924Board.org

[ideola]

There are three basic options:

• Single stage, keep it under the hood, set it and forget it
  
• Single stage, cockpit controllable
  
• Single or multi-stage, keep it under the hood, but combine it with a solenoid switch to flip into secondary stage of boost

I'm planning to increase boost to about 10 psi initially, and if I add an intercooler later perhaps as high as 15. Aside from initial tuning, is there really any need to have a cockpit switch or control knob for tweaking boost on the fly? This is going in the 941, not a track car, so aside from the coolness factor, is having cockpit control useful for any other reason on a daily driver, or should I just set the boost under the hood and forget about it?
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erstwhile owner of just about every 924 variant ever made

[Khal]

Go baby, go button. No question.




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'80 924 Turbo

[stevekat]

From my personal experience, you want cockpit controllable. The primary reason not to have it in the cockpit, is so you are not tempted to tweak it up, over time, and end up past the razors edge to much regret.

However, I find, depending on gas from fill to fill, ambient temperature, humidity, etc., if you want to operate anywhere near the max. permissible boost, you'll find yourself wanting to fine tune. If you are not planning on having your foot down for minutes on end, like on the track, this probably isn't necessary, you can always lift your foot slightly when you hear ping.

However these days, I try to set my boost so that I have no ping at max. acceleration, under high load...low risk. Some of the guys talk about running one bar, or some 15psi. I buy that they can do this on the street - they get away with it there, but I also believe that if they were on the track even if only for DE with these same settings they'd blow a hole in their piston during the first run group. On the street, the car is not under sustained boost for more than seconds at a time, typically.

I run a CGT intercooler, and a Euro DITC and 10 - 11 is about as far as I can push things if I want no ping at 93 octane U.S. east coast fuel, and be relatively bulletproof. If I go with the U.S. DITC, perhaps a little higher - maybe 12psi. Cold weather I can go better. Above 85 degrees or so, probably less. Setting things conservatively, it is just nice to know you can put your foot down and keep it there without concern.

Another reason to make things cockpit adjustable, is that when weather or gas changes, you want to make corrections, or need to make them. This involves making changes to the controller, putting the car under load, then going thru the human feedback cycle, each time stopping the car, popping the hood, adjusting the controller, retest, stop, pop hood, evaluate. A very time consuming process - very hard on one's hood release. In cockpit, it is much faster and easier.

I have a single stage. The controller provides counter-pressure to the top side of the waste gate. I'll try to post a photo of the controller, it is a vintage Greddy 'Trust.' Looks very similar, if not identical to the old 962 boost controllers one would see back in the day. In some acceleration instances, these cars boost so fast, that one would find themselves rarely getting to operate a switch for a second stage. Also, I believe it would really start to feel like work.

BTW the way, I also find, that max. boost for me is different depending on where I begin to boost RPM-wise, how fast I reach high rpm, ie: accelerating from a slow rolling speed on a ramp to high speed/rpm to merge with traffic, vs. being in highway traffic and boosting to higher speed for passing, etc. vs. accelerating from a stop through several gears. In all instances, the max. boost I record on my VDO 0 - 15 psi gauge varies modestly though this slight variation is sometimes meanginful - I think our analog systems in our cars, including wastegate are just not that predictable. I also think the DITC has reasons to respond with timing in slightly different ways in some scenarios.

Just a separate thought, for anyone that wants to run boost higher than 11 - 12 for any prolonged period of time, I'd have the pistons ceramic coated, and whatever other components inside the cylinder that are also typically coated. Just from past experience with my prior 1981 that I used to run in DE, in the late 1980's.

Sorry, I am sure this is too much information.
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"Never get out of the boat. Absolutely goddamn right. Unless you are goin' all the way."

Gone to new home: '81 924T, US version, CGT Intercooler, UTCIS-PT, Euro DITC, Greddy Trust MBC, Forged Fuchs Flat Dish 6's, Factory Recaro's.

[ideola]

Not at all, I was hoping you'd chime in! I didn't realize you'd converted over to UTCIS...did you post here about it? I'd be interested in what you map looks like, as this is a mod I'm considering in a subsequent stage for this particular car...
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erstwhile owner of just about every 924 variant ever made

[Nein37]

I understand the requirement for caution when tracking a boosted up 931 and certainly defer to your past experience with these cars, but I'm surprised that you'd get pinging running only 12 - 14 psi on an CGT intercooled car. The real CGTs ran 12.5 psi on 8.5 to 1 compression and definitely weren't on the ragged edge, additionally the US car's lower 8 to 1 compression should allow at least another 2 psi without too much worry. Time will certainly tell with regards to my car. My CGT intercooler is currently in need of some machine work on the control line connection but after its back in I'm planning on running 14psi. I'll certainly let the board know if I hole a piston though... I'm a sucker for hard won and expensive lessons.

