Welcome all 928 forum refugees!
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By Crumpler
#26760
Ok gentlemen. DE season is over and I am going back in to the garage.

Specs are as follows:

Procharger P-1SC-1 (Standard Drive!) is going on with non-helical gears.
Goal is low boost system 4-6 boost, with procharger bullet BOV to prevent compressor surge.
Currently stock ECU computers.
Currently adjustable FMU.
Currently 24 lb. four hole injectors.
Currently barrel air to water intercooler.
Wideband in cabin.
Currently 6.5 inch crank pulley with 4.75 inch blower pulley.

How does the collective feel about aftermarket knock detection? I was considering a basic signal light kit.
I have a pro doing the final tune, but I would like a safe ballpark as I attempt to set FMU, etc. The long game is either sharktuner or VEMS system.

There seem to be a few options out there. But what’s the likelihood they will give me accurate results?
The Link kit has a self calibration for an engine’s normal noise range first, which sounded appealing on paper, but also got the impression that once a knock event is detected it just stays on until you shut off.
User avatar
By Shifted
#26766
My reading of the KnockLink description and marketing material is that it flashes red when it detects knock, and stops flashing when there is no knock. This video seems to confirm that:

User avatar
By Crumpler
#26774
Excellent, many thanks.
I don’t think it would hurt anyone to have some insurance here for knock events. My concern was having to interpret false positives or negatives with the sensor.
There was some chatter on the other channel about the S3 pistons being noisy to begin with, or maybe the opposite— I stopped listening;)
User avatar
By Shifted
#26776
You're right. And I think that knocks are the biggest concern with boost and no ignition map changes. From my reading on the pre-87 32v engines, they had a fairly conservative ignition map because there was no knock sensor. Which means that there should be room for some boost without too many knocks.

What octane of gas do you have available? If you can run 93, that would help.
User avatar
By Crumpler
#26789
93 always and forever :)
You know unofficial accounts suggest that I vent crankcase to atmosphere... which probably helps octane further.
Shifted liked this
User avatar
By worf
#26879
Have you yanked on Porken?

If I was boosting an S3, I’d see if Ken could hook me up with an EZF prom that would pull timing based upon one of the unused pins going high or low (or maybe repurpose existing input) that ate from external knock detection.

I’ve a dim memory that he did something like that already.
User avatar
By Crumpler
#26923
worf wrote: Tue Oct 20, 2020 9:11 pm Have you yanked on Porken?

If I was boosting an S3, I’d see if Ken could hook me up with an EZF prom that would pull timing based upon one of the unused pins going high or low (or maybe repurpose existing input) that ate from external knock detection.

I’ve a dim memory that he did something like that already.
Dave that’s a crackerjack idea.
I have grown so used to not expecting much from the stock computers, it didn’t occur to be that I could utilize them for anything.
I haven’t yanked on Ken since I asked for any black op chips going into this last DE without the planned boost;)
User avatar
By Crumpler
#27404
Calculating for fuel injectors tonight.
I've got the top end torn down to place the knock sensor and this seemed like the time to change from the 24 lbs. if I was going to.
So far the various website spreadsheets recommend 30-32 lbs/hr
Based on:
estimated hp at crank (picked 400)
8 cyl
80-85% duty cycle
BSFC 0.55
55 psi fuel pressure ('87 FPR)

I had kicked around on old threads and really never found any consistency with injectors used for 928 SC projects.
Of the 30 lb choices, I found Accel, Bosch 0280155759, or various Ford examples. Most required O-rings sourced to fit.
User avatar
By worf
#27415
Crumpler wrote: Thu Oct 22, 2020 8:39 pm Calculating for fuel injectors tonight.
I've got the top end torn down to place the knock sensor and this seemed like the time to change from the 24 lbs. if I was going to.
So far the various website spreadsheets recommend 30-32 lbs/hr
Based on:
estimated hp at crank (picked 400)
8 cyl
80-85% duty cycle
BSFC 0.55
55 psi fuel pressure ('87 FPR)

I had kicked around on old threads and really never found any consistency with injectors used for 928 SC projects.
Of the 30 lb choices, I found Accel, Bosch 0280155759, or various Ford examples. Most required O-rings sourced to fit.
FWIW, my twin screw uses Bosch 30# injectors.

If you don't know already: Whatever injectors you get, do your best to get their opening time (latency) so as to poke that value into the ST.
User avatar
By Shifted
#27559
If I recall correctly, you don't plan to use a SharkTuner, right?

The stock fuel injector size for the 1985/86 is 24 lbs and the WSM states that the fuel pressure (with engine off and fuel pump relay jumped) should be 2.3 to 2.7 bar (33 to 39 psi).

