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Old 01-21-2004, 00:02   #1 (permalink)
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confused Big Block on the Dyno HELP

Has anyone ever dynoed a dual wheel F350 or alike? Ive just dynoed mine and have found that the dual wheels and tall gearing has really affected the power readout? its a brand new 460 with cobra cam, forgies, bal and blueprint, extractors, and a holley 850 double pumper, ect ect. i have read that these engines in stock form have around 400-450hp at the fly, so im assuming that with the mods it would be more like 500hp? Anyway the result was not much better than my old 460 engine that was stock and a little tired. my new engine pulls twice as hard as the old, so y does this not show on the dyno?
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Old 01-21-2004, 04:45   #2 (permalink)
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Re: Big Block on the Dyno HELP

what did the dyno show? was the stock tired motor the original ford motor- if so they were probably rated well under 300hp unless it was an early 70's motor with hi compression.
just curious- did the duallie fit on dyno without removing outboard wheels?
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Old 01-21-2004, 15:46   #3 (permalink)
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Re: Big Block on the Dyno HELP

Quote:
just curious- did the duallie fit on dyno without removing outboard wheels?
Yeah, but only just, and we had to strap it down hard. it only had about 4 inches either side. The Truck in question is a 79 F350 which in australia never came out with a 460, not sure about USA models? So as for ur question is it the origianal ford motor, i doubt it.

The dyno figures showed 197 RWHP only 12 up on the old engine, but as i said before, the new engine pulls twice as hard as the old 460? The torque Figures were 1250lbs tractive effort, which is pretty good. But roughly the same as the old 460.

What do u think?
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Old 01-21-2004, 18:00   #4 (permalink)
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Re: Big Block on the Dyno HELP

I'm pasting this from another thread, that got into talking dyno errors/differences-
<<< just looked at dynodynamics website- I think I see why they show less power:

the two roller design dont meet up with the tire vertically- estimate 30 degrees before and after axle centerline- theres a triangle here that causes effective pressure on the roller(weight x tangent of angle) to be exaggerated, and although its divided by two contact points, the car appears to 'weigh' more by the tire deformation. Also the small diameter rollers will cause much greater tire deformation than the big dynojet rollers. its no wonder the tire hp readings are so low...
we have to put our cars in the US on a very similar looking dyno bi-annually for emissions testing: you stand in a little room to watch, and I was amazed at how much distortion occurred on my pickup- its got 275-60-15 tires, bed was empty, and contact at each roller was really mushing the tires- I hauled a bridgeport home that weighed nearly a full ton, and tires were not noticeably mushed at all.
In my opinion, the two roller design is a piece of $@#% way to measure power. tire diameter alone will affect contact angle enough that no 'percentage' factor could ever be used for correction. Looking at the dynojet pics shows single large radius roller centered under axle. Much more sensible, but still I feel the axle mounted could be the only accurate way to measure.
Next time somebody goes to a chassis dyno, try running tires at min and max recommended pressures- see how much hp you loose to tire deformation at lower pressure...adding a couple extra psi might get you more than that new camshaft : )

1 newton = 0.2248089 pound-force
I think by 'tractive effort' theyre referring to 'pull'.

just some quick figures:
Brenx said about 10000N
10000 x .2248089= about 2250 pounds pulling force

I'll guess about 28" tires, 28/12=2.333 ft dia /2= 1.166 ft radius
2250 x 1.166=2623 ft/lb torque

I'll guess 3.5:1 final drive ratio
2623/3.5= about 750 ft/lb at the driveshaft

I'll guess about a 2.4:1 low gear (aod)
750/2.4= about 312 ft/lb at the crankshaft

I'll assume torque peaked at around 3000 rpm
(torque[ft-lb] x RPM) divided by 5252= HP
(312 x 3000) / 5252= about 180 hp

