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so I've only had a couple pulls on this turbo but at 15psi manifold i'm getting ~30psi of backpressure measured at the turbine inlet flange, before the wastegate (gate on housing)
I can believe 2:1 on my set up. (6.0 with a 222/228 .566/.571 115+2 comp cams with xrpm lobes)
My questions are:
Is this backpressure close to what you guys are seeing on your 7875s?
Would a true "turbo" cam help lower the backpressure?
I'm concerned about choking the motor before I can hit my goal of 750 wheel.
Seems about right for a .96 T4 on a healthy cam’d 6.0. Bump it a pound (watch plugs) and see if the gains are still there at the track/dyno/dash dyno whatever… As long as you’re seeing healthy gains per pound you should be fine. As soon as you stop seeing the usual gains though I’d stop.
I bet! My 5.3 with the small 1.10 T4 S475 would routinely see 2.8:1 at 25-26lbs. Think part of the reason it didn’t mind the high back pressure was the LS9’s 122.5 LSA. Might not get away with as much on your setup. Was also running a crappy china IC. I’m sure the poor turbo was pushing over 30. I kept picking up so I went with it. Trapped 143@17, 148 @ 20, 151 @ 24, 153 @ 26. Was an 8.6:1 motor and converter was slipping really bad. When you look at how efficient the big turbos or twins are these days it makes the little ones look bad!
That’s a stinker…pump gas? Did it just spike to 18 on the limiter or did you turn it up that high? How’d the plugs look at 15-17lbs? Should give a pretty clear indication if you’re on the edge heat wise. How was the timing/AFR?
I was playing with boost controller, trying to get the best resolution by altering the duty cycle...apparently <20% is not where that point is at
I only pulled one plug at 15psi and it looked really good. A little fat maybe but overall pretty good.
Shamefully I'm doing street pulls so I cant really get after it. It's basically a launch on the sloppy brake & line lock. The converter is too tight so it simply annihilates the drag radials as soon as positive pressure builds.
so here's where I think I hurt it.
no knock retard on that pull. The one prior didnt check plugs out yet. I dont think a compression test is worth it, it's puffing out the oil fill cap pretty good.
I see in the picture you have copper tube coiled up to take some heat out before it gets to the sensor. What sensor are you using? ssi? ebay china one? 0-50? or 0-100 psi? Thanks
I see in the picture you have copper tube coiled up to take some heat out before it gets to the sensor. What sensor are you using? ssi? ebay china one? 0-50? or 0-100 psi? Thanks
$16 ebay 0-100. I have an SSI sensor I test them against, they're surprisingly accurate. one thing to note is the accuracy near either edge of their limit is where they lack. if you will be measuring right at 98psi or something, get the 150psi one. does that make sense?
That’ll do it! Pop the heads off and hope it’s just the gasket. Hard to tell if a ring lands are crunched unless you pull the pistons though. I’ve had them literally look perfect. Tap them on my bench and the middle ring lands fell apart. I like to set them up super rich and pull fuel so you don’t get a lean spike like that.
I was playing with boost controller, trying to get the best resolution by altering the duty cycle...apparently <20% is not where that point is at
I only pulled one plug at 15psi and it looked really good. A little fat maybe but overall pretty good.
Shamefully I'm doing street pulls so I cant really get after it. It's basically a launch on the sloppy brake & line lock. The converter is too tight so it simply annihilates the drag radials as soon as positive pressure builds.
so here's where I think I hurt it.
no knock retard on that pull. The one prior didnt check plugs out yet. I dont think a compression test is worth it, it's puffing out the oil fill cap pretty good.
When you guys pull plugs to read them, do you cut the threads to get to the base of the electrode for a reading (plug chop in the two stroke world) or just look for color at the ground strap and and electrode tip?
If you had very high backpressure, you'd want the exhaust valve closed to prevent exhaust charge remaining in the cylinder or worse into the intake itself during overlap or intake valve opening.
So no or negative overlap too although obviously events can be played with in various ways
If you were close to 1:1, then it could almost be treated a little like a n/a setup as there should be no huge bias towards reversion.
But 3:1 would be ******* high, so that would probably like shorter durations and negative overlap.
I'm sure some of the cam experts could explain better though
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drive pressure with vsr billet 7875 
