What do you suppose might be causing this? (dyno graph)

[JakeRobb]

Hi all,

I've been a member here for a while now, but I don't post much.

Last fall, I put my '87 GN (mods in sig) on a DynoJet. It posted reasonably good numbers: 253hp and 334tq (93 octane, 15psi, no alky). But the peak was early (~4k) and the graph from there up was really squiggly.

I'd post the dyno graph, but I don't have enough posts (you need at least 4) to post images or links. I'll get it posted as soon as the board lets me. All I have at the moment is a glare-filled photo of the dyno computer screen. I'll try to get a scan or a digital picture of the printout posted, but it's going to be a few days at least before I can make that happen.

The dyno operator said that problems like this are usually caused by ignition issues. The plugs, wires, and coil were all replaced about three years ago. I'm thinking it could be the MAF, or that the replacement coil could have gone bad. I hear that they're really unreliable and prone to failure at any time.

If anyone would care to speculate or make suggestions, I'm all ears. I know very little about GN tech stuff. Is there any way to diagnose the problem, other than by replacing parts and hoping for the best?

 

[JakeRobb]

I'm told that replacing the MAF with an LS1 MAF is a good mod. What else would I have to buy to make that work?

This being my 4th post, I can now show you guys the dyno graph:

I apologize for the poor photo. I'll post something better as soon as I can get it online.

 

[JakeRobb]

I'd eventually like this car to be able to run a sub-12-second quarter mile on drag radials, without using a trans brake and without any drag-only suspension parts. We mostly drive it on the street, and I don't want to sacrifice any streetability. I figure a 1.8 60' is the best I can expect with those limitations. Please keep that in mind when suggesting things I should replace on the car.

 

[bmackinnon]

Last fall, I put my '87 GN (mods in sig) on a DynoJet. It posted reasonably good numbers: 253hp and 334tq (93 octane, 15psi, no alky). But the peak was early (~4k) and the graph from there up was really squiggly.

The dyno operator said that problems like this are usually caused by ignition issues. The plugs, wires, and coil were all replaced about three years ago. I'm thinking it could be the MAF, or that the replacement coil could have gone bad. I hear that they're really unreliable and prone to failure at any time.

If anyone would care to speculate or make suggestions, I'm all ears. I know very little about GN tech stuff. Is there any way to diagnose the problem, other than by replacing parts and hoping for the best?

1) Those numbers and graphs look reasonable up to the 'squiggly' point...
2) I'm thinking the dynojet may have had a glitch happen, or the car shifted at that point?, or the converter locked up? Or someone eased up on the gas?What is the bottom graph of?? below the hp vs. rpm, and trq vs. rpm??
3) Car won't run worth a crap with bad maf and will pop/miss significantly with a coil going bad. They are not 'unreliable and prone to failure at any time'. Does the car seem to run ok??
4) Replacing parts and hoping for the best is not an option in my book (though I see some that must think it's the only option.. ). You must have a scan tool of some sort. Scanmaster, Turbolink, Powerlogger, Direct Scan are the common ones, tailored for our cars. Some are cheaper and more user friendly than others. Your budget and ultimate ability to use will determine which one to get. Many here will help you interpret your findings, and solve any problems you may have, but you gotta' have the data. A good scan tool comparison is here:
Scan Tool Comparison Chart

That should be your next purchase....

Hope that helps...

 

[JakeRobb]

No dyno glitch. I made three pulls; they all looked like that. The car didn't shift, and I didn't lift on the throttle. The car runs and drives fine, but traps lower in the quarter mile than I expected (my best run is a 13.6 @ 99 on street tires). It doesn't feel as strong at 5000 rpm as it does at 3000 rpm. I don't know about the TC lockup.

The third graph is air/fuel.

I have an ancient scan tool given to me by the previous owner. It's made by a company called MPSI. I've never tried to use it, but I spoke to the guys at Full Throttle recently and they told me that they've seen them before and that it should be sufficient to do the job. Now I just have to figure out how it works.

Thanks for the feedback. I'll see about getting some data.

 

[Steve V]

A modern MAF with a translator is a good investment,get one from fullthrottle. Have you ever replaced your valve springs?

 

[sailbrd]

A modern MAF with a translator is a good investment,get one from fullthrottle.

I'm thinking I'll do that, but I'd like to track this problem down before I start swapping parts.

Have you ever replaced your valve springs?

Not yet. Only about 40k on the odometer. Should I be doing that already?

