72 Charger Build Planning

[skymynx]

So we are finally in the process of buying a home. It won't be for another 2 months at least till we get into the house. We will be taking the $8000 tax credit and building putting it towards building a 2 car garage. This finally allows me to stop putting all my money into savings for the house and be able to finally restore the car.

The car (a 72 charger) has a 318 with a 904 in it. Its been running a little rough, but I think I have most of the bugs worked out. I plan on dropping in a sizzler TCI transmission along with a breakaway torque converter. Will also be dropping in a Comp Cam 20-223-3. I will also be adding Hooker competition headers and a 2.5" dual custom exhaust. I currently have a Weiand action plus intake manifold mildly ported along with a Holley 670 carb.

I'm aiming for about 300 horse to the wheel. This is a car that we are building for my girlfriend, and I'd rather spend the money on the money then the motor at this point. Also does anyone have any experience with this cam? From the specs it seems like a very mild cam, which is fine by me as the girlfriend has never driven a carburated vehicle to begin with. Is the 300 horsepower a reasonable number to expect?

http://www.summitracing.com/parts/CCA-K20-223-3/

 

[72 Charger SE]

300 horse sounds a little high to me for that combination, but I don't claim to be an expert in that area. Sounds similar to the 318 setup I ran in my 72 SE for many years before switching to a 440. I think my cam was a bit smaller though, and I think I was running around 275 horse. I like the split cam profile though, since stock 318 heads seem to be more restrictive on the exhaust side.

First thing I changed after building my 318 years ago was the rear end. Mine had 2.71:1 gears, which are great for the freeway (couldn't keep the car below 75 without a lot of conscious effort) but lousy for performance.

 

[skymynx]

I plan on eventually dropping in a 8 3/4 rear end with a fairly high rear end. high 3's low 4's. Once we have the money in a year or two I'm very familiar with nitrous set ups, so I may revamp the motor to take a small 100 shot.

 

[MoparDman]

I ran an old style comp cam, a little bigger than the one you are looking at on a 340. It had 10 1/4:1 compression TRW’s, Ported 202 J heads, HD valve springs, Small tube headers and LD 340 intake. I ran it in a 73 Barracuda with a 2500 Stall converter and 391 gears. It turned on well, but I don’t think it would have worked on a lower compression motor with highway gears.

In your case, a 318 is a small engine for a big B body, and torque is just as important as horse powered when it comes to moving that kind of freight. If you are looking to build a 318 you may want to consider looking at heads first. There was a late model swirl port design that is readily available (read cheap) and they have the added advantage of having a smaller chamber thus giving you more compression. They will work well with that dual plane intake that you have.

Respectfully, I think that the cam that you have selected is too big, (477 lift 268/280 duration) especially if you do not change the heads or do something to up your compression. You should also keep in mind that your stock valve springs may not be able to accommodate that much lift. The base 318 valve spring is good up to something like .450 lift before you run into problems. The Chrysler performance catalogue has some great charts that can help in planning out the ideal combination. There is a 228/231 duration,.430/.450 lift cam that makes power between 1200 and 5200 and would work will stock valve springs. The next one up is 228/231 duration .450/.455 lift and it makes power from 1500-5800. But let’s face it, the stock small valve 318 heads are probably done breathing at much more than 5200 RPM. So the smaller cam is matched better with stock 318 heads. The other advantage of using the smaller cam is that you will not need an expensive after market transmission and torque converter. Form a cost savings point of view, you may be better off getting the stock 904 rebuilt with a trans-go stage 2 shift kit, perhaps a deep pan and add a cooler. The smaller MP cam will work with your stock converter. If your torque converter is shot, Chrysler sells a great set of economy performance converters ( P4876805AB is 1900-2100Stall for a non lockup 904).

I am sorry to say but a big Duration cam on a low compression engine in a 3800 pound brick with a big stall converter and highway gears is going to disappoint everybody but the owner of you local gas station.

Good luck with the project, I have seen some very nice budget built 318’s in recent years and I know that your 300 HP goal is achievable, it will just take a bit of planning.

 

[skymynx]

If I were to go a different route, and supercharger the little 318 what compression ratio should I look into building the motor for?

 

[72 Charger SE]

If you don't have one, I recommend getting a copy of the Mopar Performance engine book. Been a while since I had mine out, but I think I recall a section in it about turbocharged and supercharged engines. If memory serves, you will want to keep your compression lower if you are running a supercharger, since the supercharger will will be force feeding air into the engine, raising the effective compression in the cylinder. Too much compression and you will run into detonation problems.

 

[skymynx]

I'm aware of these issues as I've supercharged a few cars in the past. Never a small block mopar though. You guys have given me a few good ideas though

 

[69 Runner]

Yup. You'll need something like 7:1 or maybe 8:1 depending on how much boost you want to run etc

 

[skymynx]

Whats the compression ratio on a 72 318 sb from the factory?

 

[72 Charger SE]

I believe the 1972 318 2 barrel came with 8.6:1 compression from the factory

 

[Pistol Pete]

I believe the 1972 318 2 barrel came with 8.6:1 compression from the factory

On paper anyway. :skeptical:

 

[skymynx]

How exactly do I go about figuring out my compression ratio?