318 pistons

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needsaresto

needsaresto

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So I have this 1983 cop 318.Pretty sure the pistons are way down in the bore and with the stock 360 heads it might have 7.5:1 comp.Havent had the heads off yet but will soon.

Lookin to raise it when the motor gets redone this winter.What piston will yield the most comp without going over 9.5:1 with the heads getting a minimal cut to clean em up?
I will use an .028 head gasket as well.Might offset grind the crank a wee bit to bring the pistons up also.

A cast piston would be best as this wont be a race engine.Hypers and forged not in budget.

Just lookin for a drop in replacement in maybe .030 with a flat top and good comp height that I can get close to 9:1.
 
Off hand, I don't know, but I would look at a set of Federal Mougal pistons to get what you want.

If you can't find the ratio your looking for, the KB's for the teen @ zero deck can be used. Just use a thicker gasket.

OK, with a zero deck piston and a 72 cc head (Ave 360 chamber/open style), MP .028 gasket thick and 4.180 bore size.. You get a 9.33 - 1

If the bore size is 4.00 inch and everything else stays the same, it rises to 9.38 - 1.

65cc head = 10.21 - 1.

Thicken gasket to .054 (Fel-Pro has one like this, not sure of bore size though.) everything else stays the same, you get 9.56 - 1.
 
Kinda wierd.I found a piston at Hughes engines.Listed as a cast sylvolite that has a 1.798 compression height.This is a good deal taller than most 318 pistons.

Cant find it on the sylvolite websight tho...maybe it was a typo?

Of course they list it with some part # they made up too,so you cant track it down.

Here:

http://www.hughesengines.com/partDetail.asp?partID=10283&eTypeID=1
 
Nuther question.

Can magnum block pistons be used in an la block?
 
K,so no magnum pistons in an la?

Found a speed pro piston.STL H814,comes in std .020,040,and .060.Flat top with no valve relief.Hypers and coated skirts too.

Comp height is 1.755

So if deck height on a factory teen is 9.6
minus rod length 6.123
=3.477
minus 1/2 stroke 1.655
=1.822
minus comp height 1.755
= .067
So pistons are down .067 in the hole.
using an .028 head gasket compression comes to around 8.7:1 with 70 cc chambers,if the crank is offset ground .020.So slugs would be .047 down

This is with no block deck machining and just a slight cut to the heads for clean up.So any material I do need to remove other than mentioned will bring more comp.To get 9.1 I need a 65 cc chamber or square the deck up with an .020 cut.

I guess easier to use KB pistons.....
 
rumblefish360 said:
Off hand, I don't know, but I would look at a set of Federal Mougal pistons to get what you want.

If you can't find the ratio your looking for, the KB's for the teen @ zero deck can be used. Just use a thicker gasket.

OK, with a zero deck piston and a 72 cc head (Ave 360 chamber/open style), MP .028 gasket thick and 4.180 bore size.. You get a 9.33 - 1

If the bore size is 4.00 inch and everything else stays the same, it rises to 9.38 - 1.

65cc head = 10.21 - 1.

Thicken gasket to .054 (Fel-Pro has one like this, not sure of bore size though.) everything else stays the same, you get 9.56 - 1.[
dude i think .090 over bore would be a little much for a 318:read2:
Click to expand...
 
Umm ya .090 is too much...

I was thinkin maybe .020 overbore(if it even needs it) and deck the block.020 as well.Use the speedpro pistons.I think thier about 18-19 bucks each from summit.

Say $150 for hyper slugs.

as compared to almost $300 for KB

Either way the block will need to be decked,being a mopar.

Gotta keep cost down as much as possible.
 
why the limit of 9.5:1 built a teen-3 1 ton truck block with 68 flat top rv pistons and 340 j heads (63 ccs) and used felpro gaskets as i rember it figued out to about 9.6:1 used 88 oct reg gas back then now running it on 87 u/l crap with 8 degrees advance and 36 degrees total mach advance and about 15 degrees vac. advange with out and problems
 
440SCOUT said:
dude i think .090 over bore would be a little much for a 318:read2:
Click to expand...

That was a ref. to the gasket bore size. Notice the extra nominal rise in compresion from 9.33 to 9.38.

.090 is alot to overbore the block. It is possible. Sonic check it first.
There is a Mopar shop, can't remember who at this moment, that bores 318's out to a 4 inch size and strokes them with a 4 inch crank.

Hennsely comes to mind.
 
