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Author Topic: '87 Diplomat Police 318 Build  (Read 3597 times)

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DaveGT

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'87 Diplomat Police 318 Build
« on: April 15, 2013, 12:02:02 »

Since this is my first post, I wanted to start off with a little introduction. I bought my 87 Dodge Diplomat last summer, and road tripped from Denver to Des Moines with it.


You can read more about the adventure here.



http://dolmageadventures.com/2012/07/16/the-1k-challenge-or-i-might-be-crazy/


Shortly after I got home I noticed that the coolant expansion tank was full of oil, and I parked it. After kicking around what to do with the car for a couple of months I've decided that I want to use it as a cheap autocross and track day car.


Why, you ask?


Well, because it's different, and because since it's the cop car model it already has the heavy duty suspension, bigger sway bars, trans and PS coolers, and because it's a car I already own, rather than a car I'd have to go out and buy. And since my initial investment was pretty low ($400) I'm not going to get too worried about beating up by using it as a track car.


Since I'm on a fairly small budget I'd like to build a motor that's more on the inexpensive side of things. I'm looking for a build with close to 400whp, good torque, and fairly bulletproof. With autocross and track days in mind I'm looking for something that's going to be able to stay together up to 6k rpm.


I'd like to duplicate the little Mopar that could build which was featured in Hot Rod magazine if I could. Here's the link to the build for anyone who's not familiar with it.


http://www.carcraft.com/techarticles/ccrp_0401_mopar_318_engine/viewall.html


I have two blocks that are available to use with the project. One is a 4104230-318 block. I don't believe this is the fabled race block, since it doesn't have the X cast into the front of the block, nor does it have 4 bolt mains. However, it does have flat top pistons, compression ratio unknown. This is a 2v motor that was pulled from a mid-80's Dodge truck. Everything looks good inside the motor, the bearings were still in decent condition, and after a quick reseal the motor would most likely run without any real issues.


The second motor that I have available is the stock motor in the Diplomat. I'm not sure if this is a roller block at all, or what the compression ratio on this motor. Based on what I've read on this site the motor does have the hyper pistons and forged rods, but I'm unsure of the compression ratio.


Due to cost considerations I'd like to avoid zero-decking the block if possible. Which of these two motors will give me the highest compression ratio?


My build plan right now is as follows:


Magnum heads, (stock valvetrain)
Stock pistons and block
Cam, (not sure if I want to use the same cam from the article or if there's something better on the market)
Professional Parts Magnum intake
Edelbrock 850 Carb
Mopar orange ignition
Long tubes


Which of these two motors will have the highest compression ratio when assembled? I'm shooting for 10:5:1 compression if I can get it, or as close as I can come to that number. Initially I'm planning on running the motor on 91 octane, but at some point I'd like to tune it for e85, which is widely available in our area, and many local hot rodders are putting down serious power with.


I plan on driving the Diplomat to and from events, so the motor does need to be semi-streetable. It also needs to stay together, so reliability is a concern.


Thanks in advance for any help.


-Dave
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79dodge4ever

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Re: '87 Diplomat Police 318 Build
« Reply #1 on: April 15, 2013, 13:57:53 »

before you plan a wild build you should have the engine gone through, theres oil in the bottle for a reason and the engine might not be worth building
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DaveGT

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Re: '87 Diplomat Police 318 Build
« Reply #2 on: April 15, 2013, 15:13:03 »

I'm fairly sure the issue is a head gasket, but yes, I plan on going through the motor. Like I mentioned above, I've got 2 different 318 blocks to choose from. I'd like to use the block that's better suited to the build, but I could use some information about what that is.


