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Old 08-12-2004, 02:36 PM   #29
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Quote:
Originally Posted by mdeneen
Well, coughing up $12K or thereabouts for a replacement tow rig is definitely NOT in the cards this year. Probably in the future when my daily driver wears out and it's time for a new car, I'll consider combining the two into a new tow rig, but not now.

I've gotten some good tips and direction on how I might get a modest power boost, and I will follow up on that. It appears that a new cam, new manifold/carb and dual exhaust might be a path for a modest gain without breaking the bank.
mdeneen
Is your van a cali model? Some of the california model trucks had cats as early as 76. The rest of the 1/2 ton trucks didn't get them till 78. Some of the 3/4 and 1 tons were into the 80's before it was required. If it has a cat It will be a old restrictive ball style. A newer brick style will have better flow and might be worth the upgrade.

Watch the cam you put in there. to much cam and it will fail smog. Stick with a mild RV grind. It will give you some low end torque at a lowe RPM so that you can maintain speed in 3rd next go around.

JUST MAKE SURE YOU BUY C.A.R.B. APPROVED PARTS! Have the documentation ready when you do your smog.

I moderate a HUGE GM based website and we have folks in there all the time crying about failing their smoge tests and having to shell out big money to fix things because they put parts on that didn't have the C.A.R.B. certifications. My 75 jimmy is a 48 state model. The ONLY emmisions it had was a PCV valve and Thermac Air cleaner (preheat flap). One of the guys on the site lives in cali and had a California model 74 and he put a hopped up motor in it and new intake with no EGR. Well his truck came with EGR and EVAP and he basicly threw away several hundred bucks on that intake and some goddies that went along with it. It ended up costing him over $500 to get smogged because he didn't follow the rules and had to buy a intake that complied and find a EVAP system and figure out how to hook it back up.


All GMs from 1975 up are electronic ignition. HEI was standard from 1975-1983. in 1984-86 they went with the ESC ignition that most feel was garbage and it was prone to problems. Most people dumped the ESC when it gave them trouble and went back to HEI set up.

That Quadrajet on your van is one of the best for general use. Its the same basic carb as on all these big boy Motor homes. If it has the hot air style choke with the pipes into the intake it can easily be converted to electric for the price of the choke element and a $9 sender. I did that swap to both my 75 Jimmy that has over 300k on the body but rebuilt motor and my 1979 Blazer that had 300k on the body that I park behind my 1970 Pontiac LeMans convertible that has 200k and still has its original motor. All three of those dinosaurs start better then either of my FI trucks. Just as economical as my Fuel injected truck. Its all about the maintance. THose vehicles were taken care of.

If your happy with the truck give it a little TLC and I'm sure you will find a little extra power. Do the maintance type items like the distributor I mentioned before dropping any money on stuff like cams. You might find enough power in just little things to make you happy. If you do have a problem with the distributor and don't take care of it before a cam then you going to be disapointed till it's resolved. Getting the distributors dialed in and rebuilding the carbs really woke up both my K5's. They did quite well towing. I had Dolly towed several cars with that 75 and it never felt over whelmed motor wise. It holds it's own.
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Old 08-12-2004, 04:51 PM   #30
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mdeneen,

First; Torque moves mass and that won't change.

If a big block sounds too "consuming" have you thought about the 400 cid as a replacement? It is the sister engine to the 350 with a longer stroke (ie more torque). Combined with a 4 bbl, intake manifold, mild RV cam and headers you should have no problem pulling hills and milage will be a tad better than a big block. The fit under hood will be just the same as the 350 also. Just a thought,

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Old 08-12-2004, 08:02 PM   #31
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Originally Posted by argosy20
Torque is what the vehicle will pull, horsepower is how fast it will pull it.
Terry
Exactly. Horsepower = (torque rpm)/5252
You want to get up the hill faster? You need more horsepower.

Be sure to check the transmission. Your missing horsepower may be cooking the the tranny to a crisp.
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Old 08-12-2004, 09:44 PM   #32
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You're missing one factor in the formula...

"Gravitational resistance" while PULLING an undriven load. Horsepower gets you down the strip faster, torque gets you up the hill "consistantly".

Oscar
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Old 08-12-2004, 10:02 PM   #33
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One of the problems with the Chevy 400 engine, best I can remember, was the thin walls between cylinders and therefore a cooling problem. I wonder if using it for towing would cause more problems?
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Old 08-12-2004, 10:37 PM   #34
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I tend to agree with those who advise "no further investment" in the 1977 van. Certainly make sure it is tuned up, has compression on all eight, etc, but I wouldn't dump more than that into it. Go ahead and use it as is if necessary, but consider that there is a HUGE jump in technology and performance from late 70's to mid 80's, and another big jump in the late 80's/early 90's.

I had a GM truck with the 350 from 77 and it was a dog from all the pollution control. (BTW, I do not advocate tearing it all off - it won't gain much and just adds to the air problem.) Then I had a 1985 Blazer and it ran a lot better. Was running better at 230k when I gave it to the ex, than my 77 at 120k. Had OD, but still had a Q-jet with electronic controls. I have since had a 1994 and 1995 5.7 w/TBI and they were both great trucks with a lot more power than the 85 and OD for mpg on the fwy. Maybe not as stong as the Vortecs but extremely reliable.

Here's the deal - I sold the 95 3/4 ton HD 4x4 for $6500 w/125 k on it and it was still running great, I just wanted a new truck. That one towed the Safari effortlessly, so that is something to consider - a mid 1990's 3/4 ton truck or van with 4.10, the HD 4L80 trans, TBI. A 4x2 would be under $5K. It will do the job and last a long time, and is a relatively modern design.

