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Corrupted by power
 
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I need your Small Displacement Turbo Help! (Long)

Hi All,

Big lurker, first time post to the Pelican Turbo forum. I am embarking on a new project that is pretty atypical to most of the projects I read bout here, so am hoping I am not so far in left field that no one can help. I know there is no shortage of informed opinion and knowledge here, so fire away. Thanks in advance.

I recently retired my little MFI ‘S’ motor and since I’ve always wanted to put a turbo motor for my early 911, figured I’d build one in the spirit of my old motor. Because of this, the typical turbo doesn’t appeal to me, meaning 3 liter and up motors won’t meet my desires. Frankly, they just make too much power! Yeah, that shouldn’t be possible, but I said it anyway. Please don’t reply with the standard “Just by a 3.3 and be done with it” comments – they aren’t going to fly; my course is set.

The motor I am building is mostly specced and I already have most the parts to build the shortblock. It will be a small bore turbo, along the lines of the Baby RSR. Basic spec is for an 85mm bore x 66mm stroke, 2.3L intercooled engine. HP target is between 320 and 340HP @ 7500RPM, which calculates out favorably against my goal for boost at a conservative .8 BAR. The motor is being built to rev safely to 8000 RPM and my cam choice makes power to suit (see below).

My final decisions are down to figuring out the turbo and IC configuration. There seems to be a lot of debate between twin turbo configurations vs. using a single unit, especially regarding the throttle response. Seeing as this motor can’t rely on displacement to overcome off boost deficiencies, I want to make sure that my selection maximizes spool up.

During my research, it seems that the preference is for ball bearing turbos over journal bearing turbos, due to the efficiency gains they provide. Unfortunately, when matching my application for twin turbo applications, it seems the only ideally sized turbos that meet my needs are journal bearing turbos.

So the decision looks like it is between:
1. Using two journal bearing small turbos like the GT15
2. Going with two larger, but less ideally sized bearing turbos like the GT25
3. Going with a single ball bearing turbo like the GT28

I was convinced that twin turbos are the way to go, but modern, water cooled turbos w/ variable valve timing like the WRX, Mitsu Evo, Audi and VW 2.0T cars all make excellent throttle response and power from one turbo. From my reading, I notice a consistent theme that most turbos today are most efficient over 1 BAR, typically in the 1.2 BAR range; mine is much lower, so efficiency should be down. Dilemmas, dilemmas…

There is obviously a lot of tweaking that can be done on the A/R and compressor/turbine pitch to optimize any of these, but my question is:

Given the above options, what would you do to maximize spool up for a motor like this and get similar throttle response to what these modern cars make?

As far as full specs, here’s where what I already have:
85mm bore – Nickies w/ 7.5:1 JEs, thermo-coated
66mm stroke – SC rod journal grind, cross drilled
Custom Dougherty turbo cams: GT2 intake with the DC43 exh on a 108 lobe center (@ .050” Duration=248I/242E, lift .485”I/.484”E, 108 lobe centers)
Coated STD main bearings, grooved for cross drilled crank
R&R chromoly rods w/ ARP bolts from LN Engineering, GT3 spec (same size as Pankl Ti-rods)
2.4T 7R case, fully prepped by Ollies: shuffle pins, oil bypass, drilled for cross-drilled crank
Supertec head studs
2 liter heads w/ ‘69S valves, 39mm ports I/E, twin plugged
930 oil pump, race prepped
Properly sized George Narbel headers
ITBs

Don’t have it yet, but will soon:
EFI - Will use MegaSquirt II Sequencer system (waiting for final availability)
Coil on plug
Crank Fired
Wideband 02, w/ MAP, TPS and intake temp sensor
Apparently this ECU supports knock control and electronic wastegate/blowoff control – would love to integrate this

I am not totally in the dark here. A similar motor to my spec (but with a less aggressive cam) produced this dyno run:



Sorry to be long winded, but thanks again to everyone who battled through.
Thanks!

