924Board.org

[ideola]

I agree with Min..."Maximum Boost" is a must.

I would have some concerns regarding the suitability of a fuel dizzy on a stock normally aspirated 924 engine because it is different than the 931. I don't know the details of the differences, but they are different.

Regarding CIS modifications, I haven't had a chance to go dig up the references am thinking of, but it is fairly common knowledge that the control pressure of any CIS system can be increased by shimming the spring that controls the pressure, thereby increasing the pressure and resulting flow. I discussed this approach at length with David Lloyd when we were first collaborating on the custom 928 motor he assisted me with. Mustante Motorsports has done this on multiple race-prepped 928 engines, including strokers and supercharged applications. I will be using this technique on what amounts to a stroker engine on my 928 (if I ever get around to building it). If it's good enough for them, it's good enough for me. Feel free to contact David Lloyd if you don't want to take my word for it and hear directly from the source.

There are other references I've come across (again, I need to find them) that indicate this technique was widely used on many CIS-based systems when more fuel flow was required. I am fully aware that this does not change the fueling curve. For boosted applications, you can probably achieve some additional fuel flow with this approach, particularly if you err to the rich side, by shimming the CIS. For boost ranges beyond 6 psi, I would not trust this approach, as I imagine the fueling curve would be too far out of whack. Regardless, you will want some form of monitoring such as a wideband O2 setup, or better yet, dyno time to dial it in. This technique is clearly not as precise or as granular as EFI, but I am firmly convinced that it is workable for moderate amounts of boost (say, less than 10 psi).

There is a fascinating thread over on rennlist about a guy who raced a GT variant. I have linked to this threads multiple times in the past. I highly recommend a complete read of that thread, as there is a ton of very interesting information, chock full of very cool ideas that were successfully implemented. Here is a specific post in which Cliff references a rudimentary, screw-driver-adjustable fuel curve enrichment setup driving a single additional injector:
http://forums.rennlist.com/rennforums/showpost.php?p=4320253&postcount=47
There are even lots of photos you can look at to see how it was done.

I also recommend reading the information here regarding the concept and applicability of rising rate fuel pressure regulators. There is a ton of information available by googling as well. I have bookmarked some of these sites, but haven't yet had a chance to pull up the specific sites (other than those already linked to) to substantiate the design conclusions I've arrived at.
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erstwhile owner of just about every 924 variant ever made

[924inMN]

Cool, looks like I'm going to track down a copy of maximum boost. Sounds like necessary reading. Awesome posts, awesome feed back, 924board rocks. Prolly the best forum I have been to. Thanks. I would love to here how raceboys or vdubturbos cars are running.

[ideola]

More stuff...a quick search on "shim fuel" with "search for all terms" selected reveals some good stuff, including a post from Andrew NZ (who, if I'm not mistaken, is personally acquainted with the aforementioned Cliff), It was from Andrew's post that I pilfered a bunch of ideas and links to recommended reading. So, rather than take credit for any of this stuff, let's just say that many of the ideas I've been refining for CIS fuel encrichment came from the links listed above, conversations within the 928 community, and the links in Andrew's post here:
http://www.924board.org/viewtopic.php?t=21614
This is a particular good post for you, 924inMN, because it discusses Andrew's approach to adding a BAE kit to a previously normally aspirated 924.

Leadfoot and Endwrench have also posted fairly frequently on the topic of CIS-based fuel enrichment, so doing a search of his stuff might yield even more results. I knew I wasn't the only one thinking about this stuff.

And finally, let's not forget about water-methanol injection as a potential form of intercooling AND fuel enrichment. Now mind you, Corky Bell admonishes against this approach. HOWEVER, there are probably at least half a dozen guys here running this type of setup on a 931 (Smoothie & tuurbo come to mind). In principal, a water injection setup utilizes the same basic approach that I've described: an injector triggered by some sort of signal (whether it be ECU-based, TPS-based, or MAP-based). Clearly not as tunable or granular as EFI, but widely AND successfully used on ALL sorts of applications, ranging from stock turbo cars, modified turbo cars, and turbo-diesel tow rigs. I would NEVER recommend this as a suitable sole source of fuel enrichment for a high boost application, but the combined benefits of cooling the charge air while increasing octane are widely known to reduce the likelihood of detonation. There are lots of off-the-shelf solutions available that you should be able to readily find by googling.
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erstwhile owner of just about every 924 variant ever made

[Min]

[ideola]

Min, I do like the idea of using MS in a piggy back setup. This is an option you've referenced in the past that I overlooked until research back through what got me here in the first place. If you have any links or references on such a setup, I'd be interested in exploring that approach further.