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Old 08-12-2004, 10:40 PM   #35
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Nope, formula has been checked.

Quote:
Originally Posted by Silver Bullet
"Gravitational resistance" while PULLING an undriven load. Horsepower gets you down the strip faster, torque gets you up the hill "consistantly".
Oscar
Rechecked my calculation. Nothing about gravity. The formula (developed by James Watt) applies to trucks pulling trailers, steam turbines, office elevators and farm tractors.
Torque (ft-lbs) is work, without a time factor.
Horsepower is work (ft-lbs) applied over time and distance (rpms).

Torque will get you up the hill, but there is no way to calculate, estimate, guess, or theorize about how fast. Torque is ft-lbs. Not ft-lbs per minute.

You are correct that it takes more torque move a load up a hill than it does to move a load on a level surface.

If you apply the torque for a given time and distance, you get horsepower. mdeneen's problem is the time it takes to get up the hill.

To get up the hill faster, you need more horsepower.
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Old 08-12-2004, 10:41 PM   #36
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Quote:
Originally Posted by davidz71
One of the problems with the Chevy 400 engine, best I can remember, was the thin walls between cylinders and therefore a cooling problem. I wonder if using it for towing would cause more problems?
Thats true and because they were stroked the angles that the rods run at tend to accelerate wear. Basicly the motor "burns the candle at both ends". Big torq but short life.

383 is better. still has the struke problem but not the cooling problem. A 383 is a 350 with a 400 crank and a little bit over boar.
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Old 08-13-2004, 07:49 AM   #37
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Quote:
Originally Posted by markdoane
Exactly. Horsepower = (torque rpm)/5252
You want to get up the hill faster? You need more horsepower.
All these great responses lead me to realize that while I grasp physics fairly well in some areas, I never applied it to automotive things. So, I went back to review some basic force equations. Lo and behold, "horsepower" is work over time. 33,000 ft-lbs/min = 1 horsepower.

So, I exampled it this way: I have 10,000lbs to move UP a 2,000 foot increase in elevation. The "work" is then 10,000 X 2,000 or 20,000,000 ft-lbs. To do this work in ONE MINUTE requires then 20M/33,000 = 606 Horsepower. To do this work in TWO minutes is 303HP and so on. So, it appears as though getting up the hill at a higher RATE of speed requires proportionaly more horsepower. Putting aside losses in friction, drag and so on, the rate of increase in speed should be pretty well proportional the increase in HP. To go from 42MPH climb rate, to 50MPH would then require a whopping 20% increase in HP over whatever I have. Possibly doable. But of course, I really know ABSOLUTELY nothing about motors and cars.

mdeneen
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Old 08-13-2004, 08:08 AM   #38
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The 400 small block had siamesed cylinders, the bore was so great that there was no space for coolant passages between cylinders. They ran hot and didn't last very long.

John
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Old 08-13-2004, 01:14 PM   #39
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Quote:
Originally Posted by mdeneen
All these great responses lead me to realize that while I grasp physics fairly well in some areas, I never applied it to automotive things. So, I went back to review some basic force equations. Lo and behold, "horsepower" is work over time. 33,000 ft-lbs/min = 1 horsepower.
mdeneen
Taking your formula a little further:
A 6% slope is 317 ft in one mile. 10,000 lbs x 317 ft = 3,170,000 ft-lbs.
To do it at 42 mph requires 67.5 hp.
To do it at 50 mph requires 80 hp.
(This of course is the hp required above and beyond the 'flat surface/wind resistance/rolling friction horsepower)
So you need 12.5 additional hp at the rear wheels. Figuring 65% mechanical efficiency, I think you need about 20 more hp than you have now.

Afterthought: and thats 20 hp more at the RPM you are running, not at the redline where maximum hp is usually claimed.
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Old 08-13-2004, 01:28 PM   #40
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Mark---Your math makes perfect sense to me. And, 20 more HP doesn't sound too far fetched as a possible gain.

I've been trying to gain some intuition on torque, and I THINK I have it. Tell me if this makes sense: Since torque is a type of applied power, if I was UNABLE to reach redline RPM going up the hill, that would indicate I am short on torque. But since I DO reach redline at 42MPH, then my torque would seem sufficient for that load. Does that make sense?
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Old 08-13-2004, 01:36 PM   #41
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Quote:
Originally Posted by mdeneen
Mark---Your math makes perfect sense to me. And, 20 more HP doesn't sound too far fetched as a possible gain.

I've been trying to gain some intuition on torque, and I THINK I have it. Tell me if this makes sense: Since torque is a type of applied power, if I was UNABLE to reach redline RPM going up the hill, that would indicate I am short on torque. But since I DO reach redline at 42MPH, then my torque would seem sufficient for that load. Does that make sense?
mdeneen
My intuition tell me your transmission is shot. Your 4.10 rear end tells me that torque should not be a problem. If you had a 3.21 rear end it would be a totally different story.

Does your van redline in second gear at 42 mph on level surface with no trailer?
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Old 08-13-2004, 01:58 PM   #42
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more than that, guys

It is more than that. The increase in flat road horsepower alone (mostly wind drag) is 17 (from 30 to 47hp), assuming a frontal area of 72sf, and Cd of .75, so you actually need about 30 more horsepower delivered, when you include the hill, which is even higher than that due to mechanical losses. If you use 65%, which I think is a high number, you would need 45 more HP at the flywheel. I think that is a bit high, but certainly at least 40hp additional is in the ballpark.

The 77's only made about 160-175 hp so that is about 25% more - hard to do on an old truck and keep it reliable and even reasonably efficient.

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