First engine build question

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Greenmachine225

Greenmachine225

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Okay so first of all i know a lot of people ask about the 318 so please dont give me grief about asking again. So I’m going to build my 318 soon and here are the parts I have for it, stock 71 318 block rods and crank, I’m going to get kb167 pistons, 76 360 heads just rebuilt last week, edelbrock performer rpm, Holley 600 vacuum secondary carb, comp xe268h cam. So a couple things I was wondering about is what of the stock crank and rods are already forged? How much would I have to deck the block to reach 10-1 compression. And since I’m new to this has anyone done a similar build and maybe knows a ballpark HP number that an engine like this might make, I’m guessing around 320 but correct me if I’m wrong because I know I probably am. I’d really appreciate any input or experience you guys have.
Thanks, Carson
 
My first question is, why do you want to reach 10:1? So you cannot run pump gas? You've been reading too many forums and magazines. Throw it together with whatever compression you end up with. It will be fine, run on pump gas and make plenty of power.
 
Greenmachine225 said:
Okay so first of all i know a lot of people ask about the 318 so please dont give me grief about asking again. So I’m going to build my 318 soon and here are the parts I have for it, stock 71 318 block rods and crank, I’m going to get kb167 pistons, 76 360 heads just rebuilt last week, edelbrock performer rpm, Holley 600 vacuum secondary carb, comp xe268h cam. So a couple things I was wondering about is what of the stock crank and rods are already forged? How much would I have to deck the block to reach 10-1 compression. And since I’m new to this has anyone done a similar build and maybe knows a ballpark HP number that an engine like this might make, I’m guessing around 320 but correct me if I’m wrong because I know I probably am. I’d really appreciate any input or experience you guys have.
Thanks, Carson
Click to expand...
Carson, what you need to consider and no is what degree the intake closes. The cam has opening and closing events that will dictate the dynamic compression, Dynamic compression is the PSI the engine will crank per cylinder. There is a limit to the dynamic compression when it comes to low octane pump gas. What you really want to focus on here is having a decent Dynamic that doesn't exceed the octane at the pump. With that in mind "and we are not going to experiment or push the envelope " you want to keep the dynamic compression around 160-165 psi.

10 .1 static compression isnt as important as 8.1 dynamic when its all said and running.
 
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RustyRatRod said:
My first question is, why do you want to reach 10:1? So you cannot run pump gas? You've been reading too many forums and magazines. Throw it together with whatever compression you end up with. It will be fine, run on pump gas and make plenty of power.
Click to expand...
You’re right, I’ll just throw it together with the kB pistons, it’s not gonna be a race car so HP isn’t a huge concern, thank you
 
you will be lucky to get 7.8 to 1 with the heads unless you 0 deck block and take about .050 off the heads you might end up with about 9 to 1 but every thing else looks good for a 318
 
MOPAROFFICIAL said:
Carson, what you need to consider and no is what degree the intake closes. The cam has opening and closing events that will dictate the dynamic compression, Dynamic compression is the PSI the engine will crank per cylinder. There is a limit to the dynamic compression when it comes to low octane pump gas. What you really want to focus on here is having a decent Dynamic that doesn't exceed the octane at the pump. With that in mind "and we are going to experiment or push the envelope " you want to keep the dynamic compression around 160-165 psi.

10 .1 static compression isnt as important as 8.1 dynamic when its all said and running.
Click to expand...
Yeah I’ll probably just not mess with the deck height and be happy with what it is, thank you
 
RustyRatRod said:
My first question is, why do you want to reach 10:1? So you cannot run pump gas? You've been reading too many forums and magazines. Throw it together with whatever compression you end up with. It will be fine, run on pump gas and make plenty of power.
Click to expand...
Agreed. Just ask the manufacturers for the proper cam for your combination. Lower compression Teen with too big of a cam and stock converter and 2.. something gears is a recipe for disaster.
 
Greenmachine225 said:
You’re right, I’ll just throw it together with the kB pistons, it’s not gonna be a race car so HP isn’t a huge concern, thank you
Click to expand...

Not what I meant at all, but go right ahead. HP can be reached by MANY other variables other than compression. Static compression is but one part of the puzzle. No way would I build a 318 with static of 10:1 and a cam as small as the the 268. But you go right ahead.
 
Did you look into the domed slugs? That would help a lot. As far as static compression ratio goes, you don’t want to exceed a 9.5-1 ratio.
Your better off at a 9.0-1. Milling the heads may still have to be done.

With your mentioned cam, 350+ HP cam be realized. That will make for a really nice driver with some get up and go.
 
RustyRatRod said:
Not what I meant at all, but go right ahead. HP can be reached by MANY other variables other than compression. Static compression is but one part of the puzzle. No way would I build a 318 with static of 10:1 and a cam as small as the the 268. But you go right ahead.
Click to expand...
Like I said I’m still learning so I don’t know anything about static compression, I’ll look more into it before I build the engine
 
Greenmachine225 said:
Like I said I’m still learning so I don’t know anything about static compression, I’ll look more into it before I build the engine
Click to expand...

