View Full Version : 318 heads - 675 vs 302
12-12-2002, 12:35 AM
Okay...it seems everyone likes the new 302 heads on a 318. hear is the question...swap for swap which head will flow better WITHOUT modifications, a vintage 71-75 #675 318 head or the newer #302 head? I have a set of both heads. Both have had standard valve jobs done recently. The motor is basically stock. Which one will work better in my '73 dart with a 318?
12-12-2002, 03:40 PM
I asked a similar question a few weeks back. According to the replies I got, the 302 heads are the way to go. Everything else being equil, the 302's have hardened valve seats, and the hi swirl feature.:confused:
12-13-2002, 06:49 AM
Hey PlumCrazy its not so much the higher cfm it is the 302 allows better Volumetic Effiency. The gas hits the combustion chamber just right, and the exaust gets out of dodge fast. Thats what you need for a gasoline engine. I hope Santa brings me a set for my 318! If you look up the board I just did a post asking about the 302's and the guys loaded it with good info. Check it out.
12-13-2002, 08:54 AM
A set of x or j's off of a 340 or 360 with 2.02 - 1.60 valves would be the best to use. :D
12-16-2002, 11:13 AM
Originally posted by dwc43
A set of x or j's off of a 340 or 360 with 2.02 - 1.60 valves would be the best to use. :D
I know these heads would be better, but isn't there a problem with the 318 block interferring with the 2.02 valves? As I understand it, the cylinder needs to be notched to allow the 2.02 valve to open. Is that right?
12-16-2002, 11:16 AM
They need no mods to be installed at all. :D
12-16-2002, 01:48 PM
Cool! Thanks for setting me straight on that.:D
12-16-2002, 05:05 PM
no prob. :D
12-17-2002, 02:25 AM
X or J's are fine heads but in my opinion not great on a 318.
Frankly, they are huge on that engine - will kill your motor and turn your 9 to 1 318 into about 7.7 to 1 unless you mill a ton off off them & take them down to about 59-60 cc's.
That's a one way street because once you do that - if you ever put them back on your 9 - 9.5 to 1 340/360 now it will be closer to 10.5-11 to 1 and without a special cam you will be married to race fuel coctail.
So yes they bolt on but................ consider the rest of the story. Stick with your 302's you'll dig those a bunch on the 318 - Very snappy engine.
12-19-2002, 02:25 PM
I wouldn't consider the big heads and valves until you are looking at over 350 hp. 302's with 1.88/1.60 valves and porting will give you plenty of air up to 350 hp and much, much better low end and mileage, than the big heads.
12-19-2002, 03:27 PM
First off the 360's all run around 8.0:1 comp due to the fact all of them use dish pistons.
The 340 and 360 heads are the same cc and on a 340 depending on the year you got a cr of 10.5:1 down to the lowly8.5:1.
The 318's all run around 8:1 as well except for the '68 - '69 models which were close to 9:1 and made 230 horse.
The 2.02's and 1.60's are not too big for this engine. I've run 'em for years with some little and med sized cams over the years. With a flat top and mlled to get a 64 cc head you get 10.5:1 cr so your 59 - 60 cc's you stated are way off. A good mill of only .035 will clean 'em up to give you a good mate surface and around 9:1 cr which is good for the pump gas and exactly what you need.
To answer the question that was ask these will out flow thw 302 without mods which from a performance stand point is what you need also since all A engine heads are exhaust flow restricted. That why dual pattern cams work so good in these slightly moded engines. :D
12-19-2002, 04:50 PM
I totally agree that the big heads will outflow the 302's, but extra flow does you no good, and can actuallly cause you harm, if you don't need it We just tested a set of ported 302's that flowed 185 (same as unported big heads) on the intake and 90% (much better than the big heads) on the exhaust. This will easily support the 350hp, and the great exhaust flow will not need a spliit duration. The 302 ports are only 125 cc instead of 180 for the big heads, so you have much better port velocity for low end response. Your torque curve should be wider to the low end, so you get more area under the curve. I you are going to wind the 318 to very high rpm and make very big hp, use the big heads, at that point low end is gone anyway, but for a general purpose engine, the 302's and a tighter convertor will be more fun.
12-20-2002, 01:06 AM
Thats good to know those 302 heads sound so good. I just got a pair. I was wondering, do you think the higher efficency head design will help my car get better gas miliage ?VS the old 318 heads. Also will they still keep the good lowend power while permiting topend power... till like 5500 rpms or so?
12-20-2002, 09:41 AM
I don't have the heads on the car yet, but from what I have read and heard, the 302's should be more efficient throught the entire range, with the most benefit seen at low to mid rpm, when the small ports do good. The dyno tests I have seen usually netted about 230/235 hp with a 340 type cam (in a 318) at 5500 rpm. I would think that mileage would also improve.
The thing to remember is that these heads need to be ported and bigger valves installed to get those numbers, as they only flow about 120 cfm stock.
