Advise wanted on reviving a 318

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djpearce

djpearce

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I’m finally getting around to overhauling the motor in my 66 B’cuda and I’m looking for suggestions on which heads to use, cam & pistons/compression ratio.

A little background, this is a 1969 - 318 that I originally rebuilt in build in 1983 when I was in college. The 318 motor was a dealer replacement engine put in the car when my uncle burned up the original 273 motor some time in 1970. Since 1986 the car/motor have been off the road and garage kept due to an accident, resulting in very low mileage since the initial rebuild. At the time of the rebuild it was bored 10 over and 10.5 to 1 compression pistons were installed.

Additionally at that time, I shelved the 318 heads and installed a set of 1972 - 340 heads that were rebuilt to factory spec. For the cam, I was running one of the Direct Connection hydro “Purple Shaft” street cams from back in the day (I have no idea what one).On top was a LD-340 with a 650 cfm carb.

In retrospect, I was disappointed at the time with the performance. I think my problem was mainly that at the time I did not take into consideration the 340’s larger combustion chamber size when I chose the piston compression ratio.(Like I said collage rebuild!)

Fast forward to today, after the engines’ upcoming rebirth, I’m looking for a street able cruiser, not a monster drag car, enough horses for spirited driving.

What recommendations do you guys have on how I should proceed? I plan (at this point) on keeping the 904 auto trans and the 7 ¼ rear.

I still have the original 318 heads that can with the motor so they are still an option (at the time they were pulled they had about 70000 miles on them so most likely need a rebuild)

Anyone have some ideas on a best way forward?
 
It sounds like you have all the right parts for a good combo but with the unknown cam specs as well as unknown trans and converter specs coupled with the unknown gear ratio, it's hard to say what the thought was behind the build or where it went wrong.

That small 7-1/4 rear is a weak link.
 
Factory stall and possibly to much cam, around 270 degrees you start trading in bottom end for top end.
But I say rear gear is the main reason for disappointment in performance, if you don't gear smaller engines you'll always be disappointed. Take a 360 built like your 318 probably makes 430lbs-ft vs your 370lbs-ft.

430lbs-ft x 2.45 ( 1st gear ) x 3.55(rear gear ) = 3740lbs-ft
370lbs-ft x 2.45 x 2.94 = 2665lbs-ft
370lbs-ft x 2.45 x 3.55 = 3218lbs-ft
370lbs-ft x 2.45 x 4.13 = 3740lbs-ft

It would take a 318 with 4.10's to equal a 360 with 3.55.
 
Take the heads off and cc' them, get a good measurement on piston dome/ in the hole.
If you have flat top slightly/ slightly domed pistons the 340 heads should work with a more modern cam, maybe a stall converter.
I bet you over-cammed it and killed the bottom end on the original build.

I remember I put a 484 mp cam on a stock bottom end 318 with J heads, in high school, the sob sounded good but ran like crap until about 4000 rpms.
 
Seems the cam is an unknown factor,and an old pattern anyways. I'd shelve the 340 heads and use the 318 heads,but with the small 360 valves. Cut them to get reasonable comp,say 9.5 or so. Choose a modern cam like a Lunati or a Comp. This will get you a torquey ,responsive motor,and all under 6000 rpm.
 
I wouldn't go with 318 heads, I think its a step backwards unless you only looking make 300 hp. Which is less than your making now. If any head swap would be EQ's. With dome pistons you got to be around 8.5:1-9:1. I'd stick with 340 heads measure and calculate what it would take to get to 9:1. So you could run a Comp or Voodoo high lift 268 cam.
Plus add 3.55 gears at least and a stall, and headers if you already haven't .
 
Your piston/head combo will be fine. With the 10.5 pistons and the larger port heads, you will be in the 9.2 compression range. I built a 318 back in the day with 10.5 pistons and 360 heads to result in 9.2 compression.

The LD340 is the best intake that you can get for that combo, keep it...

I would get a cam bigger than a stock 340 cam, but smaller than the MP .484/284 cam.

If you try to put 318 heads on it, you will be taking a step backwards. Your compression will be too high. Been there - done that....
 
Thanks for all the input thus far, the torque converter was the stock one from 1966 - rear end gearing is 3.23:1
 
With that many miles I'd just do new rings and bearings and swap the cam to something like a COMP 268H. If it has good compression, good oil pressure and doesn't smoke you could just swap the cam and be done with it. Headers would be a good thing to have too.
 
