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Min
Joined: 04 Nov 2002
Posts: 2368
Location: Vernon, British Columbia, Canada
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 Posted: Thu Mar 27, 2008 2:06 am Post subject: |
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| 924inMN wrote: | | 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. |
You would put the injector, or injectors, in a place that will get a fairly even distribution of extra fuel to all your pistons. or at least that would be the idea. Ideally that would be on the plenum in the middle. Or at least thats my theory on it anyways.
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. |
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ideola
Joined: 01 Oct 2004
Posts: 15550
Location: Spring Lake MI
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| Posted: Thu Mar 27, 2008 3:02 am Post subject: |
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Again, "Maximum Boost" would be instructive.
| Corky Bell wrote: | Only two basic rules apply to the location of an injector. First, it must be aimed as straight down the center of a port as possible. Second, it should discharge at a point where air velocity is at or near its highest.
Occasionally a system will have such a large airflow or rev range that a single injector cannot provide enough fuel. In such circumstances, at least a secondary will be required, and sometimes even a third. Alignment of the secondary injector is not as critical as the primary, because the secondary is generally not used until the system has achieved a relatively high rate of airflow. In street applications, it is still desirable to point the secondary injetor downstream. Race applications, however, have occasionally aimed the secondary back upstream. Although data are scarce, this may offer slightly better atomization and is worthy of consideration.
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So on a standard NA 924 head, your options are:
1. Drill an extra injector hole in the head
2. Drill and weld injector bungs on each of the intake manifold runners
3. Add injectors in some fashion to the intake plenum
Option 1 seems darn near impossible. If you read the link I posted to Bruce's installation, you'll see that he accommodated an extra injector for each cylinder by using a non-FI Audi head, and drilling two injector inserts. Probably not a very feasible option for the NA head (although it might be possible).
Option 2 is probably ideal from a location perspective, as there is ample room on the stock NA manifold runners to drill and weld on injector bungs, which could be optionally oriented with or against the air flow depending on your preference. However, it would require some fairly skilled welding and machining abilities to execute properly.
Option 3 is probably the easiest approach. One idea I have contemplated is using stock CSVs, and orienting them as Cliff demonstrated on his GT in the links I posted to over on Rennlist. The profile of the CSV is small enough that you could probably add them to the stock intake manifold plenum by drilling the insert and bolt holes along the flat casting "rib" that runs longitudinally along the backside of the plenum. This approach would allow the addition of multiple injectors -- as few as one, as Cliff did; or as many as one per intake runner, strategically positioned -- without requiring any expensive welding or machining.
For my UWB project, I had a block-off plate machined for the stock TB location. I specifically selected a Series I 931 intake to preserve runner length, as well as to take advantage of the larger, rectangular opening for the SI-style TB, which will allow me to install up to four injectors on the block off plate.
As Min suggests, Option 3 positions the add'l fuel flow directly into the oncoming charge air, which I suspect will achieve the atomization effect that Mr. Bell mentions.
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erstwhile owner of just about every 924 variant ever made |
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71vdubturbo
Joined: 28 Nov 2006
Posts: 75
Location: Rolla, Missouri
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| Posted: Thu Mar 27, 2008 5:36 am Post subject: |
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| 924inMN wrote: | | Also, I haven't seen many people using garrett's on their porsche's, what do you guys think about them? |
I just bought what was cheap and had low miles. I knew the TD04 came from a 2.0L WRX with about the same redline so I figured that the airflow from the engine would be relatively the same. It makes full boost by 2400 rpm.
The great thing about garrett turbo's are they have tons of information about them directly on their website. This would include compressor maps, turbine maps, wheel sizes, etc... I have found some maps for Mitsubishi turbos like mine but they take a lot of searching. Borg Warners site (KKK, or 3K) sucks. I haven't found a lot of information about their turbos.
I think the whole argument about turbo brands is certain manufacturers offer different combinations of compressors and turbines that suit certain people better. Basically, it's up to you to decide who you want to go with. Just stay away from the chinese crap.
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1977 Porsche 924 - going away...
2001 Audi S4 - 2.7T, Tip |
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924inMN
Joined: 25 Mar 2008
Posts: 10
Location: Minnesota
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| Posted: Thu Mar 27, 2008 1:42 pm Post subject: |
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| This question is a little off topic but here goes. A guy on craigslist is selling a 4 speed tranny for 50 bucks (5o,000 miles apparently). I have a 5 speed, is the four better or should I stick with my 5. I ask this because I noticed vdub has a 4 speed audi tranny listed in his post. |
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Andrew NZ
Joined: 22 Jun 2004
Posts: 744
Location: New Zealand
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| Posted: Thu Mar 27, 2008 2:16 pm Post subject: |
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| ideola wrote: | | 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. |
The only reason I went that way was because of class rules. Yes it worked well in the end, but it certainly wasn't cheap or simple!! If I did it over again I'd do it the cheap and simple way and go EFI!
