rb25 RB25DET Timing Advance issues

[CLEM0]

4 minutes ago, Murray_Calavera said:When you say it makes shit power on regular timing, how much timing and how much power exactly? 

I don't know exactly the power and timing, but 15PSI on a GT3582 is about 400-450whp on most R33 setups with a safe tune. Mine made this but it needed 28* of timing I believe, as well as the fact the ECU is 2* retarded of the actual engine, so somewhere around high 20's to 30* of timing to make normal RB power

[Murray_Calavera]

Haha classic. Nismo 740's are the culprit for many of these issues. 

For example, you cannot get stoich mixtures with pump 98 at idle with nosmo 740's. You can achieve a nice stable smooth idle but it'll be rich as f**k (11ish AFR give or take). 

If your tuner targeted stoich mixtures at idle, yes it will be choppy and unstable as you describe. 

Your tuner would have put a sniffer up your car's butt when it was on the dyno which is not as accurate as you can be with a 4.9 sensor pre-cat but meh, you work with what you've got.

I'd say from here you've got 2 options, put it on e85 (you'll still have issues but many will be solved as the injectors will generally be operating in their linear zone) 

Or

Get a set of modern top feed injectors. If you want to stay on pump 98 and keep your sanity, this is the only option.

Once you've got your fueling sorted, I'd throw it on the dyno again and see how you go. This time make sure your tuner is using a set of knock ears.

 

[CLEM0]

4 minutes ago, Murray_Calavera said:

Haha classic. Nismo 740's are the culprit for many of these issues. 

For example, you cannot get stoich mixtures with pump 98 at idle with nosmo 740's. You can achieve a nice stable smooth idle but it'll be rich as f**k (11ish AFR give or take). 

If your tuner targeted stoich mixtures at idle, yes it will be choppy and unstable as you describe. 

Your tuner would have put a sniffer up your car's butt when it was on the dyno which is not as accurate as you can be with a 4.9 sensor pre-cat but meh, you work with what you've got.

I'd say from here you've got 2 options, put it on e85 (you'll still have issues but many will be solved as the injectors will generally be operating in their linear zone) 

Or

Get a set of modern top feed injectors. If you want to stay on pump 98 and keep your sanity, this is the only option.

Once you've got your fueling sorted, I'd throw it on the dyno again and see how you go. This time make sure your tuner is using a set of knock ears.

 

Thanks Mate.

I'm just assuming 740cc for the simple fact that the injector duty is 60% max and they look like the Nismo reds haha.

I'll pop them out tomorrow to confirm and i'll give them a clean.

Why are these classic Nismo 740 issues? Are they notoriously poor quality or just too big for the power?

[Murray_Calavera]

Injector flow rates are not linear in their low pulse width operating range. Nismo 740's are not happy below 1.5ms. 

If your curious about this stuff, Google injector flow rate chart. It should make more sense with a picture.

So for example, when you have 740's operating a hair over 1.5ms at idle on pump 98, your mixtures will be around 11AFR. 

Modern injectors are much better at operating in their low pulse width range which makes it possible to achieve a nice idle with good mixtures.

Edited December 8, 2020 by Murray_Calavera

[CLEM0]

12 minutes ago, Murray_Calavera said:

Injector flow rates are not linear in their low pulse width operating range. Nismo 740's are not happy below 1.5ms. 

If your curious about this stuff, Google injector flow rate chart. It should make more sense with a picture.

So for example, when you have 740's operating a hair over 1.5ms at idle on pump 98, your mixtures will be around 11AFR. 

Modern injectors are much better at operating in their low pulse width range which makes it possible to achieve a nice idle with good mixtures.

Ha. Learn something new every day I guess.

Thanks for the info.

I'll look into it. I really do think the injectors aren't the issue here, especially considering the concerning timing is at max power- but at this point i'll try anything because it literally makes 0 sense why this engine needs this timing for power. Honestly it is beyond me all the major culprits are accounted for aside from fuel, but this car used to run extremely rich so I doubt they're struggling.

 

Going to check coilpacks tomorrow too, as well as fuel pressure and injectors. They're new-ish Splitfires so I doubt they're bad- but again, nothing makes sense with this car!
 

It took me 6 months of going carless to find the right R33. I've wanted one for so long, saved up a shit tonne for it, and this is how I get re-paid! 😂Loving it so far. Done 400km in the car and been on stands more than the road

[Murray_Calavera]

The thing is though, we don't even know how much power the car made on lower timing. 

It might be the case that you pull the timing back to 20 degrees and lose 20hp and you call it a day. There are so many things that can affect the overall power the car makes, timing is only a part of it. 

One thing I can guarantee though is, Nismo 740's are not happy on pump 98 at idle or any other really low load area, like cruising on a slight decline and using a touch of throttle to maintain a constant speed (around -70KPA if your looking at a fuel map). 

