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Rasta Monsta
Joined: 12 Jul 2006
Posts: 11733
Location: PacNW
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 Posted: Sat Jan 31, 2015 5:07 pm Post subject: |
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Definitely have not, but my CIS car runs like a watch, too many dumb ass techs have said "CIS will never run right, let me put Webers on your car," and your statement that CIS causes turbo lag is utter nonsense.
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Toofah King Bad
- WeiBe (1987 924S 2.5t) - 931 S3
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jason c
Joined: 13 Jan 2014
Posts: 1018
Location: Nwi
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| Posted: Sat Jan 31, 2015 5:39 pm Post subject: |
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| Rasta Monsta wrote: | | Definitely have not, but my CIS car runs like a watch, too many dumb ass techs have said "CIS will never run right, let me put Webers on your car," and your statement that CIS causes turbo lag is utter nonsense. |
You are correct about CIS getting bashed, 99% of the time its by people who don't understand it.
You're misunderstanding what I'm saying.
I never said nor implied it causes turbo lag. Turbo lag is its own entity. The lag I was referring to was in throttle response time. There is a lag associated with CIS, with both turbo & N/A. The sensor plate is a restriction on acceleration until fully open due in part to the control pressure resistance.
Barn door AFM's have a similar effect, that's why (or partially why) people go to MAF or MAP. |
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Kenodog
Joined: 25 Jun 2003
Posts: 2669
Location: Vancouver,B.C.
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| Posted: Sun Feb 01, 2015 4:56 am Post subject: |
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Jason , I do partially agree with you. Rasta ,you too. My old car was a pretty damn fast little car, even with CIS. The tech that did the dyno didnt beleive it was a stock 'poor mans Porsche'. But the CIS components and fuel system was completely and utterly 'new' as new could be. And yes, for the 2.5 years I drove it not ONE SINGLE TIME did it fail to start or run perfectly. That includes numerous cross province trips. (Hinton ,Alberta to Steveston,BC in 7hours 10minutes)
What im building now isnt a full blown race motor however. Its a weekend fun toy for now. I will mod it crazy-like in the future.
Thanks for the input boys, I do appreciate it. NO bad ideas and NO big egos. 'Cept mine...
Leigh
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1979 Euro 931, Olive
1981 931, Sabine
1991 Ford Ranger XLT 4x4, Ricky
1996 Ford E-350 ex-FedEx Van
2014 Mazda CX-5 (Kinderwagon)
2019 KTM 790 Adventure
2024 KLX300
2024 KLX140 |
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leadfoot
Joined: 11 Dec 2002
Posts: 2222
Location: gOLD cOAST Australia
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| Posted: Sun Feb 01, 2015 9:02 am Post subject: |
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| jason c wrote: | Never seen that one either.
Have you ever even driven a CIS car before & after an EFI conversion? |
I have converted , driven and dyno'd my car with the results...
on a N/A it made f'all difference in power... and was a real headache when it came to tuning for cold starts/idle stability
agree there is a slight improvement in throttle response, but a headache to tune idle stability and cold starts... i'd also say that the redesigned manifold i made with internal bellmouths achieved the same effects on cis...
the N/A is shit as it is inefficient, the turbo head is better but is a forced induction system... I have converted heads and measured the difference in flow restriction alone...
change to a supercharger from a turbo and throttle lag is negligible...
go to a twin charger system and throttle lag is negligible...
imho both systems have merit and yet I was surprised at how far the cis could be pushed, I had a secondary fueling system in place with the twin charger system that wasn't required at 17psi boost... so control your heat, flow and overall health of the system and you can go along way with the CIS....
Stu
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress... |
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jason c
Joined: 13 Jan 2014
Posts: 1018
Location: Nwi
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| Posted: Sun Feb 01, 2015 9:12 am Post subject: |
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Ken,
I never said CIS doesn't work or cars can't run well with it. I was simply trying to add my .02 about the AFM, airflow, CIS and it limitations in reference to your build. |
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jason c
Joined: 13 Jan 2014
Posts: 1018
Location: Nwi
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| Posted: Sun Feb 01, 2015 9:21 am Post subject: |
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Stu,
Every system has its drawbacks. It doesn't surprise me EFI made little difference in power on a stock N/A motor, CIS is effective. How was your gas mileage with EFI BTW?
