David T.

Can you please shed the light to these questions:

1. How much fuel flow can stock 95' 993 N/A injectors produce? Will they be enouph for low boost supercharged engine?

2. How flexible is 95' 993 N/A computer? Can it be programmed to deliver correct fuel for superchared engine?

3. How hard is to lower compression of N/A engine to 10:1 or 10.3:1? Are there such pistons already available?

Where I'm going is, even though I appretiate all the R&D TPC guys did, I don't like an idea of 7th injector + black box and 11.3:1 compression ratio for supercharged engine. Basically I'm looking for 350-370 HP RELIABLE horsepower for Street/Track car.

As always I appreatiate your help !!!

Steve Weiner-Rennsport Systems

Hi David:

Let me try to address your questions;

1. How much fuel flow can stock 95' 993 N/A injectors produce? Will they be enough for low boost supercharged engine?
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Those should be OK in the boost range of 5-8 lbs. You might also need to raise the fuel pressure slightly, as well. Just make sure that the injector cycle is not over 80%.

2. How flexible is 95' 993 N/A computer? Can it be programmed to deliver correct fuel for supercharged engine?
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Within limits. Given the above parameters, you will be clsoe. Programming is everything however, those have no provisions for any boost ignition retard or will they increase fueling if knock sensor activity is detected. In short, this is NOT the same thing as the Twin-Turbo ECU!

3. How hard is to lower compression of N/A engine to 10:1 or 10.3:1? Are there such pistons already available?
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Nossir, not from Mahle at that CR. You would need a custom one from JE and then the domes mahcined down. You could use the Twin-Turbo P/C set and raise the boost pressure IF you had someway to control timing and boost. This should really be done with the ECU like the TT car does using inputs like charge-air temperature, cylinder head temperature, outside air temperature, timing maps, knock sensors, and fuel injector duty cycle.

Where I'm going is, even though I appreciate all the R&D TPC guys did, I don't like an idea of 7th injector + black box and 11.3:1 compression ratio for supercharged engines.
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Neither do I and there are many reasons why TT cars cost what they do. Many people do not know that the heads on Porsche's turbocharged engines are made of a different alloy than the N/A ones are. This is done to prevent cracked heads and to control distortion from heat. There is nop free lunch here,as attractive as all this sounds. In over 30+ years of making HP, nothing is free, no matter what the upfront cost is,.....

Basically I'm looking for 350-370 HP RELIABLE horsepower for Street/Track car.
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I have no doubt that you will make you targerted HP, I do have lots of doubts about the long-term integrity of the engine. To date, I've not seen one last that long although they do make good power. Fuel octane levels in your area are truly critical.

Hope this helps,
--
Steve Weiner

Rennsport Systems

David T.

Hi Steve,

Thanks for the reply. If you wish we can take this discussion off-line but I thought other people can benefit from it as well. Anyways here are my comments:

Assuming that supercharger has a more linear boost characteristics will "static" ignition retard (i.e. based on the RPMs and Air Flow sensor readings) be sufficient? Also I thought N/A computers also retard timing and add fuel when knock sensor activity is detected.

Are these comparable in quality to Mahle?

This is probably not an option because with 8.0:1 compression for good power you will need 8lb-10lb boost and supercharger will take to much power generating such boost.

But then again Turbo Heads are probably good for 500HP :-) if N/A heads can last reasonable time with 350HP I'm fine with that !

I'm hoping that if upcoming Mercedes SLK 32 AMG can have supercharged 350HP from 3.2 liters good 'ol Porsche can have it too :-)

Regards,
David T.

Steve Weiner-Rennsport Systems

Hi David:

If you wish we can take this discussion off-line but I thought other people can benefit from it as well.
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Here's hoping,........
Assuming that supercharger has a more linear boost characteristics will "static" ignition retard (i.e. based on the RPMs and Air Flow sensor readings) be sufficient? Also I thought N/A computers also retard timing and add fuel when knock sensor activity is detected.
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They do retard the timing and only add fuel based to maintain Stoich. Full throttle adds a little bit more. The TT ECU also consideres Charge-air temps and all those other things mentioned previously. These are features not found in the N/A ECU's.

Are these comparable in quality to Mahle?
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They are every bit as strong, MUCH lighter (which really reduces rod loads) but must run a little bit looser. We use them in all racing engines; N/A and turbocharged. N/A ones are sometime over 13:1 and many turbo motors are over 700 HP,.....

This is probably not an option because with 8.0:1 compression for good power you will need 8lb-10lb boost and supercharger will take to much power generating such boost.
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I understand. IMHO, the stock CR at 10.5:1 and above is too much for any forced induction applications. Engine longevity is compromised and detonation-caused engine damage is a serious issue without the proper controls and software. Nothing is free here, no matter how attractive this looks. You don't get something for nothing.

Somewhere here, I have a matrix chart that has static CR on one axis and boost pressure on the other axis to show dynamic compression. 5-8 lbs of boost with a CR of 10.5 to 11.0:1 is wel1 over 12:1 dynamically that that Sir, will not last long on pump gasoline. Without boost retard, knock-sensor and head-temp/charge-air monitoring, ring breakage and piston failure is a distinct possibility.

But then again Turbo Heads are probably good for 500HP :-) if N/A heads can last reasonable time with 350HP I'm fine with that
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Its not the HP that is the issue, its the operating temperatures of the heads and valves.

