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Old 10-03-2007, 01:39 PM
Farmer Buck
 
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Moving Torque Down the RPM ladder

Whats the most effective way to move the major torque band down to lower rpms? I think My 302 Ford turns on at about 3200. Any way to bring that down nearer the 2000 range?

Thanks!

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Old 10-03-2007, 01:55 PM
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cam change?

Lots of ways to do that... Not sure what you're running in that 302, and how fast you like to spin it so here are some guesses. One approach would be to swap in a different cam. Something around 212 to 218 duration @ .050 should do it. If you're trying to avoid that, a dual plane intake with no larger than a 600cfm vac secondary carb should help. Also small diameter full length tuned headers will make some power down low.
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Old 10-03-2007, 02:29 PM
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Valve size, intake port size, intake type, cam size and advance, carb size, exhaust tuning, all play a role in torque output, but the biggest influence of all is likely the stroke depth, and a 302 isn`t exactly a torque monster due to it`s short 3.000 stroke. So if you set up a 302 with a dual plane intake, small intake runner heads, small valves, small cam with maximum advance, a small carb such as a 2 barrel, small tube headers with dual exhaust and a crossover pipe would give some nice torque numbers, but if these same mods were done to a 351 windsor, the 351 would produce considerably more torque due to it`s longer stroke and would do so at a lower RPM. Gear ratio and transmission gear ratio also plays a role in how well torque is carried out and multiplied.
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Old 10-03-2007, 03:02 PM
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any time you pick up cubic inches you pick up torque, as a general rule.

K
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Old 10-03-2007, 05:10 PM
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This 302 is in a 74 F100 pick up that I am restoring. --Three on the tree, 2 barrel carb, points type distributor. -- I pulled the engine to clean & paint the compartment. While it was out I done bottom end bearings, seals, timing chain/gears and a clutch set, though the engine only has 60K on it.
I didn't open the top. I put on full headers, 1 1/2 inch tubes. I plan to do a HEI distributor, and maybe a holly 2b carb with some kind of nice manifold (don't know too much about them yet) ----I won't be racing the truck. I don't want to turn up alot of rpms or speed, but I'd like to have lots of low end power and be able to take off like a rabbit, but still not kill my gas mileage. ----- I think (?) I'm limited with the heads I have since they don't have hardened seats and they have the rail style rocker arms with the valves that stick up about a quarter inch to stay between the rails. ----- So with that I maybe shouldn't think cam??? (Without changing heads) (Though My real love would be for it to have a bunch of idle lope for the sound when I'm at cruise in's.)

Does that clearify what I'm looking for a bit more? Thanks!
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Old 10-03-2007, 05:13 PM
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One way to boost torque down low is to swap a roller cam in. Its expensive, but its one way to boost low end torque. At the same duration, it won't really shift the peak down, but it will add a bunch of torque below the peak.

If you shift the torque peak lower, 9 times out of 10 you reduce overall power. Its a matematical fact, but if you keep the same torque peak but improve the torque that happens below the torque peak you can end up helping HP in the process. Broadening the torque curve is the key to making more torque without neutering HP.

A good dual plane intake will help. If your torque actually peaks at 3000, sounds like you have a pretty healthy small block. Since we don't know your cam specs and head flows we can only guess, but it sounds like a great candidate for a performer RPM air gap. Its a great dual plane intake that pretty much has the torque benefits of a low-rise dual plane with almost the same flow capacity of a single plane.

Long-tube tuned headers will help make torque in the low end. Stock manifolds just suck (or blow as the case may be). They are enough of a restriction to flow that they hurt torque and power all over. Good small tube headers are a great addition.

Adding higher ratio rockers can help. Heads have a valve lift at which they flow best. Any more or any less lift flows less. If your heads can take the lift (and would benefit from it) they can broaden the torque curve by fitting more charge in the cylinder with the same duration. So the torque peak will stay in the same place, but broaden it adding torque down low and a little HP up top.

Tell us more about the engine and what you want to do.
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Old 10-03-2007, 05:19 PM
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Oh... you replied while I did.

I think the cam in that truck is already super small. Your torque probably peaks at about 1800, but it just seems slow because there isn't much torque at 1800.

A good upper end redo might be in order. The cam, heads, and intake are very restrictive.

Keep in mind that shifting the torque peak UP isn't a bad thing. For instance, right now lets guess that your torque peaks at 250 lb-ft @ 1800 rpms. If you put a cam and heads in there that hops things up so that you have 350 lb-ft at 3000 rpms, chances are you're still making 300 lb-ft at 1800. You've increased torque all over the place.
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Old 10-03-2007, 05:20 PM
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BTW, Double Vision, What effect does a cross over pipe have ?? Would you still do that with full headers? Right behind the headers??

