My stock headed 5.8 would pull any hill on the highway without losing speed at 1900-2000rpm, that was in an ext cab 4x4 with an auto trans that has a much deeper OD ratio than your manual.

 

Yeah something isn't right. Or your memory isn't very good. People make tall claims about torque of a 300. Dyno chart is the easy way to see what's really going on. 351 makes more torque than the 300 at any RPM on these graphs. I believe these are older dyno runs, around 1990.



At 1000rpm, 351W makes around 250 ft lbs. while the 300 makes closer to 230ft lbs, and it peaks at 260 ft lbs at 2000 RPM. So I don't get the 300-6 hype. My dad had a couple when I was growing up. He steered me clear of them in favor of the 351 because he said they suck to tow with. Sure they'll get ya there, but topping long hills at 45mph isn't so great.. My truck would hold OD towing a 5k lb trailer all day on flat ground (3.55 axles, E4OD, and stock tires), sometimes hold it up hill, or accelerate 65mph to 80mph if in D (uphill). 300-6 isn't going to do that.

 

Those graphs are way off but i dont expect this engine to produce low end like the 4.9 nothing i have ever driven ever has but i do want more than im getting from my 5.8

 

Okay. Post up your dyno charts.

 

I would just check the basic stuff man, start with checking base timing and go from there. Maybe the spark is weak or your fuel pressure isnt up to snuff. Maybe do a compression test and leak-down test while youre at it. Even if the engine is "rebuilt" it doesnt automatically mean it is in good shape. A friend of mine had his 87 supra inline 6 rebuilt by a local machine shop, but they put a wrong size thrust bearing on the engine. Hello crank walk. Not exactly the same thing but comparable. I also noticed you swapped fresh heads onto it, did you follow the correct tightening and torque sequence? if you dont follow this sequence it could potentially cause a loss of cylinder pressure on one or more cylinders, causing a power loss, due to uneven loads on the heads causing a warped conditon. hope this helps

 

Ive owned all three engines and I have a 302 and 351 right now my f350 4x4 zf 3.55 is exactly what sparky describes it over powers my 302 but not by a ton all 300s ive ever seen would lug dwn to like 300 rpms and still pull a hill in 3rd gear my 351 will stall by 300 rpms on flat land and my truck is in perfect tune if 351 gives up im putting a 300 in it

 

Well, your mind is made up, facts don't matter.

 

They look like factory dyno graphs to me. . .but whado I know. I know this, ive been going about this all wrong...I'm now scouring craigslist for a 300 so I can idle over mountains.

 

Great thread!

I have one each: 302, 300, 351. The gear ratios are detailed in my sig. I got a kick out of all the comments in this thread. I could talk and talk about each of my trucks, they all have different characters.

The 302 has 3:08 gears with a C6 and feels snappy everywhere, but when you get to 55mph it feels like it needs another gear to shift into. It tows a 4000 lb trailer quite well.

The 300 has 2:73 gears with a C6 and isn't as snappy but has plenty of torque to get up to speed. With the gear it can easily cruise at 75 and is the most "car like" to drive of the three trucks. This is the one when you want to get there and are not towing. I've never towed with it. But based on the difference in the way it pulls from the 302 and the 351 I understand the comments about this motor. It's a great tractor motor, but not a hot rod motor. It's down on power from the 351 but compares favorably to the 302 for pulling.

The 351 has 3:55 gears with an E4OD and is currently a little under the weather. It has a pretty paint job though.

 

My mind isnt made up im just saying from idle to 2000rpm is weak im trying to see if i have a problem and it looks like mine isnt right like i said this is my first 5.8

 

If those graphs are true why does everyone say 5.0 isnt a truck moter and cant make low end trq if thats true I se a 5.0 that says it make over 200lbs of trq at 1k rpms they all have alot of power when in there power band my 302 comes alive around 3k 351 around 2500 and 300 pulls from an idle to bout 2500 then it basically flat lines the trq is lower because the stroke is longer hence the reason they were offerd in f600s 351 nothing over f350 and 302 nothing over light duty f250s

 

The 351w makes more torque just off of idle than the 302 makes anywhere in the curve. Making it a poor truck motor in comparison to that. The 4.9 makes more torque earlier in the curve than the 302, again making the 302 a poor truck motor in comparison (though the 302 makes more horsepower). The 302 is suited for applications where you spend more time at higher RPMs and the vehicle is easier to move off of idle, like a Mustang.
The 302 is a decent motor if you never pull a trailer with your truck or put a load in the bed. But if that's what you're doing, you should have bought a car. You need to wind the motor up too far to make power, and that's just undesirable for a real pickup truck application.

 

My 351 does over power my 302 but 351 before 2k rpms is worthless from what im seeing my 351 @ 1k should over power my 302 @ 3k in that case there no comparison 3k my 302 has good power @ 1k both are worthless although the the 302 is worse than the 351 that low in rpm maby something wrong with mine but idk what good fuel pressure 6.0 tune up all msd parts all new filters runs great time @ 12° mines just a dog before 2k if someone knows something I could be missing plz let me know because mine and sparky trucks soud like twins in power aspects

 

Wow, some punctuation marks would be really helpful. I have a 5.0 in my truck now and can't wait to replace it with the 5.8 that is almost ready to install.

 

Sorry mom ill put in a period next time