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Thread: Any tips/info from people who have tuned a Roots blower?

  1. #1

    Default Any tips/info from people who have tuned a Roots blower?

    Getting ready to start tuning a 427 SBC with a 6-71 with the injectors in the top of the blower. I'm pretty confident this is going to be one of the more difficult things I've tuned so far. I think most of it will have to be tuned in open loop, since the WBO2 sensor is so freaking far away from the injectors. The fueling is all over the place with even just a little throttle. It will add 60% then turn around and take it right back out. Anyone that has done a setup like this, I would appreciate you hear your input. Thanks.

  2. #2

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    I would suggest three things:
    1) Use Custom Closed Loop settings and make the gain 0.2 in the idle area.
    2) Run zero map AE and more TPS AE. Make the idle and off idle area richer than normal. Run as low TPS Blanking as possible.
    3) Talk to Richard Nedbal (fastmanefi) about this.

  3. #3

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    Richard Nedbal 209-247-6497. Done many, and yes, they can be tricky. I setup the idle & off idle fully manual tune. No Closed Loop or Learn. AE tables are also manually tuned. Timing table usually needs to be tweaked to stop surging. Use the datalog to zero in on the correct AE settings. Cruise & WOT are no problem.

  4. #4

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    Is it even possible to use Idle Spark control?

  5. #5
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    Yes, as long as the ignition timing is flat in the idle area.
    May God's grace bless you in the Lord Jesus Christ.
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  6. #6

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    Thanks for the replies guys. I'll follow up and post some more next week.

  7. #7

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    What type of fuel injection unit(s) are you using? I have a Hilborn 4 Port Scoop Style Injector with 120 lb/hr injectors on an early Chrysler Hemi. I’m still learning the HP EFI software and I'm getting more confident in making changes and understanding what effect they have. The engine is running well, but I still have a way to go in getting everything running as best as possible.
    One of the things that I first noticed was that the engine would crank for an excessively long time before starting. In startup settings, I had to increase the fuel prime to 275%, and that seems to help. The engine still cranks for 4-5 seconds before starting, but this is only when it hasn’t been run for a while. Another problem that I had was in keeping the engine running after start, especially in cooler weather. I had to play around with the coolant temperature enrichment table and finally have a good cold start tune. I used the flowchart (Figure 29 in section 7 of the Beginner's Tuning Guide) to tune the cold start and it worked out well.
    I am currently changing the X and Y axis scaling in the base fuel table to more closely reflect the engine’s operating range. My original tune had a minimum of 2 kPa and a maximum of 180 kPa for the MAP values. Realistically, I’ll never see less than 20 kPa (vacuum) and 150 kPa (boost), so I’m changing my Y-axis values to reflect that. I’ll do the same with the RPM scaling as well. I used the information from this link: https://forums.holley.com/showthread...ase-Fuel-Table
    Once you change the scaling on the Base Fuel Table you can also transfer these values over to the Base Spark Table.
    So far, I’ve been trying to use the Closed Loop & Learn functions as much as possible, but the engine seems to still be too rich, with the actual AFR being richer than the Target AFR. After reading a few of the posts above, I think more manual tuning will be in order. I’m looking forward to following this thread for more information, good luck with your tune.
    Last edited by steve392; 10-18-2018 at 04:49 PM.

  8. #8

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    Sounds like you have got a handle on your tune. A few points that are somewhat unique with Roots blower engines, is that they can produce boost at low RPM, so the fuel curve will end up more enriched at lower RPM than you might expect. And you have to make sure the timing in that area would not allow detonation. Also, if you are fighting a surge you can take away timing in the area of the Base Spark Table when the engine revs up. Low timing will quench the surge quickly. When injecting above the blower, you'll need more AE fuel than the same engine would need if it were N/A. Have fun.

  9. #9

    Default

    Quote Originally Posted by steve392 View Post
    What type of fuel injection unit(s) are you using? I have a Hilborn 4 Port Scoop Style Injector with 120 lb/hr injectors on an early Chrysler Hemi. I’m still learning the HP EFI software and I'm getting more confident in making changes and understanding what effect they have. The engine is running well, but I still have a way to go in getting everything running as best as possible.
    One of the things that I first noticed was that the engine would crank for an excessively long time before starting. In startup settings, I had to increase the fuel prime to 275%, and that seems to help. The engine still cranks for 4-5 seconds before starting, but this is only when it hasn’t been run for a while. Another problem that I had was in keeping the engine running after start, especially in cooler weather. I had to play around with the coolant temperature enrichment table and finally have a good cold start tune. I used the flowchart (Figure 29 in section 7 of the Beginner's Tuning Guide) to tune the cold start and it worked out well.
    I am currently changing the X and Y axis scaling in the base fuel table to more closely reflect the engine’s operating range. My original tune had a minimum of 2 kPa and a maximum of 180 kPa for the MAP values. Realistically, I’ll never see less than 20 kPa (vacuum) and 150 kPa (boost), so I’m changing my Y-axis values to reflect that. I’ll do the same with the RPM scaling as well. I used the information from this link: https://forums.holley.com/showthread...ase-Fuel-Table
    Once you change the scaling on the Base Fuel Table you can also transfer these values over to the Base Spark Table.
    So far, I’ve been trying to use the Closed Loop & Learn functions as much as possible, but the engine seems to still be too rich, with the actual AFR being richer than the Target AFR. After reading a few of the posts above, I think more manual tuning will be in order. I’m looking forward to following this thread for more information, good luck with your tune.
    I'm also using Holley 120 lb/hr injectors. They are external and are below the scoop, above the blower.

    I have the same long crank time before it starts. Normally it will die after the first start then will start OK after that. I haven't had any time to mess with it this week. It idles about 55-60 kPa with 20° of timing with a 13.8 AFR, but it's on E85, so I may need to fatten it up some, but it sounds pretty good.

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