Precision 6765 turbo too small at 20+ psi????
 

So i ran my new precision 6765 billet turbo this last summer with a non divided t4 .96 ar housing. I started to turn up the boost to achieve 30psi. Im running full 3" exhaust with open a dump 46mm wastegate on a small street ported 13b-rew. At the end of the summer the turbo started to smoke under load so i sent it into precision for a rebuild. They warrantied the turbo but said that it looked like excessive thrust wear on the bearings and that its possible that there is too much manifold back pressure. I have not measured the back pressure but im thinking of switching to a bigger turbo with bigger more free flowing turbine designs. Im liking the comp turbo lineup.
So i guess im asking is what is your feed back is on a 6765 being too restrictive?

any thoughts on cranking up to a 3.5 or 4 downpipe?

Im going to do 4" for sure this spring but will that really free up that much back pressure from the manifold as thats my issue

oooops lol... went right past that info, lol!

Pics of manifold?

my 500R has zero problems after many years of hard abuse and road racing. I'm running a full 4 inch exhaust, A-Spec long runner mani.

I dont have a issue with my manifold im having a issue with the turbing wheel possibly not flowing enough* causing more back pressure. I have been talking to turblown about this and he thinks that the 65mm turbine wheel is too small for my application. Im sure the 500r kits works fine as the turbo from what i believe has a bigger turbine wheel as well as 4" exhaust is making a bigger difference than my application. Im looking to go 25-30 psi of boost.
Here is a pic of one of many manifolds i have built. im pretty sure the issue lies with this p trim turbine wheel
https://www.rx7club.com/fabrication-250/finally-fabricating-new-manifold-turbo-upgrade-945230/

Smg944 (525whp @ 27psi) , thewird, Prew and a few others are running this turbo over 20 psi if I remember correctly. I don't think any of them have had any problems as far back pressure issues. I've always been kind of dubious on the quality of Precision turbos. There's always stories floating around the interwebs, although this is hardly conclusive. Not to mention not a single compressor map to be found.
Though they are priced fairly competitively and I've got my eye one the newer Billet 6766.

Comp Turbo (Innovative Turbo) does have some interesting options. Stainless turbine housings, oil less center cartridges. Again I'm a little concerned about the quality. Innovative wasn't exactly known for making the most reliable turbos.

For me it's hard to beat an off the shelf Garrett. Even if they aren't optimally sized for rotary engines, it's hard to argue with off the shelf parts availability and quick turn around from just about any repair shop.

yes i agree. This is just what precision turbo told me they thought what caused the thrust wear. I did run the cast version of the 6765 last year pretty hard with not one issue so maybe its precision quality that caused the turbo to die early.
Supra owners do have good luck with comp turbo, precision and garrett turbo as well

+1

do you have a bb or journal 6765? could possibly be making a differance. i see 1850 F egt's at 27psi and i have made several pulls with it. i made 525 at 27psi and made 591 on 31psi 1 time. only reason it doesnt run 31psi usually is because i need to get a stronger spring to hold it there. fwiw i mostly run 23psi on pump gas and run 800cc of meth/water. egt on pump stays at 1800 F through 4th and 1850 F through 5th to 170+ mph. i like to run on the edge.

also you will see your turbine is maxed out when you flatline the powerband between 6500 and 8k rpms. have you dynoed your setup before?

my full setup a-spec billet bb 6765, big port, 3.5 dp, 3" rest of the way back and wastegate is re-routed. i did notice about a 50 F drop in egt with open dump but on upshifts it would give me a dead spot as if the boost was falling to fast and this effected my acceleration.

Does anyone have info on this turbocharger on low boost applications? Journal Bearing & Non billet.
10-14psi on a large street/race ported engine.
I was in the market between this and the T04S limited to 91 octane pump gas/low boost.
I've been searching for 2 weeks.