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Andrew
1977 RX924 race car
12a bridgeport supercharged
www.race4-dcup.co.nz |
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Raceboy
Joined: 01 Mar 2004
Posts: 2327
Location: Estonia, Europe
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| Posted: Thu Mar 27, 2008 4:28 pm Post subject: |
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If you want your new turbo setup to work properly, go with EFI. Yes, everything (almost) can be done with CIS but no offense here, but I doubt you have enough knowledge getting good results with CIS. I know I don't.
With MegaSquirt, you can get direct advice and hell, even straight and working base maps here in forum.
My advice would be to collect ALL parts you need for EFI (sensors, fuel injectors+rail+FPR, ECU, EDIS (if using MS 2.2) and then start converting. I suggest you get a spare crank pulley to get the trigger wheel installed and not having your car standing at that time.
And thanks, my car is still running nice and strong  Absolutely no signs of otherwise (*knock on wood*).
I'll be transplanting this engine to another 924 (mine) to give space 2.5 16v turbocharged engine this spring/summer.
_________________
'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold 
'84 924, turbocharged, sold.
http://www.facebook.com/vemsporsche |
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924inMN
Joined: 25 Mar 2008
Posts: 10
Location: Minnesota
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| Posted: Fri Mar 28, 2008 12:31 am Post subject: |
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| Where did you guys get your efi's. Is there a good or favorite website that you have. How much would the cheapest set up run me? Cost is really my only limiting factor. |
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Min
Joined: 04 Nov 2002
Posts: 2368
Location: Vernon, British Columbia, Canada
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| Posted: Fri Mar 28, 2008 1:03 am Post subject: |
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| 924inMN wrote: | | Where did you guys get your efi's. Is there a good or favorite website that you have. How much would the cheapest set up run me? Cost is really my only limiting factor. |
www.diyautotune.com
I'm running a megasquirt, raceboy is running vems. You can do a EFI installation for as little as 650-700ish dollars. However, I wouldn't recommend spending less than 1000 on the entire deal (wideband oxygen sensor included in that price, new fuel pressure regulator, will need various 'junkyard' bits like EDIS modules, coilpacks, that kinda thing.)
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. |
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ideola
Joined: 01 Oct 2004
Posts: 15550
Location: Spring Lake MI
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| Posted: Fri Mar 28, 2008 1:18 am Post subject: |
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We interrupt this EFI program to bring you this blast from the CIS past...
Ahhh....here it is...I was looking for this but couldn't find it in my bookmarks...I knew there was another alternative for CIS fuel enrichment.
http://www.andial.com/content/930/fuel_enrich.htm
Given other commonalities (e.g. wastegate, gearbox, CIS, etc.) between the same era 931 and 911, this setup is one alternative I had researched early on. It is definitely primitive, and has fallen out of favor with the 930 crowd due to it's lack of tunability at the high end of the RPM range...but on a 931 K26 blower (which doesn't need to puff nearly as much as a 930 blower), this type of setup might be readily adaptable and workable on a 931.
Anyway, I'm not going this route, just thought I would add it to the general knowledge base, and to demonstrate that I wasn't talking completely out of my butt when I said there were demonstrated ways of supplementing CIS...
...now back to our regularly scheduled programming
(PS, I am making a weak attempt at humor...please don't interpret this post as anything other than good-natured discussion). 
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erstwhile owner of just about every 924 variant ever made |
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Min
Joined: 04 Nov 2002
Posts: 2368
Location: Vernon, British Columbia, Canada
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| Posted: Fri Mar 28, 2008 1:50 am Post subject: |
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Thats good info ideola. It definitely ad's a data point to what we've got so far. So looks like that setup mucks with the WUR pressure. I think the fully programmable wur might be a more advanced option for similar enrichment. More expensive of course.
Min
_________________
Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting. |
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ideola
Joined: 01 Oct 2004
Posts: 15550
Location: Spring Lake MI
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| Posted: Fri Mar 28, 2008 1:53 am Post subject: |
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Oops, sorry, here's one more link that is relevant to CIS: this one is buried in my bookmarks (that I linked to earlier) under the 928 section, so you might have missed it. It is a PDF that describes how to fix AND adjust a WUR. It has been linked to elsewhere on this board IIRC, and I believe that the similarity of the K-jetronic WUR on the 928s to the 924 and 931 make this applicable as well.
