFR sta­tion­ary gears, Lanetti ce­ramic apex seals, and Series 5 RX-7 9.7:1 com­pres­sion ro­tors that have been con­sid­er­ably light­ened. On the scales, the 13B weights only 68kg, and so far Wade has ex­tracted 378hp on his en­gine dyno, but ex­pects to push this up­wards of 390hp with in­jec­tion fit­ted. “The big­gest gain is not the HP num­ber, it’s the torque im­prove­ment from a block that stays square un­der ex­treme loads”. Cur­rently, fu­el­ing is old school due to clas­sic rally rules, in the form of a heav­ily mod­i­fied 51mm IDA carb sit­ting on an MFR man­i­fold; how­ever, a full Group B car is planned, so Borla ta­pered ITBs and MoTec ECU are on the shelf wait­ing. The ig­ni­tion is taken care of by an Elec­tro­mo­tive XDi CDI unit that runs off a trig­ger wheel sit­ting be­tween coun­ter­weight and fly­wheel, as was run on the orig­i­nal MFR en­gines.

The idea is to even­tu­ally sell the com­po­nents, but not be­fore ex­ten­sive dyno and rally stage time has proven their worth. Then, fur­ther test­ing will also be car­ried out in the US by Car­los Lopez, some­one who Wade cred­its as be­ing a mas­sive help. The new en­gine will be back on the dyno by the time you read this for the next round of long­du­ra­tion big RPM tests!

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