If you are planing on just running that amount of boost you would be better off with a GT35R or a T60-1 (T04S) depending on what your power goals are. The 67MM turbos, A-Spec 500R, T04R, T04Z, PTE 6765 really shine at higher pressure ratios 20+ PSI.

You could try a 1.15 or 1.32 A/R divided exhaust housing, and combine that with a 4" dump/ full 3.5" straight through system.

I think the 67mm compressor will be close to peak flow at the 600bhp power level. Remember rotary engines are about 15% less efficient than a 4 stroke gasoline piston engine.

67mm = 75lb/min air.

Well running petrol turbo = 0.53 BSFC
Well running rotary turbo = 0.62 BSFC

I'm pretty sure I had too much back pressure with my t04r with .96 undivided p trim and 3 exhaust. I've tried a 17 psi wg spring but still inconsistent boost boost control with high boost above about 22 psi, and the wg would start opening too soon regardless of ebc start boost setting. so I just upgraded to a divided 1.32 turbine housing, the car feels the same accelerating until the tires break loose and boost threshold feels about the same. I should be getting my car back today with a 4" dp and midpipe and then will do more testing to see how it helps.

"67mm = 75lb/min air"

Will a turbo actually flow more lbs/min than its rated at if you give it a larger turbine housing like a 1.32 a/r and a 4" exhaust? Or is that rating a maximum its capable of.

something to consider when i raise boost

its a jb billet 6765. your setup is about edentical to mine.

im running about 930cc of water tho at 250psi and i have dont pulls over 170 with no issues.
This is just what precision is telling me guys but i have ran this setup all last year really hard with not one issue so im starting to think that the turbo size is just fine and that precisions bearing failed.
I dyno'd the cast 6765 last year and my graph is very linear so your right im sure its just fine.It made 535hp on 20psi on pump and pre turbo water injection (straight water) my boost holds well at whatever i set it at. I think a full 4" exhaust and slap the turbo back on and it will be fine.
And fwiw "Jobro" the car is already making over 600hp at the crank (bhp)

True.

Precision rates 67mm billet wheel at 92lb/min. Yes, I know, its without compressor map, but 2800 lbs and 163 MPH of AWD Motorsports Evo indicates 950 HP....

At what AFR?:) Just making the point, as NASA once took 12A carbureted rotary, hooked up a turbo and run it at 15:1 AFR with BSFC under 0.46. At 7 psi, water injection was needed to stop detonation and EGTs were over 1000°C:lol:

Mass flow rating is for compressor only, and its standardized for certain inlet temperature, pressure and humidity. So different hotside configuration wont change that. But its whole system what makes power, and lower back-pressure will make it more efficient in making power, even though airflow is same. What kind of gain it could be really depends on many variables, for example on how much is engine porting sensitive to intake/exhaust pressure ratio.

You can find these stories everywhere, Precision always blame back-pressure, they won´t admit poor quality.

yea that would make sense that they would blame everything but them self. I mean i have dyno graphs showing that the turbo was good till about 7600rpm at 20psi then starts to taper off..
I can complain about precision really as they did warranty it for free even tho im out shipping it to them but oh well.
I will see what im going to do in the spring time weather i keep the turbo or i upgrade and weather i will do 4" exhaust.

Just out of plain currosity what type of compressor housings is everyone running on these?

i run the ported H cover just because i like the fancy whistle sound. im still a bit of a ricer.

i run the h cover and i dont get no whistle sound :( i wish i did get a cool whistle sound. do you have the antisurge cover?

yes i have the h cover with the anti surge on it. they actually take some power away it has been proven on the supraforums. if you want it though you can post up a trade on the supraforums for a 67 anti surge h cover. you will get one no problem.

here a little of how it sounds. it does sound great and its loud i love it. you can only hear it for a split second because i shifted to 5th.

http://www.youtube.com/watch?v=nCe6ACF0uXI

i have a dbb ported anti surge cover 6765.. all it does is whistle

160+mph on nitrous most likely!