Newbie 318 piston question

[mech1nxh]

??? willrun318 ???

 

[Garys72Duster]

I hear ya! The builder must have planned on building a strong running engine, it looks like. It has roller rockers, and receipts show a hyd cam, the CRS XE274 H 10 Cam and lifter set, ordered thru Mancini in 2007. Probably will be needing some kind of octane booster in this one!

 

[AJ/FormS]

big cams do not automatically mean hi-octane gas.
It's all about heat in the combustion chamber, and the presence or absence of hot spots. Cylinder pressure is a big part of controlling it. This does NOT automatically mean Compression Ratio, altho that's a part of it. As is elevation, inlet air temp,coolant temp and AFR.
With a given compression ratio, pressure actually drops with the later-closing intake valve, of a bigger camshaft.

 

[rumblefish360]

Hence why the compression ratio is raised to compensate and high octane used for when it’s needed later when the engine starts to make power in its operating RPM band.

 

[waldune]

That is an interesting question, worth looking into.

Like the high compression height of those, would have to be used with the open chambered heads. With those valve reliefs looks like cam selection won't be a problem as far as interference is concerned.

The harder to find factory mopar pistons have a compression height of 1.78 ch sitting .040 ths down in the hole which is pretty good for factory pistons.

Aftermarket stock replacements can be 1.755 ch.

These KB399 have a 1.81 ch sitting .010 above deck.

View attachment 1715565112

View attachment 1715565120

Was lucky enough just by chance to pick up a fresh set of 318 open chamber heads at a swap meet a few years back. Did not realize until looking at them lately here that someone had installed 360 valves in those 318 heads.

So yes, this could make an interesting combination too with the KB399 pistons.

Think stock 318 open chamber heads, a mild cam, and the KB399 pistions would wake up a basic 318 engine.

Although the factory 1.78 ch flat top pistons were able to produce 9.2:1 cr @ 230 hp, stock heads, that's with a 2 bbl carb.

Looking like the KB399 pistons with 68 cc open chamber heads are rated at 9.2:1 cr too.

KB399 have the higher compression height of 1.81 ch, but maybe they are loosing some chamber volume with those big valve reliefs. Don't Know ??

Worth looking into . . .

I run closed chamber 920 heads, they did not contact but I did shave down a small space for the spark plug so they look like 340 high comp pistons now. I have used jb 167’s with the 302’s before. And also, 360 valves HURT POWER on a 318, tbe valves are too shrouded by the cylinder unless you notch them and hurt compression. Even the 302s have this problem; on a flow bench the 318 NOT anything larger like the 340 make the most streetable power (up to 500 crank) 920 castings from the 273 and first two years of la 318 have the highest port velocity and make the most power compared to any other OE head. If you’re using boost this isn’t for you; if you want a drag car this isn’t for you but up to 500 crank they are hands down the best. Make sure it’s the first 2 years of 318 production because before that they have a small bolt intake pattern unique to the 273 and you’ll never find the intake you want

 

[Dartswinger70]

Isn't there something about big valves in that sub 4 inch bore also? valve shrouding etc.? This is the thing for me its always a reengineer a turd game with 318s. the only reason they were good to me back in the day is they were cheap and plentiful direct bolt in swap with a 340 if you needed a temp motor while rebuilding the 340. they made millions of the van/truck/station wagon motors.

 

[mygasser]

why do people still go on about valve shrouding using bigger valves/ 340/360/aftermarket heads on a 318? the bore is only 90 thou (stock) smaller than the 'majic' 4" bore of a 360 which is only 45 thou (spark plug gap for reference) closer to the inlet valve. even with the added compression drop of fitting 340/360 heads to an already low compression 318 it's been proven many times they make more power. so what's the problem?
318 bashing maybe? oops, did i say that out loud?
neil.

 

[Dartswinger70]

why do people still go on about valve shrouding using bigger valves/ 340/360/aftermarket heads on a 318? the bore is only 90 thou (stock) smaller than the 'majic' 4" bore of a 360 which is only 45 thou (spark plug gap for reference) closer to the inlet valve. even with the added compression drop of fitting 340/360 heads to an already low compression 318 it's been proven many times they make more power. so what's the problem?
318 bashing maybe? oops, did i say that out loud?
neil.

Theres nothing majic about it. Every successful performance small block out there from any US manufacturer in the classic era has at least a 4 inch bore. Now you all of a sudden know better than the folks who designed those engines? You do see what Vizard and Andy wood are going through trying to make a 318 into a performance engine no? they've hit a wall fairly quick.