I'm hoping that if upcoming Mercedes SLK 32 AMG can have supercharged 350HP from 3.2 liters good 'ol Porsche can have it too :-)
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Like I said, your power gains will be realized, in spades and you should not disappointed! Durability & longevity are my concerns and the ones I hold very dearly for my customers.
--
Steve Weiner Rennsport Systems

Sam N

Steve, Dave,

The discussion has been very helpful and informative. I have been considering the TPC system. I have been to the shop several times to talk and gather info. My question for either of you is, what purpose is their piggyback/secondary black box serving in the kit? Isn't it functioning to compensate for boost, i.e. fuel, timing, adj. etc?

Thanks,
Sam

David T.

Hi Steve,

Let me clarify: "(JE Pistons) must run a little bit looser" means that piston's outside diameter is more smaller then usual, correct. Besides noise (I guess) any other drawbacks for Street/Track engine?

Another question, based on your chart what should be static compression ratio for 5lb boost to get 11.3:1 dynamic compression ratio? and where does turbo ends up with 8.0:1 and 11.6lb boost?


To summarize - proper supercharged engine should have:

1) lower compression to the levels which will give us 11.3:1 dynamic compression ratio using custom JE pistons
2) Properly programmed TT ECU - (control boost retard if supercharger indeed allows control for this)
3) Turbo heads
4) Intercooler
5) Better cooling, better oiling etc...


Now where can we compromise:

1) 4) and 5) are out of question
2) if we are getting same dynamic compression level as stock N/A engine maybe we can get away without "advanced" control TT ECU provides assuming intake air temperatures are not getting excessively high; also to my knowledge RUF is using stock re-mapped computer for Turbo BTR conversion.
3) since we will have to throw out N/A heads anyways why not leave them and see how long will they last :-)

What do you think?

Regards,
David T.

David T.

Sam actually these are very good questions to Mike or Matt @ TPC. As far as I understand they require stock chip so questions to ask will be:

* Is it a "piggyback (or interceptor)" unit I.e. does it fool stock ECU about readings of different sensors or is it an add on box simply controlling seventh injector,
* Are they actually retarding timing and how, I.e. what exactly is it based on?

Steve Weiner-Rennsport Systems

Hi David:

Let me clarify: "(JE Pistons) must run a little bit looser" means that piston's outside diameter is more smaller then usual, correct.
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JE's have a slightly higher rate of expansion and require more initial piston-to-cylinder wall clearance than Mahles'
Besides noise (I guess) any other drawbacks for Street/Track engine?
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That's it. JE offers several ring packages and some are more detonation resistant than others. Your engine builder should be able to recommend one that will be durable in this particular application.

Another question, based on your chart what should be static compression ratio for 5lb boost to get 11.3:1 dynamic compression ratio? and where does turbo ends up with 8.0:1 and 11.6lb boost?
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I would not like to see more than 8.5:1 at 5 lbs of boost without intercooling and boost retard of ignition timing. The Turbo setup runs around 12:1 but don't forget, they use boost enrichment, boost retard, head alloys suited for these operating temperatures and a host of other sensors to monitor these and other parameters withour relying on the knock sensors to "save" the engine from destruction.

Having twin-ignition is a big plus in your favor as long as the total timing is reduced 4-5 degrees on boost.


To summarize - proper supercharged engine should have:

1) lower compression to the levels which will give us 11.3:1 dynamic compression ratio using custom JE pistons
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Yes, or TT Mahles.
2) Properly programmed TT ECU - (control boost retard if supercharger indeed allows control for this)
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Absolutely. IMHO, you must roll back timing as cylinder pressures and temperatures rise.
3) Turbo heads
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Best for retention of Factory longevity.
4) Intercooler
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Absolutely.
5) Better cooling, better oiling etc...
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Any engine, especially an air-cooled one, muts have excellent control of operating temperatures to ensure any sense of reliability and durability.

Its not hard to make power,......its hard to make power without turning an engine into a grenade. Few people have the budget for a street engine with a 30-40K mile lifespan.

Now where can we compromise:

1) 4) and 5) are out of question
2) if we are getting same dynamic compression level as stock N/A engine maybe we can get away without "advanced" control TT
ECU provides assuming intake air temperatures are not getting excessively high; also to my knowledge RUF is using stock
re-mapped computer for Turbo BTR conversion.
3) since we will have to throw out N/A heads anyways why not leave them and see how long will they last :-)
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This all falls into the "How lucky do you feel" and how much risk you are willing to take on. RUF, indeed spends more on Engine Management Software and development than any other Porsche tuner outside the halls of Weissach & Zuffenhausen. This is why they are both durable AND powerful. Its not cheap nor easy to do. You pays your money and takes your chances,......


Just a data point based on 26+ years of working in the racing and high-performance end of 911 cars. There is no free lunches here. Aftermarket forced induction has been around since the BAE kits of the mid-seventies and while most of these things provided a very satisfactory increase in overall performance, virtually none of them came close to Factory durability. Frankly, after the novelty wore off with the new-found performance, people began to take notice of many mechanical issues that Factroy executions did not have. You just don't get anything for free,.....

Just my take on this so take it with a grain of salt,
--
Steve Weiner
Rennsport Systems