ik ive posted about this before, but ive never gotten a good answer. i have a '93 f150 4x4 w/ 300 i6, mazda m5r2 tranny, 35's and a 6 inch lift. ive been told that if i switch to 31's i would get much better performance. now my dilemma is i can only go 60 mph comfortably. acceleration sucks. i have a 8.8 rear with i think 3.08's (not 100% sure tho i have to check). idc if this has to be a 100 page thread but i want anyone who knows how to deal with this or has had this problem to chime in. would switching gears help or hinder. what about 4.10's or 3.73's? i want to keep 35's on my truck. could this be just that my engine is worn out??? the trucks shakes moderately at idle, but it runs great, never stalled or given any grief. would a rebuild help or what tests should i do??? what signs should i look for of poor performance??? i need your guys' expertise. it is almost unsafe to go on the highway at 60 mph. anything that you guys could say or help get my truck driving the way it should or even better is very much appreciated

p.s. sorry for dragging that out longer than i probably should have lol

 

in theory, a smaller tire will help your engine turn at a lower RPM to roll 60 MPH. thus allowing you to use the rest of your power range to help you go faster and have better acceleration.

granted, there are literally TONS of variables that can play into the situation, but i can tell you for a fact that i have seen an increase in acceleration by going with a shorter tire on some of my rigs.

so yes, the general theory is correct.

 

is there a way around going with smaller tires??? like larger gears?? ik what ive heard but more info the better..

 

Your only hope is 4.10 or 4.56 gears. The 300 six just can't pull that tall a tire. The one thing to check for make sure the exhaust / cat isn't plugged.

 

so if i replaced the whole exhaust system and got 4.10's you think that would help it???

 

4.10s would help counter the larger tires. but in reality, the straight six is simply underpowered for that application. I'm a lover of the 300, ive had several, and i hope i have several more, but really, my thoughts are that if you are looking at tires 35 inches or larger, you should be looking at a big block, or at very least a performance built small block.

so yeah, my professional suggestion, as an ASE Undercar guy with 15 years of working on this particular generation of truck in my spare time, would be gear to match the tires, and get more underhood power.

 

what would u suggest to do to my engine to give it the power it needs??? do you think that i should worry about a compression issue or anything??

 

while we are on the subject, how much work would go into swaping my 300 for a 351m?

 

really, ive looked into building a higher horse 300, parts are few and far between. im not saying you cant make it work, but it may be cheaper to look at an engine swap.

i would suggest a gear swap first. i have an F250 with 4.10s and a 36 inch tall tire (460, 5 speed, mind you) and i would probably suggest you looking at a 4.10 gear swap. some others may chime in with better gear swaps, maybe 4.56's may be better, i cant be absolutely sure. but i would do the gear swap, see where the truck drives at with the gears and the current drivetrain, and set your horsepower goals accordingly.

Side note: i saw your build thread, your truck reminds me a lot of my first truck "Shorty", which is in my profile picture. looks good man.

 

Go with 4.56 ratio with 35's, then see if you still need upgrades. Most trucks are always geared too high to satisfy the govts fuel mileage on paper.

 

My '94 F150 SWB 300-6/M5OD/3.55 LS runs stock 235/75R15's, and will pull the hinges off of Hell's doors. I'd be surprised if you had 3.08's. I may go with 31-10.50's next time but never larger. It had 32-12.50 Coursers's on it when I got it, drove awful and vibrated like a sex toy! Promptly removed them. You could possibly "get by" with the 300/35's as a mall crawler but otherwise there's no substitute for cubic inches and gearing.

 

Just as stated, tire size is hurting you along with gearing, and the 6" lift.

Now, here is a theoretical point. The lift puts you higher and therefore more drag. More drag equals more resistance. Center of gravity is raised and so is resistance.

Perhaps someone can straighten out or disapprove my theory.

The 300 is tough and can definitely pull itself, but if changing the gearing doesn't yield results your after, then a 351 or 460 is the way to go. And since you have 4wd, your gonna have to swap both the front and rear to match. It's gonna run you $$$'s, so start saving and visit the junk yards often or Craigslist.

 

haha thanks everyone anyone ever swapped a 300 for a 351 before??? or a 460? was wiring a major problem?

 

If your stock tires were 29" tall, 3.73 gears with your 35" tires would give you roughly the same (dismal) performance you'd have with the 3.08s and 29" tires.

For comparison, 4.10s and 35s would be about the equivalent of 3.31s and 29s. 4.56 and 35 would be the equivalent of 3.73 and 29s. If it was me I'd probably go with the 4.10s, but most people want the engine spinning faster than I do, so 4.56s are probably the best choice for most people.

Keep in mind, a gearing swap is about $1000 / axle if you pay to have it done. Cheaper if you know how to do it yourself (and have the patience to do it right). Cheaper still if you can find used axles already geared how you want (but good luck finding used 4.56s!). And if you are regearing axles, that's the time to get a locking diff installed if that's on the wish list.

If you do swap engines, it's a big project. Not rocket science, but it'll take way longer than you think it should. Best if you get a donor truck that has everything you need so you can swap it over rather than trying to chase down motor mounts, ECM, wiring, etc. etc. etc.

And if you go to a 351 I'd really suggest you steer clear of the 351M. Sure, it can be built to be a good engine, but so can a 351W. And the M pretty much sucks stock. That plus an M will require a different trans while a W will be closer to a drop-in, as well as having a good factory EFI system. I think the W would be a much better starting point.

 

I think you need at least 4.10's for 35's
I have 4.56's on 35 and love it 91 f150 302,auto,4x4, getting around 20mpg