In need of some 273 head education

-
68 A

68 A

FABO Gold Member
FABO Gold Member
Joined
Apr 16, 2006
Messages
634
Reaction score
87
Location
Auburn, NY
I am looking to rebuild the 273 in my dart and i would like to do it fairly cheap but at the same time increase the power over stock specs. I assume that there were different heads put on these through the years and was wondering what they would be and the part numbers of them. I do not have the casting numbers of my heads right now or i would post them, but can get them by monday if that would help. I also wondered what it would cost to get some work done on the heads that i currently have to increase flow and wether or not it is worth the money compared to buying a used set of higher flowing heads or by putting money into the bottom end to increase power. Thanks!
 
The problems with the 273 is they have no compression, the bores are to small for bigger valves and the stock heads dont flow very well. I had a 273 in my barracuda and asked the same questions. I had the bottom end rebuilt with stock replacement pistons as custom pistons were in the 600 dollar range. They were .050 down in the hole and were spec. at 8.0 to 1. I had the heads angled milled to a closed chamber to raise compression, and gasket matched the intake and exhaust. The motor ran good for a 273 but I wanted more, so I am putting in a 340\ 373 engine. Looking back I think the money I spent on the 273 was a waste for me. Some other members have 273 that run really well, maybe they can help you more. I still have the 273 heads if your lnterested. I can email you some pics if you want. Bob
 
I'm in the same boat. My 66 Dart needs a rebuild. I am putting together a
Magnum head 318 to run while I rebuild my stock HP273. The high compression in the HP273's are in the pistons not in the heads. But for max.
performance the heads should be ported by someone who knows how. The bore is so small that the heads can't be modified too much by installing larger diameter valves to improve flow. Most parts that you need to rebuild are available through your local parts store. The only hard to find part is the high comp. pistons (which I believe are available through Egge Machine). I am planning a .030 overbore block, .010/.010 crank, 10.5/1 pistons etc. I have a friend who ports Mopar heads professionally and said he could warm up my HP273 heads on the flow bench. I will port match the intake and the factory exhaust manifolds and install a free flowing exhaust. That will be good enough. If I feel I need to hot rod the Dart more I will build a 400+ cube stroker motor and go that route.. Mike
 
hi, the 273 head will provide enough flow.the casting # is last 3 numbers, 178, 234,920, these are the closed chamber head. used on 1966 -1967 273/318 motors. as for a cam, the isky E 4 grind works very well in the 273 motor. numbers are, 260 dur, 216 @.050, .425 lift, 108 LCA. it is a very streetable cam and works in a race motor also. installing larger valves doesn't help, because of small bores. how ever using a good nail head sst. intake valve will help flow.ferrea makes a valve for that head. a dual plane intake is best bet. the 10.5 piston is made by C. P. pistons, J.E. pistons.
in 1966, dodge brought out a 275 hp/273, only difference was, bigger cam, holley carb, racer brown springs, 4.86 gears, headers.
 
thanks for the advice thus far, I'm trying to do this cheap, so the way it appears is that i should just do a mainly stock rebuild and maybe a little bigger cam. It already has a 4 bbl and headers so i do have decent flow and fuel supply. I would like to know more about those higher compression pistons, however i didnt see any info about them on either of the companys websites. If you can get me a link that would be appreciated. And if anyone else has any advice i could definatly use it.
thanks again
 
In this day and time I can't believe that someone would want to put any money rebuilding a 273. A 360 is such a better way to go, money wise and power wise. As a matter of fact, you could put together a 360 stroker (408) for about the same money as a stock 273. I don't get it. The only thing to change is 1 mount bracket. 360's are available everywhere. Just my 2 cents.

don
 
dusterdon said:
In this day and time I can't believe that someone would want to put any money rebuilding a 273. A 360 is such a better way to go, money wise and power wise. As a matter of fact, you could put together a 360 stroker (408) for about the same money as a stock 273. I don't get it. The only thing to change is 1 mount bracket. 360's are available everywhere. Just my 2 cents.

don
Click to expand...
That's the great thing about our hobby / sport, different people like different things. Much better than everybody driving the same powered, same color, same type of car.
You could say the same thing about older a-bodys (which I own), why would anybody mess with one when it is much easier to buy parts for the later a-body, or worse yet lets all drive camaros since it is easier yet to get parts for... not
Don't get me wrong, if it is your choice to run a 360 that's fine and I respect that, but some people want something different for whatever reason and that needs to be respected also.

