Tuning my GTUs (long...)
09-04-08, 02:12 PM
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Tuning my GTUs (long...)
Howdy all. Now that the upgrades for my 91 GTUs are completed, I am starting to tune for best power/economy. Those of you with similar cars may be interested.
Mods of consequence are:
Original motor rebuilt by Kevin Landers, 6k on it
3rd gen housings (no diffuser in exhaust ports)
Mild 6-port street port
Full RB true dual exhaust
No cats
Airpump to actuate 5/6 ports (airpump does not pump air into exhaust)
Pineapple Racing inserts
T2 fuel pump
Cold air box
E-fan
RC Engineering cleaned / balanced injectors
MSD CDI ignition
MSD wires, heavy grounds, fresh plugs… etc
I am tuning using a PLX wideband with sensor installed 30” downstream of motor as recommended, and a SAFC2.
I chose the SAFC as it was $130 used vs. $400 for the Rtek. The Rtek adds ignition curve tuning and the ability to disable the OMP, and offers a cleaner installation, but I was not convinced it was worth the extra $270+ PDA to control it.
Without tuning, the car starts and runs great, good power, but pig-rich at higher rpm’s and throttle. By rich, I mean 12’s and even upper 11’s AFR, this is more what a turbo motor should run. So obviously there is room for improvement
I started by reading up on the various guides about SAFC tuning available on the Internet. Since it is modifying the MAF signal, the SAFC will only do anything when the ECU is actually looking at the MAF. This is known as “open loop” mode. When the ECU is in “closed loop” mode, it is just looking at the stock narrowband O2 meter, attempting to hit stoichiometric 14.7:1, or maybe just reading off a “map” for idle and warm-up.
By watching the Throttle % reading on the SAFC and the AFR reading on the PLX, it is clear the ECU attempts to maintain Stoichiometric ratio until about 35% throttle. 35% throttle is about as high as you go while cruising or even light acceleration. Past 35%, the ECU abandons the narrowband O2 sensor and begins to read the MAF.
I started by setting the HI Throttle point to 100%. Then I found a nice open road, put the car in 3rd, and held 100% throttle while modulating the brakes to hold RPM’s steady. Then I removed fuel from the map, aiming for 13.5-14:1 ratio. This seems a bit high, but from everything I’ve read, the n/a motor will just start loosing power or bucking at leaner settings, and will not damage anything.
Some sources say to try to hit 14.7:1 throughout the RPM range for optimum power on an n/a motor. I’m sure a lean mixture will cause hot exhaust gas and likely damage something eventually, so I feel fairly comfortable with the 13.5-14 range. I do have an EGT gauge to install at some point, this will help further fine-tune and validate this setup.
I performed several runs at 3k-8k in 1000rpm increments, slowly removing fuel, till I was pretty happy with the curve. 10-15% fuel has been removed from each point. I was careful to let the engine & brakes cool after each run, as this is pretty hard on the car.
Thus far the results are encouraging. The butt-dyno clearly states the car is faster, and it does sound a bit louder and rev faster. The VDI transition around 6500rpm is now noticeable: I think the effect used to be muted due to too much fuel. The extra power is most noticeable in 1st gear. First has always been fast but it is traction-limited now (sticky Dunlop Sport Z1’s), and 2nd is very stout. I would guess 0-60 times in the 6sec range – a Gtech meter may be coming
I plan to set the “low” throttle point to 40%, then develop the Lo map by holding 40% throttle and tuning for 14:1 as well. Then I’ll re-check the Hi map.
Fun times.
Mods of consequence are:
Original motor rebuilt by Kevin Landers, 6k on it
3rd gen housings (no diffuser in exhaust ports)
Mild 6-port street port
Full RB true dual exhaust
No cats
Airpump to actuate 5/6 ports (airpump does not pump air into exhaust)
Pineapple Racing inserts
T2 fuel pump
Cold air box
E-fan
RC Engineering cleaned / balanced injectors
MSD CDI ignition
MSD wires, heavy grounds, fresh plugs… etc
I am tuning using a PLX wideband with sensor installed 30” downstream of motor as recommended, and a SAFC2.
I chose the SAFC as it was $130 used vs. $400 for the Rtek. The Rtek adds ignition curve tuning and the ability to disable the OMP, and offers a cleaner installation, but I was not convinced it was worth the extra $270+ PDA to control it.
Without tuning, the car starts and runs great, good power, but pig-rich at higher rpm’s and throttle. By rich, I mean 12’s and even upper 11’s AFR, this is more what a turbo motor should run. So obviously there is room for improvement
I started by reading up on the various guides about SAFC tuning available on the Internet. Since it is modifying the MAF signal, the SAFC will only do anything when the ECU is actually looking at the MAF. This is known as “open loop” mode. When the ECU is in “closed loop” mode, it is just looking at the stock narrowband O2 meter, attempting to hit stoichiometric 14.7:1, or maybe just reading off a “map” for idle and warm-up.