Thanks!
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Old 10-03-2007, 06:32 PM
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Crossover pipes, X pipes, they help torque in the low end ranges by equalizing exhaust pressure, they work best when they are in the maximum heat area of the exhaust pipes, this area can be found by marking a line with a grease pencil on both exhaust pipes from the header collector back about 4 feet, take the truck down the road, and do a few downshifts to make sure the pipes get hot, then go back and see where the grease mark has melted and this will be the hottest area. The pipe diameter needs to be .75% of the exhaust pipe size.
You can get a cam that is not very big and it still be a help in your case. I would recommend a Crane Z cam, here`s a link to it: |
http://store.summitracing.com/partde...2&autoview=sku
Notice the powerband of this cam starts at 1200 RPM, this with headers, crossover pipe, edelbrock performer intake and a 600 cfm carb of your choice, electronic ignition with spiral core spark plug wires, double roller timing chain and a K&N air filter will give it a nice low end torque boost and a fuel economy increase.
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Old 10-03-2007, 10:03 PM
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Wouldnt a roller cam mustang 5.0 shortblock work here?
Shane
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Old 10-04-2007, 07:23 AM
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Wow, You guys all impress me! I really appreciate you taking the time to respond. Thanks so much! ( I should get you guys to redesign my tractor so I could plow an acre in the "under 12 second bracket" !! )

In a book, "Ford Windsor Small Block Performance" it says that the rocker arm ratio of the 302 is 1.6:1. It goes on to say that "Crane Cam's Gold Race Extruded Aluminum Rockers have a ratio of 1.70:1" -----------From some of the things you guys say, the increase in ratio would be good. -- Can anyone tell me if I could actually change to different rockers with the present "tall" valves that I have. The valve stems actually stick up above the spring cap and retainer nearly 1/4 inch inorder for them to ride in between the rails on the present rail rockers. It just seems to me that a different rocker would ride just on that valve stem, and with the stem being higher than the "normal" valve it would interfere with a different rocker arm geometry. Am I right??? (Admitting that I'm just guessing)
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Old 10-04-2007, 07:31 AM
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Curtis 73:: You say that my torque probably peaks at about 1800.--- I'm guessing that you are saying that since it's a truck engine it has a different cam than a car engine?? --That would sure make a difference in everything, right?? So I guess I best do some inquiring around to find that out for sure?? (Not sure where I'd find that out, but I'll talk to some of the local Ford guys around)

Thanks!
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Old 10-04-2007, 08:14 AM
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Quote:
Originally Posted by Lloyd1wv
Curtis 73:: You say that my torque probably peaks at about 1800.--- I'm guessing that you are saying that since it's a truck engine it has a different cam than a car engine?? --That would sure make a difference in everything, right?? So I guess I best do some inquiring around to find that out for sure?? (Not sure where I'd find that out, but I'll talk to some of the local Ford guys around)

Thanks!
Yep... all cams from that era are very small. The early smog era engines were neutered by low compression, small cams, and poorly flowing heads to support low-rpm torque peaks. I think that 302 was factory rated at 165 hp, meaning that the cam might be in the sub- 180 degree range.

Local ford guys, ford-specific forums, and your local machine shop can help. You can have them look up a Melling part number for a factory replacement cam for a 74 302 truck engine and they should be able to tell you duration, lobe center, and lift.
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Old 10-04-2007, 08:22 AM
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Lloyd,

the stock cam shaft and intake and heads are designed for max practical TQ at street rpms....matched to the 4600rpm's approx HP peak.....(from day one, that was the factory plan for the short stroke small cube 289/302...as much low end TQ "force" as possible)

stock cam with 1.5" headers and 390cfm 2V:
1000=189ft/lbs
1500=250
2000=288
2500=310 TQ peak
3000=309

leave the motor alone (except better ign)....

use lower gears to multiple the available TQ for quicker acceleration....over the whole rpm range....by having the motor wind up much quicker.....less expensive than any other option to gain the same results

from a stop sign:
189ft/lbs x 3.00 gears = 567ft/lbs twisting the tires
189ft/lbs x 3.73 gears = 704ft/lbs twisting the tires
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Old 10-04-2007, 08:28 AM
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cam advance

My experience isn't with Ford, (GM guy) but, advancing the cam timing 4* generally drops your power band down 500+ rpm, if just dropping the power down lower is your intention.

Long tube headers is the other way. Of course, there is a whole lot more to do to the motor to raise overall power, but, that takes more gas to run the truck.

Just my .02

Arn
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