Converting a Mazsport T3 Turbo kit to a Cobb AP
 

Car: 2005 Rx-8 GT 6Spd
Engine: Stock, 56k miles
Trans: Stock, 56k miles

Fuel: Mazsport Fuel Pump*, Mazport injector package (650 + 780, iirc), aeromotive FPR

Current EMS: Int-X

Ignition: Mazsport Coils/Igniter, NGK BUR9-EQP plugs

Turbo Kit: Mazsport Type 3, ceramic coated hot side, Greddy BOV non-recirc, Greddy profec-b II ebc

Some gauges/other crap.

Current Issues:
1. I think the int-X ate my CTS. I had to crank the gain on it up a lot to get a decent reading. Fan operation is in my book not trustworthy.
2. Over the weekend, the car started to lean out. No fuel system changes, no tune changes. I have to hook a fuel pressure gauge back up to properly diagnose it but I think the fuel pump is going. The shop had fuel pressure issues when the kit was installed which is why the aeromotive is there instead of the mazsport fpr. I played with the car a little and it was definitely going lean in low boost. The last couple days, I've been able to get it to run a few psi at the right AFR but now I don't trust it. New walbro waiting to be put in.

Other than point 1 which is the primary reason I'm looking to switch, the car has ran well for the last 23k miles. Point 2 really has nothing to do with the EMS.

Now, converting the car is not quite as simple as just unplugging the Int-X and plugging in the Cobb. I have a non-stock maf tube (which is why I'm starting this thread) and the Mazsport kit ships with 2 low impedence injectors. Low impedence is fine on the int-x, but it's a no-no for the stock ECU. Mazsport may have changed injectors over time and I never thought about it when the kit went in. It's not expensive to have KGparts rework the yellows and run all stock injectors so that's what I'm doing. Plus, my injectors will be flow matched (other than the P1s) so my front/rear afrs should be pretty close.

Back to the MAF tube. Stock diameter is 3.375 ID. My outer diameter is 3.00 with a material thickness of .070". This is an ID of 2.86". That's an area reduction of about 28%. If the stock diameter maxxes the MAF out at 5V/~49lbs air, I might max the MAF out at ~35/36. That's probably not enough headroom to push 12 psi on this kit. Is this correct thinking? Secondly, my lead in is long and dead straight (12"+) but the post MAF exit is only may 2-2.5" before a 90 degree turn. I could get a screen in the lead in but I wonder about turbulence from the short run out.

So is there any way that diameter can be calibrated for? And if not, where should I have the intake cut? I'll need a straight length of ~3.5" od pipe with a MAF mounting on it. Then I could see about getting 90 degree and straight transition couplings.

On the picture, I know you envy the vicious water spots. Thats from popping the air separator tank cap in the lincoln tunnel and spraying coolant all over a filthy engine bay.

Calling Mazdamaniac,,,

If you had an old AEM intake you could just use the MAF tube section. Cut the existing tubing about where the end of the tape measure is and install it there. About the same length.
Just a thought.

I have an email to MM saved in email drafts, but, really, with the amount of questions I tend to have (whether or not I think I know the answer), it's impractical just to machine gun them at him. There are a few people on here who have worked with the AP and might be able to offer some insight. Also, once I get the AP and fix my fuel pump situation, I can run the car off the int-X and see what the MAF signal looks like. I'm inclined to think the smaller intake diameter will create a higher velocity profile at STP and the MAF will max out at a lower mass flow value. Then eyeballing 10hp/ 1 lb air, it looks like my setup would probably be really close or actually maxxing out the MAF. If you guys are in AZ, isn't it like 7/8 am?

low impedence injectors will require the use of a resistor wired in-line (6 ohm is the factory Rx-7 low impedence resistor), and different injector latency settings in the AP

The following excerpts from technician training manuals explain the difference between low and high impedence injectors, as well as Saturated type (voltage) and peak and hold (current) drivers.

https://www.rx8club.com/attachment.p...1&d=1258061614

https://www.rx8club.com/attachment.p...1&d=1258061614

https://www.rx8club.com/attachment.p...1&d=1258061614

https://www.rx8club.com/attachment.p...1&d=1258061614

https://www.rx8club.com/attachment.p...1&d=1258062089
factory Rx-7 resistor pack

individual 6 ohm resistors http://www.mouser.com/search/Product...key71-RH10-6.0 I used to run these on my Rx-7 which did not have a factory resistor pack. Most people wire those individual ones somewhere near the ECU

Don't bother with the ballast. Just ditch the injectors and get proper ones.

Correct the intake. It will be far less trouble than trying to calibrate for that tiny one which is only good for 300 HP at best, anyway.

Both projects are only a few hundred dollars and will save you a world of trouble.

Injectors are already being taken care of. Now I'm looking for an intake with a maf mounting I can cut to suit.

Edit: I may have someone making me a maf tube kit.

Update:
1. Pulled my injectors. The injectors that were installed were as follows:
P1 - Seimens Deka Injectors - model filed off, EV1 connector, looks like high impedence, supposed to be 650 CC injectors
P2 - Stock red top 225 High Impedence Denso Rx8 injectors (usually in the P1 position) 195500-4430, Nippon Denso connector
Secondary - Bosch 780 CC low impedence injectors, EV1 connector 17113742

I now also have (4) 820 CC Rx8 Yellow Top injectors (usually P2 and secondaries) part number 195500-4450 (stock 425 cc).

I was going to sell the high flow injectors, but they don't seem to be readily applicable. I've read in another thread that for AP tuning, you generally want to keep a flow ratio between the second fuel rail injectors and the primary fuel rail injectors roughly constant. Now, is that based on 380/290 (1.31) or 425/225 (1.89). Given that I want to run the 820s across the second rail, that would put me at 625 or 434 on the P1s. I could either run the 650s I have on the P1 slot or I could get 2 more yellow tops (unmodified). 820x4 and 650x2 is a ton of fuel (4580 CC). If stock is 2150 CC, that gives me a 213% stock fuel injection (+113% over stock). If I'm doing maybe 400 at the fly wheel, that's a power ratio of 1.82 (400/220). So, i'd have more injection per horsepower than a stock car. That seems a bit much. Then again, it isn't that far off.

Also, I got the maf housing I want to run.

290 (OE red) in the P1, 380 (OE yellow) in the S and a pair of those 820 cc will give you more than enough fuel for 450+ crank HP and will be the easiest to tune on the AP.

195500-4430 and -4450 are the correct part numbers though? They generally don't seem to be listed as 290/380 injectors through other resources - it's a source of some confusion.

As it were, I don't have a set of unmodified yellows anymore. Maybe I can do a trade.