SA3R

My Dad’s 1992 JDM FD has been running for two years with the following:

Rebuilt engine, lightly touched in ports with die grinder, by rotary builder (port specs unknown to me)
2mm apex seals (unsure of brand)
Knightsports twins (modified to run non-sequential, not sure the part number of them, but have thicker turbine shafts, polished snails, with raised ‘Knightsports’ cast on them, and a different impeller design) which he also rebuilt and balanced as a set.
Power FC, Datalogit, hand controller, 850 primaries, 1200 secondaries
Air pump and cat delete.
ABS removed
Double throttle removed.
AC removed.
SMIC + alloy radiator
Turbosmart BOV
7s & 9s Leading/trailing plugs as per stock
Boost controller with 2 stage boost settings- 14psi and 20psi
Supra in-tank fuel pump with voltage reg and wiring as per stock
Fuel cooler can
Auto 3.9 diff gears

We were aware that we were seeing 100% injector duty cycle at roughly 75% throttle input, even when switched on the “low” boost setting, which was scaring everyone. We talked about upgrading the secondaries to something bigger than 1200s, to keep the duty cycle in check and still have a clean idle on the 850 primaries (secondaries were set to transition at 40% throttle- not my tune) and rev limit was set in the PFC to 9000rpm.
Time bomb? Yes, absolutely. It survived two years until last week, when I had my auto FD on the highway, and Dad had his car directly in front of me. We were overtaking each other back and forth, as this was the first time we’d had both the black FDs together on the road. I think Dad must’ve got a bit carried away and put his foot in too much, as I heard his limiter at least twice. We came to a stop at the turnoff to exit the highway. I turned and accelerated up the hill off the highway. As Dad’s car came to a stop, the idle got choppy, vacuum readings were flickering, and it would not hold idle, and died. Pushed the car to a slope, clutch started it, and it drove fine for another 5 minutes.
Stopped at destination, and without thinking, shut his car off. Tried to restart, and it just wound over, trying to fire. Pulled plugs, and all were okay except for rear rotor trailing plug, which looked white lean.
New plugs, still no start. Let it cool for a few hours, then attempted start.
It finally started, but would not idle under 1500rpm. So adjusted idle to 1500rpm or so, and went for a drive. Engine still pulled hard in low boost, felt good and clean.
Stopped back home, and shut it off. Tried restarting, and this time had uneven exhaust beats, and sounding like it was winding over too fast, without much compression. No way would it start, and hasn’t started again since.
Compression test is on the way.

I figure the car was pushed too hard, injectors too small & engine underfueled by the inadequate fuel system, it leaned out in the top end, damaged an apex seal on the rear rotor, which progressively got worse, until no start.

Undersized injectors were a bit of a “I’ll get round to that, I’ll do it” thing, which lasted 2 years from dyno to now, as the car wasn’t pushed that hard until the other day, so we weren’t too surprised.
This isn’t intended to be one of those “My car blew up, oh rotaries are so unreliable!” posts. It blew up because we were lazy, and it was just human error on the tuning side of things. My near-stock auto FD took the drive fine, and continues to drive strong. I wasnt taking it easy either, as I was trying to keep up with the old man.
We will drop the engine and K frame in one assembly, pull it apart, see what it looks like inside and this time it gets a better fuel system & re tune, so the same thing doesn’t happen again.
Probably best to always know “why” an engine went bang, to fix the issue, and ensure history does not repeat itself over and over.
Me being 25, and Dad being 71, it gives us a small project to spend time on, which is a good thing.

TwinCharged RX7

iTrader: (14)

So you wasted an engine and thousands of dollars bc you were lazy? I would have just turned down the boost until I became unlazy haha.

Tem120

iTrader: (5)

take the secondaries for your car and upgrade the secondaries on your dad's car , another option would be a rising rate fuel pressure regulator . which work pretty damn well

that would of helped with tyour fuel issue

adam c

iTrader: (2)

I think its cool that you can have some fun driving FD's with your dad. I hope I can still drive mine when I am over 70

XLR8

iTrader: (52)

Good story! Lessons can definitely be learned from this experience. I'm sure you guys will sort it out. You seem to be relatively learned, despite the lazy streak. It does happen.

As a side note, please read the forum rules on thread titling. "Cool story" doesn't exactly help others who search for information.

silver93rx7r1

iTrader: (2)

Sucks that the engine popped. It sounds like it'll be a fun father/son project tho. Pretty sweet that both you & your Dad have FDs!

CloudPump

iTrader: (2)

I'm surprised you were hitting max duty cycle on your 14psi tune with 850s and 1200s...

-Geoff

Tem120

iTrader: (5)

LoL I built my car with alot of help from my dad . his driveway , and his tools hah . It was a good experience and that alone was worth to me the difference I paid between my half running car , and having bought an already running car.


BUT the only difference is my dad hates the rx7 Hah .

SA3R

Will do. Thats the sarcastic slogan some Aussies use here, when someone starts rambling on a big long boring story that nobody particularly asked for- "Cool story bro, needs more explosions and stuff.."

Well being non sequential at 14psi, only running the Supra pump and 1200 secondaries, you can watch the duty cycle rocket upwards of 75%, 90%, etc on the PFC hand controller, once it gets into boost.
If it were my car, I would have added a rising rate reg, better pump voltage step-up controller, larger secondaries, and see how that went.
But being Dad's car, I didnt really get a lot of input, as he built it about 3 years ago, and decided to just take it easy til he could sort the lean top end out.
To his credit, it used to spin wheels into 3rd gear, with an auto diff ratio, so it went reasonably well for what it was.

We'll sort the fueling out, and possibly look at 3mm seals this time round.
Time & money isnt a huge issue, we have a shed full of FDs and some RX8s in bits, so its more of a hobby. We felt it wind over on the starter yesterday, and it does have the 'sharp' no-compression sound to it, as well as odd firing beats out the exhaust. The thing was, we had fun with the car, and building them is the other half of the fun. We know what it did well/didnt do well, so we can improve on it next time.
Dad always said he never wanted to go to a retirement home, never wanted to slow down. I think having a hobby where you have to use your head, keeps people sharp. He's a good machinist, good driver and he's no less sharp or slowed down than I am, so may as well have fun in retirement, right?