Positive Deck 318

[Garrett Ellison]

After seeing another 318 cam post, I thought I would ask about a 318 topic I would like to see get as much discussion. Has anyone built a positive deck 318 with flat top pistons similar to a 340 and what parts did you use to go about doing it? Even if it's finding a 318 block that will go to a 340 bore. I've got some ideas on my own, but I'm wanting to know if someone else has figured out a way for doing it on the cheap. Getting some piston volume into the chamber to make a 9 to 9.5:1 318 with 360 iron heads looks like a good possibility for a budget friendly performance engine.

 

[toolmanmike]

KB 167's?

 

[RustyRatRod]

After seeing another 318 cam post, I thought I would ask about a 318 topic I would like to see get as much discussion. Has anyone built a positive deck 318 with flat top pistons similar to a 340 and what parts did you use to go about doing it? Even if it's finding a 318 block that will go to a 340 bore. I've got some ideas on my own, but I'm wanting to know if someone else has figured out a way for doing it on the cheap. Getting some piston volume into the chamber to make a 9 to 9.5:1 318 with 360 iron heads looks like a good possibility for a budget friendly performance engine.

Here's you one to do some math on ole buddy. lol

DODGE KB KB399KTM-030 Keith Black KB Performance Hyper Piston and Ring Kits | Summit Racing

 

[RustyRatRod]

I know you said "on the cheap" but that ad I posted is pistons and rings.

 

[Ironracer]

I know you said "on the cheap" but that ad I posted is pistons and rings.

Darn it! Stuff really Ain't cheap, no more! That's actually a good deal, these days...

 

[RustyRatRod]

Darn it! Stuff really Ain't cheap, no more! That's actually a good deal, these days...

Pistons alone are 399. Not terrible.

 

[Ironracer]

No Sir, that is a darn good price! I have a 440 laying around, has Old TRW 11.5 forged pistons, when we pressed the stock ones out of the big rods, one got dropped outside during transit. Called em, they told me around 60 bucks... that was over 3 years ago.. wonder what it'll cost for one now? Hope I can get one. The piston isn't damaged, it has Aluminum exposure....Uhg

 

[72bluNblu]

As the owner of a 340 with over the deck pistons, I'd rather have a zero deck piston with a closed chamber head.

Hell, even my zero decked 318 with 63cc chamber heads is at 9.66:1. With a 65cc chamber that engine would still be at 9.44:1, and you can get to 65cc chambers with open chamber heads. The 308's on my 340 are at 65cc's.

 

[RustyRatRod]

As the owner of a 340 with over the deck pistons, I'd rather have a zero deck piston with a closed chamber head.

Hell, even my zero decked 318 with 63cc chamber heads is at 9.66:1. With a 65cc chamber that engine would still be at 9.44:1, and you can get to 65cc chambers with open chamber heads. The 308's on my 340 are at 65cc's.

I agree with that. "They say" flame travel "and all that" is best with a flat top, rather than dome or dish.

 

[Ted265]

Not finished but in the works, +0.060 KB167s 0.014" above deck. Will be running closed chamber alloy heads though.

 

[rumblefish360]

Here's you one to do some math on ole buddy. lol

DODGE KB KB399KTM-030 Keith Black KB Performance Hyper Piston and Ring Kits | Summit Racing

Those are the slugs that get you from here (low comp) to there! (High comp) 10.65-1 with the 6.3 domed pistons at 3.91 bore size, 4.180X.039 head gasket in a 65cc head chamber.
(A head gasket change to a 4.0X.032 would net you 10.98-1.)
Back to the larger gasket….
10.95-1 at a 3.97 bore. If you could stretch that 318 bore to 4.0, you’ll get 11.10-1. You’ll be at 332.76 cubes.
11.43-1 with the thinner head gasket mentioned above.
Now where getting some good squeeze in for a sizable cam for racing.

I agree with that. "They say" flame travel "and all that" is best with a flat top, rather than dome or dish.

While that’s true, depending on the end goal…..
David Vizard was saying no more than a .060 (IIRC) of a dome is OK to use. More than .060 and the flame front and it’s travels become compromised.

Goal dependent, it may be a necessary evil.

72bluNblu’s 318 example is a good one for a good street performer. At 9.66-1, your in good shape for a nice street cam.

 

[Garrett Ellison]

Thanks for all the replies! I'm showing that with the K-B 167's and a 9.6 deck that the pistons are .012 below deck. I've seen K-Bs listing for 318 deck height is lower than 9.6 (9.585), but I've always seen factory deck height higher than listed.

Not finished but in the works, +0.060 KB167s 0.014" above deck. Will be running closed chamber alloy heads though.

