What are good methods of estimating horsepower?

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Weight of car in pounds x 197 then divide by ET cubed equals horsepower put to ground. Not sure how to type that better on here. Did that make sense?
 
What is "ET cubed?"
Ol'forest said:
Weight of car in pounds x 197 then divide by ET cubed equals horsepower put to ground. Not sure how to type that better on here. Did that make sense?
Click to expand...
 
3200 lbs. car X's 197 = 630,400
ET cubed (or X's 3)
12 second ET X's 3 = 36
630,400 / 36 = HP
Except I got 175,011.

Dang, I missed it....
 
rumblefish360 said:
3200 lbs. car X's 197 = 630,400
ET cubed (or X's 3)
12 second ET X's 3 = 36
630,400 / 36 = HP
Except I got 175,011.

Dang, I missed it....
Click to expand...

Cubed means multiplied by itself, then multiplied again
Change "12 second ET X's 3 =36" to 12 second ET x 12 x 12 = 1728
630,400/1728 = 364.8 HP
 
That's a pretty cool formula.
You got the back calculation for 1/8thM?

Oh, I seem to remember; 1/4M ET/1.57 = 1/8M et, So 11.8/1.57 = 7.5 does that seem right?

According to to that My 367 would be pushing 450hp. IDK aboout that....
Here's How I came to that; the Car went 7.92 in the 1/8th @ 2.2 60ft.
Suppose I got a traction aider to knock it down to 1.7-60ft. Would the car then go 7.92 less .5 = 7.42? Well let's say it did for a sec.,Then 7.42x1.57 = 11.65 in the qtr. Ok, well car is 3650 at the line. So your math says (3650x197)/ 11.65 cubed = 455 hp
Idk that seems like a stretch to me
But I tell you what; That formula might not apply to me, on account of I used the GearVendor to split gears on that. So I think I did that with 4.86s and the A-833 od with the GV. So the ratios were 3.09-2.41-1.67-1.30, and I trapped at 93mph.
So I used 4 ratios to get to 93 where most would use 2(automatic) or 3)stick-car)
but honestly, first gear was useless with 15/1 torque multiplication, I had to baby it out for quite a ways, hence the 2.2 60ft. I coulda probably got the same ET with 3.73s, which woulda been an 11.52 starter gear.
I cruised home at 65 =2116rpm in double O/D;how do you like that? heehee!
My conclusion is that the 4 ratios artificially enhanced my numbers so that the little 367 appeared to make 455 hp. And that is exactly what I was hoping for, when I built it the way I did.
There is no way my engine is making over 400/420. I have piloted 500hp 340s. and that is a raging beast, compared to my little sweetheart. But I might be able to reconcile the improvement in ET, to an approximate 8%increase in average hp during the run, due to the tighter gear splits.
In any case, I am very happy with her.
I bought a nearly new 1970Swinger 340 4-spd/3.55 in fall of 70. The next summer a bunch of us highschoolers boogied out to the track to see who was king of the hill.Well that totally stock little Dart couldn't do better that 14.4 at 98 in the qtr. I was a jubilant 17 year old.That car crossed the scales that day at 3310pounds.
In 2005, my 3650 pound, 68 Barracuda went 7.92 at 93 in the 1/8. I was a jubilant 51 year old.
Sorry OP, I got carried away again....
PS; 3310x197/14.4 cubed = 218 measly mal-nourished midget ponies; according to this formula.
 
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Got to remember the formula can only calculate how much power you can put to the road, I bet even the best tractioned car can't use more than 85 to 90% of it's power effectively so 218hp wouldn't be bad for a stock 340.
 
218 couldn't be bad; I went home with a trophy that day.
I beatup on everybody. No the point was, like you say, formulas are not dynos. And 14.4 was common for virgin 340s. I think even BB E's were about there.That would make them around 240 hp;by the formula.
 
I know everyone says the drag strip is the only accurate way, but unless you car is setup to use every last hp available your not gonna get an accurate reading and also where did these formulas come from in the first place to know there accuracy.
 
AJ/FormS said:
That's a pretty cool formula.
You got the back calculation for 1/8thM?

Oh, I seem to remember; 1/4M ET/1.57 = 1/8M et, So 11.8/1.57 = 7.5 does that seem right?

