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.

I entered the specs before I lost the card.

Yes, you are going to pick up some low end torque with the cam change. Also, going to 114 LSA is going to up vacumm and smooth out the idle some. Gas milage--maybe a little better.

I'm running Dual Quads and the 30 30 cam with 254 effective duration on 114 LSA , this being a solid lifer cam, it is more efficent.:drive:

My cam is a solid roller, but what does the kind of lifter have to do with economy?..(other than the lash decreasing the effective duration).

I guess hydraulic lifters would be heavier, and they might abosrb some of the working force, so they'd be less efficient. But I don't think it would make any noticeable sort of difference.

Actually it makes a difference. Because of the design of the lobe on a Hydraulic lifter cam -you lose a little of your duration. It has to have a 'set' designed into the lobe to lock the lifter from bleeding down. Solid lifters don't have that "set" in the lobe so the lobe can be more agressive.:thumbs_up:

We are talking flat tappet cams here. Rollers are a differnet story. Yea, I know I'm stuck in old Tech.

Sorry, missed the Roller part. The trouble with trying to do work and this at the same time. :crutches:

In the case of Roller Cams, there is almost no difference in lobe design. There is a difference in lobe design between the two lifter types with a flat tapped cam.:):

In tests-- way back when, we and other people found solid lifter FLAT TAPPET cams to get better gas milage than the hydraulic lifter types. Rollers have no such issue.

For example, we found a solid lifter cam would make more power than a hydraulic cam with 10 degrees more duration. All other points being equal.

Three guys, all making stupid amounts of power out of carbed V8s... talking about fuel economy. :sm_up_there:

Yea, it is pretty funny.:smack:

:gay:

I don't understand?:huh:

Yes, but 8 mpg's gets old quick. I killed 3 birds with one stone. The cam swap went fine this week-end, although I couldn't degree the cam. The piston stop wouldn't work with the heads and dished pistons...:mad: Road manners are much improved, big improvement in non-boost torque and hopefully mileage improves..even a little bit would be nice. No lope to speak of...damn. BTW, I swapped out the s/c pulley to the larger 4 inch piece, and first impressions are no loss in boost or power. :thumbs_up:

Cool, couldn't you just slide the balancer on a bit and align it to 0 degrees to find TDC?

I fixed an issue this weekend too. Got rid of the rough acceleration problem that I was sure was a timing issue. Turned out to be a carb issue.

The best way to degree the cam is by finding tdc on the piston. That removes any tolerance stack in the crank, timing gears and key-ways. Now to schedule the dyno. I hope I didn't go too small on the cam.

Don't think it will make all that much difference. Probably just move the peak power down a few hundred rpm.

Yes, that's what I figured too. Down or up a few hundred.