318 combo help

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mopar79sean

mopar79sean

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I picked up a rebuilt 318 a while back and I'm not real sure about the combination of parts it has now and how well they fit with my project. I hope you guys can help me out.

So for the motor it is bored .060 over and has KB399 Pistons. Cast crank with stock resized rods. Fully balanced and assembled with ARP fasteners. It has ARP main studs.

No windage tray right now and the block has been Hard-blocked. Reciept says Hard-Block Tall 1/2 off. I'm not sure what that means perhaps somebody can chime in on that.

The heads are stock 587 heads with 1.88/1.60 stainless valves. No porting has been done. With these heads and the KB399 pistons I should be around 9.6 or 9.7 to 1 compression.

It has a Wieand Stealth intake. And a solid flat tappit Lunati cam. I'll attach a picture with the cam specs. I have crane gold 1.6 ratio roller rockers for it. I removed a set of pro comp 1.7 rockers from this engine. 68 340 drivers manifold and a 360 magnum passenger manifold ported to match the 340. 2.5 inch exhaust with an x pipe. Dynomax ultraflo's with 340 dart tips.

My main concern at this point is the cam I guess. It seems a little wild for what I'm building.

As for the car. 1970 Dart Swinger full street weight. Planning 3.55 or 3.73 sure grip 8 3/4 RMS streetlinx suspension. Around a 26 inch tall tire. Mini tub so I think I can squeeze in 12.5-13 inches of tire width. 833 manual transmission for now with dreams of a passon 5 speed eventually. If I get the 5 speed 3.91 or 4.10 gears may be an option. This is a street car that most likely won't see the drag strip but a few times. It will have A/C manual steering and manual brakes. Probably going with a quick fuel QFI for fuel delivery.

I think that's all the information that may be needed.

Advice on the cam would be very appreciated.
 

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That's a wicked little teen you got. It's gonna need some serious hardware to go along with it. 3500 converter, or 4 speed. 4.10-4.30 gears. You sure on that compression? That's a domed piston.

I see where you say it's a 4 speed. But IMO, 3.55 or 3.73 ain't enough.
 
I'm not certain on the compression. I haven't cc'd the heads or motor. The 567 heads run about 72 cc and those KB Pistons say 10.4 for a 68cc chamber head. I'm running a manual transmission. I think the cam is a little much for how I will use the car.

I was considering going solid or hydraulic roller on a custom grind as this cam seems a little radical.
 
I guess the other thing is the exhaust manifolds. I really don't want to mess with headers for this car. I don't think that cam will like being choked by the manifolds.
 
Thing is, if you back off on the cam much at all, it won't be a pump gas engine anymore.
 
RustyRatRod is it the compression ratio that will keep me from running a milder cam? I'm not sure how far off I could be with the compression number I gave. From what I've been looking at it should land under 10 to 1 with those heads and Pistons. Is there something I'm overlooking?
 
mopar79sean said:
RustyRatRod is it the compression ratio that will keep me from running a milder cam? I'm not sure how far off I could be with the compression number I gave. From what I've been looking at it should land under 10 to 1 with those heads and Pistons. Is there something I'm overlooking?
Click to expand...

Yes. As you go down in cam size, cylinder pressure increases because the intake valve closes earlier and earlier in smaller cams so that builds more cylinder pressure.

You cannot run much over 9.2:1 on pump gas with iron heads and no quench. Certainly not 10:1 or close.
 
It sounds like I should pull the heads and cc the chambers. I know factory castings can vary a lot. Perhaps I should look into aluminum heads?
 
The aluminum head option will help only a little. Even less if you go down in cam size.
IMHO, that teen is set up to kick some *** minus the head is and exhaust. If it were myself and I had the funds to complete the package for some brand X *** kickin, it would be the aluminum heads well prepped and bowl ported with a set of to headers into an2-1/2 exhaust. I would certainly used a 1.6 roller rocker!

The tti's will work great. Very good clearance and fit.
 
