273 for 318 swap advice

-
273 Commando

273 Commando

mooser's dad
Joined
Dec 27, 2008
Messages
31
Reaction score
0
Location
San Jose, CA
Hey guys, it's advice time for me and my son, Moose. That 273 we did early this year is a slug. He wants more GO. so we're thinking of up sizing to a mid 70's 318 my buddy will give us. The 273 has a new Comp Cams 270 Magnum solid lifter cam, Eddy Performer 318, Hedman headers,in a 74 Duster with a 904 and 8.25 w/ 3.21 gears. The heads are stock, engine is a 10-1 comp with 160 psi cylinder pressure. This thing needs a shift kit, but it's still a dog.
We were thinking of building up the 318 with the steel crank and rods from the 273, keeping the solid cam and valve gear, and putting this in the 318 with the Eddy manifold, Carter 625 AFB and headers from the 273. Whaddaya think? is this a bad idea? What about heads? I need advice since I'm not too engine savvy and I'm broke and Moose has no job! The reasons for the 318 are purely economical. I have a free one and the Schumacher mounts are 273/318 specific. HELP?!! And THANKS!
 
You don't mention what heads you have, but I'd bet they are the answer to your problems if they are 273 or 318 heads. Also, you don't mention compression ratio, but the 273 won't make much power below 10:1, where the original 273 Commando was that or more. If you know your CR, and the heads are not 360 or swirl port 318, you may be able to simply swap heads. I mention this because of your budget constraints. Otherwise, trading up for more CID is a good idea, and I'd still recommend the better heads.
 
The heads are original 64-65 castings, same as the block. The compression in the 273 is 10:1, putting out about 160 psi. I know that due to the tiny bore of the 273, that heads are a very limited choice due to clearance issues. Any other ideas perhaps?
 
I have a FREE 318, and the Schumacher mounts I have are 273/318 only. the 340/360 one's are different. Trying to go cheap. Maybe advice on more power in the 273 would be better, since it's only got about 3000 on the rebuild.
 
I like the gear idea. What about 302 heads? I've been reading the site since I posted the thread. I really don't feel like building another engine. If a head swap and gears will wake up this thing, that suits me fine. Oh, the cam specs are 270 deg. advertised, 224 @ .050 and .468 lift in and out, cut on a 110 deg. lobe separation. I thought this would idle lumpy, but it sounds like a 340 and makes decent vacuum too, about 12 in/hg. This thing starts and runs great. It just aint fast or tire burnin' fun like I was hoping for. Aint mine though, it's my son's first car. I'm a big block guy. you can find me on FBBO as " 69 R/T". I will welcome any advice on making the "Moosemobile" faster.
 
Sounds like the extra six or seven hundred pounds of the Duster over it's mid 60's predecessor is what's doing you in, so the 45 extra cubic inches of a 318 sounds like a good answer if you're not willing to run a loose converter or change to stiffer gears.

Rods, not the crank are probably the weak spot, and if the 318 is a '67 it should already have a steel crank. 308 casting heads from a 90-91 TBI pick up are considered the best bang for the buck, provided you don't have to dump a lot of coin freshening them up, and you make sure your pistons are zero deck or close to it.
 
Not sure if a tire burning first car is a good idea for your son anyway.
Have him drive the car the way it is for awhile. Let him learn the road.
If more power is what you want,build a 360.
 
273 Commando said:
I have a FREE 318, and the Schumacher mounts I have are 273/318 only. the 340/360 one's are different. Trying to go cheap. Maybe advice on more power in the 273 would be better, since it's only got about 3000 on the rebuild.
Click to expand...

""Maybe advice on more power in the 273 would be better""

Ignition curve???

Cam timing???

Convertor?

More gear will definitely help.
 
Johnny Dart said:
Not sure if a tire burning first car is a good idea for your son anyway.
Have him drive the car the way it is for awhile. Let him learn the road.
If more power is what you want,build a 360.
Click to expand...

Couldn't agree more. 273's are high RPM screamers like 340's, and very efficient on gas. Did you use 340 valve springs? With your combo it should wind up good but will never have the torque of a 360 let alone a big block. Check your timing and make sure the four barrels are opening all the way when you mash on the pedal.
 
Timing is set at 12 deg. static and totals around 36 deg. mechanical. Add about 12 more deg. for vacuum advance. I fished around for a short slot advance cam for the distributor specifically to run a lot of initial timing for low end. The kickdown is set for WOT and it opens all the way, however the tranny up-shifts waaaay too quickly and doesn't part throttle downshift as I'd like, so my next step is a shift kit. My choice is either a Transgo TF2 or the B&M transpak......any suggestions?
 
"however the tranny up-shifts waaaay too quickly and doesn't part throttle downshift as I'd like, so my next step is a shift kit. My choice is either a Transgo TF2 or the B&M transpak......any suggestions?"

Does it have a floor shifter or column? Do you have a tach? If floor shift, does it pull hard if you manually shift it? Sounds like the kickdown linkage should be lengthened on the bottom transmission lever. Double check the kickdown lever at the transmission. Disconnect it and make sure it goes all the way back when you mash the pedal.

Take the 318 but 302 heads need work to flow well. Your engine should be fine if you get it sorted out.
 
You must log in or register to reply here.
-

Back
Top