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-   -   How much boost is safe? gen4 6.0/l92/7875 (https://ls1tech.com/forums/forced-induction/1912563-how-much-boost-safe-gen4-6-0-l92-7875-a.html)

CasperCasper 12-30-2018 10:23 PM

How much boost is safe? gen4 6.0/l92/7875
 
Well all the parts are in, engine is torn down and I'm just past the halfway point with my turbo build. I've got a 3rd gen LQ4 I'm doing 4th gen pistons and rods in. Cam is a 225/230/112. Heads are L92s. Going in a second gen camaro, 3400ish lbs, 3:08 rear gear and a 4 speed. Turbo is a VS 7875 We've got 94 octane fuel up and here and I'm trying to figure out what a safe boost number is. Should this last on 12 lbs? Car will have about 20 passes a season on it and driven on the street lots. Any idea what kind of power it will make?

Game ova 12-30-2018 10:31 PM


Originally Posted by CasperCasper (Post 20023214)
Well all the parts are in, engine is torn down and I'm just past the halfway point with my turbo build. I've got a 3rd gen LQ4 I'm doing 4th gen pistons and rods in. Cam is a 225/230/112. Heads are L92s. Going in a second gen camaro, 3400ish lbs, 3:08 rear gear and a 4 speed. Turbo is a VS 7875 We've got 94 octane fuel up and here and I'm trying to figure out what a safe boost number is. Should this last on 12 lbs? Car will have about 20 passes a season on it and driven on the street lots. Any idea what kind of power it will make?

Probably 600. I just wonder if you are attempting to run one of the old school 4 speeds behind this mill, if so, I don't see it lasting long.

forcd ind 12-31-2018 05:43 AM

The tune is going to be important, when the boost comes in, where the timing is, fuel, etc.
You can take two identical engines, one guy can drive it all year, the other guy will blow it up
in a day, lol. Are you intercooling it, 12 lbs should be safe, I ran a sim engine and its over
4 years old and still going strong.

jimmyg 12-31-2018 06:03 AM

Gapping rings, robust fuel system, meth,good tune. All these things will make it live a long time . Nobody stays at 10 -12 lbs . So you might as well take care of these things now and not have issues later.














JoeNova 12-31-2018 06:23 AM

You're not going to break it with a 7875. That's a really poor turbo choice for that combo.

CasperCasper 12-31-2018 02:15 PM


Originally Posted by Game ova (Post 20023215)
Probably 600. I just wonder if you are attempting to run one of the old school 4 speeds behind this mill, if so, I don't see it lasting long.

The trans is fully built, not just a standard 4 speed haha. Rollerized, custom gear set etc. I sure hope it lasts. Got it out of a late 90s nascar as weird as that sounds.


Originally Posted by forcd ind (Post 20023258)
The tune is going to be important, when the boost comes in, where the timing is, fuel, etc.
You can take two identical engines, one guy can drive it all year, the other guy will blow it up
in a day, lol. Are you intercooling it, 12 lbs should be safe, I ran a sim engine and its over
4 years old and still going strong.

Ya I've got a pretty big intercooler for it, the biggest I can fit. Its approx 33 x 13x 3.


Originally Posted by JoeNova (Post 20023264)
You're not going to break it with a 7875. That's a really poor turbo choice for that combo.

Why do you say that? My goal was to have a lighswitch like combo for fun street use with my 4 speed. I had fun with 430whp so I'm sure 600ish will be fun!

JoeNova 12-31-2018 02:19 PM

If a quick 600 is what you want, it'll make it.

Game ova 12-31-2018 02:21 PM

A China 7875 turbo is enough to take you to low 9s (at your weight) if you turn it up. Oh, and put a Hydramatic in it.

SLOW SEDAN 12-31-2018 03:03 PM

Those old 4 speeds are cool! I ran a 76/75 on a 6.0 with more then double the boost your planning on, was fun to drive and spooled up quick.



Originally Posted by JoeNova (Post 20023458)
If a quick 600 is what you want, it'll make it.

Agree, 76mm doesn't have enough balls to hurt gen 4 internals. He can have fun with it and not worry about it.


Originally Posted by Game ova (Post 20023461)
Oh, and put a Hydramatic in it.

I'd rather walk! hydra anything turns cars into boring piles of shit lol If you cant run 10's with a manual turbo LS then you are just doing it wrong.

Game ova 12-31-2018 04:23 PM


Originally Posted by SLOW SEDAN (Post 20023482)
Those old 4 speeds are cool! I ran a 76/75 on a 6.0 with more then double the boost your planning on, was fun to drive and spooled up quick.




Agree, 76mm doesn't have enough balls to hurt gen 4 internals. He can have fun with it and not worry about it.



I'd rather walk! hydra anything turns cars into boring piles of shit lol If you cant run 10's with a manual turbo LS then you are just doing it wrong.

I used to be a fan of rowing gears, until I realized a few things. I was sick of the heavy clutch in stop and go situations, the cost of clutch required to reliably hold what the car makes, also didn't really care for continually unloading the suspension between shifts. Last but certainly not least is, I know a guy with the exact same car as I, makes the same power.... but was lightyears faster only because of his th400 (rear end too). That was the tipping point, well that and just enjoying driving the car more. One more thing, I can completely rebuild this 400 for a fraction of what your clutch cost, nevermind the fact that it will also live longer.

ddnspider 12-31-2018 04:29 PM

OP- Thats going to be a great driver combo that will be tons of fun on the street.