However, you have a fuel pressure regulator from 1987, which should be giving you a fuel pressure of 3.6 to 4.0 bar (52 to 58 psi).

Higher fuel pressure with the same opening times means more fuel will be delivered for each opening, meaning it will be rich already.

My personal experience has shown that as manifold pressure rises above zero, it causes the fuel pressure to also rise, due to the signal line driving the fuel pressure regulator. Which means that even more fuel will be delivered. So, all things being equal, you're rich to start with. Which is why you have the fuel management unit (FMU) to reduce the fuel pressure under boost to get your AFR where you want it.

You bring up the duty cycle, which is a good thing to consider, but you have to take into account that the LH halves the injector pulse width under high load and RPM. What happens is that instead of the injector opening once every engine rotation, it starts opening once every engine firing (once every other rotation). This allows more time for the injector to stay open, effectively increasing how much fuel it can deliver by a factor of two. If you look at the injector duty cycle as logged by the SharkTuner for a stock 1987, you will see it suddenly jump from ~60% to ~120% a little above 5k rpm, and continue to climb to around 150% at the rev limit. Obviously, you can't exceed 100%, so what's really happening is that the fuel being delivered by opening once every other revolution is twice what it could deliver by opening only once per revolution.

My reading of the 85/86 duty cycle is that it has even more headroom before it needs to halve the pulse rate. And with your higher fuel pressure, that's going to be reduced even further.

In other words, your 80% maximum duty cycle calculation will actually work out to only 40% of the injector's capability.

Or, to put it another way, take the injector that meets your maximum fueling needs without halving the injection pulse rate, and then get 75% of that size and you'll be in the general ballpark. If you need 30 lbs without halving the injector pulse rate, then you should be ok with 22, theoretically. And that's before even factoring in the rising fuel pressure from the boost. Which further reduces the required injector size. Easily to under 20.

In other words, what you have now should work just fine.

For reference, I have 60 lbs injectors in my car. Without boost, at maximum rpm/power/load, they topped out at about 43% duty cycle. They never reached a high enough load for the LH to halve the pulse rate.

With 11.6psi boost, they top out at around 65% duty cycle. Again, without halving the pulse rate, but in this case because I disabled that feature in the SharkTuner for smoother fueling transition between cells and because I don't need it with my larger injectors.

Even though my power output went up somewhere in the neighborhood of 90%, the duty cycle only went up by around 50%. Due to the higher pressure in the fuel rail, which is driven by the manifold pressure driving the fuel pressure regulator. I tuned around that higher pressure by cutting fuel a LOT as I approach the maximum load/rpm. Since you won't be able to tune your LH, you'll be using your FMU to achieve the same result.

For what it's worth, the Murf Stage 1 kit for the 1987+ motors (6-8 psi) retained the stock injectors. You have the same injectors and the same FPR as that kit was built around.

Bottom line, I don't think that you need to change your injectors.


But, I am FAR from an expert. So, take my commentary with a big grain of salt :)
User avatar
By Crumpler
#27597
Hey Dave, thanks for the feedback. I didn’t realize you your sitting on a twin screw variant. Was it a DR kit?
I found Ken BTW, he said while pulling timing was possible in theory for the S3, but not practical, I’m paraphrasing:).


Chris, that’s excellent data again thank you, that’s a pretty convincing story. I will see how it goes with the 24’s first.

Now here’s today’s dog exploratory surgery:
Two pair of creepy, semi-mummified laytex gloves, and a chunk of glass.
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User avatar
By Shifted
#27624
All from the same dog? I wonder if it ate the glass before or after the gloves....which one it thought would solve the indigestion of the other? At least the timing is just right to use as part of your halloween costume. Please post photos of you wearing the gloves...
User avatar
By Shifted
#27772
I think it's really fascinating what you do. I wish that I could be an observer when you do these surgeries. You must have some serious skill to retrieve these items and put the animals back together so that they can return to normal lives.
User avatar
By SeanR
#27778
For injectors I'm using these on everything that's boosted.

https://www.racetronix.biz/p/63-lb-hr-s ... t/fi114961

You can save some money and not get the flow matched set as it's really not necessary.
User avatar
By Shifted
#27807
SeanR wrote: Sat Oct 24, 2020 8:11 am For injectors I'm using these on everything that's boosted.

https://www.racetronix.biz/p/63-lb-hr-s ... t/fi114961

You can save some money and not get the flow matched set as it's really not necessary.
That's a whole lot of injector. What boost levels do you use it for and what % injector open time does it result in? Stock fuel pump?

Mine are Siemens Deka IV 60 lbs EV1 Long and I'm barely using them even without halving the pulse rate, even at 11.6 psi.

ETA: I looked at the spec sheet for the ones that you linked to, and they are the exact same ones that I bought. Interesting that they advertise them as 63 lbs, when everyone else calls them 60 lbs, and the spec sheet says 61 lbs at the specified test pressure (300 kPA, or 43 psi).

