built up 318 oddly low MPG's? hp rating?

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The double pumper is killing you. They are not set up for fuel mileage.

Even if you adjust the stuff you can, the PVCR and everything else in the metering blocks are still set up for a fat mixture, and things are only ever going to be so good with that 727.

The car would also drive a ton nicer with a 570 or 670 street avenger on it.

Getting an actual compression ratio out of the motor at this point is going to cost a ton more than a carb. To get it anywhere near good, you would need pistons, and/or a set of heads with smaller chambers.

Those pro products intakes are horrible also. I don't know if its possible for it to knock your mileage down any, but it probably is....

On the other hand, your car looks GREAT. Or at least the small pieces of it we can see.
 
A double pumper is pretty much the opposite of fuel economy. These guys http://www.holley.com would never have recommended that carb for your combo.

You'd need to take a pretty heavy cut on those heads to bring compression up. Like .060 or so. That can get expensive when you add the costs off cutting the deck surfaces, intake surfaces, shorter pushrods, gasket set, etc... Then there's the issue of the big ports. If you had a 3000+ RPM converter, 3.91 or deeper gears and a cam with more than 230 @ .050 duration you could take advantage of the flow potential. But you don't. A mild street 318 generally does better with 318 heads. Well prepared 318 heads can support 300-325 HP pretty easy. 360 heads will support 400-450, but will hurt low end response on a 318 (if you're building a 400+ HP 318 low end response won't exist so who cares).

So what should you do? Cutting the heads you have now will be expensive. Swapping 318 heads, a regular Performer intake and a more reasonable carb could also be expensive. You could always leave the heads alone and swap in a 360 short block...

3000 RPM at 60 MPH seems a bit high for 3.55 gears. Are you running lowrider wheels and tires? A 26" tire should be more like 2800.
 
turns out I have vacuum secondaries. on a holley 650

I have 225/60/15 tires in the rear. I have another low profile single plane intake, I think it is a Holley street dominator. I thought the dual plane high rise air gap was good, how does that hurt my fuel economy that much? I just thought it made it flow better and atomize the fuel better. 318 heads
 
You can pull the heads without pulling the engine, but have to pull and teardown the engine to get the block decked.

Regarding run of the mill (i.e. stock) pistons, there are two different specifications. The 71 and later LA318 pistons sit lower in the block than the earlier pistons do. I'd estimate a gain of 0.4 in CR by swapping those out.

The gearing thing is more than just the rear end gear ratio. It also involves the height of the entire wheel tire package. e.g. If you were to go to a larger tire, it would lower (numerically) the revolutions per mile of the engine. Compare going from a 205/60-14 to a 205/60-15. Rev/Mile 851 vs 817. 205/60-15 vs 235/60-15, 817 vs 772. A low number means fewer rpm to attain a particular speed. This is good for fuel economy, bad for acceleration.

Until you lock in on your wheel/tire package, getting the speedometer to read accurately is going to be like nailing jello on a wall. Once it is set, the rule of thumb is one tooth per 3 mph error. It the speedometer is reading 63, when your GPS says you're doing 60, need to get a speedometer gear with one tooth more than the one you have in the car now.

IMO, the carb is OK in terms of cfm. An air valve secondary is a better choice for a 318/auto combination. Consider having the secondaries adjusted so that they open later in the pedal travel.

One of the things I'm having to come to terms with in terms of setting up a carburetor is how to deal with ethanol laced fuels. It doesn't produce the bang for the buck that the old stuff did. There's a point where all I'm doing is pouring more fuel down the carb and getting nothing more from it. My goal is to stay just short of that point.
 
alright good to know, there are a few non-ethanol places around where I live and I have tried a full tank on it, I didn't really notice much at all when it came to power and since it was $.60 more a gallon I just went back to regular. My plan is tomorrow reset and tune mu carb, floats, mixture, idle settings, choke, the works. Then drive it a bit, maybe invest in an MSD box. other than that I can't do much. Sounds like decking the heads is too much work, im not going to pull the engine so it may come down to putting it on a lift, pulling the oil pan and putting in new pistons. any recommendations on which ones at this point? i figure some good KB 9:1 pistons, maybe 9.5:1 if you guys think the heads are lowering my standard compression gouge number so i will end up with 9:1.
 
A vacuum secondary carb is much more reasonable for this combo, and should be pretty close out of the box. Try putting the jetting back, and make sure the power valve is 2 numbers below your cruise vacuum.

You can't (or shouldn't) just install new pistons in existing bores. At a minimum the bores would need to be honed to seat new rings. For best results the bores should be resurfaced to the next oversize. If the engine has minimal mileage since the .030 resurface you could probably get by with a light hone. In any case I wouldn't personally attempt this with the engine in the chassis, but I suppose it could be done.

