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Author Topic: '87 Diplomat Police 318 Build  (Read 3596 times)

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Re: '87 Diplomat Police 318 Build
« Reply #15 on: April 16, 2013, 18:42:27 »

E85 is junk. It's not cheaper than regular gas. There's the illusion that it's cheaper because it's subsidized through the state using your tax dollars....so you're paying for it one way or another... It also has less specific energy than gasoline, so it takes more than 1 gallon of E85 to produce the same power as 1 gallon of gasoline. Look up the LHV (lower heating value). The guys you know making "big power" on E85 are using it with high compression ratios because it takes more "squeeze" to extract the same amount of energy from a given volume of E85 than it does the same volume of pure gasoline. I won't even mention the corrosion it will do to your gas tank if you ever let it sit.....like over winter.

If you want to make power out of your 318, you'll need to lose the stock pistons. You can follow what they did in the build you posted, but for $4300, it isn't a budget build. I spend a little over 1K more than that for my 408. The thing is, if you're going to start spending 4K in parts, would you rather it be for a 318 or a 360? I went through this when I built a 383...it cost the exact same amount of money to build a 383 as it would have been to build a 440, but I ended up with  less compression, less power, less future potential....etc
E85 is a niche. It's not for making a street build motor go well. It builds water and becomes usable quicker, is much more corosive, takes more to burn, it's alcohol-oriented high octane fuel.

When he says high compression he means 10.5:1-12.5:1 with iron heads or a bit more with aluminum heads.

For the 318 to need 850 on E85, you'd be talking about feeding a monster- even if it is 318-331ci. Not 6k-ish, more like 7200+. Most people don't build 318s that hot- usually just 340s and 360s. (they aren't dirt cheap, and the extra 100-300 to upgrade blocks is not much to scoff at when doing one)

I'd swap the pistons before changing the deck/heads.
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Sublime440

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Re: '87 Diplomat Police 318 Build
« Reply #16 on: April 16, 2013, 18:44:58 »

What's the least expensive way that I can increase compression?

What's wrong with re-using the stock hypers, assuming they are flat tops? Realistically, how much would I have to mill the block to get to my desired compression ratio?

You'll just have to pick a set of pistons that are within your budget and go with a set of magnum heads. You want to look at the compression height (or compression distance) on the piston and pick one that is taller than stock (the distance from the center of the pin to the top of the piston).

Take your deck height and subtract the rod length, the compression height of the piston, and half the stroke and you'll get how far in the bore your piston will be and how much you'll potentially have to deck the block to get near zero deck.  For $1500 you may get close but you might have to look for good deals or buy some of the Summit brand stuff, which isn't bad by the way.

The stock pistons are a dish design if I remember correctly....they're also about 0.060" in the bore......way down there and no chance for decent compression or quench. All quench does is allow you to run 93 octane on an engine with 10.5:1 compression by forcing the fuel mixture to the side of the chamber near the spark plug, where the flame is the hottest, the molecules are also more compact and energized, you get a better air/fuel mixture within the chamber, you get a more complete combustion, and a cooling effect across the top of the piston after ignition. So you don't need 105 octane or whatever the equivalent is.

These cop engines are talked up a lot, but they aren't that special performance-wise. Durability, yes.

You can use these web pages as tools to figure out which pistons to pick (by the specs given) and what you'll have to do as far as decking and head chamber selection to get the compression you want.
http://victorylibrary.com/mopar/deck-height.htm
http://www.csgnetwork.com/compcalc.html
« Last Edit: April 16, 2013, 18:51:53 by Sublime440 »
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