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273 Heads On A 318


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#1 SATFISH6768 (converted)

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Posted April 11, 2005 at 02:25 am

JUST LOOKING FOR SOME THOUGHTS ON THIS. FIRST SOME BACKGROUND. I HAVE THE 273 HEADS WITH ADJUSTABLE ROCKER ARMS. THEY HAVE JUST COME BACK FROM THE SHOP. I HAVE AN EDELBROCK AIR GAP INTAKE, EDEL CAM/LIFTERS , EDEL CARB AND DOUBLE ROLLER TIMING CHAIN. WAITING TO GO ON AND IN. WONDERING WHAT PUSHRODS TO BUY. ALSO WONDERING IF BRINGING THE COMPRESSION LEVEL UP WITH THE SMALLER CC HEADS IS A GOOD OR BAD IDEA. I KNOW I HAVE TO HOG THE RUNNERS OUT PRETTY GOOD TO GET THEM TO FLOW BETTER AS WELL AS GASKET MATCH INTAKE AND EXHAUST PORTS. ANY OTHER IDEAS WOULD BE GR8T.

THANKS
P-DUB

67 TWO DOOR SPORT SAT

#2 TWX

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Posted April 11, 2005 at 10:46 am

What did you do for your valves? 273s had much smaller valves, and you'd probably lose quite a bit of top end if you put stock 273 heads on a 318.

Also, the intake manifold bolts on differently on the 273 than on all of the other LA engines. Does your intake manifold account for that?

#3 Volunteer

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Posted April 11, 2005 at 12:23 pm

I guess the more important question would have to be "what year is the 318?"
ALL 273/318 cyl. heads had 1.78"intake and 1.50" exhaust valves. The small (closed) chamber heads were used through 1967, and this included the first year of the 318 (LA) engine. Using 'pre- 68' closed chamber heads on a later 318 would be worth no more than a half-point increase in compression, as the (early) heads were about 57cc's and the later (-675's) were around 63 to 65.
BUT, you must take into consideration the fact that Chrysler used thin steel shim gaskets at the factories and replacing them with 'compos' will (theoretically) increase the deck height by 15 or 20 thou., worth just under a half point compression (decrease) by itself.
I would recommend you CC the chambers and calculate the deck/chamber volume between the top of the pistons and the top of the deck. All that's left is the thickness of the (head) gasket, and perhaps any volume should the pistons be notched. The stock valves will flow adequately to 4500 rpm's at a max (valve) lift of .450".
With 'mechanical' rockers you need the OEM or equivalent pushrods as used with the SOLID cam.
Finally, as far as intakes, the 273 heads from the beginning (1964) thru? 1965 used a different fastening system than ALL THE OTHER later LA engines so STAY AWAY from them. For sure, the (-920) castings are 'good to go'.

#4 TWX

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Posted April 11, 2005 at 06:55 pm

I forgot, doesn't the 273 have soft-seat valves? That would be a problem for modern gasoline, wouldn't it?

#5 SATFISH6768 (converted)

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Posted April 11, 2005 at 07:10 pm

Thanks guys for the feedback. They are 67 heads. They have new hardened valve seats, silicon guides, valves, and springs. The 318 in question is a 76 with a
2 barrel. I like the 318. The compression numbers I have read for the 76 was somewhere around 8.5 to 1. I'm not looking for a full race or anything crazy but would like to get 350 to 375 out of th 318. Right now with the parts I'm going with, it seems feasible except for the heads ? I have thought about just buying the edelbrock heads from Jegs but was trying to do with what I had first.

P-Dub :huh:

#6 TWX

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Posted April 11, 2005 at 08:07 pm

Thanks guys for the feedback.  They are 67 heads. They have new hardened valve seats, silicon guides, valves, and springs. The 318 in question is a 76 with a
2 barrel.  I like the 318.  The compression numbers I have read for the 76 was somewhere around 8.5 to 1. I'm not looking for a full race or anything crazy but would like to get 350 to 375 out of th 318.  Right now with the parts I'm going with, it seems feasible except for the heads ?  I have thought about just buying the edelbrock heads from Jegs but was trying to do with what I had first.

P-Dub :huh:

<{POST_SNAPBACK}>

Eeeh. more than one to one is always work. What have you done to the block itself? You could probably have it milled to a zero-deck, but you'll have to take it completely apart to do that safely anyway if I'm thinking straight, so if it's torn down that far you might as well do whatever else you'll need to with it as far as machining goes anyway...