Kieth Black KB167 pistons have a taller compression height than typical replacement 318 pistons. They are popular because they bump compression about a full point. With 318 heads, especially closed chamber 302 or magnum castings 9.5 compression is pretty easy to achieve. You could probably get 9.0 with the 360 heads, but some milling may still be required. Before the KB167's showed up, the domed "11.5:1" pistons were popular. With 360 heads they would yield 9.5-10.0 compression, albeit with a less than optimal chamber shape. During the 70's and 80's that was a pretty common way to go.

Heck, as long as you're gonna replace the pistons, why not replace the crank too. A 4" stroke crank would bring your displacement to 390. Then the heads and intake wouldn't seem quite so large (but the cam would seem kinda small).

Skip the MSD unless you really think you have an ignition issue. There's nothing wrong with MSD, but it ain't magic. There's nothing wrong with Mopar ignition either. Both are adequate. But if you do have an ignition problem fix that first before monkeying with the carb.
 
Ya i probably wont be really messing with the engine, i'm only 17 and have been building it for 16 months haha heck I want to drive it now before I got to college in 6 months. Any money I could put into this engine will go to a 360 stroked to a 408 someday, I only built up this one because the bottom end was already done.

I agree with the MSD stance, everyone seems to have one but I hear they dont add a whole lot, but if my ignition craps out on my again i'll just put the money into the MSD.

Could be i am also letting the engine warm a little too long and my electronic choke isn't set quite right and it idles up to a healthy 1800 haha I think i'll set it down to 1200 and let it only warm up a min before driving it, they are cast iron heads so I can't to a lot of harm there if I grandma the car in the mornings.
 
I think your best bang for the buck solution, based on everything you've told us, is to sell those 360 heads and get yourself some 318 or even 273 heads.

While the heads are off, use a straight edge and a feeler guage and figure out how far below the deck your pistons are sitting at top dead center.

Then use a compression calculator, like the one at keith blacks website to figure out what chamber size heads you need to get the compression ratio you want. That will help you choose the right heads and/or decide how much to mill off them.

One more word of caution. Not only are mopar blocks commonly taller than spec, but the 273 heads I've cc'ed had chamber volumes larger than spec. So you should cc the heads if you can.
 
I agree, swap the heads and be done. 66-67 273 heads should be easy to find, nobody wants them and will give you better compression than anything else. If you do have a vac sec I'm sure 650 can be tuned to work fine. I'm sure that intake manifold is fine, def don't want any type of single plane on it.

I just had my car's original 273 heads re-done and swapped them for open chamber 318 heads that were on the newer engine. That, plus porting, and the xe268 cam really woke it up but I have not driven enough to check MPG.

According to my measurements, I gained almost a point of compression, I'm at about 8.56:1 now by going to the 273 heads, milled .015, and Mr Gasket 1121G head gaskets (and that makes me think you're probably 7.5:1 or lower, depending on the actual chamber CC and what head gaskets are on there).
 
73 Plymouth Duster said:
Ya i probably wont be really messing with the engine, i'm only 17 and have been building it for 16 months haha heck I want to drive it now before I got to college in 6 months. Any money I could put into this engine will go to a 360 stroked to a 408 someday, I only built up this one because the bottom end was already done.
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If that's the case IMHO, leave the engine as is, tune it the best you can and be happy with it. Maybe go taller on the rear tires to help your highway rpms once you burn the old ones out.

Drive it before you head off to school.:thumbup:
 
If you go with 273 heads make sure they are the later style with the 3/8 intake bolts. I know 64 & 65 used smaller 5/16 bolts at a different angle. I think 66 and newer used the 3/8th bolts at the standard angle.
 
65DartGTConv said:
If you go with 273 heads make sure they are the later style with the 3/8 intake bolts. I know 64 & 65 used smaller 5/16 bolts at a different angle. I think 66 and newer used the 3/8th bolts at the standard angle.
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Yes, you want 66-67. There may have been differences there also, but I know that the 2bbl, 4bbl and Commando engine in 67 all used the SAME EXACT head, and that's what I had on mine. Unfortunately the rest of mine was just a 2bbl not a Commando :p
 
I agree with SirDan, in your circumstances I don't think it would be worth it to go through the trouble of swapping heads just to get back some MPGs. Tune it up the best you can and have fun with it now and in the meantime do research on building a proper engine from the "block"-up. Also research how to tune Holley carburetors and have at it; when it comes to classic muscle cars and hot rods 90% of the time you have to do it yourself if you want it done right.

IMO the only "right" way to fix your engine is to swap the pistons and zero-deck the block to raise your compression. Any other method is more of a band-aid fix and will be more trouble than it's worth, esp. if you are satisfied with the performance the way it is now.
 