In the meantime, for those of you that don't have a Rennlist account and can't see the pix in the above-mentioned thread, here is a clip of the magazine article Cliff referenced in his thread, which clearly shows the single add'l injector he plumbed into the backside of the intake manifold on his 160-MPH GT variant.

You can also clearly see at least one add'l port on the backside of the manifold for the second enrichment injector he mentioned that he was going to install, but never got around to.

Rudimentary. Cheap. Simple. Effective. It can be done. And I will also echo what Andrew NZ said in his thread. While I know EFI is ultimately where I'll end up on my build, there is something really attractive to me about the period-correctness of maintaining and milking the CIS setup for all it's worth. This same principle was one of the design considerations that went into my choice of modifying the stock intake manifold rather than building something completely custom like -nick's custom intake or PwrGTOGuy's ITB setup. On the topic of -nick's EFI conversion, you might be interested to PM him with a query regarding his total outlay, which I did some time ago. It corroborated my own research into the topic, which indicates an EFI conversion costing in the range of $1500-$2000. This is not to discredit Min's (or anyone else's) success at installing EFI for less. I merely offer it as an alternative point of comparison.

I sincerely do not mean to "rub this in" to anyone who has taken a different approach. I am not suggesting that these alternatives are superior in any way. What I am suggesting is that there are LOTS of ways to solve problems such as these, so don't ever let anyone tell you your good idea can't be done (unless you try to foist the ridiculous idea of an electric supercharger on us for the umpteenth time!). All that's required is some research, common sense, a lot of thought, a lot of patience & persistence, some more noodling, and a tiny bit of ingenuity. Remember bruce76-924, who fitted a late 944 style dash, even though our own FAQ proclaims it can't be done?!

Incidentally, Bruce was also the guy who successfully fitted up multiple fuel dizzies, although he also said he wouldn't take that approach again, which encouraged me to look at other alternatives such as the rising rate FPR, which is my favorite option at the moment.

Finally, for anyone that's interested in benefiting from any of my collected research, I've posted my car-related bookmarks online. If you download the file, you should be able to add these into your Firefox bookmarks and they'll be properly formatted into folders and sub-folders.
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erstwhile owner of just about every 924 variant ever made

[71vdubturbo]

[804kid]

to start it off, min and ideala should not be fighting, i thought honda guys were the haters no porsche owners ... second how to you switch your car from cis to efi? and what are the benefits

[Min]

[71vdubturbo]

You pull virtually everything that has to do with CIS besides the fuel pump. Add EFI injectors, fuel rail, FPR, coolant and intake sensors, ECU and associated wires. Then tune away.

EFI offers much more control of fueling. You can tune specific fuel parameters for specific RPM and MAP values. Plus, I like it because it doesn't take up much room.
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1977 Porsche 924 - going away...
2001 Audi S4 - 2.7T, Tip

[Min]

for piggyback, I'd probably use this.
http://www.diyautotune.com/catalog/megasquirti-programmable-system-pcb22-unassembled-p-28.html
139 dollars. Unassembled. Solder it up yourself, they have assembled kits for more cash

Benefit of using it that way is that later, you can add sensors, and eventually go with full EFI control.

Min
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Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting.

[Min]

[ideola]

[Min]

[924inMN]

Well, I think informal plan so far is to try to use the stock cis as best I can. I really don't want to run much more than around 7 psi, so if I can get the stock cis to work with that I will. Although a piggyback or supplementary fuel injector that I can program to the boost/fuel curve sounds appealing and reasonably cheap. I'm thinking I'll put an ic in to keep intake's cool. What do you guys think about putting an oil cooler in before or after the turbo. I've seen them on dirt bikes and atvs, but I'm not sure if it would be practical or pointless. Also, I haven't seen many people using garrett's on their porsche's, what do you guys think about them? My buddy has a 300zx and is always talking about garrett's, so thats the only turbo I'm somewhat familiar with. I've seen some decent deals on ebay, and my friend got a pretty nice used one for cheap. Also have seen affordable rebuild kits.

[924inMN]

Oh yeah, If I piggyback where do I put the injector? I assume it would be on the intake manifold? The more I read about it the more I think using stock cis plus a piggyback is the best way for me to start out. Learn about the whole process and then if my budget permits eventually switch to full efi.