Gear ratio

[Hardball]

An interesting bit on my 77 F100 Custom, short wide, 400 2V C6.

I re-built the 400 at about 110k miles with a small compression increase and RV1 cam with no retarded timing. The rear gears were 2.92 ratio. Where the engine wanted to cruise at speed, the truck was going too fast in mph. I switched to a limited slip set of gears at 3.31 ratio. A much better balance of engine and land speed....and the mpg actually improved slightly. The truck is still a for gas mileage though. It's mostly for utility and coolness these days.

Put in new leaf springs too. Much nicer without the Ford droopy rear end.

 

[LEB Ben]

Doing less work to maintain and get to speed can have that effect.

 

[BuzzGun79]

Hardball,first of all your running an rv cam with a 2 brl carb.you can do this but your not getting the performance out of your cam.think about going to a 4 brl carb with a dual plane high rise intake.this will give not only more power at low end rpm,but more effiency as well.you will get more out of your cam & the cylinder heads as well.also i assume you are running headers & dual exhaust.if not you need to.i would stay in the 600-650 cfm range on a 4 brl.just keep your foot out of them secondaries & you will be amazed.give it some thought.

 

[LEB Ben]

I'll agree that letting that thing breathe will open it up a bit, but it's nothing that will set the world on fire...intake, carb and headers might notice 30rwhp. So if you're on a budget, take that for what it's worth.


Next...I see this all the time, "RV" cam really doesn't tell anybody anything except for a general class of cam...and that "RV" classification can vary wildly. It's like hot rodders saying they have a 3/4 race cam...WTF is that supposed to mean...except for, I didn't build this engine and have no clue what's in it, but I still want to sound cool.

 

[Alvin in AZ]

Yeah, post the cam specs and what diameter tire your running?

Butthead in AZ

 

[Jolly Green]

Next...I see this all the time, "RV" cam really doesn't tell anybody anything except for a general class of cam...and that "RV" classification can vary wildly. It's like hot rodders saying they have a 3/4 race cam...WTF is that supposed to mean...except for, I didn't build this engine and have no clue what's in it, but I still want to sound cool.

That's the kind of cam I have. It's awesome!!

 

[BuzzGun79]

here is an example of an rv cam, back in the early 80s i purchased 1 for my 77 stepside w a stock 351w.it was a summit brand although it was not listed as an rv cam the counterman considered it one..take that for what its worth.the duration int./exh. was 204/214 degrees lift int/exh..448/.472 rpm range 1,500 -4,000.i already had the headers & installed a 4brl during the swap. since i pulled a trailor w the truck i wanted my power at lower rpms.believe me i understand about being on a budget,but bottom line,you should not install a performance cam till you aquire the necessary related components to get the most out of it.just doesnt make sense to me,but thats my opinion.

 

[Blue Goose]

I agree, Buzzgun79...

 

[LEB Ben]

here is an example of an rv cam, back in the early 80s i purchased 1 for my 77 stepside w a stock 351w.it was a summit brand although it was not listed as an rv cam the counterman considered it one..take that for what its worth.the duration int./exh. was 204/214 degrees lift int/exh..448/.472 rpm range 1,500 -4,000.i already had the headers & installed a 4brl during the swap. since i pulled a trailor w the truck i wanted my power at lower rpms.believe me i understand about being on a budget,but bottom line,you should not install a performance cam till you aquire the necessary related components to get the most out of it.just doesnt make sense to me,but thats my opinion.

We're all entitled to our opinions, no doubt. And I even agree with you, but when working on a budget in these days and times...a bumpstick with straight up timing will be the best bang for the buck and yield waaaaaay more gains than any of the other 'bolt-on' type go-fast parts combined. But like I said, I do in fact agree with you, let that sucker breathe.

And my point with the 'rv' cam generalization was only that it's a generalization for cams that optimize power through a lower rpm powerband. But then raises the questions of how radical the cam actually is and 'low rpm pulling' can vary from person to person and from vehicle to vehicle.

 

[Jolly Green]

And what i meant was that the PO did the rebuild on my engine and this is exactly what I have run into. After market cam...but I have no clue, without cracking it open, as to what it is exactly.

Still, that cam with the timing set in it, and (knock on wood) I'm very pleased with how my engine runs in low-end and overall power...and pretty much everything. I still only have a little over 40k on the rebuilt engine which was done about 15 years ago. Still goes real strong, with duals hooked up to manifolds and the stock Motorcraft 2150. I'm happy with it.

Still...i agree with you guys, too. If my truck didn't already run so well, I'd have already done more upgrades. Someday when I want to tear it down, I'll probably ask Ben for the 400 build specs that I've see you post before and do it that way. Not that it isn't a good running truck now, but if were to do a rebuild myself, I might as well do all I can to have it reach its full potential.

 

[Alvin in AZ]

And what i meant was that the PO did the rebuild on my engine and this
is exactly what I have run into. After market cam...but I have no clue,
without cracking it open, as to what it is exactly.

A degree wheel and careful measurements can tell you from the "outside" too.

Alvin in AZ
ps- Where's the OP?