Dual plane vs. single plane for a 318.

[Smoke20]

I'm sure that I'll get a few   jokes about this, but most of the threads here pertain to the big block 383 and 440s.  

I have a small block 318 with a cast iron 340 manifold, and an Edelbrock 600cfm carb. I plan on getting ceramic coated Hooker super comp headers and a full exhaust this spring.

I've read here that my manifold is not a good choise because of turbulence due to the difference in the port size. So what type manifold should I get, dual or single plane? What's the difference anyway?

[Plumcrazy]

Stick with a dual plane. You will get better low end torque and throttle response.

[Chryco Psycho]

If you can find the LD4b intake that has the smaller 318 port size , some later cop caravelles have the 318 4 bbl from the factory so you may be able to find one of those too

[Smoke20]

So I guess a dual plane is better for the low end and a single plane isn't?

[Plumcrazy]

So I guess a dual plane is better for the low end and a single plane isn't?

Correct

[Plumcrazy]

If you can find the LD4b intake that has the smaller 318 port size , some later cop caravelles have the 318 4 bbl from the factory so you may be able to find one of those too

I'm thinking those later manifolds were for spreadbore type carbs but I could be wrong.   If so you will need an adapter to run a Holley or Edelbrock carb.

[cudaken]

 Smoke, every think about doing 360 heads? I heard they will work with a 318.

Now what the hell is a caravelle?

                      Cuda Ken

[Plumcrazy]

Smoke, every think about doing 360 heads? I heard they will work with a 318.

Now what the hell is a caravelle?

                                Cuda Ken

I'm thinking thats what they called the Diplomat/Fifth Avenue in Canada

[Ghoste]

Kind of.  It was the Plymouth version of the Diplomat up here.

[Smoke20]

Smoke, every think about doing 360 heads? I heard they will work with a 318.

Now what the hell is a caravelle?

                                Cuda Ken

Ya know, I haven't thought about that. I'm not a mechanic, so what would 360 heads give me? More low end torque or high end HP or both? And what's this squarebore and spreadbore mean?

I need to be edumacated!

I just want this car to be a ballsy weekend cruiser. It has to be relatively affordable as I have a wife, mortgage and three kids that come before the mopar.

[79JON]

Id go with a Dual Plane as said before.   Ive got a 318 and put a Edelbrock Performer on there with a 600 carb.   Thats with the stock 318 heads.   You've got to get every bit of torque you can get out of the 318 and a Dual Plane is the best.   Ive also wondered about putting 360 heads on a stock 318 long block.   Does it make a big difference or is there not much of a difference??

[Chryco Psycho]

360 heads on the 318 work OK , But it sofens the bottom end power & drops the compression a bit as well , iiif you are going to use the 360 heads I would recommend the 308 castings used in 87-92 trucks

The Caravelle was the Plymouth version of the Diplomat

[Ghoste]

Squarebore is a carb that has four venturis the same size.  A spreadbore has small primary bores to give better economy and throttle response and large secondaries to let the engine breathe when it needs to make power.  There are intake manifolds made to accomodate both styles of carbs.

[cudaken]

 You could cut the heads a little to bring up compression. When I drove 318's what I did not like was there lack of top end, power fell of fast after 4000 RPM's.

Neil knows better than me, but I think the 69 4-speed 340 cam would work well with the 360 heads.

But what ever you do Smoke, dont go by what I say alone! I have read about the LA engines but all I have ever done to one was stick on a fuel pump. I am a BB guy my self.

                                                         Cuda Ken

[Plumcrazy]

Squarebore is a carb that has four venturis the same size.   A spreadbore has small primary bores to give better economy and throttle response and large secondaries to let the engine breathe when it needs to make power.   There are intake manifolds made to accomodate both styles of carbs.

I liked the spreadbores.   Flip the air cleaner lid upside down and those things would sound like they were going to suck your hood down through them

[grouseman]

I've been down all the roads you're talking about with my 318. 

You need to make a decision right now.  Do you want a responsive, torquey street engine, or a wide-open throttle all-the-time race engine? 

WOT race engine: In addition, you'll need to change the torque converter to something looser to get the engine's rpms up at launch.  And you'll likely have to get the rear gears at least down to 3.55 or lower.  Headers and dual exhaust to open up high-revving power.  So there is just as much extra expense after doing your engine changes.

For a responsive torquey street engine, you're on the right track, and have pretty much all the ingredients.  The factory 340/360 intake is an excellent design and hard to improve upon.  There was no such thing as a 318-specific 4 bbl manifold, they just used the same 360-port manifold onto the 318 heads.  The port mismatch is not something to worry about for a street car.  The Edel Performer intake has smaller ports and it will give similar performance capability.  The LD340 is a BIG racing dual plane; it'll kill your low-end throttle response.  The early 340 intakes were bored for square bore carbs like the AVS, AFB and your Performer.  Later intakes were drilled for Thermoquads.  TQs are better performers all around vs the older square bores, but what you've got will work well. 