Last edited by BARknucklehead; 05-26-2009 at 12:25 PM..
Old 05-26-2009, 09:48 AM
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So, 320-340 hp out of 2.3 L at .8 bar?
I don't think you can get there that way.
Better up the boost to 1.1-1.2 bar. You might need to run a lower static compression ratio than 7.5:1.
As a data point, Porsche's first turbocharged racing engine had a 2.1 L displacement and ran 1.4 bar of boost, producing 490 hp @ 7600 rpm (source: Porsche 911 Story, 7th edition, pg. 269).
Sounds like an interesting project. Good luck.
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Old 05-26-2009, 02:48 PM
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Quote:
Originally Posted by 911nut View Post
So, 320-340 hp out of 2.3 L at .8 bar?
I don't think you can get there that way.
Better up the boost to 1.1-1.2 bar. You might need to run a lower static compression ratio than 7.5:1.
As a data point, Porsche's first turbocharged racing engine had a 2.1 L displacement and ran 1.4 bar of boost, producing 490 hp @ 7600 rpm (source: Porsche 911 Story, 7th edition, pg. 269).
Sounds like an interesting project. Good luck.
You are totally right - I did some calcs and .8 Bar is closer to 305 HP w/ a reasonable efficient IC. Better to keep the half point, since the small displacement will need all the static CR it can get for off boost acceleration.

1 Bar gets ~350HP, based on said calcs. @ ~12 HP per psi (basic rule of thumb, all other variables remaining static), this basically jives out. Water/alcohol injection would support this on pump gas. Maybe a future project?

BTW, the 2.1 RSR still pencils out at 380 HP a .8 Bar, per my calcs...something is fishy.
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Last edited by kenikh; 05-26-2009 at 08:57 PM..
Old 05-26-2009, 04:55 PM
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I was going to build a small displacement turbo engine for my own car a few years ago....You are following the right path building the bottom end as robustly as possible.

Why are you limiting to 0.8 bar boost?

Put a 0.7 spring in the wastegate, and use a boost controller to select your boost..

Why 85mm? 84 is standard 2.2/2.4 bore... You can get the nickies or Mahle cylinders... Then get a JE 2.4S piston.. It will be forged, and low c/r..probably 8.5:1 which is fine for a EFI controlled turbo engine.. This may be a more economical path

I'd use other than 2.0 heads..go for some heads with as large port/ valves as you can get..More aggressive cams i.e. more lift and duration.. Also you make no mention of lightweight valve components i.e. Ti retainers. Also hi perf springs will be necessary if you want to spin the engine that high..

Narbel headers are mild steel...M&K exhaust has some interesting mods of stainless SSI headers, the secondaries are shortened and a v band clamp is welded on.. This is ripe for easy twin turbo apps.

You could save a bunch of money by using a 3.2 manifold... in lieu of ITBs.. The Nth degree of performance will be realized with ITBs

Are you going to twin plug the engine?

I'm a bit confused on your description of the EFI set up... Will you be setting up the MSII sequencer for sequential injection and direct spark? If so in addition to the crank sensor you will need a CAS (cam angle sensor) you can take this obviously from one of the cams, or use an old distributor to provide the signal.. You can control a COP system with just a crank sensor though ...

That MSII sequencer looks very interesting...I may have to pick one up..

Quote:
Given the above options, what would you do to maximize spool up for a motor like this and get similar throttle response to what these modern cars make?
No unless you can get variable valve timing and variable turbo vanes...

Sorry I strayed from which turbo to select...I'll ask Bill which turbo he told me I should use when I was going to build a 2.0 turbo...
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Old 05-26-2009, 06:25 PM
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Not an expert but here are some thoughts.

7R case starts reaching its limit at about 270hp. At the heat of a turbo with severly increased combustion pressures and you might be taking a risk. Might be better to find an early sand cast aluminum case if durability is important.

