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The problem is that people's goals are different. Not everyone cares about ET, or wants to bring in power on the street so they get traction, or rev to 7500, or has plenty of space to put whatever turbo they want. Some people want to blow tires off and make torque at 2500 rpms at part throttle like OEM vehicles. They can't fit a big T6 turbo and don't really care if they're making out their turbo because turbos are cheap now. Different strokes for different folks. Then again most people think they have a street car because it's technically legal to drive on the street too.
VS Racing told me the 78/75 billet turbo I have from them was good to 950 RWHP (with the .96 A/R) After reading up a lot on them, I'm beginning to suspect what they meant by "RWHP" was Richard Holdener Wheel Horse Power. I.E., In a perfect world with every part perfect and 5% driveline loss.
I've heard the 7875 can make 1000 is that accurate?
I haven’t seen that out of a regular 7875 but the upgraded version in the video I posted above made over 900 wheel and probably would have been close to 1000 wheel had he not run out of injector. My buddy ran 9.70’s at over 140 with a regular doodoo 7875 in a full weight trans am with stock ls1 heads, stock non ls6 intake and a sloppy 2 cam. This was his first turbo build and his third test trip to the track.
then someone told him he needed a bigger turbo. Car went slower. I advised against that. He ended up having to put a bigger (383) more radical engine to match the bigger turbo. I know someone else who did the same thing and hated the bigger turbo because he said it didn’t spool up till like 5000-5500.
look bro, your getting your underwear all in a wad over a street car. The 7875 gen 3 is a very good choice with minimal compromises to do what he wants. Are there turbos out there that would make more power? Yes. But he’s not building a straight up drag car like you keep acting like he is. He’s building a nice driving street vehicle that will outrun his buddy’s car. And it’ll do that with a gen 3 7875. Using a t6 housing is going to make it lag even more and you damn well know that. I’m not sure why you are hell bent on directing someone to over turbo their first build. Reminds me of guys telling people to put a big ole nasty cam in a daily driver with a stock stall.
Zero panty wad. Just trying to give facts to someone instead of opinions. Everything you've stated is opinion as you have given no direct comparison to other turbos. I've literally run a T4 S476 and switched to a T6 S480 on a 370 engine with no other changes... Have you?
I get not everyone is building a "race car". To say things like "et" and "trap speed" don't matter is ridiculous. That is data that directly correlates to acceleration and performance. Which is the whole point of building any turbo car. He gives an exact power amount... and 800whp doesn't describe a nice driving street car. You can't plant 800WHP on a street car. I've ditched all the T4 turbos as singles long ago. And no, that doesn't mean it will lag more than a t4. My T6 setups are better all around.
Matt Happel swapped a T4 78/75 with a t6 S480 on marks mustang w/ no other changes. They state the S480 made boost more quickly and made about 100hp more across the board, at the same boost level. I've experienced the same. With my 2" divided hotside my S480 T6 4.8 setup spooled just as quickly as my 1.10 T4 S475 5.3 did on a 2.5" hotside. I had to take power OUT and limit boost by speed to get it to hook on the street with a 4.8! So why would anyone want a turbo that delivers 100 less HP at like boost levels and makes boost more slowly.
The OP has a goal. The T6 is better suited for a 370 w/ an 800whp goal, period.
Last edited by Forcefed86; 02-13-2023 at 03:28 PM.
ET is ENTIRELY dependent on the setup of the car. And MPH also is highly dependent on how well the car leaves, hooks, and translates power to the ground. Neither guarantee a fun street car and the inverse isn't guaranteed either. Plenty of big turbo cars are lousy on the street, and plenty of small turbo torque monsters are a blast on the street and run crap times at a track. This is exactly the problem. Most people buy a turbo too big because they want "efficiency" and "room to grow" and then have to change all sorts of stuff on their setup because they're "not using the turbo properly". Had they gone with a smaller turbo and used it where it's meant to be or max it out, the car would be exactly what they wanted. The dude could literally spend less than $300, have an easier time packaging it in the truck, and see how he likes it with minimal work. I'd love to hear the example of when someone SHOULD use a small T4, because everyone now pushes 80+mm T6 turbos.
