273 Commando Engine Build

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MonkeyTrev

MonkeyTrev

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I am hopefully about to be purchasing a 273 Commando engine that I plan on installing into a 65 Barracuda Formula S. I plan on doing a complete restoration on the Formula S, but I want to do some engine upgrades to the Commando engine such as Cam, Heads, Intake.

I know alot of people are going to recommend just put a 318 or 360 and I know that is the quick and easy way to go, but I do not care that much about big power since I already own a built 360 powered 65 Cuda. I want to do a more factory look and feel.

I am planning on taking the block and getting it bored .30 over and keeping the factory crank and rods. I will be purchasing a new set of commando pistons from Egge. I want to keep the factory domed piston design if possible.

The cylinder heads could be kept as the factory set or I have a set of the 318 Fast Burn "302 Casting" heads. I am leaning towards getting bigger valves and doing a little port work on the 302 heads. If I was to install the 302 heads on the 273 block would that allow me to use any small block intake manifold? I know pre-66 intakes were a different angle for the intake bolts.

The intake manifold is still up for debate as I want to put a aluminum intake and remove any brand names cast into the aluminum and I will be painting it all red to kinda hide the intake at first glance. I am looking at intakes and trying to decided which intake will work best for my situation because I will be keeping the factory chrome air cleaner and it sits pretty tall already on the factory intake. If anyone could measure the factory 4BL height for me I would appreciate it. Most of the modern intakes seem to be around 5in for intake height.

The oil pan will be factory, but I will be installing a windage tray and still deciding on oil pump (Factory, High Volume, or High Pressure). The ignition will be either factory dual point or Mopar Electronic (I will hide the orange box).

The camshaft is still being decided on, but I know its a big choice to get increased performance. I have a sweet spot in my heart for Isky Cams, but I am open to either brands.

I am wanting to get advice about the 273 build and information about the cylinder head swap and if that will open up more intake manifold options. Factory the engine is rated at 235hp, I would love to get 300-350hp out of the build.
 
MonkeyTrev said:
I am hopefully about to be purchasing a 273 Commando engine that I plan on installing into a 65 Barracuda Formula S. I plan on doing a complete restoration on the Formula S, but I want to do some engine upgrades to the Commando engine such as Cam, Heads, Intake.

I know alot of people are going to recommend just put a 318 or 360 and I know that is the quick and easy way to go, but I do not care that much about big power since I already own a built 360 powered 65 Cuda. I want to do a more factory look and feel.

I am planning on taking the block and getting it bored .30 over and keeping the factory crank and rods. I will be purchasing a new set of commando pistons from Egge. I want to keep the factory domed piston design if possible.

The cylinder heads could be kept as the factory set or I have a set of the 318 Fast Burn "302 Casting" heads. I am leaning towards getting bigger valves and doing a little port work on the 302 heads. If I was to install the 302 heads on the 273 block would that allow me to use any small block intake manifold? I know pre-66 intakes were a different angle for the intake bolts.

The intake manifold is still up for debate as I want to put a aluminum intake and remove any brand names cast into the aluminum and I will be painting it all red to kinda hide the intake at first glance. I am looking at intakes and trying to decided which intake will work best for my situation because I will be keeping the factory chrome air cleaner and it sits pretty tall already on the factory intake. If anyone could measure the factory 4BL height for me I would appreciate it. Most of the modern intakes seem to be around 5in for intake height.

The oil pan will be factory, but I will be installing a windage tray and still deciding on oil pump (Factory, High Volume, or High Pressure). The ignition will be either factory dual point or Mopar Electronic (I will hide the orange box).

The camshaft is still being decided on, but I know its a big choice to get increased performance. I have a sweet spot in my heart for Isky Cams, but I am open to either brands.

I am wanting to get advice about the 273 build and information about the cylinder head swap and if that will open up more intake manifold options. Factory the engine is rated at 235hp, I would love to get 300-350hp out of the build.
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Talk @66fs his engine probably similar to what you want.
 
If I was to do a 273, I'd probably use magnum replacement heads notch the bore if needed, zero deck or maybe small dome pistons, a cam with intake around 215@fifty .500 lift on 110, 650 china airgap and headers.
 