CasperCasper 12-31-2018 07:45 PM


Originally Posted by SLOW SEDAN (Post 20023482)
Agree, 76mm doesn't have enough balls to hurt gen 4 internals. He can have fun with it and not worry about it.
.

Awesome! That's really what I'm hoping for. So leave it at 10 and thrash on it by the sounds of things :)

badass68 12-31-2018 09:00 PM

4 speeds like a M22 and super T-10 are much stronger than T-56ís. After all they were put behind factory Big blocks. Iíve ran them and theyíre fun till you start making power faster then you can shift. With a turbo, you wonít mis a standard. IMO lower power, standard is more fun and 500+ automatic all the way.

Game ova 12-31-2018 09:13 PM


Originally Posted by SLOW SEDAN (Post 20023482)
Those old 4 speeds are cool! I ran a 76/75 on a 6.0 with more then double the boost your planning on, was fun to drive and spooled up quick.




Agree, 76mm doesn't have enough balls to hurt gen 4 internals. He can have fun with it and not worry about it.



I'd rather walk! hydra anything turns cars into boring piles of shit lol If you cant run 10's with a manual turbo LS then you are just doing it wrong.


Originally Posted by badass68 (Post 20023643)
4 speeds like a M22 and super T-10 are much stronger than T-56ís. After all they were put behind factory Big blocks. Iíve ran them and theyíre fun till you start making power faster then you can shift. With a turbo, you wonít mis a standard. IMO lower power, standard is more fun and 500+ automatic all the way.

Factory big blocks back then made all of 230.... at the crank, and the torque of the average turbo setup is on a different planet as well. But yea, I'm with ya, hydra is killing in boost land. (Didn't mean to quote all that)

Luke19901 01-01-2019 09:03 AM

Why do you say that? My goal was to have a lighswitch like combo for fun street use with my 4 speed. I had fun with 430whp so I'm sure 600ish will be fun![/QUOTE]


75mm turbine is very very small for 6.0

I would be starting at 7-8psi and adding one at a time. exhaust back pressure, boost and power graph will tell you when you're reaching the point the turbine is choking and back pressure is building.

I would thing that 10 psi vs 12 psi... the 12 psi graph will roll over earlier, make peak power at lower RPM and the boost will fall away with RPM. that's the signs of back pressure and turbine flow reaching limits..... use the data to tell you if 12 psi is doable.

if you're finding you have issues with detonation at 12 psi that another indication there is a turbine flow restriction. you'd be far better off with a T4 75mm borg warner turbo on 6.0 and pump. 6.0 will spool even a big turbo pretty quickly


CasperCasper 01-01-2019 09:35 PM

Thank you all very much for the detailed replies! I've actually got a lot of money sunk into my trans, bellhousing clutch etc. I totally see the appeal of an auto price wise but I just love rowing gears!

SLOW SEDAN 01-02-2019 09:59 AM


Originally Posted by Game ova (Post 20023519)
I used to be a fan of rowing gears, until I realized a few things. I was sick of the heavy clutch in stop and go situations, the cost of clutch required to reliably hold what the car makes, also didn't really care for continually unloading the suspension between shifts. Last but certainly not least is, I know a guy with the exact same car as I, makes the same power.... but was lightyears faster only because of his th400 (rear end too). That was the tipping point, well that and just enjoying driving the car more. One more thing, I can completely rebuild this 400 for a fraction of what your clutch cost, nevermind the fact that it will also live longer.

Only heavy clutch I've had is stupid single disks, the dual and triple setups have been fine. Clutch for 1000hp is basically same price as a good converter. Clutch can be rebuilt for $200 so not exactly a big expenditure when the auto trans took $100 of fluid every few months.

ddnspider 01-02-2019 10:30 AM

I had a 76gts on my 383 and it was GREAT on the street, and not bad at the track either (mid 10's @3800lbs). Yes, I could have use a larger turbine, but after mapping it out and talking with Jose at Forced Inductions....his words exactly were "383 stick for the street, T76GTS. 383 stick for the track, T88."

SLOW SEDAN 01-02-2019 01:15 PM


Originally Posted by ddnspider (Post 20024257)
I had a 76gts on my 383 and it was GREAT on the street, and not bad at the track either (mid 10's @3800lbs). Yes, I could have use a larger turbine, but after mapping it out and talking with Jose at Forced Inductions....his words exactly were "383 stick for the street, T76GTS. 383 stick for the track, T88."

76/75 was good for the street, but so were two 69/73's lol Not sure why guys like Jose and LJMS are hung up on a manual not spooling a turbo, in many cases the manual can actually spin them up faster then the auto. Those guys swore an 80mm would be too big, then an 85mm would be too big, swore a 91mm would be too big, swore twin 76's would be too big, but only keeps getting faster. Same guys said a manual needed to use a smaller cam, get the fuck outta here with that nonsense lol Went to a bigger cam and went faster, not shocking.

ddnspider 01-02-2019 02:26 PM


Originally Posted by SLOW SEDAN (Post 20024368)
76/75 was good for the street, but so were two 69/73's lol Not sure why guys like Jose and LJMS are hung up on a manual not spooling a turbo, in many cases the manual can actually spin them up faster then the auto. Those guys swore an 80mm would be too big, then an 85mm would be too big, swore a 91mm would be too big, swore twin 76's would be too big, but only keeps getting faster. Same guys said a manual needed to use a smaller cam, get the fuck outta here with that nonsense lol Went to a bigger cam and went faster, not shocking.

I'm not saying there aren't better turbos out there for the c.i., but I think for the goals it can do the job well enough and give better area under the curve depending on the intended RPM range.


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