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I wonder if it makes sense to get the 7875 even if I don't plan to shift over 6200rpm? Although a lot of the dyno's I've seen of the TC78 the power falls off above 5000rpm.
It is a cost benefit thing. I believe the 7875 is better than the 7868 in about every way. Is it worth $500 more? That's about the price difference. Even if it is only 50 hp more, what else can you spend $500 on that will give you 50hp? A cam and springs even cost more than that.
Some people believe that the 68mm turbine chokes up the exhaust side, that's why it falls off. I'm not really a believe in that fact. I think it is just that the 68mm turbine doesn't create enough power (shaft hp of the turbo) to run the 78mm compressor wheel at high loads. It takes over 100 shaft hp to max out the 78MM compressor, and I don't think the 68 can generate that much, the 75mm turbine calculates out to about 130 shaft HP on my engine at 20 PSI.
The reason I don't believe it is just backpressure, is based upon reported exhaust pressure readings on some systems, and the waste gate is wide open as well at high power levels. There is adequate avenue for exhaust if you take an open waste gate into account also.
Yea I guess your right and I agree if I gain 50hp this turbo it is easily worth every penny.. I think it will gains that power above 5000rpm where the other turbo falls off. Plus I plan to up the boost to about 15psi where the TC78 will be choked even more the gains will be huge.
It's already a done deal. I just hope the 7875 fits without any issues on a truck manifold kit. I'm told it should be a direct replacement with no problems so I'm crossing my fingers!
I've never ran the TC-78. I owned one for a brief moment in time, and traded it for the 7875.
Here is a photo of the 7875 showing off her 75 mm turbine side. That's how I had to fit mine, put the turbine housing in the car, then slide the rest of the turbo into it.
Big thanks to ScottyBG for this post. There is no way of getting to the top driver side flange bolt unless you remove the compressor from the turbine side...
Also I expected the turbine housing to look a lot bigger on the 7875, but it is only very slightly bigger... The compressor housing on the other hand is noticeably larger...
Now what should I expect one first drive with the 7875? Am I going to make less boost then I did with the tc78 with the same WG spring?
I went from a TC78 to a T7875, big difference.
The TC78 came into boost like a light switch and with a M6/4.10/street tire combo it was hard to apply power consistently.
The T7875 is much louder and required me to install an additional 255 pump in my tank at the same boost pressure as the TC78 which tells me its moving a larger volume of air.
The power is much more linear and at 7 lbs. feels faster than the TC78 at 11 lbs.
Overall a much better turbo and with the 5.3 in my garage almost complete 700+whp is in the immediate future lol.
Big thanks to ScottyBG for this post. There is no way of getting to the top driver side flange bolt unless you remove the compressor from the turbine side...
Also I expected the turbine housing to look a lot bigger on the 7875, but it is only very slightly bigger... The compressor housing on the other hand is noticeably larger...
Now what should I expect one first drive with the 7875? Am I going to make less boost then I did with the tc78 with the same WG spring?
Don't remove the turbine housing, remove the bolt right above the mounting flange, leave the flange loose with one bolt in it, lift the turbo and install the bolt while holding the turbo up and start threading the mounting bolt into the hotside and it will go together in one piece.
I tried that first with no luck. There was no way to get a wrench in there with the compressor atttached. It really didnt take long to remove the turboje sode amd get all the bolts nice and tight.
I went out and drove it and was pleasantly surprised. On my setup for some reason the 7875 is as loud as the tc78 if not a little bit louder! Didnt go wot yet. Getting the flu so I prob wont get to go WOT for a few days...
Great to see you got it up and running! Please update your impressions once you get well and have more time to compare it to what you had. I'm pleased my experience helped. Even though it is possible to do it by other means, taking the turbine housing off makes it cake.
If you watch sloppy mechanics youtube channel, that's how Matt takes his turbo on and off too. He removes the main part of the turbo, with the drain line attached, then removes the log manifold with the exhaust housing and wastegate all in 1 piece.
I went from a TC78 to a T7875, big difference.
The TC78 came into boost like a light switch and with a M6/4.10/street tire combo it was hard to apply power consistently.
The T7875 is much louder and required me to install an additional 255 pump in my tank at the same boost pressure as the TC78 which tells me its moving a larger volume of air.
The power is much more linear and at 7 lbs. feels faster than the TC78 at 11 lbs.
Overall a much better turbo and with the 5.3 in my garage almost complete 700+whp is in the immediate future lol.
I missed this post before. That is great to hear! Did you make more or less boost when you switched to the 7875? My 7875 was def louder then the tc78. I'm betting I will need a second pump as well!
I missed this post before. That is great to hear! Did you make more or less boost when you switched to the 7875? My 7875 was def louder then the tc78. I'm betting I will need a second pump as well!
The boost remained the same, it just took a lot more fuel.
