6870 DBB .85 A/R 3 Bolt Buick Housing-Backpressure Data

jmendlik

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Oct 1, 2001
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Anyone else have any data on backpressure logging using this turbo on a 231-250 CU Buick Engine?

Heard alot of discussions that this turbo has very high pressures (2:1 or more even on low boost) with the 3 bolt .85a/r setup. Looking for data points...Seen data with 274 CU engine only..



JM
 
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87GN_Bart

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Jul 12, 2016
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Great turbo for 109, experience back pressure with the 274 motor at 28 plus lbs of boost. I ran 9.40 at 146 with the 4.1, great all around turbo, spools like an NA car.
 

jmendlik

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Oct 1, 2001
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My first hit with low boost on my 250 CU stroker motor with 12psi boost netted 17psi Back pressure. 1.44:1

will test at higher boost when rain stops and my new transducer arrives tommorow.

Im using a TurboSmart EBoost street electronic boost controller( 1 solonoid ) to control the gate and so far all is good. I have a 12psi spring in my PTE 46MM Waste gate and the controller is turned off--for now..WIll be adding boost tomorrow and see where this all goes.


PTE 46MM Gate dumped to open air & 3" THDP.....
 
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forcefed3.8's

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May 26, 2002
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I dont see where it makes a huge gain in my experience. I switched from a 7168 to a 7270. It gained back pressure for sure, had to add co2 pressure to the gate to get lost boost back. So far I have picked up 1.2mph in the 1/4 and still havent gotten all the boost back.
 
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troyk

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Jun 7, 2001
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When I bought my 6870, Precision salesman suggested that he would de-rate the turbo by 200hp if on 3-bolt.

I plan to have all the needed sensors installed on my car for this info, but it is not running yet & it is a 4-bolt, stroked.
Currently waiting on the fab shop on liq intercooler & dp. And waiting for the PnP mega squirt to come out. The motor is in the car.
 

forcefed3.8's

Buckeye Bullet
May 26, 2002
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North Ridgeville, Ohio
I made more with a 7168, but with a better intercooler, and more timing and a leaner AFR. They are very close, if you arent in the 8s, it is doubtful you will see a difference. If I had to pick between the 2, I would go with the 7168 just because back pressure was lower, so it will be easier to make power if your set up isnt optimum for back pressure.
 
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007gn

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Nov 25, 2011
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Who makes a 7270 turbo ??? I have the 6870 already. Is back pressure any less when using a 3.5 inch dp compared to using a 3 inch dp with the 6870 in a 3 bolt housing.
 

forcefed3.8's

Buckeye Bullet
May 26, 2002
3,571
610
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37
North Ridgeville, Ohio
Who makes a 7270 turbo ??? I have the 6870 already. Is back pressure any less when using a 3.5 inch dp compared to using a 3 inch dp with the 6870 in a 3 bolt housing.
Thee 7270 is custom from Precision. I dont have real numbers to answer your 3vs3.5 down question. I would never use a 3" on a set up looking for low 10s or faster.
 
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007gn

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Nov 25, 2011
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Thee 7270 is custom from Precision. I dont have real numbers to answer your 3vs3.5 down question. I would never use a 3" on a set up looking for low 10s or faster.
Thanks for taking the time to respond. I decided to go with the .96 V band housing and also I’m going to do a 3.5 inch downpipe from GN one and alter it as needed and I’ll just weld the Vband flangeon my current three boat header. I’m hoping the 1201x valve springs are enough for my 224/224 camshaft & 1.7 rockers. I have a 18 Blade ptc nl & 3.23 gears im using a precision front mount intercooler . Gn1 race ported heads & Champion on center intake with 80 pound injectors and Alky With RaceTronics double pumper. Any help or Advice is well appreciatedI the car will Be street driven & raced a lot against v8s With power adders so I need to be fast as it should be Mike from Full Throttle handled the build of the engine and its parts Soon as he finishes buttoning everything up I’m going to set it back down in the car and wrap things up from there and of course I’ll keep you and everyone posted on his progress
 

007gn

Active Member
Nov 25, 2011
126
28
28
When I bought my 6870, Precision salesman suggested that he would de-rate the turbo by 200hp if on 3-bolt.

I plan to have all the needed sensors installed on my car for this info, but it is not running yet & it is a 4-bolt, stroked.
Currently waiting on the fab shop on liq intercooler & dp. And waiting for the PnP mega squirt to come out. The motor is in the car.[/QUOTEyes I’m looking forward to seeing how well that ms3 performs also.