Got a Dashdyno for the GXP - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


Performance, Brainstorming & Tuning Talk about modifications, or anything else associated with performance enhancements. Have a new idea for performance/reliability? Post it here. No idea is stupid! (please use Detailing and Appearance for cosmetic ideas)

Reply
 
 
 
Thread Tools Search this Thread
Old 01-02-2009, 02:18 PM   #1
Senior Member
Posts like a 4 Banger
Thread Starter
 
Join Date: Jul 2006
Posts: 127
Thanks: 0
Thanked 0 Times in 0 Posts
2.3 Turbocoupe is on a distinguished road
Default Got a Dashdyno for the GXP

I got a Dashdyno SPD for Christmas, and have been able to connect it to the GXP to gather some OBD2 data.

I have to give this item a mixed review so far. I will go into further detail after I've had some time to learn how to use all of the functions. I am a little more comfortable with it now, but it had me cussing up a storm the first time I tried to datalog a run. Once you learn how to do it, it'* not too bad, just a little cumbersome. But getting there was a big PITA, and I think they could make it a lot more user friendly. I've datalogged extensively with an LM1 on the TBird, and that was simple by comparison. By the time I had actually recorded a run and was able to play it back, it felt like a major accomplishment.

More bad news - it does not display knock retard. Damn, that might just be the most important piece of data for any type of tuning. It is supposed to work for GM in general, but probably the Northstar PCM (aka big brother) has it buried in some unreadable code. Nobody on the Cadillac forums knew of another scanner that could read read knock retard on the NorthStar. Ugh.

Anyway, I'll pass along a few casual observations on the data I've observed so far:

A/F - I am reading the commanded A/F with the dashdyno. I thought it would be super-rich at WOT, but it is really not too bad. It is commanding from 12.0 to 12.6. It commands 12.0 in the midrange, and then slowly leans to 12.6 in the higher rpms. Certainly there is room for improvement, but I wouldn't call that pig rich. I do plan on hooking up my LM1 to see what the actual AFR is. The Dashdyno can log the LM1 signal if both are configured correctly.

Timing - looks like this is where they went really conservative. Here are a few data points from a 2nd gear pull:
RPM / Degrees
4000 / 13.0
4500 / 13.5
5000 / 14.0
5500 / 19.0
6000 / 24.0
6300 / 24.0

Also, timing is pulled during shifting. I figure they did this to save the tranny and keep the car going straight. I have a datalog showing -8.5 degrees during the 1 / 2 shift. Not sure if that is a fluke, I need to try it again.

The IAT on these cars is integral with the MAF sensor. I am currently running a 3.5" FWI using metal exhaust pipe and silcone connectors (which I need to post up on separately). I have seen IAT temps up to 30 degrees higher than ambient when stuck in traffic or idleing for a few minutes. Yikes! I am going to add some insulation to the metal tubing, but it'* probably just a classic heat soak situation.

I'll be passing along screenshots in the future after I've collected more detailed information. Is all of this academic? I do think there is hope for some crude tuning. It is going to require manipulating the MAF sensor readings at WOT. I can't think of any other way. The MAF signal can be modified by either using a MAF translator or some trickery in the inlet tube. The important think to keep in mind here is that you only want to modify the readings at WOT - if the MAF readings are modified while the car is in closed loop, the PCM will adjust the fuel trims and cancel out the change.
2.3 Turbocoupe is offline   Reply With Quote
Old 01-02-2009, 10:47 PM   #2
Administratus Emeritus
Certified Car Nut
 
GXP Venom's Avatar
 
Join Date: Jan 2006
Location: Purgatory, Pennsylvania
Posts: 16,538
Thanked 7 Times in 4 Posts
GXP Venom is on a distinguished road
Default

Nice writeup on your new "toy", I've been searching for a MAF translator for a Northstar forever and only seem to find other people asking the same question in searches.. Jet Chip makes a performance MAF for the LD8, but Custom 88 shelled out the $350 and didn't write anything spectacular enough about it to make me want to toss out the cash. He has the Shortstar and it may well be that the MAF will do better in the LD8 it was actually designed for.

Timing is ultra conservative for a "sports engine", aint it. And you can feel that surge of power on the old "butt dyno" where it makes the big change high into it'* torque curve. Having the limiter set at 6500, you would think they would have been a little more generous further down in the mid range.

I have noticed the timing pull during WOT shifts without nitrous and agree it'* to save the tranny grief. Or should I say save warranty grief. Keeping the car going straight is a definite. For a car advertised to be all but absent of torque steering, I have had my share of grief when the nitrous hits at 2500RPM in second. Not sure of the torque rating for a 4T80. . But the Impala SS used the tranny as well and it puts out 323 Lbs. And I figure to be there or a little above spraying. At 33,000 miles she is still solid, but a bit looser than new.

The engine can definately use a richer A/F. I have noticed that upon running out of nitrous pressure, the car still runs more agressively with just the gas spray coming out of the "wet" nitrous/gas combo nozzle. And doesnt stumble. So I have been leaving the system on even when the nitrous is empty, or just off. It'* TPS activated so the extra gas just sprays at a WOT.

The 30 degrees above ambient IAT suprises me with a 3.5 FWI. Wonder how much improvement you'd see swapping the steel pipe for 3 1/2 inch CPVC. You'd lose a little ID volume in the pipe but I bet the cooler temp rise would more than offset that.

