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We all see the extremely budget turbos available yet not many people seem to actually want to try them out. Some won't based on fabricated predispositions, some for fear of parts failure, and others because they just want a name brand. I decided to try it out. I got in touch with @MaXpeedingRods to try out one of their turbos. In full transparency, they did not pay me for this. I wanted to see what these budget friendly turbos can actually do. So I set out to characterize and compare their GT45 turbo (GT45 T4 T66 Wet Float A/R .66 A/R 1.05 GT45R V-band 600+HP 600PS Universal Turbo Turbocharger) to the ON3 Performance 70mm.

Some of the data is based on a turbo 4.6 two valve (2v) application while the rest is based on a small block Ford (SBF) 347 motor. I had to do this as my 2v was down during this testing time. With that I need to express that the 70mm was at a disadvantage as the exhaust side was too small for the size of the 347 motor. The other piece I need to express is that these two turbos are not direct competitors with each other. They perform for two different applications and this is corroborated in the data. But since the compressor sides are so close there is some comparison we can do and we can characterize the turbos. A quick rundown of the 2v: forged rotating assembly, ported heads, MHS stage 1 cams, 4r70w, Holley terminator ECU, ON3 turbo kit and pump 91. The rundown of the small block ford: 347ci, pump 91 octane (for this test), “mild turbo cam”, aftermarket heads, forged rotating assembly, dart block, th400 with a converter meant for a higher HP application.
GT45 specs.PNG

The time it takes to spool is a turbo is often one of the biggest factors in a turbos feel. A quick responding turbo feels good in the seat of the pants. Often we try to get our turbos to mimic blowers or to feel as if it is not even there. This is an area where the 70mm turbo out performed the GT45. This is a symptom of the exhaust side of the turbocharger. The 70mm’s exhaust side is about 17% smaller with a smaller A/R housing as well. Physics is on the side of the 70mm. On the 4.6 2v the 70mm spooled on average 27% faster (P-Value:2.85E-05) . Its mean spool rpm was 2721.6 (+/- 74.7) while the GT45 spooled at 3712.3 (+/- 60.1) rpm on average. On the SBF, the 70mm averaged a spool rpm of 2524 (+/- 30.8) while the GT45 averaged 3284 (+/- 67.6) rpm. Now, when it comes to seat of the pants feel, that GT45 was fun. It came on hard when it finally got spooling. The 70mm came on quickly but it was soft and made the car feel almost as if it was just a big power N/A motor. Something to think about when it comes to deciding on your turbo options.
gt45 spool.PNG

Intake air temps speak to the compressor design as well as when a turbo is running out of steam. When a turbo is being spun too hard it will continue to make boost but intake air temps drastically rise causing the turbo to make no more power, just heat. This is seen around the 15 psi mark (roughly 600 hp) on the 70mm turbo. It starts to become quickly inefficient around this power level. At 6 psi both the GT45 and 70mm IAT’s are low 90’s with no statistical difference (p-value=0.249). At 10 psi the IAT’s were low 110’s with no statistical difference (p-value=0.571). 15 psi is where things became interesting. As previously mentioned, the 70mm was getting a little out of its efficiency range and this is what I believe to cause the IAT’s to start to increase at a greater rate than the GT45. The 70mm peaked IAT’s at 138 while the GT45 only peaked at 126 degrees. This did show to have a significant difference (p-value=0.0281). Keep in mind that beautiful San Diego provided a consistent 71 degree outside temps the entire time.
GT45 iat.PNG

So this is probably what the turbo nerds were looking for. All the other data is great to look at but back pressure tells the truth about a turbo. Basically if there is too much backpressure the turbo can not continue to make more power. This is often illustrated as a ratio (boost pressure to back pressure). As a general rule of thumb, most drag racers want their back pressure ratio to be around 1:1.5 and at around 1:2 the turbo is almost out of steam. Now that is a very rough generalization so don’t take it as gospel. Many OEM and turny-turn guys want their turbos around that 1:2 ratio because of the good response that often comes with that. At 6 psi the 70mm peaked at a 1:0.73 and the GT45 peaked at 1:0.65. Not significantly different (p-value= 0.10). At 10 psi the 70mm had a ratio of 1:1.49. This is definitely in the 70mm’s sweet spot. The GT45 had a ratio of 1:0.8. This was significantly different (p-value=5.44E-4). Finally at 15 psi the 70mm had a ratio of 1:2.17 while the GT45 was only at 1:1.21. This did show a significant difference between the 70mm and the GT45 (p-value= 1.4E-6). What this is telling me is that the 70mm is just too small on the exhaust side for this specific application at this power level. It also shows me that the GT45 does have some more left in it.
gt45 Backpressure.PNG

Finally lets talk about power. Truthfully this does not tell a great story as there was no significant difference between any of the power runs. In full transparency, we were not trying to optimize every last part of the tune to squeak out every last HP capable. It was run on crappy California 91 octane on low timing. Ambient temps were all 71 degrees, oil temps were within 2 degrees of each other at the start of every run, and coolant temps were always 180 degrees at the beginning of the runs. The 70mm made 432 at 6 psi, 515 at 10 psi, and 598 at 15 psi. The GT45 made 426 hp at 6 psi, 511 at 10 psi, and 607 hp at 15 psi. At 6 psi the 70mm had a 2.3% increase in power over the GT45 but at 15 psi the GT45 had a 1.5% increase over the 70mm. What I can extrapolate from this is that the GT45 does have more to go at 15 psi while the 70mm is really starting to run out of its efficiency zone at that power level. For reference this car is normally run on C16 with a much larger turbo with roughly 25 degrees of timing in it at 15 psi. On this test it was 12 degrees of timing at 15 psi and 91 octane. It was just an old tune we had for the car that would work.
gt45 hp.PNG
In conclusion we see a few key takeaways. First off, the MaXpeedingRods GT45 impressed me especially considering the price tag. The ON3 Performance 70mm turbo performed well at low and medium horsepower levels (550 and less) on the SBF application. The compressor flowed well but the turbine side was just too small at higher boost pressures (view back pressure data). This is where the MaXpeedingRods GT45 came alive as it has that larger turbine side of the turbocharger. It was consistently flowing more exhaust gasses which allowed it to make over 600 wheel hp at a sub 1:2 boost to back pressure ratio. At a 1:2 ratio the turbo is generally out of steam on the exhaust side. Hopefully soon I will be able to test the maximum horsepower potential of this turbo. As far as spool time, this is where the ON3 Performance turbo greatly outperformed. And this is no fault of the GT45 design, it is simply because of the exhaust side of the 70mm being smaller. For a mild powered car that wants great manners and a quick spool that 70mm really shined. With that, the GT45 is definitely a turbo to start to consider with a larger displacement motor or when looking to make more power. I do plan on putting some more miles on the GT45 to see how it holds up to the wear and tear of daily usage.
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