I guess we all have different opinions on what is "impressive" and what is not. What do YOU mean by "not impressive"??? If you were hoping to run 11.50's at 115 mph at your local drag strip, then you would not be impressed. You have the right carb and intake. Your heads will serve you fine, especially if it's a little over bore and higher compression pistons. The only thing left on the engine to question is the cam. I would say around a stock 340 cam would be perfect. You could run the above listed combo with either headers or manifolds and dual exhaust. This combo would also work with a stock 904 converter (around 2000 stall). So figure out your cam, and don't forget the most important piece, tuning it right! If you put in a bigger cam, you need to advance the timing. When I was a teen, I put in a direct connection cam and timed it the same as it was before, and it was a BIG dawg.... lol ! I advanced the ignition timing from TDC to about 14 degrees BTDC and the car took off like a rocket!!! Your gears, stall, and headers will decide on what use you have for your car
 
See,heres the problem with running a large port head on a 318 like the 340 head. It lacks port velocity until you get the rpm's up. So you end up trading off bottom end torque (good for fun on the street) for top end horsepower, which needs gears and a loose torque converter. My point is,with a little pocket porting and bigger valves,a 318 head is a lot more fun on the street. The compression can be sorted out with a thick head gasket.
 
Take ot all with a grain of salt, but i might get a mildercam, machine the old teen heads to flowand make it look more like a stock boat anchor, shake the pants off people with that
 
What exhaust system do you have? Headers, the manifolds? Single? Dual?
 
-I have done it both ways,a couple of times.
-Bigport openC heads onto stock LC 318 = soft bottom end,esp with an A/T.Smallport openC heads onto 340/360 = Dynomite bottom end, esp on 340. I attribute the results to the c/r change and port velocity.
-The worst combo was 69X-heads onto 73-318 into 71 Monaco,with 340 cam; all oem parts. No amount of tuning could get that beast off the line. But passing gear was a blast.I later figured the c/r was around 7:1
-The funnest was a complete 318-2bbl top end on to 69-340, into 65 Valiant wagon.
-Those bigport smog chambers are pretty big on a 318, esp when the 318 pistons are down in the hole.The c/r falls into the basement, along with efficiency.That, coupled to a typical oem convertor, and highway gears is a disaster for performance.
-The cure for your diss-appointment is not that far away.A little compression change goes a long way.And is likely the all-round best answer.Big gears and hi-stalls have their place, but with low compression, will keep costing you dollars forever.Whereas the compression change and a tune will bring the bottom end up to an acceptable level, and will save you money at the pump. Later a modest change in either gears or stall will perk it right up.
-The smallport heads may not be your enemy.They can work really well up to 4500rpm or so, and where is most of your driving done?If you get the c/r up, you can run either heads. A good place to target is flat-tops and a zero deck. Then.... if you can find them, an old set of closed chamber smallport heads.You could probably get close to 11:1 with those. Unfortunately, those smallport heads become a problem in the higher rpms.
-The bigport heads @ zero deck will get you close to 8.5c/r. A 65cc head and zero deck gets you near 10:1
-A closed chamber has the advantage of quench, which if used correctly, can allow a bit higher c/r before detonation arises and can get you better fuel mileage.
-So all this mumbo-jumbo boils down to is this: Focus your needs and desires, then build accordingly.Street use demands the widest parameters and the most careful co-ordination of parts.
-I believe that for most of us,the flat-top/zero deck engine is the most versatile street base,then careful co-ordination of c/r, through head and camshaft selection to achieve a dynamic c/r for your available fuel, that still allows a normal engine running temp, and full advance without detonating.
-Some will say, and others have proved that c/r is not the be-all/end-all.Well I think that needs a qualifier. A 7/1 318, NA, is a slug. And a 13/1 street motor is hardly a street motor. So the qualifier, for most of us with limited pocketbooks,is this;get the c/r to 10:1,+/- 1.0. The bigger the cam the higher the c/r and vice-versa.Then make it work with Dynamic c/r manipulation. The dynamic is far more important than some think. The Static or computed c/r is just the way to build the motor to achieve the Dynamic.Dc/r calculators can be found on-line.With a small engine like the 318 a guy really needs to focus his expectations.
-I know this is a long reply, and I truly hope you are able to make use of it.
EDIT
When I say compression falls into the basement,check out this math; the formula is c/r= (CV+cv)/cv where CV is cylinder swept volume, and cv is the total chamber volume. A stock bore 318 has a swept of 651.4cc. with an open chamber bigport head of 70cc, a gasket of about 8.4cc, pistons down in the hole .137 thats 27cc and no eyebrows, this is how it looks;
c/r= (651.4+70+8.4+27)/(70+8.4+27)= (651.4+105.4)/105.4= 7.176. Thats in the basement, and that right there is the problem. Now if you bring the deck up to zero and lose those 27cc and maybe pick up a pair of 5cc eyebrows the cv falls to 83.4cc. doing the math the new c/r comes to 8.81. thats a 23% improvement. Couple that with an early closing intake to pull up the dynamic, and then you will have something. Unfortunately, you will be married to it, because as soon as you put in a bigger cam, the low end goes soft. The only cures are gears or stall. Neither of which are long-term solutions in a daily driver.
The real cure is more cubes. A 360 has a swept of 737cc and with pistons down at .100, and with the same gasket and head, c/r comes to 8.44. So with no machining at all, you are only down .37 point,as compared to a machined and rebuilt 318. Now the fun starts. Say you put some new flat tops in that 360, at zero deck. So all youre doing is boring .030
Swept is now748.3, and again with all same parts totalling78.4, the c/r builds to 10.54. Now you can use all your current top end parts including the cam kit. Or you can swap out the cam to one in the 230* to 240* and the extra 41.8 cubes will help keep your low end from going soft. A cam in the 220* will get you a ton of torque, at 10.5c/r. With a 904 you can run almost any gear/TC. Now you can leave the engine alone, and play with gears and stall as funds are available. I can guarantee with a 10.5c/r 360, with a 223* cam, in an A-body, with a good tune it will do every thing you want it to as per post#1. I built one like that. It went 106 in the quarter,fried the 275/50s, cruised at 2200, and I could lean it out to get 36mpgUS.It did it all without overheating or breaking down, and with full timing using 87 octane E-10.
So how much will it cost? Thats not a fair question. The better question is how much more will it cost than to bring the 318 up.Well; the 318 will need pistons,decking,hot-tanking, and a cam swap. The 360 will need pistons and hot-tanking, and maybe no decking and reuse your cam. The net difference is the cost of the core LESS the cost of a cam kit; so almost nothing! Well almost. The 360 might need a few things that the 318 cannot donate, such as main bearings, oil pump,etc.
Thing is for very little MORE money you get WAY more bang. And the future mods are already planned for with the basic short block. Sorry for the long rant. Happy decisioning.
 