It'* great to see someone try to overcome a non flashable PCM with ideas other than the nitrous. At 33k miles on the car I still think of as new, I worry a little more about how far I'll get with this engine spraying nitrous the way I do. (Getting married has slowed the bottle fills ) Cant wait to hear more data/observations as you get accustomed to your cool gadget.
GXP Venom is offline   Reply With Quote
Old 01-05-2009, 11:00 PM   #3
Senior Member
Posts like a 4 Banger
Thread Starter
 
Join Date: Jul 2006
Posts: 127
Thanks: 0
Thanked 0 Times in 0 Posts
2.3 Turbocoupe is on a distinguished road
Default

Venom, that is surprising about running faster with the nitrous fuel jet only, I’d expect the opposite. I will have to see what happens when I modify the MAF signal. By the way, I really do want to spray this thing one day.

I'm not surprised that the aftermarket MAF doesn't help. The MAF on the GXP is also used on the 2004 - 2005 CTS-V amoung other LS motors, so it is plenty big enough. Yes it has the screen, but the ID of the inlet is 3.75", so it should not be very restrictive. Not having the screen means the MAF signal will likely be inconsistent, which is nothing but trouble.

On the LS1 forums, that engine seems to respond very well to timing advances up to 26 – 28 degrees, and AFR of up to 12.9 when running premium fuel. I know, different engine, but I don’t think anyone really knows exactly what the Northstar likes.

I’ve decided to get this translator: MAF Translator

We will see if I can actually fool this PCM. "Big Brother" might figure out what I am up to and throw a code. In theory it ought to be ok. At WOT, it is not reading the o2 sensor, and relies on the MAF to know how much air is entering the engine. It only learns about MAF reading changes at part throttle, so the key is that with the translator, you only modify the signal at WOT.

Here is a thread I started in the support forum for the Gen 2: Will the Gen2 work for me? - Full Throttle Speed Tech Support

Regarding the Dashdyno, yesterday I tested the performance function. It is capable of measuring time to speed (0 - 60 for example) and 1/8 mile and 1/4 mile times. It does not have an accelerometer, but uses the VSS (vehicle speed sensor) to monitor acceleration. I found a good spot near my home where I can safely make an 1/8 mile run – great visibility and absolutely no side streets or entrances. I recorded the following times:

0 – 60: 6.3 sec
1/8 mile: 9.6 sec at 77.9

For reference, at the track I previously ran a best 1/8 mile pass of 9.5 at 76.5. So the numbers from this gizmo are definitely in the ball park. They can’t be relied upon as absolutely correct, since the slightest grade on the road will throw the numbers off. However, just like a G-tech, if this device can consistently record performance numbers, it will let me know what actual gains I am getting with any changes made. I will be making all runs on the same stretch of road. I am going to make a few more baseline runs to check consistency. It was windy when I baselined, so I might throw that one out.

I am going to reverse test the 3.5” CAI I am currently running against the fully gutted airbox. I want to make some additional baseline passes to make sure the times are consistent, then I can reinstall the airbox and see what the net change is (if any). Sure the 3.5 FWI looks cool, but the numbers won’t lie.

The dashdyno also has a dynamometer function. You enter a bunch of data including temp, humidity, and barometric pressure so it is corrected back to standard. Again the numbers may not be absolutely accurate, but should reveal increases and decreases in horsepower and the rpm where they occur. I have not yet tried the dyno function.

Last edited by 2.3 Turbocoupe; 01-05-2009 at 11:11 PM.
2.3 Turbocoupe is offline   Reply With Quote
Old 01-05-2009, 11:30 PM   #4
Administratus Emeritus
Certified Car Nut
 
GXP Venom's Avatar
 
Join Date: Jan 2006
Location: Purgatory, Pennsylvania
Posts: 16,538
Thanked 7 Times in 4 Posts
GXP Venom is on a distinguished road
Default

It kind of surprised me as well. And to fully check it out, I have a toggle switch in the car to activate the nitrous system power as well as the TPS activation switch. And over and over again I would WOT and as I accelerated flip the switch activating the system on and off and the car surges forward when I would activate the switch i.e. start spraying gas into the throttle body. A very noticeable surge of power with no hesitation whatsoever. Makes me think they fuel starve the engine as part of the detune from the 300HP version??? Whatever reason, the engine takes, and likes the extra gas. It'* a moderate spray, I have the 75HP orifice in the nozzle at the moment, If it were warmer, and I wasnt in the middle of a tearing apart and rebuilding everything it seems on my 94 Ram 3500, I would try out the larger gas orifices.

I read through that thread you linked. Altering the MAF signal just for WOT sounds like good idea and start at getting more out of the stuborn high strung bitch. LOL
GXP Venom is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Any non GXP's with GXP body? Grimm General GM Chat 5 11-23-2006 03:34 PM
GXP Owners...GXP Badge PIC wanted and NEEDED! bonnie94ssei Lounge 26 05-28-2006 07:00 PM
Your May COTM Winner: GXP Venom's 2005 GXP! Mortehl Your Ride: GM Pictures & Videos 41 05-17-2006 03:11 PM
2005 Bonneville GXP -vs- 2006 Grand Prix GXP carlmorrell General GM Chat 21 02-19-2006 08:29 PM
SC GXP vs V8 GXP bigd Bonneville GXP/ Northstar Powered Cars 9 04-30-2004 12:21 AM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 08:54 PM.


We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.