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After a long thought, i have decided to S/C my 997.1 C2S.
Will rebuild the engine first, for safety reasons (145.000 km on the clock ).
The main debate is whether or not to lower the compression ratio in order to boost at 10 psi.
M97.01 has a static compression ratio of 11.8:1, VF Engineering sells their product with 6 psi pulley. That means that the accepted effective compression ratio (by VF standard) will be 16.62:1 on 91 octane fuel and at sea level.
In order to achieve the same amount of Effective CR (more or less) will need to lower static CR at 10.5:1 (achievable either with pistons or thicker head gasket-depending on the condition of the engine during the rebuild). This would affect the sharpness and response of the engine at lower and mid-ish rpm.
On the other hand, there is a thought of keeping the stock CR at 11.8:1 (along with stronger head studs and a reliable head gasket-not thicker than OEM!!!) in order to save the cars Daily Driven feel. Given the fact the car will use 100 octane fuel at all times would it be "ok' from a thermodynamic perspective to run 19.83:1 effective CR at peak level (7300 rpm)???
The main reason for pre-ignition (detonation) is high temp which is caused by a number of factors in this situation - most effective of all is pressure - thus effective compression ratio. Another factor, also very important, is fuel. I need to calculate if it is possible for a 100 octane fuel to cause pre-ignition @ that level of ECR.
Maybe i have miscalculated a variable, but since this is a technical question what is your thoughts?
PS.
1. Given the fact that this is a very technical question-"issue" please have the patience to back up your opinion with real facts and not personal statements that declare your liking on the project.
2. No, i do not wish to save on the TT or any other car.
I ask that because that is the single most important variable that is going to guide your setup. Your tuner should already have experience with a setup like this and should be able to guide you to picking parts. If not, then it is going to have to be complete trial and error which can cost you months and months of time and tens and tens and tens of thousands of dollars.
I have had another C2S in the past which i also supercharged. I am planning to use the same parts that are included with the VF kit. My tuner has experience with Porsches and other FI projects.
Furthermore, i will supervise the whole build. AFR will be in the rich zone below 12.5 in order to protect the engine from a lean mixture.
Don't have a significant HP target in mind. I just need to feel satisfied with the setup!
IMHO I would leave the factory comp ratio for a couple of reasons. I assume you can do a pulley change to lower boost there for youlr effective comp ratio would be lower. If want you want to “turn it up” you can get good gas to run but wouldn’t be required all the time. 2nd If you or someone else ever decided to remove the s/c the car would be very doggish with no s/c and lower static comp.. just my opinion......
IMHO I would leave the factory comp ratio for a couple of reasons. I assume you can do a pulley change to lower boost there for youlr effective comp ratio would be lower. If want you want to “turn it up” you can get good gas to run but wouldn’t be required all the time. 2nd If you or someone else ever decided to remove the s/c the car would be very doggish with no s/c and lower static comp.. just my opinion......
That's was exactly my thought! Keeping stock static CR will give me an edge later on if i want to ditch the SC option.
If your doing a custom build which it sounds like you are. I would keep the same compression but go with a better piston and crank setup. Something like CP, Diamond or Wiseco with a knife edged crank. Then run e85 after the proper injector and pump sizing.
Your not going to lose off boost power and e85 is much easier to find and safer to tune then 100.
I have had a couple lower compression setups (non Porsche) and ended up going back to near stock CR on rebuilds. Unless your running big boost keep the more streetable setup
If your doing a custom build which it sounds like you are. I would keep the same compression but go with a better piston and crank setup. Something like CP, Diamond or Wiseco with a knife edged crank. Then run e85 after the proper injector and pump sizing.
Your not going to lose off boost power and e85 is much easier to find and safer to tune then 100.
I have had a couple lower compression setups (non Porsche) and ended up going back to near stock CR on rebuilds. Unless your running big boost keep the more streetable setup
E85 is very difficult to find on pump gas station in Greece (...where i leave) although i totally agree with you would be the optimum choice. I am afraid the best i could do is go with 100 octane fuel. Wossner offers forged pistons both in 99.5 mm and 100 mm diameter on 11.8:1 CR.
I think the main reason of using Forged Pistons is to avoid piston break in case of pre-ignition or detonation ... am i correct?