#7 SATFISH6768 (converted)

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Posted April 11, 2005 at 08:25 pm

The driving force behind this idea is the article Junkyard Jewel from HotRod Mag http://www.hotrod.co.../113_0304_junk/ it is very interesting but they use a newer head, bigger valves and get the chambers down to 53cc's. With the exception of the bigger valves can't you get these heads to flow close to the same numbers? No I haven't done anything to the engine but it does look that I will have to get some work done on that to. They put new rings and bearings in but that wouldn't be that big a deal.

P-Dub

#8 USA-aok

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Posted April 11, 2005 at 08:36 pm

You seem to be well 'on track' with your 'hop-up'. There has been LOTS of info recently posted regarding the -302/-308 castings. I believe the (-302's) were small-valve (semi-closed) with swirl-ports while the (-308's) were similar but had bigger valves. They both 'debuted' around '85?
I DO stand to be corrected. :unsure:

#9 SATFISH6768 (converted)

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Posted April 11, 2005 at 08:44 pm

Thanks for the info. 1985 vehicles I'll keep my eyes open

P-Dub

#10 TWX

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Posted April 11, 2005 at 09:23 pm

You seem to be well 'on track' with your 'hop-up'. There has been LOTS of info recently posted regarding the -302/-308 castings. I believe the (-302's) were small-valve (semi-closed) with swirl-ports while the (-308's) were similar but had bigger valves. They both 'debuted' around '85?
I DO stand to be corrected. :unsure:

<{POST_SNAPBACK}>

I can't find the book that I have with casting numbers, but I believe that it was '87, maybe '86 at the earliest. Those last generation non-Magnum trucks are probably the best vehicles to get the heads off of...

#11 Bearhawke

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Posted April 11, 2005 at 09:46 pm

I believe that your 1985-89 M bodies fitted with the 318 2 barrel have those good Swirlport heads along with roller cams.............the 4V 'police' motors had some variation of the 360 head..............

#12 SATFISH6768 (converted)

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Posted April 11, 2005 at 10:08 pm

Thanks to all, keep the info coming. I'm serving over in Kuwait right now and when I get home I'll have some time to do all this stuff correctly. I just want to be very well informed before I get back so I can use the time wisely as well.

P-Dub
Knowing is half the battle.
GI Joe

#13 Tweety Bird

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Posted April 12, 2005 at 08:16 am

My 302 heads came from a van, though I don't know what year. I rambled through the local Pull-N-Save, removing valve covers, until I found the casting number I wanted.

Good luck over there. Stay safe, and thanks for your service.

#14 valiant67

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Posted April 12, 2005 at 10:04 am

I believe that your 1985-89 M bodies fitted with the 318 2 barrel have those good Swirlport heads along with roller cams.............the 4V 'police' motors had some variation of the 360 head..............

<{POST_SNAPBACK}>

Those 318 2v M bodies with the swirl heads actually said premium gas was preferred but they would run on regular while the 318 4v only required regular. I remember that oddity from my old 88 and 89 m bodies.

#15 SATFISH6768 (converted)

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Posted April 12, 2005 at 09:49 pm

I really appreciate all of the info. I was wondering if anyone might know how many cfms the ol 273 heads flow. If anyone has any old books laying around that has those old numbers in them that might be helpful too. Does anyone have any suggestions on a good how to book on rebuilding or hot rodding these small blocks?

Thanks again,
P-Dub

Never be oblivious to the obvious.

#16 TWX

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Posted April 12, 2005 at 10:21 pm

Those 318 2v M bodies with the swirl heads actually said premium gas was preferred but they would run on regular while the 318 4v only required regular.  I remember that oddity from my old 88 and 89 m bodies.

<{POST_SNAPBACK}>

The combustion chambers were something like 56cc instead of the high sixties for the older ones and the 360 ones. Much, MUCH better compression, to the point of making me wonder if a 318's 302 swirl port head would actually be a better choice on a 360 that's mostly lower-RPM street driven than anything else, or if it'd make sense to buy them and have 1.88 or 2.02 valves installed, and the main intakes ported to 360 size.

#17 SATFISH6768 (converted)

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Posted April 13, 2005 at 06:31 pm

Yep the 273 heads are 57cc and can be milled .030 to get a 53cc head for a total of 9.5 to 1 compression. To me that seems pretty dang good but the flow thing is still the issue. According to HotRod Mag they had to do a lot of work in that area. They also stated that a 2.08 valve could go in to the heads without any issues of clearance. Quote " Contrary to popular misconception, 2.02-inch intake valves fit the 318's bores without a problem; in fact 2.08-inch intake valves won't hit. " But they also used a set of 302 heads, milled .050 for a 52cc combustion chamber with an overall 10:1 ratio.

P-DUB


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