@toolmanmike has the skinny on the Isky cam you'll want, I forget the model at the moment... E65?? or something like that.
If you have a '65 and earlier engine, then the 302 heads will allow you to use any of the standard LA manifolds as you mentioned, without a huge increase in chamber volume. I would not install larger valves, since 2.02s will require a bore notch, and the resultant valve shrouding sort of negates any improvement- I believe 1.88s are the largest you can go without notching. Stay with the thinnest head gasket you can find, and try to stick with a gasket with the smaller (non 340/360) bore size.
The factory 4 bbl. manifold was a single plane, so staying with a street oriented single plane will keep things looking stock. The Holley Street Dominator and Eddy 318 Streetmaster come to mind, with the Holley being my preference.
To keep the air cleaner height down, you may need to use a shorter filter element, and don't forget that the baseplate will need to be replaced in order to fit a carb with a 5 1/8 inlet. Most people just use the bottom plate off of a cheap aftermarket chrome 9 or 10 inch filter.
Also be aware that the 302s may end u causing some minor fitment issues with the stock driver's side manifold- the larger "emission style" exhaust pads interfere with the downleg of the manifold. I usually run a header flange between the manifold and the head to gain the needed clearance. Some people have gotten away with grinding the pad for clearance, but I have personally hit the water jacket with minimal grinding... junk head. Oh, and drill/tap the air injection ports to plug them while you're at it.
 
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Professor Fate said:
@toolmanmike has the skinny on the Isky cam you'll want, I forget the model at the moment... E65?? or something like that.
If you have a '65 and earlier engine, then the 302 heads will allow you to use any of the standard LA manifolds as you mentioned, without a huge increase in chamber volume. I would not install larger valves, since 2.02s will require a bore notch, and the resultant valve shrouding sort of negates any improvement- I believe 1.88s are the largest you can go without notching. Stay with the thinnest head gasket you can find, and try to stick with a gasket with the smaller (non 340/360) bore size.
The factory 4 bbl. manifold was a single plane, so staying with a street oriented single plane will keep things looking stock. The Holley Street Dominator and Eddy 318 Streetmaster come to mind, with the Holley being my preference.
To keep the air cleaner height down, you may need to use a shorter filter element, and don't forget that the baseplate will need to be replaced in order to fit a carb with a 5 1/8 inlet. Most people just use the bottom plate off of a cheap aftermarket chrome 9 or 10 inch filter.
Also be aware that the 302s may end u causing some minor fitment issues with the stock driver's side manifold- the larger "emission style" exhaust pads interfere with the downleg of the manifold. I usually run a header flange between the manifold and the head to gain the needed clearance. Some people have gotten away with grinding the pad for clearance, but I have personally hit the water jacket with minimal grinding... junk head. Oh, and drill/tap the air injection ports to plug them while you're at it.
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Thank you for the great information regarding the engine build! I know the factory intake is a single plane, but I only plan on street driving the car and a dual plane would add better low end torque. I had not even thought of the air cleaner base plate and I appreciate the info. Do you have a link to the header flange you mentioned in regards to the larger exhaust pad? I was unaware there would be any issue there.
 
MonkeyTrev said:
Thank you for the great information regarding the engine build! I know the factory intake is a single plane, but I only plan on street driving the car and a dual plane would add better low end torque. I had not even thought of the air cleaner base plate and I appreciate the info. Do you have a link to the header flange you mentioned in regards to the larger exhaust pad? I was unaware there would be any issue there.
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Some info here:
273 or 318 or both help
Header flanges are available from many sources, this one is available from Speedway:
Small Block Fits Mopar 273-360 Header Flanges | eBay
They are commonly used by people building their own headers.
The intake manifolds I mentioned are not high-RPM manifolds, and give up very little on the bottom end; mostly due to their small port (273/318 sized) size, and not losing velocity due to the inherent mismatch between the small heads and manifolds designed for the larger 340/360 ports. The bad part is neither is available new, used is your only route.
One other thing you may want to consider in your build: you mentioned using thestock crank. While it's a good unit, depending on the transmission you want to use you may want to consider using a later model 318/340 crank- if you plan on using a later transmission ('68 and up) there are differences in the crank flange and the pocket for the convertor nose that would best be addressed ahead of time. If using a '67 and earlier trans., this should not be an issue though.
 
