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Thread: Holset VGTs and drive pressure discussion.... Aries_turbo look!

  1. #1
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    Holset VGTs and drive pressure discussion.... Aries_turbo look!

    So I'm in the planning stages of a new build, and am planning on using a HE351VGT. I already own a couple and am really drawn to the technology. They use a 60mm cold side and I think it's going to be a great fit for my power goals on a boosted 3.0. For those not familiar with this turbo it has a 60mm compressor and the hotside uses a sliding ring that makes it adjustable from 4 to 25cm. So it has the potential to spool instantly yet flow well up top if a guy can take advantage of its adjustable hotside.

    I picked up these turbos back when they were new and have read everything I can about controlling them. There are some electronic controllers on the market but they are for diesels and are very expensive. The first mechanical one I saw a guy used a 8psi WG can that changed the hotside from like 8 to 14 when it hit 8psi. The new one I am seeing guys doing are limiting how small it can get, say 10cm and then are using drive pressure to open it up with a spring to control/restrict how fast it opens. Neither are bad setups, but I'm wanting to get a little fancier.

    Aries_Turbo really got my gears turning when he suggested somehow, maybe electronically using a setup that maintained a 1:1 drive pressure. We have all seen how getting that "perfect" 1:1 ratio effects HP. So I quickly got to thinking... and think I may have found a mechanical solution. Weld a arm onto the gear that currently moves the sliding ring. Then hook a dual diaphragm WG can to it. Like the ones the 84 turbo used. Feed one side with boost pressure and the other with the drive pressure. Since the drive pressure is typically higher, it should overcome the boost pressure and open the hotside up until it equalized. Then theoretically it should maintain a 1:1 ratio as the RPM and drive pressure goes up. The problem is without boost pressure it's just going to go wide open to 25cm and never build any boost. So I think a pressure switch and solenoid would be needed so the can doesn't get any drive pressure until you reach the desired boost level. I am sure a external WG would still be needed to control boost. Not sure how the WG opening would effect this contraption, as it is bleeding off drive pressure too. But I think the dual diaphragm setup would still open up the sliding ring. With the turbo limited to say 7cm and 20psi of boost its still going to have a drive pressure above 1:1.

    Am I making sense? I can try to draw out a diagram if that helps. Just wanted some second opinions if I am on the right track here. I think if this works I could get instantaneous boost and not be choking the motor at 8000 rpms.

  2. #2
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    Re: Holset VGTs and drive pressure discussion.... Aries_turbo look!

    All I know is, those things weigh like 200lbs. Heaviest damn turbo I've ever held.

  3. #3
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    Re: Holset VGTs and drive pressure discussion.... Aries_turbo look!

    How about an adjustable bleed. I don't know if I actually believe in the concept that equalizing drive pressure is going to be good for anything but fun. I would rather experiment to see what boost level drive pressure was equalized and cap it off there if I thought it was that important. Otherwise at this point you have no idea how much boost you will even run, and modifications that decrease backpressure will change how much boost you run, even if in reality you can't support that. A car like yours is going to want to manipulate boost to keep traction more than anything. I haven't really researched the boost control schemes for megasquirt 1 if there are any, MS2 either. MS3 has a lot of modern options and its an uphill battle figuring out the old stuff.
    I would be kinda interested if you could somehow have two canisters helping keep the A/R change more linear (since I have no idea what would happen to boost if that thing ripped open anywhere between 5-15psi, whatever you have it set at). That would take some creative fabrication and a lot of space.

    Definitely need an external wastegate since the motor will break a piston before that turbo runs out of pressure creating ability.

    Feel free to experiment with drive pressure controlled boost as I would love to see data on how it would actually function (not on any HP gains).
    7cm at 2500 rpms. Hit the gas and drive pressure would be lower so boost would build faster than a fixed proper sized turbine.
    7cm at 5000 rpms. Hit the gas and drive pressure would be higher so boost would build slower than with a fixed turbine???? ??????? Might prevent wheelspin.
    Last edited by Ondonti; 09-08-2015 at 06:39 AM.
    Brent GREAT DEPRESSION RACING 1992 Duster 3.0T The Junkyard - MS II, OEM 10:1 -[I] Old - 11.5@125 22psi $90 [U]Stock[/U] 3.0 Junk Motor - 1 bar MAP [/I] 1994 Spirit 3.0T - 11.5@120 20 psi - Daily :eyebrows: Holset He351 -FT600 - 393whp 457ft/lb @18psi 1994 Spirit 3.0T a670 - He341, stock fuel, BEGI. Wife's into kid's project. 1990 Lebaron Coupe 2.2 TI/II non IC, a413 1990 Spirit 3.0 E.S. 41TE -- 1993 Spirit 3.0 E.S. 41TE -- 1994 Duster 3.0 A543 1981 Starlet KP61 Potential driver -- 1981 Starlet KP61 Parts -- 1983 Starlet KP61 Drag 2005 Durango Hemi Limited -- 1998 Dodge 12v 47re. AFC mods, No plate, Mack plug, Boost elbow -- 2011 Dodge 6.7 G56

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    Moderator Turbo Mopar Staff Vigo's Avatar
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    Re: Holset VGTs and drive pressure discussion.... Aries_turbo look!

