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Discussion Starter #1
Another post had me wondering... How real world realistic is this hp/tq estimator?
My specs:
Gen VI 454 +.030 (460ci) 4.28"x4.0"
Decked .010. PTD .025"
Compression: ~9.9:1
Stock crank ground .010
Lunati Cam: 241/249 @.050 .625/.625 110 LSA
Heads: L29 Chevy heads 2.19/1.72, port matched, 100cc bowls, 246 intake runners
Straub push rods, Lunati roller lifters & Comp roller rockers
Intake: Edelbrock Performer 2-0
Carb: Holley HP 950 cfm

Doug's ceramic headers into Flowmaster exhaust.

Are these rpms etc realistic with my specs? How accurate are the calculators? I just don't feel like my 3,300 lb 69 w/ 3.31s is going to turn near 11.29 in the quarter even though it's really running strong now. This is of course assuming I'll get it to hook also. Some might say 3.31s are too tall a gear, but the ideal gear for going through the traps @ 5,500 rpms is 3.35:1. Then again, that calculator also had me at 10.36 in the 1/4 @127 mph. I'm just not buying it...

RPM Hp/Tq

2000 198 / 520
2500 256 / 537
3000 313 / 547
3500 375 / 563
4000 435 / 570
4500 484 / 564
5000 520 / 546
5500 527 / 503
6000 512 / 448
6500 484 / 391
7000 434 / 325






Here is how my cam measured out when I degreed it:

 

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My experience having built many motors is that the free engine simulators are worth every penny you spend on them. They are generally off by twenty to thirty percent, being far too optimistic. I base this on actual dyno tests after I screw a motor together.

They are all pump and fill and base horsepower on air flow. Unless you enter your measured cfm, or off of a manufacturer's flow chart then the numbers they produce have no hope of being accurate.

Were they do have value is in comparing changes in a cam (probably why CompCams gives theirs away). The numbers are wrong, but the changes that are caused by a cam change are; and model the actual results closely.

Big Dave
 

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Discussion Starter #3
My experience having built many motors is that the free engine simulators are worth every penny you spend on them. They are generally off by twenty to thirty percent, being far too optimistic. I base this on actual dyno tests after I screw a motor together.

They are all pump and fill and base horsepower on air flow. Unless you enter your measured cfm, or off of a manufacturer's flow chart then the numbers they produce have no hope of being accurate.

Were they do have value is in comparing changes in a cam (probably why CompCams gives theirs away). The numbers are wrong, but the changes that are caused by a cam change are; and model the actual results closely.

Big Dave
So you think using my specs that it would be more realistic to drop my numbers by 20-30%? Seems like that would be a relatively anemic 454. That would mean 369 hp and 399 lbft. In your experience are those two numbers really what you think I have realistically?
 

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As another anecdotal data point, Desktop Dyno was within like 7 numbers for my old build (with an admittedly crappy tune and some gasket issues) and 30-40 numbers low for my new build with a proper tune compared to the results on an actual engine dyno. Boosted small block. So I don't think you can say it'll always be higher or lower or whatever. The more accurate your specs are, the more likely it probably is to be closer to real world. And like Dave said, it can also be helpful for comparing heads/cams/whatever.
 

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I had my car on a chassis dyno, I was amazed at how close the desktop dyno was to the dyno. Something like 5-10hp/tq on the numbers.

I did also have very accurate engine build data to input. I guess within 5 degrees or so of air temperature to input since I don’t remember temp on dyno day. that does make a noticeable difference in numbers.
 

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chassis dyno is really the only way to determine how much HP/TQ is "getting to" the wheels

1/4 mi time slips are what show the "car" will do which include not only HP/TQ but: gearing, tire size, 60' time, DA, etc. All those components together determine what a car will run in the 1/4 mi.

IMHO calculators assume all factors are optimum, especially 60' and DA conditions, so you have to take any of those results with a * in front of them

Take it to the track. If your car is sorted, especially in suspension and tire area, your 60' should be good. .100 gain in 60' is generally .200 gain at the big end

bottom line, run it at the track and work on 60'. Once that is as good as it gets with your tire, suspension and TC (or clutch release/holding capabilities) tuning adjustments to see if there is any HP to gain (timing, jetting)
 

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Take it to the track and go from there ;)

Way more fun than a dyno IMO :yes:
 

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Too many people get hung up on the number. Desktop dyno and a real dyno are both tools. Use them as a tool to improve the number from where it currently is.
 

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Too many people get hung up on the number. Desktop dyno and a real dyno are both tools. Use them as a tool to improve the number from where it currently is.
Absolutely correct

Dynos are tuning tools nothing more. They are great for measuring before and after changes good for fine-tuning to get maximum power
 

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Discussion Starter #10
Thanks for the comments guys. I'm not really hung up on the number. It's more of a curiosity thing. I didn't build this one to be a race car. I might run it at the track once or twice, but I built it just to run on the street.
As far as using the dyno and desktop dyno as a tool like most seem to be talking about, I need to have a baseline first. We'll see if I can get out to a track this spring. I don't think that'll tell me really what I need though. It's not set up to be a race car. I don't have slicks for it and the only thing the suspension will have going for it are traction bars and bolt on sub-frame connectors. I live out in the boonies now, so I don't even have a clue where the nearest 1/4 mile track is yet.
 
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