Notices
Forced Induction Superchargers | Turbochargers | Intercoolers

Is backpressure not an issue if power goals are low?

 
Old 11-28-2018, 09:56 PM
  #1  
TECH Enthusiast
Thread Starter
iTrader: (1)
 
foxsl's Avatar
 
Join Date: Jan 2014
Posts: 520
Likes: 0
Received 1 Like on 1 Post
Default Is backpressure not an issue if power goals are low?

I always wanted a Borg Warner s400 75 mm to put into my 6.0 lq4 (gen 4 rods) mustang. The issue is that it is HUGE and a pain to fit. I will probably never ever see the full potential of it as my ultimate street car goal is only 600 rwhp. Realistically 520-550 rwhp daily driven. Lq4 has a btr stage 2 turbo cam.

So I've been thinking of a much smaller turbo to go with that will still give me my 550 rwhp goal. However I've read that turbos with small exhaust wheels and housings really restrict larger displacement engines like a 6.0.

I suppose a safe rpm to stay under 6500 rpm with boost so let's say it will rev to 6300.
Let me know how damaging backpressure would be.
foxsl is offline  
Old 11-28-2018, 10:00 PM
  #2  
Launching!
iTrader: (3)
 
Join Date: Mar 2013
Location: Lincolnton nc
Posts: 218
Likes: 0
Received 0 Likes on 0 Posts
Default

I made 580whp on a 78/75 on 3 t4 turbo a few years back on 10/11psi, 6.0, had the wrong cam and would break up above 6200,
ls13ater is offline  
Old 11-28-2018, 10:20 PM
  #3  
TECH Regular
iTrader: (16)
 
007FJ's Avatar
 
Join Date: May 2014
Location: Texas Gulf Coast
Posts: 473
Likes: 0
Received 0 Likes on 0 Posts
Default

I’m no expert but read stock 48 builds on his truck and nova. You can go small and make your power needs easy.
007FJ is offline  
Old 11-28-2018, 10:22 PM
  #4  
TECH Regular
iTrader: (16)
 
007FJ's Avatar
 
Join Date: May 2014
Location: Texas Gulf Coast
Posts: 473
Likes: 0
Received 0 Likes on 0 Posts
Default

I mean that stock48 made some major power on less than giant turbos so you can meet your goals easy I believe
007FJ is offline  
Old 11-28-2018, 10:23 PM
  #5  
TECH Enthusiast
Thread Starter
iTrader: (1)
 
foxsl's Avatar
 
Join Date: Jan 2014
Posts: 520
Likes: 0
Received 1 Like on 1 Post
Default

Originally Posted by ls13ater View Post
I made 580whp on a 78/75 on 3 t4 turbo a few years back on 10/11psi, 6.0, had the wrong cam and would break up above 6200,
do you think it was breaking up from the spark plug flame being blown out?
foxsl is offline  
Old 11-28-2018, 10:25 PM
  #6  
TECH Enthusiast
Thread Starter
iTrader: (1)
 
foxsl's Avatar
 
Join Date: Jan 2014
Posts: 520
Likes: 0
Received 1 Like on 1 Post
Default

Originally Posted by 007FJ View Post
I mean that stock48 made some major power on less than giant turbos so you can meet your goals easy I believe
Stock48 got me interested in LS turbo setups 4 years ago from his results but I think the setup I was reading about had a borg warner s400 being used.
foxsl is offline  
Old 11-28-2018, 10:36 PM
  #7  
TECH Veteran
iTrader: (22)
 
truckdoug's Avatar
 
Join Date: Nov 2013
Location: Portlandia
Posts: 4,874
Received 2 Likes on 2 Posts
Default

I had a china billet 7875 on a mild cammed 6.0 and it was ridiculous. torque for days.
truckdoug is offline  
Old 11-28-2018, 11:00 PM
  #8  
TECH Regular
iTrader: (16)
 
007FJ's Avatar
 
Join Date: May 2014
Location: Texas Gulf Coast
Posts: 473
Likes: 0
Received 0 Likes on 0 Posts
Default

I went Pte 76/75 billet on mine right now because I’m not giving up on ac. I’m about 90% complete from the t56 procharger setup to a 4l80 / v3 Huron speed combo. I have afr 225s on a built iron block. I hope to make at least something above 800. I think it’s going to roll pretty good regardless. 3.50 Midwest 9 and a 258 circle d triple.
007FJ is offline  
Old 11-29-2018, 12:39 AM
  #9  
12 Second Club
iTrader: (3)
 
Redbull87's Avatar
 
Join Date: Nov 2010
Location: Toronto Ontario Canada
Posts: 666
Likes: 0
Received 0 Likes on 0 Posts
Default