Do you have any information on the compression numbers I'm looking for?
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81SportCoupe

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Re: '87 Diplomat Police 318 Build
« Reply #3 on: April 15, 2013, 17:18:35 »

hey Dave, I think no matter which way you build your 318 that 850 carb is going to be overkill. That is for a very large displacement engine, not a middle of the road-sized 318. No matter how mean the cam and heads, that 850 is too much for a short-stroke engine like a 318. With the stock rear end gears, will will miss that low end torque you will be giving up with that carb. Is there a reason you do not want to run a 360, besides fuel mileage? Sounds like it would suite your needs, and cost you no more to build.
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79dodge4ever

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Re: '87 Diplomat Police 318 Build
« Reply #4 on: April 15, 2013, 17:26:11 »

hey Dave, I think no matter which way you build your 318 that 850 carb is going to be overkill. That is for a very large displacement engine, not a middle of the road-sized 318. No matter how mean the cam and heads, that 850 is too much for a short-stroke engine like a 318. With the stock rear end gears, will will miss that low end torque you will be giving up with that carb. Is there a reason you do not want to run a 360, besides fuel mileage? Sounds like it would suite your needs, and cost you no more to build.

that is correct 850 is too much, here is the formula to figure out how much is required, its always a good idea to oversize by abit but not that much

Engine size (CID) x maximum RPM / 3456 = CFM
CFM @ 100% volumetric efficiency

so 318x6000RPM (we will say, most won't ever see that)/3456= 552.08 CFM so a 625 CFM is plenty

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DaveGT

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Re: '87 Diplomat Police 318 Build
« Reply #5 on: April 15, 2013, 19:48:03 »

My biggest reason for wanting to run the 318 and the 850 carb are pretty simple, I already own both of them. I've got 2 blocks to choose from, I'd like to use the block that's going to offer the best compression ratio if I can.

I'd prefer to reuse the stock pistons and avoid zero decking the block, simply to save on costs. I'd like to get the engine together and running for as close to $1k as I can.

I realize this is a pretty low number, particularly when I still need to buy a cam, heads, and a bearing/re-ring kit, along with gaskets.

I'm hoping the 850 will work with the e85. Typically, motors set up to run on e85 require much larger fuel needs than motors running on unleaded gas.

E85 applications typically require 25% more fuel on average, so the 850 is going to be quite a bit closer than you might think. I think a 750 would be a better carb for this setup, but sometimes you've got to run what you've got.

E85 also allows much higher compression without concerns about knock, I'd like to be at 10:5:1 or over if I can. It also will typically make more power than a motor that's running on 93, and while fuel consumption increases considerably, it's also much cheaper in Iowa where it's subsidized by the state.

http://www.hotrod.com/techarticles/hrdp_0801_e85_ethanol_alternative_fuel/viewall.html

This is a great article that covers some of the basics of running e85 if you're curious at all.

So, I'm still looking to see if there's any way to find out what compression ratio my two 318s are. Also, is there a calculator that I can use to figure out what the compression ratio will be the Magnum heads?

Thanks guys!
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brotherGood

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Re: '87 Diplomat Police 318 Build
« Reply #6 on: April 15, 2013, 20:35:45 »

Ok, heres my 2 cents. I am currently in the process of installing my 318. It is a stock bottom end 318 out of a 79 Aspen. I put a summit cam, and magnum heads on it, with the M1 intake and qjet.

Your goal of 1k, is about where I am. However, I paid 35 bucks for my heads, and got shop pricing on everything else I needed. Not to mention the deals/bartering that were made to get the price down even more. That being said...if you space it out, its not bad.

Will you have another vehicle to drive while this is being built?

Knowing what I know now about building this, heres what I'd do to try and reach that goal. Id use whichever block, assuming theyre both roller blocks. Regardless, Id use a roller block. I'd also (personally) zero deck the block..because as it was explained to me-its pointless to have high compression if you don't have sufficient quench. Then, the mag heads, and either an M1 or Eddy intake. You can also redrill the heads to accept an LA intake, but that's up to you. The Crosswind intake has a reputation for bad quality..so I would advise staying away from it if youre wanting reliability.

The 87 cop compression should be in the library somewhere, for the other one though, we'll probably need the date code if its got one.

Hope this helps.
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'86 Dodge Diplomat AHB. Rebuilt 318 LA/Magnum, cop 904, 8.25 rear.

DaveGT

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Re: '87 Diplomat Police 318 Build
« Reply #7 on: April 15, 2013, 21:22:49 »

First of all, yes, at the moment I've got plenty of spare rides. This is intended to be a fun car, I'm building it primarily for autocross events and open track days.