(note actual hp at crank probably considerably more, as we backfigured from the tires- and that was after all the losses thru the drivetrain...probably 200+ hp motor in actuality)>>>

The first part, is just something i THINK might explain why the two roller dyno was showing 33% power losses versus the 15-20% on the single roller types...if i'm thinking right, tire pressure(and hold down strap pressure) will have a big effect on output, especially on the double roller type...but then someone mentioned getting a higher reading on the dynodynamics double roller...no idea how this could happen except gross calibration error. I hope someone out there will play with tire pressures on a dyno to see if this could explain the losses. I would have thought the dual wheels might have given more accurate reading, but then you mentioned having to strap it down really tight, so who knows...I believe the single roller dynojet uses heavyweighted rollers as 'flywheels', and just measures the time to accelerate them- if so, no way of really having calibration errors, but still tire deformation has to come into play here somewhere.

The second part, i was wondering if wheel power could be backfigured to the crankshaft, i think the math is right, but dunno- hopefully someone out there has numbers they can plug in, in the above format, to see if it sounds anywhere near correct...really dont matter, but was just 'wanting to know' if it could be worked out.

as for the 460, 500 hp should be reasonable if compression is decent(9.5/10:1), but I know some of the 'smog' low compression ones were rated VERY low on hp...still made decent torque, but peaked so low, kept hp figures looking silly for an engine of that size.
one other thought on the duallie- most people know better, but i have seen a couple around with one newer tire on the rear, or perhaps rotated from the front...a definite no-no with duallies as any diameter difference means one tire or the other has to slip due to the bigger one travels farther per rev than the smaller one... most everyone knows this, but still ive seen them in the tire stores buying one tire to replace a flat...hello friction...sorry for even mentioning this, but figured just in case...

someone please, next time at any chassis dyno, try a run at min recommended tire pressure, max recommended and let us know if this tire distortion is the problem or not...

Ps- are there a lot of duallies in Australia? I work for a company that makes the aluminum wheels for alcoa/ford, we've been running near 1000 a day for the last 4 years, just wonder where the heck they all go...rarely see them around here : )
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Old 01-23-2004, 18:44   #5 (permalink)
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Re: Big Block on the Dyno HELP

Quote:
Ps- are there a lot of duallies in Australia? I work for a company that makes the aluminum wheels for alcoa/ford, we've been running near 1000 a day for the last 4 years, just wonder where the heck they all go...rarely see them around here : )
Yeah there are a few, but far out numbered by jap diesels. Where i live in Melbourne (2nd Biggest city in Australia) even more a rarity is the old school type Ftruck dually like mine. The problem is the price of fuel down here, and with the big v8 trucks they just guzzle the fuel and send everyone broke. Ive got my thing on duel fuel Petrol/LPG so its not as expensive to run. Petrol is around 95cents to $1.10 a litre and LPG is between 35cents and 58cents a litre on any givin day. the price always goes up on the weekend.

Thanks heaps for all the information u have givin me, its all a little over my head, but am learning whats what pretty quickly. a couple of guys on other threds have just simply said that 460s wont make any more power than it did, but i dont belive them. At the end of the day, my truck weighs 3.1 tonnes and i load it with up to 5 tonnes, thats a total of 8.1 tonnes!!!! What i dont understand is how a small block 302 or 351 can make shitloads more power and torque on a dyno, but there is no way those motors could pull the kind of weight my 460 does??
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Old 01-23-2004, 21:14   #6 (permalink)
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Re: Big Block on the Dyno HELP