Excessive backpressure makes for an unhappy motor longevity wise. I can tell you as of last week seeing my gains of eliminating as much backpressure as i could.I went from 692whp and 650tq to 766whp/811tq on less boost.My only changes were adding bigger e-cutout and fender exit exhaust. Im running a t4 turbo on a cammed 6.0 that felt lazy until now.
Redbull87 is offline  
Old 11-29-2018, 01:06 AM
  #10  
TECH Veteran
iTrader: (22)
 
truckdoug's Avatar
 
Join Date: Nov 2013
Location: Portlandia
Posts: 4,874
Received 2 Likes on 2 Posts
Default

i was thinking we're talking pre turbine backpressure aka drive pressure
truckdoug is offline  
Old 11-29-2018, 01:06 AM
  #11  
TECH Enthusiast
Thread Starter
iTrader: (1)
 
foxsl's Avatar
 
Join Date: Jan 2014
Posts: 520
Likes: 0
Received 1 Like on 1 Post
Default

Originally Posted by Redbull87 View Post
Excessive backpressure makes for an unhappy motor longevity wise. I can tell you as of last week seeing my gains of eliminating as much backpressure as i could.I went from 692whp and 650tq to 766whp/811tq on less boost.My only changes were adding bigger e-cutout and fender exit exhaust. Im running a t4 turbo on a cammed 6.0 that felt lazy until now.
What are your turbo specs? Wow huge gains, what boost pressure was this at?
foxsl is offline  
Old 11-29-2018, 01:12 AM
  #12  
TECH Enthusiast
Thread Starter
iTrader: (1)
 
foxsl's Avatar
 
Join Date: Jan 2014
Posts: 520
Likes: 0
Received 1 Like on 1 Post
Default

I made this thread basically to see if my btr stage 2 turbo cammed lq4 6.0 could use a t4 CX racing Gt45 turbo that has a 1.15 AR turbine, 76 mm compressor wheel (103 mm exducer) and 77.4 mm turbine along with a 88.9 mm inducer.

If someone thinks this turbo will cause back pressure issues on a 6.0, please let me know and if so, how damaging is that back pressure in this situation with a 550 rwhp goal.
foxsl is offline  
Old 11-29-2018, 01:54 AM
  #13  
TECH Regular
iTrader: (16)
 
007FJ's Avatar
 
Join Date: May 2014
Location: Texas Gulf Coast
Posts: 473
Likes: 0
Received 0 Likes on 0 Posts
Default

You will be fine at that power level
007FJ is offline  
Old 11-29-2018, 02:33 AM
  #14  
TECH Junkie
iTrader: (1)
 
Join Date: Sep 2004
Location: Stockbridge GA
Posts: 3,101
Likes: 0
Received 0 Likes on 0 Posts
Default

Originally Posted by foxsl View Post
I made this thread basically to see if my btr stage 2 turbo cammed lq4 6.0 could use a t4 CX racing Gt45 turbo that has a 1.15 AR turbine, 76 mm compressor wheel (103 mm exducer) and 77.4 mm turbine along with a 88.9 mm inducer.

If someone thinks this turbo will cause back pressure issues on a 6.0, please let me know and if so, how damaging is that back pressure in this situation with a 550 rwhp goal.
You would very likely hit your modest goals safely with an even smaller turbo. Numerous LQ9 Escalades are running low 12 sec times with 67mm Garrett clones. Foot braking 5 or 6 lbs of boost makes for serious instaspool. I would not recommend going that small, but that is just an example of how little you need to worry about this.
gametech is offline  
Old 11-29-2018, 03:03 AM
  #15  
TECH Enthusiast
Thread Starter
iTrader: (1)
 
foxsl's Avatar
 
Join Date: Jan 2014
Posts: 520
Likes: 0
Received 1 Like on 1 Post
Default

Originally Posted by gametech View Post
You would very likely hit your modest goals safely with an even smaller turbo. Numerous LQ9 Escalades are running low 12 sec times with 67mm Garrett clones. Foot braking 5 or 6 lbs of boost makes for serious instaspool. I would not recommend going that small, but that is just an example of how little you need to worry about this.
That is good to hear, I am excited to try something that I can fit somewhat sanely into my engine bay.
foxsl is offline  
Old 11-29-2018, 03:15 AM
  #16  
TECH Junkie
iTrader: (1)
 
Join Date: Sep 2004
Location: Stockbridge GA
Posts: 3,101
Likes: 0
Received 0 Likes on 0 Posts
Default

Originally Posted by foxsl View Post
That is good to hear, I am excited to try something that I can fit somewhat sanely into my engine bay.
Just keep in mind that if you do go with a fast spooling small turbo, you cannot just keep turning it up. At some point you will be doing little more than heating your intake charge. This can put you in dangerous territory for detonation. As long as you stick to realistic goals, you can have one hell of a fun ride. Too small or too big will leave you disappointed, broke, or both. edit-- Your rpm goals are not necessary for your HP goals. The small turbos on big motors make huge torque numbers without spinning too high.
gametech is offline  
Old 11-29-2018, 03:46 AM
  #17  
TECH Enthusiast
Thread Starter
iTrader: (1)
 
foxsl's Avatar
 
Join Date: Jan 2014
Posts: 520
Likes: 0
Received 1 Like on 1 Post
Default

Originally Posted by gametech View Post
Just keep in mind that if you do go with a fast spooling small turbo, you cannot just keep turning it up. At some point you will be doing little more than heating your intake charge. This can put you in dangerous territory for detonation. As long as you stick to realistic goals, you can have one hell of a fun ride. Too small or too big will leave you disappointed, broke, or both. edit-- Your rpm goals are not necessary for your HP goals. The small turbos on big motors make huge torque numbers without spinning too high.
What rpm would you safely take a setup like this 76 mm gt45 on a gen 4 bottom end 6.0?
I definitely hear you on the increased heat at high boost, however due to me having a turbo cam, I would guess that maybe I'd hit my 550 rwhp goal on around 11 psi or less with that turbo. I'll be using a 3 inch cored front mount intercooler.
foxsl is offline  
Old 11-29-2018, 12:53 PM
  #18  
TECH Fanatic
iTrader: (2)
 