Small displacement, short stroke, low compression, cams that will support a usable power band up to 8000rpm -- and I suspect low end power and response is not going to be in the cards.

For example, a K27-7200 turbo supports 320 hp. Boost starts to come on at 2500 with full boost at about 3200rpm on a 3.3. Put in on a 2.2 and boost will start at about 3700 rpm with full boost at 4500rpm.

Further, you will not likely get low overlap cams to work well at the rpm you want to reach. Thus, boost will come on later with the same turbo.

Also, you may need a larger lower restriction hot side for less back pressure so there is less hot gasses being pushed back in through the exhaust valve and past intake valve up into the intake manifold.

Think a step beyond a 911S 2.2 (906?) in terms of power band and throttle response. You will probably want the turbo and cams to come in at about 6k to work right. No reason to go twin turbo that adds complexity and weight and you will be looking for turbos that make about 160hp each.

What would be fun would be to run an MFI set up with your 2.3 turbo set up.

The best.
Old 05-26-2009, 07:44 PM
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Interesting project.
How far outside the box are you willing to go? With engine management combined with tiny displacement you can try something really different - a single VNT from the 996tt.
Max reduction in lag and just about the perfect size for 0.8bar from 2.2L engine.
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Old 05-26-2009, 09:00 PM
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Corrupted by power
 
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TimT, I was really hoping you'd chime in. OK, one thing at a time...

Quote:
Originally Posted by TimT View Post
I was going to build a small displacement turbo engine for my own car a few years ago....You are following the right path building the bottom end as robustly as possible.

Why are you limiting to 0.8 bar boost? Pump gas

Put a 0.7 spring in the wastegate, and use a boost controller to select your boost..

Why 85mm? 84 is standard 2.2/2.4 bore... You can get the nickies or Mahle cylinders... Then get a JE 2.4S piston.. It will be forged, and low c/r..probably 8.5:1 which is fine for a EFI controlled turbo engine.. This may be a more economical path. Already have the Nickies. 8.5:1 is much higher than I had supposed safe. Provides some very interesting options.

I'd use other than 2.0 heads..go for some heads with as large port/ valves as you can get..More aggressive cams i.e. more lift and duration.. Also you make no mention of lightweight valve components i.e. Ti retainers. Also hi perf springs will be necessary if you want to spin the engine that high.. Already have Ti retainers and Supertec springs...heads already have the sickest port job you've ever seen.

Narbel headers are mild steel...M&K exhaust has some interesting mods of stainless SSI headers, the secondaries are shortened and a v band clamp is welded on.. This is ripe for easy twin turbo apps. Mine are already ultra hi-temp coated

You could save a bunch of money by using a 3.2 manifold... in lieu of ITBs.. The Nth degree of performance will be realized with ITBs I already own the ITBs and HATE common plenums

Are you going to twin plug the engine? Absolutely!

I'm a bit confused on your description of the EFI set up... Will you be setting up the MSII sequencer for sequential injection and direct spark? If so in addition to the crank sensor you will need a CAS (cam angle sensor) you can take this obviously from one of the cams, or use an old distributor to provide the signal.. You can control a COP system with just a crank sensor though ... Sequential fuel injection and direct spark are both possible, if I read the Maegamanual correctly...

That MSII sequencer looks very interesting...I may have to pick one up.. That damned thing is a Motec for pennies



No unless you can get variable valve timing and variable turbo vanes...If I could find a variable vane turbo, I'd do it for sure.

Sorry I strayed from which turbo to select...I'll ask Bill which turbo he told me I should use when I was going to build a 2.0 turbo...GREATLY appreciated
Old 05-26-2009, 09:08 PM
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Damn, jackpot! 911ST, I was hoping you'd chime in, too.

Quote:
Originally Posted by 911st View Post
Not an expert but here are some thoughts.

7R case starts reaching its limit at about 270hp. At the heat of a turbo with severly increased combustion pressures and you might be taking a risk. Might be better to find an early sand cast aluminum case if durability is important. Steve Weiner assured me that a properly prepped small bore 7R's threshold is far above 300HP. The baby RSR was mag cased.

