flatair

Was poking around 9M's website and found some interesting information in their section on 964 engine modifications:

Hot Film Conversion
The theory behind this popular conversion is that if the original (volumetric) flap-type air-flow-meter is replaced with a more efficient and accurate (mass flow) hot-film unit, by using an air mass measurement device the DME automatically compensates the fuel mixture for air density and temperature changes. In theory this allows the DME to inject precisely the right amount of fuel for maximum power at all times and when combined with the less restrictive flow of the meter itself the conversion typically gives 290-300bhp. . Unfortunately, due to the flow limitations of the pre 92 aluminium inlet manifold, we recommend that this conversion is used on engines fitted with plastic injection systems, so early engines will have to be retro-fitted with the plastic manifold assembly to achieve similar results

Is this feasable and advantageous to use on the 993?

MoTeC engine management
Experience with the standard injection system has clearly demonstrated to us that it is not possible to achieve enough fuel flow to sustain over 300bhp because the injectors (at standard fuel pressure) do not pass enough fuel into the engine to get the optimum mixture. Secondly, because of this flow limitation, the Motronic DME must open the injectors continuously at high load/high rpm in normal use, thus not even operating sequentially (opening the injector in time with the inlet valve to atomise the fuel into a moving air stream). This is detrimental to the performance potential of the engine.

Our solution is to use larger Bosch injectors with a new programmable Motec ECU to allow us to accurately map the fuel and ignition to the exact needs of the engine. If you need confirmation of the abilities of the system, we recently took a typical 964RS with K&N/throttle body/cat bypass/cup pipe that would have produced around 285bhp & 370Nm with the stock DME and our chip. After fitting it with a fully sequential Motec M48 ecu with our custom adaption loom and larger injectors. After a couple of sessions on our rolling road we settled on a very healthy 324bhp and 401Nm. With more work who knows, we may have achieved more? The system also cured the annoying 964RS trait of hunting at idle, so much so that it could be driven up to 20mph in 4th gear at idle using the clutch only, then throttled heavily to pull away cleanly up to the red line.

Further advantages to selecting Motec engine management are that following any subsequent improvements (cams, capacity, inlet system, supercharger, turbo) the engine can be re-mapped quickly and easily, the options of wide band lambda control (full power mixture correction), traction/launch control & data logging. Systems start at £4000 fitted, please call for details.

Are the injectors pretty much wide open at WOT/high rpm on the 993 as well? Can the 993 stock DME be programmed to use larger injectors or use stock injectors at a higher fuel pressure or would we have to go to a motec system?


most of the 1995 onwards 993 engines have the later clamped on camshaft gear. It is this gear that is prone to slipping in use and is impossible to set perfectly accurate to the desired cam timing. You can get them near enough (i.e. within production tolerance) but in my opinion (and most other engine tuners) it is not accurately enough

Can this be remedied (i.e. backdate to the 964 style)?

Christer

My car has been built by 9M - although to a further degree than their Motec +1 package. You can PM me if I can be of help or just ask anything here. I am not affiliated with 9M, and certainly do not know everything but am happy to help if I can.

Jagbuff

Motec is really a powerful engine management tool, however; you really need to know what you are doing (not for amateur mechanic) and you need a race team budjet to afford the basic set up. Also, unless you have a dyno thit is just tinkering. 4000 UK pounds sound on the low end, you probably want to add at least another 2000 UK pounds for the Lambda and datalogging function. Not cheap, still it's cool to download the data and look at the engine parameters, rpms, temp, boost etc... not that I know what to do with but make me feel like a race engineer

graham_mitchell

Flatair, some great questions there! I have seen the 9M website and wondered the same things.

WRT the camshaft, see this thread: https://rennlist.com/forums/993-forum/158816-before-you-start-tuning.html

flatair

Jagbuff, Christer,

I'd love a Motec, fantastic units but quite a bit of change and setup work to be done with one of these (not to mention I don't think it'll pass street inspection here in the U.S.)

Actually what I'd like to get to the bottom of is how capable/flexible is the stock DME? Can the fuel maps be adjusted for larger injectors? I believe this is being done with re-mapped & cammed E36 M3's. The guys at 9M have some good points, and are seeing GREAT results with the 964 and motec - now if we could do it properly with a modified stock DME, it would unlock some significant HP for all of us. If the stock DME gives us some barriers, how about something like the Unichip? (although I've heard some mixed reviews on that one)

Graham,

Thanks for the link, that's some good news - I wonder why Porsche switched to a clamped on camshaft gear? Cost reduction? Seems like 9M is saying that they slip under use - which would lead me to believe that even if we have our cam timing adjusted and matched for more power, they might eventually work their way out of sync again.