Efi takes full advantage of a modded motor, you can "out do" CIS with mods. |
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leadfoot
Joined: 11 Dec 2002
Posts: 2222
Location: gOLD cOAST Australia
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| Posted: Sun Feb 01, 2015 2:56 pm Post subject: |
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About the same from memory with it N/A, you could tune it lean to get more mileage but I found the drive-ability suffered, you had to go richer to stop idle hunting and on throttle snap but paying attention to not afterburn too much,
on that particular engine after forced induction and cam my mileage went out the window, about 30% for an extra 100hp approx
Have you seen any merit by enlarging the outlet on the afm? IIRC it was smaller (58-60mm??) than my t03 inlet at 63mm, didn't have my ally welder then so left it stock...
Stu
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress... |
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jason c
Joined: 13 Jan 2014
Posts: 1018
Location: Nwi
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| Posted: Sun Feb 01, 2015 4:37 pm Post subject: |
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Ive never had to do that. I haven't run a turbo with a larger inlet than the afm outlet. I can see port matching would be beneficial if the rest of the system can flow enough. Did you flow all the individual components or everything as a system & compare it to your turbo flow rate?
If the sensor plate can flow enough, I would expect to see gains by allowing the turbo to breathe on the inlet side. Restrictions after the turbo can be overcome to a degree.
This leads me back to my point about using EFI. If the motor is modded to the point where the sensor plate area becomes the restriction, you're better off going to EFI because of the difficulty re-engineering the AFM. Its not as simple as just opening it up like a throttle body. The size & shape of the AFM opening is special and then the fuel distributor must me matched to it for the afr to be correct throughout the rpm range.
I do have a certain red/white 931 in mind for some serious mods, it will have EFI though so I won't be doing any tests on the AFM. Everything else will be tested thoroughly. 
What EFI system did you use & did you retain the stock ignition? I plan to use an electromotive tec3S or tec3r. |
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leadfoot
Joined: 11 Dec 2002
Posts: 2222
Location: gOLD cOAST Australia
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| Posted: Sun Feb 01, 2015 10:44 pm Post subject: |
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Wolf3d programmable fuel/ign, locked dissy triggering ignition module...
electromotive have some pretty comprehensive manuals on their site...
For the current engine I'm running a retuned map tune with the stock ecu, it's 340hp in stock trim which is more than adequate...
Stu
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress... |
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jason c
Joined: 13 Jan 2014
Posts: 1018
Location: Nwi
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| Posted: Mon Feb 02, 2015 12:14 pm Post subject: |
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| Never tried wolf. I'm familiar with electromotive though. |
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daniel
Joined: 18 Jun 2009
Posts: 686
Location: Sydney, Australia
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| Posted: Mon Feb 02, 2015 2:14 pm Post subject: |
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I am forced to run CIS on my race car and have only come up on one serious limitation. It seems that linear mixture control goes out the window when you go for more and more radical cams. I presume it is to do with the change in the air pulsing through the engine upsetting the very precise balance that the factory worked out when making these systems.
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Over the top of skyline, total brake failure.... hit the wall at over 200 kp/h at the dipper, so anyone who has to brake for the esses is a pussy.
1977.5 Race Car, CAMS Group S Spec
1989 944 Cabriolet |
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jason c
Joined: 13 Jan 2014
Posts: 1018
Location: Nwi
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| Posted: Mon Feb 02, 2015 2:18 pm Post subject: |
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| You are correct Daniel, CIS does not like radical cams. It is sensitive to pulsations from overlap. |
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daniel
Joined: 18 Jun 2009
Posts: 686
Location: Sydney, Australia
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| Posted: Mon Feb 02, 2015 2:23 pm Post subject: |
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That been said, I can get the mixtures close enough that it does not matter in the rev range that I use
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Over the top of skyline, total brake failure.... hit the wall at over 200 kp/h at the dipper, so anyone who has to brake for the esses is a pussy.
1977.5 Race Car, CAMS Group S Spec
1989 944 Cabriolet |
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