Better heads

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7duster4

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I have a mildly built 318 in my '74 Duster. It currently has the stock 318 heads that were cleaned up with a 3-angle valve job. A friend of mine has a pair of 340 heads sitting on the shelf. I don't know what year they are or what car they came off of, but they came off a 340. What would the gains be in installing these heads on my engine? I have a 340 cam/valve springs with an edelbrock performer intake and carb. The block has been bored .30 over with 9.1 compression. Would the gains in power be very noticable? Or are there better heads available?

All info is appreciated. Thanks
 
340/360 heads have too big of ports/valves for a mild street 318. You might notice a small jump in power on the very top end of the RPM band, but lower-RPM torque would most likely drop off. A better choice in heads would be factory #302 heads from an '86-'91 318 engine. They have smaller closed chambers and swirl ports. A pair of those ported with bigger valves would give you the best all-around performance for a 318.

I'd also recommend a more modern fast-ramp cam such as the Lunati Voodoo 262/268 or Comp Cams XE262. They have a bit less duration than the 340 cam but more lift, so torque on the low-end is improved over the stock 340 cam but high-rev power is still good (if not better).
 
The gain would be very little, if any, because 340 heads have much larger combustion chambers than 318 heads so they'll lower your already low compression by about another point. They do flow better but the problem is the very low compression with them. Their are allot of better heads out there. Mostly depends on how "racey" you want to get. A good middle ground head that flow real good and will keep the compression up is the Magnum style head. If your lucky enough to find a good used set that aren't cracked and don't need much work they'll give you a nice perf. gain but remember you'll also have to change over to magnum valve train components. Engine Quest makes replacement Magnum style heads that are heavier duty than the originals and are priced reasonable. If it were me looking to improve the perf. of a 318 that's where I'd look. JMHO
 
engine quest heads would be the best approach...

can get them with drilled for LA intake manifold also...
 
70aarcuda said:
engine quest heads would be the best approach...

can get them with drilled for LA intake manifold also...
Click to expand...

I dunno.... Aren't those still a bit big for a street 318? I think to really get the most potential out of those heads you'd have to do a bottom-end rebuild with flat-top zero-deck pistons for compression/quench and beefy enough rods, etc. to handle 6500+ RPM.
 
MOPEkidD-3 said:
I dunno.... Aren't those still a bit big for a street 318? I think to really get the most potential out of those heads you'd have to do a bottom-end rebuild with flat-top zero-deck pistons for compression/quench and beefy enough rods, etc. to handle 6500+ RPM.
Click to expand...

Why do you think that? They have essentially the same combustion chamber design and size as stock 302 heads (Heart shaped chamber, 62 cc's) The ports are larger but they still have real good velocity from the flow measurements I've seen. Also as far as the port size of the 340/360 heads killing all the low end torque on a 318 that's a bunch of bunk IMO. About 20 yrs. ago before I knew the 340/360 chambers were bigger than the 318's and would lower the compression me and a buddy of mine put my 74 360 heads (stock but rebuilt) on his 78 318 and it ran fantastic especially considering the compression was probably only about 8 to 1 at most. It had 3.21 gears and with everything except the heads absolutely bone stock it broke into the 15's. Sorry I can't give an exact time, just been too long to remember but I do know it was in the 15's which isn't bad for such a small engine in a full size truck. It did have a 72 340 intake with a thermoquad on it also but the jetting was stock. The 340/360 heads do loose some bottom end but from my experience with them it wasn't a huge amount like allot of people say. JMHO
 
MOPEkidD-3 said:
I dunno.... Aren't those still a bit big for a street 318? I think to really get the most potential out of those heads you'd have to do a bottom-end rebuild with flat-top zero-deck pistons for compression/quench and beefy enough rods, etc. to handle 6500+ RPM.
Click to expand...

Fishy's response is very good and on target. While I would prefur a smaller port, the Magnum port isn't to large to have adverse effects on a large degree.

Your idea of rebuilding the 318, as above, would have great bennifits with any head used, but it would be just a bit better with a closed chambered head and the quench it would have.
 
Well, okay, if you guys say so. It just seemed like he would have more cylinder head than he could effectively use (at least for now). But if the price is right I guess there's no reason not to.
 
Well, yea, there probably is more head there than the engine needs right now. But it will work OK.
Theres a catch in cylinder heads though. It's the money in your pocket vs. the choice of heads. In many cases, people want to know what would be the best head. OK, cool. Then theres, I only have $500 to put forth on the cause.
Do we port the head we have or do we go for a set of larger heads?
Alot is build dependent and what we are willing to live with....or without.
 