Quote:
Originally Posted by rx1300
a couple of guys on other threds have just simply said that 460s wont make any more power than it did, but i dont belive them. At the end of the day, my truck weighs 3.1 tonnes and i load it with up to 5 tonnes, thats a total of 8.1 tonnes!!!! What i dont understand is how a small block 302 or 351 can make shitloads more power and torque on a dyno, but there is no way those motors could pull the kind of weight my 460 does??
one thing- you did get near 200rwhp on a dynodynamics, so with whats been seen on other threads, you have about 1/3 more at the crankshaft- if its a lower compression motor 300hp aint bad- especially if its giving you a lot of torque right off idle to get all that weight motivated. where a smallblock can get more than 300 hp easy, it probably wont get it down low where a big truck would want it...stoplight to stoplight the bigblock probably pulls you around never needing over 1/4 throttle, probably never making over 100 hp- but it does the job. a smallblock in similar power demand would need more gearing, more shifting, have to rev higher and wear out faster.
Something that would be interesting to see would be CFM thru the carburetor per ft/lb torque- ill bet under 3000 rpm where day to day driving is done the bigblock will be 2-3 times the torque...especially if its a high powered smallblock as the big cam and heads required for high rpm really hurt the bottom end- usually this is compensated for by a loose torque converter and steep gearing, but these wont work very well on a work truck. apples and oranges.
Bottom end torque you can feel on the street, stoplight to stoplight, everyday, without ever putting your foot to the floor, high rpm horsepower is really only useful on the racetrack or getting in trouble on the street. A 12:1 289 with 5.13 gears would be quicker, but would probably be noisy enough to attract the police, and your arm would tire from all the shifting. would get old quick. a purring bigblock will effortlessly get the job done and last a long long time. stroked smallblocks can make monster torque too, but the very short rods/deck heights create extreme rod angles that side load the pistons, etc, etc...they have to wear out faster from the increased friction.
If youre on the street where you cannot legally get ALL your horsepower to the road, what good is it? Its there in the hot smallblock, you can probably smell it from the fuel dripping out the tailpipes, and hear it from the loud unrestricted exhaust, and unsteady, lopey idle, the straining sound it makes trying to accelerate legally with a 10" torque convertor overheating the transmission, etc... but in legal driving around town, your 8 ton mild 460 probably gets from stoplight to stoplight just as fast.
Low rpm torque is long term streetable fun you can feel put you in the seat all day everyday stoplight to stoplight- max horsepower is short term serious business you measure in a handful of seconds a few times a week.
do a little porting/cam work to extend your torque curve a bit if its not strong enough, put nitrous on it if you need 15 seconds of adrenaline a week. then just drive it the other 10,065 seconds a week and enjoy it.
for the street you cannot beat the useable power of a bigblock.
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Old 01-24-2004, 04:57   #7 (permalink)
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Re: Big Block on the Dyno HELP

perfectly said, and well summed up. its almost as if you know me, the truck and the type of work i do!!! You sound just like my mate who built the engine for me, thanks again.....
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Old 01-25-2004, 20:52   #8 (permalink)
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Re: Big Block on the Dyno HELP

Wondering about something I remember reading many years back...actually think I was still in high school, around 1980 or so...anyway, Bruce Crower built up a towtruck motor with some rediculous compression ratio- I think around 16:1 mechanically, and ground a special camshaft that opened the intake so late, that the engine never got a full breath of air- effectively keeping effective cylinder pressure around 150 psi(if I remember right) about the same as any other motor. His idea was to make the combustion chamber so tiny, that at ignition pressure would rise extremely fast in the tiny area, creating piston force similar to a normal open chamber motor- due to the limited air/fuel, burn was finished before bottom of the stroke, but during the first part of the powerstroke, worked like normal. If I remember right he got something like 40% better fuel economy, and only a few percent less torque out of the motor. Does anyone out there recall if this type of setup was ever offered for a 429/460?
I never realized that you guys in Australia are paying a buck a litre for fuel- I can see where owning an oil well would be a requirement for running a big motor! Here gas runs 1.25/1.75 a gallon depending on absolutely anything unrelated happening in the news, and we get upset when its much over 1.50
I guess either we should be happy, you guys should be furious, or both...
I'll try to find some more info on Crower's setup...if its still out there, might be something to look into for a truck setup.
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