318 pistons

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Alex "Berkowitz"

76 brazilian hardtop
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Hi!

I'm rebuilding my 318 down here in Brazil, on a budget.

Our 318's are a bit diferent from yours, for exemple, the stock compression ratio was around 7,5:1 (pistons were as low as 0.149" from the deck).
Our gas today has around 15% to 22% ethanol, so a lot more tolerant to compression than it used to be.

I was considering the Sealed Power 285Ap pistons, using the compression calculator ate the summit page, it gave me a 8.28:1 compression ratio, using the deck measured by a friend with those exact same pistons (0.064"), combustion chambers with 64cc, compressed head gasket with 0.039" tickness, and bored to 3.940.

But I found a different set of pistons, also from sealed power, the 526AP.
They seem almost the same, but the compression hight is 1.745" against 1.720" from the 285AP, and they are flat heads with no valve reliefs.

Has anybody used them?
By the description at the site, thats the only differences between them.

I'm running Summits k-6901 camshaft (218/228 @ 0.050, .441 lift), with stock 1.75"/1.50" valves.

Thanks!

(ow, I know KB-167s would be the best, but with our taxes, they get here for US$ 793.00, while the 526 would get here around US$ 352)
 
The problem with using a friends deck clearance measurement is it might be different from yours, that said I ran the numbers for those pistons with a different calculator. Assuming a 9.6" blueprint deck height, and indexed crank, etc, those pistons should be .077" in the hole. With a 64cc chamber, .040"x4.14" gasket, and the 0cc flat top, I calculated 8.48:1. It'll more than likely be a little less than that unless the decks are cut down below blueprint height. There's nothing wrong with those parts selection to save some cash, but I would definitely recommend you degree your cam and maybe even advance it a couple degrees to keep some of your cylinder pressure.

As long as you're not expecting it to be an 11 sec terror, I think you'll be happy with it.

Just my .02...
 
txstang84 , tanks!!

No, I do not intend to be na 11 sec terror!
lol

Just want a nice and "fair" 318 to go on roadtrips to meetings and ocasionally burn some rubber.

You calculated the EXACT same CR than the guys at Summits "help desk" (they just responded), I must be using their calculator the wrong way.
The calculator you used, is it available on the web?

I'm measuring my entire engine, as we have a lot of uncertainty and "guessing" down here.
For exemple, Brazilian Chrysler shop manual states deck height is of 0,01" with stock pistons, but up to now, I haven't found a single deck on my engine that measures less than 0,152"!!
That 9.6" blueprint height you mentioned, is it from the bottom of the cylinder to the top?
I guess thats an important measurement I must get, but haven't removed my pistons yet.

Would you mind showing me the data you put on the calculator, just so I can check what I'm doing wrong?

8,5:1 is already a lot better than our advertised stock CR, of 7,5:1, but is still a bellow the 9 - 9,2:1 I would like.

The cylinder pressure you mentioned, is it just because of the low CR?
Or there's something wrong with my parts selection?

Thanks again!
 
The calculator you used, is it available on the web?
Click to expand...

Yup!

http://torinocobra.com/Randys_tools.htm

The deck height is measured from crank centerline to the top of the deck...most opinions I've seen from seasoned Mopar guys say that NO production block measures blueprint deck height unless it was an accident. Most machinists can square/parallel deck a block down to blueprint height or at least equalize them to a common lower number.

Along with that, 318 replacement pistons are typically anywhere from .040"-0.160" down in the hole. It is what it is. The numbers I used for the data entry was

bore=3.94
stroke=3.31
cyl=8
head gasket thickness/diameter=0.040"x4.14" (typical sizes for a few head gaskets)
piston deck height=self-explanatory
piston ring height=varies by piston mfr and intended use, but many SB slugs I've seen are between .25-.31"...I used .28 I think
piston skirt clearance=again, it varies based on the use and mfr, but I used .003"
piston dome/dish volume=as advertised-true flat tops are 0cc
cylinder head chamber volume = 64cc as given by you

When I mentioned cylinder pressure; I referred to having a low static compression ratio with a larger duration cam often diminishes cylinder pressure at lower RPMs, therefore make it feel a little lazy. If you advance the cam timing a little bit, it will close the intake valve sooner by however many degrees you choose, and increase cylinder pressure...makes it feel a little peppier without having to advance your timing as much...just part and parcel of the whole tuning experience :)
 
I wouldn't use them you could get the same with a .050 head cut and a thin head gasket . plus no valve reliefs.I used a set of badger piston that were flat top ,no valve reliefs for a 360 build that were advertised to raise compression but were lower compression then the dish stock ones ,also had to cut off .100 of deck to get them.015 below deck ,then with a 454 lift cam had to have pistons flycut .125 for valve clearance.sometimes everything just snow balls.
 