I'm into this motor for around $500 right now. I could invest some money to make it a better performer. TTI headers are an option and I'll look into some aluminum head options.
 
RustyRatRod said:
Yes. As you go down in cam size, cylinder pressure increases because the intake valve closes earlier and earlier in smaller cams so that builds more cylinder pressure.

You cannot run much over 9.2:1 on pump gas with iron heads and no quench. Certainly not 10:1 or close.
Click to expand...

RustyRatRod is the compression ratio you are talking about static or dynamic? I'm learning as we discuss this. Thank you for your input.

I ran some number through the calculator on Keith blacks website. I'll attach a picture of those numbers. Of course these are hypothetical numbers based on a best guess of how the motor is set up. I really need to pull the heads and "blueprint" the top end of the engine.
I think I've input the numbers correctly.
 

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I was referring to static. But that is still too much dynamic compression. It needs to be under 8:1 to be assured of no spark knock on pump gas. Now, if you had aluminum heads and or some quench, you could go more. But like Rumblefish said, even still you would be pushing it.
 
I have run that ratio with iron heads and anPurple 292/.509 Hyd. On 93 octane. I don't know if you can do less octane. Take your time tuning the carb and distributor in.

The move to closed chambered heads IF your Pistons will clear the closed chamber will go up a point close to about 11-1, give or take.

I'm running a 11-1 / 360 now. Flat tops and Edelbrock heads. The cam is a sizeable solid cam for the street.
 
Yeah well the 508 Mopar cam is a cylinder pressure killer so you can get by with more. lol
 
Your main concern being to wild of a cam and your mini tubing?
Would It Hurt to run what you have now and ajust if needed?
 
j par said:
Your main concern being to wild of a cam and your mini tubing?
Would It Hurt to run what you have now and ajust if needed?
Click to expand...

My main concern was the cam and if it was too much for this combo for a street driven car that will rarely see track time.

We are finding out dynamic compression ratio is a little higher than desired for a street car on 91 or 92 octane.

The mini tub isn't a concern it was a detail about how the car is set up. I guess I thought too much information is better than not enough.
 
With a 318 we are normally trying to figure out how to get the compression up not how to get it back down.

So from what I'm learning so far the dynamic compression ratio of this motor is really too high for pump friendly performance on the street. I need to do everything I can to get that back down as close to 8.1 as I can.

I looked at several aluminum head options and so far all options are closed chamber heads with 65 cc chambers or less. This is going in the wrong direction even with the advantage of aluminum heads. These pistons won't work with a closed chamber head as far as I know.

The iron heads on the the engine now by design are open chamber 72cc heads. According to my web research the chamber volume can vary quit a bit. I read anywhere from 70-76cc.

I think I can gain some volume by going to 2.02 valves and de-shrouding the cylinders. This would also give me the chance to do a nice port and polish and bowl work on the heads.
I could gain some more volume by running a thicker head gasket. I found a flow comparison chart that list this head stock flow and fully ported. Even ported the numbers aren't that impressive but they probably aren't too bad for a street driven 318.

The next item to look at to improve the dynamic compression ratio is the cam. Thanks to Rusty I started to look into this a little more. The important variable for dynamic compression ratio for the cam is the intake closed ABDC. Some cam grinds bleed off more cylinder pressure than others. The current cam does a decent job of bleeding off cylinder pressure but I may find another that will do better.

It looks like this "bargain" engine is turning into a little challenge to make it a pump friendly street performer.

Again thanks for the help guys. Keep the comments coming.
 

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I'll try again on that flow chart. It's a little blurry for me.
 

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RustyRatRod said:
Yeah well the 508 Mopar cam is a cylinder pressure killer so you can get by with more. lol
Click to expand...

Ain't that the truth.

Sorry if I missed this but what thickness head gasket are you running?
 
Re run the calculation with a .055 head gasket. There avilable.
 
Sean, I took the liberty of fixing the chart a bit, I hope it's more legible now.
 

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