Chuck
 
I would/should run a 360+ cube motor in my 66 Dart but the HP273 is the stock motor. If I wasn't interested in keeping the car original I would do that.
When I first started looking, I wanted a 64 Dart with a slant 6 so I could
hot rod it and not feel guilty about it. In 66 there were only 1237 HP273/
4-speed Darts made and that includes hardtops and convertibles. I choose to keep mine original. toolmanmike
 
i didn't want to put alot of money into it, and if i did put something like a 360 stroked or not, i would probably have to change the transmission and would definatly need to change the 7 1/4 rear and those were things that i did not want to get into. I'm just trying to make the dart more reliable and nicer shape than it is currently in so that i have more money to rebuild my 68 Barracuda that will probably have a stroked 360 in it, along with alot of other newer expensive parts. However i did have a 318 block for the barracuda that is ready to be assembled and i think i'm just gonna build that and put that in the dart for now. Hopefully the rear will stay together.
 
I love my 273ho, i just rebuilt her but need to take her apart again and replace the head gaskets. My compression was lower than it should be and i thnk the head gaskets might be to blame. Also i want to check everything out to make sure nothing is damaged. I had the heads completely rebuilt because the valves were really worn. The keepers were diggin into the valves making it have improper valve lash. The guides were worn as well so rebuilding to stock was what i wanted. I plan to port the heads when i take them off this time. This will give me time to make sure i put everything together the right way the first time:) I like trying to make the stock engine do things others don't think they can do.
 
I'm with ya there! Mike
 
I have the 273 motor also. It was rebuilt in july and has not got over 2000 miles on it yet. It is a strong running little motor and has a few details to work out yet. But it will crank and go and sometimes is hard to start after warm up but it will crank in less than 5 to 10 secs of turning it over. I am working on that however. I would like to have a more radical idle but it seems I can't achieve that because of small bore size and low compression. I did a compression test on it tonight and found out that it really is a small motor. The readings are :

1= 115 2=125
3= 110 4=110
5= N/A 6=115
7= N/A 8=105

Now I couldn't read the 5 and 7 cylinder because of the header being in the way because I have the push and hold type compression tester. I need the one with hose to read them. I don't know why the readings are so low being a new motor. Cylinder number 2 read 125 ??? Are the readings about right for a 273. The guy that built the motor said that it is a 9.8 to 10 compression motor. So I really don't know.
 
I'm posting here to avoid the fist fighting in your other post...lol. Sorry to highjack. But really, any engine needs to be asembled and parts chosen properly. See how many 289 Mustangs get 302s in them. There are some, but original only means one way. The 273 can run great too, especially in these light cars.

My feeling about poor hot starting is that the compression was low. That isnt caused just by the lower compression pistons or head gaskets. What you are testing is the amount opf pressure the cylinder builds on a typical compression stroke, as it is currently assembled. That last bit is the real meat here. The cam timing and size are what really makes it or breaks it. Whne the engine is cold, the fuel will stay in liquid form easier. It gets more into the cylinder easier, and it fires right off. Leaner mixes are harder to fire. That's why I'd bet if yours wont restart easy, you need to pump the gas a few times while it's turniong over and it will. Your readings with a fairly middle of the road cam should be in teh 140-160psi range with a low static ratio piston and the cam I seem to recall you having. It's low because the cam wasnt degreed, and it's in wrong. I've fixed several egnien for fellows who never knew the engine had isues until I drove it and told them. IN every case, the timing set or the cam was an issue. I one case, a 383, it showed 120psi in all 8 after being warmed up. I took the front off, and found the timing chain off one tooth (retarding the cam), and the cam itself (the MP 383HP resto cam) off 6 degrees (again retarded). After repair, the same engine warmed up had 175psi. It went from not spinning the tires w/3.23s in an 68 RR, to not stopping spinning the tires until 2nd gear. You need to find out if that's the case. It's definately low. way low even for a low compression engine.
 
moper said:
I'm posting here to avoid the fist fighting in your other post...lol. Sorry to highjack. But really, any engine needs to be asembled and parts chosen properly. See how many 289 Mustangs get 302s in them. There are some, but original only means one way. The 273 can run great too, especially in these light cars.

My feeling about poor hot starting is that the compression was low. That isnt caused just by the lower compression pistons or head gaskets. What you are testing is the amount opf pressure the cylinder builds on a typical compression stroke, as it is currently assembled. That last bit is the real meat here. The cam timing and size are what really makes it or breaks it. Whne the engine is cold, the fuel will stay in liquid form easier. It gets more into the cylinder easier, and it fires right off. Leaner mixes are harder to fire. That's why I'd bet if yours wont restart easy, you need to pump the gas a few times while it's turniong over and it will. Your readings with a fairly middle of the road cam should be in teh 140-160psi range with a low static ratio piston and the cam I seem to recall you having. It's low because the cam wasnt degreed, and it's in wrong. I've fixed several egnien for fellows who never knew the engine had isues until I drove it and told them. IN every case, the timing set or the cam was an issue. I one case, a 383, it showed 120psi in all 8 after being warmed up. I took the front off, and found the timing chain off one tooth (retarding the cam), and the cam itself (the MP 383HP resto cam) off 6 degrees (again retarded). After repair, the same engine warmed up had 175psi. It went from not spinning the tires w/3.23s in an 68 RR, to not stopping spinning the tires until 2nd gear. You need to find out if that's the case. It's definately low. way low even for a low compression engine.
Click to expand...

