9krpmrx8

iTrader: (46)

Oh the flaming hasn't stopped, it has just stopped in this thread. The Isuzu V-6 swap is the first recommendation when swaps are is discussed in every rotary or RX-8 related FB group across the globe.

kickerfox

I'm famous!

WaitingforFI

iTrader: (1)

Famous indeed... not all fame is good fame

kickerfox

Haven't put the top end on yet. Still deciding if I want to dive into the heads. If I do it'll probably set me back another grand.

In the mean time... (for those interested)

The Isuzu ECU uses a GM MAF sensor. It outputs a frequency positively proportionate to airflow. I'm not sure how linear it is but as airflow goes up, frequency goes up. You can see it working here for those who missed the video.

I plan on eliminating the MAF and using the AEM FIC-6 piggyback. The FIC-6, unfortunately, doesn't have frequency-based MAF output. Only voltage-based. The FIC-8 has frequency-based MAF output but is $250 more.

If I could convert the FIC-6's voltage output into a frequency, able to drive the Isuzu ECU, I'd save $250 and probably learn a few things in the process.

Behold - The MAF VCO! Using RadioShack's limited components, this circuit will output approximately 500-25khz with a 0.5-5v input. I made the lower and upper frequency points adjustable in case the Isuzu ECU throws MAF codes for too low or high of a frequency. It may not be ideal but it works. Inputs and outputs are both buffered. I will probably zener clamp the output to 5v though.

Leon R

Doesn't FIC-6 allow to run speed density? So not need for the GM hotwire MAS?

kickerfox

I intend on eliminating the MAF sensor. The FIC-6 can use a MAF voltage or it's onboard MAP sensor as the load input. The problem is that the GM MAF sensor (and the mated ECU) uses frequency to report airflow. The FIC's output is only a varying voltage. So even if I use the FIC's MAP sensor (and I intend to do so) I still need to convert it so the factory ECU will function.

The circuit above will convert the FIC's voltage output into a frequency that the stock ECU will understand.

Leon R

That sucks about not being able to manipulate frequency signal. Apexi AFC did that in 1990's!!! Why would AEM loose that feature in a much newer product?

Are you sure that it can't do vortex frequency?

kickerfox

The FIC-8 can do frequency out. The FIC-6 can't. Difference in price is ~$250 but I don't need all the FIC-8's extra features. I just need frequency out. I'm working on simplifying this circuit atm. If it works well I might have a few extra boards made and throw them on ebay. Seems to handy of a device for those running piggybacks.

Leon, do I remember you from the Miata forums?

kickerfox

I played with that circuit and eliminated 3 transistors by controlling the IC a little differently. It's working great in the emulator so time to make a PCB layout and get etching.

Here's the specs:

Internally regulated.
Operating supply voltage 12~38v.
Low operating current.
0-5vdc buffered input (surge and noise protected).
Selectable 5v/10v regulated output (33us) (current protected).
Adjustable minimum frequency. 0v in = 100~400hz.
Adjustable maximum frequency. 5v in = 1900~17,000hz

That should make it pretty compatible with w/e the Isuzu ECU is expecting. Saves me $250 too. The FIC MAF map will first be filled to use the onboard MAP as load thus converting the system to speed density. Then the FIC fuel map will be filled out to reduce the duty cycle to compensate for the larger injectors and additional fuel under boost conditions. And that's that for the electrical systems. Everything should work wonderfully.

Leon R

No, I am old timer DSMer. My venture out to Miata world is limited to buying and adapting some Miata parts to my 4g63 powered Triumph TR7, so I surfed the forums, but didn't contribute.

My connection to Isuzu is thru my VehiCROSS (had one for 18 months now) which is greatly underpowered! I keep going back and forth between adding a mid-mounted turbo or performing an LS4 swap.

