mpmarino

iTrader: (1)

Hypothetical (LOL)

Let's just say I was considering putting a LS9 Cam in my 5.3; not that I would because its a bad idea.

OK, according to the recent CarCraft article, here are the results of the LS9 cam in a stock 5.3 on an engine dyno. Of course that's not what you're gonna get in a car, but at least it's an idea of what's going on.

ls9 cam 211/230 .558/.562 122.5lsa
/6200/ 420hp
/5100/ 393tq
/2500/ -41tq
/3500/ -20tq
/4500/ -2tq
/5500/ +51tq/53hp
/6500/ +90tq/112hp

Gains up top are huge, losses down bottom are huge. What's the problem? Too much lift? LSA too wide? Probably yes and yes but I'm just a newb.

I am asking that you make a guess as to what would happen if I installed that cam (hypothetically of course) while at the same time installing new pistons which bumped the static compression ratio up from 9.5:1 to 10.5:1? Do you think the increased cylinder pressure would recover the low end grunt? Hypothetically

TIA

99Bluz28

iTrader: (35)

That cam's designed for a larger forced induction motor, raising the cr 1 point will help some but it's not going cancel out the TQ loss below 4K. Faster cam lobe ramp rates and dropping the lsa down to 117 or less along with 2-3 * of advance on the cam would take care of most of it.

This is from the article:
Note that peak torque production never varied by more than 15 lb-ft with any of the factory cams; the duration simply shifted the torque curve higher or lower in the rev range. Whereas the LM7 produced peak torque at just 4,300 rpm, the LS7 and LS9 cams produced peak torque 700–800 rpm higher.

mpmarino

iTrader: (1)

thanks, I'm just trying to get a small grip on cause/effect without climbing the steep learning curve. Too many of those right now

Anyone else have an opinion? (Not that I don't respect 99blu's)

AutoCruzer

Just between you and I, the LS9 cam is intended for a supercharged application that really needs to 'bleed off' some power down low because of the excessive (and thus unusable) torque that is generated at low RPM with a Roots/Screw type supercharger.

Putting the LS9 cam in a 5.3 robbed it of 0.9 liters of displacement and also created an engine that is basically only good at high engine speeds versus the 6.2 it was intended for which could afford to give up some low end torque (especially considering that said 6.2 would be supercharged).


Also, take a look at the specs - 211 intake 230 exhaust. The LS9 has good heads so a long intake duration would be unnecessary for the power needs of most drivers and it would increase emissions. The relatively long exhaust duration keeps the power from falling off as fast as it might above 6000 rpm.

The 122.5 LSA should give a very smooth idle, good tip-in power and an emphasis on top-end power as opposed to a narrower LSA. It should also keep the torque curve relatively flat as opposed to a narrower LSA which would give a more mountain shaped torque curve and likely a more pronounced mid-range punch.

The lift which exceeds .550 inches on both the intake and exhause lobes lets the engine breathe, but again that much lift begans to lean toward high-rpm power as opposed to low and mid rpm torque.