I've got a old type push and hold compression tester. I think I am going to look for one that is the one you screw in. Are they more accurate?
 
moper said:
I'm posting here to avoid the fist fighting in your other post...lol. Sorry to highjack. But really, any engine needs to be asembled and parts chosen properly. See how many 289 Mustangs get 302s in them. There are some, but original only means one way. The 273 can run great too, especially in these light cars.

My feeling about poor hot starting is that the compression was low. That isnt caused just by the lower compression pistons or head gaskets. What you are testing is the amount opf pressure the cylinder builds on a typical compression stroke, as it is currently assembled. That last bit is the real meat here. The cam timing and size are what really makes it or breaks it. Whne the engine is cold, the fuel will stay in liquid form easier. It gets more into the cylinder easier, and it fires right off. Leaner mixes are harder to fire. That's why I'd bet if yours wont restart easy, you need to pump the gas a few times while it's turniong over and it will. Your readings with a fairly middle of the road cam should be in teh 140-160psi range with a low static ratio piston and the cam I seem to recall you having. It's low because the cam wasnt degreed, and it's in wrong. I've fixed several egnien for fellows who never knew the engine had isues until I drove it and told them. IN every case, the timing set or the cam was an issue. I one case, a 383, it showed 120psi in all 8 after being warmed up. I took the front off, and found the timing chain off one tooth (retarding the cam), and the cam itself (the MP 383HP resto cam) off 6 degrees (again retarded). After repair, the same engine warmed up had 175psi. It went from not spinning the tires w/3.23s in an 68 RR, to not stopping spinning the tires until 2nd gear. You need to find out if that's the case. It's definately low. way low even for a low compression engine.
Click to expand...

Well I tired of playing around. I went into the motor and the dots aren't lined up. Here is some pics:

DSC00454.JPG


DSC00451.JPG


DSC00452.JPG


DSC00453.JPG
 
WOW! Would the engine even run being that far off. Are you sure its on #1 compression stroke TDC? Bob
 
The timing mark on the cam gear is supposed to be at 6:00, and crank gear at 12:00 when properly set, make sure you aren't somewhere off of TDC when checking this. It looks like you might be coming up on 180 degrees off TDC in these pics. Also I have seen mis marked timing sets. Had one I installed on a car and didnt check the centerline, car ran but not right. Pulled it apart and the cam gear mark was off several teeth, this was a TRW replacement part - not a piece of junk. Since then I always centerline cams when building a motor.
 
Judging from the first pic, I think if you turn the crankshaft one complete turn,you will find the cam gear mark will be at 6 o'clock and the crank gear mark will be at 12 o'clock. Remember,the crank turns twice for every one turn of the cam.

Just my observations....
 
Good info about the timing/cam/compression, something I might look into on my stock 273.
 
I have removed the cam and when I go back in with the new one I will make sure everything is right. I did a cam change years ago and didn't degree the cam which I thought might been a bad idea latter on. But I matched the dots on the cam gear and the crank gear 6 o'clock and 12 o'clock and the car ran fine. So I will try that again this time with a new timing gear set. I will get a true roller this time and maybe all will be well. I've done this type of thing before but I'm a A1 certified mechanic. LOL.
 
Thought this might be a good place to mention it. I have an Offy Equa-Flow 360 single plane intake manifold to fit the early (64 & 65) 273 heads. Here's a pic. Manifold only, I want to keep the ancillary stuf. I just haven't pulled it off yet. Anybody interested?


:burnout:

Manifold 2.jpg
 
bobscuda67 said:
The problems with the 273 is they have no compression, the bores are to small for bigger valves and the stock heads dont flow very well. I had a 273 in my barracuda and asked the same questions. I had the bottom end rebuilt with stock replacement pistons as custom pistons were in the 600 dollar range. They were .050 down in the hole and were spec. at 8.0 to 1. I had the heads angled milled to a closed chamber to raise compression, and gasket matched the intake and exhaust. The motor ran good for a 273 but I wanted more, so I am putting in a 340\ 373 engine. Looking back I think the money I spent on the 273 was a waste for me. Some other members have 273 that run really well, maybe they can help you more. I still have the 273 heads if your lnterested. I can email you some pics if you want. Bob
Click to expand...

And what do you base your facts on? Did you flow test them? What was the % of volume? How much flow do you need for the 273 head. I belive the CR on the 2bl 273 was more like 8.8 to 1.
 
You must log in or register to reply here.
-

Back
Top