I understand. Be careful is the number 1 rule. "I" would not go much past 7.5 DCR.
 
rumblefish360 said:
Did you look into the domed slugs? That would help a lot. As far as static compression ratio goes, you don’t want to exceed a 9.5-1 ratio.
Your better off at a 9.0-1. Milling the heads may still have to be done.

With your mentioned cam, 350+ HP cam be realized. That will make for a really nice driver with some get up and go.
Click to expand...
Do you have any recommendations for domed pistons, I haven’t looked into getting domed, I’ve just heard that the 167 pistons are good
 
Static ratio is just the simple math that you just need to know the numbers on to do the math. Google “compression ratio calculator “ and click on the “Wallace racing” site.

You’ll need to know a few things like cylinder head cc amount, gasket sizes, piston valve relief cc or some cc amount.
 
Do a search for "Cheep as dirt"...........similar build to what you are doing...use it as food for thought, an idea.......you can dial in your compression ratio by specifying chamber volume, deck height, head gasket thickness........work this out on paper, it's cheep, easy to do, you can run as many different senaraios as you have paper, when you find something you like, that's what you tell your machinist
 
Man I wish we could combine all the good information that has been written here in all the threads about 318's. It would save a lot of steps.
 
Here are some computed numbers for you, OP:

With the parts you originally described and typical 360 head chamber sizes of that year, your static compression ratio (SCR) with .028" thick head gaskets (Mr Gasket PN 1121G) would end up around 8.6. I would shoot for around 9.5 SCR for your first build. To get to that SCR number, mill the heads about .040-045" and don't mess with decking the block.

With that level of head milling, be prepared to change pushrod lengths. You might not have to do so, but then again, you might. You should also have the intake side of the heads milled by approx the same amount.

With that 268 cam, you will end up with a dynamic CR (DCR) of about 7.6. Those numbers will make it a fairly snappy street engine, with good low RPM torque taking off. It will not fall into the 'this is a dog' class of engines LOL

While I agree with MO about the 8+ DCR for a 'better' engine, IMHO staying more down in the mid 7's for DCR would be wiser for you with your 1st build. That will be safe to run on pump premium and not be too touchy to tune for a newcomer to avoid detonation.
 
I wouldn't go above 8 DCR for love nor money, if this is going to be a 100% street engine. humid hot day in the 90s plus idling in a traffic jam. No sir. Not me. You want to make DAMN SURE you can run on pump gas? Do like what's his face said up there in post #20. Want to build an engine that spark knocks at the WORST possible time? Then crowd the DCR to 8 or more and have at it!
 

MOPAROFFICIAL said:
Just make sure the dynamic isnt lower than 8.1 and not higher than 8.4.

Static compression can be 10. Or 9.5, just get a good dynamic=cranking psi.
Click to expand...

Remember though, it ain't everybody has perfect humidity free weather like you do in Southern Commiefornica. lol
 
LOL.... Well actually, humidity is your friend. Studies in the 80's showed that a hot humid day was the equivalent of adding 3-4 point in octane, versus a cool, dry day. It is those dry crisp fall days that are 'challanging' days

I ran 8.3 DCR for almost 100k miles in my iron-headed 351C, stock TC, a VERY small torque cam, and drove it daily, and even towed my rally cars with it. But it had quench, polished chambers, and, while I was not all that experienced, I WAS very careful with ignition timing. And, if I drove down to sea level , it would knock all the easier. I could make it knock but kept the ignition timing conservative to avoid that.

And the 8:1 DCR in my sons AL headed 340 with quench is a breeze to stay away from knocking at 1500' AMSL .

So yes, it can be done and not too hard if you are careful in tuning, but my impression in this proposed 1st build is that going lower on DCR is a bit better for the OP. Since the OP is near sea level, then that makes the idea of going lower in DCR a bit more compelling, IMHO.

Edit to add: OBTW, the OP lives in the land of 91 pump premium which, from all reports here, seems a bit worse for knocking problems. And, IIRC they change to 'summer blends' out there too which aren't supposed to be any good for higher CR engines. (Just repeating gossip on the last point BTW).
 
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nm9stheham said:
LOL.... Well actually, humidity is your friend. Studies in the 80's showed that a hot humid day was the equivalent of adding 3-4 point in octane, versus a cool, dry day. It is those dry crisp fall days that are 'challanging' days

I ran 8.3 DCR for almost 100k miles in my iron-headed 351C, stock TC, a VERY small torque cam, and drove it daily, and even towed my rally cars with it. But it had quench, polished chambers, and, while I was not all that experienced, I WAS very careful with ignition timing. And, if I drove down to sea level , it would knock all the easier. I could make it knock but kept the ignition timing conservative to avoid that.

And the 8:1 DCR in my sons AL headed 340 with quench is a breeze to stay away from knocking at 1500' AMSL .

So yes, it can be done and not too hard if you are careful in tuning, but my impression in this proposed 1st build is that going lower on DCR is a bit better for the OP. Since the OP is near sea level, then that makes the idea of going lower in DCR a bit more compelling, IMHO.
Click to expand...

You come down here on a hot humid day and say that. You'll change your mind real quick. I don't care what those 30 plus year old studies showed. lol
 
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