Zero panty wad. Just trying to give facts to someone instead of opinions. Everything you've stated is opinion as you have given no direct comparison to other turbos. I've literally run a T4 S476 and switched to a T6 S480 on a 370 engine with no other changes... Have you?
I get not everyone is building a "race car". To say things like "et" and "trap speed" don't matter is ridiculous. That is data that directly correlates to acceleration and performance. Which is the whole point of building any turbo car. He gives an exact power amount... and 800whp doesn't describe a nice driving street car. You can't plane 800WHP on a street car. I've ditched all the T4 turbos as singles long ago. And no, that doesn't mean it will lag more than a t4. My T6 setups are better all around.
Matt Happel swapped a T4 78/75 with a t6 S480 on marks mustang w/ no other changes. They state the S480 made boost more quickly and made about 100hp more across the board, at the same boost level. I've experienced the same. With my 2" divided hotside my S480 T6 4.8 setup spooled just as quickly as my 1.10 T4 S475 5.3 did on a 2.5" hotside. I had to take power OUT and limit boost by speed to get it to hook on the street with a 4.8! So why would anyone want a turbo that delivers 100 less HP at like boost levels and makes boost more slowly.
The OP has a goal. The T6 is better suited for a 370 w/ an 800whp goal, period.
your experience is, I’ll admit, much more than mine on race cars. I’ve built two street cars, including the complete manifolds and exhaust, crossover, intercooler piping etc. one was. 5.7 and the other was a 6.0. Both had 7875’s and spooled quickly with no lag. Maybe he should take your advice and put a super large t6 on it so it’ll lag bad where the truck has a chance at hooking. Probably won’t be much fun to drive tho. Me, I’d rather have something fun to drive and the turbo doesn’t come on like a light switch. I watched a dyno test last night with a comparison between a 7875 gen2 and a s475 and the s475 came on sooner but didn’t make the power that the 7875 did. Then I watched another t6 s475 vs 7875 gen2 and the t6 version lagged badly(which was mentioned) and it did make more power than the 7875. In my opinion, the 7875 is a good choice for a middle ground whereas the s475/80 have too many choices and if you choose it the wrong way, it’ll be a dog or it’ll fall on its face in the upper rpm. Seems like the 7875 is a better all around, no thought-choice. But hey, whatever. Ain’t my car/truck.
Alright, I have read through this multiple times.. Both the 7875 and the s475 are what I have narrowed it down to for sure--I see @Kfxguy had a few videos of his with the 7875 and that thing seems to run!
Pretty torn on what to buy--hopefully within the next month or two so still time to decide.
I do believe both will meet my goals wit the s475 being a little better on spool with a drop in power up top
also allows me to go bigger later if I want
EDIT: may do t4 still undecided. I want to use a truck exhaust turbo log/manifold with a t4 flange already on it
Alright, I have read through this multiple times.. Both the 7875 and the s475 are what I have narrowed it down to for sure--I see @Kfxguy had a few videos of his with the 7875 and that thing seems to run!
Pretty torn on what to buy--hopefully within the next month or two so still time to decide.
I do believe both will meet my goals wit the s475 being a little better on spool with a drop in power up top
also allows me to go bigger later if I want
EDIT: may do t4 still undecided. I want to use a truck exhaust turbo log/manifold with a t4 flange already on it
keep in mind, the t4 s475 spooled sooner than the 7875 but the t6 s475 spooled much later than the 7875.
also. I found this out over this past week. If you have a restrictive exhaust after the turbo, it will spool later.
I built a muffler (not modified but built the whole thing) that is muffled on one side and straight through on the other. I had to do some adapting to get it to work with my current exhaust until I can rebuild the whole thing (this weekend). I’ve noticed even though the exhaust is straight through with the cutout open, it spools slower than it did when I had a cutout close to the turbo. It probably lags another 1500-2000rpm. So a free flowing exhaust helps.
