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Discussion Starter #1
Last night I made the 3rd dyno pull with GXP. I planed to do these pulls after installing various power adders and post the actual results to help give people with similar add ons an idea of what they have or will gain.
My first pull was my 2009 GXP with a GMPP stage tune, Solo high flow cat, and a GMPP Cold air intake. Results were 282 wheel HP. Then I took it home and fought with the installation of a Hahn intercooler. Chuck claims that it will gain 27 HP, pretty close in my case. It added 26.4. So now I'm at 309.6 HP and I go back home and install a solo Mach shorty. Sounds great, and it feels like there is more power, but the dyno said wrong. It fell back to 304. What the....? Solo said I could expect 15 to 20 HP, and I actually lost power rather than gaining more. The tech running the dyno downloaded the gm tune to take a look and see if he could figure out what was happening to my power. His best educated guess is that the flow increase from the IC, Solo cat & Mach shorty, and the CAI have contributed to the fuel system running leaner than optimum, and that he believes that he can adjust this in the tune. Has anyone encountered a situation like this?
 

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Don't let anyone adjust that tune, that is not very familiar with our platform and tuning for it. You need a tuner that understands our cars, specifically.

I would bet you anything that he is not familiar with DI and how lean it runs.

As far as mods and HP/Torque Gain, with the GMPP tune: The GMPP tune does remove the OEM "Learn Down" Torque management to 260 lbs of torque. But at the end of the day, it is a canned tune. So it is unlikely that you will see significant gains with individual mods. The only reported gains observed, without additional tune over the top of the GMPP is typically from a High-Flow CAT. Beyond that, nothing else really makes much of a difference, if any. The canned tune will no longer "Learn Down", and it will now tend to "Learn Up"; but only to a certain extent. To maximize you need someone that is thoroughly experienced at tuning our cars.
 

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Discussion Starter #3
Actually the reason that I am working with this shop is that the dyno man states that he has worked with the LNF in Chevy cobalt and says that he is familiar with GMPP tune. He recommended that I take some time and think about it, certainly ask some questions. Is there some way to tell how competent he is?
 

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You can install as many mods as you want and you wont gain a single hp, all your power is found in the ecm with a few clicks of the mouse.
Ask this tuner if he spends any time on the hptuners forum, if he doesn't then run away because all the lnf tuning info is there.
 

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Do you have some numbers as to what he thought lean was? With the DI set up it will run much leaner than your typical fuel inj. If I am reading the gmp tune right you will be as lean as .95 lambda(13.9 afr) and as rich as .87(12.8) depending on rpms. Much leaner than I would have ever run my supercharged car in the past, but DI is different and some will want run them way too rich because that is what they know. From the little digging I was doing .86 to .88 is ideal for gas.

Just ask some more questions, he shouldn't be offended. If you're not comfortable with his explanations, try to find someone else, or pick up hpt and find a known lnf tuner and do some remote tuning with them. Keep us posted.
 

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Discussion Starter #6
I did not get a print out of the chart showing the lambda numbers but there were alot of .95 and some .87 he also spent some time looking at egt and torque demands. My understanding of the LNF is less than basic, but I have read a little on the lambda fueling and torque demands. I originally choose the GMPP tune so that my warranty would not be effected. With the learn down feature out of the way, I thought I would see the benifit of other power add ons. The increase from the Hahn IC was very noticeable, 282 without, 308with. I just don't see how i could loose power by replacing the stock exhaust with a 3" Solo mach shorty. Even if there is no additional power to be gained with this system,it shouldn't lose it. I do not want to change tuners to a trifacta or HP, I'm sure they are good quality and probably make more power than mine, but I am satisfied with what I have. I just don't understand why some of the horsepower left me, and where it went. If we knew maybe I could get it back.
 

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I would never have guessed that a larger IC would net that kind of a HP increase. What were the before and after torque numbers?
 

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Here's the technical explanation that might help...

The exhaust side restriction is in the exhaust manifold, turbine housing and cat. Anything you do past that will not make much difference, and like you've seen could actually hurt power. The reason you lost power basically comes down to cold air is heavy. If you have a restriction upstream, and increase the pipe volume downstream of that, the exhaust slows down. When the exhaust slows down, it gets colder and heavier and is harder to push out. The smaller stock pipes help keep the exhaust moving and don't let it slow down and cool off as much as an aftermarket wide open setup would. Most guys think this means "It needs backpressure". That's wrong. NO exhaust system "needs" backpressure. What it needs is velocity. What you did is killed exhaust velocity and flow. Going to a high flow cat will help a lot. Going also to a big manifold and turbo will make that exhaust perfect. Sorry! That should only cost you about $4k and void your warranty!

The stock GMPP tune is lean, not rich. You got good advice from these guys, listen to it. If the guy thinks it's rich, run away. Tuning an LNF is not easy, and just because he's a "tuner" DOES NOT mean he can properly tune an LNF. There are only a small handful of guys in the country I can honestly say know how. There's hundreds that think they know.

If you're happy with how it runs and sounds, just drive it and enjoy it! If you want to make the exhaust work better, go for a high flow cat and it will make a pretty good difference. It will also make it louder though.
 

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Discussion Starter #9
I had a number of people tell me that the IC would not gain any HP. This was the main reason that I spent the $$ to dyno it. the first pull without the Hahn was 346.1 Torque and 283.6 HP. After adding the IC I got 366.4 Torque and 309.7 HP. So I guess Chuck lied to me, cause he said I would get 27 HP but I only got 26.1. By the way, this has the stock inlet and outlet piping from the turbo to the motor.
 

