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Has anybody compared the two to see how accurate they are? Also how accurate is the hp to weight to quarter mile times on the desk top?
 

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I have have not had my car dyno'ed yet, but I feel that the desk-top will be different than the actual dyno. Here's why:
Desk-top is not very specific. There is no place to put what kind of rockers you are using, what kind of intake, and a lot of other factors that affect HP. The deck-top for my motor said around 370, but I believe it will be more because I have power-adding parts that I could not include in the DT.
LMK if you do it (desk-top and real) And what you find out.
TTYL
Matt
 

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Well, I will think differantly. MonsterMach brought this to my attention, and it makes wonderful sense. Though he is not even sure as I am not sure either... Desk Top Dyno assumes everything is working 100 % perfect, and in real life, how often is this happening?

Jeff Given
 

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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.
 

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Desktop dyno almost always ends up higher than reality. I try to go very conservative on the inputs and it still seems high.
 

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I am not sure what version of desktop dyno you guys are useing but mine I put in head flow numbers at various lifts, lifter types, exact profile on the cam

like anything the more info you give it the closer it will be
 

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Discussion Starter #9
Well I was just wondering what kind of times that I am looking at getting at the strip this next year. I have a 351 cleveland dynoed at 524 hp @ 6700rpm's going into a '71 Mach 1 with a c6 3500 stall and 4:11 rear. Am I dreaming to get into the 12's?
 

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That should run mid to low 12's if that number was flywheel dyno horses. You may be a little understalled and undergeared though.


<font size=-1>[ This Message was edited by: Hottarod on 1/6/02 3:57am ]</font>
 

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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.
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.
 

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to add one thing though, my friend's version of desktop dyno does have a place where you can input head flow #'s if you know them from .100 to .800" lift in cfm #'s. We used it to put in the #'s from Canfield's website to build my virtual 351W for "project sleeper". I will be building my engine to the #'s inputted into the program and hopefully I will get close to the #'s it estimates that my engine will put out. Of course there will always be some variance but I built in a cushion so that my goals with the granada will be reached even if I'm short a small amount on the #'s.

He's quite good at putting in the #'s to get the #'s that should appear with the program. He did up my LT1 engine for my Formula and came within a couple hp and torque to what I dynoed at the shop. Got the #'s at the wheels and worked back to what it made at the crank and it's very close.

Like the person said above, it's a tool and will work properly only if the person using it knows how to use it, and it's better then just spending cash slapping things together and praying to the hp/torque gods that all your time, money and effort will pay off in the end with an engine that meets or exceeds your goals.
 

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I think it's off about 20% but I'm up a 6000' also, but the dyno I think programes evrything at 0000':roll:
 

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If my local buddies version, and Chilly460's version of my new engine combo is anywhere close to being legit/real/accurate, My ass/back are gonna be in a world of hurt next season!
Last years combo came in around 10 hp high and 40 ft lbs TQ higher than actual dyno. My .002
 

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to add another thing to this post, keep in mind that desktop dyno gives you the #'s for hp/torque as gross #'s. Those #'s should be converted to net #'s before you plug in the #'s for dragstrip dyno if you have that program to get an idea what your car with the proposed engine combo will run at the strip.

My friend has that program too and that is fairly accurate also. Dragstrip dyno came within a 10th of what I run at the strip with my Formula. Again for good output you need good input.
 

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I had a 351c 12:1 pump gas motor running 11.44 @119 4.10 28'' Slicks with a c-4 that had an Art Carr 9'' 3,000 Stall. I foot brake the car at the line and it pulled the wheels. The cam was a Crower solid roller .592/.610 290/300 The motor was a 30 over with a Torker intake and a Barry Grant Stage 3 750...(that carb just out of the box lowered et by .6 sec). So you should have no problem being in the 11's with proper tuning. I shifted the motor @ 7200 Rpm and it ran like a raped ape..now the 460 I have does more at a lower rpm....as the say no replacement for displacement!
[email protected]
 

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I had a 351c 12:1 pump gas motor running 11.44 @119 4.10 28'' Slicks with a c-4 that had an Art Carr 9'' 3,000 Stall. I foot brake the car at the line and it pulled the wheels. The cam was a Crower solid roller .592/.610 290/300 The motor was a 30 over with a Torker intake and a Barry Grant Stage 3 750...(that carb just out of the box lowered et by .6 sec). So you should have no problem being in the 11's with proper tuning. I shifted the motor @ 7200 Rpm and it ran like a raped ape..now the 460 I have does more at a lower rpm....as the say no replacement for displacement!
[email protected]
 

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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.
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.
 
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