Technical LA 318 and getting proper quench, possible?

^^^^yep, in between working, been searching. Can’t find a solution without too much compression.
So will stick with itthe way it is, at a minimum square the decks, and run it.
Thanks all.

 

You can get your 225 HP with the pistons down in the block, your existing heads with a custom camshaft. Its been done to death on the For A Bodies forum. As mentioned, there is no quench to be had on those heads unless you go for custom pistons. Bullet Cams or Oregon Cams can set you up with the custom cam but if you do a search on the abovementioned forum you will become more informed of a low-compression 318's potential. If you decided to change cyl heads then:
https://www.speedmaster79.com/Mopar...-65cc-Hydr-R-Complete-Aluminum-Cylinder-Heads. Today is the last day and yes they are on back order but the price is attractive.

 

Minimal quench allows for higher compression without detonation.
Quench is a by-product of design.

There really is no such thing as quench on some engines like Hemis or full open Chamber Heads [except for the dead space by the head gasket O-Ring]

A lot depends on your intended usage?
The engine doesn't care about compression ratio's only cylinder pressures.

If you're building a high-perf engine you need higher static compression to offset cylinder pressure losses from valve overlap.
If you're building a daily "shopping basket" leave the static compression low and try and shorten the duration/overlap in the cam timing [cylinder pressures will go up]
The smaller cam will fall on it's face as rpm climbs, but will pull better from "off idle" [a small 4 barrel carb will offset some top end breathing issues]

This ^^^^ is why Truck engines are lower compression and most Luxo Barges have low compression and matching high rear-end ratios

For a goal of 225 hp aim at 262 ft/lbs at 4500 rpm. AND if possible 310 ft/lbs at 3800 rpm [which is quite achievable and a nice flat power/torque curve]
You would only need a 420 cfm Carb

Just use you existing open chamber heads and do a competition valve job and start looking for the highest lift and shortest duration cam available.



If you're thinking about buying 318 Magnum heads
Buy a whole 318 magnum engine from a junkyard and refresh it. [install KB pistons while you are refreshing it]
You get magnum heads and stud 1.6 rockers AND roller cam.

You will need a magnum specific intake or re-drill the heads for earlier bolt angle.

You will be miles ahead of the game using a cheap 5.2 [318] Magnum

 

I have a '73 318 in my 2200 lb '24 Dodge Brothers Roadster. Stone stock 2 barrel engine. 904 auto, 3.21 gears. Runs REALLY strong which surprised me. That engine is going to come out and go in my '62 Lancer that I have a tired 340 in, then the Lancer is going to go to my oldest daughter. The 340 will get freshened up and go in the roadster.

Years ago Dad and I built a 318 to run in or '71 340 Duster circle track car until we had a 340 done to go in it. Ran '67 small chamber heads, with stock 318 piston turned around to straighten the piston throw, 340 cam, double roller timing chain and a windage tray. 4 barrel iron intake and Holley 4barrel carb. Made compression ration about 9-1. Ran like crazy! Run like a 340? No, but not bad at all.
When Mopar finally put a 4 bbl on 318's they used the 340/360 intake with the large ports which mismatch the small 318 ports but that still works rather well! Been there done that. 273 4 barrel intakes have smaller ports but also work ok. Edelbrock LD4B intakes are perfect for 318.
Mopar windage tray gains about 20 HP for very little money. 340 cam is excellent.
Don't run the big 340 heads.
Mopar should of done like Chevy and do a power pack engine with the 318. They had all the parts!

Dave

 

What would be considered "good" fuel mileage with a carbed V8 running around town, or even on the highway?
I didn't (and still don't) drive my stuff chasing MPG, but back then, around town was in the 13-15 mpg and highway was 20-21. About the same as my current EFI 5.2 Magnum with the OD trans in my 4x4 truck.

If you kept your foot out of the secondaries, the low buck improvements you make for performance improvement are the same things that would improve the mpg.

Most modern EFI V8 motors are lucky in the 15-16 range in town, and mid 20s on the highway, most of which is because of the good rear end gear for around town, and the OD and lock up trans for the highway. Most of those modern cars/motors that claim the great mpg have less CID then a 318.

For the record, the cost of fuel in my town is lower now then its been the last 4 years.

 

Well, let me ask for a comparison sanity check.
Open chamber heads with a flat top piston vs a closed chamber head with a dished piston.
Would either of those two be worse/better than the other?
When I pulled the last SBC apart, 62/3 CC heads, dished with 4 valve reliefs.
I think the total dish with the reliefs was in the 16-18 CC range.
Ran fine. SCR advertised at 9.2:1 if memory serves.
So if I was to deck the block, run a flat top piston with this 318 and open chamber heads, could I expect similar with a 9-9.5 ratio?

 

Does anyone make a dished piston for a 318 ?

Or something else, that would fit ?

 

Sounds like you have an engine that is basically ready to go , relube, new gaskets etc. . If it was mine I would add a cam to perform as I wanted and run it, also use a thinner head gasket to gain a smidgen more compression. Any cam grinder worth his or her salt should be able to get you a cam to meet or exceed your power and economy expectations. Oregon cams, Hughes engines, or Mancini racing are good sources for Mopars as well as Isky, etc etc.. One good thing about Mopars are the large diameter lifters , can handle fast rates of lift, also I believe just about any performance cam for the 318 will require corresponding springs.
Happy motoring
Dan

 

Flat tappets are a bit of a crap shoot lately.
If you have to, research "break in oil".

