On some engines like Windsor Fords small block Chev's and Chrysler wedge motors, the Desk Top Dyno results seem fairly accurate. However, since Desk Top Dyno doesn't ask for port sizes the program assumes typical small or big block port dimensions. With engines like 427 Hi-risers, SCJ 429's, and Cleveland 4V's, the intake runner size is far from conventional. As a result the program doesn't take into account the slower than ideal intake runner velocities and will give results than are so optimistic that it's ridicules. I've found the Performance Trends Engine Analyzer to be far more accurate in cases like this. Another factor is that the Desk Top program does not take into account resonance tuning but instead simply uses an estimated flow volume figure at each RPM level to calculate it's torque numbers. The Performance Trends program takes into account, port dimensions, resonance tuning on both the intake and exhaust side as well as total flow volume to determine the engines torque potential. Because of that, changing the header primary tubing lengths on the Performance Trends Engine Analyzer program will create a dyno graph very similar to the way an actual engine reacts to the same change on an actual dyno. Doing the same thing with Desk Top Dyno will not. Having said that though, in most cases, using the Desk Top Dyno program is still a lot better than trying to sort out a combination on our own by just relying on what we might think or estimate will work best.On 2002-01-04 22:23, built351c wrote:
Desktop dyno also does not ask for head flow numbers and many other factors. At most desktop dyno is just a rough estimate. When I put the numbers in for my cleveland. I got 580hp on desktop on the dyno it made 465hp a far cry from 580hp.
I always go conservative too. I found out I was not going conservative enough on the original Desktop dyno, not the lastest version, dyno2000. Dyno2k has the same head selsction as desktop dyno. When simulating my 289 headed 302 I used low perfomance pocket porting large valve for my heads. My heads had been ported fairly well and valves enlarged to 1.94/1.6. Should be the right choice right? Wrong. Once I got dyno2k I played around some more. clicking on the intake flow button will show the flow figures the computer is using. Clicking on this for the low performance pocket porting large valve head shows a peak of [email protected]" of water being used with a 2.02/1.6 valve arrangement. Though not impossible I haven't seen a set of 289 heads flow this yet. That means the whole flow curve is off for a 289 head with that description. Now go back and look at the base low performance head and you will see more realistic flow numbers. These were also figured with a 2.02 valve. By simply inputing a smaller valve into the engine building chart, you are telling the program it is flowing a certain amount less than the 2.02 valve. When I did this I came with very realistic numbers. So you could kind of say that valve size dictates runner volume on the original desktop dyno. We lived in a Chevy world for 40 years. It seems everything in this program is based off the small chevy still. A low perfromance large valve pocket ported ford small block head will flow just about what a stock 350 chevy head will, around 190 peak [email protected]" of water. Silly that everything is still based of the small chevy isn't it, now that Ford has become such a big player in the aftermarket.On 2002-01-04 23:15, clevelandstyle wrote:
Desktop dyno almost always ends up higher than reality. I try to go very conservative on the inputs and it still seems high.