Tahnks again for everyones input - I need to get under the hood and get some casting numbers to see what I have.
 
Yeah, I kinda thought so. 1/2 your problem is the factory early A manifolds. I know 64 & 65 are terrible and you'll give back a lot of power there. Much worse than even the later 2bbl logs. I have a '66 with a 340 and the factory '68 hipo manifolds. It fit fine. You might want to look into them or a set of headers if you're serious. The only other change I'd make is a more modern camshaft and make sure the pistons have valve reliefs. Otherwise it's a pretty solid combo.
 
Agree with Moper, using manifolds will really limit you IMO. Any decent cam is going to want a better flowing exhaust.
 
Agreed on the factory exhaust manifolds, but headers in a 66 Cuda are a PITA to fit. I like the idea of looking for a set of factory '68 hipo manifolds.
 
-Back in post #3, 273 talks about gears. and his measuring stick is a 430ftlb 360. Thats a very nice number and usually goes with a similar amount of hp; namely 430hp. However getting there is not cheap. And getting there requires quite a bit of support works(more money). And after getting there, the chassis will need to be upgraded as well as the rest of the powertrain(yet more money). After the beast is safe and reliable to drive, a very substantial amount of money will have been spent.
-The point Im trying to make is this; that although the numbers look good( and would be dynomite), the cost involved in getting there need to be considered, and so IMHO, the comparison might be misleading to some. No doubt, gears will wake up a 318, the trade off is at the other end, in terms of; noise, vibration, limited cruising speed/time,mpgs, etc
-If you are needing to stick with the 318, I stick by my earlier post.
-If you can find a few more bucks, score a low mileage,early 360 2bbl engine long block, and put your induction on it. You will never be sorry about the money spent,versus the same amount of cash thrown at your current 318.If your 340 heads are in good shape, you can use them on a 360 shortblock. The 360 is 42 cubes bigger, and likely 42 ftlbs better and has way more potential for hp. Up here they go for $250 to $450 at the wreckers, and often can be had with a trans for same cash. So you spend a few hours cleaning it up, and checking stuff and some gaskets. Badaboom, its smiley time.
-Of course, budget for a rear end soon. And you may be able to go down a gear size or two from current, depending on your planned useage.
-Did anyone mention turbocharging? Your current pkg is ripe for it. With a bigger sz rearend and 2.76s. I probably shouldnt have planted that seed. Anyway... happy decision making.
 
AJ/FormS I wasn't advising the OP to run 4.10 or whatever gear. At first I thought since he's running a 7 1/4 rear he probably had some kind of highway gear instead of the 3.23 he has which is just barely a performance gear :)

My point was if your gonna build a 273/318 and want to play with the big boys 340/360/408 you need to gear it. Or don't build it cause you'll never keep up. I know if I build my 273 I'm gonna have to run 4.88-5.13 gears.
But if your happy with let say a 300 hp 318 with 3.23 gears there nothing wrong with that it would be a fun car but if you want to smoke the average mild 360 out there, your gonna need better flowing heads and a lot more gear.

Torque is king (not really HP is) but theres two ways to do it cubic inch or through gearing.
 
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