Have an '83 318 & want to hang some pistons on some rods and drop them in to cut the down time. The rods I have spotted are '71 (318). Are these (yrs) both pressed pin and the same weight (645 casting iirc). Thank you for your time.

71 318 rods could be floated from the factory. 318 rods from a truck engine are lighter than the 360 rods. the car 318 rods are lighter than the 318 truck rods. i have used both in engines before. if memory servers me correct, the truck rods are about 50 grams lighter, and the car rods are about 100 grams lighter. i have a set of truck rods at the shop. i will weight them and post the weight. kenny

318 truck floated rod-714 grams (049)
360 pressed rod-751 grams (645)
340 pressed rod-764 grams (496)
340 floated rod-756 grams (496)
could not find a rod from 318 car. 67-72 are the years that used the lighter rod.
i weighted one rod with each number, they will vary some. kenny

Kenny thank you very much for takin the time to lookup (& post) these

i also am building a 318 for milage. i have kb flat top pistons, eagle I-beam rods (600 grams), and a cast crank. the rod/piston combo weights 1240 grams. i will have the crank lighted some. tring to get the lightest rotating assemblie. good luck. kenny

I'm thinking the bobweight will not be as imp on a max mileage build that will do a minimal amt of accelerating as opposed to a ground pounder but I'm gonna grind/polish/match everything then give the weight # & the crank to the grinder. Quench for sure/Mag heads. Thought about checking into an "Atkinson (sp) build w very high comp & a specific cam to bleed it off & much better mileage but sacrifice in power but a mileage build (& a 318 to boot) I'm not seeking power from this one. Any thoughts?

i feel any loss of weight on the rotating assembly will be that much less load on the engine and should increase power and less fuel needed to maintain a certain rpm. i have polished all number of rods. if max reduction on metel is taken from both small and big ends and side beams are done the same, the 318 rods can be taken to about 650 grams. it takes me 30-45 min. to do each rod. with the pistons and heads (magumns)i will be using, i will be at 9.9 c/r. kenny

The MPG differance will not be noticed during cruise but it will help city driving MPG where you have to accelerate it over and over, once you are cruising the momentum keeps them going pretty much the same.

I would just start with the SCAT I beams though, they are 595 grams and are a better rod. If you spent 30 minutes a rod X 8 that means you are gonna spend 4 hours (whats your time worth?)plus you should have them resized for a perfectly round bore to reduce friction and you are still gonna have 40+ year old rods that are 50 grams heavier and that 50 grams can be removed from the crank too so you lose over 800 grams from the rotateing assy and get a much better rod.

I think if I was doing it again with no expense spared I would use a custom flat top with no valve releifs, they always had carbon in them when the rest of the piston top was pretty clean, that means the fuel in there was not burning very good. For a more budget oriented deal you could get a replacement cast piston with no valve releifs and mill the block to zero deck it. For a super serious effort get some used NASCAR rods off e-bay as long as you can find with honda rod journals, get your crank turned down to use them and get a custom flat top with no releifs. If you run any kind of piston where narrow rings are optional use them, also use a zero gap ring if possible. Run a magnum head with re-drilled intake bolt pattern so you can use LA intakes and bolt on a offy dual port. For off the shelf headers find the smallest one you can with full equal length tubes or if you want to make or have some made get them with 1.5 inch primaries about 48inches in length and a 2.5 inch collector mandrel bent to some 2.5 in 2.25 out mufflers of you choice and 2.25 dual out lets. For an carb you can not do better than a t-quad, just start leaning it out till it starts running a little rough then richen it up one step, might as well set up the secondaries for max power since you can decide to use them or not. For an ignition run a MSD6 or similar ign with matching coil. Set up your distributer to run 18* initial and 35 total mechanical all in by 2000, vaccume advance will help but you will not need much, look for a can marked around 5 or 8 degrees and adjust the vaccume advance up till it surges/bucks going down the road or pings then back off a hair. Put a crank scraper in and no tray since this motor will not turn over 5000 it will just be pointless and probably actually hold oil on the crank. For a cam you can go a couple different ways, 114 LSA to keep the mix from getting diluted, no more than 200* @ .050 run as much lift as you can get within those perameters, a roller will obviously reduce friction if you can afford it and a solid roller even more but those kind of lobes will be hard to find, if you want to run abnormally high compression like an atkins cycle just retard the cam to keep the dynamic compression low enough.

I think doing all that can give you an easy and honest 5mpg increase over a foctory 318 2bbl.

Above that I think one of the easiest thing to do to increase MPG on the high way is a higher rear gear, my motor felt like it needed another gear by 55 mph because it made so much TQ down low, I was still pulling almost as much vaccume at 70MPH as it did at idle so it could have easily pulled another gear as in an OD gear or something like a 2.20 rear gear (mine was 2.76 and I experimented with a 2.94 for a little while and MPG dropped pretty bad). Some guy will tell you to go big on the cubes so the motor don't have to work so hard and go to a lower gear but that simply is not true or all the 542 hemis with 4.56 gears would get 50 mpg. Build you car like I said (assumeing it is not a barge or truck) and you could get 30+ mpg and have more power than stock.

HotrodDave your 29MPG was what (originally) sparked my interest in this & I saved the other extensive thread

flat top pistons with no valve relief will be down in the cylinder .100. will be hard to cut the block to zero. also, there would be an issue of valve to piston clearence. that is were the valve reliefs come in. with the piston closer to zero deck, the reliefs give the clearence for the valves. with no reliefs flat top pistons, closed chambered cylinder heads, and thin gasket, you will have to run a very small lift cam. i would also buy aftermarket I beam rods instead of working a factory set. factory rods are stouter than most prople give them credit for. the time it takes to do a set of factory rods is not cost effective. unless you are tring to save money or just hard headed like me. kenny

The edge of an intake valve on a stock magnum is like .060 from the surface of the head, a fel pro head gasket .s .039 thick that gives around .100 clearance at TDC and a short duration cam like you would do for this motor are not gonna be open that high at TDC now throw in a VJ and you got plenty of room and if not you certainly would not need the big valve releifs of the KB 167 or even a stock piston, mabey a nick of a notch but not much. Obviously mock it all up and check but I bet it would not need much if any notch