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Did some logs from a dig and of course had to throttle control the tire spin which kills 100% TPS but car felt really good. I turned off the EBC to figure out gate pressure and I’m managing 13ish psi on the gate alone through a full exhaust with a highflow cat. Traction is a problem in 1st and 2nd even before boost with the drag radials but I’m seeing 7-8ish lbs in first not at 100% and shifting 5500-6k. It also seems that I can start to see boost in a non locked converter in as little as 25% throttle. I’ll try to get the log up to share at some point.
now I’m looking at fuel flow vs HP. All the online calculators put me around 700-750hp crank at 16lbs which is 93.7% duty on a 60lb injector calculating a .6 BSFC ratio. 13lbs is around 650hp and low to mid 80s duty cycle.
car feels really good on the street compared to the 78/75 and doesn’t really feel all that restrictive at 5500-6k compared to the 78/75.
I also can’t tell if the turbo really increased BP pre turbo now that I gained 3psi after increasing preload on the WG. Not sure why I was only getting 10lbs previously as I’m clearly getting 13psi consistently on just the gate and I didn’t increase spring rate just preload. My guess is a spike in BP which would crack the WG valve and bleed some boost which it’s now not doing with the added preload. I can’t tell when it opens as I’m recirculated but that’s what I’m thinking.
Did some things so let’s see what happens. I doubt it will affect much but figured I had to do it anyways.
swapped out the smaller K&N turbo filter for another bigger K&N I had on another project. I don’t think this was causing any issues with backpressure but figure it can’t hurt.
I pulled the cheap Amazon 100psi sensor and swapped it out for a 100psi higher resolution low dollar motorsports sensor. I then verified it read 0psi with key on engine off (oil pressure input). Put a new splash guard in the wheel well to protect the filter as I had none and wheel was kicking $hit into the filter.
readjusted the EBC so setting 1 is 30% duty and 2 is 45% and I’m getting about 13psi on gate spring now.
other than that I need to jack the car up and get under it. I think I want to pull a spare 02 sensor plug and swap in another 100 psi sensor and log pre and post turbo BP. Or I can remove my wideband and just use that which I have easy access from the engine bay.
only other thing I would try is to pull the turbo again to get the t4 casted elbow out so I can drill and weld another bung on the bottom side which is a flat side and not directly in the flow path on a bend. Then see if that affects my readings at all. Otherwise if it all checks out I have no idea why it would be causing so much preturbo BP.
here is the filter that I pulled (shorter on left) and the new bigger on the right. I need that tight 90 elbow to clear and it still deforms slightly getting it in. Otherwise I might put on a turbo guard with the big openings and hope I don’t suck anything up but this is a street car and I put a good bit of miles on it so I want some filtration.
Well... no buono! Just reviewed a log from a pull this AM, looks like no change. Still seeing 40psi BP on 16lbs of boost. If I can find time I'm going to pull the turbo and do a few things including relocating the BP bung location even though I don't think it will matter much.
Just wondering … do you think it would be possible to make a hybrid 70/75? Like put the billet 70 wheel on a 78/75 but swap the compressor housing? The 70/70 has been running good so I will likely leave it as I don’t have to worry about balancing the turbo but I wonder if that would be possible… I have two 78/75s on the shelf a cast gen 1 and a billet gen 1.
Just wondering … do you think it would be possible to make a hybrid 70/75? Like put the billet 70 wheel on a 78/75 but swap the compressor housing? The 70/70 has been running good so I will likely leave it as I don’t have to worry about balancing the turbo but I wonder if that would be possible… I have two 78/75s on the shelf a cast gen 1 and a billet gen 1.
My guess is that it is possible. The turbo that I had built by Work uses a 72mm compressor with the smaller S400 exhaust wheel.
Just wondering … do you think it would be possible to make a hybrid 70/75? Like put the billet 70 wheel on a 78/75 but swap the compressor housing? The 70/70 has been running good so I will likely leave it as I don’t have to worry about balancing the turbo but I wonder if that would be possible… I have two 78/75s on the shelf a cast gen 1 and a billet gen 1.
Don't see why not, Precision makes both a 70/75 and a 71/75. Guys swap wheels on diesels all the time without balancing. Sometimes I wonder if the ebay turbos are even balanced to begin with, hard to imagine they give AF when they sell under $200.
Don't see why not, Precision makes both a 70/75 and a 71/75. Guys swap wheels on diesels all the time without balancing. Sometimes I wonder if the ebay turbos are even balanced to begin with, hard to imagine they give AF when they sell under $200.
Exactly and I feel like the compressor side isn't balanced since I never see balancing marks on them. Always on the exhaust wheel middle area do I see grinding or material removal. Only issue is I know the 78 uses a whole compressor housing (cover and backing plate) vs the 70/70 so I would have to see how that could unbolt and swap. What do you guys think about the 70/75 in .96AR? I feel like the compressor isn't really out of steam and if anything I'm being limited by the exhaust side.
Exactly and I feel like the compressor side isn't balanced since I never see balancing marks on them. Always on the exhaust wheel middle area do I see grinding or material removal. Only issue is I know the 78 uses a whole compressor housing (cover and backing plate) vs the 70/70 so I would have to see how that could unbolt and swap. What do you guys think about the 70/75 in .96AR? I feel like the compressor isn't really out of steam and if anything I'm being limited by the exhaust side.