What year Commando engine will you be getting? What transmission. Will you be running headers or original manifolds? Original heads flow better than 302 heads, unless the 302 heads are ported by someone who knows what they are doing. When you get the engine check head castings before you do anything. Then have your block checked to see what diameter the cylinders will clean up before buying pistons. You can also go wild and run large port milled 360 heads with 1.88 intake valves, but you have to check for interference carefully. Anything with more flow will only push you past 7,000 rpm if you do everything right. If running 66 up small port heads (273 and 318) Weiand makes a nice dual plane, Holley Street Dominator is a low rise, good all around, universal carb, single plane intake. Offenhouser also make a nice intake that will also fit 64-65 heads. Of course there is the original Edelbrock D-4b for 64-65 heads or the LD-4b for 66-up heads. You can also run later intakes on using angled washers on 64-65 heads. As for a Cam an Isky E-4 is as close as you can get to an original Commando off the shelf. Isky, Racer Brown, and other good cam companies will also custom grind a solid cam exactly for your combination. With good machine work, stock heads, E-4 cam, stock intake and carb should make 265 hp with flat top 2 barrel pistons.
 
I just built a 273 similar to what you describe that you want. I have not put it on the dyno yet because neither me or my buddy with the dyno has had time. I bought a set of .030 over Race Tech custom flat tops that will give me 9.6 compression with 58cc chambers and an .028 head gasket. I used a set of of 302 heads that turned out nice, but if I had it to do over again I would use a new set of Magnum heads from Engine Quest. They flow better right out of the box. They have 1.92 intake valves, which may need the tops of the bores to be notched, but that's no biggie. I'm using a Weiand 8007 intake, which is for the small ports and will be using a Mopar Performance electronic ignition system. Dougs D450 headers with dual exhaust. The hydraulic roller cam is from Bullet Cams and is a fairly mild grind with .447 lift on both sides with 1.5 roller rockers. It has 272 duration. I'm going to run a 4 speed and probably 3.23 gears.
 
Your not gonna find much info on 273 especially over a stock commando build, When I was thinking doing a 375-425hp 273 I read/watched a lot 4.8l LS and 2 valve 4.6l ford engines you just translated to what that be for a 300-350 hp 273.

A stock 4.8l LS dyno in dyno trim like 330hp which is something like 9:1 220-230 cfm heads headers etc.. and super mild roller cam. It's all in the heads will make or break your combo goals.

I'd use a magnum replacement.
 
If it was my car, I would keep it pretty much stock. Without spending a huge amount of money, it will never be really fast. There is a lot of money out there on the street right now. Enjoy cruising around on pump gas in a fun-fast car that's dependable. You can always build a serious stroker motor when your wallet allows it.
 
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So his choices are, near stock 273 or a built 408, guess there's no middle ground :)
 
pt70 said:
If it was my car, I would keep it pretty much stock. Without spending a huge amount of money, it will never be really fast. There is a lot of money out there on the street right now. Enjoy cruising around on pump gas in a fun-fast car that's dependable. You can always build a serious stroker motor when your wallet allows it.
Click to expand...

How many 273's have you built?
 
All the OP wants is 300-350 hp which is about 1.08-1.26 hp per cid, fairly realistic numbers.

Hp is basically airflow over time aka cfm, which heads and cam is mainly responsible for. Cam wise you'd probably want to be on the tamer side while accomplishing your goals of 300-350 hp, somewhere in the 210 to 225 intake duration. So you want the heads to do the majority of the work. Stock heads with that cam range and decent cr probably get ya 250-300 hp, mild head work add 25 hp, fully ported get you there and more. Stock 360/magnum heads and a 225 cam easy 350+ hp, ported either more hp and or smaller cam to reach 350+ hp.

Now displacement, a 273 is gonna make these peak hp numbers in the 5500-6500 depending on, A. how much peak hp and B. how efficiently you make it, tq per cid. Now the trick is to make these higher rpm power without sacrificing low rpm driveability, Now the more gear and stall you run the less this a problem. Optimal gearing for the 1/4 mile for these are probably in the deep 4's so if running around 27" tires with 3.23 you'd probably want to stay around a 210 cam, a 225 cam I'd want at least 3.73 and 3000 stall. Don't forget tire size is a gear ratio, a 24" is 1 to 1, 26" = .92, 27" = .89, 28" = .86, 29" = .83. A set of 3.23 with 26" tires is the same effective ratio as 3.55 with 28.6" tires.
 
