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Thread: Getting Dome Pressure close to Boost Pressure.

  1. #1

    Default Getting Dome Pressure close to Boost Pressure.

    I have my setup just like below. The handful of hits I've made I found that commanding 10 psi on the dome sensor gives me a little over 7 lbs of boost. Made a few hits today with dome pressure at 18 psi and I saw around 12/13 lbs of boost. It's not a Holley dome sensor, it's the one below I bought. Could that just be the culprit or is there a way to offset the two to match? Also, I can't view my datalogs unless I record it on my laptop. I have it triggered at 80% TPS, it's not highlighted to download for whatever reason.
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    Last edited by 427LSX; 07-31-2019 at 05:23 PM.

  2. #2

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    Your results are typical. Dome pressure and actual boost may never match. Has to do with spring rate in the gate, size of the wastegate, backpressure, etc. As backpressure goes up, you might need more dome to keep the boost on track. For example, my 5.3L with an S475/83 needs 27 psi on the dome with a 3 psi spring to make 20 psi of boost. A buddy’s car needs only 19 psi on the dome with a 5 psi spring to make 17 psi of boost. Every car/combo is different. Just give it what it wants to get the boost your after.

    As far as datalogging, read the directions again. Probably just one settings that’s off. After a run, hit the “Datalog” drop down along the top of the screen. Laptop hooked up, key on DON'T GO ONLINE, select “Download Datalogs” pick the ones you want. Hit Download and wait. Once it says Download Complete you should be able to open the datalog (using the same drop down menu).
    Last edited by 3 window; 07-31-2019 at 05:33 PM.

  3. #3

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    Ah OK, thanks. It's honestly not too far off, but I was wondering. After rechecking, when I commanded 18 psi on the dome, it got to 15 lbs of boost, so there seems to be a about a 3 lbs difference between dome & boost. My problem might've been, I was "Online" then when trying to get the last datalog from the way home from work today. All the others I could click on, but the "Download Datalog". Thanks bud!

  4. #4

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    You bet. Good luck.

  5. #5

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    Thanks. Are you using a bump in button with the Holley solid state relay for the transbrake? I can't get mine to work, and not totally sure it's software or hardware related, so figured I'd start with the software side. I have mine wired like this:
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    and have it configured like this:
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    Last edited by 427LSX; 08-01-2019 at 05:19 PM.

  6. #6

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    I have a bump button, but I use a small circuit board and a regular relay. Very simple really. I’m sure someone will chime in on the SSR setup. Plenty of guys doing it.

  7. #7

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    Turns out, it was my valve body/solenoid was stuck. I yanked it off this morning and got it working, hitting the track tomorrow.

  8. #8

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    Good luck, keep us posted.

  9. #9

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    I went to the track to test on Saturday for the first time. The first test it didn't bump in, 2nd test it bumped in too deep. 3rd pass I pulled a 1.50 60', ran like a 10.0 @ 141 on 9 lbs boost ramping in at 5 sec. Last pass I tried to leave with more boost and spun the tires, car shifted into 2nd, but once the car settled I hit the gas again, ran it through with a 11.2 @ 147 MPH, datalog showed 14 lbs of boost. Tuning in the boost off the transbrake and after takes time, I had it ramping in too slow come to find out. Last pass I had it ramping in at 4 seconds. Can't wait to ramp it in faster and twice as much boost. Also, do you know if the bump in button can also be used as the scramble button as well?

  10. #10

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    You probably could use the same button if it needs to see the transbrake input to be active. Make another input and from the bump button and set it up to activate as the scramble once the transbrake is released. Easy enough to check in the garage (car off of course, LOL). MPH shows promise and nice power. If the car can handle it, crank the boost in as soon as possible. More power drives the tire into the track harder and will hopefully hold it there. A lot of getting it to stick and stay stuck is the shocks. Good shocks are worth there weight in gold. I just went 1.5 on a Nitto 275/60 two weekends ago. Not the most popular tire, but I’m sure they would’ve handled a 1.4x. I kept being the power in sooner & sooner. Last pass I got really aggressive, but left the rear shocks too soft on compression and it whacked and bounced the tire at the hit. Tried getting all the boost in by .8. Granted, my car only runs 6.50s, but even that came with a ramp of 1.3.

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