6870 vs 6875

[BrianJ]

Double post

Edited February 21, 2021 by BrianJ
Double Post

[BrianJ]

On 12/12/2020 at 6:17 PM, hattori hanzo said:

30psi on the nose 

it was not taking any more and making any more power, hoping the head unlocks a bit more and its capacity to take 35psi or so

Thats interesting as I also found the relative "limit" (you could always cram more I suppose) or point of diminished returns to be right at 33psi on my 6466 0.84 T4. I also had a similar best trap speed very close to yours at 147 and dyno'd at a smidge over 770 at that boost level, that setup was a 2.6L, 10:1 comp, 282s, and a PPG box. 

 

When you say not taking anymore, do you mean you were getting minimal gains like ~ 5 hp per additional PSI? Or had Boost Duty cycle/WG maxed out? 

 

Your car is always great to see and very well done. Congrats on a real weapon. 

[hattori hanzo]

On 21/02/2021 at 11:08 AM, BrianJ said:

Thats interesting as I also found the relative "limit" (you could always cram more I suppose) or point of diminished returns to be right at 33psi on my 6466 0.84 T4. I also had a similar best trap speed very close to yours at 147 and dyno'd at a smidge over 770 at that boost level, that setup was a 2.6L, 10:1 comp, 282s, and a PPG box. 

 

When you say not taking anymore, do you mean you were getting minimal gains like ~ 5 hp per additional PSI? Or had Boost Duty cycle/WG maxed out? 

 

Your car is always great to see and very well done. Congrats on a real weapon. 

It was putting on less, more like 2/3hp per psi so was pointless.

 

since we have added a 4" TBE, 1.15 rear housing and the new head hoping to get a bit more out of it by dropping the back pressure.

 

Machining delays have put a hault to the new build, but hopefully have the results in may or so i guess.

[Old man 32 GTR]

Back to turbo selection, just saw the new Garrett G40 1150, seems like it comes in t4 divided in all rear housing A/R’s. 
is this turbo comparable to what’s been discussed or does it fall into the big/laggy category. 
I’m going to give GCG a call today and have a chat about it 

[Lithium]

On 10/12/2020 at 9:21 PM, SiR_RB said:

68mm comp wheel will max out well before the 75 rear 

 

This was said ages ago but just for sake of accuracy - people have definitely been able to squeeze more out of the 6875 than they could with the 6875.   The turbine definitely helps, even if the 68mm compressor is pretty much tapped it does help squeeze enough that if you're looking for absolute max power from a 68mm inducer it's worth doing.

 

 

[r32-25t]

Would be nice if the 6875 was available with a twin scroll rear

[Old man 32 GTR]

On 7/4/2022 at 4:21 PM, r32-25t said:

Would be nice if the 6875 was available with a twin scroll rear

Yep, would be perfect if it did, don’t understand why as the 7675 has twin scroll rear and I may be wrong but I’m assuming the rear is the same. I spoke with a shop today who advised to go 7675 with the 1.12 twin scroll rear housing, with the correctly set up manifold (proper twin scroll) with twin gates, can get the 7675 to have the same/similar response as a 6870. 
for me this would be a wicked set up and if I decided to go sequential in the future would make more then enough power. 

[r32-25t]

All the gen2 precision with a 75 and above don’t have twin scroll options

[Piggaz]

On 7/4/2022 at 5:28 PM, Old man 32 GTR said:

Yep, would be perfect if it did, don’t understand why as the 7675 has twin scroll rear and I may be wrong but I’m assuming the rear is the same. I spoke with a shop today who advised to go 7675 with the 1.12 twin scroll rear housing, with the correctly set up manifold (proper twin scroll) with twin gates, can get the 7675 to have the same/similar response as a 6870. 
for me this would be a wicked set up and if I decided to go sequential in the future would make more then enough power. 

I find that extremely hard to believe. A 7675 is a significantly larger snail than a 6870. 

[BK]

On 07/04/2022 at 5:53 PM, r32-25t said:

All the gen2 precision with a 75 and above don’t have twin scroll options

They do. The Sportsman versions of the gen2 7675 and 7685 are available in divided T4 housings. Even the 8385 and 8685 has them available in T4 divided.

[r32-25t]

So it does, I never looked at that one before just looked at the first few and thought the rest must follow suit 

[BK]

On 07/04/2022 at 4:58 PM, Old man 32 GTR said:

Yep, would be perfect if it did, don’t understand why as the 7675 has twin scroll rear and I may be wrong but I’m assuming the rear is the same. 

Don't get too excited though as the Sportsman gen2 7675 rear housing don't fit the more common gen2 7675HP.

The Gen2 CEA 6875, 7275 or 7675 all share the exact same 75mm turbine wheel (82mm inducer, 75.08mm exducer) and fit turbine housing group E.

Other housings for different turbines include 62mm CEA - turbine group B, 66mm CEA - turbine group C, 70mm CEA - turbine group D, Promod - turbine group F.

On 07/04/2022 at 9:03 PM, r32-25t said:

So it does, I never looked at that one before just looked at the first few and thought the rest must follow suit 

Turbine groups B, C and D all have divided T4 housings available - turbine group E or F does not, so Brett is kinda sorta right when referencing turbos you'd actually use.

