318/904/8.25 - advice needed?

[sdb8976]

Hello, I've been wrestling with conflicting information for... well, cumulatively, a couple years now. I have a recently top-end rebuilt 318, with the 340 purple cam, specs:
Valve Lift (INT/EXH): .429/.444

• ADV Duration (INT/EXH): 279/289

• Duration @ .050" (INT/EXH): 209/220

• Centerline (degrees): 114

• Power Range (RPM): 1200-5200

as well as....
An eliminator-style airgap intake (4bbl), holley 4160 600cfm carb.
904 transmission with tf-1 kit, freshly rebuilt
8 1/4 axle with 2.71:1 gearing

My question, or plea for advice is, aside from headers (duh) do I need to change the gearing in my diff if I do not plan on racing at all? It's purely street, cruiser status. The car is a 1976 Plymouth fury sport. numbers matching! Anywho, if anyone on here feels like taking the time to even say "you're fine" or "get bigger gears" I'd appreciate the heck out of it.

 

[dukeboy_318]

Hello, I've been wrestling with conflicting information for... well, cumulatively, a couple years now. I have a recently top-end rebuilt 318, with the 340 purple cam, specs:
Valve Lift (INT/EXH): .429/.444

• ADV Duration (INT/EXH): 279/289

• Duration @ .050" (INT/EXH): 209/220

• Centerline (degrees): 114

• Power Range (RPM): 1200-5200

as well as....
An eliminator-style airgap intake (4bbl), holley 4160 600cfm carb.
904 transmission with tf-1 kit, freshly rebuilt
8 1/4 axle with 2.71:1 gearing

My question, or plea for advice is, aside from headers (duh) do I need to change the gearing in my diff if I do not plan on racing at all? It's purely street, cruiser status. The car is a 1976 Plymouth fury sport. numbers matching! Anywho, if anyone on here feels like taking the time to even say "you're fine" or "get bigger gears" I'd appreciate the heck out of it.

What stall converter?

 

[PP1RT]

Your fine. Your upgrades wont give you much extra til a little higher rpm but there is nothing wrong with highway gears. You will be able to pass a couple gas stations..

 

[sdb8976]

Cool, thanks PP1RT. Haha yeah it'll be going back to my mom eventually so not being a total guzzler would be good.
As far as what stall converter, maybe you have a suggestion? I have to buy a new one as my old one failed spectacularly.

 

[wyrmrider]

IDK about that being a purple cam
looks like a stock 340 cam or 360 HP cam
Advertised duration looks like a crane number
you will want to run a 340 style converter with that cam
however the heavy car will take a while for the converter to catch up especialy with 2 series gears
makes a freeway flyer not a stoplight car
I'll check those cam specs and get back to you after dinner
do you have a make and a part number?
whats the compression ratio on the 318, has it ever been rebuilt with cast re builder pistons? what heads?
do you have the cranking compression

 

[JimKueneman]

My Coronet is basically the same except for FiTech EFI instead of the carb. It won't be a tire burner but once it get rolling it will pull like crazy from 1500 to 3000 RPM.

 

[wyrmrider]

specs for your cam are exactly the same as the Stock 340 grind, for example Elgin E-578S the advertised duration would be at SAE- .006 at the valve or .004 at the lifter with 1.5 rocker ratio- Same as Crane
The really long seat duration, even if changed to Comp Cams .006 is still going to give you a 268 degree advertised duration cam
and a 270 class cam is pretty big enough for a low compression 318
I would not change converter and gears to try and make that cam have more off the line go
live with it for a while- It might work real well out on the highway when you hit passing gear- or Bonneville
for comparison the Cam I use in these is 204 @ 50 with .305 lift wheras you get .286 lift from a 209 duration cam @.050- the seat numbers mine is around 256 @.006 or 260 @.004 10 degrees shorter- gets the intake valve closed early to start making some dynamic combression

 

[66 Sat]

Personally I've never understood the need for gears deeper than say 3.23 for a daily driver or cruiser. It's great being the fastest away from the lights but kinda sucks getting passed by everyone on the freeway 'cos you can only cruise at 50mph. I've had a '69 318 Barracuda with a 2.76 rear end and a 351 Ford Falcon with 2.92 gears (both autos) and they ran strong. They'd only run high 14's in the quarter but click down into 2nd at say 40mph on the road and they would fly. The 318 had an Edelbrock Performer intake and cam, 600 Holley and headers and it all worked well together.

 

[JFLN]

Hi, You have a heavy car, for cruising, that mama is going to drive later on. So here is my 2cents.
Exhaust- forget the headers. Find later 340/360 exhaust manifolds and run dual 2.25 pipes to the back.
Converter- the 340 used a 145k 1900/2100 stall converter. This will help your heavy car get rolling. It will also match your cam.
Gear- your 2.71 is fine but 3.23 will be more fun, get the car rolling and is still a good cruising gear.
Cam- your cam is more than you want. A 360 2 barrel cam or something in the 250/[email protected] range would be better. If you keep your cam it will work good with above suggestions. Especially with 3.23 gears.
Intake- again your intake is more than you want. Find a 340/360 stock intake or edelbrock performer.

 

[wyrmrider]

I've rune 3.23 Mopar with OD works great
I'd just change the cam- most likely a custom grind 250-256 range at .006 is spot on should have .300 or better lobe lift (for the intake)and asymetrical profile
otherwise you have to change gears and converter- as said above and it will still be sluggish that cam was designed 50 years ago, back when we had much worse springs
x2 on the exhaust manifolds headers will not solve your problem