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Old 09-20-2007, 12:59 PM
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GM 350 torque curve

I'm building a tractor that will use a 1990 Chevy 350 from a van. It's completely stock as a tractor is all about low rpm torque. I figure the torque peak around 2000, which is what I plan to govern at. But my question is about what rpm the engine will make at least 200 ft. lbs? I'm guessing somewhere around 1500 rpm. Anybody have any thoughts?

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Old 09-20-2007, 01:15 PM
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I would estimate that the torque peak would be between 2500 and 3000rpm on that motor. Will you be using a GM Automatic transmission as well? You'd have the advantage of employing the auto's torque converter to multiply torque.
And simplify the install.
You could swap in a smaller diameter torque converter (if nesssessary) to increase the stall speed allowing you to get into the gasoline engine's best torque output rpm range.
2000 to 3500rpm.
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Old 09-20-2007, 01:24 PM
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I fabricated a shaft that transmits power from the clutch to the original tractors transmission. The original engine was a 225 ci, that had a torque peak about 900-1000 rpm.
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Old 09-20-2007, 05:18 PM
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This seems like a real interesting project Harold. Have you decided on what induction you`ll be using? Injection? 2 barrel carb? 4 barrel carb? Of course injection would give the best torque, but if your not going through the hassle of running injection then I would recommend the use of the Rochester Dualjet. This carb is just the primary half of a Quadrajet, it has real small butterflies for lots of velocity to make lots of torque down low. The factory intake shouldn`t be hard to find for it either, they came on small engines like 305`s, 267`s and they have real small intake runners for high velocity high torque at low rpm. if you wanted you could maybe look at other cams and see what cam company offers a real small RV cam that has improved torque characteristics over the stock grind. If no interest in a cam swap I would at least install a new double roller timing chain and I would install it advanced 4 degrees to lower the torque band all the more. Does the engine still have the swirl vane heads that came on it? if so they would be your best bet, the swirl vane heads coupled with the Dualjet carb and the small runner high velocity intake the engine will have stump pulling killer low end grunt.
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Old 09-20-2007, 06:13 PM
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Several years ago I installed and ran the stock 350 Vin K engine complete with fuel injection, computer, etc. Had alot of fun ripping out small trees on my property, pulling neighbors out of snowdrifts etc., but it never seemed like it ran right.So I decided to go (for now) with the stock cam, heads, intake manifold but use a basic GM HEI distibuter, MSD 6A with carb. No computer stuff.I modified the TBI intake manifold to accept a single barrel Holley model 1909 carb. They used these on 63-64 Ramblers with about 200 CI engines. Using a 350 would maximize intake velocity. I figure @2000 rpm I would running off the main jet so using my wideband O2 sensor, would be easy to tune. I'm not at all worried about peak horsepower as when running the TBI setup I would need no more than about 20% throttle @2000 rpm in order to just churn both tires when chained to a big tree. Yes, the idea to use a RV cam and advance a few degrees is an excellent one.
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Old 09-20-2007, 07:05 PM
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The TBI intake sure isn`t the hot tip, as it suffers from poor fuel distribution and "fuel steer" This is why I recommended the use of the Dualjet carb and intake. It`s hard to say if it would be in the main jet not underload, but when underload you could bet it would be. Either way it`ll work but just wanted to lay in a 2 cents worth. Good luck on your project Harold.
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Old 09-21-2007, 08:53 AM
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Thanks for the tip on using the non-tbi intake. So any older SBC intake bolt right on to my 350 block?
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Old 09-21-2007, 09:25 AM
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Any of the older intakes will bolt on, but the 4 center bolts have to be slotted, this isn`t a big deal and it`s been done many times. You can do this at home with a carbide cutter and make your own angle washers or have a machine shop do it. I`d think any cast iron 2 barrel intake would do the job, many of them have small runners for high velocity as well. While the TBI intakes suffer with the problems I mentioned, I don`t think it`ll cause any real world problems being you don`t plan on revving it past 2000 RPM, plus it eliminates the hassle of having to slot the bolts so I`d say just stick with what you have. If you run into issues later and highly doubt you will, then you can switch to a older intake.
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Old 09-21-2007, 09:37 AM
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Thanks again, think I will take your advice and use what I have. While on the subject, some small blocks have no water retrictors on the rear water passages, some have an approximate 1/2 hole restrictor, and the last 5 L I tore down had a complete block. When I tore down my '90 I didn't pay attention. The fel-pro gasket I bought doesn't address the issue. Any recomendations?

Last edited by Harold56; 09-21-2007 at 09:38 AM. Reason: spelling
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Old 09-21-2007, 09:53 AM
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Quote:
Originally Posted by Harold56
I'm building a tractor that will use a 1990 Chevy 350 from a van. It's completely stock as a tractor is all about low rpm torque. I figure the torque peak around 2000, which is what I plan to govern at. But my question is about what rpm the engine will make at least 200 ft. lbs? I'm guessing somewhere around 1500 rpm. Anybody have any thoughts?
Wrong answer, torque is just a force measurement like you leaning against a wall. Without movement it doesn't do anything. Horsepower does the work no matter the engine speed, it's a function of torque times RPM. Limiting RPMs at 2000 will make an extraordinarily weak engine because while the torque may be a high static value when calculated into work (horsepower) the RPMs aren't there to do much effort. The RPMs need to be allowed to climb to the engine's horsepower peak where it can do (and does) the most effort ("work" in a physics sense). Someone suggested a high stall converter, this is an excellent direction to go, giving the engine the freedom to rev into it's power band in any selected gear before loading it down, this where it can do the maximum amount of work.