Did your machinist say how much had to be taken off the decks? What year of block are you working with there?

 

[Rat Bastid]

We live in a Chevy world. When Vizard is talking about a .060 dome he’s still living in the 1960’s and 70’s and looking at GM’s horrible plug locations. Low in the chamber, bad position relative to exhaust valve.

You can look at the very best NA stuff out there today and most of them are running a dome of .100 to .150 or maybe even a bit more.

They are concerned about flame travel as much as anyone else and yet they have domes. Does it increase the piston weight some? Sure does and yet they still do it.

The blanket statement that a dome of any size is a power killer is painting with far too broad a brush. The increase in power from the proper compression ratio far outweighs what little downside there is from a small dome. By far.

 

[69FBCuda]

So what is the advantage to popping the piston into the head vs switching to quenched heads?

 

[rumblefish360]

Dualy noted and agreed. It was a general and blanketing statement I made. Dome size and shape are just part of the equation considering the head chamber size and shape involved.

I did mention that it maybe a necessary evil. I agree, the added weight is nothing to be concerned about when you need to squeeze to get where you’re going in.

We live in a Chevy world. When Vizard is talking about a .060 dome he’s still living in the 1960’s and 70’s and looking at GM’s horrible plug locations. Low in the chamber, bad position relative to exhaust valve.

You can look at the very best NA stuff out there today and most of them are running a dome of .100 to .150 or maybe even a bit more.

They are concerned about flame travel as much as anyone else and yet they have domes. Does it increase the piston weight some? Sure does and yet they still do it.

The blanket statement that a dome of any size is a power killer is painting with far too broad a brush. The increase in power from the proper compression ratio far outweighs what little downside there is from a small dome. By far.

 

[Rat Bastid]

So what is the advantage to popping the piston into the head vs switching to quenched heads?

You mean a dome or running a positive deck to get quench?

 

[rumblefish360]

So what is the advantage to popping the piston into the head vs switching to quenched heads?

Popping a piston into the head? Flat top or dome?
Quench head?
Getting a quench is not a single style cylinder head issue but a matter of getting the piston and cylinder head chamber in a certain relation to each other. Commonly it is a flat top piston and the flat area of the head chamber.

 

[69FBCuda]

So a domed piston into a quenched head yields high compression vs a positive deck piston in a non quenched yields what? more compression with a stock head? I guess what I'm asking is why change out the bottom end when you could easily change heads.

 

[Rat Bastid]

So a domed piston into a quenched head yields high compression vs a positive deck piston in a non quenched yields what? more compression with a stock head? I guess what I'm asking is why change out the bottom end when you could easily change heads.

You build it right the first time.

 

[Garrett Ellison]

i.e. the word budget, when using heads with 340/360 sized ports. Not that you could reasonably expect to get close to quench (unless it's a 12:1 race gas affair, then run .027 gaskets and mill mercilessly!), but that's going to come in with a fresh bottom end for less than a set of worked budget aluminum heads.

 

[rumblefish360]

So a domed piston into a quenched head yields high compression vs a positive deck piston in a non quenched yields what?

A domed piston into any head chamber yields more compression. Get the idea of a “Quench head” out of your head. It’s messing you up. Think big chamber small chamber. The amount of quench is the distance and area of the piston in relation to the head.

Then….

A flat top piston that runs above the deck will yield more compression than a flat top piston even with the deck and even more when it sits below the deck. But how much each example yields requires a little math. The following is needed to know;

Bore size
Stroke
Head gasket thickness
Head gasket bore size
Cylinder head cc amount
Any cc amount in the piston. It could be a 6cc dome or 6cc valve reliefs
Then, where the flat of the piston sits. Below deck? At zero, (dead even) or above.

more compression with a stock head? I guess what I'm asking is why change out the bottom end when you could easily change heads.

Depends on the cc amount of the chamber vs what ever head your comparing it to. You could take a small chambered 318 head and mill it a lot. Let’s say we can take it down to 60cc’s. That’s an easy 5 less than a OOTB Edelbrock head. You could also take a W5 that starts out at 59cc’s and mill that down to 50cc. The iron W2 came in many versions. Some as large as 72 cc’s.

It all depends on what you have and where things sit.
Go over to Wallace racing -> Wallace Racing - Automotive Calculators
And play with there compression ratio calculator.

 

[72bluNblu]

Obviously domed pistons will give more compression than flat tops if everything else is equal, but everything else doesn't have to be equal.

For me, the easiest thing to deal with is a flat top piston. Makes the math easy and lowers your chances for interference. And can yield good compression numbers with open or closed chamber heads depending on what you're looking for. Especially if you're just looking for a good pump gas engine with 9 to 9.5:1 compression, you can easily do that without domes with lots of different heads.

