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leadfoot · Posted: Fri Apr 10, 2015 1:19 pm Post subject:

I kept the CIS in my twincharged application...

As a simple setup...
use a 1200cc or equivelent SC, an M62 is around 1000cc so would work ok in lower boost setups...
I prefer the aisin blowers (roots) found on toyotas for their compact sizing...
You can change the pulley to fixed or run an rpm controlled activator, about $99 from summit and keep the clutch
with the high comp n/a keeping it around 5/6psi should work well...
get around a 180mm crank pulley and temporarily lock the clutch with 12V and see what the stock pulley config makes, then get your controller if happy or go to fixed smaller size on the sc...
As far as fueling goes, get a 931 WUR, if you need extra fuel you can shim system pressure up in the dissy pretty easily, up to 80psi before the injectors start leaking, but cross that bridge at the dyno... map your A/F and go from there... see what you need to add...
run your sc out through a FMIC and then to throttle, have a decent sized plumb back BOV recirculating the excess air at idle back to the sc intake...
The biggest hurdle will probably be relocating the CIS, potentially to the front of the engine... Have a look at the 931 setup and even get the same mounting bracket??, disconnect the fuel lines and get new ones made from a brake shop, should be fairly easy to do for them... you never know you might be able to bend the old ones to where you need them with a brake line bending tool...
TBO I can't remember how intrusive the N/A dissy is and whether you can move it around enough to give yourself some clearance...
p.s this whole thing will be a lot cheaper if you can weld too...
Stu
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

Raceboy · Joined: 01 Mar 2004 Posts: 2326 Location: Estonia, Europe

Yes, 931 distributor is bolt on to 924.
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'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.
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Raize · Joined: 18 Sep 2013 Posts: 176 Location: Scotland

I'm planning on mounting the SC under the intake manifold.

The N/A fuel dissy is very intrusive but also sits quite high. I do find myself wondering if the supercharger can sit "underneath" the fuel dissy in it's normal position.

There is a mount for the 931 alternator on the block that would probably need to be cut off to allow the SC to sit as close as possible to the block.

I've got some braided injector lines from a scrapyard 924, so that gives me some flexibility for moving the CIS around.

Carrera RSR · Joined: 08 Jan 2010 Posts: 2309 Location: Somerset, UK

You need to search Porschenewbe's posts on here and DrJohn on Porsche owners club UK forum. He's already forgotten more about supercharging a 924 than most know
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
Now www.924board.org/viewtopic.php?t=34690
Then www.924board.org/viewtopic.php?t=31252

ideola · Joined: 01 Oct 2004 Posts: 15548 Location: Spring Lake MI

leadfoot · Posted: Sat Apr 11, 2015 10:50 am Post subject:

Raize · Joined: 18 Sep 2013 Posts: 176 Location: Scotland

It appears that I was mistaken about the easy availability of M62 chargers in the UK. Having spent some time learning to identify between M62, M45 and M65 (which is actually an M45!) the M45's outnumber the M62's on EBAY by 20 to 1, and are priced accordingly.

I can get an M45 for around £100. Anything else is prohibitively expensive £500+. I'll just have to deal with the low boost and the heat. Even so, 200hp should be possible.

Anyway, I found this thread:
http://www.924board.org/viewtopic.php?t=22018

If two N/A CIS distributors can fuel an engine running at 47PSI absolute (32PSI boost), that should mean a single N/A CIS distributor can fuel an engine running at 23.5PSI absolute (9PSI boost) - unless bruce76-924 had other mods to the fueling system that he didn't mention.

Carrera RSR · Joined: 08 Jan 2010 Posts: 2309 Location: Somerset, UK

As I said before, seek out Porschenewbe's thread. Take a look if you don't believe me!! https://www.flickr.com/photos/16693103@N03/14908547259/in/set-h72157647078865445 that's how to supercharge a 924.

And if you want to know how an M90 fits, its here (subject to memebership to access the tech threads) https://porsche924.co.uk/forum/viewtopic.php?t=15052
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
Now www.924board.org/viewtopic.php?t=34690
Then www.924board.org/viewtopic.php?t=31252

Raize · Joined: 18 Sep 2013 Posts: 176 Location: Scotland

From a technical and packaging viewpoint that build is definitely one of the best I've seen although an M90 seems awfully big for a 2L engine. Incredibly clean engine bay though - I'd definitely do something like that if I had the budget.

However I'm trying to keep things cheap hence no EFI conversions and minimal "reconfiguration" of the engine bay.

This M45 supercharger from a Mercedes has a bypass/recirculation valve (or possibly a secondary throttle body? It will work as a bypass valve anyway) built into it - looks like it's electronically controlled. Just need to work out a way to actuate it. I'm thinking some kind of pressure sensor before the throttle body.

Alternatively I could use the earlier type:

This earlier type has no built-in valve but the "second" outlet is obviously meant for a recirculation/bypass system. I could then plumb in a separate, mechanical valve in the obvious place.

Any thoughts, opinions or ideas?

nickthompson · Joined: 26 Mar 2013 Posts: 873 Location: Central Georgia

Take that section off and weld up your own custom peice. Then you don't have to worry about it.

Carrera RSR · Joined: 08 Jan 2010 Posts: 2309 Location: Somerset, UK

Raize · Joined: 18 Sep 2013 Posts: 176 Location: Scotland

Raize · Joined: 18 Sep 2013 Posts: 176 Location: Scotland

I'm still wanting to use the N/A fuel dizzy if I can. It'll be calibrated to give between 12 and 14 AFR for whatever airflow you put through it (it would be stupid otherwise!). So even if it's not perfect for a boosted engine, it may work after a fashion.

Does anyone have figures for the flow rate of a N/A CIS fuel distributor at the top of the air plate travel with stock system pressure?

I'll test it myself at the weekend if noone has these figures.

Also, is the relationship between system pressure and flow rate linear on CIS? I read about people increasing the system pressure for more flow. I REALLY don't want to shim the fuel pressure on my daily driver in the name of science, so I'd REALLY appreciate an answer on this one if anyone has it.

morghen · Joined: 21 Jan 2005 Posts: 8880 Location: Romania

If you use an S1 WUR i think the NA cis will do just fine. Honestly i find no reason why it would not flow as much fuel as the turbo one if you control it with the turbo WUR.
It would be a great project if you kept it simple. As many OEM parts as possible, as little changed parts as possible. If you change loads of parts and re-engineer everything its also nice but it will take you years and cost like a new boxster.

One thing that comes to mind when thinking about NA on boost is the injectors popping out on boost. The NA keeps the injectors in their seats with some o-rings while the turbo has threaded plastic/brass nuts that the injectors screw into.
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