What was your cost to get the block zero decked? Like you I can buy everything at absolute cost, which will help keep prices down. I don't know if the earlier block that I currently have taken down is a roller block or not, the numbers show that it's a "race" block, although it doesn't have the X cast on the front of the block.

How can I tell if it's a roller block or not? Where can I find the date code? The block was pulled from a mid 80's Dodge truck.

Do I need special rings for the cop car motor? I know it has the hyper pistons, and according to the information I've found on here, it's got different rings from the factory.

If I can find a deal on the M1 or the Eddy intakes I'll go that way. If I have to buy a new one, I'll most likely roll the dice with the crosswind simply due to cost.

If the E85 works out I'll likely think hard about upgrading to FI with a MegaSquirt based system and twin turbos next year. Even with the high compression E85 at 105 octane ought to be enough to keep the motor from pinging or knocking.
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brotherGood

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Re: '87 Diplomat Police 318 Build
« Reply #8 on: April 15, 2013, 22:17:02 »

This engine that's going in didn't get zero decked. Heck, it was supposed to be a quick 300 dollar refresh and swap: we started 4+weeks ago, and added at least a couple hundred bucks and its still not done. The race block statement intrigues me though, I don't know that I've heard of a race 318 block-not that I don't believe you. I've just never heard of it.

Basically, you're turning it into a protouring car. Right? That's what I'd eventually like to do.

Somewhere on here there's a thread on roller blocks vs. Non roller. I dont remember off the top of my head what the visual differences are, but after 85, they were all roller block.
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'86 Dodge Diplomat AHB. Rebuilt 318 LA/Magnum, cop 904, 8.25 rear.

DaveGT

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Re: '87 Diplomat Police 318 Build
« Reply #9 on: April 15, 2013, 22:45:25 »

http://www.forabodiesonly.com/mopar/showthread.php?t=68184

This guy has the same block as I do. The casting number equates to a race block, apparently it was an over counter special at the Mopar parts counter. Some of them could be had with 4 bolt mains, and there were other internal modifications. Apparently they may have also been used as replacement blocks as well. Mine doesn't have the X stamped on the front of the block, however it does have flat top pistons that are near (less than 1/16 of an inch) from the top of the block.

How much compression did you estimate you're losing by not zero decking the block? Did you measure the stock pistons to see how far they're sitting down in the bores? Sounds like we're both working on similar builds.

Are you basing yours off the CC article I posted earlier? I'll be interested to see what kind of horsepower numbers you're making if you end up putting it on the dyno.

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270SE

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Re: '87 Diplomat Police 318 Build
« Reply #10 on: April 15, 2013, 22:50:32 »

How can I tell if it's a roller block or not? Where can I find the date code? The block was pulled from a mid 80's Dodge truck.
'85-up blocks should all be roller whether they have a flat tappet or roller. I have a late '84 or really early '85 roller block. 

Do I need special rings for the cop car motor? I know it has the hyper pistons, and according to the information I've found on here, it's got different rings from the factory.
It's still a 318. The walls are the same, the cop cars used different rings for their application was all.

If I can find a deal on the M1 or the Eddy intakes I'll go that way. If I have to buy a new one, I'll most likely roll the dice with the crosswind simply due to cost.

If the E85 works out I'll likely think hard about upgrading to FI with a MegaSquirt based system and twin turbos next year. Even with the high compression E85 at 105 octane ought to be enough to keep the motor from pinging or knocking.
E85 loves compression, so I can see that.

Oh, and CR will be close to stock with Magnums. The thing about 318 heads being almost as large as 360 heads is BS or no 318 going to 360 heads would ever see a drop in CR. '84-down is lower than '85-up by .4 point or so. Hyper pistons would likely be replacement so may have more CR. Either way, anything stock or close to will have 9:1 or less.

