318 head options ... again!!

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scott2683

scott2683

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Hey folks,

So I'm still looking into some heads for my 318.

- I found a guy with a nice set of #308 heads - but I understand these are not as good as the #302 heads and will not raise compression?

- I have a set of factory heads from a 71 318 - Would taking them into the machine shop and having 1.88/1.60 valves in help with HP and maintain compression?

- I also found these on ebay, they guy is willing to work out a deal on. http://www.ebay.com/itm/Mopar-Cylinder-Heads-360-Small-block-new-valve-job-fit-318-340-aar-t-a-r-t-oem-/251944538007?

The engine is bored .030 over.
high compression pistons - not sure what brand
I just ordered comp cams xe268h cam for it.
3.23:1 gear ratio
Edelbrock performer / 600 CFM edelbrock carb

- The previous owner had the factory heads rebuilt to factory specs. Even with the bottom end being somewhat built this car is so much slower my old 318 that my dad and I built. I would just like to get a few more ponies out of the motor. It runs strong so I would hate to swap it out for a 360. But I'm craving horse power. I bought my last set of heads from arrowhead racing, the heads worked great on my old 318, but their customer service was pretty crappy, I almost hate to buy from them on principle.

Any help would be appreciated, I'm not looking to break the bank, I'd like to be as conservative as I can. The car is a driver, I don't anticipate running it down the drag strip any, I just want a fun runner.
 
In any engine Compression is King. The tighter compression, the more fuel you can get to burn effectively . That's what forced induction is all about. Of course, you can have too much compression with an Engine not set up correctly. One of the ways to maintain static compression is a three angle valve job. Seals tighter. If you are seeing lower power output from this 318 from the one you built, Lots of possible causes. I have seen builds comparing closed port heads to higher flowing heads, and it was its about a wash, BUT at normal RPMs, like the ones used on a street driven car, the closed port heads win hands down. Larger valves might lower compression if the valves get sunk into the heads to do the valve seating, three angle valve jobs. I am not the pro here, just my 2 cents worth MT
 
Thanks for your help Tim! The more threads I read on these forums, the more confusing it becomes!
 
How far from the deck are the pistons when at tdc? Use that, diameter and thickness of head gasket and finally volume of cylinder heads to figure out compression ratio. If those 308 heads were shaved and had bigger valves your cr could be in the low 9:1 area and that would work. Same with the 302's and they would probably have better port velocity. Get a converter to mach that cam and it should be a descent combo.
 
My opinion is the opposite as Mopar Tim. Flow will ALWAYS trump compression. Compression certainly helps and is important, but giving the choice between the two, flow trumps. Means you have .030 over high compression pistons, I would go with the 308's any day over the 302's. Here is an example of compression vs. flow: one 318 is all stock including 2bbl and single exhaust, but 11.1 compression pistons were added. The other 318 has 4bbl, headers, and a 340 cam with 360 heads. compression is 7.9 to one. which one wins the 1/4 mile???? the one with much better flow, not the one with much better compression. Obviously, ideal is compression with flow....
 
318willrun said:
My opinion is the opposite as Mopar Tim. Flow will ALWAYS trump compression. Compression certainly helps and is important, but giving the choice between the two, flow trumps. Means you have .030 over high compression pistons, I would go with the 308's any day over the 302's. Here is an example of compression vs. flow: one 318 is all stock including 2bbl and single exhaust, but 11.1 compression pistons were added. The other 318 has 4bbl, headers, and a 340 cam with 360 heads. compression is 7.9 to one. which one wins the 1/4 mile???? the one with much better flow, not the one with much better compression. Obviously, ideal is compression with flow....
Click to expand...

You need a balance of both, among other things. Just putting high flow heads in a teener with low factory compression, is not a good build. a 318 does not require much in the way of flow, not enough displacement to fully utilize all the extra capacity, hence, the stroker craze. MT:burnout:
 
Thanks for all of the information. If I were to use the 308's, would they be ok stock?
 