 

[JakeRobb]

Sorry. The above post was me. I'm using my father-in-law's computer, and forgot to sign him off and sign in as myself.

 

[87natl]

+1 on the valve springs.

How many YEARS on the valve springs?

 

[salvageV6]

I can't see the A/F scale on that graph, maybe it's pig rich?

What boost and timing on those pulls, for 15psi. it's normal.

The stock motor is done at about 5K anyway, don't bother with anything above that, lock the converter at 5K-5.2K to lower the rpms back into the power band.

Looks like a dyno. sheet from a pretty stock car.

 

[JakeRobb]

I can't see the A/F scale on that graph, maybe it's pig rich?

I'll get the real graph posted soon, but I can tell you that the a/f numbers are fine.

What boost and timing on those pulls, for 15psi. it's normal.

When I mash the gas, it spikes up to around 19psi, and then drops back down and holds steady at 15psi. I don't know about the timing.

Looks like a dyno. sheet from a pretty stock car.

Yeah, mostly stock. K&N, catback, power plate, and tuned for 93. It has an aftermarket fuel pump, adjustable wastegate, and adjustable fuel pressure regulator, but I'm not really taking advantage of any of that at this point.

I have a set of 36# injectors, ready to install (my father in law got a good deal on them and bought them for me). I know a lot of guys go with 60# injectors. Would I be wasting my time with the 36s, or are they big enough to reach my goals?

 

[GNVYUS 1]

I believe that very bottom line in the AF/R graph is a 12:1 line and you were under it so you probably are running fat.

Didn't look like they did any smoothing on the graph so those jagged lines are most likely that.

Agree with the stock comments and your graph, I was going to ask about the power spike but then you said the 19psi comment. Time to open up the wastegate hole on the turbo exhaust housing to help that out.

 

[JakeRobb]

I had my Z28 dyno'd at the same shop, and I have a better image of that graph. Using that as a reference:

I believe that very bottom line in the AF/R graph is a 12:1 line and you were under it so you probably are running fat.

The red line is 13:1, so I guess you're right about that. I'm pretty new to this stuff, and someone told me it looked like a good tune.

Didn't look like they did any smoothing on the graph so those jagged lines are most likely that.

No smoothing is indicated on the Camaro graph...

Agree with the stock comments and your graph

Found this stock dyno graph in another thread:

Looks to me like my graph isn't very stock-like at all. The peak numbers are appropriate, but it's definitely doing something weird.

I was going to ask about the power spike but then you said the 19psi comment. Time to open up the wastegate hole on the turbo exhaust housing to help that out.

I'm not familiar with this procedure. Is it something I can do at home? Where can I get more details?

 

[GNVYUS 1]

If that last line is 12:1 then you are good there, even if it were 11:5 you would losing only a touch of HP up top but are safer in the knock department.

Ya, the Camaro graph and your GN graph look different in smoothing so don't get too worried about it, a lot of shops do the smoothing as it looks nicer and tends to fatten up the power numbers.

If I remember correctly, the stock power graphs are based off of engine dyno's, not chasis dyno's. Yours is stronger than the stocker considering that dyno info but the top end does look like it's falling faster than it should.

Locking the converter will give you back lost efficiency in the drivetrain and increase those top end numbers. Agree with the valve springs comments on it contributing to the top end falling off fast. IMO, 40k and it's time for new ones.

Concerning the spiking, take off the downpipe, the smaller hole is the hole that needs to be opened up. You will use the carbon ring to guide your dremeling of it. Do not get too close to the outside of the carbon ring as the puck will not seal it and cause a bigger problem. I use a shop vac to suck up the debris while I open up the hole and even round out the inside.

It could take you only 30 minutes if you have everything ready and don't have the BGC downpipe.

 

[JakeRobb]

If that last line is 12:1 then you are good there, even if it were 11:5 you would losing only a touch of HP up top but are safer in the knock department.

That sounds fine to me.

If I remember correctly, the stock power graphs are based off of engine dyno's, not chasis dyno's. Yours is stronger than the stocker considering that dyno info but the top end does look like it's falling faster than it should.

Right. It looks like my peak rear-wheel numbers are in line with the stock flywheel numbers, which makes sense to me given the intake, exhaust, and chip. I am more concerned with the shape of the curves.

Locking the converter will give you back lost efficiency in the drivetrain and increase those top end numbers.

How do I lock the converter? Is that something that's done via the chip? How do I know if it's locking? I can tell when I'm just cruising, but is there an easy way to tell at WOT?

