|
What's holding me back????? WARNING: Long Story Alert!!! Need some help with identifying what's wrong with my engine build/tune. So, long time ago (2010), I supercharged my stock LS2 GTO. MP112, stock engine/exhaust and made 494 rwhp/514 rwtq@ 8psi. Fast forward 6 or so years and start racing the car and end up blowing the engine (expect a lean condition at the end of the track when I let of the throttle). I decided to build a fully forged 5.3, same MP112, with Stage II PRC 5.3 heads, 1 7/8" headers, LS9 cam and 9:1 CR. When I finally got the engine together I went and got it dyno tuned and it only made 404rwhp/415rwtq...talk about disappointment after spending a lot of money. Needless to say, I decided the tuner was garbage and got HPT Pro and started doing my own tuning. Took it to the track and got the tuning for the first two gears done and needless to say there was A LOT of changes to the tune and the car dropped almost half a second after about 5 passes of logging and making changes. Started having trans issues and that put me down for quite a while. Then life intervened and the car sat and sat. I eventually swapped in an F-Body trans and a Mcelod twin disc clutch. Recently got the car back up and running and decided to get the old MP112 rebuilt, added an 8" crank pulley and added meth injection. Took it to get dynoed (at a different shop) and made 462 rwhp/480 rwtq@14psi. A little lower than I was expecting but the car ran well so I decided to leave it be. Then, a couple weeks ago, I came across a screaming deal on a brand new TVS 2300 and pulled the trigger. It's got over drive rear pulleys and a 3.2" front pulley. With my overdrive crank pulley this should put the blower a few thousand rpm below what Magnuson told me the blower would max out at. I decided to take it back to the same place (only found out after the fact the guy that did the tune last time was let go about 6 months ago) and just got the car back today. Car made 475rwhp/515rwtq@20psi. Now, I will say, the power/tq increase in the mid-range increased quite a bit but im baffled by the lack of power up top. The power has always peaked around 5400 rpm with this cam and engine combo, which seems kinda low to me. I would THINK, that with the combination of part I have I should be in the mid-500s for power so i'm wondering if maybe my cam might be the limitation right now. I haven't downloaded the tune yet but I plan on it tomorrow. The car feels great but I know there's something off. Sorry for the long post but id appreciate any help. |
The only thing that jumps out at me is the idea that your cam may be installed a tooth or more off. You seem to have looked over most other possibilities. Other than that, you would need severely clogged cats or a terrible tune combined with high IATS to kill that much power. |
What does it weigh and what's it trap in 1/4? |
Cranking compression test can tell you alot. Can you run one? |
Kinda ran into this problem with my dads car (turbo 5.3) who recently switched to meth injection.... seemed like it was really lazy and down on power.... so we took it to the track, took three sets of plugs, found the leanest cylinder and tuned off that.... his car had a “conservative tune”.... the timing mark wasn’t even on the strap and we added 5 degrees (1 degree at a time per pass) before it even was reading on the plugs.... take it to the track/dyno and check some plugs they will never lie! |
Power seems low for 20psi. A cammed 5.3 with 14-15psi should net 650hp at the crank which should be 500+ at the tire either way u dice it. Sure a supercharger eats a bit of power to make boost and at 20psi I’m sure it’s eating a lot prob 100hp which seems close to what your doing. |
Thanks for all the replies. I think the problem may be the cam timing is off a tooth, as suggested above. I have no 1/4 mile drag strip anywhere close so it might be a while before I can get some runs under my belt but I will investigate the cam and see what I come up with. |
Any idea of cranking pressure? What ICL was the cam installed at? |
What kind of dyno? My 5.3 Nova made 414 at 14 PSI on a heartbreaker dyno (dyno dynamics). It made over 700 on a dynojet at 16 or 17 PSI a few months before. My 4.8 Corvette made 300whp at 8 PSI on that same heartbreaker dyno. I swapped the cam and switched to a smaller converter with more slip, and switched to E85 but didnt add any additional timing at all, and it made 560 on a dynojet smoking the cheap tires. With 4 more degrees of timing and traction it would have made 600-620 on the dynojet. The dyno matters. I would personally blame the M112 (only because I don't like them lol). Which version do you have? Cam timing is another obvious culprit but is usually very noticeable. |
Originally Posted by JoeNova
(Post 20154491)
What kind of dyno? My 5.3 Nova made 414 at 14 PSI on a heartbreaker dyno (dyno dynamics). It made over 700 on a dynojet at 16 or 17 PSI a few months before. My 4.8 Corvette made 300whp at 8 PSI on that same heartbreaker dyno. I swapped the cam and switched to a smaller converter with more slip, and switched to E85 but didnt add any additional timing at all, and it made 560 on a dynojet smoking the cheap tires. With 4 more degrees of timing and traction it would have made 600-620 on the dynojet. The dyno matters. I would personally blame the M112 (only because I don't like them lol). Which version do you have? Cam timing is another obvious culprit but is usually very noticeable. Im not sure of the dyno, ill have to ask. The first dyno was with an MP112 and the second was with a TVS2300. I think it's the cam timing. Based on all the info ive researched the LS9 cam should be peaking around 6100-6200 rpm and im only peaking at 5400. I remembered the other day that when I installed the Innovators West pulley a couple years ago I also installed a hex-adjust timing set and I may have advanced the cam...but I cant find my notes from the install so I wont know for sure until I take the cover off and verify the timing marks. |
| All times are GMT -5. The time now is 12:59 AM. |
© 2026 MH Sub I, LLC dba Internet Brands