What Mopar Tim meant to say was "a low HP 318 does not require much in the way of flow"

A high HP 318 requires a high flow head. The compression of the motor just needs to support the octane gas you plan to run. If you are going to spend money, spend it to get the higher flow. You can always use thinner head gaskets or mill the heads if you are really sweating the compression ratio.

Going from 8:1 to 9:1 compression does not yield a 2% increase in power. For all that work your 200 HP motor now makes 204 HP....congratulations!
 
Mopar Tim said:
You need a balance of both, among other things. Just putting high flow heads in a teener with low factory compression, is not a good build. a 318 does not require much in the way of flow, not enough displacement to fully utilize all the extra capacity, hence, the stroker craze. MT:burnout:
Click to expand...
I agree on a balance of both, but to say compression is king is what I had a different opinion on. The OP listing states he has .030 over (higher compression pistons), and he is using the xe268 cam (higher flow). The 308's would work great with this combination. You ONLY NEED about 8:5 to 1 compression. People run 10's at almost 130 mph with that kind of compression. In fact, there is a member here that was going very deep into the 10's, with a 318 cubic inch motor, not a stroker. Do not sell the 318 out short, or choke it out with no flow.... It is more cubes than the fox body 302's, and the Ford guyz not only love their 302's, but they build them to run
 
scott2683 said:
Thanks for all of the information. If I were to use the 308's, would they be ok stock?
Click to expand...

Stock would work great. the 308's have been argued to out flow the X and J heads on the exhaust side both being stock. If anything, if compression is a concern, you can have them milled .030 and bolt them on!
 
Mopar Tim said:
In any engine Compression is King. The tighter compression, the more fuel you can get to burn effectively . That's what forced induction is all about. Of course, you can have too much compression with an Engine not set up correctly. One of the ways to maintain static compression is a three angle valve job. Seals tighter. If you are seeing lower power output from this 318 from the one you built, Lots of possible causes. I have seen builds comparing closed port heads to higher flowing heads, and it was its about a wash, BUT at normal RPMs, like the ones used on a street driven car, the closed port heads win hands down. Larger valves might lower compression if the valves get sunk into the heads to do the valve seating, three angle valve jobs. I am not the pro here, just my 2 cents worth MT
Click to expand...

I strongly disagree with this. My 5.2 in my 3800 lb Dakota has 8.86:1 compression. Dynoed 290 at the tires. Ran a 13.27 @ 103. Peak flow of the heads was, IIRC 241 @ .500 lift. Ported magnum with 1.97 intake valve
 
I agree with all above, but how come when an engine is worn out, needing new rings, it loses power? Same flow, same heads, only difference is compression. This is a complicated dissscusion and im not versed enough to explain my thought on it. I know my thoughts, I just find it hard to explain. MT
 
I really appreciate everyone's opinions and real life experiences. I'll probably go with the 308's. I emailed the member here on the forum that had them, so if he responds in the next couple days, that the route I think I will choose. I can work on engines, and rebuild them, but my knowledge is quite limited when it comes to the science behind some of this stuff. I just don't know how people did anything before the internet ... I would be lost without you guys and google :)
 
Tell us how the 308's work. I would lean toward the 302's with an opened up 1.60 exhaust valve. That way you get a nice quench and an added exhaust exit, then you can work the roofs of the exhaust (dont touch the floors) grinding off the EGR bump or any other anomalies on the roof, smooth them out and port match to the gasket.
 
302 Heads are your best bet as far as performance goes, the 308 heads will work fine just not as well. Here's an illustration of the difference they make:

UDOW4pI.jpg


YQ1MvaH.jpg
 
All the comments favoring flow refer to quarter mile times and speeds.......all emphasize mid to top end power for best drag strip times. Makes sense.

The OP says his car is a driver.......but not sure what he wants as a 'fun runner'....winding it out on an interstate to 120 mph or short burst of acceleration? IMO, emphasis should not be on max HP over mid to high RPM but good torque for driveability and good low to mid range RPM performance. Your low RPM torque is going to come from compression....my most drivable and fun street engines have been high compression ones. Even with high flow components, the CR increase makes all the difference. IMO, the cam selected is kinda straddling the fence.....a bit past where I would put it for a lower RPM torque motor.

BTW, I built my 1st v8 performance engine 41 years ago, with quench pistons and all that good stuff. It all came from Hot Rod and Car Craft magazines (my 2 magazine purchases EVERY month), plus reading general books on performance engines. You studied more and figured it out yourself; all the interactive learning was at the strip, the track, or the hot rod shop. Less of the 'bolt-on' mentality 'cuz with heads there were the factory pieces and not much else. The general principles in NA, carburated engines was pretty much known 40-50 years ago: flow mods, quench pistons, vacuum vs mechanical carbs, etc.; 1 HP per CI was very doable. Roller lifters were just barely coming on; common today, exotic then.
 
Deceus said:
302 Heads are your best bet as far as performance goes, the 308 heads will work fine just not as well. Here's an illustration of the difference they make:

UDOW4pI.jpg


YQ1MvaH.jpg
Click to expand...

This is what I was trying to say. Thanks MT:burnout:
 
nm9stheham said:
All the comments favoring flow refer to quarter mile times and speeds.......all emphasize mid to top end power for best drag strip times. Makes sense.

The OP says his car is a driver.......but not sure what he wants as a 'fun runner'....winding it out on an interstate to 120 mph or short burst of acceleration? IMO, emphasis should not be on max HP over mid to high RPM but good torque for driveability and good low to mid range RPM performance. Your low RPM torque is going to come from compression....my most drivable and fun street engines have been high compression ones. Even with high flow components, the CR increase makes all the difference. IMO, the cam selected is kinda straddling the fence.....a bit past where I would put it for a lower RPM torque motor.

BTW, I built my 1st v8 performance engine 41 years ago, with quench pistons and all that good stuff. It all came from Hot Rod and Car Craft magazines (my 2 magazine purchases EVERY month), plus reading general books on performance engines. You studied more and figured it out yourself; all the interactive learning was at the strip, the track, or the hot rod shop. Less of the 'bolt-on' mentality 'cuz with heads there were the factory pieces and not much else. The general principles in NA, carburated engines was pretty much known 40-50 years ago: flow mods, quench pistons, vacuum vs mechanical carbs, etc.; 1 HP per CI was very doable. Roller lifters were just barely coming on; common today, exotic then.
Click to expand...

And here I thought I was crazy preaching this! Thanks im not over the hill yet!:burnout:MT
 
Where does it say in the Mopar Performance article that '302 heads are used? J.Rob
 
RAMM said:
Where does it say in the Mopar Performance article that '302 heads are used? J.Rob
Click to expand...

The heads they used were modeled after the 302, same design (closed chamber swirl port) with slightly bigger valves. I also agree nm9stheham, that cam is really pushing it for a fun machine, it'll have nice stumble to it but something like the xe262 would take a little off the top end and add a decent amount to the low and mid range rpm power.
 
either way would work, but remember, when mother mopar went to build the 318 magnums, they used 360 ports on a 318. Results???? The best performing stock head ever used in mass production on a 318, 340, or 360. I'll still take flow to the bank any day, anytime.
 
nm9stheham said:
All the comments favoring flow refer to quarter mile times and speeds.......all emphasize mid to top end power for best drag strip times. Makes sense.

Ummmm..... when you take a 318 2bbl, and add small 4bbl, 340 cam, better flowing heads, the 60 foot times drop as well as the 1/4 mile times...
Click to expand...
 
That's the problem building a stock short block 318 is Compression vs airflow, if all thats expected is 300 hp or less, stock heads are the best choice.

Problem with that mopar performance dyno comparison is one we don't know any of the variables. Like CR, head flow number etc... plus their were trying to sale those heads and plus it doesn't really apply to this build since it's mainly comparing ported heads. Most people run unported heads, a stock 318 open vs closed vs 360 vs 308 vs magnum etc.. would of be better.

A percentage of the gain of the ported 302 vs ported 360 would of been the compression bump probably 15 hp or so and the rest could of been from better port job and or the swirl port and or better combustion chamber.

308 heads also have swirl ports.

Magnum probably would be your best option better CR and flow.
 
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