76mm compressors have made over 1000whp so I don't see a 70mm being an issue for you at 700hp. Precision rates their 6875 at 1150hp, could just buy that but they are certainly proud of it.
Pulsar makes a 6775 for import class stuff. It's a bit larger though. https://www.pulsarturbo.com/?s=class+legal this would also use the 9 blade turbine so even lower bp. They also have the 7375 G copy along with VS
Never been much point to the larger compressor on the 75 turbine on low power/boost applications IMHO Just adding lag and still capped on the exhaust side.
76mm compressors have made over 1000whp so I don't see a 70mm being an issue for you at 700hp. Precision rates their 6875 at 1150hp, could just buy that but they are certainly proud of it.
After getting some decent seat time on my new set up, I definitely would have went with a different sized turbo that came on faster than what I have. I have a VS gen 2.5 7875 1.25 AR and it turns on around 3300-3400, for my usage something coming on sooner would be better for my usage.
Granted, I haven't turned it up yet(running 7lb spring), so it's possible I may think differently with some more boost.
Well I tried to swap the 70 compressor on the 75 turbine and it didn’t work out. Everything bolted up just fine till I got to the wheel which I test fitted and the bore is a match. However the length is not! The 78/75 turbine is at least .1” shorter than the billet 70/70 so I barely got 1 thread poking out past the edge of the wheel. Clearly not enough so I had to put them both back together and that was a waste of a few hours. I throught about shaving down the tip of the billet 70mm blade like 3/16” to give me enough thread but thought it would affect the balance even tho there is enough meet for it. VS said they could
build me a 70/75 for $750 lol so I could either try to sell the 70/70 or just modify what I got and see what happens. I can’t believe now much lighter the billet 70 wheel is compared to the cast 78…. Huge difference! Besides the shaft length they are literally the same everything.
For $hits and giggles I swapped back on the billet 11 blade 78/75 to get some data. I did find a leak on my crossover at one of the vband connections SMH so I pulled the 2.25” crossover and swapped back on the original 3” crossover till I figure out what’s wrong with it (I realize the 3” is not good hence the smaller crossover I just yanked). I also picked up another copper gauge install kit and added a 100psi transducer in the downpipe for the 78/75. This way I can log pre and post turbo back pressures. I will also see if that 200 cell high flow cat really messes with the flow that much. I also made a new -10 drain.
I just finished buttoning it up today and did a quick startup to check for leaks and were good. I will try to drive it to work this week and get some back to back logs with the cutout open and closed and see what she does. If the pre turbo backpressure comes down below 2:1 I might look into selling my 70/70 abs getting a 70/75 style.
Don’t worry it’s got a few coils up by the sensor.
So I ended up getting a billet eBay 78/75 for $290 to my door as the shaft looks extra long on them. Got it today and I’m super impressed with the quality for $290 abs looks 95% identical to my Vs racing stuff.
I took them apart and verified they are basically the same units except a few differences. The shaft thread is slightly different, bolts to compressor housing backing plate are different thread pitch and The shaft is longer on the ebb at as well as the turbine blades look more rounded on the edge near the center. Also the oil feed on the VS is 1/8 NPT and the eBay is M12x1.5 so I got new feed coming. The 70mm blades are taller and have more of a downward pitch from the center out and has a smaller diameter center shaft area.
I was able to transfer everything over from the billet VS 70mm so I basically have a 70/75 billet turbo now! I’m still going to test the billet 11 blade 78/75 on the car prob Friday and then swap this one on. I also picked up a rebuild kit from VS for the 78/75 gen 1 turbos and the parts look identical On the Vs and eBay turbos. The eBay compressor housing is huge tho and I tried to weigh the billet 70 and 78 wheels for a comparison but it maxed out my 500 gram scale so no dice. Not as noticeable difference between the billet 70 and billet 78 blades. But it’s still lighter and the machine work (ridges) are better on the VS but not by much. Really impressed with the eBay turbo which also has Oring seals even tho all the stuff online said RTV.
im going to creakote the 75 turbine and center section before putting it on the car but I’m excited to see how the larger exhaust wheel and smaller compressor effects spool and backpressure.
My billet 7875 ebay turbo is still going strong too. Been a big fan and for the price its a no brainer. Im surprised you didn't try to do the opposite and create a 7870 lol.
My billet 7875 ebay turbo is still going strong too. Been a big fan and for the price its a no brainer. Im surprised you didn't try to do the opposite and create a 7870 lol.
ha! I actually did, since I had the billet 78 wheel and housing I threw it on the 70 turbine. So I got a unique 7870 as well which could be the new 7665 lol.
ha! I actually did, since I had the billet 78 wheel and housing I threw it on the 70 turbine. So I got a unique 7870 as well which could be the new 7665 lol.
ha! I actually did, since I had the billet 78 wheel and housing I threw it on the 70 turbine. So I got a unique 7870 as well which could be the new 7665 lol.
I am very interested in your results, because you are building a turbo that is similar to mine!
06-18-2022, 10:27 AM