 

[toolmanmike]

Use the big valve heads and notch the bore to help the shrouding issue. I think the notches are more for valve clearance than shrouding. The notches I have seen don't look like they do much at all.

 

[MOPAROFFICIAL]

Hi everyone. I'm just curious as to the reason why more people don't use or recommend the kb399 domed pistons as a easy way to boost compression in their 318 builds. Lack of compression seems to be the biggest hurdle to fix when building a 318. Just curious I'm sure there is a reason. Thanks.

Lack of octane is and tuning skills could be a possible reason.

Most motors w/9.5 compression and or cranking around 150-175 psi make plenty of power ..and while the low/mid tq would surely benefit from more squeeze.. we return to my first statement..

 

[Dartswinger70]

There are way too many hurdles with a 318... once you clear one there is another. Yes its great if you have a bunch of parts laying around and a machine shop and plenty of time for trial and error. Guys get excited because of the same crank dimensions as a 340.
you know even back when i was a kid the misinformed would say "a 340 is a 318" its funny to me that it still goes on now.

 

[Dartswinger70]

Use the big valve heads and notch the bore to help the shrouding issue. I think the notches are more for valve clearance than shrouding. The notches I have seen don't look like they do much at all.

I believe it applies only at high rpm no? like that's where the airflow in the cylinders would be effected. i bring this up because with the 340 heads 6000 rpm was the goal to be met. they had an advertisement for the 340 Swinger in 69 and 70 that read 6000 rpm all day for $2800 its a quick throttle response RPMs up quick plenty of torque and HP throughout up past 500-5500 RPM. that was 340 i think when building a 318 this has top be acknowledged that's why the big valve heads and shrouding come up in a serious conversation I would think at the least there would be turbulence at high RPM disrupting the airflow etc. Im guessing in a 318 well below 6000 RPM

 

[mygasser]

Theres nothing majic about it. Every successful performance small block out there from any US manufacturer in the classic era has at least a 4 inch bore. Now you all of a sudden know better than the folks who designed those engines? You do see what Vizard and Andy wood are going through trying to make a 318 into a performance engine no? they've hit a wall fairly quick.

no all of a sudden at all. check out the bore sizes of gm ls motors. the 4.8,5.3 and 5.7 are all from a lot to a bit smaller than a 318. nobody says they can't perform with small bores do they? my point was the 318 isn't much smaller than the 4" bore everyone seems to think is the benchmark for performance

 

[Dartswinger70]

no all of a sudden at all. check out the bore sizes of gm ls motors. the 4.8,5.3 and 5.7 are all from a lot to a bit smaller than a 318. nobody says they can't perform with small bores do they? my point was the 318 isn't much smaller than the 4" bore everyone seems to think is the benchmark for performance

318s are fun if you like being at around 200 Horsepower. 200 horse is fun but it isn't scary fun. Id like to see 300 horse 318 build and the receipts on how much it cost. You know people would buy a 340 car before the low compression engine came out and take it to a tuner and get 300-325 horse easily with a stock motor. Maybe they'd swap a cam in. it didnt take much, it takes alot with a 318. Im speaking of cost specifically.

 

[273]

Cost has a lot to do with circumstances, you could easily pay a $1000 for a rusty 340 block.

If starting just from a block the parts are gonna be similar and same with cost.

 

[George Jets]

Surprise > Look what I found on a stock 318 roller engine with the bore scope.

Just checking things over as it has great power, get up and go.

It also has the 1406 4 bbl and the hot fire E-Core coil ignition on top of it being 9.2:1 302 headed original engine.

324 cubic inch cramming into the 318 combustion chamber raising the compression ratio to 9.5:1 with the .040 over bore.

Good way to make more power on the 318s.

By the way, the hot fire ignition has burnt back the carbon deposits on the piston tops over the last year, 90,000 mile engine. Now I can read that it has a .040 over bore, leaving carbon in the marking spots yet so that I can still read it with the bore scope.

Exhaust is just as clean as that spark plug.

When it was the smog running engine, everything was burning black > piston tops, plugs, out the tailpipe too.


edit:

This last picture is after I set the timing back to 8° BTDC because the hot fire ignition is burning so fast that it is advancing the ignition by 4° putting it right at the factory setting of 12° BTDC.

Amazing.....