If I was ever going to upgrade, it would be this turbo or the gen 3. But as I mentioned earlier, I upgraded the housing and seems to do what I want. It used to only be able to make about 18lbs in 3rd but now it’ll make 21 in second (maybe 16 before) and 24 in third now. I still have more I can do if I wanted to make more power, but I’m not worried about it right now.
I went to roll race someone last night. Like an idiot, I turned it up because I wanted to really hurt their feelings (it was a 392 charger) and for a 50-60 it’ll spin still but it’s manageable. He made me slow to a 30 and that’s a bad idea for me. I left it in second, he hit them I hit and it obliterated the 275 drag radials and almost spun around in the middle of the road. Yea…no. I didn’t have time to turn it back down at that time. Had to make new maps last night to counter that.
ET is ENTIRELY dependent on the setup of the car. And MPH also is highly dependent on how well the car leaves, hooks, and translates power to the ground. Neither guarantee a fun street car and the inverse isn't guaranteed either. Plenty of big turbo cars are lousy on the street, and plenty of small turbo torque monsters are a blast on the street and run crap times at a track. This is exactly the problem. Most people buy a turbo too big because they want "efficiency" and "room to grow" and then have to change all sorts of stuff on their setup because they're "not using the turbo properly". Had they gone with a smaller turbo and used it where it's meant to be or max it out, the car would be exactly what they wanted. The dude could literally spend less than $300, have an easier time packaging it in the truck, and see how he likes it with minimal work. I'd love to hear the example of when someone SHOULD use a small T4, because everyone now pushes 80+mm T6 turbos.
The reason they all run big turbos now is because they all want 1000hp. I think someone should go with a T4 if they have a realistic goal of 600ish whp for a snappy street car. Esp. with a manual trans. But there are much "snappier" turbos than the 78/75. Also if a "less snappy turbo" can make 100 more HP at like boost, then this also means it can make the same power as the 78/75 at less boost. As I mentioned the 78/75 is a flawed design by nature anyway with too large of a compressor wheel VS exh. wheel. I'd suggest an S475-s476 over it, as they perform better in my experience. Its simply a better design. If you look at the "Race" turbo T4 lines form Precision you see the same trend. They go bigger on the exh wheels. If I were to go T4 again on a budget, I'd go with another S476 w/ 87/96 exh wheel in a modified 1.25 T4. That turbo ran great and picked up just under 5 mph when maxed out on my car over the standard cast small 1.10 T4 S475.
As far as going too big and having poor response, that sounds more like a tuning or hotside issue. As I mentioned, with a super tame 4.8 I was making way too much boost/power too quickly and had to dumb it down to get it to plant 30" MTDR's on the street. Tried slicks as well. With a healthy 370" motor and any S475 turbo, the last thing the OP is going to worry about is response. He will be pulling power trying to get it to hook, esp at 800ish hp levels.
Packaging can be a bear. No real way around that. I can say that I went from a T4 to a T6 S400 and it hardly took up anymore room on my car. I mean I had very small engine bay rx-7 with the flat factory hood. I did have to cut off the goofy marmon 5" DP flange and weld on a T4 V-band. Aside from that the old DP and all just slid into place.
Also I agree the older 78/75s are smaller than the S475s, but they don't perform near as well. The new 78/75's are the same size as the S400 turbos and cost alot more. I run 2 of them on my Model-T. I picked them for price and aesthetics. At they time they were one of the few available in mirror image.
Last edited by Forcefed86; 02-13-2023 at 04:00 PM.
keep in mind, the t4 s475 spooled sooner than the 7875 but the t6 s475 spooled much later than the 7875.
also. I found this out over this past week. If you have a restrictive exhaust after the turbo, it will spool later.
I built a muffler (not modified but built the whole thing) that is muffled on one side and straight through on the other. I had to do some adapting to get it to work with my current exhaust until I can rebuild the whole thing (this weekend). I’ve noticed even though the exhaust is straight through with the cutout open, it spools slower than it did when I had a cutout close to the turbo. It probably lags another 1500-2000rpm. So a free flowing exhaust helps.
