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Discussion Starter · #1 · (Edited)
Hey all. I recently embarked on a mission to mod a low mileage MC SS in the most cost-effective way possible, covering all the usual bases (intake, exhaust, rockers, pulley, etc) in order to see what a modestly priced upgrade to the car would net you in power. The following is an intro to the project and also the initial stock dyno results respectively. Later on I will update this thread with the final dyno results. I'm hoping this walk will help people gain a more tangible understanding of how mods synergize with each other and stack up to produce a net result. Enjoy!

Project Intro and all the mods unboxed and explained
Stock Dyno results and mod installation

Coming soon... final modded dyno results
 

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You do a bit of "jump to conclusions" mat on some of your assumptions. Heat soak isn't too terrible in these, as the difference of ~15degF isn't crucial to a ~10hp drop in these. Solid lifters? Just spend some time learning what these engines do, and what works at the level you're trying to be at. Spending too much time tinkering with simulations and hypotheticals won't help as much as filtering through suggestions/info to find what's actually made people perform appropriately at XX mod levels. There have been 3800 owners who spent $500-1K to gain ~100hp, and guys who spent $2K+ and barely get ~50hp... guess who would still post more about what people should do? Today is even worse than it was when 3800's were still new/popular, because there's much less accountability without forum history vs. social media feeds disappearing.

That's not your main deal, though. You started with an unhealthy setup making ~30hp below stock, and didn't resolve it. You need to be more dug into the tuning aspect and scanning AFR (preferably with a wideband) to see what it's telling you. That drop-off at 5k+ could be due to fuel dumping in, spark pulling back for various reasons in the tables, failing fuel pump/filter, weak power/electrical connections, etc. If you leave it alone with the current setup, it has potential to cause increased issues later.

I can see you getting in the 240whp ballpark with the things happier (guessing you did 90 or 105 springs? skimmed the vids). On a 3.2-3.4 pulley, you'll be able to adjust fueling and get timing to be a bit more aggressive under heavy throttle, but I would keep it less stressful while accomplishing your troubleshooting. Another simple check would be adding octane (they sell VP octanium for ~$22-25 at parts stores for a solid improvement). This could give you a hint as to what may or may not be hurting performance, if it improves during that use.

Torque flash is something all of these cars do, and it's actually a closer value to what is at the engine. These engines usually have similar hp/tq numbers, even modded, +/- 10-20%.

Keep at it, and have fun learning the car.
 

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Discussion Starter · #4 ·
Perhaps I should have qualified my speculation a bit better but honestly, heat seemed to be the most likely cause for an otherwise identically shaped run, just offset lower. This dyno shop had a poor cooling solution IMO.

I agree the stock car was already underperforming but I really can't figure why. The ECU was stock, the car had 30k miles on it and was driven regularly but sparingly, with regular maintenance intervals (was owned by a dealership manager previously). It should be just like all the other stock cars out there with a similarly shaped curve. Granted, the stock car may have had gummed up this or clogged that but certainly after doing the mods I did (which included changing all fluids and filters), this would not likely be an issue anymore, yet the new dyno curve pretty much followed the old one.

I didn't change springs because I didn't want to put the timing chain at risk from the increased load but since I only did 1.8 rockers, I think it's fine.

One thing I did notice. While my N/A grand prix gained a huge KR/spark advantage from the U-bend delete, this car didn't. It doesn't knock a lot or anything but I wasn't really able to increase timing at WOT. Combine this with the fact that there's a clear drop off after 5k and it's almost like the exhaust is plugged. But I replaced everything up to and including the resonator. Unless the mufflers, crossover or rear bank is plugged, which again it shouldn't be with this amount of miles on the car, I really can't explain the odd shaped curve.
 

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I'd toss some springs on, because even stock we have issues up above 5500. LS6's go for cheap most anywhere, and are good for even a moderate cam, let alone 1.8-9's.

You can try a pull with the exhaust dropped to guarantee it, and also try the fuel bump, if you want. Scan data might help, too, if you have it.
 

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Discussion Starter · #6 ·
I'd have to check a scan to know for sure (about time for another one anyway) but I know I'm rich at WOT. I just don't know if the rich condition correlates to the 5k RPM. Without a wideband I've been using O2s to tune and as you know, this is somewhat unreliable but then, not much you can do without a wideband that is reliable. If I was N/A I'd unplug the MAF or disable closed loop but with boost I figure the O2 method is better. I'm trying to get just under 900mV because I'm thinking maybe I can't advance the timing with such a rich condition.
 

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You'll want a little above 900mV to be on the safe side. We usually stuck to the low 900's and adjusted other things from there.

The car is going to try being safe once you're in the throttle for a bit, and richens in one table, I believe (AFR vs. RPM and/or time, I think). Don't worry about MAP-only tuning, because our PCM's don't have the broader tables and settings like LS folks and others.

If you're going to be getting into the details of optimizing the build, might as well go for a WB soon. I use PLX's (~$200 or so, still), and run the signal to the (deleted) EGR position wire to read the 0-5v output without any need for A/D inputs. Might go for an Innovate or AEM soon, just because it'll come with a boost controller or E85 sensor I'm looking at.
 
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