On a related note does the DITC retard timing when the temp sensor gets higher intake temps? Which would work to protect the engine from detonation in the summer.

I also would prefer a cockpit adjustable boost controller, one with a calibrated maximum allowable boost would make it safer, not only from your own desire to increase boost but also from any passenger that might wonder what the cool little valve is beside their leg.
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1981 931 CGT replica, OEM CGT intercooler, .8 BAR WG spring, GTS Headlights, Innovative Wide band A/F, A/C delete, 16" Fuchs, Weltmeister 200lb lowering springs, Bilstein HDs front, Koni Sport rears.

[Nein37]

Almost forgot. Does anyone know where to source a boost controller setup like the ones in the GTR cabins?
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1981 931 CGT replica, OEM CGT intercooler, .8 BAR WG spring, GTS Headlights, Innovative Wide band A/F, A/C delete, 16" Fuchs, Weltmeister 200lb lowering springs, Bilstein HDs front, Koni Sport rears.

[stevekat]

Nein37/John, I think the difference is fuel here in the U.S. In warm weather I get pinging with the euro DITC at somewhere over 11psi, with the U.S. box somewhere over 12psi, both with the the intercooler. If one thinks about it, this is a pretty hefty increase over the stock U.S. boost pressures of 6.2 - 6.8 psi. BTW, my notes show the CGT having 10.45psi to 11.3psi boost. Let's compare sources since you show a higher number of 12.45 psi.

Also this takes into account my observation mentioned above that the boost max and/or timing/detonation seem to behave slightly differently depending on acceleration circumstance. I could go higher boost and have no detonation in most circumstances, but to have it in no circumstances I must be more conservative. Other members might want to try the various acceleration scenarios and note back if they observe different boost/timing/detonation behaviors.

The ceramic coating, once an engine is apart is probably a notable and reasonable cost help to any short term acceleration meltdown issues.

Dan, regarding the UTCIS, I posted briefly regarding the install and first impressions. Not sure I followed up with much more detail.

http://www.924board.org/viewtopic.php?t=29664&highlight=utcis

The unit was eventually loaded with the map for Unwired Tools own 924 Turbo test vehicle (handy for us and once that was straightened out things have been good - so I haven't messed with it - didn't have the need. If anything, based on the narrow band A/F meter I have, it tends rich if anything under boost. However, the car is transformed. I am not sure if it is all attributable to the UTCIS vs. a good WUR, since my relatively brief ownership of the car I never had a working WUR to compare, but I am very satisfied in my systems current operation.

A link to some earlier detail of getting the UTCIS going (the last couple of pages.)

http://www.924board.org/viewtopic.php?t=29626&postdays=0&postorder=asc&start=60

I had some issues that I recall were related to falling back to a default 930 map. BTW, my car continues to go rich at about 3300 rpm regardless of boost, I believe related to OEM systems function, not the UTCIS. I think in an earlier discussion we found some signal out of the DITC or from the tach to the lamba unit that likely triggered this behavior, though I'd like to understand it better.
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"Never get out of the boat. Absolutely goddamn right. Unless you are goin' all the way."

Gone to new home: '81 924T, US version, CGT Intercooler, UTCIS-PT, Euro DITC, Greddy Trust MBC, Forged Fuchs Flat Dish 6's, Factory Recaro's.

[stevekat]

Dan:

Here is a boss boost controller, if you can find one. I think they are pretty hard to come across. I think I got lucky. It seems similar to the 962 units I recall, though it may be different. Those may in fact have been made by Greddy though. The units I recall in the 962's do not have the sticker on the knob. Nein37/John mentioned in another thread a unit from a GTR, but I am not sure what they look like.







I have tried to find photos online of these vintage units, and have not been able to locate one. I did find a photo of a 962 that had one that looks like this though.

The knob had an interlock - if you push down the knob and shaft interlocks internally with the valve unit and you can adjust. Release and the shaft/knob pop back up. So the setting cannot get inadvertently bumped. The unit appears rebuildable. Very high build quality.

The photos could be better, but I just jumped outside quickly into the howling wind and cold to snap a few with the cell and its built-in flash.

John, are these similar to the GTR units you are speaking of above?
_________________
"Never get out of the boat. Absolutely goddamn right. Unless you are goin' all the way."