I had installed an 11 lb. spring in the TC78 and my tuner said I was on the ragged edge of lean and suggested I reduce my boost level or add more fuel pump.
I put the T7875 in it at 7 lbs. and he immediately suggested a pump upgrade, we then went back and forth three or four times to get the AFR dialed in.
The car pulls harder at 7 lbs. with the T7875 than the TC78 at 11 lbs. so its definitely working.
The turbine is loud AF too which gives me a stiffy lol.
It is because it is a T series housing, since it is a T series turbo. The TC or Huricane is a smaller series of turbo. The next size up is the midframe, then the Y2K, then the thumper in the Turbonetics line up. Going down it would be like going to a 60 series turbo, these are just classes for turbos from a marketing prospective. If you go through the Turbonetics catalogue you will see them in order of size. This is like going from a 300 series in a BW to a 400 series, 500 series, everything gets bigger.
It is because it is a T series housing, since it is a T series turbo. The TC or Huricane is a smaller series of turbo. The next size up is the midframe, then the Y2K, then the thumper in the Turbonetics line up. Going down it would be like going to a 60 series turbo, these are just classes for turbos from a marketing prospective. If you go through the Turbonetics catalogue you will see them in order of size. This is like going from a 300 series in a BW to a 400 series, 500 series, everything gets bigger.
Well and to that point I figured that a 78mm inducer was all that mattered but then I learned that volume of air is determined by the size of the compressor housing and is what really dictates horsepower produced, not PSI.
That's why my T7875 makes more power at the same boost level as the TC78 and I'm sure the larger turbine doesn't hurt either lol.
The ******, I see you have 60 lb injectors in your sig? I would have though you would have run out of those by now on your combo?, you must not be running E85? How are they for duty cycle?
The ******, I see you have 60 lb injectors in your sig? I would have though you would have run out of those by now on your combo?, you must not be running E85? How are they for duty cycle?
I'm running straight pump unfortunately, all you guys with your readily available race gas make me really jealous lol.
E85 is almost non-existent here in the PNW so I gotta make due with pump swill plus I drive the car everywhere- legit AF street car status.
A friend of mine made 700whp on 60's with pump and a little meth so I think I may do the same.
I don't know what my duty cycle is since I have Pat G. remote tune it for me, it must not be too high or he would've suggest a change.
I only added another 255 to my stock bucket when I ran out of fuel and since then its been money, been toying with the idea of putting the 11 lbs. spring in too.
I'm looking at a cheap pump option. I'm thinking of just doing a 340lph pump with my hotwire and see if that will get me 700rwhp. That and use my corvette regulator/filter. My 255lph pump with hotwire has me right around 570rwhp right now so I would think the 340lph should get me damn close to 700rwhp...
You will be close. Being close is dangerous, considering were dealing with cast pistons and boost here. If I went to the effort of pulling the basket out of the tank, I would invest in a dual pump setup. You could go with using your current 255 and just buying another pump, and about $100 worth of wiring and plumbing parts, have a dual pump setup if you DIY. If you put a 340 in, you'd be buying a new pump either way. You could put in a 340 and pair it with your 255 also, they don't have to match. I'd just add a 340 to your 255, and put it on a hobbs switch. Or you could go with something like Lonnies, or Squash, I think that Chris1313 or something like that is also doing something with dual pumps on here too.
You will be close. Being close is dangerous, considering were dealing with cast pistons and boost here. If I went to the effort of pulling the basket out of the tank, I would invest in a dual pump setup. You could go with using your current 255 and just buying another pump, and about $100 worth of wiring and plumbing parts, have a dual pump setup if you DIY. If you put a 340 in, you'd be buying a new pump either way. You could put in a 340 and pair it with your 255 also, they don't have to match. I'd just add a 340 to your 255, and put it on a hobbs switch. Or you could go with something like Lonnies, or Squash, I think that Chris1313 or something like that is also doing something with dual pumps on here too.
Mine has forged wiseco pistons. It's all forged except the crank actually, with arp rod bolts and ARP headstuds, but that doesn't mean I want to go lean either.
Thing is I have no plans of changing out the stock lines, fuel rail, or 60lb injectors. From my research that should have me limited to 700-750rwhp with the injectors being the limiting piece. With twin pumps I will need an all new harness and a bunch of other stuff to make it work as well. I should be past the point of my current 255lph/hotwire from what racetronix tells me as I am now.
I'm now pushing 11psi on a 7875 turbo so it should be in the 580rwhp range and my a/f still stays steady at 11.2...
Basically my plan is to throw the 340lph pump in for $100 and hopefully be good to 700rwhp. I always have my eye on the a/f and it will be tuned for more boost with my tuner there so worst case it's not enough and I have to find a way to add the 340 to the 255...
02-03-2017, 02:23 PM
