I have a good friend that runs the local demo derby scene. He runs mostly early to mid seventies gm cars but runs a 318 and 727 trans in everything. We can build a very strong car that will take alot of abuse and usually do fairly well.. Lately, however, we seem to be getting left behind in the powerplant department. Alot of the local guys are running small block chevy motors that seem to run really strong and also seem to run just as well without coolant as they do with. Our little 318's will take alot of heat but do eventually heat up. Were also lagging behind in the horsepower. We have a 318 magnum out of a 96 dakota that were looking to build over the winter and I was just looking for advice on what we can do to this motor to help the cause.

Why not a 360?

We havent ruled out a 360 but the 318 was a freebie. Figured wed play around with it and see what happens. Once we figure out what works we'll probably build a 360 to run.

Does it have to use all stock internals? If so, spin the pistons 180 degrees in the bore to loosen up the thrust on the cylinder walls. You may also have to swap the pistons around in the bores to get the valve relief orientation right. I have a stock but lightened cast crank out of a 318 Magnum motor just sitting here also...

Regrind the roller cam (bullet cams $150) headers, a crosswind intake if your on a budget or edelbrock rpm magnum (not cheap) a windage tray from a 340 and a 625-650 cfm carb.

Were on a bit of a budget but not against spending a little money on parts if it looks like it will be money well spent. would like to stay with mostly stock internals if possible.

I built a 341" 318 based roller block motor 3.55" stroke with 6" aluminum rods) that revs to the moon..it may be for sale soon 'cause I'm building a 414 incher.

I can offer some tips if you need it

Id love to hear any tips anyone has to offer..... I'm also looking for information on ways to keep the engine cool or make it run just as good at 220 degrees and up as it does at 160 to 180.

I built one earlier this year for Al Pienne's 66 dart. This was a budget hydraulic cam 318 build, a solid cam would be more in line with something higher reving although the lighter magnum valves can bump up RPM potential with a hydraulic.

1) 71 LA 318 .030 over with KB167 flat top pistons.
2) Cast 318 crank and early 318 rods for reduced inertia.
3) I ported a set of OEM magnum heads with stock 1.92 valves.
4) Comp 280H cam with stock magnum valve train (and MP retainer and springs).
5) Mopar dual plane magnum intake (OOTB).

The first time he drove it was without a tach and he said it seemed to never stop pulling. Said it was an animal.

Now he has a tach and the last I heard he saw the needle at 7K.

Steve Dulcich did a Mopar Muscle article on a similar 318 build but with unported heads, heavier crank/rods as well as a MP single plane intake. Some of the choices for my 318 combo were made with the intent of getting a car down the track quicker. I am still waiting for track results from Al.


318's can be fun.

if your going to use stock internals, then at least take the rods out and grind all the casting flash off them, then take the rotating assembly out, crank, rods, pisons and get it dynamically balanced. once thats done you can reassemble using good bearings and rings and the short block should be good to go. if your using the magnum block the heads oil through the pushrods. get a heavy wall hollow pushrod to make sure they don't bend or starve for oil. i like the magnum heads other than intake choices that are available. with a carb its hard to beat the M1 single plane intake for a high revving engine. also definitely regrind the cam as was mentioned and you should be pretty good to go.

first of all what are the rules? the do and dont...

and if are useing a 318 and evryone else is runing a 350, then it will be tough.. i know you have a freebee 318 ad they do run well well.. if you do the same to a 360 it will be easier to make the HP and TQ..

lighten up everything on the teen...

For a demo derby wouldn't a big motor make more sense, i mean you are trying to get a big car with no traction anyway moving with its bumper in a tire and the other tire flat, a 360 would still rev to 6k no problem with just a solid bottom end , maybe good resized rods/bolts as for running without coolant i would say good synthetic 20/50 oil, maybe slightly overfilled, and the carb on the rich side, Big solid 7 blade fan.

the magnum 318 is not your father's old LA318....

they rev and make very good power, even stock. enough to push my 4700lb truck to mid 16's in the quarter.

the limiting factor are the light valve springs that float at about 5200 RPM.

on the cheap, I'd run it as is, save a carb intake, and swap the valve springs and retainers from a couple of junkyard '94-up GM 3.1 or 3.4L V6's......you could regrind the cam, as well, I'd go fairly mild on the ramps, given the extreme duty of the application, probably something like bullet's HR262/300 lobe for both intake and exhaust.

my 9:1 mag headed 318 seems to make best power with about 30 degrees timing, BTW...I'm using bullet's HR259/316 lobe for intake and exhaust. makes great power.

Are you running on dirt/mud or blacktop? If dirt/mud, traction is key, not power, and a stock 5.2 oughtta be more than sufficient. Either way, car durability and heat control are your 2 biggest concerns.

Avoid temptations about rebuilding with new pistons, tight piston clearances for high HP, etc. That’s high-performance advice, and a derby engine is a completely different animal. For a derby engine to survive, you want it LOOSE so that it doesn't seize when you get it hot. The more power you make, the more heat you make. A 318 Mag was rated at 220-230 hp, ~50 hp higher than a 318-4 barrel -- I can’t imagine a derby car needing more than that (traction will be the issue)

SBMs do well in tolerating heat, so a Mag with a roller cam ought to be even a little better (less friction). If you use a Mag, make sure that your water pump and front cover match, Mag’s serpentine system uses a reverse-rotation pump. Remove all your freeze plugs and clean the block out thoroughly to optimize your cooling. Install a new oil pump and timing chain. Get it running well. Install in car.

I have a buddy that has run demo derbies for 20-ish years. He will NEVER run a bigblock - too heavy, too hard to cool, and the extra power isn't beneficial (his opinion). He even prefers a 318 over a 360 because they run cooler and the extra bit of power from a 360 reduces runtime if the cooling system punctures. A good combo is 3.91-4.56 gears with a SG or spool and an engine that will rev quick.

Patrick's cam/spring advice is good too (as always), and for the suggestion for a slower-ramp than his normal recommendation - .