Gone to new home: '81 924T, US version, CGT Intercooler, UTCIS-PT, Euro DITC, Greddy Trust MBC, Forged Fuchs Flat Dish 6's, Factory Recaro's.

[ideola]

Steve, how is the plumbing setup on that?
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erstwhile owner of just about every 924 variant ever made

[stevekat]

I have to resize those photos, however I upgraded to OSX 10.6.2, and lots of my software no longer works, including my photo editing apps. (Done.)

This valve depicted is marked for inlet and outlet - so that's important.

Inlet comes from the CGT intercooler, from the fitting where the over-boost switch is also tapped. The inlet hose goes from the intercooler (or charge tube depending on your setup) into the inlet of the boost-controller. The outlet of the boost controller goes into the top vent of the waste gate.

So the normal set up of the waste gate is retained, and no modification occurs to the waste gate system, other than using manifold pressure as a metered source (through the boost controller) to the vent side of the waste gate to counter its normal actuation forces. Essentially the pressure coming out of the boost-controller is used to push back against the forces acting on the normal unmodified actuation side, thereby increasing the pressure required on the unmodified part of the system to open the valve.

I used a nipple that came with a spare waste gate to plumb the hose.
_________________
"Never get out of the boat. Absolutely goddamn right. Unless you are goin' all the way."

Gone to new home: '81 924T, US version, CGT Intercooler, UTCIS-PT, Euro DITC, Greddy Trust MBC, Forged Fuchs Flat Dish 6's, Factory Recaro's.

[ideola]

How about the connection on top of the wastegate? You have an S2, so I suppose it already came with a banjo style vent line???
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erstwhile owner of just about every 924 variant ever made

[ideola]

[stevekat]

Thanks for the photo of the GTR controller. Cool. May or may not be a Greddy. Looks like a similar design, but not the exact same unit.

My car already had less interesting controller, and therefore had a nipple on the existing waste gate (that stands straight up.) My spare waste gate has a banjo fitting. I installed my spare waste gate, after re-building it, with the straight up nipple from the original waste gate. Another waste gate I have has a vent.

I ended up re-using the straight up fitting, as I re-plumbed the cirduit when I was having my J-Pipe replaced by a local shop. I'd have preferred to use the banjo, but the hose sizes I had at the time, and some other fitment issues (minor) had me jump back to the original straight nipple due to time pressure and not wanting to waste the techs time with my detail work. I'd prefer not to use the straight nipple as I recall it may gently touch (with the hose and clamp) the transmission tunnel insulation. If you used a banjo, I believe if one took the time you could orient its direction so it didn't touch or interfere with any components.

I'd also have preferred to use silicon hose with embedded web reinforcement, but I didn't have that available, so I used high pressure fuel injection hose. My first preference would be the factory style braided cloth covered hose, but I wasn't sure what size I would need before the job, and it is pretty expensive, so I didn't pre-source it.

I think in a pinch, if you had neither a nipple or banjo, you could take apart the vent and braze a nipple on to its threaded base. Or maybe even use an NPT nipple if you weren't too concerned about the threads in the top of the vent - maybe.
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"Never get out of the boat. Absolutely goddamn right. Unless you are goin' all the way."

Gone to new home: '81 924T, US version, CGT Intercooler, UTCIS-PT, Euro DITC, Greddy Trust MBC, Forged Fuchs Flat Dish 6's, Factory Recaro's.

[jazz guy]

Dan,
IMO you should definitely go with a cockpit controller. The ease of use and flexibility of a cockpit controller are well worth the effort. The flavor of control is up to you.

The style that stevekat has described has a number of positive attributes:
Ease of installation/simplicity
Wastegate plumbing can remain untouched
Inexpensive
Years of time in-service on board member's cars. I've had mine on for close to 20 years and john h, I believe, has used this style even longer. I'm pretty sure there are a number others using this style as well.

From my experience, this style does a fine job of holding consistent boost levels. Certainly good enough for applications aimed to perform at moderately elevated levels, but not on the razor's edge. For years I never had to fiddle with the boost knob unless I wanted to change the pressure. The last year, I've had to pay attention because max boost tends to wander a little over runs. I believe this has little to do with the controller and is caused by a very old wastegate diaphragm which has never been changed.

[jazz guy]

stevekat,

To follow up on one of your earlier points:

Are you saying that you can't run over 12 pounds of boost without pinging? Or is it that you can't run over 12 pounds for a full track session without encountering some pinging?

At 12 pounds; how long do you estimate that you can run, mostly on boost, before pinging starts to show up?

Cheers, Brian