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ideola
Joined: 01 Oct 2004
Posts: 15550
Location: Spring Lake MI
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| Posted: Fri Mar 28, 2008 1:57 am Post subject: |
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| Min wrote: | | I think the fully programmable wur might be a more advanced option for similar enrichment. |
Yeah, I agree, if the UTCIS stuff is as good as it sounds, it seems like the ultimate happy medium between doing nothing and full-blown EFI conversion. There are some threads over on Rennlist where the 911 guys were bemoaning the fact that the UTCIS setup kept being delayed for release. Apparently, our friend epsylon is one of the first p-car owners to have installed it. It will be interesting to follow those developments for sure.
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ideola
Joined: 01 Oct 2004
Posts: 15550
Location: Spring Lake MI
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| Posted: Fri Mar 28, 2008 2:21 am Post subject: |
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This from "Water-Cooled Volkswagen Performance Handbook" by Greg Raven on the topic of K-jetronic fuel enrichment
| Mr. Raven wrote: | ...in the early days, we rigged up switches in parallel with the cold-start enrichment system, but this was crude and experimental.
If you are putting together your own system or if you run into problems, you will have to spend some time dyno testing and taking EGT and oxygen sensor readings until you get everything straightened out. Things are not as bleak as they seem, however. Although you can easily run a motor into meltdown on the dyno by keeping it in boost for several minutes, in real life, you will be lucky to stay in boost more than a few seconds at a time. This is one reason why fuel enrichment systems that seem all wrong theoretically can provide a sufficient margin of safety for street applications.
One rumor about [forced induction] CIS motors is that the CIS cannot supply the fuel needed by the motor because the fuel pressure to the injectors is kept at a constant while the boost pressure rises. The example usually given is that if you had 6 psi of fuel pressure and 6 psi of boost, the pressure differential across the injector would be zero, so you would get no flow. Although this is an extreme example, if it were true it would mean that the fuel injection's ability to operate gets worse at the precise time the motor needs fuel the most.
As it turns out, this is not the case. The dynamcis of injecting a fluid into a gas are fairly complex, but suffice to say that because air is compressible and fuel is not, the injectors will work fine at any boost level you are likely to use. |
...then he goes thru a series of calcs & explanations regarding fuel vs. boost pressure. here's the punchline...
| Mr. Raven wrote: | | Playing with the numbers a little, you can determine that the stock CIS fuel injection is good to 27 psi of boost in this respect. |
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erstwhile owner of just about every 924 variant ever made |
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Min
Joined: 04 Nov 2002
Posts: 2368
Location: Vernon, British Columbia, Canada
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| Posted: Fri Mar 28, 2008 2:53 am Post subject: |
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| ideola wrote: | | Mr. Raven wrote: | | Playing with the numbers a little, you can determine that the stock CIS fuel injection is good to 27 psi of boost in this respect. |
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From your brief quote, it honestly sounds like he's referring to the injectors themselves being capable of opening at 27psi of boost. Rather than being able to deliver the required to flow to keep the motor alive at that level. But its a small quote, quite easy to misunderstand.
Min
_________________
Custom means it didn't come from a box.
1980 n/a with EDIS and Megasquirt II Injection. 7 different colors and counting. |
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ideola
Joined: 01 Oct 2004
Posts: 15550
Location: Spring Lake MI
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| Posted: Fri Mar 28, 2008 3:19 am Post subject: |
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Yeah, to clarify, I interpreted what he's saying as the injectors themselves could open at 27 PSI boost, but he says nothing specifically about the ability of the overall system to deliver that sort of fuel flow. Didn't mean to imply that CIS could handle 27 psi 
From what I understand, you have to look at the CIS as a system based on how it was installed for a specific head / induction setup, and supplement it based on targeted HP. I read elsewhere, I think it might have been at K-jet.org, that most CIS systems are good for somewhere in the neighborhood of double the stock HP of the car they were installed on. So for a NA retrofitted with some sort of aftermarket forced induction, I would think that with a bit of fiddling such as described elsewhere, the stock CIS could be made to deliver enough fuel to avoid too-lean conditions in short bursts of boosts for probably at least 175 HP?
For my monster build, I'm looking at more than doubling the stock HP, so supplemental fueling is a must.
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924 FAQ (Technical)
