GUITARJUNKIE28

s6 front and rear irons, cosmo intermediate, resurfaced housings with dry-film lube. late closing streetport, exhaust opens about 2mm early and closes about 2mm late. just a crack early opening on the intake ports, but not very far off from stock. s4 t2 (8.5) rotors, RA super seals, atkins solid corners, stock sides, all stock springs...

never did a compression test, and don't really intend to, but this is just a wonderful motor. pulls 18-19" of vacuum @ 850 rpm, and pulls 25ish" on decel. that's good for a stock motor, but that's GREAT for a ported motor.

ok, now that all that's out of the way, i run about a 12-15* negative split at idle and i've been able to get the idle as high as the low 14s (afr) ans still have it very smooth. everything up to 14:1 is glassy smooth, but what's interesting is although it's just a bit on the rough side, it doesn't actually start misfiring until the afr is about 15-15.2:1

cruising afr's are typically in the mid 15's, but it'll go as lean as the low 17's without running rough or surgning. i aim for about 15.5:1ish under light load. any leaner doesn't have any noticable affect on fuel economy. split starts at about 20*, and does sort of a bell curve to zero @ zero boost/vac.

egt's during cruise are ~725-750c under light load (measured with a k-thermocouple), about an inch after the turbo flange, inside the turbo housing. timing is through the roof... 50+ degrees in the higher vacuum places. i also have a post-turbine greedy egt just for a visual reference. that one typically reads about ~100*ish c lower than the pre-turbine, but it can vary from ~75-200*c. those values shouldn't be taken as exact measurments because it's a different thermocouple, made by a different mfr... it's just a ballpark thing.

moderate load (about zero vacuum/boost) egt's are about 800-825c, with zero split, and about 30-32* timing

i've been able to milk about 23 mpg out of a full weight fd (just a tad over 3k lbs with me and a full tank of gas), but can't seem to break 24 yet. my normal cruising speed is 80-85 or so...obviously slowing it down will help out, but i doubt it'll be anything really drastic. average fuel economy is about 18-19...half city, half freeway, with a few boost runs here and there. when i rape on it, fuel economy is in the low teens. a t66 @ 1.3 bar does eat up quite a bit of gas
on the 9.5:1 motor, fuel economy was easy to come by, but the 8.5's are just doggy for gas milage.

anyone wanna share your negative split info: idle afr's and fuel economy, etc?

GUITARJUNKIE28

just for reference:
haltech e8,
plx r500 wideband with the pre-turbine egt
greedy boost and post-turbine egt... 52mm, non-peak/hold (the cheapies)

btw, i know the idle seems REALLY lean, but it has been verified with 3 widebands. the r500, the cheapie plx (forgot which model) both those used the 7057 sensor, and the thrid wideband was my turboxs tunerpro that used the 6066 sensor.
all widebands were withing a few tenths of eachother, and all this stuff has been measured pretty close to sea level (1000 ft or less)

at 4500 ft elevation, the wideband reads pretty lean... ~14.8-15.5 afr at idle, depending on air temp, what kind of mood it's in, etc... i'm not advertising it running that lean though, since widebands get a little cracky with altitude changes.

GoodfellaFD3S

iTrader: (213)

I don't think I missed it....what primary fuel injectors, stock?

fritts

iTrader: (5)

Has having lots of split cause response issues in those areas? Also do you feel any surging at cruise or idle? Whenever I screwed around going really lean at cruise it would surge and response on throttle input would be an issue though I believe that may have been a function of the accel pump.

rotarygod

iTrader: (1)

Dave, at idle you don't need very much negative split but outside of idle all the way to almost ambient pressure, you can run quite a bit. At the most extreme vacuum loads you can get away with 40 degrees or more of negative split. Make sure to be at least to no split before you get to ambient and definitely before boost. Your leading timing stays as it would with conventional split. The only thing that changes is the split as it goes into negative.

GUITARJUNKIE28

i did the idle split where i could run it the leanest. i drive in traffic a lot, and the relatively lean idle (~13.4-13.8 ish) helps save even more gas.

injectors are 720/1600. the smaller the better for the primaries, just as long as you have plenty of fuel up top... i hate doing 550/1600 combos. they always stage like ***.

fritts, no response issues at all. as soon as i dump on the throttle, the throttle pump activates and i've got plenty of fuel.

patriick

iTrader: (3)

great thread.

i'm interested in the 550/1600 staging comment since i run that combo (w/PFC). can you go into more detail? Why wouldn't turning on the secondaries sooner compensate?

rotarygod

iTrader: (1)

How are you staging the injectors? Are you doing it based on load or rpm? I like to do it on load and just like the factory staging I like to decrease fuel to the primary injectors by quite a bit after the stage point.

patriick

iTrader: (3)

Not sure who this was directed to, but I'm assuming guitar since the Power FC doesn't offer the option to choose between load and rpm afaik.