☆☆☆☆☆

 

[Newbomb Turk]

why do people still go on about valve shrouding using bigger valves/ 340/360/aftermarket heads on a 318? the bore is only 90 thou (stock) smaller than the 'majic' 4" bore of a 360 which is only 45 thou (spark plug gap for reference) closer to the inlet valve. even with the added compression drop of fitting 340/360 heads to an already low compression 318 it's been proven many times they make more power. so what's the problem?
318 bashing maybe? oops, did i say that out loud?
neil.

Exactly. The valves open on the centerline of the bore. You can use a 2.055 valve on a 318 and they aren’t shrouded.

It’s a giant crock of ****. And why most 318 builds are embarrassing.

Plus, running a piston with tractor rings just doesn’t make sense.

 

[junkyardhero]

This last picture is after I set the timing back to 8° BTDC because the hot fire ignition is burning so fast that it is advancing the ignition by 4° putting it right at the factory setting of 12° BTDC.

can you explain this and define what a "hot fire ignition" is?

 

[krazykuda]

Isn't there something about big valves in that sub 4 inch bore also? valve shrouding etc.? This is the thing for me its always a reengineer a turd game with 318s. the only reason they were good to me back in the day is they were cheap and plentiful direct bolt in swap with a 340 if you needed a temp motor while rebuilding the 340. they made millions of the van/truck/station wagon motors.

I've run 2.02" intakes in 318's for decades with no problem...

If you are going to run 340/360 heads on the 318, it's good to use10.5:1 compression pistons on a street engine to keep your compression up to a level where it is more efficient... 340/360 heads on a stock 318 piston engine will make the compression down near 7.5... 10.5:1 compression pistons on a 318 with 340/360 heads will bring you near 9 1/4 compression...

 

[mygasser]

I've run 2.02" intakes in 318's for decades with no problem...

If you are going to run 340/360 heads on the 318, it's good to use10.5:1 compression pistons on a street engine to keep your compression up to a level where it is more efficient... 340/360 heads on a stock 318 piston engine will make the compression down near 7.5... 10.5:1 compression pistons on a 318 with 340/360 heads will bring you near 9 1/4 compression...

no worries about finding decent gas then at 7.5:1

 

[273]

why do people still go on about valve shrouding using bigger valves/ 340/360/aftermarket heads on a 318? the bore is only 90 thou (stock) smaller than the 'majic' 4" bore of a 360 which is only 45 thou (spark plug gap for reference) closer to the inlet valve. even with the added compression drop of fitting 340/360 heads to an already low compression 318 it's been proven many times they make more power. so what's the problem?
318 bashing maybe? oops, did i say that out loud?
neil.

When you look at the out comes of similar 318/340/360 builds I don't see a huge hp difference so for a general build 318's valve shrouding don't seem to make much difference, people over worrying theory over practical again.

 

[mygasser]

When you look at the out comes of similar 318/340/360 builds I don't see a huge hp difference so for a general build 318's valve shrouding don't seem to make much difference, people over worrying theory over practical again.

agreed a 318 can make similar power, it just needs more.... cam, compression, revs.... more

 

[Dartswinger70]

You know 20 years ago I bought 71 318 and 904 air cleaner to trans pan for $40 that was scrap price then

 

[junkyardhero]

I was thinking about the comment "the 4 inch bore doesn't matter" or something similar as conveyed. For the sake of argument I agree with that however newer LS was mentioned that is a dual overhead cam 4 valve engine correct? Now a pushrod engine with 2 valves inline ha the 4 inch bore to accommodate the 2.02/1.94 valve sizes there's no denying that that's why engines like 327/340/289/302 were the small blocks in the pony cars. 300 horse was the target for the street in those engines . Now how difficult is it getting a proven 300 horse out of a 318 and how much does it cost?

the LS is a conventional pushrod V8

i posted a 330hp 318 recipe above. you're more than welcome to go shopping and do the math.

 

[Dartswinger70]

Has anyone tried using 273 hip recipe on a 318? closed chamber heads the 273 type piston etc? I think Uncle Tonys 318 had the closed chamber head the one in the 72 Coronet. Knowing him though he probaly had flipped down in the hole 318 pistons need to get the pistons up and cut valve releifs etc.

318 can be fun when trying to figure this out always seems to be a hurdle though with the LA 318
1. The block cant be bored to 4 inch
2. the down in the hole pistons with pressed wrist pins and somewhat limited selection of pistons
3. the heads
4. the compression ratio in general
5. the low rpm powerband

now looking at this why not try and eliminate some or all of it by using a different engine?

seems like common sense no? i think a 273 commando eliminates 3 off that list
1. the down in the hole pistons
2. compression ratio
3. the rpm/power band

340 we just wont go there no need to i think(hope) someone will get it.