Join Date: Nov 2015
Posts: 1,432
Likes: 0
Received 0 Likes on 0 Posts
Default

I make about 650 crank HP at 12-14psi on a stock 5.3 with a custom blower cam with a VS 78/75 cast turbo. Puts be around 550rwhp conservative. Enough that I needed DR's for the street. I also have the standard GT45 ebay special 1.05AR sitting in the box and I was going to use that on the cheap. But its a big, heavy, old school style turbo so i decided to slim it down and that GT45 is still sitting in the box lol. Ive run a 76/65, cast 78/75 and now getting ready for the billet wheel VS 78/75. They are CONSIDERABLY smaller and easier to package than the GT45 and they are a ALOT lighter. The 78/75s are good for 800hp which is about the limit of the 3" DP and the 3" Vband on the back of the turbo. Slap in the $400 VS cast 78/75 and boost to 11psi and you'll be set and make your power goal and have more to spare.

My 87 TA is a under bumper breather (very poor airflow to the FMIC and rad etc) and on the street in the hot *** summer 90+*F I see IATs in the 100-125*F range with the FMIC (cheap $90 ebay 3" IC) and then I have a small shot of wiper fluid which helps as I run **** 93 pump only gas. If I had better airflow would prob see slightly lower IATs. I was running a dual sensor IAT gauge pre and post IC and saw 150-170*F IATS pre IC and 100-130*F post intercooler before the meth activated.
customblackbird is offline  
Old 11-29-2018, 01:15 PM
  #19  
TECH Fanatic
iTrader: (1)
 
Kfxguy's Avatar
 
Join Date: Apr 2017
Posts: 1,643
Likes: 0
Received 2 Likes on 2 Posts
Default

Man look. You cannot go wrong in your situation with an on3 or VS racing cast 7875. I'd prefer a VS racing because Virin answers emails quickly and ships amazingly fast. This monday morning I ordered a billet 7875 to upgrade my cast 7875 and the new turbo was at my door step yesterday (Wednesday) when I got home.
I have a stage 2 BTR NA cam. Seems like the lobe seperation is the difference in the turbo version and NA version. Mine pulls to 7000 rpm. I have not dynoed the car but there no way its not over 550 rwhp on 10lbs. 5.7 with ported 243 heads and that cam. Just remember to change the plugs when you go boosted to a NGK TR7ef, lesson I just learned and the guys on this forum helped me out.

My setup currently has a 3" down pipe thats smashed to about 2" side where it goes inbetween the frame rails and manifold. fulls exhaust also. I recommend the 7875 because its smaller, spools really quick, cheap and will support more power than your goal.
Kfxguy is offline  
Old 11-29-2018, 02:14 PM
  #20  
TECH Enthusiast
Thread Starter
iTrader: (1)
 
foxsl's Avatar
 
Join Date: Jan 2014
Posts: 520
Likes: 0
Received 1 Like on 1 Post
Default

Originally Posted by Kfxguy View Post
Man look. You cannot go wrong in your situation with an on3 or VS racing cast 7875. I'd prefer a VS racing because Virin answers emails quickly and ships amazingly fast. This monday morning I ordered a billet 7875 to upgrade my cast 7875 and the new turbo was at my door step yesterday (Wednesday) when I got home.
I have a stage 2 BTR NA cam. Seems like the lobe seperation is the difference in the turbo version and NA version. Mine pulls to 7000 rpm. I have not dynoed the car but there no way its not over 550 rwhp on 10lbs. 5.7 with ported 243 heads and that cam. Just remember to change the plugs when you go boosted to a NGK TR7ef, lesson I just learned and the guys on this forum helped me out.

My setup currently has a 3" down pipe thats smashed to about 2" side where it goes inbetween the frame rails and manifold. fulls exhaust also. I recommend the 7875 because its smaller, spools really quick, cheap and will support more power than your goal.
I've considered the 7875 in the past but was always scared away as everyone said I will have big issues with the backpressure on a 6.0
Thanks for the info along with the other people that posted.

I'll just have to go with a 7875 and see how it works out. I've been told that I'd have extra hot exhaust gas temperatures that may burn out the exhaust valves and other issues but like a few have said, at the mild power level of 550 rwhp, I may be fine.

Last edited by foxsl; 11-29-2018 at 02:37 PM.
foxsl is offline  

Thread Tools
Search this Thread

About Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
 
  • Ask a Question
    Get answers from community experts
Question Title:
Description:
Your question will be posted in: