Ready to upgrade the Turbo on your Diesel?

Transcription

1 Ready t upgrade the Turb n yur Diesel? Tday s diesel engines represent the state f the art in technlgy with high pwer density, excellent drivability, and gd fuel ecnmy. Frtunately fr the diesel enthusiast, they are easier t upgrade fr additinal perfrmance and the aftermarket is respnding with mre ptins fr yur high perfrmance needs. As the majr air system cmpnent, the turbcharger is a vital part f the perfrmance equatin and chsing the right turb is critical t meeting yur perfrmance targets. S why wuld I want t upgrade my Turb Diesel engine? Better twing perfrmance -- Maybe yu bught yur truck t tw that gseneck fr wrk, t get yur 5th wheel t the next resrt r the bat t the lake. It sure wuld be nice t get up t freeway speeds quickly and maintain highway speeds in hilly terrain. With the right upgrades, that can be dne safely and efficiently. Cmpetitin Use -- Mre and mre enthusiasts are interested in heavily mdifying their vehicles fr cmpetitin use. Sme are weekend warrirs that use their vehicles during the week fr rutine duty then g t the track n the weekends while thers are building strictly race vehicles that give up streetability fr the demands f the track. Mre fun -- Fr many, making mdificatins fr increased perfrmance is a way f persnalizing the vehicle and t have a bit mre fun with the daily drive. There is a satisfactin that cmes frm mdificatins that put yu back int yur seat a little harder when the light turns green. And, there are always the grudge matches at the lcal drag strip. What d I need t knw t chse the right diesel upgrade turbcharger? The amunt f pwer that a diesel engine makes is directly prprtinal t the amunt f fuel injected int the cylinder and that fuel needs sufficient air fr cmplete cmbustin. Fr smke-free perfrmance, the engine needs abut 18 times mre air (by mass) than fuel. S clearly, as mre fuel is added, additinal air needs t be added als. In mst applicatins, the stck turb has sme additinal capacity fr increased pwer, but as the cmpressr reaches the chke limit (maximum flw), the turb speed increases rapidly, the efficiency drps dramatically, and the cmpressr discharge temperature ramps up very quickly. This creates a "snwball" effect in that the higher discharge temps mean higher intake manifld temps and higher exhaust gas temps. The lwer efficiency means that mre turbine pwer is required t reach the same bst causing higher back pressure in the exhaust manifld. This can usually be seen n an engine with a perfrmance chip (at the highest pwer setting) and maybe an intake r exhaust upgrade. Under heavy acceleratin, smke is puring frm the tailpipe as the EGT's and turb speeds are climbing int the danger zne requiring a prudent driver t back ff the acceleratr pedal early t keep frm damaging the engine. Under these cnditins, the stck turb is running n brrwed time. With an upgrade turbcharger selected t cmpliment the extra fuel, smke is drastically reduced, EGT's are under cntrl and, since the turb is perating in a mre efficient range, hrsepwer and drivability are enhanced. When the mdificatins get mre serius, a bigger turb is a must have t cmpliment even mre fuel.