I guess what I'd like to see is a nice matched setup that hopefully will pass U.S. emissions - hotter cams, some sort of cold air intake that actually works - perhaps with a less restrictive airflow meter, headers & mufflers, larger injectors to properly support the higher output, and a reprogrammed DME to tie it all together. All for significantly less than a 3.8 upgrade....I'm not asking for too much am I?

Thanks for the feedback guys

flatair

Premier Motorsp

The clamped on cam gear is not a problem. In fact all the water cooled 911 engines (except std 996) ie Cup, Turbo, GT3R use a similar system. The cam gear is bolted centrally into the cam, with no other means of anti-rotation. It works fine.

This style of cam gear can in fact be set more accurately than the earlier style since you are not working with a finite number of holes as with the earlier style. The factory 993 cam setup tools are not super accurate, since they depend on the location of some bolt holes on the cam housing. These bolt holes do not seem to have a very close tolerance in their positioning.

The whole 911 cam timing thing is a little bit overstated. Going exactly by the manual will get you within about .15mm at best. The weak link in the procedure is that you never find the true TDC.

Chris Cervelli
Premier Motorsports

914und993

OK, I have some ballpark numbers here but I can't be certain they are correct. If anyone has different information, or can corroborate them, please do.

The stock 993 has 24 lb/hr injectors which at 285 hp are operating at an 83% duty cycle, assuming a 14:1 air/fuel mixture. If you are going to run richer, which the 993 does at peak horsepower, the fuel injectors probably are running at near 100% duty cycle (on all the time). This comes from a fuel injector spreadsheet, and some figures from Accel fuel injector data sheets. It isn't gospel, but simply serves to give an idea.

To get significantly more horsepower from a 993, you need to flow significantly more air one way or another. The fuel injection system is not the limiting factor - though not to say that some fine tuning might not yield some sorts of gains.

Chip

viperbob

993s already have a Mass Air Flow sensor. The flap door system died with the 964s...

flatair

From what I've heard and read, injectors should be sized to flow somewhere around 70% max. A 285hp (around 240 hp at the wheels) 993 will be running somewhere north of 83% if running a 'safety margin' richer than optimum 14:1 AF ratio. I've heard that various fuel injectors will go static (wide open) anywhere in the 90-100% duty cycle range, so we're probably pushing wide open with a stock car if we're not already there. When they go static, we lost ability to accurately meter fuel. Add exhaust, headers, intake, and chip (say we add 20 rwhp) and you might be pushing the limits. Now consider if they're not brand new and a little clogged. Also I've *heard* some injectors flow less as the duty cycle increases *shrug* thus I supposed another reason why it's good to size an injector slightly on the conservative side (as long as you can maintain a proper idle and part throttle driveability).

Ok so now I admit I'm playing "armchair tuner" here as all of the above is from heresay or reading (do you believe everything you read). But 9M is getting some great results with their 964 engines, that we should be able to achieve with the 993 engines. The injector thing might not achieve huge results on a stock car, but combined with other modifications (even RS cams) may be quite significant. I may be full of crap here but I figured I'd pose the idea to those who know.

Cheers!

flatair

Christer

I can't really add to this, because all the work on my car was done at the same time and so I cannot possibly say whether one or 2 of the mods made a significant difference. It also doesn't help as my car is not one of their standard packages so the Motec needed a lot of input from 9M to make it run well. I think we used the Motec +1 map they developed but ran it a bit richer to be on the safe side during the running-in period. Its been fine tuned now, but its going back in late this year for further work. I think I need to test some different intake/exhaust options...

Also, on the DME side I think 9M get some really good results with their remaps but cannot vouch for the results personally.

flatair

Yah I think the only way to make it a common and feasable upgrade is to figure out a way to do it using the stock DME. Any DME gurus out there?

tonytaylor

I asked this question and the answer was yes but IIRC requires some expensive software/codes from Porsche before you can even start to remap the DME. It wasn't economicaly viable - hence the use of Motec which is superior in any case.

( hope I've rembered that right )

flatair

Thanks for the info, Tony. Pehaps we could prod one of the outfits that already do Porsche DME reprogramming to put some effort into a large injector setup? I know Steve W does it, who else is well known for DME programming?

maurice97C2S

I for one would love to hear Steve's opinion on the injector capacity issue ....

cheers, Maurice

TomF

Bruce Anderson, PCA Tech Guru, used to call the Mass Air Flow Sensor conversion for the 911 and 964 a "Cash Flow Generator" for good reason. Lots of bucks, little return in performance.