According to to that My 367 would be pushing 450hp. IDK aboout that....
Here's How I came to that; the Car went 7.92 in the 1/8th @ 2.2 60ft.
Suppose I got a traction aider to knock it down to 1.7-60ft. Would the car then go 7.92 less .5 = 7.42? Well let's say it did for a sec.,Then 7.42x1.57 = 11.65 in the qtr. Ok, well car is 3650 at the line. So your math says (3650x197)/ 11.65 cubed = 455 hp
Idk that seems like a stretch to me
But I tell you what; That formula might not apply to me, on account of I used the GearVendor to split gears on that. So I think I did that with 4.86s and the A-833 od with the GV. So the ratios were 3.09-2.41-1.67-1.30, and I trapped at 93mph.
So I used 4 ratios to get to 93 where most would use 2(automatic) or 3)stick-car)
but honestly, first gear was useless with 15/1 torque multiplication, I had to baby it out for quite a ways, hence the 2.2 60ft. I coulda probably got the same ET with 3.73s, which woulda been an 11.52 starter gear.
I cruised home at 65 =2116rpm in double O/D;how do you like that? heehee!
My conclusion is that the 4 ratios artificially enhanced my numbers so that the little 367 appeared to make 455 hp. And that is exactly what I was hoping for, when I built it the way I did.
There is no way my engine is making over 400/420. I have piloted 500hp 340s. and that is a raging beast, compared to my little sweetheart. But I might be able to reconcile the improvement in ET, to an approximate 8%increase in average hp during the run, due to the tighter gear splits.
In any case, I am very happy with her.
I bought a nearly new 1970Swinger 340 4-spd/3.55 in fall of 70. The next summer a bunch of us highschoolers boogied out to the track to see who was king of the hill.Well that totally stock little Dart couldn't do better that 14.4 at 98 in the qtr. I was a jubilant 17 year old.That car crossed the scales that day at 3310pounds.
In 2005, my 3650 pound, 68 Barracuda went 7.92 at 93 in the 1/8. I was a jubilant 51 year old.
Sorry OP, I got carried away again....
PS; 3310x197/14.4 cubed = 218 measly mal-nourished midget ponies; according to this formula.
Click to expand...
Yeah, IDK... The reason I posted this thread is because my Dad said that the setup we've installed in my Dart will make about 400 hp... Maybe a bit more...
Was hoping to be able to generally figure this out just by the setup and car.

Its a 383, 727, 8 3/4, 742 posi, 323 gears in rear atm, and I have 2800 stall, and 27 diameter rear tires...
With 750 edelbrock carb, Street dominator holly aluminum intake, stealth aluminum heads, (aluminum radiator and water pump housing, etc), Comp Cam 268 extreme energy (hydraulic), 9.0 - 9.3 compression (currently), stock gaskets, etc...

Is this a good street setup for my '70 Dart? I will probably raise the compression by a few methods later on, but this will be how she sits for now...
 
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273
Empirical numbers amassed by Mopar, back in the 70s. Bulletin book #40

OP.
The compression is definitely out of the ballpark for the 268 cam, but you have two things going for you; 1) the lightweight Dart , and 2)lotsa cubes
Depending on your gears and TC, you could have a pretty good performer; 2.76s and an 1800 are not gonna jump.
3.23s and 2400 now its coming alive.
3.73s and 2800 you will be hauling.

The Wallace calculator spits out 7.3/141psi on a 9.0 Scr. The lack of cylinder pressure will definitely be felt with small TCs and gears. So If you haven't picked a gear yet I humbly suggest at least the 3.55. This will be easy to sell, should you decide to go bigger later.This is the go-to gear for a streeter. With 3.55s Ima thinking a 2400 will put you up the torque curve far enough to not notice the soft bottom,too much. But if you really want to bark the tires, a lil more is better; like the 2800, or even a lil more.The 2800 I picked on account of 65mph = 2850 with 3.55s and 27s, so slippage and heat generation will be minimal.If hiway use is not important to you then a 3000 should snap pretty good already.
Now I gotta warn you Ima stickman, so hang around a bit, someone with more experience will be along shortly.
I think you will be fine, with the combo you already have, namely 2800,27s and 3.23s. At least for a while.
.
 
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If your just looking for a guesstimation
I just base it off engines torque since it don't vary too much 1 to 1.5 lbs-ft per cubic inch.
Unless you have big roller cam very high CR big port heads and intake and exhaust to go along your probably making under 1.25:1 lbs-ft:cid so 1.15 is a nice conservative number for a decent street build. Eg. 360 x 1.15 equals 414 lbs-ft and generally an engine will be at 90% of its peak torque at peak hp so 373 lbs-ft so now you got to guesstimate where you engine hp will peak rpm wise. Say you figure 5500 now you just put that in the hp equation 373 x 5500 = 2,051,500 now divide by 5252 = 391 hp.
 
AJ/FormS said:
273
Empirical numbers amassed by Mopar, back in the 70s. Bulletin book #40

OP.
The compression is definitely out of the ballpark for the 268 cam, but you have two things going for you; 1) the lightweight Dart , and 2)bigger cubes
Depending on your gears and TC, you could have a pretty good performer
Click to expand...
323 gears in rear atm, and I have 2800 stall, and 27 diameter rear tires... the XE (extreme) 268 that I have is different than the 268 regular cam isn't it? Sigh, not something I know a ton about...
COMP Cams - Performance Camshafts, Lifters, Valve Springs, Rocker Arms
SO, I definitely need to increase the compression aye?
 
