273 with 360 heads/valves

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66fs said:
I always had to drive my car the next week.
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Which is why my 360 has a 230* cam, and an O/D. At about 1.10 to 1.15 hp/cid, it's tame, almost zero maintenance, goes 93 in the eighth@3650lbs,and with o/d returns pretty good fuel mileage. Win,win,win. I painted it Orange. I guess I coulda painted it early-red........
 
66fs said:
The only thing that might give a run for the HP 273 would be a HP 360 from 74-76 and it would have to have the 340 cam and valve springs. I also thought we were talking stock? Once you upgrade a 360 to the same level or higher, all the same goodies, the 360 should win. A lot of people discount the 273 but don't realize that 235 HP at 6,000 rpm will kill a 318 with 230 HP at 4,000 rpm. Same for a 360. They made 360's since 1971, mostly 2 barrels. A 5.9 Magnum with a cam and good intake and carb, should, but not a stocker in a truck. I've had or built everything except magnums, an RB, and a Hemi. I know what they all do and where their strengths and weaknesses lie. We all decide how far we are willing to go and how much time, money, and aggravation we are willing to put up with. Knowing what it takes to run and survive without breaking parts is big with me. I never had the luxury of a race car, I always had to drive my car the next week.
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Not arguing with you there but remember the power ratings back then were skewed most of the time for marketing and insurance reasons, no WAY a 318 2-bbl would come close to the hi-po 273 4-bbl. Remember too the gross ratings were without full exhaust attached and the 2" single exhaust that came on 318 cars chokes it down really bad. I still remember when I got dual exhaust put on my Duster with its old worn-out 318, it felt like I picked up 50+ HP.

As member '273' said a bone-stock 5.9 Magnum out of a truck with no mods other than a dual-plane intake with a carb will make 300 HP easy even with factory exhaust manifolds. In fact if you look at the 300 HP crate 360s from MP that's exactly what they are. Put both of them in a car with the same weight, drivetrain, chassis setup, and exhaust I think the Magnum would beat an HP 273 pretty easily. The '74-76 360 4-bbl is much weaker also with the tiny flat-tappet cam (Mags have rollers) and the sub-8:1 compression (Mags are true 9:1) not to mention those log exhaust manifolds with 1 7/8" center outlets. Then of course you have the heads, up to .450" lift or so the Magnums have much better flow over J heads with higher velocity as well.

If the 5.9 Magnum had made the same power in 1993 as a 360 4-bbl from 1974 I think the engineers would have been considered failures lol.

I also think Mag heads on the 273 would be the way to go if looking at bigger-valve heads. Small closed combustion chamber, high velocity ports etc. etc.
 
Regarding True Horsepower Range's

1968 and 1969 ....... 318/230 HP ~ 2-Barrel

Was way over-rated. The NHRA has re-factored that Engine Combination to where
it should be ....... 185 HP

We Dyno'd them for Mopar > 'Back-in-the-Day, and they came in
anywhere between ....... 182 to 188 Horsepower.
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Now, the Mopar '318 Marine' was rated at 240 Horsepower.

It was equipped with >
* 9.0-1 Pistons
* 'Special' 318 Marine Camshaft
* 273 Barrel 4-Barrel Intake Manifold with 'enlarged' throttle-bores.
* Carter 600 AFB {1 7/16" Primary and 1 11/16" Secondary}.

It too was over-rated.

They were closer to ......... 225 Horsepower
 
I hate to get off topic, the way we do. My point was, High Performance will pretty much beat a standard engine, even if the standard engine is of considerably larger size. More so if the HP engine was from the 60's to mid 70's. The original question was could you put a pair of 360 heads on a good 273 short block. Since I had actually done that, and was definitely impressed with the combination. I put in my 2 cents. Then, as always happens it turns into a "360 is best" thread? My 273 with the 72 340 cam and J heads, and 71 340 carb and intake would take most anything with the right gears. It is not fair to compare that engine with anything resembling stock. I personally do not want a low rpm engine so therefore do not have any 360's, even though I had the best ones ever made. If I go big, I run a 383 in an A body. Better flowing heads, steel crank, and will still wind up plenty high, for next to nothing.
 
69 Cuda 440 said:
Regarding True Horsepower Range's

1968 and 1969 ....... 318/230 HP ~ 2-Barrel

Was way over-rated. The NHRA has re-factored that Engine Combination to where
it should be ....... 185 HP

We Dyno'd them for Mopar > 'Back-in-the-Day, and they came in
anywhere between ....... 182 to 188 Horsepower.
-------------------------------------------------------------------------------------

Now, the Mopar '318 Marine' was rated at 240 Horsepower.