I switched from a 750 DP holley to a 600 edel, and went from 8 to 12 mpg instantly, and thats with a 408 stroker, 727 and 4.10 geared 8.25.

I put in a dana 60 with 3.73 gears.

Then went to a Thermoquad AND installed a wideband AF gage, and got 14+ mpg hwy.

However, when I put in a TKO 600 and further tuned the carb, I got (get) 23+mpg hwy on the interstate @ 70 mph, and 18+ mpg hwy backroads (stop and go, small town, 60 mph tops).

Lose the Holley, get a carter (especially a ThermoQuad), get a wideband AF gage, and learn how to tune your carb. And keep the vac advance hooked up.

My duster runs low 12's (best of 12.003), BTW.
 
That's awesome, jimmyray. ...Nice when it all comes together like that: horse power AND economy! Nice work.
 
Ya I think if I want to do anything it'd be to keep my eyes out for cheap 318 heads but it isn't a daily driver and If I wanted fuel economy I wouldn't have bought this car to begin with haha.

I just tuned the carb myself today, front float bowl was way high and secondaries were low,
then I used a .015 feeler gauge to measure my gap on the accelerator pump,
I finally hooked up a vacuum gauge to the intake manifold and tuned the mixture, it started at around 14 and I ended up with 16 on the vacuum so we'll see if that helps.

Thanks for all your guys help
 
you set accelerator pump clearance at .015 at wide open throttle with the pump actuator fully depressed...
 
yes i did.. do the ... mean that's bad? that's what all the tune up specs say to do. anyways I found this paragraph on this website. I said I was getting 16 in of HG in my manifold and indeed they say 16-18 is normal.

All engines require an acceptable air/fuel ratio to run properly, even at idle. Stock or mildly tweaked engines generally idle at 16-18 inches of intake manifold vacuum between 750 and 900 rpm. Carburetors equipped with adjustable mixture screws allow the tuner to change the amount of fuel delivered to the engine creating an ideal idle mixture.

http://www.mopar1.us/engine2.html
 
MOPEkidD-3 said:
I agree with SirDan, in your circumstances I don't think it would be worth it to go through the trouble of swapping heads just to get back some MPGs. Tune it up the best you can and have fun with it now and in the meantime do research on building a proper engine from the "block"-up. Also research how to tune Holley carburetors and have at it; when it comes to classic muscle cars and hot rods 90% of the time you have to do it yourself if you want it done right.

IMO the only "right" way to fix your engine is to swap the pistons and zero-deck the block to raise your compression. Any other method is more of a band-aid fix and will be more trouble than it's worth, esp. if you are satisfied with the performance the way it is now.
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I don't think it will be as much about MPG as HP. A 318 with 7-7.5 comp and heads with big ports and valves plus a moderate cam would be seriously slow and not fun at all to drive IMO.
 
mplex2000 said:
I don't think it will be as much about MPG as HP. A 318 with 7-7.5 comp and heads with big ports and valves plus a moderate cam would be seriously slow and not fun at all to drive IMO.
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He said hes 17, more than enough engine for him rite now! When he wants to go fast he can just slap a supercharger on it.:thumbup:
 
Honestly, in the end its hard to drive a project and work on it too. I suggest a commute beater to get 25mpg and put your money into your car the way you want. You state you are going to collage (and good for you) but, collage should be your main focus and not dealing with car issues. Get your education and get that good paying job then enjoy the hobby, because doing both is hard.
 
Look, something that seems to be missing here is "making the most of what you have."

FIRST step in that process is to determine what you DO actually have.

1---Run a compression/ leak down test to get some idea of the condition of the engine.

3--Use a piston stop to verify ABSOLUTELY that the timing marks are correct

3--Determine if the cam is in time. You can get some idea of this by determining the cam specs, and by marking the balancer or even tearing it down enough (pulleys) to mount a degree wheel. Pull the driver side rockers to relieve pressure on the lifters, and use an indicator on a rigged--pushrod device to determine when the no1 valve events happen

4--Most important of all is to completely go through your ignition timing and determine "what you have". You want to find out what you have for initial timing, (at idle), what you have for mechanical advance, and how much the vacuum advance is applying. Along with this effort, inspect and make sure the ignition system is in good shape, wires, plugs, cap, etc

5--AFTER you have done all of the above, go through the carburetor. Read the plugs, experiment some with jetting. Jets are not all that expensive. Make certain that the float level is correct.

6--Go through and KNOW for sure what you have for gears and tires, and verify that the speedo/ odometer is correct. If any in your family has a GPS, you can check the speedo against the GPS.
 
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