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Discussion Starter #10
The comment that he made was that there were a lot of .95 lambda showing which indicated that it was alittle lean. It was also a little cooler the night we did this last pull which he said could have effected the result. (although the computer is supposed to correct for that) so it sounds like he is on the right track. My car has had a Solo high flow cat on it as from the beginning, so I can't really gain anything else there. It may be worthwhile to do a turbo heat wrap/heat sheild and maybe wrap the manifold too. I'm not inclined to have someone mess with the program. I just was hoping to find where the power went. I did see a great gain from Hahn, and according to Solo I should have seen 15 to 20 HP from their Mach exhaust. This may only be true in HOT weather?
 

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So I guess Chuck lied to me, cause he said I would get 27 HP but I only got 26.1.
Im trying to find some sarcasm in here but don't see it, are you actually complaining about 0.9hp you didn't get?
The comment that he made was that there were a lot of .95 lambda showing which indicated that it was alittle lean.
The lnf runs .95 in the midrange and drops to .87 in the upper rpm range
I did see a great gain from Hahn, and according to Solo I should have seen 15 to 20 HP from their Mach exhaust. This may only be true in HOT weather?
Compounding hp figures like that doesn't work, if each mod nets 15hp then all 5 together simply won't net you 75hp total.
 

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Discussion Starter #12
No sarcasm. If Chuck reads this maybe it will make him giggle. In my opinion Hahn could not have been more spot on with his projected power increase. I wish others were that accurate. I'm 53 years old and have been hot rodding and racing since I was 16. I have years of buying power adders that don't come close to delivering what they claim. In this case it was dead on the money.
I was not particularly looking for a 20 HP gain from the solo exhaust, but I thought I would see something. I was not expecting to see a loss of power from it. The effect of temperature as stated by the GM tech may be the root cause of this loss.
 

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Discussion Starter #14
Reaching the limits of tune is a very real possibility, that I have been keeping in mind. I know that the learn down is not shut off on the gm tune but raised to higher level. I tried to find out if anyone knew where that higher limit was set at before I started doing the dyno testing and adding the IC and Solo. If I could have found out what the limit was, I may not have bought some of these parts.
 

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Don't let anyone adjust that tune, that is not very familiar with our platform and tuning for it. You need a tuner that understands our cars, specifically.

I would bet you anything that he is not familiar with DI and how lean it runs.

As far as mods and HP/Torque Gain, with the GMPP tune: The GMPP tune does remove the OEM "Learn Down" Torque management to 260 lbs of torque. But at the end of the day, it is a canned tune. So it is unlikely that you will see significant gains with individual mods. The only reported gains observed, without additional tune over the top of the GMPP is typically from a High-Flow CAT. Beyond that, nothing else really makes much of a difference, if any. The canned tune will no longer "Learn Down", and it will now tend to "Learn Up"; but only to a certain extent. To maximize you need someone that is thoroughly experienced at tuning our cars.

I picked up about 15 HP with a K&N and custom SRI (only mods at the time were GMPP and catless DP). I have the chart somewhere.
 

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Reaching the limits of tune is a very real possibility, that I have been keeping in mind. I know that the learn down is not shut off on the gm tune but raised to higher level. I tried to find out if anyone knew where that higher limit was set at before I started doing the dyno testing and adding the IC and Solo. If I could have found out what the limit was, I may not have bought some of these parts.
Can you return the exhaust?

I believe a header is made?

Since you've been around vehicle maintenance and mods I'm sure you'd agree with what GMtech and Shabby were saying as far as too much exhaust volume capacity (flow, people talking about "backpressure", and velocity which creates or at least helps keep heat in the exhaust gas), as well as compounding of HP statements relative to multiple add ons.

I'm in a similar boat I suppose in that I have the GMPP tune and don't plan to go aftermarket since this is a GM part number add and install. One item I would seriously consider adding though is the Hahn IC (have to look at the price again, I know it's expensive) for the HP gains you stated, and secondly the high flow cat. But, from the reading I've done on here I'd say that you have pretty much done what you can to maximize the power from your motor RELIABLY at this point, OR going ahead and adding the larger turbo possibly (even then it might be best to get the money back from the exhaust and put it to the larger turbo). The larger turbo seems to really be able to kick things up, but again for substantial cost, and likely not under any GM warranty, which is why I won't go there.

So if you are dyno'd at like 309whp, that would translate to flywheel or crankcase HP of around 325hp or so? That would be very nice to have.:thumbs:

Edit: I guess the one other issue with IC HP gains is that the Hahn graph shows that you really gain nothing until you are getting above 60mph.

Double edit: No codes with the Solo high flow cat? That's the one add I have been looking at for now, showed 15hp/8lbft and I'd think this would be more immediate and across the powerband.
 

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Crank hp would be more like 360.

I think the dyno shows how efficient it is in comparison after just a few seconds of WOT. I think we see a bigger difference in 3rd and 4th because the Hahn flows better and cools more efficiently.
 

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Discussion Starter #18
Solo will take the exhaust back, but It fits better than the magnaflow i once had on it and it sounds better than stock or magnaflow. I guess the increased flow will be available if I switch the tune to westers or trifecta. It is possible that a power gain from the exhaust will only show up during hot weather.
 
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