Adjustable Exhaust Cam Affect Low-end Power?

[JimX]

I had my PowerFC tuned recently, and although it's now got a lot more mid-range and top-end, anything under 2500rpm or so is totally dead, actually worse than it was before. It even seems to stumble and misfire fairly often, like it's dumping way too much fuel in. Could this be the result of adjusting the cam wheel which was done with the tune? Is there any way to compensate for it? If not then I'm tempted to sacrifice the extra top-end power by putting the wheel back to zero degrees. Once above 2500rpm though the car is entirely different, and it gets from 5000 to 7000rpm in the blink of an eye. (well, maybe one blink each for 5000-6000 and 6000-7000 )

The only other thing that has been "changed" since the drop in low end power are the injectors, which are now 550cc. But it idles about the same as before, so I don't think this is the problem at all.

I've got the old settings written down, is there any point in experimenting with the old timings to see if I can get it to run any better? Or shouldn't I bother because the cam wheel has been adjusted?

[cookie300zx]

your tuner could have tuned it just for top end power. get an awesome top end figure, but lose low-midrange. seeing as you don't drive around everyday at 7000rpm, i would get it re-tuned so that you get a fat mid-range gain, however you will lost a little top end. car will probably feel faster though, and the power/torque will be in a more useable part of the rev range.

Edited November 24, 2005 by cookie300zx

[paulr33]

have you considering increasing the timing in the low / end range? i too had the same problem after 3 powerfc tune;s and adjusted the low end timing myself and it came out awesome. unbelievable how well it drives once you do the low level ign timing increasments yourself. where are you located?

[JimX]

Well last night I finished writing down all the settings from the tune and typing them up into a spreadsheet. I also recorded the old settings before the tune from when I'm fairly sure it had more bottom-end, so I'm ready to experiment without worrying about losing track of anything. I'm not 100% sure it's got less low-end than before, it could just be my imagination. But I'm fairly certain it has lost a bit, mostly due to the stumble/misfire it gets when warm.

I've attached both sets of my settings to this message, anyone got any hints?

JimX_PowerFC_Ignition.zip

[The Mafia]

lol Paul... Stuff mapping them out manually. Go the DATALOGIT hehehe

[Cubes]

JimX,

To know what ign. values you are using at WOT we need to know what load points are used at what RPM.

Do a quick Map trace with WOT from low RPM and let us know.

To me it looks as if the 15-16loadpoints have been fiddled with.. up from the std 18 that is.

You may also get away with running more low end ignition timing providing you don't load it up and try and make all your boost at say 2000rpm.

[Sydneykid]

This is the default ignition map for an RB25DET via a Datalogit screen grab. Have a look at the low load/rpm points and compare them to what you currently have.

cheers

[Bl4cK32]

why did the tuner pull out the low end timing??

[JimX]

JimX,

To know what ign. values you are using at WOT we need to know what load points are used at what RPM.

Do a quick Map trace with WOT from low RPM and let us know.

To me it looks as if the 15-16loadpoints have been fiddled with.. up from the std 18 that is.

You may also get away with running more low end ignition timing providing you don't load it up and try and make all your boost at say 2000rpm.

<{POST_SNAPBACK}>

Ok, questions questions!

Firstly, do you want me to post a map trace with just WOT from idle to redline? Or just in the range I'm getting the stumble? I think I'm going to have to find a spot where I'm not going to run over people/pets or get done for hooning/street racing/speeding

Secondly, I know I've got "boost" written down but I had that from another map that someone sent me. I had copied it over and didn't check it on the hand controller because I don't know where it's set. So I don't know if load point 20 is indeed 1.6 bar of boost, or anything else for that matter. Where is it on the hand controller menus? And how do you "fiddle" with them? I have no idea if they've been modified or not, or why I should modify them.

Thirdly (maybe relevant), the AFM is set to "Super 90 VH41" or something, which I'm not 100% sure matches the Q45 AFM because it says VH41 which I've never seen elsewhere. Am I supposed to be using "Custom" instead?

why did the tuner pull out the low end timing??

