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Supercharged N/A with CIS
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Raize  



Joined: 18 Sep 2013
Posts: 88
Location: UK

PostPosted: Tue May 05, 2015 6:21 am    Post subject: Reply with quote

I like CIS too but I can't argue with the fact that it only flows 800cc/minute across all four injectors. The N/A CIS just doesn't seem to give enough fuel to be able to safely do anything with it.

1.1bar on a 931 must make around 240hp. What's your AFR like at WOT, 6000rpm? Did you raise CIS system pressure? How much by?
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morghen  



Joined: 21 Jan 2005
Posts: 7871
Location: Romania

PostPosted: Tue May 05, 2015 5:15 pm    Post subject: Reply with quote

I'm reserved on hp numbers but if i'm not mistaken Porsche made @280hp on 1.1bar out of this engine.
Regardless, i have not done anything to the CIS. I installed a wideband sensor and a gauge for it. AFR is 10.5 at 6000RPM.

I had runs with it while adjusting the mixture at 8-9AFR so it can definitely deliver more fuel.
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Raize  



Joined: 18 Sep 2013
Posts: 88
Location: UK

PostPosted: Thu May 07, 2015 5:40 am    Post subject: Reply with quote

Just had a really cool idea for the N/A CIS. You could have a circuit that completes when the CIS air plate is at it's maximum position. The circuit will activate the cold start valve which provides an additional 100cc of fuel per minute. Given that the air plate tops out at 800cc/minute, you'd get a 12.5% increase in fuel.

So if your mixture was 12:1 when the air plate topped out, it would then suddenly become 10.6:1 which is still OK and not ridiculously rich. It would then creep back up as air flow rises further.

This seems way better than the previous uses I've seen of the cold start valve where it's activated by a pressure sensor in the manifold. If you just run it when manifold pressure gets high, you'd have the same extra fuel at 2000rpm as you would at 6000rpm which would probably not be very good.

Not perfect - not at all. But it protects the engine from that lean condition that could ultimately destroy it at high revs and boost - and the rest of the time just runs like normal (ie, low revs high boost - which is actually more realistic for a street car).

And of course if you're right, morghen, the air plate won't top out and the circuit won't actually be needed (which would be fine with me!). But if more fuel IS required... it'll be there.


Last edited by Raize on Thu May 07, 2015 6:59 am; edited 1 time in total
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morghen  



Joined: 21 Jan 2005
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Location: Romania

PostPosted: Thu May 07, 2015 6:05 am    Post subject: Reply with quote

Sounds good, give it a go.
I think no matter the problem there is a cheap solution around the corner.
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Rasta Monsta  



Joined: 12 Jul 2006
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Location: PacNW

PostPosted: Thu May 07, 2015 9:48 am    Post subject: Reply with quote

Why not just run MS on your enrichment injector (writing a map taking RPM, boost and WOT into account)?

An on/off switch at a mechanical metering plate height sounds a little primitive. . .might as well put a big red button on the steering wheel.
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WEASEL149  



Joined: 19 Aug 2005
Posts: 595
Location: UK, Sheffield

PostPosted: Thu May 07, 2015 9:22 pm    Post subject: Reply with quote

Rasta Monsta wrote:
. . .might as well put a big red button on the steering wheel.


Hmm now there's an idea...
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leadfoot  



Joined: 11 Dec 2002
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PostPosted: Fri May 08, 2015 10:12 pm    Post subject: Reply with quote

Be realistic, budget build you're not making 200 let alone 280 off a stock ageing n/a... clutch, driveline, tranny and brakes spring to mind.
If you get 3psi intercooled at the manifold it will be a completly different car.
Save up, buy a turbo model later on... Rebuild engine or do an engine swap for a more modern donk... and I would never put a mechanical device inline of the airflow into the engine unless you were absolutely sure nothing could come loose,
If you are smart you will pick an sc, install it and do a dyno run to calculate fuel requirements after you have exhausted the 931 wurs ability to keep up...
Your just wasting your time guessing with theory and to be quite honest my calculations never looked like yours, they were based on airflow, VE abd absolute pressure.
Stu
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Raize  



Joined: 18 Sep 2013
Posts: 88
Location: UK

PostPosted: Sat May 09, 2015 6:10 am    Post subject: Reply with quote

I agree - I've taken theory to the limit and it now needs to be put into practice.

I'm dead set on the Eaton M45 supercharger simply because it's absolutely the cheapest you can get, and pretty efficient for a roots type. It's also well sized for a moderately boosted 924 and has a useful inlet/outlet positioning.

Not intending to use an intercooler at all as I've read that the restriction of airflow outweighs the gain from cooler temperatures at below half a bar of boost.

I'm pretty sure I can add this SC for less than £1000 (assuming I do everything I possibly can myself including welding), maybe even less than £500. With the Turbo price going crazy in the UK, it's good value for money.
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morghen  



Joined: 21 Jan 2005
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Location: Romania

PostPosted: Sat May 09, 2015 6:48 am    Post subject: Reply with quote

Not sure what limit but i'm happy to hear you're done with the theory and ready to do some work.
I'm excited about this project and i think it can be a refreshing new way to enjoy the 924 NA. If you keep it really simple and find a cheap recipe of lightly modding the 924 into a bit more power, the 924 could be reborn as an afordable cool practical vintage sports car.
If you make 160hp out of it at crank it will be soo cool and sound so cool that i think people will once again love the 924 as it should be loved.
The 944 is considered as the propper cheap porsche to have but with a simple and cheap recipe the 924 could join in on this label.