    It has to have a wastegate because even wide open it will still boost creep on a 4g63.

    I don't get this concept of 'equalizing' boost and drive pressure by varying the turbine section. If the turbo is creating a higher driver pressure than boost pressure, it's because it REQUIRES that much drive pressure to make that boost pressure. Opening up the turbine section at that point is just going to lower boost.

    Since we can be fairly certain that it will still continue to build more boost even in the fully open position, I would just control it the same way we do a stock wastegate can: Don't let it see any pressure until it reaches a target minimum boost, then give it boost pressure, let it open up all the way, and the wastegate will control boost rise beyond that point.

    I have been sitting on one of these for my SOHC 3.0 3000gt for years now, and have thought about this many times before.. This is the conclusion I came to.

    Dont push the red button.You hear me?

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    Re: Holset VGTs and drive pressure discussion.... Aries_turbo look!

    A CO2 powered controller would probably do that job perfectly. They are made to control both sides of an external wastegate setup. One side of the wastegate has boost pressure to open the wastegate like it normally would. The controller then regulates compressed CO2 to the opposite side of the wastegate which helps close it to generate whatever boost level you want. You could likely run the exhaust pressure to the side that would open the vanes and then have CO2 pressurize the side of the canister that would close the vanes. That way if/when you run out of CO2 you simply have low levels of boost rather than uncontrolled boost. A good friend has a BoostLeash on his car and it works amazingly well and has options to regulate boost based off of RPM and/or time as it's meant for 1/4 mile racers. We've accidentally seen 30+psi boost out of a 5psi spring when it was programmed incorrectly.
    “If the people of the nation understood our banking and monetary system, I believe there would be a revolution before tomorrow morning.” -Henry Ford

  6. #6
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    Re: Holset VGTs and drive pressure discussion.... Aries_turbo look!

    Realistically all this would be pointless on a FWD car. But, I love stuff like this and that's why I was wanting to bounce ideas off you guys. There are ways around the traction issue though. Possibly by starting the hotside at a large size, say 14cm or by using a two stage boost controller. Say low boost is 10 psi and high is 20. Since it would need to see 20psi for the solenoid to open giving the turbo drive pressure on low boost it would just stay at 14cm. But that could be a tuning nightmare... unless you used the "nitrous" side of the MS to allow different maps on the low boost vs high boost. But at that point things are getting very complicated.

    Vigo, I think it would still have no problem building boost. If I used a pressure switch set to the target boost hooked to a solenoid so it only saw drive pressure once the target boost is reached. If the boost dropped below that, it would no longer see drive pressure and start closing. I think this would happen very quickly and possibly "float" the hot side size to the maximize the hot side size/flow while maintaining the target boost level. It may be higher then a 1:1 ratio, but it should be as close to 1:1 as possible while maintaining the target boost level.

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    Re: Holset VGTs and drive pressure discussion.... Aries_turbo look!

    I don't think you would be able to use even 10psi with that turbo in 1st gear. Maybe if it ramps up very gently, which it might do with a big a/r. I had a lot of luck 10 years ago with an ebay turbo that had a giant hotside in comparison with the compressor side. It would really not lose traction at the track, but ran similar MPH at the same boost. Holset is more jumpy with the boost ramp up.
    I think its a fun experiment and with the VGT you can try things other people can't without swapping out expensive parts.
    Brent GREAT DEPRESSION RACING 1992 Duster 3.0T The Junkyard - MS II, OEM 10:1 -[I] Old - 11.5@125 22psi $90 [U]Stock[/U] 3.0 Junk Motor - 1 bar MAP [/I] 1994 Spirit 3.0T - 11.5@120 20 psi - Daily :eyebrows: Holset He351 -FT600 - 393whp 457ft/lb @18psi 1994 Spirit 3.0T a670 - He341, stock fuel, BEGI. Wife's into kid's project. 1990 Lebaron Coupe 2.2 TI/II non IC, a413 1990 Spirit 3.0 E.S. 41TE -- 1993 Spirit 3.0 E.S. 41TE -- 1994 Duster 3.0 A543 1981 Starlet KP61 Potential driver -- 1981 Starlet KP61 Parts -- 1983 Starlet KP61 Drag 2005 Durango Hemi Limited -- 1998 Dodge 12v 47re. AFC mods, No plate, Mack plug, Boost elbow -- 2011 Dodge 6.7 G56

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    Moderator Turbo Mopar Staff Vigo's Avatar
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    Re: Holset VGTs and drive pressure discussion.... Aries_turbo look!