The Sportsman 7675 has a completely unique 82mm inducer 84 trim turbine wheel (which would have a bigger 75.16mm exducer according to my calculations) and unique internally bigger housing for itself, with a bigger exhaust discharge meant for 4 inch exhausts.

[jet_r31]

On 4/7/2022 at 4:58 PM, Old man 32 GTR said:

Yep, would be perfect if it did, don’t understand why as the 7675 has twin scroll rear and I may be wrong but I’m assuming the rear is the same. I spoke with a shop today who advised to go 7675 with the 1.12 twin scroll rear housing, with the correctly set up manifold (proper twin scroll) with twin gates, can get the 7675 to have the same/similar response as a 6870. 
for me this would be a wicked set up and if I decided to go sequential in the future would make more then enough power. 

We all wish... You cant beat physics.. Especially when they are all the same design... 😂 

Just adding the turbine from 70 to 75mm id expect it to be 500rpm lazier let alone bunging on a 8mm bigger comp wheel

[Lithium]

On 12/04/2022 at 2:00 PM, jet_r31 said:

We all wish... You cant beat physics.. Especially when they are all the same design... 😂 

Just adding the turbine from 70 to 75mm id expect it to be 500rpm lazier let alone bunging on a 8mm bigger comp wheel

Does my head in, I have no idea why workshops do that kind of thing - feels like it's just getting customers to dump all the money with them as well as ending up with a big number result at the end which get other people's attention, but pushes the person who is actually wanting to build their "dream vehicle" past the point of no return and it's now more or less a dedicated straight line acceleration car.   I guess if people believe it when they're given that speel they potentially are half trying to talk themselves into it anyway, in which case that's fine haha.

The only way that would seems plausible is if the rest of the setup has significantly changes, like adding a solid amount of displacement and/or fixing issues that the setup previously had haha.   Even then, with the huge amount of added "mass away from the axis" will cause a much much higher moment of inertia... if the threshold doesn't seem that much worse, the transient response will be rubbish by comparison.

I would wait for a couple of results to come out, but if you're looking for something bigger than a 6870 that still drives like a reasonable street setup then there is a possibility than the G40 1150 *could* be a really solid option.  I've already seen someone claim to go from a Precision 7275 to a G40 1150 and claim a significant improvement in driveability and not losing any power but no specific data yet.

The 6870 is something of a beast in terms of how much power it makes versus how usable it is, so really anything that is capable of making more power is likely to add more lag as well.   I suspect there may be interesting releases before the end of this year that could mix it up, but we'll see...

 

Edited April 12, 2022 by Lithium

[usmair]

A friend had a G35-1050 an RB30. Made 840hp and could not push further due to back pressure. They appear to be better suited to an Rb26

Switched to a 6875 and has made over 1000hp. That's peak power only for a few RPMs, call it 950hp for most of the top end rev range.

[Dose Pipe Sutututu]

On 13/04/2022 at 9:07 PM, usmair said:

A friend had a G35-1050 an RB30. Made 840hp and could not push further due to back pressure. They appear to be better suited to an Rb26

Hence the new G40 just makes so much more sense however not to say Precision turbos aren't good - they're king of big power.

[jet_r31]

Yep lith

Ill stick with 6870 for now

Whats coming out later in the year? 

[jet_r31]

On 4/13/2022 at 8:37 PM, usmair said:

A friend had a G35-1050 an RB30. Made 840hp and could not push further due to back pressure. They appear to be better suited to an Rb26

Switched to a 6875 and has made over 1000hp. That's peak power only for a few RPMs, call it 950hp for most of the top end rev range.

Out of interest on topic.. Off topic

Tao/hypergear can build a g35-1050 comp wheel turbo with a cut down gt42 turbine to 70mm in a bb housing for a pretty good price

Be cool to try seeing as its a more appropriatly sized turbine

Edited April 15, 2022 by jet_r31

[Old man 32 GTR]

On 12/4/2022 at 12:20 PM, Lithium said:

I guess if people believe it when they're given that speel they potentially are half trying to talk themselves into it anyway, in which case that's fine haha.

 

Lol, this 100% describes me, I just needed that little push. 
Its killing me because I want it to make big power, but I also want it to be able to make moderate power and be nice to drive (but I feel this will all come down to how good the tune is). 
obviously you can’t have your cake and eat it too in this scenario, I will be making sacrifices one way or another. 
A good friend of mine has been pushing me to a 7675 from the start, he was running this turbo on his 2.7 R34 was running this setup in front of a getrag and later an Albins sequential. I’ve been in that car and it was a little laggier then my 6870 (and my 6870 was bolted to a rb30. 
Well I now own a 6875 and a 7675 so I can go either way, but to be completely honest I never really liked the fact the 6875 was not twin scroll. I still like the G40 1150, maybe I should buy one of those too? Lol

[klutched]

Looking at downsizing from my 7685 down to a 6870 or G40-1150 to help keep the new box setup alive 😂 6875 was in the mix but as stated above, no twin scroll housings. Not sure if 6870 1.32 would be too small on a 3.4 or to step up to a 6875 .96 regardless of TS housing.