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My 2002 f350 is about ready for a different turbo. I would like to put a gtp38r as I would be installing a better hpop and stage 1's but I also have a stock turbo laying around that I would like to build into a 38r if possoble .
Rebuilding the stock turbo with a 360* thrust washer kit, upgrading to a billet compressor wheel, and 1.0 turbine housing will give you the closest thing to a 38r.
$500-700...Billet wheels weren't the rage when I did the 1.0 housing. But, with a stock wheel, Ported compressor housing, and the 1.0, there was a definite improvement when I had maxed out my stock injectors. With the a billet wheel, I would have seen more of an improvement in spool time and air quality than with my combination. I sold that turbo and went with a 38r just before going with Stage 2 singleshots. Even then, I saw an improvement with an upgrade to a billet compressor wheel on the 38r.
I have a 38R upgrade and so you are aware that no one sells a rebuild kit for the 38R. You have to send the turbo in to Garrett for THEM to rebuild it and it's not cheap, very expensive. Not trying to turn you away from the 38R just informing you.
My original post was geared to the cost factor between the two. You can upgrade the stock turbo to give great results, but the larger compressor side of the 38r will always outperform the stock GTP38 in air flow because of its larger size.
I, too, had the Stage 2 singles while running the 38r. With the mods listed in my signature, I dyno'd over 450 rwhp. I had the billet wheel and 1.15 turbine housing on it at the time. I later switched to a modded 1.0 which gave me better drivability and low end torque with no increase in EGTs. I never got to dyno it with the 1.0, but the truck did pull stronger, had faster spooling, and less smoke. The new owner has been very well pleased with it and its towing of his ~10k# fiver.
I'm in the process of building a turbo that matches the 38R. From the start I didn't plan on building it to match the 38R but with all the black Friday specials and discounts I was finding it just ended up that my turbo will be very close to a 38R. The list is long. The only thing that is not new is the center baring housing (don't know the name).
My new parts. 360 bearing kit, new shaft, RR ported housing billet wheel, Balancing, 1.0 AR, ATS ported housing and EBPV housing. Even with the discounts I could have bought a 38R for less. The only thing I keep telling myself so I don't feel foolish is. My turbo will be able to rebuild and I was able to ceramic coat the part as I build the turbo.
The turbo is not completed, so I can't comment on the performance just yet. Hopefully in the next few weeks it will be in the truck. A lot of other repairs will be done at the time of install. Leaky up pipes for starters.
Turbo decisions are always tough. By the time you spend the money to upgrade the stocker you are almost 1/2 way to the cost of a 38R. Then the 38R isn't rebuildable. etc. etc. Do I need the bigger turbo? Will the stocker struggle & scream?
The first decision to make is the HP level you are after (as stated above by kamstutz).
375-400 hp is a nice setup and can be easily obtained without having to go too crazy on some of the modifications. But still, turbo, injectors & HPOP quickly add up and consume the budget.
Here is a graph (thank you ErnestEugene) comparing the compressor maps of the GTP38 and the GTP38R. The brown operating envelope is the stock GTP38 and the blue envelope is the GTP38R. For now, don't pay attention to the RPM lines.
Stock GTP38 max's out at @ 60 lb/min
GTP38R max's at @ 72 lb/min
assuming this example is at sea level (14.7 psi) and our max boost goal is @ 30 psi.
To obtain 375 HP - you will need about 50 lb/min air.
pressure ratio = 30(boost)+14.7 (pressure)/14.7(pressure) = 3.04
400 rear wheel HP goal
assuming this example is at sea level (14.7 psi) and our max boost goal is @ 30 psi.
To obtain 400 HP - you will need about 53 lb/min air.
pressure ratio = 30(boost)+14.7 (pressure)/14.7(pressure) = 3.04
Plot these two point on the graph and we get the green dot for 375 hp and the orange dot for 400 hp.
As you can see the modified stock GTP38 can handle the task but is quickly reaching its envelop limits (brown line). The closer the plotted dots move up and to the right of there envelope the lesser the efficiency (and more heat ). The 38R can handle the task at a lower position and more to the left in it's operating envelope. Basically the closer to the center the more efficient.
This is just some ballpark calculations, there is much more to it - but this will get you close enough to make an educated guess. Both turbos can handle the 375-400 HP task, one just does it more efficiently (and with less heat) and leaves room for upgrades in the future. But is it worth the additional $$? That's your call.......
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). The 38R can handle the task at a lower position and more to the left in it's operating envelope. Basically the closer to the center the more efficient.