So because you saw one comparison 2 different cars on a dyno, it means all will be have that way? A lot of how the turbo reacts and how it spools is dictated by the tune and part combo. Because you saw one T6 car spool slowly and another T4 spool quickly doesn't mean much. Unless they left the tune the same on the same car and swapped turbos only... that's not a comparison of anything. Also lets not forget the power differences at like boost. So even if the 78/75 is making more boost... it will be making less power.
As far as what a T4 S475 can do on a 6.0... Lets look at Stock48's times leaving on a foot brake. Remember the OP is talking about a 370" motor as well.
This is a 3350lb all steel nova with a baby cam. I've yet to see even the nice new 78/75's trap like that on a 3300lb car. He leaves on 1lb of boost on the foot brake. It spools VERY quickly. A T6 would worth 5mph easy and he could still leave on the foot brake.
T4 just makes it EASY compared to a t6 since I can mount it directly to a manifold(summit or cheapy from amazon).
I am still torn, yall aren't helping LOL--really you are. Thank you for the input.
s475 vs 7875 for 800rwhp. I would think a gen 3 would do it for sure.
If you want a T4 that performs well I'd spend the extra money and contact someone like Jose at Forced Inductions. I can see not wanting to fart w flanges. Though they do make bolt on T4 to T6 flanges. The $789 78/75 will fall short of your WHP goal with a 370 IMO. But it will still be "fun". Grab one of the cheaper small 78/75s and when your disappointed with it, just toss another one on the other side.
The new 78/75s are BIG. same size compressor as a T6 S400. I have 2 of them on one of my cars.
...Also if a "less snappy turbo" can make 100 more HP at like boost, then this also means it can make the same power as the 78/75 at less boost.
As far as going too big and having poor response, that sounds more like a tuning or hotside issue. As I mentioned, with a super tame 4.8 I was making way too much boost/power too quickly and had to dumb it down to get it to plant 30" MTDR's on the street. Tried slicks as well. With a healthy 370" motor and any S475 turbo, the last thing the OP is going to worry about is response. He will be pulling power trying to get it to hook, esp at 800ish hp levels..
Nobody cares about making the same power at less boost. Short of maxing out a turbo and dumping heat, no one cares if you have to run 20 psi instead of 16 when you're spooling 500 to 1000 rpms soon.
Youve posted enough about your own setup that we can agree that it's not the scenario that @Kfxguy and I are referring to. You post an example of car that weighs 3300lbs like it's impressive. That's featherweight. Your whole viewpoint is entirely skewed, and it's based your experience, which is totally cool. It's just not what we're talking about.
So because you saw one comparison 2 different cars on a dyno, it means all will be have that way? A lot of how the turbo reacts and how it spools is dictated by the tune and part combo. Because you saw one T6 car spool slowly and another T4 spool quickly doesn't mean much. Unless they left the tune the same on the same car and swapped turbos only... that's not a comparison of anything. Also lets not forget the power differences at like boost. So even if the 78/75 is making more boost... it will be making less power.
As far as what a T4 S475 can do on a 6.0... Lets look at Stock48's times leaving on a foot brake. Remember the OP is talking about a 370" motor as well.
This is a 3350lb all steel nova with a baby cam. I've yet to see even the nice new 78/75's trap like that on a 3300lb car. He leaves on 1lb of boost on the foot brake. It spools VERY quickly. A T6 would worth 5mph easy and he could still leave on the foot brake.
the test was back to back. Same engine. Turbo swap only. Not two different cars.
you posting an 8.90 slip. Good for you. Where in this thread do you get the idea that the op, having a street truck, indicated he wanted to go 8’s? You way off in left field bro.
op, while you are at putting a 90mm t6, go ahead and tube chassis it, big block on methanol, tub it out, put a holley computer in it. I mean why not? Just skip the fun street car, that’s what this dude what’s you to do. Hell, might as well skip all that and build a funny car, just forget about the truck. You set out for 800hp but might as well add another 0 to it and make it 8000hp. People crack me up!
02-11-2023, 12:32 PM
I.E., In a perfect world with every part perfect and 5% driveline loss. 