By watching the Throttle % reading on the SAFC and the AFR reading on the PLX, it is clear the ECU attempts to maintain Stoichiometric ratio until about 35% throttle. 35% throttle is about as high as you go while cruising or even light acceleration. Past 35%, the ECU abandons the narrowband O2 sensor and begins to read the MAF.
I started by setting the HI Throttle point to 100%. Then I found a nice open road, put the car in 3rd, and held 100% throttle while modulating the brakes to hold RPM’s steady. Then I removed fuel from the map, aiming for 13.5-14:1 ratio. This seems a bit high, but from everything I’ve read, the n/a motor will just start loosing power or bucking at leaner settings, and will not damage anything.
Some sources say to try to hit 14.7:1 throughout the RPM range for optimum power on an n/a motor. I’m sure a lean mixture will cause hot exhaust gas and likely damage something eventually, so I feel fairly comfortable with the 13.5-14 range. I do have an EGT gauge to install at some point, this will help further fine-tune and validate this setup.
I performed several runs at 3k-8k in 1000rpm increments, slowly removing fuel, till I was pretty happy with the curve. 10-15% fuel has been removed from each point. I was careful to let the engine & brakes cool after each run, as this is pretty hard on the car.
Thus far the results are encouraging. The butt-dyno clearly states the car is faster, and it does sound a bit louder and rev faster. The VDI transition around 6500rpm is now noticeable: I think the effect used to be muted due to too much fuel. The extra power is most noticeable in 1st gear. First has always been fast but it is traction-limited now (sticky Dunlop Sport Z1’s), and 2nd is very stout. I would guess 0-60 times in the 6sec range – a Gtech meter may be coming
I plan to set the “low” throttle point to 40%, then develop the Lo map by holding 40% throttle and tuning for 14:1 as well. Then I’ll re-check the Hi map.
Fun times.
09-04-08, 10:15 PM
#3
on a street tune you are flying blind. I've tuned a few Rx-7's, FD and FC turbo and nonturbo, standalone and piggyback, and the *** dyno isn't precise enough. There is no ideal AFR for every engine, only guidelines. Don't worry about detonating the thing, that's highly unlikely in my experience. You will just lose power.
I ran in the mid 13's AFR with the CAS rotated several degrees on my s4 n/a which made 172rwhp (this was before the Rtek was available). You need to get on the dyno and get some kind of timing control if you want to milk those extra 3 hp out of the car. I wouldn't bother with EGT on an n/a car, although I am putting together a dual 0-5v EGT setup in my turbo manifold for my T2. No matter how good your instrumentation is, you are only going to squeeze a couple hp more out of it.
I ran in the mid 13's AFR with the CAS rotated several degrees on my s4 n/a which made 172rwhp (this was before the Rtek was available). You need to get on the dyno and get some kind of timing control if you want to milk those extra 3 hp out of the car. I wouldn't bother with EGT on an n/a car, although I am putting together a dual 0-5v EGT setup in my turbo manifold for my T2. No matter how good your instrumentation is, you are only going to squeeze a couple hp more out of it.
09-05-08, 09:27 AM
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on a street tune you are flying blind. I've tuned a few Rx-7's, FD and FC turbo and nonturbo, standalone and piggyback, and the *** dyno isn't precise enough. There is no ideal AFR for every engine, only guidelines. Don't worry about detonating the thing, that's highly unlikely in my experience. You will just lose power.
I ran in the mid 13's AFR with the CAS rotated several degrees on my s4 n/a which made 172rwhp (this was before the Rtek was available). You need to get on the dyno and get some kind of timing control if you want to milk those extra 3 hp out of the car. I wouldn't bother with EGT on an n/a car, although I am putting together a dual 0-5v EGT setup in my turbo manifold for my T2. No matter how good your instrumentation is, you are only going to squeeze a couple hp more out of it.
I ran in the mid 13's AFR with the CAS rotated several degrees on my s4 n/a which made 172rwhp (this was before the Rtek was available). You need to get on the dyno and get some kind of timing control if you want to milk those extra 3 hp out of the car. I wouldn't bother with EGT on an n/a car, although I am putting together a dual 0-5v EGT setup in my turbo manifold for my T2. No matter how good your instrumentation is, you are only going to squeeze a couple hp more out of it.
I have been impressed though by how noticeable a difference the fuel curve thus far has made. it is a very different running car now.
the egt is lying around from a previous project... overkill for n/a, I agree, but what the heck
Cheers
09-05-08, 12:48 PM
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12-09-08, 03:10 PM
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Maximizing in-town mileage is all about keeping the throttle low - around 35% or less. This keeps the car off the MAF map, and running a stoich. ratio. And, of course, shifting early: 3k rpm's or less I would think, well before the secondary injectors kick in.
Cheers
12-09-08, 07:30 PM
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I'm too lazy to read everything that's been posted, however, if you're tuning an NA motor for more power you definitely don't need the TII fuel pump. The NA runs really rich as it is.
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