2 In rder t decide n the apprpriate turbcharger fr yur diesel engine, the very first thing that needs t be established is the pwer target. Since turbchargers are sized by hw much air they can deliver and airflw is prprtinal t engine pwer, a realistic hrsepwer gal is critical t make the right chice. The cncept f a realistic gal needs t be stressed in rder t ensure maximum perfrmance and satisfactin. Sure, everyne wuld like t have a mega-hrsepwer vehicle but past a reasnable limit, as the pwer ges up, the reliability, drivability and day-t-day utility is diminished. Things are mre likely t g wrng, wear ut and break dwn as the utput climbs. Mst prject vehicles can fall int ne f the fllwing general categries: Intended Use Daily Driver / Wrk Truck / Tw Vehicle Weekend Warrir Extreme Perfrmance Cmpetitin Apprximate Pwer Increase Over Stck +150 Hrsepwer Reliability, +250 Hrsepwer +350 Hrsepwer 400 Hrsepwer and up Imprtant Factrs Drivability, Perfrmance, Reduced EGTs, Lw Smke Still needs t pull regular duty during the week and have fun n weekends Street Driven but everyday drivability cmprmised fr high perfrmance capability 100% perfrmance, n cmprmises Great, S what Garrett turb d I chse? Let s take each case and calculate a turb chice based n the intended pwer increase. The first step is t read the Turb Tech 103 article n This article explains the reading f a cmpressr map and the equatins needed t prperly match a turb. The examples given, hwever, are fr gasline engines, s we are ging t wrk sme additinal examples here using thse same equatins but with a diesel engine. Matches will be calculated with an Air Fuel Rati (AFR) f 22-t-1 fr lw r n smke perfrmance. Likewise a typical Brake Specific Fuel Cnsumptin (BSFC) is in the range f Let s get started! The first example will be fr the Daily Driver/Wrk Truck/Tw Vehicle categry. This includes vehicles up t 150HP ver stck. But wait, this pwer level can be accmplished with just a chip r tuning mdule. S why bther with a new upgrade turb? An upgrade turb will enhance the gains made by installing the chip and ther upgrades. The extra air and lwer backpressure prvided by the upgrade turb will lwer EGTs, allw mre pwer with less smke and address durability issues with the stck turb at higher bst pressures and pwer levels. Because this will be a mild upgrade, bst respnse and drivability will be imprved acrss the bard. EXAMPLE: I have a 6.6 liter diesel engine that makes a claimed 325 flywheel hrsepwer (abut 275 wheel hrsepwer as measured n a chassis dyn). I wuld like t make 425 wheel hp; an increase f 150 wheel hrsepwer. Plugging these numbers int the

3 frmula and using the AFR and BSFC data frm abve: Recall frm Turb Tech 103: where, S we will need t chse a cmpressr map that has a capability f at least 59.2 punds per minute f airflw capacity. Next, hw much bst pressure will be needed? Calculate the manifld pressure required t meet the hrsepwer target. Where, MAPreq = Manifld Abslute Pressure (psia) required t meet the hrsepwer target Wa = Air flw actual (lb/min) R = Gas Cnstant = Tm = Intake Manifld Temperature (degrees F) VE = Vlumetric Efficiency N = Engine speed (RPM) Vd = engine displacement (Cubic Inches, cnvert frm liters t CI by multiplying by 61, ex. 2.0 liters * 61 = 122 CI) Fr ur prject engine: Wa = 59.2 lb/min as previusly calculated Tm = 130 degrees F VE = 98% N = 3300 RPM Vd = 6.6 liters * 61 = 400 CI = 34.5 psia (remember, this is abslute pressure; subtract atmspheric pressure t get gauge pressure, 34.5 psia psia (at sea level) = 19.8 psig)

4 S nw we have a Mass Flw and Manifld Pressure. We are almst ready t plt the data n the cmpressr map. Next step is t determine hw much pressure lss exists between the cmpressr and the manifld. The best way t d this is t measure the pressure drp with a data acquisitin system, but many times that is nt practical. Depending upn flw rate and charge air cler size, piping size and number/quality f the bends, thrttle bdy restrictin, etc., yu can estimate frm 1 psi (r less) up t 4 psi (r higher). Fr ur examples we will estimate that there is a 2 psi lss. Therefre we will need t add 2 psi t the manifld pressure in rder t determine the Cmpressr Discharge Pressure (P2c) Where, P2c = Cmpressr Discharge Pressure (psia) MAP = Manifld Abslute Pressure (psia) = Pressure lss between the Cmpressr and the Manifld (psi) = 36.5 psia T get the crrect inlet cnditin, it is nw necessary t estimate the air filter r ther restrictins. In the Pressure Rati discussin earlier we said that a typical value might be 1 psi, s that is what will be used in this calculatin. Als, we are ging t assume that we are at sea level, s we are ging t use an ambient pressure f 14.7 psia. We will need t subtract the 1 psi pressure lss frm the ambient pressure t determine the Cmpressr Inlet Pressure (P1). Where: = Cmpressr Inlet Pressure (psia) = Ambient Air pressure (psia) = Pressure lss due t Air Filter/Piping (psi) = 13.7 psia With this, we can calculate Pressure Rati ( ) using the equatin. Fr the 2.0L engine:

5 = 2.7 We nw have enugh infrmatin t plt these perating pints n the cmpressr map. First we will try a GT3788R. This turb has an 88mm tip diameter 52 trim cmpressr wheel with a mm inducer. As yu can see, this pint falls nicely n the map with sme additinal rm fr increased bst and mass flw if the hrsepwer target climbs. Fr this reasn, the GT37R turb family is applied n many f the Garrett PwerMax turb kits that are sized fr this hrsepwer range.

