Boondocker GT28RS Yamaha Apex EFI turbo system

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Isabel Horn
6 years ago
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1 Boondocker GT28RS Yamaha Apex EFI turbo system Boondocker[ ] principals and tech gurus Rocky and Dave flew from Utah to Buffalo NY Intl Airport (30 miles, no turns, three traffic lights to DTR on the same Buffalo airport Rt 33 that becomes Pearl St in Batavia next to our shop) to meet Wisconsin madman and owner of this sled Jason Stoviac (you=ve surely seen Jason=s name here with big D&D twin stuff) and equally mad D&D consultant Glenn Hall to independently dyno tune Jason=s Boondocker Apex turbo here. The most interesting aspect of this session was that it appeared that the Boondocker guys were shooting for 400 HP (surely doable on the edge) and the owner of the sled Jason wanted to go home with a good running sled, whatever HP. Jason s argument was his stock rods were inadequate, but I know that if deto is controlled stock rods are dandy. The Boondocker guys felt the same confidence level. But since Jason had the big bucks invested he had veto power over the horsepower we would top out at.. In designing their Apex kit, Boondocker opted to hang their upgrade GT28RS ball bearing Garrett turbo on the right side of the frame above the [modified] oil tank. A custom stainless steel header feeds exhaust gas to the turbo mounted on the right side of the right frame railabove the oil tank. This is a reasonable compromise considering the MCXpress and Bender rear mount turbos are further from the exhaust ports, and the Afront mount@ turbos like kits sold by Jeff Simons requires a new smaller gas tank to make room for the hot turbo hung behind the engine next to the new gas tank. Also Boondocker utilizes a larger boost-referenced bypass regulator which causes fuel pressure to increase as boost rises. A second high pressure fuel pump is plumbed inline with the Boondocker GT28RS kits. The excellent fuel pressure is documented in the accompanying dyno test data. Boondocker uses a brazed-tube intercooler in front of the engine obtained from a supplier in Australia. Jason Stoviac and Glenn Hall had originally planned to enter this Apex in last December=s DTR SnowWeek Adirondack shootout, but the 40 or so hours required to change Apex pistons put that on hold at least until next year. If you=ve followed my DTR dyno posts on NA EFI Cats using Boondocker EFI systems, you know they are my favorite dyno fuel tuning tools for EFI F6 F7 F8 F9 and F10 Firecat twins as well as MachZ modified twins. Being able to add and subtract fuel as required makes trail mod or full mod dyno tuning a snap when utilizing a fully instrumented dyno like we have here. Now Boondocker has added a Aboost@ or Amanifold pressure@ feature to their Boondocker Box (that=s what I call them) so adding positive Manifold pressure to the Apex or other turbofriendly engines can be accommodated with this new fuel controlling technology. Boosting a NA EFI engine is no easy taskbsome means of determining added airflow from supercharger or turbocharger boost must be used to determine added fuel necessary to support the extra air (O2). In the case of the Boondocker Apex boosted system, manifold pressure is measured by the ABoondocker box@ and the appropriate alterations to injector pulsewidth are

2 made. The accuracy of those adjustments are shown in the following dyno data. And instructions for adjusting the Garrett ball bearing turbo to whatever boost is desired are included in the Boondocker turbo kit.. Besides the boost measuring controller override system, the higher performance GT28RS Boondocker turbo system includes: higher flowing injectors. That=s where the box excelsbbeing able to reduce injector pulsewidth lower than stock in certain situations (cruising) where it is necessary if larger injectors (necessary to support big HP) are to be used for part throttle cruising with reasonable fuel mileage. The GT28RS turbo is said to be good for 280 HP according to Garrett internet info, and detailed compressor map and tech explanation is available at But even though Garrett rates their GT28RS ball bearing turbo at 280 HP, past experience with undersized turbos (Aerodyne included) allows us the privilege of running at higher HP levels for short periods of timebnote the fact that we blasted this engine to HP for short periods of timebsurely off the northeast end of the compressor map but great fun just the same. Jason=s Apex was fitted with unique 9-1 forged JE turbo pistons which theoretically allowed pump gas operation at 12.5psi. Boondocker chief Rocky felt that low compression with moderate boost level would create the lowest peak combustion temps while delivering big HP on pump gas. Low peak combustion chamber temps stave off detonation. Jason Stoviak, had seemingly scrimped by leaving stock con rods in his engine during the 40 hour piston upgrade. Having beefy forged con rods would provide the warm and fuzzy feeling of security when we boosted Jason=s engine to the max power available with the GT28RS, but perhaps budgetary or time restraints meant leaving stock rods in place. But are aftermarket forged rods really necessary? Stock Apex torque is about 76 lb/ft at stock 150 HP. If we double Apex torque to 150 lb/ft (equal to 17.5psi boost 280 HP) with boost the peak compression load on the con rods is only 20% higher than stock! And tension loads on the rods are equal to stock or less (low RPM HP peak). The key here is that both NA and turbo peak combustion chamber pressure occurs at about 18 degrees ATC. NA combustion chambers pressure subsides rapidly whereas boosted combustion chamber pressure holds its advantage well beyond TDCBat about 90 degrees ATC boosted combustion chamber pressure is maybe 3 or 4x higher then NA but still lower than peak! So stock rods should be happy at big boosted HP levels. So since the peak compression loads on Jason=s stock rods at 300HP was theoretically only 20% higher than stock 150HP NA, his fears of catastrophic failure were unfounded. We ran all dyno tests on VPC16, and this would provide all octane necessary to tap out the Garrett GT28RS turbo. As long as deto is avoided, stock rods should be adequate for 350+ HP. But if Jason were dumb enough to operate on high boost on low octane gas, detonation could result which could cause