Small displacement, short stroke, low compression, cams that will support a usable power band up to 8000rpm -- and I suspect low end power and response is not going to be in the cards. See the dyno sheet above...depends on your point of refernce, but the inferior spec on that sheet still made as much power down lows as a 2.4S, which is enough for me - I just want it even better

For example, a K27-7200 turbo supports 320 hp. Boost starts to come on at 2500 with full boost at about 3200rpm on a 3.3. Put in on a 2.2 and boost will start at about 3700 rpm with full boost at 4500rpm. The K27 is dinosaur tech compared to Tial housed Garrett ball bearing turbos. A journal bearing GT25 Garrett will make 400HP in a MUCH smaller package, with better A/R and a modern ball bearing mechanism. My point is to find the right small turbo to make that power and spool up fast. The K27 ain't it.
Further, you will not likely get low overlap cams to work well at the rpm you want to reach. Thus, boost will come on later with the same turbo. I trust John Dougherty and he says these cams will tear your face off. The dyno above is damned impressive IMO and my cam spec is far superior - this is from John who specced both cams: mine and the ones in the dyno above

Also, you may need a larger lower restriction hot side for less back pressure so there is less hot gasses being pushed back in through the exhaust valve and past intake valve up into the intake manifold. Cool - My headers are 1.5"/38mm, which is pretty favorable by my calcs. What are you thinking in terms of specs?

Think a step beyond a 911S 2.2 (906?) in terms of power band and throttle response. You will probably want the turbo and cams to come in at about 6k to work right. No reason to go twin turbo that adds complexity and weight and you will be looking for turbos that make about 160hp each. This was my plan, but it seems from some other correspondence that a T3 works really well as a single for this config, so a more modern and efficient turbo might fit the billbetter than a twin.

What would be fun would be to run an MFI set up with your 2.3 turbo set up. I have one that would work, but like the progrmability and the extensibility of computer controlling everything - you and Burn Bros should form an MFI turbo cheer club; you might convince me

The best.
Old 05-26-2009, 09:22 PM
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Corrupted by power
 
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Holy Trinity; thanks RarlyL8!

Quote:
Originally Posted by RarlyL8 View Post
Interesting project.
How far outside the box are you willing to go? With engine management combined with tiny displacement you can try something really different - a single VNT from the 996tt.
Max reduction in lag and just about the perfect size for 0.8bar from 2.2L engine.
So obvious, I can't believe I didn't think of it. I am sold unless someone can come up with a reason not to.

From what I can read, the stock 996 turbo is the K16; is this correct? For some reason I thought the VTG turbo were Borg Warner. I thought these were 997 only, though. Any clarification would help.

Last edited by BARknucklehead; 05-27-2009 at 07:56 AM..
Old 05-26-2009, 09:47 PM
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Quote:
Originally Posted by TimT View Post
...and low c/r..probably 8.5:1 which is fine for a EFI controlled turbo engine.. This may be a more economical path
Tim,

Can you explain why 8.5:1 is OK when it sounds like getting even .8 Bar at that CR sounds like it would be impossible? What are the variables that would allow this with EFI? Ignition mapping w/ load sensing, etc? Fuel enrichment for charge cooling? Love to hear some toughts on what you gain/lose at this static CR...
Old 05-27-2009, 06:20 AM
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I thought about the VAT also. Historically managing them was out to the abilities of most. I do not know if that has changed. This is the only way to reach the goal of low rpm full boost and carrying 8k I suspect.

As to the hot side I was referring the the turbine, not the tube size. If it spools at low rpm it will make a lot of back pressure up top. With the cams you will need to carry 8k this should be an issue. Talk to your cam builder.

Trying to reach boost by 3k and pull to 8k is a sizable task.