Wish i had more time to play with the 924, or wish i had the brains and money of now 10 years ago.
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Cédric  



Joined: 27 Aug 2004
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Location: Sweden

PostPosted: Sat May 09, 2015 6:59 am    Post subject: Reply with quote

Before the 931came along there were a kit you could buy with a supercharger and carb, looked very simple. I have it in a magazine article, if i remember correctly they stated 160hp. Haven't read it in years so i don't remember the details. Maybe should scan it.
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chris79  



Joined: 29 Jan 2014
Posts: 551
Location: milan

PostPosted: Sat May 09, 2015 8:20 am    Post subject: Reply with quote

Today I installed new injectors and o-ring on My 924 Na, now all injition system parts are new, I tested car for 20 minutes, performances are very good even with stock Engine if in Perfect status.
Turbo project is not more expensive, but if a lot of work is made by itself.
It would be interesting to find some simple bolt on for ligthy optimize engine, but, as I Read in this forum and in many old 924 articles, it's impossible to increase power with standard and simple tricks.
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leadfoot  



Joined: 11 Dec 2002
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PostPosted: Sat May 09, 2015 2:15 pm    Post subject: Reply with quote

Raize wrote:
I agree - I've taken theory to the limit and it now needs to be put into practice.

I'm dead set on the Eaton M45 supercharger simply because it's absolutely the cheapest you can get, and pretty efficient for a roots type. It's also well sized for a moderately boosted 924 and has a useful inlet/outlet positioning.
prefer this crossflow design
http://www.ebay.com/itm/96-97-Toyota-Previa-TCR10-TCR11-2TZ-SC-Kouki-Super-Charger-Supercharger-/191509502083?hash=item2c96db1883&vxp=mtr

non intercooled this is what I'd do...
ditch the sc manifolds, use another abv and throttle body, chop down the engine intake manifold halfway after the wur mount and weld on a 90/100mm box section (same width as the sc outlet, mount sc directly to this with slotted flanges on either side of the box (just use the outer studs and remove the others) , setup forward/back alignment to your crank pulley, cut sc outlet hole in box section using gasket template, add tensioner/belts.
setup your throttle ABV on the inlet side of the sc between the CIS
done.
this will give you most simplest setup and direct airpath.


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chris79  



Joined: 29 Jan 2014
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Location: milan

PostPosted: Sat May 09, 2015 8:40 pm    Post subject: Reply with quote

Anyone tried the only bolt-on that seems adding hp to engine ?
Change timing to 10 degree to 0.
This can work even on 924 na euro 125 hp ?

http://s148.photobucket.com/user/fiat22turbo/media/Porsche924/Histerical/Articles/Engine/Bolton1_2.jpg.html?sort=3&o=4#/user/fiat22turbo/media/Porsche924/Histerical/Articles/Engine/Bolton1_2.jpg.html?sort=3&o=4&_suid=143116417660104786263135495192
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Raize  



Joined: 18 Sep 2013
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Location: UK

PostPosted: Sat May 09, 2015 10:22 pm    Post subject: Reply with quote

chris79 wrote:
Anyone tried the only bolt-on that seems adding hp to engine ?
Change timing to 10 degree to 0.
This can work even on 924 na euro 125 hp ?

http://s148.photobucket.com/user/fiat22turbo/media/Porsche924/Histerical/Articles/Engine/Bolton1_2.jpg.html?sort=3&o=4#/user/fiat22turbo/media/Porsche924/Histerical/Articles/Engine/Bolton1_2.jpg.html?sort=3&o=4&_suid=143116417660104786263135495192


Euro already has the timing advanced to 10 BTDC as standard. The american cars had timing at 10 ATDC for emissions reasons. Very little to be gained there - too much timing advance can actually reduce power as the peak pressure can end up working AGAINST the piston as it comes up on the compression stroke. Needless to say this is not good for the engine either.

Leadfoot: I can't really get used Toyota superchargers in the UK, I guess noone ever bought supercharged Toyotas here.
I was envisaging just keeping the standard inlet manifold and throttle body, and just having a pipe from the SC to the throttle body. This pipe would of course have a 90 degree bend immediately exiting the SC, and a 180 degree bend to go into the throttle body. Not really sure how restrictive that would be. The 924 N/A induction system has pretty much the same thing already and seems to work OK.
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leadfoot  



Joined: 11 Dec 2002
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PostPosted: Sun May 10, 2015 6:39 pm    Post subject: Reply with quote

If you can find a scrapyard and pick up another manifold it would be better to modify this for performance, engine space and throttle response, get a 60~65mm single butterfly tb from a ford etc and ditch the stock progressive tb.
Is the m45 youre looking at a 76mm pulley?? What boost do you want to actually see at the manifold?
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