If it wasn't for your and Brad's projects, I would have been 100% committed to the LS4 . So while I am thankful for you doing this project, I still think that you are crazy for choosing this engine! But then, to most people we are all crazy for swapping engines

kickerfox

Leon - boost it! You know... I ALMOST considered putting a built 4G63 in the car. I wanted more off-boost torque though. How's the Vehicross feel with the v6 in it? How would it feel with a manual trans? How would it feel with a manual trans and ~1000lbs shaved off? How would it feel with a manual trans, 1000lbs shaved off, and 2x the torque?

So here are some videos showing the factory Isuzu MAF signal here, and the emulated signal here.

Circuit board layout is finished and I can probably etch them and build a board in the next few days. It's noce and small. 1.7" x 1.3"

EDIT - oops! So I wired up the MAF on the bench again (to see what the peak frequency might be with a blow gun on the sensor) but my scope was having a hard time tracking the signal. Then I noticed I had the scope set on 10mv/div and the MAF output was only 20mv. I swore I had measured higher then that last time. Turns out the Isuzu ECU actually provides a 5v signal (verified) to the MAF and the MAF grounds it in 40us durations at w/e frequency corresponds to airflow. The signal is also inverted. I'll have to swap the NPN output buffer with a PNP and remove a pull-up resistor for my MAF converter to work right, but I'm 99% sure it'll work. Once the prototype is finished I'll ship it off to my buddy Brad who has a turbo v6 Amigo.

kickerfox

And here it is. Does exactly what it's supposed to do.

Steve Dallas

Did you build the 1st RX-8 time machine to go back and get that thing, or are you having trouble mastering the camera technology?

kickerfox

Don't you have a stereo to be wiring? :P This camera eats batteries like candy. I got tired of setting it up. lol

kickerfox

Here's a pic of the Isuzu and RX-8 throttle bodies side by side. Isuzu's is 60.5mm. 8's is 70mm. I'll be using the 8's TB on the Isuzu engine. It may not be as sensitive or touchy as I thought it was going to be. I had been under the impression the 8's TB was larger then it is. I read it was 75mm. It's only 70mm.

Steve Dallas

Yeah, I probably do need to get to that at some point, but during track season, the stereo is never on.

Anywho... I just picked up this little project, which will consume a good bit of my free time in the near future.




Back to your regularly scheduled ill-advised engine swap...

kickerfox

Fury or Belvedere?

kickerfox

I had the clutch line made this morning. Summit had the adaptor to put an AN -3 fitting on the GM slave cylinder. My line has that AN -3 on one end and a banjo bolt on the other to fit the 8's clutch master cylinder. The hose is 5 feet long so I can mock up the flywheel/clutch/pp assembly next to the car for testing. Hopefully the 8's master can disengage it fully. That bleeder is going to be a !#%#@ to get to.

EDIT - It dawned on me that I don't need the bleeder since the line is at the highest point of the slave. The bubbles will float there way up. The Solstice does the same thing, no bleeder. Too bad I drilled the bell housing already.

kickerfox

I got the mock-up block together last night. I'll be using it for all the fitment and fab work. Once everything is welded, like engine mounts and exhaust, I'll swap in the new engine then start on wiring.

I have a lead on a 3.9 r&p and that got me into gear calculations again.

Here's some of the numbers.

Trans_______Final_________Width__________RPM@75mph ____Redline MPH____NA TQ@wheels +gain%

RX-8 6-spd__4.44____16.709:1 to 3.746:1______3550_________186@9000_____2640lb 100%
Solstice_____4.44____16.665:1 to 3.244:1______3050_________181@7500_____3566lb +135% (6666lb boosted +252%)
Solstice_____3.90____14.625:1 to 2.847:1______2675_________206@7500_____3130lb +118% (5850lb boosted +221%)

kickerfox

Mocked up the trans only tonight to check input shaft length.

The tip of the input shaft makes it into the end of the crank at least 3/4" or so. The pilot bearing from a Miata fits the Solstice input shaft. The Miata bearing OD is smaller then the hole in the crank. It all adds up a simple spacer being all that's needed to make that work.

