one of my friends is getting frustrated with his truck, now before i ask the question, let me cover the bases by letting you all know whats all done to the truck...... first off its a 79 F150 with a swapped in 351 that was professionally built(mild in my book), not sure of compression ratio or cam specs, but has a holley single plane intake and 650 cfm holley. still has the stock manual trans and T-Case, 9" locked rear with 5.13 gears, D44 in front with 5.13's and is still open, superlift 6" suspension and 3" body lift, 42" Super Swamper TSL.
now the problem, when hes in a mud hole, 4 low and granny gear(1st), there is no problem, however if he tries to grab 2nd gear for a little more wheel speed and to go faster than 2 mph, the motor falls flat on its face and seems like there is not enough power there to turn the tires, so he ends up going back to granny gear and reving the hell out of the motor, in 4 high, this happens in 1st gear as well, motor falls on its face, but going down the road in 2 high, its like night and day diffrence, motor runs strong and pulls this heavy truck just fine. Could it be a lack of torque the motor is producing? the engine builder claims this should pull about 350 HP at the crank. or is it that the gearing in the trans is too steep for what hes asking it to do? hes contimplating finding and swapping in a C6 in place of the manual, would this help or hurt? he uses this truck primarily off road and does everything from mud, rocks, sand, hills, canyons, washouts and whatever else he can find to try and conquer.
I have helped with the building of this truck and though i dont agree with his way of thinking sometimes, i can usually find a way to get him back to reality and whats "safe" and what isnt.

Any suggestions or comments? All are welcome.

here are my comments...

If it has a 3 speed, the first gear is like 3 to one and the second is 2 to one. With 5.13's and 42's, that's a bit high geared for my tastes. I run 5.13's and 38's.

Also, as I'm sure you know, 42's and D44's don't mix well. Even with good shafts and CTM's, that's just too much for them.

Good luck and it sounds like a cool truck!

-Jack

yes, we have already noticed that the axle shafts are less than desireable, broke 2 sets last year before we started welding around the knuckle joint caps and arount the yokes for added support, since we started doing this, have not broken 1 yet, not the right way to fix it, but its working for now, anyone know of a front diff we can put in and retain the coil spring lift without breaking the bank?

It is a 4 speed, however, most people while driving on the street using the vehicles for everyday use dont use first gear because of how low it is and most can get by by starting in 2nd.

Im guessing that it is an np435 tranny. we have one my my dads f250 and with a load in it there is a huge drop off between first and second (pretty much a stock truck) My guess would that there is just to much of a gear change to keep the rpms up. The auto might help or maybe try a duel tcase adapter or something like that. I dont play in mud so these are just kind of guesses.

Matt

Swap to a dual plane manifold and possibly a carb spacer. Single plane set-up is for high RPMs. I suspect the rest of the motor was built for high RPM's also (cam, heads, exhaust etc.) I prefer low end grunt (torque) vs high end horsepower for truck motors. International Harvester took this philosophy and thats why bone stock Scouts pull so well.

I've got an NP435 in my F250 with a 390 and there is no way you are going to get a clean shift form granny first into second, especially in mud. You are going form 6.something to 2.something when you go from first to second, plus it has been my experience that the non-synchro first doesn't like to come out of gear at higher RPMs either. If you are in such deep mud that you can't motivate those tires form 4Low in second then it might be time for a 460.

to be pulling 350hp outta 351m with stock pistons is probably not going to happen with a streetable cam and under 6000 rpms. there is no aftermarket on the shelf pistons for the 351m to bump compression.

he should start out in second.

when hes in 4 low 2nd gear(1rst) thats about the same as 4 hi granny ....I woudl think with the gearing he should be able to start in at least 4 hi grannt, and even 4 hi 2nd gear. My truck pulls all 39 boggers in the mud with no probs in 4 hi 2nd gear and i only have 4.10 gears? even with that 351m i would think you shouldnt have probs with the gears you have. i dont know?:confused:

Are you sure, it does not fall on its face because its running to rich, or the carb is too big?

I don't know about his motor but I have a pretty weak 302 same drivetrain as he does except 60/14b with same ratio, but 39's and this weekend I was in 4 low 1st(second) and 2nd(third) gear for wheelspeed in the mud at praire city and get'n it. Keep in mind my motor is weak as fawk.
So it has to be the motor in his case or something fawked up in his t/c.

ps: mud really sucks:barf:, I'm not doing that again.

Throw in the C6, he will be much happier.

Swap out the single plane manifold for a dual plane (ie. Edelbrock Performer) and it sounds like maybe you have too much cam (how much vacuum you got at idle?). Shouldn't be that doggy.:(