Confusing desktop dyno numbers.
 

I was playing around with the valve lift on desktop dyno with my engine, seeing what the difference between 1.5 and 1.6 rockers would be.

My cam is 236 in 242 ex/ .520 in .540 ex/ 110LSA with the 1.5 rockers. Changing the exhaust rockers to 1.6 (increasing the valve lift to .576) I gain 6 hp at peak rpm, but when I change the intake rockers to the 1.6 (increasing valve lift to .555) the peak hp goes down 2 hp.

What's the verdict? Am I maxing out the potential of my AFR 195 heads? Or should I not trust the software?

I don't the answer. :huh: Out of curiosity, how accurate is your desktop to real number? I'm curious to know where it'd put me at.

It's pretty accurate, it's always a little optimistic because it assumes perfect AF ratio and timing. And I need to find my cam card to find the intake/ exhaust valve opening/ closing degree points to get it closer. The more info you have the better. Which is why it probably wouldn't work for you. Unless your heads are listed in the program (and stock LS1, much less ported LS1 heads are not) you need to know the flow rates of the head across the rpm band (and I have that data).

And the peak rpm points are not accurate. Probably because it doesn't take into account the weight of the reciprocating assembly and valve float. So I just go by what the numbers are where I know my engine actually peaks out, at around 6K. And it's much more accurate that way.

I can send it to you if you want...

Wow, if I go with the 1.65 instead of the 1.6, my valve lift will go from .520/ .540 to .576/ .594. :thumbs_up:

Make sure your springs are rated for the new valve lift.

The peak should be higher than 6k with that cam. BTW, I'm pulling my cam this week-end (242/248/110) and going to a 230/236/114. My off-idle torque and fuel economy were really bad....:mad:

The springs are ok for up to .6 lift. How much fuel economy do you think you'll gain with that cam?

With less than 10 degree change in duration it is not going to give much better milage. Over the years I found cams with an effect duration of 214* to give the best gas milage to power. This is in a 350 Chevy. Compression is the other milage added. The higher the better. :rolleyes:

How did you enter the cam specs (IO/IC, EO/EC) if you didn't have the cam card? Did you just guess?

Also, a friend ran my engine combo for the Chevelle and it was way off and yes he did use the correct flow rates for my Edelbrock Performer RPM heads. Desktop Dyno 2000 showed 737hp@7000 & 650tq@5000. I've run my car on a chassis dyno and it made 461rwhp and 462rwtq. Given a 20% loss that's around 550hp.

If you want to run it and see what yours comes up with, here's the info for my engine:

Standard bore Chevy 454
12.25:1 compression
Heads: Edelbrock Performer RPMs 60559
Flow Intake/Exhaust
.100 76/70
.200 146/132
.300 210/156
.400 255/181
.500 294/207
.600 314/228
Comp Cams Solid Roller 11-692-8
.622 lift I/E
246 at .050 I/E
110 Lobe Center
106 Intake Center
Specs at .050
IO: 17 EO: 57
IC: 49 EC: 9
Victor Jr Intake
Holley 850 built by The Carb Shop (flows 950 cfm)
Hooker Competition Headers 3" exhaust with Flowmasters

My static c/r is 8.3, so the big cam with it's close 110 lsa yields very low efficiency at cruise. A lot of the intake charge is lost due to the overlap. The 114* lsa combined with the lesser duration will help torque and fuel mileage considerably. I will build more boost, which will maintain the upper rpm power.