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Discussion Starter · #1 ·
I made it to the track Sunday. 1/8 mile. Truck did good. About the same as the first time I took it out with the fresh 406.
8.05 et
85.1 mph
1.807 60ft
Question is... Why so much difference in the Wallace calculator, and the Robinette?
I like Robinette's numbers better. LOL!
The truck is down to 3800 now. 3980 with me in it.
Also, according to these calculator's I should be way faster on the big end. Is it the Box Kite effect that's killing me that bad??? Truck is a 78 C10.
It trapped out at 103 in the quarter. The guy next to me ran a 12.5 in his mile per hour was 105 in the quarter. These calculators are showing we both should have been a lot faster! He was in a car by the way. And not a box kite!
525009
525010
 

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True Hotrodder
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You may like the other one but it appears that the Wallace calculator is rather accurate. The other calculator may not be as accurate due to the math equations and assumptions. We see this in ET prediction software. Minor variances in different parameters can make quite a difference when you're looking to run dead-on. Not unusual to try different programs that "fit" the vehicle as far as predictions.
 

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Robinette calculaor seems wildly optimistic on 1/4 mile MPH....the stuff myself and friends have that runs 120 MPH in 1/4 mile is 10.80-11.10 range on ET.

Last time I looked NHRA conversion factor for 1/8 mile to 1/4 mile E.T. was 1/8th mile ET x 1.57 = 1/4 mile ET....which puts you at a 12.65....that's not going to be aywhere close to 120 mph.
Most street strip and drag cars pick up about 21-24 mph 1/8 to 1/4....puts a 12.65 ET somewhere near 106-110 mph...and that mph for 12.65 jives with cars I've run in the past.
 

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Discussion Starter · #4 ·
Robinette calculaor seems wildly optimistic on 1/4 mile MPH....the stuff myself and friends have that runs 120 MPH in 1/4 mile is 10.80-11.10 range on ET.

Last time I looked NHRA conversion factor for 1/8 mile to 1/4 mile E.T. was 1/8th mile ET x 1.57 = 1/4 mile ET....which puts you at a 12.65....that's not going to be aywhere close to 120 mph.
Most street strip and drag cars pick up about 21-24 mph 1/8 to 1/4....puts a 12.65 ET somewhere near 106-110 mph...and that mph for 12.65 jives with cars I've run in the past.
I just want to know how much power Im putting down!
Not gonna go on an engine Dyno, and the chassis Dyno has too many variables.
I would be happy with 500 ft. Pounds.
 

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Not an expert on this, so .... I’ve found the calculators are all aimed at NA vehicles. They seem to make the assumption that you can get the car off the line. I agree with that.
That seems in line with what Eric mentioned above 1/8 vs 1/4 mile trap speeds as well.
There is a piece of disconnect here - you motor’s HP/TQ has nothing to do with how you get it off the line IMHO. Excellent chance that it could be accurate or ‘pretty close’, but no guarantee. If you don’t get off the line we’ll, then these calculators are worthless.

Why don’t you want to put it on a chassis dyno?
 

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Discussion Starter · #6 ·
Not an expert on this, so .... I’ve found the calculators are all aimed at NA vehicles. They seem to make the assumption that you can get the car off the line. I agree with that.
That seems in line with what Eric mentioned above 1/8 vs 1/4 mile trap speeds as well.
There is a piece of disconnect here - you motor’s HP/TQ has nothing to do with how you get it off the line IMHO. Excellent chance that it could be accurate or ‘pretty close’, but no guarantee. If you don’t get off the line we’ll, then these calculators are worthless.

Why don’t you want to put it on a chassis dyno?
From what I understand they are good for tuning, and squeezing out power. But are not accurate for power numbers due to too many variables. I guess it wouldn't hurt to try.
There's one right around the corner from me, but the guy has a project sitting on it, he won't be moving it anytime soon.
But that's a good question. I think I will go strap it down, just to get a baseline. There is another shop, not far away. Yes that is a Good Idea! Thanks.
 

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I'm not sure how it applies to 1/8 mile, I would think it would still track out the same....but 1/4 mile MPH versus vehicle weight is a pretty accurate way to figure out HP level. This calculation comes really close, is not impacted at all by ET or how the car launches, nor by good or bad gearing in the rear axle.

Quick check there says figuring for a 10% driveline loss your 1/8 MPH indicates 381 flywheel HP and 343 RWHP....but if driveline loss is worse, say the 20% tossed around in muscle car circles rather than newer crowd with their low drag brakes amd lighter driveline parts, then HP goes to 425 flywheel HP for that same 343 RWHP.
 

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Discussion Starter · #8 ·
I guess I need to get on that Dyno, and see what I'm missing. Was kinda expecting a little more than 425 from my combo. Do you think it's the 200 cc heads holding it back? Or maybe the 3 inch 3 chamber Flowmasters? LOL!
 

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I'd be suspect of a dyno owner/operator's results that puts projects on the dyno for any period of more than 24 hours.

But you will still see differences in modifications/tuning, i.e. moving the timing a couple of degrees either way to see what the net result is. Hopefully he has an AFR gauge that he can throw in the tailpipe.
 

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Also I don't believe the calculators factor in converter slip. So if you don't have a converter that works well you could be slipping 10-20% and losing a ton of mph. Might calculate that as well if you know your RPM and MPH at the 1/8 and 1/4. Dyno numbers are pretty useless IMO. The operator can skew the correction factors and inflate or deflate numbers. They are great tuning tools and I'm all for using them in that aspect. But I've put several car lengths on "1000' hp dyno cars... and I know i'm no where near 4 digit power.

Weight VS trap is a pretty good estimate IMO and Wallace's numbers are darn close to what my setups run.
 

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Discussion Starter · #11 ·
Also I don't believe the calculators factor in converter slip. So if you don't have a converter that works well you could be slipping 10-20% and losing a ton of mph. Might calculate that as well if you know your RPM and MPH at the 1/8 and 1/4. Dyno numbers are pretty useless IMO. The operator can skew the correction factors and inflate or deflate numbers. They are great tuning tools and I'm all for using them in that aspect. But I've put several car lengths on "1000' hp dyno cars... and I know i'm no where near 4 digit power.

Weight VS trap is a pretty good estimate IMO and Wallace's numbers are darn close to what my setups run.
I,m really just trying to figure out my power.
I have a high dollar FTI Converter, so I should be good there. Everything I read tells me I should have a solid 500 horse motor, but Wallace comes up WAAAYYYY Short. I'm also wondering if Aerodynamics are killing my mph on the big end. I'm in a Squarebody Chevy...
 
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