 

Between .060” and .100” piston top to head quench area is bad for detonaton. Either machine to get .050” or less or stay over .100” and detonation chances are lessened. Compression in the mid 8’s with no quench can run really well with a short duration cam with good lift and lobe separation of 108-110. Keep overlap low.

 

One option would be to have old lifters resurfaced, not sure if a new cam and lifters were installed when the engine was rebuilt? Might have brand new lifters.
Dan

 

It should have new (well 20+ year old) lifters. Was a mild cam I had the shop install, assume/hope they used new lifters!

 

The short answer is it doesn't really matter which combo if you're under 250hp

A lot of engines are "inverted Hemis" aka Heron head.
So the flame propagation behaves the same as an Open Chamber / Hemi with flat tops. [The advantage of Hemi's is not the chamber but the valve and port angles]

If you had a closed chamber head, with a dished piston that mirrored the area of the chamber, you would ideally want the quench close to the impossible zero.
0.025" is considered a safe minimum for a 4" bore [due to pistons rocking in the bore]

The problem with quench is it is an area where the flame propagation produces heat without enough charge to push the pistons down the bore [like the old Harley Joke]

In an ideal situation you would want an open chamber head with the pistons protruding out the bore without contacting the head.
I think David Vizard did some R & D on quench and found you could "UP" the compression without knock when quench was reduced.
He was experimenting with boosted engines and normal thinking is "thicker gaskets = lower compression = more boost" but the R & D proved the opposite.

Open Chambers slow down flame propagation so more spark timing is useful , BUT open chambers produce more NO2 so they are not favourable in modern designs.
Compare the spark timing on a SBC to an LS will show this difference.

ps: the Harley joke is ... "They have been converting hydrocarbons into noise without the side effect of horsepower since 1903"

 

A little epoxy would help the manifold.
Also: https://www.forabodiesonly.com/mopar/threads/318-pistons-to-bring-compression-up.483229/

 

The stock rods could be bushed, to accept Chevy pistons, if that helps.
I haven't compared compression heights.

 

If you found something that sticks up a fraction, it can be decked to get what you need.

 

327 pistons are 1.675 compression height vs 1.741 for stock [which is further down]

You could go to Chevy 302 pistons [expensive] to get a 1.800 compression height !
But why bother when KB's are available at 1.810" compression height and no bushing of the rods is required.

Dropping a set of KB's into a lowly open chamber 318 [68cc] would yield 9.29:1 compression with no machining

This would be a reasonable low budget DIY option [Or a complete junkyard Magnum engine]

 

That’s a possibility, but an issue happens when “what’s it take to get the decks square”?
It’s been mentioned here that .045 was used. Unsure how far the KBs would stick up.
If I get the kids seat done Friday, I’ll get the intake and heads off to get an idea.

 

On a stock 9.6" height block the KB's should be 12 thou down the hole.

Chrysler's decking was piss poor quality control but usually it meant not enough was cut [instead of too much]
This usually resulted in the pistons being too far down the bore.

If you zero decked the block to KB pistons [12 thou off the top] it would yield a 9.55:1 compression ratio

Just pull the heads and measure the 4 corners at TDC [if it is less than 70 thou down the hole, a KB swap won't fit]
But even then you could get ruthless with a 40 thou thick gasket. [5-10 thou above]

edit: some parts list KB's at 1.805" and others at 1.810" height

 

See what the chambers look like, and what the deck height is now.

 

Plans are for this Friday. I have the exhaust manifold off, tomorrow will get the intake off (hopefully) then start on the heads

 

Are you married to those heads ?

 

No . But I’m leeching $$ into something else right now. If I had the funds, I’d have went with the deal posted earlier for the Al heads

 

Doing some searching at work, I found .030 over pistons for the Magnim block. Pin height 1.65? As I recall, so a “rebuilder” piston for the new style 318. Okay, so that puts me at (from a true 9.6 deck height) .031 in the hole based on the KB pistons with a 9.6 deck.
Surely, another .015, (if my memory is working, heck, .025 would be like zero decking a SBC)) etc, would be an easy cut (but I’m not a machinist) which would put them where the KBs would sit, and be 250 less, this engine doesn’t need or want (I asked it) Hyper coated pistons.
Seems like a plan to me.
Oh, when I spoke with the 318, is was a bit grumpy, started bitching at me for letting it sit by itself for so long…

 

Google tells me high NO2 (Nox) is caused by a lean condition. But that could be over come via idle seating/changes in the carburetor, couldn’t it?
And I’d guess it could be monitored with a heated O2 sensor, adjusted accordingly?

 

What is the gasket thickness on these ?

 

Some of the 318 heads, the Quench Pads in the chamber, are recessed from the gasket surface.
https://www.motortrend.com/uploads/...4z-mopar_cylinder_head-combustion_chamber.jpg
Is that what some people are calling an Open Chamber ?

NO clue what Chrysler was thinking there.

 

Just heading to bed, but not a clue on the head gaskets. I’ll check the link when I get up, hate the shift I’m on and OT, like the check though!

 

Mike, I had to go back and re-read through the thread to figure out where you were headed. I missed this this the first time.
What you are after would be a stone stock 69-70 318. Do you have an FSM from that era?

• Compression Ratio: 8.8 to 1
• Horsepower @ R.P.M.: 230 @ 4400
• Torque, lb-ft. @ R.P.M.: 320 @ 2000

If the deck or heads have been cut then so much the better. Change to a little peppier cam and your done.

 

Correct, I think this is the video where he talks about another engine builder trying to build a cheap boosted engine, and used thicker head gaskets to reduce compression. It lacked power and couldn't handle as much boost as expected. Correcting the quench solved those issues.