Watch out for those thin gaskets from MP. I blew out one in 5 mins on a 360. If they are the grey ones I wouldn't use it.
 
340demon said:
why the limit of 9.5:1 built a teen-3 1 ton truck block with 68 flat top rv pistons and 340 j heads (63 ccs) and used felpro gaskets as i rember it figued out to about 9.6:1 used 88 oct reg gas back then now running it on 87 u/l crap with 8 degrees advance and 36 degrees total mach advance and about 15 degrees vac. advange with out and problems
Click to expand...



Did you cut those heads to get the 63 cc chamber, if not they would have been closer to 70 CC's
 
340demon said:
why the limit of 9.5:1 built a teen-3 1 ton truck block with 68 flat top rv pistons and 340 j heads (63 ccs) and used felpro gaskets as i rember it figued out to about 9.6:1 used 88 oct reg gas back then now running it on 87 u/l crap with 8 degrees advance and 36 degrees total mach advance and about 15 degrees vac. advange with out and problems
Click to expand...

I want to limit comp as the cam will be small too, so no point in having higher than 9.5.Your 9.6 is close to what want tho.Musta had those heads shaved a fair bit to get 63 cc chambers.Also want to keep gas mileage decent so 9:1 ideally.


Leads to a machining question.Whats more cost effective at raising comp;shaving heads or decking a block?

Who made those pistons you used?Whats the comp height?Valve reliefs?
 
street demon said:
Watch out for those thin gaskets from MP. I blew out one in 5 mins on a 360. If they are the grey ones I wouldn't use it.
Click to expand...

I've never had a gasket problem with the thin gaskets from mopar. Were the surfaces clean and flat? Most people don't think about the deck surface but it can be out just like the head surfaces. Up to .004 distortion will seal the cylinder and more than this or a combination of the deck and head surface being more than this and the gasket will blow.
 
needsaresto,
Your fuel mileage will be determined from the size of the port and valves used, smaller ports and valves the better the mileage will be, just as the larger the worse.
Compression will determine the amount of power and the amount of octane that will be needed and not how much fuel that will be burnt.

Example: I have a large port engine with a large port intake manifold, and it uses 1+ gal per run and I have a small port engine with a small manifold and the engine uses .5 gal per run and makes more Tq. and low end Hp. Both engines are 10.5 compression and similarly built but the amount of area that needs to be filled to correct the fuel curve was totally different. And had to change this or the engine would have run lean.
 
He does have a point about running alot of compresion on a small cam though. The Iron head doesn't help.
 
He could run a bit more cam with more overlap and kill some compression but then the driveability and and need for a converter and more gear comes into play. But even though a cam with [email protected] would still be very driveable on the street and say a 108 centerline.
Or like has been mentioned a thicker gasket.
 
BJR Racing said:
needsaresto,
Your fuel mileage will be determined from the size of the port and valves used, smaller ports and valves the better the mileage will be, just as the larger the worse.
Compression will determine the amount of power and the amount of octane that will be needed and not how much fuel that will be burnt.

Example: I have a large port engine with a large port intake manifold, and it uses 1+ gal per run and I have a small port engine with a small manifold and the engine uses .5 gal per run and makes more Tq. and low end Hp. Both engines are 10.5 compression and similarly built but the amount of area that needs to be filled to correct the fuel curve was totally different. And had to change this or the engine would have run lean.
Click to expand...

Cant completely agree on the port size theory.Doesnt take into account chamber shape and efficiency which affects flame travel.True a smaller port will have better velocity.But a swirl port creates a better burn=more efficient.Thats part of the deal with some smaller ports.

Agree more comp will not burn more fuel but more comp really needs more cam.More cam delivers more fuel...

I just want a cast inexpensive piston for a 9:1 motor with an open chamber head.Just wanna keep things simple.
 
needsaresto said:
Cant completely agree on the port size theory.Doesnt take into account chamber shape and efficiency which affects flame travel.True a smaller port will have better velocity.But a swirl port creates a better burn=more efficient.Thats part of the deal with some smaller ports.

