XJ-L31

Does anyone have a dyno curve for an L31 with an Lt4 hot cam (or other performance cam) with the stock intake (csfi or mpfi) setup.
I'm trying to see the horsepower and rpm range for the stock intake.
I found some dyno curves posted by one member, but they seem to be falsified. Found a member that made 300rwhp with a 350 and 330 with a 383, but no dyno curves . Thanks

gravedigger472

This is the best I have for you. Stock L31 vs L31 with 1995 LT1 stock cam swapped in. Both before and after on the same dyno. This is a chassis dyno, so numbers at the rear wheels. Also, this was on old personal truck.

Edit: The before numbers are 225hp 291tq, after 233hp, 299tq. Also, both were on bone stock computer, stock intake, stock air filter, stock manifolds, just a 2.25" mid pipes and Magnaflow cat back.

gravedigger472

Oh and just for giggles, here is the video of said dyno runs

XJ-L31

Thanks gravedigger,

This helps. I found a dyno plot for a stock 95 LT1.
Do to so many variations between the dyno tests, I can't directly compare the LT1 horsepower to the L31. But plotting your data against the LT1, shows the L31 intake limit where the horsepower drops off at 5200 rpm.
It also appears that the L31 intake has more low end torque below 3500 rpm. Although not decisive, it does show something.

Any more dyno plots out there?

Vortec350ss

iTrader: (20)

While the intake is limping up top for sure I think it's the vortec heads that give it the torque advantage

XJ-L31

Yea it could be the heads. It's hard to make assumptions without more data.

Fast355

Stock block 5.7 Vortec with the 395' marine cam, 1.6s, Tri-Y headers, stock 1-ton cats, muffler, and exhaust, through a 4L80E and 3.73 geared 10.5" 14-bolt. 2nd gear pull with the converter locked. The blue line was an attempt at a 3rd gear pull but the converter was unlocked and it the 98 mph speedlimiter pretty quickly.

XJ-L31

Those results are good considering such a mild cam.

Fast355

My thoughts as well. It did have 1.6:1 roller rockers, but that is still only around 199/209 @ .050 on the duration and the cam sits 3* advanced on a 109* LSA. Its all about low-end power and torque.

I found this little test using an otherwise stock vortec and the 395' cam with factory 1.5:1 rockers. They also ran a better intake manifold and 750cfm carb on a dyno with long tubes, no cats, and limited accessories. Looks like its making about the power it should be. I noticed that they shimmed the stock valve springs to get more spring pressure. He was really hoping for a little more power. I really think the factory springs are giving up in this engine. Maybe someday in the future it will get an upgrade to some Comp Beehives. May also change to the Elgin E1136 cam. It is 210/215 @ .050 on a 110* LSA with a little more lift. At the same time he wants a Marine intake on it. I guess if that happens there will be a new dyno.

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