It was equipped with >
* 9.0-1 Pistons
* 'Special' 318 Marine Camshaft
* 273 Barrel 4-Barrel Intake Manifold with 'enlarged' throttle-bores.
* Carter 600 AFB {1 7/16" Primary and 1 11/16" Secondary}.

It too was over-rated.

They were closer to ......... 225 Horsepower
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What are the specs on the "special marine" camshaft???
 
Mopar Performance always said you had to notch the bores.

When it comes to heads, Magnums trump every stock head, in my book, and the EQ's are damned impressive. I almost built a Magnum-headed 273 once but a 360 fell in my lap.
 
MOPEkidD-3 said:
Not arguing with you there but remember the power ratings back then were skewed most of the time for marketing and insurance reasons, no WAY a 318 2-bbl would come close to the hi-po 273 4-bbl. Remember too the gross ratings were without full exhaust attached and the 2" single exhaust that came on 318 cars chokes it down really bad. I still remember when I got dual exhaust put on my Duster with its old worn-out 318, it felt like I picked up 50+ HP.

As member '273' said a bone-stock 5.9 Magnum out of a truck with no mods other than a dual-plane intake with a carb will make 300 HP easy even with factory exhaust manifolds. In fact if you look at the 300 HP crate 360s from MP that's exactly what they are. Put both of them in a car with the same weight, drivetrain, chassis setup, and exhaust I think the Magnum would beat an HP 273 pretty easily. The '74-76 360 4-bbl is much weaker also with the tiny flat-tappet cam (Mags have rollers) and the sub-8:1 compression (Mags are true 9:1) not to mention those log exhaust manifolds with 1 7/8" center outlets. Then of course you have the heads, up to .450" lift or so the Magnums have much better flow over J heads with higher velocity as well.

If the 5.9 Magnum had made the same power in 1993 as a 360 4-bbl from 1974 I think the engineers would have been considered failures lol.

I also think Mag heads on the 273 would be the way to go if looking at bigger-valve heads. Small closed combustion chamber, high velocity ports etc. etc.
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From the flow numbers I have seen, J heads in stock form flow about the same as Magnum heads. The EQ magnums appear to be a significant improvement. 1.92 intake valves are a bit scary on a 273. But it is interesting, since the replica road racer in Australia or New Zealand did just that. I guess, I just like the shaft mounted rockers and solid cams. The HP 360's from 74-76 were no slouches with the 340 cam and valve springs. If they had any compression they would have been something, but that all changed after 1971.
 
Thanks for all of the info guys. Yes, I'm well aware that picking up a 318 or a 360 is cheap and will most likely make more horsepower/gains with the same modifications done to a 273. Idk, I just like to explore different ideas and options. Curiosity is what gets me.

Don't forget that this is not a HiPo 273. It has a 2 barrel carb and 8.8:1 compression from the factory. So, if it needs pistons due to bore wear, 10.5:1 pistons are going in.

As for what direction I'll go, idk. When my Dart gets back after the engine swap, the 273 will come back with it. At that point it will be just another spare engine. I won't have a car to put it in. I could tare it apart and fiddle around with different parts. From what I'm reading, some people have experience with the 1.88 valves fitting with no notching, others say it should be notched. Right now, the going rate for them is practically free, so why not?

I kind of want to find a spare early-A (slowly leaning towards a wagon) or another Dart (again, early-A) in the next 3 years or so. So, I have time. I'm just picking up affordable, left over parts on the market for another build. It's kind of fun trying to find parts and build a car with "used" stuff. This build (if it ever happens) should be less stressful and a little more fun as my '68 Dart should be running and driving.

I'm not sure I mentioned this or not, but I just remembered, I have a spare 273 block sitting in my garage. So, when I get the heads, I could always do a quick mock up without tearing apart my current 273.
 
It would be fun if someone would make zero deck flat top pistons (without having them custom made ). I would think they would work well with a nice set of ported 273 or #302 casting heads. I wonder what the cores sion ratio would be.
 
^^^ Calculates out to 8.2:1 with flat tops, 64 cc comb chambers (what we measured with some 675 heads from a '68 2 bbl 273), 5 cc valve reliefs, and .039 gasket height.

You'd need to go to 58 cc Magnum heads to get the CR up to 8.8:1 with flat tops and the same valve reliefs and gasket.

Guess that is why the high perf versions had pop-up pistons.
 
toolmanmike said:
It would be fun if someone would make zero deck flat top pistons (without having them custom made ). I would think they would work well with a nice set of ported 273 or #302 casting heads. I wonder what the cores sion ratio would be.
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They were produced at one time.

'Forged-True' made them as a Super-Lite Race Piston.