[GTSBoy]

Also...compression and leakdown test time. Low comp might make it tolerate a lot of timing.

[CLEM0]

3 hours ago, GTSBoy said:

Also...compression and leakdown test time. Low comp might make it tolerate a lot of timing.

Was 125-128 across all 6. Not amazing numbers but very consistent, and was using a really cheap compression tester for these readings, which doesn't usually give accurate 'high' readings according to most, and they use them to check conistency more than anything.

Why would low comp allow it to tolerate high timing? And why would it actually mean it won't make power without this timing? I know it'd make overall less power than one with say 150PSI across all 6, but surely that doesn't mean it needs damn near 30* for power

[GTSBoy]

40 minutes ago, CLEM0 said:

Was 125-128 across all 6

You should test again with a known good tester, just so you know where it really sits. Mine are all up around 170 (on a Neo) on a recently calibrated known good tester. That's about as good as it gets. >200000km too.

55 minutes ago, CLEM0 said:

Why would low comp allow it to tolerate high timing?

The amount of timing and engine will take is a direct measure of how efficient the engine is. The more timing, the less efficient. A high static compression ratio and valve timing that traps a large % of the intake charge in the cylinder creates an effieicnt engine. The high comp is making the most out of what you trap in the cylinder. The valve timing is not wasting flow that was drawn into the cylinder, thus maximising power from breathing capability.

Conversely, a low static comp ratio is not making the most out of what gets into the cylinder. You make less torque when you have less expansion after the bang.

A high comp engine will not tolerate as much timing as a low comp engine. It will ping. Same with boost. Take an engine with boost and a tune that is right on the edge of pinging, add some more boost - insta ping. Same with just adding compression. So, a healthy RB25 with lots of boost on 98 might not want more than 20-22° of timing in the middle of the rev range. But if that engine is down a lot of comrpession, it might be able to swallow a few more degrees without pinging. The "low efficiency" state of the engine can be compensated for (a bit) with added timing. Not as good as having a healthy compression ratio and less timing, but certainly better than having both a low comp ratio and no timing!

 

Another question comes to mind. Weere in the timing map are you seeing 28°? Just at high revs, or at max torque revs? What is the timing like in the 4000-5000rpm region? Can you show us the map?

[CLEM0]

55 minutes ago, GTSBoy said:

You should test again with a known good tester, just so you know where it really sits. Mine are all up around 170 (on a Neo) on a recently calibrated known good tester. That's about as good as it gets. >200000km too.

The amount of timing and engine will take is a direct measure of how efficient the engine is. The more timing, the less efficient. A high static compression ratio and valve timing that traps a large % of the intake charge in the cylinder creates an effieicnt engine. The high comp is making the most out of what you trap in the cylinder. The valve timing is not wasting flow that was drawn into the cylinder, thus maximising power from breathing capability.

Conversely, a low static comp ratio is not making the most out of what gets into the cylinder. You make less torque when you have less expansion after the bang.

A high comp engine will not tolerate as much timing as a low comp engine. It will ping. Same with boost. Take an engine with boost and a tune that is right on the edge of pinging, add some more boost - insta ping. Same with just adding compression. So, a healthy RB25 with lots of boost on 98 might not want more than 20-22° of timing in the middle of the rev range. But if that engine is down a lot of comrpession, it might be able to swallow a few more degrees without pinging. The "low efficiency" state of the engine can be compensated for (a bit) with added timing. Not as good as having a healthy compression ratio and less timing, but certainly better than having both a low comp ratio and no timing!

 

Another question comes to mind. Weere in the timing map are you seeing 28°? Just at high revs, or at max torque revs? What is the timing like in the 4000-5000rpm region? Can you show us the map?

Thanks for the explanation mate. I guess that makes sense. I'll give the car another comp test with a better tester. I think it'll be below 140 regardless.

 

It makes mid to high 20's under full boost/max power around 6.5k rpm. I don't know exactly because i'm focussed on not crashing at that time, but a glance showed that. Low knock on apexi. I don't have datlogit cable or whatever its called sadly. Under high revs, low load its around 35+ * of timing (4-5k no boost).

Tuner said car made bugger all power with any sort of normal timing. Any way to share map from apexi power fc without the cable to upload the map?

 

 

[GTSBoy]

3 minutes ago, CLEM0 said:

Any way to share map from apexi power fc without the cable to upload the map?

You just have to go through the map on the handset and write down values.

[CLEM0]

4 minutes ago, GTSBoy said:

You just have to go through the map on the handset and write down values.

Will do tonight. Cheers

[BK]

For reference:

This is what the stock RB25 Apexi ignition table looks like in the Power FC. Note RPM is cells N1 - N20 in 400rpm increments, so N20 is 8000rpm. P1 - P20 is the load scale. You really need to do a map trace on the hand controller to see your max load as most cars won't be hitting P19, P20. So for this map most RB25s would be at 23 at full load redline.