If it's going to be a simple street cruiser why don't you use stock '69 318 pistons. My '69 Barracuda came with factory 9.2:1 comp ratio. When I pulled the heads the pistons were .039 down in the hole. I believe that's the tallest piston you can get in a stock 318. The stock heads were 69cc and the replacement 302 casting heads were very close to that also. You can save money and still get the compression you're looking for!!!

treblig
 
...why don't you use stock '69 318 pistons...
Click to expand...

Because unless you have a special part number recommendation, all 318s from 67-91 have exchangeable part numbers and this...

...(ow, I know KB-167s would be the best, but with our taxes, they get here for US$ 793.00, while the 526 would get here around US$ 352)
Click to expand...

He's working from another country which means shipping costs for already expensive stuff makes it all the worse. And it's not like it needs to have 9:1 to run well. A properly built 8.4:1 318 will run well if the cam is degreed in and the heads flow well. Furthermore, just because the specs show 9.2:1, means nothing about the reality of the matter. If your engine in particular was only .040" in the hole, that's fantastic, but the reality is most of them were somewhere around .060-0.080" in the hole. All the aftermarket ones available are about that unless you have the block decked or offset grind the crank.
 
txstang84 said:
Because unless you have a special part number recommendation, all 318s from 67-91 have exchangeable part numbers and this...



He's working from another country which means shipping costs for already expensive stuff makes it all the worse. And it's not like it needs to have 9:1 to run well. A properly built 8.4:1 318 will run well if the cam is degreed in and the heads flow well. Furthermore, just because the specs show 9.2:1, means nothing about the reality of the matter. If your engine in particular was only .040" in the hole, that's fantastic, but the reality is most of them were somewhere around .060-0.080" in the hole. All the aftermarket ones available are about that unless you have the block decked or offset grind the crank.
Click to expand...

Alex was trying to get good compression without having to spend too much money. He also said that he was building a street car not a race car. Attached you will see the "How To Hot Rod Small Block Mopars" stock piston specs. I also have a factory '69 Service Manual which says the same thing. The piston height of my pistons is 1.77. This is why I had .039" in the hole and 9.2 compression. If you look at other years (newer pistons) the piston height gets shorter and shorter. My point was that Alex can spend a lot less money if he buys stock (tall) '69 pistons without sacrificing compression. I do not know if he can get the exact pistons as my engine BUT I know they would cost way less than the ones he's looking at. The P/Ns are also there for him to see.
Alex was trying to save money and I was giving him one way. I'm sure there are other ways also. Buying expensive pistons isn't always the best solution when you have to pay import taxes.

treblig
 

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Are these part numbers still available at a Mopar dealer? More importantly, if they are, how much are they for the set? The part number he mentions is readily available for a fair of money. ($106 from Summit-and they do ship to Brazil)

I'm abundantly aware of what you're trying to accomplish by offering alternatives and that's great-that's what we all live for, but the simple matter of facts are that any Mopar part number will be more costly compared to any other brand...then he'll have to ship it...or coordinate with a local business there for shipping.

I have that same book, but just because the part number is there doesn't mean it's still available. If they were, I could stroll up to the Star Dodge in Abilene, Texas and order a set of "645" 340 floating rods...or a new forged 340 crank with the prescribed part number in the book. Those charts are there for identification purposes more than anything.

Buying expensive pistons isn't always the best solution when you have to pay import taxes.
Click to expand...

We're apparently not reading from the same sheet of music here...I'm aware of this, but the pistons he wants to use are only $106 from Summit plus the onerous shipping...so I'll defer to back my first question: Are those part numbers still available from a Mopar parts dealer, and how much are they?
 
If the Summit pistons are that cheap then it wouldn't be worth trying to find a stock set even if they were available??

treblig
 
From what understand the 1.745 is the tallest cast piston still available. .010-.020 off the block and heads for clean up and a thin gasket will put you at a decent CR more than enough for the cams you would want to run in a 318. I think people get to caught up trying to squeeze every last CR out of the engine. Heads are the biggest cork on power for that engine.
 
Treblig said:
If the Summit pistons are that cheap then it wouldn't be worth trying to find a stock set even if they were available??

treblig
Click to expand...