Flat-Top ~ Zero Deck

Compression Ratio w/.020" Thin-Steel Head Gasket
* 57.5 CC Cylinder Heads ........ 10.1-1
* 60.5 CC Cylinder Heads ......... 9.7-1

If you wanted Valve-Reliefs 'fly-cut' in the Piston Top, it removed 3.73 CC's
and lowered the Compression by {-.4}
 
If I remember correctly, 273 2 barrel flat tops are only .020 in the hole and light. The piston pin is monstrous.
 
with 318 blocks on every corner of the world, and sometimes for FREE, a 273 makes ZERO sense to build. The 318 gives you affordable pistons where the 273 requires expensive pistons. There is no advantage to a small bore and a expensive piston. Now if you have one orig to your car, then that would make sense.
 
69 Cuda 440 said:
They were produced at one time.

'Forged-True' made them as a Super-Lite Race Piston.

Flat-Top ~ Zero Deck

Compression Ratio w/.020" Thin-Steel Head Gasket
* 57.5 CC Cylinder Heads ........ 10.1-1
* 60.5 CC Cylinder Heads ......... 9.7-1

If you wanted Valve-Reliefs 'fly-cut' in the Piston Top, it removed 3.73 CC's
and lowered the Compression by {-.4}
Click to expand...
I was thinking about the .021 " thick shim gasket earlier..... If the heads were closed chamber, then with a true zero deck, you would not have adequate clearance between piston top and head. So, I assume these Super-Lites were in the hole a bit.

FYI, I can only get the 10.1:1 CR with these pistons flat decked and no valve relief, which means .021 piston to head clearance, so I have to wonder how realistic that combo is/was. With them .020 in the hole to gain piston to head clearance, then CR is around 9.6:1 .
 
66fs said:
If I remember correctly, 273 2 barrel flat tops are only .020 in the hole and light. The piston pin is monstrous.
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The pin was heavier and the total pin+piston weight for the 273 and 318 was the same. I assume that was done to make a common production crank with the same balance.
 
nm9stheham said:
The pin was heavier and the total pin+piston weight for the 273 and 318 was the same. I assume that was done to make a common production crank with the same balance.
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That would be my assumption also, but I have no inside information.
 
replicaracer43 said:
with 318 blocks on every corner of the world, and sometimes for FREE, a 273 makes ZERO sense to build. The 318 gives you affordable pistons where the 273 requires expensive pistons. There is no advantage to a small bore and a expensive piston. Now if you have one orig to your car, then that would make sense.
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273's had all the good parts plus the piston is not down in the hole. I have all the pistons I need for the four 273's I have. Got them all reasonable. Besides, I'm not racing. We have 300k on the last one we did 30 years ago. Will cruise all day long at 100 mph and get mid 20's mpg at 70 mph. And like MuuMuu101, I had a bulletproof short block and a set of low mileage 1.88 intake 340 heads. I never cared for a 318, although as you say there is nothing wrong with a 318, especially with the available 9:1 pistons. I have 273's, 340's, 383's a 440 and 4 early Hemi's. I'm good with those.
 
nm9stheham said:
I was thinking about the .021 " thick shim gasket earlier..... If the heads were closed chamber, then with a true zero deck, you would not have adequate clearance between piston top and head. So, I assume these Super-Lites were in the hole a bit.

FYI, I can only get the 10.1:1 CR with these pistons flat decked and no valve relief, which means .021 piston to head clearance, so I have to wonder how realistic that combo is/was. With them .020 in the hole to gain piston to head clearance, then CR is around 9.6:1 .
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Correct Sir

I should have stated that with the 1968 and 1969 {Open Chamber 60.5 CC}
Cylinder Head was to be used with the .020" Thin-Steel Head Gasket.

The 1967 and earlier {Closed Chamber 57.5 CC} Cylinder Head must be used with a .039" Thick Head Gasket.

Changing the Net Compression down to ........
 
66fs said:
273's had all the good parts plus the piston is not down in the hole. I have all the pistons I need for the four 273's I have. Got them all reasonable. Besides, I'm not racing. We have 300k on the last one we did 30 years ago. Will cruise all day long at 100 mph and get mid 20's mpg at 70 mph. And like MuuMuu101, I had a bulletproof short block and a set of low mileage 1.88 intake 340 heads. I never cared for a 318, although as you say there is nothing wrong with a 318, especially with the available 9:1 pistons. I have 273's, 340's, 383's a 440 and 4 early Hemi's. I'm good with those.
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Cool story bro......273s had all the "good parts" ? you mean the early ones that had adjustable rockers we all rob off of them, right? The heads were terrible, rods were tiny, bore was small, that engine requires a DOME piston to even get to 10.5 to 1 compression ....crank was ok....what were the "good" parts? crank and rocker arms? I have a customer with a 96 ram van, 318 magnum with 365K miles on it also.........just sayin
 
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