Is backpressure not an issue if power goals are low?
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.
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.
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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.
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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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 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.
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 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.
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; Nov 29, 2018 at 02:37 PM.