<{POST_SNAPBACK}>

I don't know, I just picked up the car and went. But to me it looks like it has more timing down low than either the previous tune or the factory one. Which bit are you talking about specifically?

Last comment to keep it all in one post: Paulr33, I've got a copy of your map you put into another thread, I'm going to use it to modify my own tune. I notice you've got a lot more timing down low, is there anything I should be wary of when doing the same to mine? I'm thinking of slowly increasing the large differing values up by a few degrees each time rather than just doing a blind copy and paste of everything. Goodbye to another tank of fuel experimenting with all this I think!

[paulr33]

be careful when you fiddle with timing. dont load someone else's tune as it will vary greatly. certainly compare but i wouldn't load it. drive car about for a few minutes warm it up, then when water temp is 80 or optimal value goto setting on hand controller and ign/inj corr and set ign correction up a few degree's. say 4 degress. so the value for IGN is +4. you'll notice the idle should change note a little when you do it. now go for a short drive (low load) and see how it feels. does it feel more "responsive" and more "lively" if so then this is good. watch knock when driving around under MONITOR and make sure its not knocking. if you see knock over around 20-30ish then back off and revert the IGN correction back to 0 or power off the car. when you turn the car off the IGN correction will go back to 0 as its a test mode only, it wont save the correction value for you. it will knock considerably more under high / heavy load so i dont suggest doing much flat out redline runs or high / heavy load. medium should be ok again make sure you watch knock. also check for black smoke and listen for detonation and tread carefully.

[paulr33]

also it may depend on how the cam gear is dialed in, mines at 0 top dead centre so 22 on the hand controller is in fact 22deg whereas if yours is dialed in at +3deg or something like that then the numbers you see on the hand controller may be "off-scale" if that makes sense

[Cubes]

Paul,

Cam timing and ignition timing are not related as ignition timing is based on the crank's postion not the cam position.

Which is why its always important to recheck ignition timing after you have fiddled with the cam's cam belt etc. Its not as simple as dropping the CAS back in its origional position.

Adjusting the exhaust cam gears position or centerline is only going to change the position of the CAS in order to achieve a set ignition timing of say 15degree's.

Edited November 29, 2005 by Cubes

[paulr33]

my bad

[JimX]

Thanks for the advice guys, I'll give it a go when I have some time hopefully this weekend.

[JimX]

Ok, I've done a leetle beet of testing tonight. Tested just mainly low-mid range throttle, especially around the "stumble" zone of around 2000rpm. I dialed up an extra 2 to 5 degrees and at 3 or above it seems to get rid of the 2000rpm stumble/misfire altogether and give a noticable extra bit of power too (obviously - not firing means no power!). I need to record exactly which part of the map it's using there, but from memory it was around the L6/N6 area.

It seemed to be fairly good all round on about +5. I never took it above 4250rpm (used the hold setting to check) and the knock never got above 21-24. Usually the maximum knock on the map it has now is around 19 or 20, but at maximum noise it sometimes gets up to mid-high 20's. Does this mean that I can somewhat safely kick up most of the timings below 4200rpm (N10, 4000rpm) by 5 degrees? I'll only adjust up to the highest load point I'm seeing on the map trace. unless someone thinks I shouldn't?

I'll also use Paulr33's map as a guide to see roughly what maximum timing I can have at each point, like if there is a big difference between his and mine, I could experiment there with slightly higher values. (this is what I was always going to do, not load his map straight in) Thanks Paul

[Cubes]

Usually the maximum knock on the map it has now is around 19 or 20, but at maximum noise it sometimes gets up to mid-high 20's. Does this mean that I can somewhat safely kick up most of the timings below 4200rpm (N10, 4000rpm) by 5 degrees? I'll only adjust up to the highest load point I'm seeing on the map trace. unless someone thinks I shouldn't?

<{POST_SNAPBACK}>

Mine doesn't work that way.... Mine will be fine say hanging around the 20 to 30's... Dial in one more degree and it will spike over 60.

Suck and see as the old saying goes.

[JimX]

Ah goodo, I'll make sure I have a co-pilot to see where the spikes occur if at all. But today I am starting on the brakes. Need to be able to stop properly before I can test the go-fast