Then, the mag heads, and either an M1 or Eddy intake. You can also redrill the heads to accept an LA intake, but that's up to you. The Crosswind intake has a reputation for bad quality..so I would advise staying away from it if youre wanting reliability.
Crosswind has poor quality control like some of the Demon carbs were bad for. Making sure it's free of flash and you don't overtorque would make it a fine choice.
« Last Edit: April 16, 2013, 18:18:52 by 270SE »
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brotherGood

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Re: '87 Diplomat Police 318 Build
« Reply #11 on: April 15, 2013, 23:17:14 »

My very mild setup is due to run high 13s or so in the 1/4. A different cam, converter, and headers would make it even faster I'm sure. The pistons were flat tops, but they were not measured. Dad was being shown how to build one, and they didn't care to do the science stuff. Assuming its stock, I believe stock depth is .012 in the bore at TDC. don't quote me on that though. I wasn't chasing a huge compression ratio as much as I'm referring to quench. Another member here explained quench to me, and I've been kinda paying attention to that.

I am actually basing my build off of (yet) another members..see 1980Volare. I've seen his car and heard it..in that configuration it was pretty good. His current setup..another time. I would love to get dyno time eventually, just for curiousity..if I can ill post it up.
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'86 Dodge Diplomat AHB. Rebuilt 318 LA/Magnum, cop 904, 8.25 rear.

DaveGT

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Re: '87 Diplomat Police 318 Build
« Reply #12 on: April 16, 2013, 15:17:13 »

If stock is going to net me somewhere around 9:1 then I'm going to have the block zero decked. I really want to get at least 10.5:1 compression if I can, I wouldn't even mind 11:1.

It looks like the plan is to use the block in the Diplomat, the truck block is going back into another truck with just a cheap rebuild, and the 360 heads off the cop motor. With the 340 cam it should be a nice little street motor for the truck, plenty of torque.

Once I get that block back together I'll pull the motor from the Diplomat, freshen up the heads to get the first 318 back together, and then I'll start tearing into the cop car motor to see what I've got. It should have the windage tray, the hyper pistons, and the rest of the cop car equipment.

I've got a line on a set of Magnum heads that I need to go look at today, once I get ahold of those I'll only need a cam, intake, and my rebuild parts. Should be a couple of weeks to get through the machine shop, but I'll have plenty of time to get some racing in this year.

Pretty excited to see this motor come together. I've already taken plenty of crap for building the 318. Everyone keeps asking me why I don't go out and get a bigger block.
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Sublime440

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Re: '87 Diplomat Police 318 Build
« Reply #13 on: April 16, 2013, 16:46:18 »

Zero decking the block and getting quench has nothing to do with compression ratio. Most of the time, when you zero deck the block you will see a gain in compression, it just depends on the type of piston you use. You can have 0.035" quench and still have a low compression ratio (huge D dish piston like what's attached). You want to use a flat top or one similar with very small valve reliefs since you probably won't need the clearance anyway

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

You can go the route of new pistons, magnum heads, decent cam, etc and just take your time and find good deals. The 850 is going to be waaay too  big for your 318, I don't care what they say about "engines drink E85 faster"....fuel flow and volume are constant no matter which fuel you use....you just extract power from one or the other better. For reference, I have a 870 on a very thirsty, big cam, high flow heads, etc 440 and it still is a pita to tune properly at times.
« Last Edit: April 16, 2013, 16:56:59 by Sublime440 »
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DaveGT

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Re: '87 Diplomat Police 318 Build
« Reply #14 on: April 16, 2013, 17:42:53 »

I'm well aware of the downfalls of E85. Yes, I realize it's taxpayer subsidized, and it has a lower volumetric efficiency that standard gasoline. However, in order to run high compression it's hard to beat a fuel that clocks in at 105 octane, compared to the 93 that's available at pumps in my area.

However, I'm not looking to build a daily driver here. What I want is an engine that revs quickly, can rev to 6k without valve float or other issues, and makes good power. I need to accelerate quickly during an autocross, and I need a motor with a big enough powerband that I'm not constantly shifting to stay in the powerband.

No, I don't think $4300 is really a "budget" build, and yes, there are other, more attractive blocks that would likely net bigger power numbers. However, what I'm trying to do here is a build an inexpensive car that I can autocross competitively and have a lot of fun with.

I'd like to spend less than $1500 assembling the motor. I want to use as many parts that I already have as I can in an attempt to keep costs down. I can most likely come up with a smaller carb if needed.

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?
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