3 loads on pistons and con rods to be 10x higher than stock with probable catastrophic results. There are many early articles on our DTR website dealing with detonation, what it is, and the havoc it causes, mostly written by Kevin Cameron. I read them all at least once a year. Not needing to argue over what torque level is safe and not safe for rod durability, we opted to stay at or below 350 HP, which easily matched the airflow capacity of the GT28RS. We have posted a group of Jason Stoviac s Boondocker turbo Apex dyno runs, from 12.5 psi (pump gas safe with the 9-1 pistons for reasonable lengths of time) all the way to 27 psi. The highest HP shown is the final three second, steady state dyno stab, which created 375 HP for three seconds. The engine was run WOT, dyno control at 9470 RPM, three data points were manually recorded, the GT28RS surely had its= tongue hanging out. Jason was jumping about lobbying for aborting the dyno test. Since he owns the machine, his wishes were honored. After that short stab, intercooler temp rises, air temp rises, airflow CFM drops as charge temp climbs. When it comes to gonzo HP turbo engines, there are big good intercoolers and good big intercoolers. On the dyno, since it was warmer than normal for sleds, the Boondocker intercooler did not receive a fair share of cooling air! As a result, charge air temp was likely higher than normal, and it s probable that 400HP plus can be achieved in short winter air blasts, even though that boost/ airflow level places that outside the Garrett island on its GT28 compressor map. Here are a group of dyno tests, stock Yamaha Apex (except 9-1 JE pistons), from pump gas to 27 psi race gas settings with the Boondocker GT28RS turbo system. Boondocker turbocharged Yamaha Apex various boost levels 12.5psi boost EngSpd STPTrq STPPwr ManPrs A/F1 Air1+2 Fuel P BMEP VolEff RPM Clb-ft CHp inhg Ratio scfm psig psi %

4 psi boost EngSpd STPTrq STPPwr ManPrs Time-S BMEP A/F1 AirTmp Fuel P RPM Clb-ft CHp inhg Second psi Ratio degf psig

5 psi boost EngSpd STPTrq STPPwr ManPrs TsTim2 AirTmp A/F1 Air1+2 Fuel P RPM Clb-ft CHp inhg second degf Ratio scfm psig

6 psi boost EngSpd STPTrq STPPwr ManPrs AirDen A/F1 Air1+2 Fuel P BMEP RPM Clb-ft CHp inhg lb/cft Ratio scfm psig psi psi boost, richen high boost setting EngSpd STPTrq STPPwr ManPrs AirDen VolEff A/F1 Air1+2 Fuel P RPM Clb-ft CHp inhg lb/cft % Ratio scfm psig

7 psi boost, lean out high boost fuel flow EngSpd STPTrq STPPwr ManPrs TsTim2 AirTmp A/F1 Fuel P BMEP RPM Clb-ft CHp inhg second degf Ratio psig psi psi boost three second steady state readings, cool intercooler

8 EngSpd STPTrq STPPwr ManPrs Time-S A/F1 Air Temp Fuel P BMEP RPM Clb-ft CHp inhg Second Ratio degf psig psi

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