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Join Date: Jan 2010
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EFI cam choice

I'm collecting parts for my EFI project:

87 930
Carrera manifold
VEMS ECU
original engine internals
single plug wasted spark ignition
Headers
Zork
K27-7200
1 bar spring
light weight flywheel

Is the norm to go SC or can I go more radical with the EFI control?

Old 10-16-2010, 04:33 PM
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OFF THE BOOST PIPE NOW...
 
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964 cams
Old 10-16-2010, 06:04 PM
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Old 10-17-2010, 07:29 AM
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How are you going to use your car or what are your goals?

Throttle response and drivability over power or big power?

A great build is 8/1 pistons, ports, .8 bar boost, 964 cams, and GT35 turbo, on EFI.

If going to all the effort one might want to work toward that.

Note that the stock internals are limited to about 6700rpm or the rod bolts become questionable.

The K27-7200 turbo will quickly hit its limit on EFI with 964 cams. It would be a better fit with something like a torque build on EFI, stock cams, with larger intake ports. Could work well with the stock 4 spd if diving in traffic a lot.

I am not an expert but I would not see any reason for a wasted spark single plug. Just let the EFI fire the stock system. Better yet add MSD on top of that.

The next step up might be a wanted spark twin plug.

Last edited by 911st; 10-17-2010 at 01:59 PM..
Old 10-17-2010, 07:33 AM
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the wasted spark works great on turbos because it eliminates the distributor, the distributor needs to be retarded so that at wot it never advances past a certain point(cant think of stock timing right now). in an electromotive system for example you can run more initial timing because all aspects of the timing are computer controlled not mechanical.this helps in 2 ways. gives you more low end power and helps lower turbo lag
Old 10-17-2010, 07:28 PM
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Possibly a single wasted spark would be an upgrade if he was keeping his CIS. That would get him to some programmability on the ignition side. However he is going EFI which can trigger the stock ignition and be mapped to any values one wants.
Old 10-17-2010, 09:31 PM
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I'm going wasted spark, because VEMS supports it easily and it will make twin plugging easier if/when I go that route. So it looks like it'll be cheaper to go with a lowish RPM torque monster based on my current mods and collected parts?

My driving mostly consists of romps around town with little hi-speed and no track use (at least yet). I rarely find a use for 4th gear and considered a future R&P switch to make all four gears more usable, but I'm intrigued by the stock cam carrera manifold 7200 lower end grunt that may be possible as it seems it may be more suited to my driving style (not to mention easier on the budget). What else should be added to this formula to maximize the outcome? I know advanced and accurate spark control can play a major factor in keeping the pre-boost torque numbers up, that will be easy to manipulate with VEMS. Thanks for any input.
Old 10-18-2010, 06:41 AM
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I am running a dougherty 964 in my setup which is similar to yours.
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Old 10-18-2010, 07:03 AM
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You could re-time the cams for even more low end.

If you wanted you could bump compression about a half a point by having the rods rebuilt and offset bushed about 1mm. Or buy JE turbo pistons.

Just a note, the effective compression ratio is about 1 full point higher with the stock cams longer compression stroke duration compared to a 964 cam. That is, the stock cam has a compression stroke that is 153 deg in duration, the 964's lasts 124 deg's.

Twin plugs speed up low compression ignition and can help low end in some ways more than on boost where there is not as much power gain to be had as ignition is already pretty fast. TP's also may alow running more boost with less sensitivity to detonation.

Anything you can do to reduce exhaust back pressure before or after the turbo and or restriction before or after the turbo's cold side inproves its response and extends the HP effecency range it will support.

The biggest opportunity is to manage boost by rpm. With this you might be able to run say 1.2 bar by 3500rpm. If needed you could pull some boost as you approach TQ peak where you will be most sensitive to detonation to say 1 bar, then tapper boost to keep HP withing the limits of your turbo. Porsche and other makers have been doing this for years on there EFI cars.

You should be able to use an ATM boost solenoid with your EFI. See this thread for some info about this. ELECTRONIC CIS fueling & BOOST control

If you can wade through it there is also some clues on running a lot of boost at low rpm in this thread. Cis monster

Lastly, based on comparing the area under the intake valve seat to the cross section of the intake port, I believe CIS motors are a 'port restricted motor'. Thus, opening the intake ports should help. I think opening the ports can increase air flow potential per stroke as effectively as running a more aggressive cam with the stock ports. However, more agressive cams can make there power at a hight rpm which let's them more more peak HP.

Again, this is a non tradational approach to tuning a 930. However, others have gone this way and it seems a be a very good fit with the stock wide ratio 4 speed. It trades peak HP for greater average HP.

Could be fun.

Last edited by 911st; 10-18-2010 at 08:13 AM..
Old 10-18-2010, 07:52 AM
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DonE built a very potent EFI 930 using Performance Development improved GT2 cams.
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'85 930 Factory Special Wishes Flachbau
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Old 10-18-2010, 06:21 PM
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Evo GT2 cams on an EFI engine with that manifold work very nicely.
Old 10-18-2010, 09:44 PM
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I think the 964 cams work well in 450 to 550 hp engines and they're what I'm using. If you want more power than that then GT2 Evo are the way to go.
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Old 10-19-2010, 05:54 AM
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I like my K27HF with Elgin SC330's.
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Old 10-19-2010, 03:40 PM
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I had 964 cams on a similar engine (but with a K29) and they were excellent. Additionally, the change to an 8:41 r&p made that engine behave like a scalded cat in around town driving--just amazing off-the-line.

Old 10-19-2010, 04:14 PM
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