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Crap I think about.

80' 427

80' 427

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So I one of the things I promised myself I would do going to school at 100 years old is a cool summer daily. I have a come to the conclusion a wagon would be the best to still allow me to full fill the duties of being a dad. A 66-72 chevelle wagon is my preferred choice. The planned drivetrain is a big block and a tko or t56 manual. So here is the conundrum. Mileage isn't super important but the better it is the more I can drive it. So I think getting 550ftlbs of torque and 500hp would be reasonably easy. Still those are WOT numbers. How do you figure out the power an engine makes at 5% Throttle? I can calculate the approx power required to travel 65 mph but how do you figure out the power it makes and what rpm it makes it at? My buddy dynoed some side by sides recently for a large atv manufacturing company to compare competitors. A 90 HP unit made 7hp at 25% Throttle and actually made more low end torque than the wot numbers but obviously fell off once the load met the power. At 50% Throttle it jumped to 80 HP. Of course we know the area of throttles opening is not linear so that equates part of the limitations. Anyone have any ideas or knowledge sources? If you used say a beam type torque wrench to turn a rotating assembly and measure the tq required can that number be used to calculate parasitic losses at different rpm? Does a 496 make enough tq to pull a vehicle at enough of a lower rpm to over come those losses vs a 454 or 427 or?
 
Huh, after our afternoon padfest in my thread I was thinking about some of these same things.
Like how much power does it take to move a 3500lbs car down the road at a certain speed. What's the drag Coefficacy at speed and how does that effect the total power outlay. A truck will use more more than a car or the same weight due to drag. What is usable hp? If you don't spin to 7 grand then a big number at 7thousand rpm is useless.
i was thinking that it would be easiest to figure out how much hp you needed at say 2100 rpm. ( say that's why you were spinning at final drive ratio) Given your drag and vehicle weight and then build your engine to double or triple that number at that rpm.
 
If you use the HP calculators land speed racers use you can figure HP at say 65. You just need frontal area. Cool enough, how do you know where an engine makes that horsepower? Part Throttle power is completely different than wot and I am not sure you can even use the wot peak as a point for gearing. We know bsfc is the lowest at peak torque but efficient use of fuel does not mean at 1200rpm it doesn't make enough power. At 1200 rpms a 454 pumps 272400 at Wide open Throttle and if it pumps 272400 cubic inches of air it needs 18500 cubic inches of fuel at stoch. If say the cylinder filling was .1% (possible knowing that there is a depression under the Throttle blade). That is .08 gallon per min or 4.81 gallons per hour divide 65 mph by 4.82 gallons per hour and you get 13.51 mpg. Still I made up the cylinder filling so we need to figure out a Delta p with the ATM pressure.
 
Is there a tool to measure throttle position vs rpm for older engines?

I think I figured out once my gmt400 w/ 454 needed 75 horse to go down the road at 65.
 
If I remember correctly my 406 made the most power when the bsfc was closest to stoch. I would like to do some testing with altitude and humidtiy. On the dnyo to see how it effect the bsfc and power output.
 
...my 86 Suburban is titled as a station wagon...:whistle:
 
Based on my new cars instant MPG display, lowest engine RPM does not equal best MPG. This would seem to be the reason for cylinder deactivation. With modern drivetrains they could easily reduce RPM's with trans/rear axle ratio, but they don't seem to take that route.

It's easy to see in the car because I have six gears to select from, going one up or one down at the same speed instantly shows the gain/loss from the RPM difference.

The truck is much harder to compare due to the gear spread/lack of gears and lack of instantaneous MPG readout.

Somewhere on the home computer I have figures for the trucks that are supposedly from GM, indicating HP necessary to drive at various MPH's.
 
I understand that low rpm is not perfect but I don't think you want to use peak tq either.
 
80' 427 said:
I understand that low rpm is not perfect but I don't think you want to use peak tq either.
Click to expand...

If you find something out, post up.

I agree, it's likely something in the middle, but I'm not sure where it's derived. You'd think that there would be some sort of rough calculation (at least) that could be used to figure out most efficient RPM based on the engine itself, regardless of the vehicle platform.

The 305/350 debacle IMO proves that displacement alone isn't the answer. Without looking at dyno derived figures of both throughout the RPM range, it seems pretty well established that the 305 and 350 don't achieve appreciably different MPG numbers in the trucks. If it were solely displacement, it should lead to a 13% improvement on highway MPG.
 
I found a pretty good discussion last night on the eng-sci page. I don't get it all but it talks about bsfc charts. One thing to think about is a 305 and 350 have the same stroke so most of the frictional losses would be the same. Some where I read a hundred years ago about the fact that if you only have one choice to increase displacement you are better to bore than to stroke because a longer stroke increases frictional losses. This is part of the reason I would consider a 454 over a 496. I think a 454 would make an easy 550ftlbs. The old David Visard suggestion is if you increase the engine displacement you should lower the rpm but obviously if you go from a 283 to a 502 you can't all of a sudden let it idle down the highway. I guess all comes down to the fact that fuel holds so much BTU and it takes an amount to keep the a/f correct in a partially filled cylinder. Obviously BSFC is an important part of this. I was hoping that I could use my thermodynamics to determine cylinder filling with the delta P but that is far from fresh in my mind. If there was one thing I learned in engineering school it is that calculations and real world numbers are usually fairly different.
 
The only bad thing about the wagon is for some reason I want to build a engine that looks like a stock 396 that was offered as a towing option.
 
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