The input shaft has a fairly long spline on it. I'm pretty confidant it will engage the clutch disc without a hitch. Only thing left to verify is the throw out engaging the pressure plate. I can only go back about 1/4" or so but I can space it forward as far as it takes.

Hopefully my flywheel is done tomorrow so I can actually plumb it up. I'm dying to see what the clutch feels like.

kickerfox

Turns out this trans is also used in the 4800lb H3 Hummer.

Updates:

No flywheel yet.
Pilot bushing designed and off to CNC.
No go on the 3.9:1 gearset (was FC not FD)
Bought S-10 clutch for mock-up/testing.
Ordered Solstice driveshaft.
About to chop up the RX-8 driveshaft to get the rear flange. -DONE-

The 8's stock driveshaft is very light. Most of it's weight is in the metal bits on each end. I'll be using the diff end of the 8's shaft and welding it to the Solstice driveshaft once I cut that 3-bolt rubber coupling flange off of it. Maybe I'll get lucky and one of them will fit inside the other. I wouldn't trust butt-welding it. The Solstice shaft looks skinny but guys have put 400+ through it. We shall see.

Here's a couple pics.

TeamRX8

iTrader: (25)

https://www.rx8club.com/series-i-maj...5/#post4591806

kickerfox

The flywheel and pilot bushing were finished today. Pilot bushing is a prefect fit. The flywheel (Nissan 300zx) also fits now but I'm not 100% sure if I like it or not. Using the matching Nissan pressure plate isn't ideal. Of the two concentric slaves I have, neither fits correctly without a shim. The Colorado slave fits the Nissan PP fingers fine but needs a 1-1/2" spacer behind it. The Solstice slave would work with a 1/2" spacer but the throwout bearing is too small for the Nissan PP fingers and the clutch line isn't easy to adapt too. The other issue bothering me is the size of the clutch disc. Largest I can go is 9.5" so a 3.8L Camaro disc would work and I have aftermarket options but I'm likely going to need a 6-puck ceramic to hold the torque. 6-pucks tend not to be very streetable.

So...

I started thinking about using a different pressure plate and having the flywheel drilled to match it. Then I thought, if I'm going through that trouble, why not just drill the original Isuzu flywheel to fit a different PP? (The Isuzu PP was a pull-type which won't be as easy to work with.)

If I use the Isuzu flywheel, I can use a 10.5" clutch from a 80s Camaro v8. Right out of the box the organic disc is designed to hold 280lb-ft of torque, the kit is only $99, and there's a TON of cheap aftermarket options as well. So I bought one to try it. Turns out the OD of the PP fits within the Isuzu flywheel but I'll need to do a little machining to it. Also, the Isuzu flywheel is 1/8" closer to the trans and the v8 Camaro PP is 1/2" taller then the Nissan one. This put the required spacer at 7/8" instead of 1-1/2" I'm more comfortable with that.

This is starting to look like a much better option. I should have investigated it in the first place.

kickerfox

Dropped the Isuzu flywheel off for modifications before I send it for resurfacing. Should be finished tomorrow. The driveshaft should be showing up tomorrow too.

Moving right along...

Universal engine mounts get pricey so I started looking into other OEM designs that would be easy to work with. Turns out a 1980 Jeep mount will bolt to the RX-8 subframe and leave a nice stud to work off of. $8 each.

Energy Suspension makes a $30 replacement as well.

kickerfox

Haven't done too much on the car. I've been swamped at work and moving on top of it.

BUT!!

I don't know if I'm just nuts or if I did this to spite you guys... ...I bought an Amigo! I got a deal on it because the engine is shot. Since I have a spare engine (in addition to the one going in the 8) I figured why not. Cheap fix and I could use a spare car. It is a 5-speed 4WD with power stuffs and a sunroof! woot!