The only two options on PFC are "Pri/Sec transition (%)" and "Sec transition (ms)".

twokrx7

iTrader: (1)

perhaps you forgot to mention two other PFC settings ... Injection vs. Acceleration TPS1 and Injector Overlap. I never experienced issues with staging 550's and 1600's with the PFC.

rotarygod

iTrader: (1)

Yep I was referring to Dave (GJ).

GUITARJUNKIE28

my staging is somewhere around 2-3psi... i forget exactly where i put it.

i'm using a haltech e8.

for any 550/1600 combos (whenever i couldn't avoid them), i'd try to use the primary hold staging on the haltech. keeps the primaries wherever they are, then adds secondaries starting from 0, or wherever you tell it to. that might help smooth things out a bit, but so would a jumbo fuel pump...

slo

iTrader: (1)

Does anyone have a stock ign map showing split and preferably also advance for the rx8?

I wish the haltech could do staging with both load and rpm. sorta like a rolling staging bar.

GUITARJUNKIE28

variable load/rpm would be pimpness.

j9fd3s

iTrader: (3)

we didnt print it out, but you can watch it on the factory scan tool.

idle is -5BTDC L and 15ish btdc T, split goes away really fast with load.

2500rpm cruise is 36btdc L 24-26 btdc T, floor it @2500 and it goes to 5-10btdc L, then it comes up and is at 30btdc L with about 10 degree split after 7000rpms.

if your foot is off the gas, the L is ALWAYS -5.

jacobcartmill

iTrader: (6)

i have a hard time believing your big street port motor is pulling 19 inches of vacuum. it shouldnt be having to sucking nearly that hard at idle when you open the ports up.

patriick

iTrader: (3)

GC, have you tried the 9.0 rotors at all? if so, was there a noticable improvement in gas mileage or off-boost response compared to the 8.5 rotors?

GUITARJUNKIE28

that's because you didn't take into account the cosmo intermediate iron. the runners are larger, while the ports are smaller and open later (think velocity). on top of that, i adjusted the secondary plates so they're completely closed @ 0 throttle, so @ idle, the engine is being fed 100% by the primary ports, instead of letting a little air bleed in through the secondaries. this not only increases vacuum, but cleans up the charge a tad, so i can run it leaner at idle.

GUITARJUNKIE28

the higher the compression ratio, the better the gas milage.
same goes for throttle response.

but building the engine correctly can have as much of an impact on fuel economy as the compression. if it's put together with sloppy tolerances, the compression/vacuum will go down and it'll need more air to make the same amount of power--this is bad for fuel economy.

since i used the low compression rotors, i gapped the side seals pretty tight. this helps out with cranking compression and fuel economy.

patriick

iTrader: (3)

[EDIT] right, i should have asked if you had logged mpg with the 9.0:1 rotors for comparison purposes.


this interests me since my motor has a similar setup (T2 rotors, 3mm seals, and solid corners). how tight did you gap them?

sdminus

I am intrested in that rx8 data. I ran -5 split at 17.7 afr cruising and had no issues at all. I ust tapered the neg split to 0 by 0 vac. The car did seem much nicer to driver. Had better response but im unsure if it was any better economy wise. the egts were still quite low if i remember correctly. If i am reading this correctly the rx8 runs -20 split at idle ? how does the split change under decel of light vac ?

Scott

dpf22

^^ ditto

GUITARJUNKIE28

the last time i used a 9.0 motor in the fd was right when i popped the 9.5. i was pissed and tossed something together with spare parts i had laying around. the 3mm apex seals were used, and there was way too much slop in the rotor groove, but i figured what the hell... no way i'd do that with a customer's engine, but for my personal vehicle ( taken into consideration that i intended it on being ONLY temporary)...eh. only new parts in that motor were the coolant seals. it got a best of 22mpg, but it was definately a 1-day job. when i finished building the engine that's in the car now, i pulled that motor--still running just fine and disassembled it to be reallocated for various other projects.

pretty damn tight... ~.0015-.002 i wouldn't do that on any engine that used anything higher than the 8.5 CR rotors. the temps are just too hot and the seals expand too much.

but remember i've got dual big oil coolers, 9 1/2 qt oil capacity, and i'm using the 5w30 oil. the thinner oil can suck heat out faster than the thick stuff. oil and coolant temps are wherever i want them to be.

GUITARJUNKIE28

i'm not sure if you're asking about a stock rx8 motor or what...what computer were you using?

j9fd3s

iTrader: (3)

actually a movie would show it better, but the negative split disappears quick with load, cruising @2500rpms, in 6th, its running a 4-6 degree split @ 36 BTDC L, put your foot to the floor and it goes to about 10-12 BTDC L, and climbs

zero throttle is always -5 btdc L, trailing does move around a little @zero throttle,