Putting a single barrel carb will cripple the output; first it's capacity is too small to allow the engine to rev into its best power band. Secondly it will not allow the 180 degree intake to operate properly which will further reduce specific torque and horsepower. If you do nothing else, simply putting an adapter plate on the TBI intake with a 2100 Holley 2 barrel will be the better choice, by far.

The engine you have is rated at about 210 horsepower at a pretty lazy 4600 RPM, what with the sleepy cam, swirl port heads, and 400 CFM TBI. To get this power you need a carb of the same flow size.

Bogie
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Old 09-22-2007, 04:54 AM
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This project is sort of unique as I don't need or want power. The original Allis Chalmers engine was rated @45 Hp @1400 rpm. With that I could pull a 3 bottom plow, yank my truck from the mud and drag really heavy things around my property. Of course, the laws of physics with the variable "time" still apply so while work was being done, it was being done slowly. When I was running the stock TBI set-up I quickly learned that doing things fast with anywhere near the potential power of the 350 got dangerous on a 5000 Lb. tractor. Most jobs I simply let the engine idle. I selected the SBC for the cool "wow" factor. So, my goal is to make about 75-100 Hp at a governed 1800 RPM. With the right components/set-up I might even be able to reach that power level at a lower rpm.
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Old 09-23-2007, 09:24 PM
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I figured a 350cid version of my Ford motor might make a good truck motor. My '88 T-bird has the low-output 302 with factory ratings of 275lb/ft @ 2000rpm, and 155hp at 3250rpm. It makes a good bit more power now that the cat had to be gutted, and maybe some more torque, too, if my trusty butt-dyno's any way to tell. With 3.45 gears & posi, it will snap your neck just like a real motor right off idle, but falls on its face shortly thereafter. I strongly suspect it would yank a stump out of the ground, but would not accelerate fast enough to avoid getting splattered by said stump. Sound like they were thinking tractor motor the day they designed that one, and I do occasionally use it to pull stuff around the yard.

It has a tiny roller cam with .050" duration of ~180*, and heads famous for being high-swirl, but low-flowing, kinda like your SBC swirl-ports. Your stock flat-tappet cam from the '90 350 has a duration of 179*. I don't know if they make a SBC roller with similar figures, but that might be one way to go if it's available. Might get a little more torque out of it with 1.6 rockers, if not.

I had thought about my old small-port 283 heads and the old 4G that's attached to them, but I think the swirl-ports & dual-jet combo mentioned above might work even better. Keep us posted.
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Old 09-24-2007, 10:25 AM
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Harold,
(4th and last try to post this....dang server)

for a worst case scenario...to get a "lets see" example....I plugged a anemic 70's stock 350 into my antique* DD

8/1CR
350cfm carb
350cfm exhaust and stock manifolds
196/204/112/4*advanced cam

RPM's TQ/HP
600 134/15
800 189/28
1000 229/43
1200 258/59
1400 276/73
1600 289/88......A/F mix reached 100%
1800 299/102
2000 304/116
2200 305/128.....TQ peak
2400 305/139.....200 actual cfm thru the carb

my conclusion: you will have to really screw up the 90' 350 to "not have" way more TQ than you need!

*I can't enter jet sizes or spark timing for a specific rpm to find the best "tuned" value for a fixed rpm motor

ps: note at 1400 rpms you have almost twice the hp and since TQ max generally equals cubes.....you have about 50 more ft/lbs at 1400 than the 215 cube motor.....

I'd seriously consider adding a roll cage for a possible "walk over" flip

Last edited by red65mustang; 09-24-2007 at 10:31 AM.
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Old 09-24-2007, 12:43 PM
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Great info! Pretty much what the seat of my pants were telling me after driving both set-ups. Yes, the stock 350 has way more power than needed, hense the governed rpm's around 1800. One of my earlier posts mentioned the danger factor. Once while was dragging a tree turning about 4,000 in 1st gear when the tree got caught in an imovable object, (a much bigger tree). Before I could throttle back or push in the clutch the lug tires dug in, violently tossing the tractor around while the front wheels were pulling up. Lesson learned.

Still not sure on what I should do with the rear water jacket opening in the intake manifold. Should I block, leave open, or something in-between? should
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Old 09-24-2007, 02:34 PM
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You can block these without issue. If you swap intakes to a carbed intake, they`ll be blocked anyways. One thing I meant to mention to keep in mind is I`m guessing you won`t be using the serpentine belt system that came on the engine original, so you`ll need to get a standard rotation long snout water pump. The serpentine system usually ran the water pump in reverse rotation. The V belts are in standard rotation and when you try to run a reverse rotation pump in the standard rotation it runs hot. you could use any water pump from 70 on as long as it`s not a corvette pump, which was a short snout pump so this is something you could tell the parts guy unless you have a pump laying around already. If not I would just ask for a pump from a 80 model chevy caprice or pickup with a 350.
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