So my 1990 F150 5.0 with C6 clocking either 68,000 or 168,000 just seems to be lacking in the power department. I would place money on a Chevy 305 blowing me in the weeds, a 305, just a measly boat anchor for crying out loud . It's got 3.08s in the rear, I'm sure has an effect, but getting it to even squak the tires? Pointless. Matted to the floor it barely gets rolling from a stop . On dry dirt, I might be able to get two tire rotations. Grass isn't a problem as would expected. With a brake stand, There's no way they are breaking free, dirt or pavement . Now it sounds like I just wanna burn my rubbers off which is not the case, I just expected a neat reaction, but only found disappointment for a V8, and of course friends laughing their ***'s off. So my question is, what is there that I can check to find my ailment?

 

How long have you had the truck.
Have you given it a complete tuneup with fuel, oil, air filters, plugs wires and cap, checked for codes, and replaced all the oils.

As far as gears go, 308s are for a 3000lb car with 24" tires, not a truck with 29-30" tires. You're losing a lot of acceleration and low end torque to the wheels with that.
If you're looking for cheap upgrade, just swap a lower gear rear axle under it. It's easy to find 350 gears in these trucks, and complete axles are cheap. If you have a 4x4 the front is an easy swap also.

 

Ive had it for a year now. I have done some tune up including all fluids and filter changes, except for the fuel filter now that I think about it, Spark plugs and the coil. I have not done the wires just because they look practically new and the truck runs fine. Now the 3.08s are because of the trans only being a 3 speed. If I were to drop 3.50ish gears in it, how badly would it scream on the highway at 65?

 

Yes, the gears are the crutch of the problem. Likely really nice for highway cruising and gas mileage but for power.....not. With the lack of OD, I guess that is why they had such a fast gear ratio.

Did not know they offered a C6 with a 302 back then? Thought only the 460?

Find 3.55's or even 3.73's, but be prepared to loose some fuel mileage. Not that they are that great to begin with.

 

I knew 3.08's for a truck seemed a little odd, but wouldn't expect it to make this much of a difference, and the C6, yes its a small block bolt pattern C6.

 

My '89 F150/302 has AOD, so I guess they were just transistioning over back then and you could order either. The OD in the AOD is pretty steep, .66%. I can run about 70 in OD at 2000 rpm with 3.55 gears with 235/75/15 tires.

Working the numbers, it changes my rear axle to basically 2.34:1. You are 1.31% faster(with your 3.08), so at 70 mph you are at 2620 rpm now. Going from 3.08 to 3.55 is 1.15% so now you are going to be at 3000 rpm at 70 mph.

Around town, I don't use OD, so your mileage won't suffer much. I get a pretty consistant 16 mpg daily driving. Actually highway isn't much better, like 18-19 mpg. Pushing a brick at 70 mph just don't help.

 

Thanks for the figures. Now lets say I ran 70 at 3000 rpm, should I worry about prematurely killing my engine over time?

 

Not really, just your wallet....

 

Well that's normal. Everything does these days. I just worried about running those higher rpm's all the time would hurt my poor old girl. She needs to last me a few years.

 

3K rpm is not bad at all. Yup, will eat you out of house and home in fuel costs. Keep the oil changed and drive it.

 

Gears aren't the only problem with this truck, I have had 2 early 5.0s with 3.55 gears that were still complete dogs. The solution to the problem is simple and not terribly expensive but not easy.. you need to replace the stock cam and exhaust system.

 

I thought they went to the AOD trans in 1990 and the last year for the C-6 was 1989. And if he want's to spin his tires, wouldn't he be better off with a 3.73 or a 4.10 ratio?

 

3.08 are too high for these trucks. And if the OP has 31 inch tall tires---the combination will only be worse.

I have 4.10s and these gears really wake up these 5.0s. Especially when the 4.10s are used in combination with the original 235/75 tires.

When I was shopping for one of these trucks and made test drives-I was amazed at the difference between the common 3.55s and the 4.10s. Made every 5.0 feel like a very healthy 5.8 and made the M5R2's first gear feel like a granny first gear.

Also the Supercab with it's added 300 pounds also made a large difference in perceived acceleration.

 

Check the timing. My truck was really sluggish when I first got it. Come to find out the timing was way off. After setting it correctly it's like a whole different truck.

 

Timing is a cheap upgrade. Stock is like 8*? Put it up to 10-12* depending on the grade of gasoline you want to run. It will perk it up.

I put shorties and true 2 1/4" duals on my '89 and it really didn't effect anything(mileage or power). No cats. Unhooked the air pump also.