I don't recommend 360 heads for this type of setup, especially the older style. You will IMMEDIATELY lose significant compression due to larger chambers.  This also kills low end response and you ONLY see a benefit on top-end breathing.  You could mill the heads (and the intake face) to gain back compression, but then you risk too much lifter preload (another topic) as you've brought the rocker arms closer to the cam.  It's not worth it.  Leave the 360 heads to 360s or racing 318s.  A better bet (again for a street engine) is to consider having the 318 ports cleaned up with a 3-angle valve job and open up the bowl area, maybe better valves.  A little clean-up cut, to bump compression a bit, won't throw any of the geometry off.  This route will give you a little better c.r. and better flow without the need for big, slow-moving ports.  Money spent on heads is money well spent. 

As good as the 340 camshaft is in the 340 and the 360, it is a 35+ year-old design.  And it was designed with 10:1 compression and the rest of the drivetrain in mind.  Consult somebody like Comp Cams or Hughes Engines for a modern design for your combo.  Get their recommendation, and then ask about the cam one step BELOW that.  It is better to be slightly conservative on the cam choice rather than the other way.  Upgrade the valve springs, mandatory, and the timing chain.  Even with the stock bottom end, the factory rockers with a modern cam and new springs should take you above 5,500 rpm without a problem. 

Remember that the intake valve closes as the piston is going up.  That means you're not taking in or compressing a full 318 cubic inches worth of air, but something less.  Let's say your stock cam actually compresses on 280 cubic inches at lower rpm.  The longer-duration 340 cam closes further up the stroke (pushing some air back out - reversion) so it only is compressing 255 cubic inches.  That's a 10% loss in low-end torque.  Granted, it will make up for it on the top end IF that's where you wish it to be and have built everything else the same way.  If you coupled a 340 cam and uncut 360 heads on a stock 318, you'd have an absolute dog off idle.  Believe me. 

Spend the time to learn about the mechanical and vacuum advance curves and how to alter them.  Trial and error, test and tune, and you can get big results.  Ignition is very important.  Every factory adv. cannister that has a hex shape towards the vac nipple is ADJUSTABLE via an allen wrench (forget the size).  This won't cost any $, except for maybe lighter springs.  Don't forget to learn how to jet your carb properly. 

Headers help above 2,500 rpm (thereabouts) and hurt below.  And ceramic coated headers sound $$$.  They also add heat and clearance problems.  You decide.  Do the full dual exhaust for sure, and have an H or X crossover installed.  The exhaust will sound much better and it will help low torque as well. 

Wife, mortgage, kids, I hear ya.  But you're very close.  Cam, lifters, spring, timing chain.  Distrib springs.  Carter/Edelbrock carb jetting kit.  Full dual exhaust.  Head port/bowl work.  And you'll have a nice torquey package. 

grouseman

[cudaken]

 He, He, He Smoke, I bet what you have is starting to look pretty good to you right now!

We are real good at spending other people money

Buy a 50 HP NO2 set up and never come back to the site, yoy will be happer in the long run.

Talking about the snowball effect. I staterd out looking for a 6_pack set up and wound with a $12,000 boat anchor with a Blower.

                                   Cuda Ken

[grouseman]

Cuda Ken has a real cautionary tale, that's for sure.  But you're very close to a reasonably responsive street engine, and you can do it in stages. 

First, hook up the dual exhaust, as that gives good bang for the buck and you can always put header$ onto it later if you wi$h. 

Second, get a jetting kit and play around with it to learn how it all works.  Learn all you can about changing your distributor curves as well.  This is cheap/free and you will learn a lot along the way. 

Next, you could do either the cam or the heads, depending on your time and money.  But neither will reach their full potential until the other is done as well.  Remember, you don't want to hog out the port or put in giant valves.  Maintain port velocity and go for smoother flow as the focus.  While you're there you could have the ports bevelled out to the 340 intake ports. 

None of these changes will put you into the radical side of things, you're staying well within stock parameters.  So you will not need to change anything in your drivetrain like converter or gears.  If you're running 2.76s, you'll still have good response off idle and power throughout, but it will not let you get into the upper rpms very often.  A switch to 3.23s (or 3.55 at most with this combo), will really wake things up.  The 3.23s give a 17% increase in torque multiplication - equivalent to a 372 cid engine!  Again, this would be my only drivetrain recommendation, and you may already have 3.23 gears. 

Good luck with it!

grouseman

[Smoke20]

Wow! There's alot to digest. 

I definately want to go the route of a torquey street machine, so from what you've said Grousman, I should stick with my 340 manifold, do the headers/exhaust and a jetting kit. The $$$ saved on not buying a new manifold can help level the expense of ceramic coated headers.
Then I can get the heads/cam done later. The cam looked after market when we put the 340 intake on it, but I have no idea what it is in terms of lift/duration.

I'm not sure what gears are in it now, either. How do I find that out?

[Chryco Psycho]

jack upo the rear of the car & see if there is a tag on the diff OR rotate the driveshaft & count the nuber of turns to get a full rotation of the tire , [both tires must turn equally for this to be accurate ]

[Smoke20]

jack upo the rear of the car & see if there is a tag on the diff OR rotate the driveshaft & count the nuber of turns to get a full rotation of the tire , [both tires must turn equally for this to be accurate ]

Cool. I think I got it. So if it takes 3 and a half turns of the drive shaft to equal one full rotation of both tires, then I would have 3.55 gears. If it's 2 and three quarters it would be 2.75 gears, etc.

Here's for hoping for a pinch more than 4 turns!