There are a bunch of benefits to a aftermarket forged piston. One of them to your point is definitely stronger and more durable for high heat and detonation. Some other typical benefits.
-Lighter
-Dome design for various configurations and valve relief.
-compression ratio changes.. off the shelf and custom.
-bore sizes... You can use this for a couple reasons. To add litres say to 3.8 to 4.0 or to compensate for material lost in a honing process. Higher millage cars or some with minor bore score you can hone the cylinder a few mm without replacement. New rings work to a certain size then you need a bigger piston.
I can tell you that there are 3 critical things that RUF did when developing the supercharger setup that's in my car:
lower the compression
you have to separate where the intske air volume and intake air temperature are taken. Volume can be taken at the normal MAF, but temperature has to be taken at the intake manifold after compression in order to get proper info into the DME so it can properly adjust the fuel trim
They replace the normal C2S DME with one from a TT in order to have the necessary parameters available to properly tune the motor.
Make sure you leave the knock sensors active so they can sense detonation and pull timing
I'd be very careful with the VF kit as there was another member here who was tracking mixture with durametric and at higher RPMs, the car was leaning out and there wasn't a way for him to adjust for this using the stock DME and tune supplied with his sc kit from VF. Maybe if you'll be writing a custom tune then you can account for this in your setup.
My RUF setup looks like this (press launch motor not my actual one, unfortunately) and anything shown in green or yellow is something that was changed from stock.
Thank you very much for the support and information guys!!! Really appreciated.
@platinum997 : Dont know if the car needs to bore out or not . I dont have any indications that it will... but since it already had 145.000 km on the clock this is very likeley to happen. Thats why i am preparing my selve to go forged. Depending on the score we ll go 99.5 mm or 100 mm.
@Petza914: I have noticed that RUF kit has no intercooling system at all...that's kinda.. risky! Furthermore they use ASA Compressor in comparisson with VF. I can get info on the Vortech unit (1000 CFM) but i cant get anything on the ASA in order to make proper calculations.
Thank you very much for the support and information guys!!! Really appreciated.
@platinum997 : Dont know if the car needs to bore out or not . I dont have any indications that it will... but since it already had 145.000 km on the clock this is very likeley to happen. Thats why i am preparing my selve to go forged. Depending on the score we ll go 99.5 mm or 100 mm.
@Petza914: I have noticed that RUF kit has no intercooling system at all...that's kinda.. risky! Furthermore they use ASA Compressor in comparisson with VF. I can get info on the Vortech unit (1000 CFM) but i cant get anything on the ASA in order to make proper calculations.
Again....THANK YOU GUYS very much!
The intercoolers are integrated into the intake manifolds for a more compact setup and the intake manifolds themselves are aluminum, rather than the plastic ones from a stock se
TheThe ASA compressor used in the kit is proprietary and built exclusively for RUF by ASA. You can get ASA to service it directly but only if you provide a copy of the RUF certificate of authenticity, so they're probably protecting the details of the kit so it can't be easily copied. Since the R-Kompressor kits are so rare, I actually had the opportunity to buy a spare complete setup atca reasonable cost from someone converting to turbo setup, which I did, then sent it to ASA in Germany for a complete rebuild so now I have a hot spare in the event I need to rebuild mine at some point, plus have a spare of everything in the kit should I need a part in the future.
I am thinking of using a Paxton NOVI 2000 (capable of 1400CFM - 970 HP). This way i might be able to go with a mild boost of 6-7 psi. Would this affect the power delivery in the low - mid rpm range (going with a bigger blower than a 1000 cfm unit i mean)???
Well,just wanted to give you guys a heads up on the Project.
Went with Vortech V2 Si Trim (Capable of 1100 CFM akka around 780 hp)
...and gone forged with Wossner standart compression ration 11.8:1 pistons
...forged H Beam Connectin Rods
... new sleeves
...ARP head studs
...also replaced all con rod bearing -head gaskets etc.
At the moment i am breaking in the engine and it works just FINE!
Will start with installing the supercharger later this month... and try around 12-13 psi. Will keep a close eye on EGT and other indicators...but my back up plan is to go with Water/Meth if i don't like the numbers.
09-25-2017, 12:42 PM
S/C Project on the way.