I built my street legal 273 Commando with solid competition Isky camshaft (advertised 312 duration and .580 lift) and stock '65 heads (but used a 340 Edelbrock Tarantula which fit by elongating the holes slightly) and 600 CFM double pumper Holley. Was a four-speed with 4.56 rear end. TRW dome pistons (factory profile). Then the unequal length Cyclone headers. Must have been good for 300+ horsepower. Best quarter mile at Fremont Raceway circa 1976 was 12.72 ET at 108 MPH (third photo is after I sold it in 1980 when the new owners [Renteria Brothers] replaced the 273 with something larger).

65 Valiant1.jpg


65 Valiant5.jpg


Valiant wheelie.png
 
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273 said:
So his choices are, near stock 273 or a built 408, guess there's no middle ground :)
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I was thinking of his 273 with a 4'' stroker kit. He mentioned that he wasn't interested in a 318 or a 360. So how about a 331 cubic inch stroker? 3.23 gears. Sounds like a fun car to me. Maybe I'm just getting old.
 
pt70 said:
I was thinking of his 273 with a 4'' stroker kit. He mentioned that he wasn't interested in a 318 or a 360. So how about a 331 cubic inch stroker? 3.23 gears. Sounds like a fun car to me. Maybe I'm just getting old.
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To me if I was to build a 273/318 would be because there size and the 3.31 stroke.
But If the OP just wants to stick with the stock block for whatever reason but stroking was ok,
a 4" stroker with 360 or magnum heads or even ported out stockers would make decent power, bore size would eat some but 400 ish hp shouldn't be to hard at a reasonable rpm.

But I really don't get strokers, I'd just go 360 in that case, same with 408 i'd go with a 400 or 413 if I wanted around 400 cid even a 383 is close enough with an over bore. If your gonna spend money stroking an engine build a displacement we don't already have, 470 to 540+.
 
Plenty of power to be added to a 273 for next to no money, especially a Commando 10.5:1 engine. Cam, intake, and headers are all it takes. The rest is plenty strong enough and the heads flow into the 190s with minimal clean up.
 
66fs said:
heads flow into the 190s with minimal clean up.
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That's about 5.7 cfm per cid for a 273, a 360 would need 256 cfm heads and a 340 = 242 cfm, 408 = 291 cfm.

She should breath and spin well and enough cfm to make mid/high 300 hp.
 
Why not a set of Speedmasters?
www.forabodiesonly.com

273 blower cam

Hey y'all, Currently got a isky E4 260 adv, 108 lsa solid cam. Want to try a hydro, what do you think of this one: JEGS 200160: Hydraulic Flat Tappet Camshaft & Lifters for Chrysler: 1964-Up 273-340-360 and 1967-Up 318 - JEGS High Performance Has same overlap but 12* more exhaust duration...
www.forabodiesonly.com www.forabodiesonly.com
 
66fs said:
What year Commando engine will you be getting? What transmission. Will you be running headers or original manifolds? Original heads flow better than 302 heads, unless the 302 heads are ported by someone who knows what they are doing. When you get the engine check head castings before you do anything. Then have your block checked to see what diameter the cylinders will clean up before buying pistons. You can also go wild and run large port milled 360 heads with 1.88 intake valves, but you have to check for interference carefully. Anything with more flow will only push you past 7,000 rpm if you do everything right. If running 66 up small port heads (273 and 318) Weiand makes a nice dual plane, Holley Street Dominator is a low rise, good all around, universal carb, single plane intake. Offenhouser also make a nice intake that will also fit 64-65 heads. Of course there is the original Edelbrock D-4b for 64-65 heads or the LD-4b for 66-up heads. You can also run later intakes on using angled washers on 64-65 heads. As for a Cam an Isky E-4 is as close as you can get to an original Commando off the shelf. Isky, Racer Brown, and other good cam companies will also custom grind a solid cam exactly for your combination. With good machine work, stock heads, E-4 cam, stock intake and carb should make 265 hp with flat top 2 barrel pistons.
Click to expand...
Do you run the flat top 2 barrel pistons to lower the compression ratio? I have changed plans for the build a bit. I am putting Power Steering & A/C into my car and it will be a family cruiser and possibly a daily driver if the build goes well. I am not as concerned with power as I am with reliability and fun. I am still thinking about building a 273 or 318 Commando Clone for the car. I do not think the 10.5-1 compression would be practical in a daily/family car.
 
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