More fuel for thought

FINE-TUN­ING FOR IN­NO­VA­TIVE NEW THROT­TLE BODY

VANTAGE - - Bulletin | News - WORDS JOHN SIMIS­TER

IN THE LAST IS­SUE OF VAN­TAGE (Win­ter 2016) we drove an As­ton Martin DB5 pre­pared by GTC En­gi­neer­ing and fit­ted with Jenvey’s in­trigu­ing new Her­itage Throt­tle Body sys­tem, de­signed to look like clas­sic We­ber DCOES but fea­tur­ing mod­ern fuel in­jec­tion and fully-mapped en­gine man­age­ment.

We were im­pressed, but this brand new sys­tem was still a work in progress and there were a cou­ple of drive­abil­ity is­sues, chiefly when com­ing off idle or the over­run. John and James Win­sor at GTC were keen for us to try the car again af­ter more devel­op­ment time, so we duly reap­peared at the com­pany’s work­shops near Sil­ver­stone for Take Two.

The DB5 is now run­ning on an Emer­ald K6 en­gine man­age­ment sys­tem, mapped by Emer­ald it­self, and the idle con­trol valve is now plumbed-in to give a smoother, more sta­ble idle and bet­ter pro­gres­sion mov­ing away from it. There has been some vis­ual tweak­ing, too, with pe­riod-look­ing trans­par­ent fuel pipes making the in­stal­la­tion look even more like the orig­i­nal car­bu­ret­tor sys­tem.

It took just sec­onds to sense the im­prove­ment. The start­ing is in­stant, the idle per­fect with a slight hiss from the con­trol valve while it stays open to feed the ex­tra air a cold en­gine re­quires. The hiss sub­sides as the en­gine warms.

There are no jerks, flat-spots or surges, just a rich, smooth flow of torque from idle speed to high revs. It feels fab­u­lous, as if ev­ery hy­dro­car­bon mol­e­cule is con­tribut­ing some­thing use­ful, and the throt­tle re­sponse is in­stant. It’s hard to imag­ine how a Marek straight-six could run more ef­fi­ciently than this. Point proved and mis­sion ac­com­plished.

Our story stated that the throt­tle bod­ies are avail­able in 38mm, 40mm, 42mm and 45mm sizes, but ac­tu­ally that’s not quite right. Scrub the small­est of those, and add 48mm, for the cor­rect range. Mean­while, GTC is fit­ting its sec­ond Jenvey Her­itage Throt­tle Body sys­tem to a DB5 GT. A what? Yes, a DB5 short­ened and light­ened in DB4 GT fash­ion some years ago. Should make quite an en­ter­tain­ing ma­chine.

IM­AGE GTC/TIM ANDREW

From the top GTC have fur­ther honed the Jenvey in­jec­tion sys­tem, which now looks even more like a clas­sic carb set-up, thanks to retro fuel pipes

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