Did SW know you are going w a turbo on you R case? We are talking a lot more heat and potently expansion. Having said that there has been one builder I read about the built a 2.7 twin turbo he used to drag race that made big HP w/o a problem. Road Racing might be different.

Best of luck and look forward to the project.
Old 05-27-2009, 09:19 AM
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Quote:
Originally Posted by 911st View Post
I thought about the VAT also. Historically managing them was out to the abilities of most. I do not know if that has changed. This is the only way to reach the goal of low rpm full boost and carrying 8k I suspect.

As to the hot side I was referring the the turbine, not the tube size. If it spools at low rpm it will make a lot of back pressure up top. With the cams you will need to carry 8k this should be an issue. Talk to your cam builder.

Trying to reach boost by 3k and pull to 8k is a sizable task.

Did SW know you are going w a turbo on you R case? We are talking a lot more heat and potently expansion. Having said that there has been one builder I read about the built a 2.7 twin turbo he used to drag race that made big HP w/o a problem. Road Racing might be different.

Best of luck and look forward to the project.
This motor is a change of direction, so wasn't factored when I built the case. In talking to him later, he didn't feel it would be an issue, so have decided to move forward. I am still tryin to tease out all of the particulars in this regard, but all looks to be OK as long as I'm not greedy.

I assume managing the variable vanes is through electromechanical control, not by pure mechanics (like a bypass). I will have to research the ECU capabilities more to confirm that this isn't beyond my capabilities - I am not so skilled as to write custom code for vane actuation.
Old 05-27-2009, 09:51 AM
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OK, looks like I cleared up a misconception on my part. Only the 997 uses VTG (variable turbine geometry), not the 996.

As a recap, these adjust flow by altering the air incidence angle upon the turbine. Basically, the 997 Borg-Warner VTG turbo is just a more modern version of the variable vane technology that was piloted in production back in 1989 in the old Chrysler Shelby CSX turbo POS. Older variable turbos were indeed mechanically actuated, but were unreliable in gasoline engines due to high exhaust temps (compared to diesels). The new Borg-Warner VTGs use aerospace materials and thus are very reliable and make great pressure.

The 997 Borg-Warner VTG appears to be computer controlled, but have yet to verify...anyone know for sure?

One other note: apparently "variable vane", "variable turbine" and "variable nozzle" turbos all refer to the same thing.
Old 05-27-2009, 02:40 PM
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Sorry about the 996/997 confusion. Yes 997 is the variable speed turbo I was refering to.
I'm sure it can be made to work with less complicated engine managment electronics.
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Old 05-27-2009, 03:01 PM
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Quote:
Originally Posted by RarlyL8 View Post
Sorry about the 996/997 confusion. Yes 997 is the variable speed turbo I was refering to.
I'm sure it can be made to work with less complicated engine managment electronics.
Cool - was just looking at some Garrett VNT-25 installs on other marques. Very interesting, although they are finicky (can get sticky). You can use them without ECU management, but then your boost is 100% RPM dependent, so forget regulating boost to load. They are a neat turbo, though. The CSX Shelby did use ECU control. They are limited as manufactured to ~250 HP, but supposedly you can install a GT28 turbine in them, which apparently supports 400HP with minimal impact on spoolup...interesting option.

I'd bet that the 997 vane actuator (and the VNT-25, for that matter) is analogous to a stepper motor, which MegaSquirt can control. BTW, those 997 turbos are like hen's teeth - you pretty much have to buy them new, which is an EXPENSIVE proposition.
Old 05-27-2009, 05:17 PM
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Quote:
What are the variables that would allow this with EFI? Ignition mapping w/ load sensing, etc? Fuel enrichment for charge cooling? Love to hear some toughts on what you gain/lose at this static CR...
Since you already own a bunch of the pieces you need roll with it..

Yes better control of all aspects of the engines operations..I'm going to delve further into the Microsquirt sequencer and what it can do.. It may have available channels where you can use knock sensing.