Thanks for everyones feedback.

After doing a search I have seen a lot of posts about about the later 302 swirl heads. Sounds interesting. The money is one factor but another factor is the job itself. I have never performed a head swap before and would definetly be a big job. If I do decide to do something it wouldn't be until down the road.
 
One thing about the magnum swap is cost. LA heads like the 302 would be cheaper but need substantial porting to flow with the magnum

The magnum swap requires magnum head bolts,oil through push rods,possibly a magnum style intake manifold (unless the heads you get are drilled for LA ),so there are some extras involved.
 
A head swap really isn't as big of a deal as you might think. It just takes a little while draining all the fluids and depending on the condition/cleanliness of your engine and intake/exhaust manifolds it's really pretty simple once you get stuff out of the way. I thought it was a huge deal too until I ended up pulling my 318 from my Duster and realized how simple these cars really are. Dirt and grime can make a task seem much more daunting, though.
 
7Duster4;

It is true, there are plenty of good head choices out there for you to choose from. Just wanted to tell you what we did to a friends 1972 Challenger 318. We pulled the factory heads, intake and camshaft. Installed a set of '915' castings from a '72 340 with the 1.880 valves. We freshened up the seats but did no porting. The matching TQ carb and intake manifold, the MP purpleshaft, 272/268 with .450/.455 lift. A set of 1 5/8 tube headers. 3.91 gears. This car was wonderful on the street and very tractable, ran 14.56 @ 96 . I felt this made a great combo and cheap enough. JMHO.

Terry
 
Out of all the posts I've not seen anyone ask the right question as of yet. How many rpm's are you wanting to turn this engine and what type of driving are you going to do with this engine most of the time?

Using heads that have large ports and valves and have capabilites of 6500 + rpm's aren't going to be very useful on the street if the engine isn't ever going to see the potential of the heads. Using the right head for the application is far more important than just using magnums or spending $$$$ on them.

Some of the biggest dog's I've ever seen was the 318 magnums with the same heads that the 360's had on them, just as factory production was. One of the only reasons that the factory used these heads is/was they could help keep cost down and performance isn't a issue. Will they work, sure they will, but are they the best head for the application more than likely not. To me it just seems foolish to spend $$$$ on parts that don't or won't get the job done.

A good set of older style 318 heads will easily support 400/500 HP when properly done. From the artical in the mopar action mag. the head comparision deal didn't impress me very much. What most people don't see is the amount of volume verses the amount of air flow obtained and where the airflow happens at (what lift). Are most people that read this artical going to run a .550 lift or more on the street for a daily driver, most likely not. So posting good #'s with a given head at higher rpm's than would normally be turned on the street isn't a good reference IMO.

What most people feel is the amount of Tq. that a given engine makes and not the hp that it makes. HP is felt when the vehicle gets moving, Tq. is felt as the vehicle starts moving. The harder the vehicle moves from a standing start the more HP one thinks they have, but this isn't a true way of assuming the engines output or HP. The seat of the pants feel is very misleading. This is where strokers are so impressive as Moper generally states. But then even too they have there limits. So for the life of me I just can't see putting a 160+ cc head on a engine that will never use the amount of volume. Hey a engine is a air pump and putting a larger opening on a pump that can't use the greater amount of air won't make more power or Tq.. And just saying that you have this set of heads on the engine doesnt mean that it will make more power.

I've seen many racers take a set of modified stock castings off a engine and use a set of aftermarket aluminum heads and not gain anything, just as I've also seen the heads make a large difference. By being a bit more conservative in the way of cylinder heads is generally the safest bet. Most all performance head companies sell the amount of performance that there part will make and or capabilities of it, but they can't tell you what to put under them to get you there the most effective way.

As Moper and I have said many times, theres always different ways to achieve the results that's needed or wanted. We both look at value to $$$$ spent but from different perspective's, this is what makes this site so versitle and informing.
 
Your right Bobby. There are things missing from the OE post like, weight, gear ratio, stalll speed tire size and intended purpose of the car,

This is a general question that gets (From me) a generally conservitive answer. On this engine, I would be looking at porting the stock head or a 302. But it becomes a cost factor vs performace issue.

Will the 340 head deliver more performance over a dead bone stock 318 head? I say, YEP! But at a cost of low end torque. Even though he's not turning high RPM's where the head will perform best, it's going to perform in the mid range and up alot better than a OE 318 head.

I'd rather the Magnum head over the 340 head. I'd rather a set of 302's over the Magnum head.

