how hard do your guys trucks launch?
my truck:
390 stock CR
stock stall conv
tranny less than 5,000 miles
comp 252h cam (idle to 4500)
4 bl carb and intake
full time 4x4 t case
the gears are deaper than 4:11 it runs about 2800rpm at around 55

I know its not a drag car but the truck just seems slow off the line.
it seems about impossible to break the tires loose even in low range.


i'm geting sick of chevy's beating off the line
highrider76

 

how big are your tires

 

31 1050 kumho venture mt

 

With that short of gearing it should take off quick...

I have very tall gearing in my 79 (2.75), so I have to stick with the stock tire size, and it takes off reasonably well... it also keeps the revs down on the freeway and doesn't do too bad around town for mileage.

 

Full time case converted to part time? If not, seems your trying to break loose 4 tires instead of 2. Taller than 4.10 gears, and 31 inch tires. . .what rpm's are you turning trying to get of the line? Your engine might not make much power in that rpm band. Maybe try launching in 2nd gear to see if it launches harder.

 

What size of Carb?
Are you downshifting to first gear on the take off?
How's the timing?
Does the engine have any exhaust leaks?
Does it have headers?

I had a similar problem and it was the power valve on the carburator.
Also check the accelerator pump for flow. Take off the air cleaner and with the engine off, pump the accelerator and see if you are getting a squirt of gas?

This motor should have more pep than that. I'm just wondering if your transmission is starting off on first gear?

How's the truck if you take off with a rolling start? Say rolling at 10-15mph, doe it move then?

Answer these questions and we will try to figure this out?

 

my 78 w/302 & 4speed manual launces pretty hard if i fut it in granny 1st and dump the clutch.found out i had bad u joint in my drive shaft that way also

 

I think my 77 F-100 302 has a better jump then my 79 Bronco 400. Both are pretty stock, and the 77 has about 1,500 miles on the engine which is better than 71,000 on my 79, but I know that 400 has more torque than a 302. My problem is prolly similar to yours, just don't know what it is.

 

carb is a 650 holley vac sec
no headers
timing @ 12deg base
stock exhaust manifolds
No exhuast leaks
accell pump is shooting gas
from about 15 mph it seems to accellerate alrightnothing spectacular but alright
and i am starting from 1st gear

 

im kinda haveing the same problem with my truck and im seeming to think that it is the torque converter getting a little tired and wore out. that and someone put a high stall converter in it but u might think about putting a new converter in it to match ur power band

 

how should i check out the power valve?

 

I think my torque converter is going bad too..my 60' times are getting worse and worse....i dont know if rebuilding the motor, and not putting in a new converter sped up the wear on the old converter or not....

My 60' time..not 0-60..but dead stop to 60' time is 2.226....and i cant remember what it used to be, but it was better. Im in 79 F-250.400....C6....NP203 P/T..truck is 5460 pounds dry, and im about 180-190... Drag strip is about 5280 feet above the sea..

--John

 

My next project is to drop the tranny aand put a new rear main seal in the truck so it would be an optimall time for a new converter, but it seems like mine is alright its stalling around 1200-1500 rpm or stcok wich seems about right right for the cam that starts at idle

 

Are the vacuum secondary working properly on the Carburator?
Check for any vacuum leaks?
Make sure your vacuum advance on the distributor is working?
I think 12 degrees for the timing is a bit high, try running at 10 degree, check to see if it makes a difference.

Power valve is located on the front of the holley carb. Its 1 inch round and bolts on. Will need to take off the front cover, the one with the fuel inlet. This is going to require buying a front cover carburator gasket and the power valve. Or you can buy a complete carburator kit and it will include the power valve and gaskets. Price around $45.00. Don't forget to soak the carburator in carb cleaner.

Also, Replace the coil with a high energy coil, It helps performance. price about $29.00



Let me tell you a true life story, There was a time also where I was not getting much power to my rear wheels, The truck had a rebuilt 390 CiD, 4 speed transmission, Headers, I had installed an 4 barrel Edelbrock Performer Intake, The truck ran good for about 1000 maybe 2000 miles. Then, my truck started losing power. Started replacing parts left and right (distributor, upgraded spark plug wires, and you so on).

Sprayed Carb cleaner along the base of the intake, where it meets the heads. Didn't notice any change in RPM's. I was puzzled, I was thinking this motor had power and now it's not running great, Ran it like that for about another 30,000 mile or 1 1/2 years. One day my brother asked me if I wanted to buy this 390 engine block with heads he had rebuilt about 3 years ago and was just sitting there for $300.00 bucks. Ok, I had another 390 rebuilt motor and decided to pull out this 390 cid out and put it on my work truck.

Here I am with two 390 engine on engine stand. I'm all excited, for a moment I sat there thinking the older engine ran good and now it ain't. Then I start stripping the old engine, Removed the headers, and notice a few leaks from the header gaskets. It had seemed like the header port were smaller than the exhaust ports on the head. That was Problem # 1. This had created a few exhaust leaks. The header were for a 360-390 engine and seemed like they were engineered with a defect. I went to parts store to look at other 360-390 headers and notice the same problem on those ones, Decided to go with stock exhaust manifolds.

Okay, Then pulled off the edelbrock performer intake. There also I had noticed leaks along the base of the intake. That was Problem # 2. I could only conclude that the heads on my truck had been milled (Head being milled is when they shave the base of the head to make it flush and level) The Engine block was also milled where the head sits. substantially. This created the intake to sit a bit higher than if the heads and engine were not milled. This, would say had created leaks on the intake gasket. Decided to go with Original Equipment (OE) 2 barrel intake with a rebuilt OE 2 barrel carb. My reason being it would hold the torque to the bolts better and was engineered by the Ford Company and was designed better.

Dropped in the Old engine back on the truck with OE exhaust manifold and OE intake manifold.
Truck run really good again, and has very good take off for a 2 barrel. Just the way a 390 engine should run. Has over 5,000 miles now.

Just something to think about, Don't give up.