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273 said:
If your just looking for a guesstimation
I just base it off engines torque since it don't vary too much 1 to 1.5 lbs-ft per cubic inch.
Unless you have big roller cam very high CR big port heads and intake and exhaust to go along your probably making under 1.25:1 lbs-ft:cid so 1.15 is a nice conservative number for a decent street build. Eg. 360 x 1.15 equals 414 lbs-ft and generally an engine will be at 90% of its peak torque at peak hp so 373 lbs-ft so now you got to guesstimate where you engine hp will peak rpm wise. Say you figure 5500 now you just put that in the hp equation 373 x 5500 = 2,051,500 now divide by 5252 = 391 hp.
Click to expand...
So, by that equation, I'd have 415 hp...
 
How did you get from 391 to 415? what did I miss?
You got headers on that thing?
What size exhaust, and free flowing?
With 9/1, I think it will be tough to crack 400, into street exhaust, with a 268.
To answer the compression question, Only if the 400 is some how magical to you.That 383 will be a beast in the 70Dart. Just wait until you drive it. You will have so much torque,it will scare you,lol
On the street the hp number is almost meaningless. Far better it is, to have 350 ftlbs at 2800, than to have 400hp at 5500. See with 3.23s 5500 is over 55mph at the top of first. But 2800 is 28mph, And if you are not familiar with 350 ftlbs at 28 mph, well you are close to finding out.You are gonna need 275s atta minimum, and you might as well buy a spare set.
 
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AJ/FormS said:
How did you get from 391 to 415? what did I miss?
You got headers on that thing?
What size exhaust, and free flowing?
With 9/1, I think it will be tough to crack 400, into street exhaust, with a 268.
To answer the compression question, Only if the 400 is some how magical to you.That 383 will be a beast in the 70Dart. Just wait until you drive it. You will have so much torque,it will scare you,lol
On the street the hp number is almost meaningless. Far better it is, to have 350 ftlbs at 2800, than to have 400hp at 5500 See with 3.23s 5500 is over 55mph at the top of first. But 2800 is 28mph, And if you are not familiar with 350 ftlbs at 28 mph, well you are close to finding out.You are gonna need 275s atta minimum, and you might as well buy a spare set.
Click to expand...

Sweet! Thanks for your time AJ!
And yes, I got Shumacher headers on it, n haven't installed the rest of the exhaust just yet...

My Rear tires are 255's atm... Hmmmm, I'll hafta be cautious :) I Did offset the springs some, and get custom wheels so I'm right in the center of the gap... 275's are only .5 inches wider though in Cooper Cobras, I have room for those... Maybe I'll pick up a pair, n pop em on after I burn those 255's up real quick...
 
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Hey that goes without saying.
But why bother stabling 400 ponies under the hood, if you can't let 'em run once in a while. They need their exercise.
I mean it takes less than 50 hp to maintain 65 mph, so why do manufacturers supply us with cars that can exceed 50 hp?
I'm not driving 3 hours to the one racetrack in the entire province, to blast off a couple of runs that tell me exactly what I already know.And then drive 3 more hours home.
99.9% of the time I am a good law abiding citizen. But every once in a while I hit it,to redline, in 1st/over, which is 65.8 mph.And I may not be traveling in a straight line. And the tires may not have stopped spinning.And I have a reserve fund if Mr policeman does not find it as exhilarating as i do.
I pick my spots, and my times, and I keep my cool. In 16 years it has cost me just $369.Can. Which might be $250 US. If it makes any difference, both tickets I received were for Imprudent driving. Not speeding. Not Dangerous driving. But Imprudent driving. Which is a catch-all ticket for spinning tires excessively,not signalling,and driving too slowly,etc.
One was for doing a 360*. About 150ft or more in diameter (oval actually), on gravel, around a couple of defunct silos, on private property.Copper said" you know you can't be doing that here,eh? But you sure do it well. You know I'm gonna have to write you up,eh.";his words.Canucker.
The other was for spinning tires up to 30mph, on a public road,in a 35 zone.Copper said he had been following me around for a while, and that I "looked like a trouble-maker", and I finally slipped up. He was hungry and wanted to go for lunch. Serves me right for a custom paint-job.......I don't know how I missed him,lol.
 
I use one of the following, usually in this order:
1. Experience
2. Total guess
3. Reading the entrails of a freshly sacrificed non-fertilized hen. But for this one you have to have the right bowl and a wood fire going on bare earth.
 
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