Official 318ti Forced Induction (FI) FAQ Thread. This thread will be dedicated to frequently asked questions related to Forced Induction. Please post your questions here, and I'll combine all the questions and answers and keep them at the top of the thread.
Read "Maximum Boost" by Corky Bell for a better understanding of turbos. Read "Supercharged!" by Corky Bell for a better understanding of superchargers.
Questions:
What FI systems are availabe for the 318ti? Current there are only 2 systems available for the m42/m44 motor.
- Mosselman makes a low boost turbo kit (5-6psi). http://www.kormanfastbmw.com/turbos.htm
- Downing Atlanta (DASC) make a supercharger for the m42 and m44 that uses an Eaton M62 roots supercharger. See additional information below.
- SEAM is currently developing an intercooled twin screw supercharger. More info will be posted when it is released.
- Midnight Auto is selling a supercharger kit, but it's more of a collection of parts than a complete bolt-on kit. I recommend you DON'T buy this kit.
How much boost can I safely run? On a completely stock motor you can safely run 8psi of boost using a rising rate fuel pressure regulator (RRFPR). With larger injectors and software you can run up to 12psi. The m42 motor has forged internals, making it a better candidate for high boost, unfortunately there aren't many options for ECU tuning with the OBD1 m42.
Who makes tuning software for a FI 318ti?- NickG - www.techniquetuning.com - NickG sells 3 different tuning packages for boosted m44's. He also sells software for N/A 318's. The stage 3 package includes larger injectors, larger MAF and software. This is the best software available for 318's at this time. NickG can also do custom programming for unique setups.
How much HP will my car make? This depends on what else is done to your car, what condition your motor is in and how much boost you're running. With the DASC I've seen dynos that run from 170 to 210 rear wheel horepower (rwhp) running stock boost (7.5psi). You should have around 200 rwhp with the stock DASC on a healthy motor.
I haven't seen any dyno charts for the Mosselman turbo kit, please post them if you have them. I remember reading that the turbo kit made considerably less power than the supercharger.
What is the DASC and where can I buy it? DASC is the Downing Atlanta supercharger. It can be purchased directly from Downing Atlanta (
www.downingatlanta.com) or through several reseller. The kit retails for ~$3300, without installation.
Details:
Eaton M62 roots supercharger
Cast aluminum intake manifold and elbow
No intercooler (none needed)
7.5psi of boost stock
Uses a RRFPR for fuel management
C.A.R.B certified (OK for use in California or anywhere emissions are controlled)
4-10 hours to install (can be installed by a DIY-er)
OK for use with automatic transmission
OK for use with traction control
Complete bolt-on kit, no additional parts needed
Most common FI system for the 318, safest FI system for the 318
Where can I get a smaller pulley for my DASC? Smaller pulleys are available from
www.pulleyboys.com Can I run Water Injection with the DASC? Yes, but you should spray the WI after the blower. I stripped the coating off my supercharger by spraying before the blower.
Can I use a Blow-off Valve (BOV) on the DASC? No, the DASC uses a by-pass valve when not under boost.
What should be upgraded when going with a FI system? Clutch - The stock clutch will slip a little bit if you really push the car hard.
Exhaust - A cat-back exhaust system will make a really big difference with FI.
Brakes - If you go faster, you should be able to stop faster. High performance street or track pads should be good enough.
Spark Plugs - Go with a spark plug that is one heat range colder. For an NGK plug that's a 7.
What is the R-Speed check valve? The R-Speed check valve is a one-way valve that goes on the vent tube between the injectors and the intake elbow. The valve will provide an additional 0.5psi of boost. Buy it here:
http://rspeed.net/miata/item.asp?dep...2&prod=101-005 $40 w/o shipping. Note: NickG's Stage 2 and 3 tuning packages eliminate this hose and the need for the check valve.
Can I use the (insert chip name here) chip with the supercharger/turbo? No, chips that are designed for N/A motors advance the timing too much for FI applications. Be sure to swap back to your original chip before installing a FI system.
How is ignition controlled with FI on a 318? The stock ECU is capable of controlling ignition timing as long as you run less than 9psi of boost. The ECU uses 2 knock sensors to monitor knock and makes changes based on knock/temp/load/etc. Aftermarket tuning software uses a different ignition and fuel map to control ignition, but still uses the knock sensors.
Can I install big injectors or a big MAF? Yes, but you will need either aftermarket ECU tuning or a piggyback to control them. You can not use the stock ECU to control larger injectors or a larger MAF.
Is there any difference in adding F/I between m42 & m44? There are more software options for the m44 because it is OBD2. The m42 has forged internals so it
should be able to handle more boost than the m44. In order to tune the m42 for high boost, you'll need to run piggyback fuel and ignition controllers (and tune them). Currently the best option is to use the DASC on a m44 with NickG's stage 3 tuning and run 10-12psi.
Will gas mileage be affected? Good question. Gas mileage will decrease in town, but increase on the highway (if you use cruise control), this is because it takes less throttle to bring the car up to speed.
Your OBC will show that you are getting crazy good gas mileage, but it's not accurate. Once you install a RRFPR, you need to multiply the gas mileage by 0.666 (so 30mpg = 20mpg) to get an accurate mpg rating. Overall, it's not a very noticeable difference.
I've got 50K/100K/a bazillion K on my car... is it safe to S/C or will my engine blow up? It depends on the health of your motor. I would do a compression test before purchasing a FI system. Check to make sure the compression is even across all cylinders and that you have at least 150psi in each cylinder. It all depends on how well the car was maintained. Take it to a mechanic if you are unsure. I installed the DASC on my car at 100k miles, I haven't had any problems with it.
Will I need to upgrade my drivetrain? Tranny? Diff? This is something that you should decide after you install the supercharger. If you find that you have traction problems, you might consider upgrading to a limited slip differential (LSD) and/or some larger wheels. The 5 speed transmission can handle the additional power without issue. You might want to go with a stiffer clutch if you notice any slippage, but the stock clutch will work for most people. The automatic transmission will also hold the power, just be sure to limit the full boost shifts.
What is a Rising Rate Fuel Pressure Regulator (RRFPR)? A RRFPR is a device that increases fuel pressure in the fuel system. The RRFPR is plumbed inline with the return fuel line, after the fuel rail. It has a vacuum line that attaches to the boost side of the intake manifold (after the turbo/supercharger). When the RRFPR sees boost on the vacuum line, it "pinches" the fuel line, causing the fuel pressure to increase. Additional fuel pressure means more fuel is sprayed every time the fuel injector is opened. The RRFPR works well for FI systems under 10psi, after than the RRFPR is unable to provide enough pressure to run a stoich mixture.
Is there a way to lower the blow temperature, other than spraying water? Chad (ZeroG) designed an air-to-water intercooler for the DASC. I believe he still posts on this forum. More info on the air to water intercooler can be found at
www.itsallaboutspeed.com. Spraying a mixture of water and methanol seems to be the best way to cool FI systems that don't use intercoolers.
Also, if I install NOS with the supercharger, do I put the NOS nozzle before or after the blower? Because of the extreme temperature and pressure of spraying Nitrous Oxide, you should spray AFTER the supercharger. I would recommend a 4 nozzle wet system to ensure an even mixture (since most intake manifold are asymmetrical).
Forced Induction FAQ - Required reading for n00bs! 
Threaded Mode