The confuesing thing about swirl ports is that they are misunderstood, if you would use high flow in place of swirl port you would better understand the meaning behind the words. (not to say that you don't understand you more than likely do) but It's not the chamber that creates the swirl, it's how the port is shaped. The chambers were designed for better emissions which aided in better efficientcy. The actual area is similar in the chambers from the early to late engines cc wise. The best chamber that they have come up with so far was in the W-8 and W-9 heads and the P-5 and P-7 heads. The only engines that I've seen this on, on the street from Mopar is on the 3.3 and the 3.5 caravan engines that have this chamber shape.
If they would use this chamber shape in the commandos and the W-2 they would really have something that would kick some serious butt. But unfortunately they only use it in the W8/9 and the P-5/7 series which doesn't lend itself to our use now. Maybe they'll wakeup, I've talked to head manufactures and until they would get a large order they won't even consider it.
Click to expand...
 
BJR Racing said:
Then the piston that you need is a H116CP from seald power.
Click to expand...


Umm,I think thats a 360 piston...I dunno sumpin tells me it wont fit in my 318,lol!!

I cant seem to make it fit George...Git me a bigger hammer!

Duh...O.K Ralph...

All kidding aside...Comp height is what I need with a big chamber...
 
BJR Racing said:
needsaresto said:
Cant completely agree on the port size theory.Doesnt take into account chamber shape and efficiency which affects flame travel.True a smaller port will have better velocity.But a swirl port creates a better burn=more efficient.Thats part of the deal with some smaller ports.

The confuesing thing about swirl ports is that they are misunderstood, if you would use high flow in place of swirl port you would better understand the meaning behind the words. (not to say that you don't understand you more than likely do) but It's not the chamber that creates the swirl, it's how the port is shaped. The chambers were designed for better emissions which aided in better efficientcy. The actual area is similar in the chambers from the early to late engines cc wise. The best chamber that they have come up with so far was in the W-8 and W-9 heads and the P-5 and P-7 heads. The only engines that I've seen this on, on the street from Mopar is on the 3.3 and the 3.5 caravan engines that have this chamber shape.
If they would use this chamber shape in the commandos and the W-2 they would really have something that would kick some serious butt. But unfortunately they only use it in the W8/9 and the P-5/7 series which doesn't lend itself to our use now. Maybe they'll wakeup, I've talked to head manufactures and until they would get a large order they won't even consider it.
Click to expand...

Yup I do understand about swirl ports and "shaped" air fuel charges.The chamber shape and quench promotes burn.Sorry if I sounded confused.My wife accuses me of that all the time,lol..

I am starting to think I may be better off just shaving the heads down rather than trying to find an inexpensive piston to bring comp up.

Was thinkin that if the 318 needs an overbore why not try to kill two birds with one stone?Get the right oversize piston that will bring comp up as well..Seemed to make sence to me.
Click to expand...
 
needsaresto said:
Umm,I think thats a 360 piston...I dunno sumpin tells me it wont fit in my 318,lol!!

I cant seem to make it fit George...Git me a bigger hammer!

Duh...O.K Ralph...

All kidding aside...Comp height is what I need with a big chamber...
Click to expand...

Yep,
Sorry I have 2 threads mixed up ..............Duh
 
Was thinkin that if the 318 needs an overbore why not try to kill two birds with one stone?Get the right oversize piston that will bring comp up as well..Seemed to make sence to me.[/QUOTE]

So what compression height are you looking for?
 
BJR Racing said:
Was thinkin that if the 318 needs an overbore why not try to kill two birds with one stone?Get the right oversize piston that will bring comp up as well..Seemed to make sence to me.
Click to expand...

So what compression height are you looking for?[/QUOTE]

Well a comp height of 1.755 with a .028 gasket and 70 cc chamber yields somewhere around 8.14:1.Pistons down about .067.Crap comp...

To get 9:1 without changing anything but piston comp height the piston needs to come up .040.So a comp height of 1.795 would work for me.I realize the KB has 1.81 comp height,but thier not really in the budget, at least not for this motor.

Alternately if the crank can be offset ground and stroke increased .020,this will raise the pistons 1/2 that amount,or .010.Comp height needed is now 1.785 for 9:1.This may have to be done anyways depending on the crank.

If the block is decked and cleans up at say .020,now comp height needed is 1.765.I think this is extra $$ and the long way around to get 9:1.Sure the motor will be better for it,but this is a budget engine.

Sorry for being long winded.Just thinking things out.
Realistically,the best most economical approach is just to overbore and get the right piston.

This motor will go back into the cop car and the cop car will be sold to raise funds for my Dart.So the budget for it needs to be strict. Thats why Im looking for the right piston.It can be a cast piston.The motor wont be much more than 320 h.p.Im not averse to using a brand X piston either...
 
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