Agree with the valve springs comments on it contributing to the top end falling off fast. IMO, 40k and it's time for new ones.

Fair enough. What's a good valve spring? Is there anything else in the top end (pushrods, rockers, etc) that would be smart to change at the same time? I know on my LS1, the first thing I need to change in the top end are springs and pushrods.

Concerning the spiking, take off the downpipe, the smaller hole is the hole that needs to be opened up. You will use the carbon ring to guide your dremeling of it. Do not get too close to the outside of the carbon ring as the puck will not seal it and cause a bigger problem. I use a shop vac to suck up the debris while I open up the hole and even round out the inside.

That sounds fine. Are there instructions on the web anywhere that would walk me through an R&R of the downpipe, or is it pretty straightforward?

It could take you only 30 minutes if you have everything ready and don't have the BGC downpipe.

Speaking of which, would I be better off just buying a larger, aftermarket DP? From what I've heard, a 4" DP is a simple swap and is worth gobs of horsepower.

 

[JakeRobb]

Well, I figured out how to use my scan tool today.

I can't see any indication that anything is wrong based on the scan tool's output. No trouble codes, reasonable voltages coming from all available sensors, and everything behaving as expected.

The KR reading says 0 about 99% of the time. I did a 0-80mph run, and it went to 1 around 4000 rpm, back to 0 after the shift. I saw 2 momentarily when I let off the throttle at 80mph, then back to 0. I am assuming this is degrees of retard, but I haven't confirmed that in the user's manual.

Assuming that the readout labeled "TCC Solenoid" is my torque converter clutch, it is not locking up in first or second. I haven't had a chance to test third yet.

 

[GNVYUS 1]

Locking the converter can be done in the chip and it's done in 3rd gear. You can do it with a paper clip in the ALDL, that info can be found on this site and GNTTYPE.ORG I believe. You wouldn't want to lock the converter any sooner than 3rd as it will bog down the motor, especially while cruising around. I have two TT chips, one doesn't lock the converter ( street chip ) and the other does ( race chip ).

Really no need to change anything else other than the springs, and those can be found here.
FULL THROTTLE SPEED - Item Description Page
I would call and talk to Mike about any specs on the springs.

I don't recall any detailed instructions on the turbo's exhaust hole opening, but it's pretty straight forward. Many try to keep it no larger than 1 1/8th. It really depends on the size of the downpipes puck.

If you have the stock downpipe and plan on making a lot of power, then any good 3" SS downpipe with test pipe/dump would be a great addition while it's off.

 

[Ed Valvo]

Peak power around 4500 RPM is typical for stock cam and heads. The jumpy lines could be the "Smoothing" feature in the Dynojet program. I have a few dyno graphs with jumpy lines. Dyno shops will change the Smoothing rate to smooth out the lines and make them look nicer.

 

[JakeRobb]

Locking the converter can be done in the chip and it's done in 3rd gear. You can do it with a paper clip in the ALDL, that info can be found on this site and GNTTYPE.ORG I believe. You wouldn't want to lock the converter any sooner than 3rd as it will bog down the motor, especially while cruising around. I have two TT chips, one doesn't lock the converter ( street chip ) and the other does ( race chip ).

Ideally, I'd prefer to use the same chip for both street and race. Is locking up in 3rd really so bad on the street?

Really no need to change anything else other than the springs, and those can be found here.
FULL THROTTLE SPEED - Item Description Page
I would call and talk to Mike about any specs on the springs.

Thanks, but the link doesn't work. Can you post the item code?

I don't recall any detailed instructions on the turbo's exhaust hole opening, but it's pretty straight forward. Many try to keep it no larger than 1 1/8th. It really depends on the size of the downpipes puck.

If you have the stock downpipe and plan on making a lot of power, then any good 3" SS downpipe with test pipe/dump would be a great addition while it's off.

I'm thinking that 450rwhp will be enough to reach my goals. Does that count as "a lot of power"?

 

[machinegun]

Your issue is not an uncommon one. From your sig and this thread, One of the first items appears to be valve springs. If the car is falling off at 4000 usually this is caused by the factory valve springs being weak. I would replace the valve springs, and then look at tunning the car. These should pull through 5000 with no issues.

My daily driver runs 12.6's with not much more than you have.

It is not mentioned but I had 42.5 lb injectors, DIY alchy kit and ran 2.2 60's on the 16 bfg's with the stock turbo, downpipe gutted cat hooker exhaust and red 104 chip on 22 lbs of boost

1.8 on the drag radials and 12.20's would be the norm.

hope this helps