With 8.5:1 you will get crisper off boost throttle response.. though maybe not so much with a small displacement engine. I just put that out as anecdotal..We have built a number of 8.5:1 turbos... some with CIS.... and haven't experienced problems that were purely c/r related...

The new Porsche 997 turbo runs 9.0:1 cr Granted they are water cooled... .. On a related note our 935 clone is 8.7:1 and we sometimes run it at 1.6 bar... usually it runs at 1.2 bar...The only failure this engine sees is if it is over revved... other than that bullet proof..

Back to the engine management side.. you can run fat in areas of the map to keep EGT in check..

Your engine will be a real fun engine... especially in a light car...

My car weighs 1846 wet
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Old 05-27-2009, 05:29 PM
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Quote:
Originally Posted by TimT View Post
Since you already own a bunch of the pieces you need roll with it..

Yes better control of all aspects of the engines operations..I'm going to delve further into the Microsquirt sequencer and what it can do.. It may have available channels where you can use knock sensing.

With 8.5:1 you will get crisper off boost throttle response.. though maybe not so much with a small displacement engine. I just put that out as anecdotal..We have built a number of 8.5:1 turbos... some with CIS.... and haven't experienced problems that were purely c/r related...

The new Porsche 997 turbo runs 9.0:1 cr Granted they are water cooled... .. On a related note our 935 clone is 8.7:1 and we sometimes run it at 1.6 bar... usually it runs at 1.2 bar...The only failure this engine sees is if it is over revved... other than that bullet proof..
MUST KNOW MORE. How are you getting these pressures at this CR w/ such large pistons? Is it ECU regulated for short bursts? FAT fuel maps to cool the charge on load?

Quote:
Originally Posted by TimT View Post
Back to the engine management side.. you can run fat in areas of the map to keep EGT in check..)
Damn, I can't trust whatIi read. High CR, big boost and reliability...WTF??? And to think I thought I needed water injection to get over 1 Bar...

Quote:
Originally Posted by TimT View Post
My car weighs 1846 wet
SICK.

I will probably come in at 2100 lbs - this car will have some creature comforts, albeit not many. Mostly carpet, engine pad, some tunes, etc. All steel body hurts weight...

Last edited by BARknucklehead; 05-27-2009 at 09:18 PM..
Old 05-27-2009, 09:15 PM
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Stole this pic from another thread of the MFI pump with a boost enrichment can mounted on it incase you want to rethink you EFI idea. I would keep the ITB's w the pump mounted in its original location and put the IC on top of every thing.

Or you could mount it off to the side like the factory did.

Quote:
Originally Posted by Flieger View Post
Old 05-28-2009, 09:09 AM
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Quote:
Originally Posted by 911st View Post
Stole this pic from another thread of the MFI pump with a boost enrichment can mounted on it incase you want to rethink you EFI idea. I would keep the ITB's w the pump mounted in its original location and put the IC on top of every thing.

Or you could mount it off to the side like the factory did.
Well, my ITBs are MFI ITBs and I do have a really nice PFI rebuilt RS spec MFI pump...I was talking to Burn Bros again and he thinks that piping up this kind of enrichment circuit isn't too hard. He thinks I should go this route.

You guys are killing me.
Old 05-28-2009, 09:12 AM
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Join Date: Apr 2000
Location: Austin, TX
Posts: 7,471
I have looked into this too. I have spec'd a similar build for the next year or so.

btw, the 997 Borg Warner VTG turbos are electronically operated. I have not been able to figure out if they are direct voltage or PWM actuated. yes, Megasquirt can run this system on either a boost value, rpm or possibly both depending on your ability to code. You would use the configurable output to run the system.

Now just need to figure out how to fit a ducktail under the decklid for 350 HP of hidden, sleeper fun!

Off to continue looking for a donor engine.

FYI, I don't think you need to wait for the sequencer to arrive. The standard MS unit should function just fine - especially considering the rpm range where you will be building boost.
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Old 05-28-2009, 01:09 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #20 (permalink)
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