The open chamber 340/360 heads run like 65-73cc for the chamber. But even the ones that are 73cc's can be cut down to 65. The 308's that I have on my 340 were 65cc's from the factory. They got up to like 66/67 with the bowl work for the 2.02/1.60 valves, and back down to 65 with a small cut to true them up.

Forget the quench numbers, the problem with the over the deck pistons is that if you want to change heads at any point most of the aftermarket heads are closed chamber. Then you end up with a piston to head interference issue, and you either buy the modified Eddy's for 340's (which puts you back with an open chamber head) or you run a really thick head gasket. My pistons are only .018" over the deck, and it makes a closed chamber head a problem, which makes most aftermarket heads a problem. Not impossible by any means, but it can get complicated. And if the goal is just a nice street engine there's no reason to deal with complicated.

With a flat top piston it's just easier to deal with, you can run open or closed chamber heads and set the exact compression with a reasonable thickness head gasket and/or a small cut on the heads, which they may need anyway if you're dealing with rebuilding 340/360 heads. And if you start doing anything with the heads other than a straight up stock rebuild, you rapidly approach OOTB aluminum head prices.

 

[toolmanmike]

Obviously domed pistons will give more compression than flat tops if everything else is equal, but everything else doesn't have to be equal.

For me, the easiest thing to deal with is a flat top piston. Makes the math easy and lowers your chances for interference. And can yield good compression numbers with open or closed chamber heads depending on what you're looking for. Especially if you're just looking for a good pump gas engine with 9 to 9.5:1 compression, you can easily do that without domes with lots of different heads.

The open chamber 340/360 heads run like 65-73cc for the chamber. But even the ones that are 73cc's can be cut down to 65. The 308's that I have on my 340 were 65cc's from the factory. They got up to like 66/67 with the bowl work for the 2.02/1.60 valves, and back down to 65 with a small cut to true them up.

Forget the quench numbers, the problem with the over the deck pistons is that if you want to change heads at any point most of the aftermarket heads are closed chamber. Then you end up with a piston to head interference issue, and you either buy the modified Eddy's for 340's (which puts you back with an open chamber head) or you run a really thick head gasket. My pistons are only .018" over the deck, and it makes a closed chamber head a problem, which makes most aftermarket heads a problem. Not impossible by any means, but it can get complicated. And if the goal is just a nice street engine there's no reason to deal with complicated.

With a flat top piston it's just easier to deal with, you can run open or closed chamber heads and set the exact compression with a reasonable thickness head gasket and/or a small cut on the heads, which they may need anyway if you're dealing with rebuilding 340/360 heads. And if you start doing anything with the heads other than a straight up stock rebuild, you rapidly approach OOTB aluminum head prices.

I always wondered if a flat top engine would work a little better because the flame front/combustion explosion is a more even force on the whole piston surface. Just spit ballin'

 

[Rat Bastid]

Obviously domed pistons will give more compression than flat tops if everything else is equal, but everything else doesn't have to be equal.

For me, the easiest thing to deal with is a flat top piston. Makes the math easy and lowers your chances for interference. And can yield good compression numbers with open or closed chamber heads depending on what you're looking for. Especially if you're just looking for a good pump gas engine with 9 to 9.5:1 compression, you can easily do that without domes with lots of different heads.

The open chamber 340/360 heads run like 65-73cc for the chamber. But even the ones that are 73cc's can be cut down to 65. The 308's that I have on my 340 were 65cc's from the factory. They got up to like 66/67 with the bowl work for the 2.02/1.60 valves, and back down to 65 with a small cut to true them up.

Forget the quench numbers, the problem with the over the deck pistons is that if you want to change heads at any point most of the aftermarket heads are closed chamber. Then you end up with a piston to head interference issue, and you either buy the modified Eddy's for 340's (which puts you back with an open chamber head) or you run a really thick head gasket. My pistons are only .018" over the deck, and it makes a closed chamber head a problem, which makes most aftermarket heads a problem. Not impossible by any means, but it can get complicated. And if the goal is just a nice street engine there's no reason to deal with complicated.

With a flat top piston it's just easier to deal with, you can run open or closed chamber heads and set the exact compression with a reasonable thickness head gasket and/or a small cut on the heads, which they may need anyway if you're dealing with rebuilding 340/360 heads. And if you start doing anything with the heads other than a straight up stock rebuild, you rapidly approach OOTB aluminum head prices.

You can still use the pistons that come out of the deck with a closed chamber head. You just mill down the quench pad for zero deck and then reduce the dome in the same way to get the compression where you want it if you have to.

 

[rumblefish360]

Gasket thickness and clay come to mind…..