I bought mine from FiveOMotorsport.com for about $500 for the flow matched set of 8. They had really great customer service and threw in the bigger o-rings for free. Personally, I think that getting a flow matched set is a really good idea. I can't imagine buying a set that wasn't flow matched. Here was my flow report:
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User avatar
By Crumpler
#27893
Nah, my job might smell worse but it is just like anyone else’s. The longer you do it the more comfortable you are at it.


Ok, thanks guys, I will check out the injector choices.
What are the real specs for the o rings. With calipers I get 13mm OD on my current ones, top and bottom. Does that sound right?

Also another curve ball, new blower orientation doesn’t work at old location. I would have to further wikiup radiator hoses and also choke down the inlet more. That’s just too problematic. I’m going to look at the old A/C location and see what I can come up with.
User avatar
By Crumpler
#30348
SC is set up at new position . Some progress.
Bracket work was just as tedious the third time.
Multiple advantages at the old A/C position, at least for the S3 configuration. I think IMO did this spot for his SC back in the day.
Tensioner placed.
More to come.
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User avatar
By Crumpler
#32665
Not the most productive weekend ever, but did get top end assembled and set BOV.
By rights I think the BOV should be as close to the throttle plate as possible, but in S3 land that turns into just after blower, I am hopeful it won’t make a big difference.
It’s a procharger BOV. There are no published specs on spring rates, maybe to protect the secret sauce. My assumption would be it’s compatible since it’s a SC company.
It’s also not the biggest vacuum signal line going into it, but we will see.
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User avatar
By Shifted
#32974
The two main reasons why most people recommend putting the BOV close to the throttle plate are:

1) So that the pressure is relieved from the throttle body as soon as possible. This is more about reducing pressures that can blow something apart (e.g. a clamped on silicone connection) and allowing a smoother return to idle or lower RPM.

2) So that as little air as possible is lost and pressure can be built up faster. This is focused on having faster boost response when downshifting or coming off of and then back onto the throttle.

I think that these are theories that have diminishing returns the lower the pressure. Above 15 psi, and definitely in the 25+ range, they probably make a noticeable difference when transitioning to/from boost. At your pressure levels, it might be demonstrable, but I doubt that you'll notice a difference most of the time.

Your vacuum signal line looks like a decent size from the photo. What size is the line?
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By Crumpler
#33301
Shifted wrote: Tue Nov 10, 2020 7:36 am The two main reasons why most people recommend putting the BOV close to the throttle plate are:

1) So that the pressure is relieved from the throttle body as soon as possible. This is more about reducing pressures that can blow something apart (e.g. a clamped on silicone connection) and allowing a smoother return to idle or lower RPM.

2) So that as little air as possible is lost and pressure can be built up faster. This is focused on having faster boost response when downshifting or coming off of and then back onto the throttle.

I think that these are theories that have diminishing returns the lower the pressure. Above 15 psi, and definitely in the 25+ range, they probably make a noticeable difference when transitioning to/from boost. At your pressure levels, it might be demonstrable, but I doubt that you'll notice a difference most of the time.

Your vacuum signal line looks like a decent size from the photo. What size is the line?
Ok, that makes sense to me.
On calipers, the OD of the line is 8mm. Looks to be next size up from the port sizes on the TB.
User avatar
By Shifted
#33305
An 8mm OD line is probably 1/4" ID, which is ideal for the BOV. Should work well as long as it has a similar sized connection on the throttle body. One way to know for sure! :)
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By Crumpler
#37208
I’ve got some time this week to get in the garage.
God, I’m starting to sound like Jerry.
Anyway, covid silver lining: same amount of food and the in-laws cancelled their Thanksgiving visit!

Had to relocate the intercooler pump to under the passenger fender. Tedious.

The intercooler set up is a challenge for 85/86.
Never got any hope of buying a custom Murf. Unit or that stage two number that Carl had. So I found a barrel intercooler that would fit.
My concern is the core size 4x8, was the biggest I could get in there and it seems limited.
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User avatar
By Shifted
#37243
That looks really good!

Generally, most people say that anything under 8psi doesn't require an intercooler. I'm not a subscriber to that philosophy, but it's good to know that most people who forgo an intercooler don't have issues. Will you be able to monitor knocks real time? Air intake temperature?
User avatar
By Crumpler
#37268
Thanks Chris, yeah while the plan is low boost system, having it out on the track without an intercooler made me nervous.

There is a knock sensor installed in the forward position. It will be wired to a signal light in the cabin. Hopefully it will give me diagnostic readings.
I had a distant plan of both air temp and coolant temp gauges, but nothing in the pipeline yet.

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