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post #1 of 39 (permalink) Old 03-07-2008, 04:34 AM Thread Starter
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Turbo & back pressure?

I have the baby GT4294R with a 1.01 exhaust housing and 530 hybrids. This turbo seems to pull a bit better off the bottom and spools as fast as the 38R I had so I've been very happy with the trubo.
I finally got a gauge hooked up to measure back pressure and did a few runs last night and wanted to know if this sounds right, from 0 to 40 psi boost pressure the drive pressure is lower, like at 30psi boost, drive pressure is 25. Is that normal or is my gauge not reading right?
At 40 psi boost, drive pressure evens out at 40psi.
At 45 psi boost, drive pressure is higher at about 50, guages are getting harder to watch at this point and need a co-pilot.
I have hit 52 psi in the race program so I figure drive pressure would be over 60PSI. Sound normal so far?
OK now for the big question, how much difference in reducing drive pressure would going to the 1.15 housing make and how would it effect spool up? Are we talking small differences or huge differences?
Thanks

2000,CC,4x4,auto
some bolt on stuff from Bean & BTS
Some used and some home made stuff
463hp/991tq 10/01/05 mustang dyno 10k rollers
458hp/923tq 04/14/07 dynojet dyno
490hp/1025tq 03/08/08 mustang dyno 10k rollers
03/08/08 1st runs ever, 13.5 & 13.264 @ 100.65mph screwing up both launches, 7600#'s, #2 only
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post #2 of 39 (permalink) Old 03-07-2008, 06:46 AM
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Re: Turbo & back pressure?

Differant turbo, but I noticed very little differance when I went from the 1.00 to the 1.15 on the 38r. But the drive pressures dropped a ton!

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post #3 of 39 (permalink) Old 03-07-2008, 04:14 PM
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Re: Turbo & back pressure?

I think it wouldn't be as snappy on the bottom and your drives won't be as high up on top.


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post #4 of 39 (permalink) Old 03-07-2008, 04:25 PM
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Re: Turbo & back pressure?

Gordon, did you use any kind of a pressure snubber? When I had my mechanical back pressure gauge I had to use the snubber, this caused the back pressure gauge to move sluggish. Might be part of the problem.

[CENTER]01 F-250 SC PSD,430k,16 Isspro Gauges, AFE-2,CCV Mod,IAH delete,map reg,Modded H2e, 6.0 IC, 230/100, Studs, 910 springs, Forged rods, Hydra chip, Swamps HVHF IDM, MBRP 4" dual's, Aero, 6" tip's, 4" Revtek lift, 37/12.5/16.5 MT's
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post #5 of 39 (permalink) Old 03-07-2008, 04:33 PM
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Re: Turbo & back pressure?

Gordon, just remember that the EBP is just your engines work, you can only change the pressure (work) as it is applied to the wheel. Basically how fast do you want to spool, and when, do you want to sacrifice low end for top end? Do you want more midrange drivability? The A/R is going to affect all those things. It will change the dynamic of the truck considerably. Dirve pressure that is in sync or higher than you manifold pressure is not a bad thing at all. It is when the numbers are far apart from each other, and when pressure that is being exerted is extraordinarily high from what most people run at....
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post #6 of 39 (permalink) Old 03-07-2008, 06:03 PM Thread Starter
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Re: Turbo & back pressure?

Sorry it took so long to get back on a computer.
Yes I used a snubber and had to modify it a bit as it wouldnt show any back pressure at 10 psi of boost. Drilled out the hole a bit and now seems to work better.
Yea I dont want to loose spool up and bottom end to gain a little on top since I dont drive wide open all the time. Was just wondering if the drive pressure I have on top is way wacked out, like will I break anything, if I dont go to the 1.15 housing?

2000,CC,4x4,auto
some bolt on stuff from Bean & BTS
Some used and some home made stuff
463hp/991tq 10/01/05 mustang dyno 10k rollers
458hp/923tq 04/14/07 dynojet dyno
490hp/1025tq 03/08/08 mustang dyno 10k rollers
03/08/08 1st runs ever, 13.5 & 13.264 @ 100.65mph screwing up both launches, 7600#'s, #2 only
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post #7 of 39 (permalink) Old 03-07-2008, 06:06 PM
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Re: Turbo & back pressure?

Quote:
Originally Posted by cota View Post
Sorry it took so long to get back on a computer.
Yes I used a snubber and had to modify it a bit as it wouldnt show any back pressure at 10 psi of boost. Drilled out the hole a bit and now seems to work better.
Yea I dont want to loose spool up and bottom end to gain a little on top since I dont drive wide open all the time. Was just wondering if the drive pressure I have on top is way wacked out, like will I break anything, if I dont go to the 1.15 housing?
Don't go changing a housing just because you read somewhere that there is this "golden" ideal drive-pressure rating...If you like the way the truck drives now, and your wastegate is functioning just fine, keep it the way it is now. You won't break anything.
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post #8 of 39 (permalink) Old 03-07-2008, 06:12 PM Thread Starter
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Re: Turbo & back pressure?

There is no waste gate on this turbo.

2000,CC,4x4,auto
some bolt on stuff from Bean & BTS
Some used and some home made stuff
463hp/991tq 10/01/05 mustang dyno 10k rollers
458hp/923tq 04/14/07 dynojet dyno
490hp/1025tq 03/08/08 mustang dyno 10k rollers
03/08/08 1st runs ever, 13.5 & 13.264 @ 100.65mph screwing up both launches, 7600#'s, #2 only
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post #9 of 39 (permalink) Old 03-07-2008, 06:13 PM
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Re: Turbo & back pressure?

Quote:
Originally Posted by cota View Post
There is no waste gate on this turbo.
Well then if pressure is steady and at a safe level then even better.
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post #10 of 39 (permalink) Old 03-07-2008, 06:20 PM Thread Starter
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Re: Turbo & back pressure?

Whats safe? 40PSI boost and 40PSI back pressure sounds great.
52PSI boost and 65PSI back pressure I'm not so sure about.
I do have the 910 springs and studs but have not read much about drive pressure effects on head gaskets, rods and valves.

2000,CC,4x4,auto
some bolt on stuff from Bean & BTS
Some used and some home made stuff
463hp/991tq 10/01/05 mustang dyno 10k rollers
458hp/923tq 04/14/07 dynojet dyno
490hp/1025tq 03/08/08 mustang dyno 10k rollers
03/08/08 1st runs ever, 13.5 & 13.264 @ 100.65mph screwing up both launches, 7600#'s, #2 only
cota is offline  
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