    Vigo, I think it would still have no problem building boost.
    Well, the only thing the variable hotside is really going to change is how quickly boost rises from one number to another. We already know based on the size of the wheels that if you were to lug it down you could build boost at 2000 rpm anyway, it would just depend on how jiggered the hotside controls. I mean, you could probably set it up to be able to hit 20 psi @ 1500 rpm, but that's a pointless capability. A 'normal' he351 would still spool reasonably early, so the variable hotside isn't REALLY useful for lowering your boost threshhold but more for controlling the rate of boost rise like Ondonti was just talking about.

    Based on the 4g63 uses i saw where it still boost creeped even with the hotside all the way 'open', my feeling is once you get up to a certain minimum boost # that you would want for the vehicle to be 'fun to drive', you would just open the hotside all the way up and let it build boost up to maximum (controlled by external wastegate) as if it was a 'normal' turbo from there.

    If that boost rise wasnt fast enough you could delay the point at which the hotside actuator sees boost just by adjusting a grainger valve. It would be hooked up just like a normal wastegate actuator except that all it would do is control when the turbo switches from 'faster spool' to 'slower spool'. So what i would be concerned about is not so much WHEN it hit ~6psi (example of a helpful/fun boost level at low rpm), i would just be fiddling with how quickly it went from 6 to 15.

    Although if you want to build a complicated control system you could actually leave the hotside 'big' in 1st gear so that you probably didnt lose traction until higher rpms. Although even that may be pointless as my 3.0/5spd car didnt hook up 1st on street tires even with very little power mods.

    Dont push the red button.You hear me?

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    Re: Holset VGTs and drive pressure discussion.... Aries_turbo look!

    So does opening up the vanes improve power because once the thing is spooled up you have less backpressure creating the same boost pressure? (just like a larger a/r turbine housing would do, decrease threshold but improve top end power). The problem here might be that its unneeded on an engine this large? I was temped to use a single VGT in a compound setup but Vigo's points are making me realize that is silly to even care about boost down that low. As long as you can get the converter doing what you want it, that would be what matters to me.
    I also wonder if a nice boost controller can accomplish everything we are talking about doing here except opening up the A/R huge to gain some top end power. If you are pulling boost to save traction it does not matter to make extra power with optimized turbine A/R. It will only matter when you are all in unless you are trying to save a few miles per gallon.

    If those tires are drag radials, I would think you can run 3-5psi in 1st gear, 7-10psi in 2nd gear, and 12-15psi in 3rd gear depending on your setup and how clean and warm the road is. Probably ramping higher as rpms go up. This is just to give an idea of how you would actually need to control boost. 5psi will be like the 15psi you are used to. 4th gear you can hook up with a lot of power on a good road. Bad road and you can't even put down half in 3rd.
    I only have experience with 225/50r15 BFG drag radials that were new, and I didn't like them as they didn't hook 3rd gear completely and sent me all over the road. Once ran borrowed 205 drag radial BFG's and they were terrible at a track because they were so short.

    Would be really cool if these tires you have can put down a lot more power. Years ago I kinda fantasized about running them based on comments from some local SFWD racers.

    Also pretty sure you said there was a dyno down there where you could tool around with something I have never seen data on. See if you can actually make power with the A/R opened way up. My guess would be that it matters more the harder you are pushing the turbo. At some point its like putting 4" intercooler pipe on a stock 8 valve draw through T1.
    Last edited by Ondonti; 09-12-2015 at 07:10 AM.
    Brent GREAT DEPRESSION RACING 1992 Duster 3.0T The Junkyard - MS II, OEM 10:1 -[I] Old - 11.5@125 22psi $90 [U]Stock[/U] 3.0 Junk Motor - 1 bar MAP [/I] 1994 Spirit 3.0T - 11.5@120 20 psi - Daily :eyebrows: Holset He351 -FT600 - 393whp 457ft/lb @18psi 1994 Spirit 3.0T a670 - He341, stock fuel, BEGI. Wife's into kid's project. 1990 Lebaron Coupe 2.2 TI/II non IC, a413 1990 Spirit 3.0 E.S. 41TE -- 1993 Spirit 3.0 E.S. 41TE -- 1994 Duster 3.0 A543 1981 Starlet KP61 Potential driver -- 1981 Starlet KP61 Parts -- 1983 Starlet KP61 Drag 2005 Durango Hemi Limited -- 1998 Dodge 12v 47re. AFC mods, No plate, Mack plug, Boost elbow -- 2011 Dodge 6.7 G56

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