6 Fr the next example, let's lk at the Weekend Warrir. This categry is fr daily driven vehicles that have up t 250 hrsepwer ver stck r 525 wheel hrsepwer. Plugging that pwer target int ur frmula yields an airflw requirement f: And a pressure rati f: = 45.5 psia = 3.3 Lking at the previus map, the cmpressr des nt flw enugh t supprt this requirement, s we must lk at the next larger size cmpressr. (Technically, the engine culd prbably easily make this pwer with the previus cmpressr, but it wuld be at risk f mre smke, higher EGT's and backpressure; kind f like pushing a stck cmpressr t far ) The next larger turb is a GT4094R and is shwn belw. Anther ptin that culd als be cnsidered is the GT4294R which has a slightly larger inducer cmpressr and the next larger frame size turbine wheel. The larger wheel inertia's will slw dwn the respnse a bit, but prvide better perfrmance at the tp end f the rpm range.

7 Fr the next example, let's lk at the Extreme Perfrmance. This categry is fr real ht rd vehicles that have up t 350 hrsepwer ver stck and wners that are willing t give up sme f the daily utility in rder t achieve higher pwer gains. Plugging that pwer target int ur frmula yields an airflw requirement f: And a pressure rati f :

8 = 50.8 psia = 52.8 psia = 3.8 Fr this flw and pressure rati, the GT4202R is apprpriate and is shwn belw. Since this is appraching a pressure rati f 4-t-1, we are abut at the limit f a single turb n an engine f this size.

9 Additinal pwer gains can be had with mre bst r a larger single turb, but it is getting clse t the edge f the envelpe in terms f efficiency and turb speed. The final case is the Cmpetitin categry. Since this is a special case and there are s many ways t g abut an ultimate pwer diesel applicatin, it is nt pssible t cver it adequately in this article. There are, hwever, sme general guidelines. At this pwer level, as stated abve, it is a gd idea t cnsider a series turb applicatin. This is a situatin where ne turb feeds anther turb, sharing the wrk

10 f cmpressing the air acrss bth cmpressrs. A larger turb is designated as the "lw-pressure" turb and the smaller secndary stage as the "high pressure" turb. The lw-pressure cmpressr feeds the high-pressure cmpressr which then feeds the intake. On the turbine-side the exhaust first passes thrugh the high-pressure turbine and then n t the lw-pressure turbine befre being ruted ut thrugh the tailpipe. We can still calculate the required mass flw, but the pressure rati is mre invlved and questins shuld be discussed with yur lcal Garrett PwerMax distributr. T calculate the required mass flw, we use the nrmal equatin. This time the pwer target will be 500 wheel hrsepwer ver stck, fr a ttal f 775 wheel hrsepwer This air flw rate will apply nly t the lw-pressure cmpressr as the high-pressure cmpressr will be smaller because it is further pressurizing already cmpressed air. In mst cases, the high-pressure turb tends t be abut tw frame sizes smaller than the lw pressure stage. S in this case, after selecting the apprpriate lw-pressure turb (hint: lk at the GT4718R cmpressr map), a GT4088R r GT4094R wuld be the likely candidates. One mre cmment n chsing a prperly sized turbine husing A/R. A smaller A/R will help the turb cme up n bst sner and prvide a better respnding turb applicatin, but at the expense f higher back pressure in the higher rpm znes and, in sme cases, a risk f pushing the cmpressr int surge if the bst rises t rapidly. On the ther hand, a larger A/R will respnd slwer, but with better tp end perfrmance and reduced risk f running the cmpressr int surge. Generally speaking, the prper turbine husing is the largest ne that will give acceptable bst respnse n the lw end while allwing fr mre ptimal tp end perfrmance. This infrmatin shuld be used as a starting pint fr making decisins n prper turb sizing. Of curse, fr mre specific infrmatin n yur engine, cnsult a Garrett PwerMax distributr.