Not exactly sure what you're saying here...are you asking me would it be worth it to look for a stock type specific replacement piston in oversize (pending inspection by a machinist)?

Sure, can't hurt to look-but I'm a bit of a cynic and doubt they exist except in some old musty closet somewhere in rural Kentucky, therefore, for all intents and purposes, unavailable.

Or...

Would the benefits of about ~.5:1 compression from a stock replacement type piston outweigh the reduced cost of readily available pistons from Summit?

Not in my opinion...unless he were able to find a set of those slugs and his block was good enough to take them.

Current assertions are that 1 pt of CR in a given combo is worth 4% improvement in hp...he may yield 2% by that logic. So, for every 100hp, a 2hp increase...yeah, I'm not writing home about that one.
 
txstang84 said:
Not exactly sure what you're saying here...are you asking me would it be worth it to look for a stock type specific replacement piston in oversize (pending inspection by a machinist)?

Sure, can't hurt to look-but I'm a bit of a cynic and doubt they exist except in some old musty closet somewhere in rural Kentucky, therefore, for all intents and purposes, unavailable.

Or...

Would the benefits of about ~.5:1 compression from a stock replacement type piston outweigh the reduced cost of readily available pistons from Summit?

Not in my opinion...unless he were able to find a set of those slugs and his block was good enough to take them.

Current assertions are that 1 pt of CR in a given combo is worth 4% improvement in hp...he may yield 2% by that logic. So, for every 100hp, a 2hp increase...yeah, I'm not writing home about that one.
Click to expand...

I thought I was pretty clear. You said that the Summit pistons were only $106. If the OP can get them that cheap ($106) and they meet his needs then "it would not be worth it to look for stock pistons even if they were available". My point is....the Summit pistons are cheap and readily available. Stock pistons may be impossible to find in the correct piston height. So "If the Summit pistons are that cheap then it wouldn't be worth trying to find a stock set even if they were available??"


PS - Translation... you're right!!!
Treblig
 
I just love this site!

Thank you ALL a LOT for the inputs!

I had no idea this was such a "delicate" matter...
I didn't even know about half the terms and calculations I heard here for the first time.
I was just reading about "quench height", wich was another thing I had never heard off, and I just found it looking deeper on some input that was given me here.

For now, I guess I'm gonna go the route of 526Aps and shave something off the decks, just have to figure out how much would be ok without interfering on rocker geometry and intake fit.
I called the machine shop, and they would charge me US$100,00 to shave both decks up to 0,04" if that would be my will.
This way I would still be US$ 350,00 away from what the KB167s would cost me.

Just have to find out if it would really be Worth it.

What would your input be on this matter?
http://www.hotrod.com/techarticles/engine/1311_ideal_quench_height/

0,060" max quench??
My engine has around 0,188" as it sits today.

Recalculating my numbers on the calculator txstang84 gave me, with this 526APs and shaving 0,04" from the decks and "regular" 0,04" gaskets, I would get 9,12:1 CR.
But I guess at least rocker geometry would be screwed with this, wouldn't it?
I mean, stock rockers...
 
For your purposes, quench really won't matter unless you're dealing with close chambered heads. I can't get the article to load for some reason, but what they're likely saying is that anything bigger than .060" negates any effects that quench can provide. For a general street build, it's inconsequential anyway unless you're breaking past about 9:1 with a small cam.

Quench's purpose is to improve combustion chamber turbulence when the piston is on it's way up-the squish effect pushes the mixed chamber into the wedge area to keep the mixture homogenous and to reduce the chances of detonation/pre-ignition.

And if your pistons are still .040 in the hole, even with the .028" gaskets, you've already past effective quench distance, plus the relief cast into the heads.

EDIT: just thought about the rocker geometry question. Depending on how much you shave from the block and heads, and the thickness of head gaskets, you may need a different length pushrod. Many engine builders on here will tell you that you shouldn't buy pushrods until the long block is assembled and you can properly measure for lifter preload...I tend to agree with that assessment.
 
Ha ha! Honestly, if I wanted parts from Mopar dealer that was local to me when I lived in Abilene, I'd rather drive to Blake Fulenwider's...spiteful, but I couldn't stand going there.
 
Thanks a lot txstang84!!!

Understood the quench subject,and loved your input on pushrods.
First time building an engine, all I could think on fixing the rocker geometry was adjustable rockers...more than one way to skin a cat I guess!
 
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