One more missing tid bit of info from the OE post, the price of the 340 heads. Free is great. $500 is still good. This is a thought in my mind vs porting and new valve gear for the (IMO) best power route. The price of doing the head and/or finding the head in addition to the porting price.
 
Rob,
Another thing that I failed to mention is the fact that the fuel mileage or the lack there of, from the resulting of the larger ports and port volume and slower air speed of the port due to the valve size will require a much larger cfm carb with a adjustment of larger jets. Now you could just adjust the jets in the carb but then the fuel curve of 12.5:1 will go out the window. In this case the use of the smaller ports and valves will create more velocity and the need for larger jets and larger cfm carb won't be needed. This way the response of the engine and the low rpm operation of the engine will be much better. In general terms the engine will become more efficient and make more HP and Tq in a useable rpm range. When I say general rpm range I'm talking about Idle to 5500 rpm's or so, depending on the rest of the combination.
 
Just for reference here's a 318 head that I'm currently working on for a customer for a street application. The head casting # is 2843675 which is a old late 60's or early 70's head.

Stock out of the box form:
lift...........Int..............Exh.
.100........79...............75
.200........122.............104
.300........184.............123
.400........188.............130
.500........188.............134

this head had 115 cc intake runner and 56 cc exh. runner and a 62 cc chamber as casted.

Now the modified version, this includes gasket matching and bowl porting and a good VJ, no chamber work was done and the stock factory valves were retained.

Lift.............Int..............Exh.
.100............84...............74
.200...........134..............115
.300...........185..............142
.400...........205..............193
.500...........207..............199

The intake runner is 117 cc's and the exh. runner is 60 cc's I can do a set of heads like this for about $550.00 with all machining. Being he's local there's no shipping but $100.00 more should cover this at todays rates.

Valve sizes are 1.78/1.50
 
I hear ya Bobby, I'm with ya on that. The mention of a smaller carb is also why I often recomend a 600 or so and not a 750.

On the head, how would a 1.88/1.60 with a properly opened up bowl porting work.
 
Rob,
Here's a friend of mine's 302 with a 135 cc runner and 340/360 intake port opening and a 1.98 intake valve as the 1.88 valve was getting thin and were run for many years before we realized what we were leaving on the table. The easiest thing to do was to enlarge the intake valve to a size that could be useable without getting too crazy with it.

lift..........Int
.100........84
.200.......136
.300.......202
.400.......219
.450.......219
.500.......209
 
For the amount of valve size and port volume difference the larger valve head with the larger port runner would have to flow 233.91 cfm's for the port size and 223.56 for the valve size or a average of 228.70 be as efficient as the smaller valve and port size. As we can see this isn't going to happen without a good bit more work, so in this case bigger isn't better and the smaller head is a better choice. Or we can look at it in reverse the smaller head is 6.5% more efficient.
 
Bobby, that 675 head is an option i've used before too because of the smaller chamber. In this car, we dont know all the info. If no other changes are made in terms of camshaft, I would be leaning towards the stock replacement Magnums. It's my opinion that the gain from the smaller chambers and the extra lift and duration of the 1.6 rockers would help the setup, enought o offset the minor loss in response fromt he larger volume. If this car is a 100% street car, and geared for highway, with a stock convertor, I think there will be little "net loss" felt by going with the larger volume head. IMO Magnums in stock form are too small for a 360, ad too large for a 318...lol. But a 318 with some mods and perhaps compression in the 9.5ish range I think would be just fine. That choice being made, change the heads, you have to buy pushrods, lifters, and have the heads drilled for the LA intake. Now you're into spending more cash to get them on and running, and that set of 302s starts to look cheaper. I agree with Bobby that smaller is better, but I tend to lower the rpm threshold where I might consider something else as an option.
 
Every time I start leaning toward buying some EQ heads, BJR gets me thinking I should work on my 302s. Somebody needs to do a cost breakdown for ported 302s versus a magnum conversion. Maybe that would help me make up my mind.
 
67,
What do you have in mind for the use of your heads, as they might not need to be fully ported, but partially ported. It's not often that a head needs to be ported for the street, but will need some work to make them better and get more performance out of them. Most street heads don't need any more than what we do for bracket racing, which is a good gasket match and some bowl work along with a good valve job. The most important things are the valve springs for the cam used and the clearence for the retainer to guides and the valve job and last but not least the matching of the ports. The bowl work will be determined by the amount of cam used, if you have the cam already. If not then get the head work done first and then get a cam to where the heads work the best. The later is the best way.
 
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