12-20-2002, 07:02 PM
That's why you need to use the x or j's with the big valves. Dollar for dollar (no money paid out 'cause they dont need porting) will make more torque and hp. With a dual pattern cam,headers,weiand manifold and tq you will make more than the 235hp you found. It will have a much broader and flatter torque curve throught the entire rpm range. As the pros say you cant race a dyno. They are good for the inital tunning, but my real world numbers and my car will beat you. :D :D
12-21-2002, 05:16 PM
OOOPs typo--The ported 302's did 335hp not 235.
12-22-2002, 03:00 PM
Plumcrazy, The 302 heads, with 188/160 valves, ported or not, are your best bet. If you're not doing 6500 - 10,000 rpm, you don't need BIGGER.... You'll love these heads, and so will the engine. Merry Christmas To You All, and a great New Year :)
12-22-2002, 07:15 PM
X's or j's wont flow enough to go 7,000 - to 10,000. 6500 would be about max and I'll still out run those 302's. Dont get me wrong the 302's are o.k.,but do not compare to the x or j's and that's from exsperience not racing a dyno or a flow bench. :D
12-23-2002, 01:19 AM
dwc43, I'm bettin you're right, about the heads, BUT, I read the question as a " Which pair of pants should I wear'?? type of question! As a bias party, to which, I'am, I really saw a big DIFFERENCE in the running of my engine, 318/ 302s/188/160. In closing, I know you, and the others, are right, as far as heads go...... You all have a great Christmas, and a happiest of new years. LOVE this site, :D
12-24-2002, 12:12 AM
Thanks All...you've been somewhat of a help. But my question was never really answered. ITS WAY TOO EXPENSIVE TO PUT 1.88int & 1.60ex INTO #302 HEADS! stock for stock which is better...STOCK #302 heads or STOCK vintage 675 heads. A standard valve job is 150-200 bucks. Some garage porting abd thats it. Once you add up the cost of Installing larger valves and any port work...you might as well start to consider aftermarket heads. Its not a question that large valve #302 heads will be best. WHAT ABOUT STANDARD SIZE VALVE #302 heads?????
12-24-2002, 12:25 AM
Well the 302s arent that expensive, i got a pair from Alabama Cylinder heads for 500 bucks after the cores were exchanged, they covered shipping.. ive seen standard 318 heads for 400 bucks and i doubt shipping was covered on them
12-26-2002, 11:56 AM
The stock 302 heads are the better bet. I've got a set of 675's from my 72 dart, and a set of 302 from my 86 van. I understand that, for the street, the 302's will give better combustion and therefore better mileage and a little better performance. Even in stock form.
If you were to do some minor work to them, I'm sure the differences would be noticable. For a MILD street engine, the 302's would make the better choice.
Hope this helps.
12-26-2002, 12:51 PM
Plum: As I said in my last post, the stock 302's we tested only flowed about 120 cfm on the intake and about 72% on the exhaust. This will support only about 240 hp, so if you want more than that, you will need the bigger heads. The stock 302's will still give you much better low/mid range than the big heads, but will crap out pretty early. One head I have has casting flash that covers almost 1/2 of the intake port at the valve guide. They have a lot of potential, but aren't great out of the box.
12-26-2002, 06:45 PM
For a budget buildup, the 302's are best. No milling needed, stay with stock valves for budget concerns, a used set should run about $125 a pair at a pick and pull. Yes, without a port job, they don't flow that much, but a 318 shouldn't need that much for a street application. X or J heads are expensive out of the box, require milling to get a decent compression ratio and frankly don't offer that much more efficiency than the 302's. yes they flow big #'s, but the 302's can as well. Leave the X and J heads for the 340 and 360 crowd. Get a set of 302's, run them, if they don't make as big hp as tyou want, then pull them and run larger 1.88/1.6 valves, They will run really strong then. I used a set in my '79 LeBaron buildup and they gave a remarkable performance gain over the stock '79 heads. I used a thermoqud on a 360 intake, along with a Torquer cam, along with slight milling on the heads and a minor port matching job. This gave the car a really good performance kick for less than $1000 on the rebuild. I never dyno'd the motor, but the desktop dyno gave back a 314 hp at 5500 rpm figure. Of course we all know that desktop dyno's are a bit over optimistic, but I would guess that a 275 gross hp wouldn't be out of the question, this from an engine that was rated at 120 hp stock. The heads are probably wourth a solid 15-20 hp over the stock 318 heads. cruzerjd
12-26-2002, 11:47 PM
Thanks All!!...Great point about flow rates Turbododge. We all want big numbers from our mods. My current project is way short on cash, but i have to do something this winter or i'll go nuts! So it sounds like 302 heads from the pick and pull, disassembled, some minor flash removal with the dremal, a quick 3 angle valve job and Im off! hmm...this leads me to another question...but that is another posting...anyway..thanks!
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