273 - 273 Commando

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Barracuda67

Barracuda67

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Whats the difference?
I know compresion is something like 8.5 in the 273 and 10.5 in the 273 Commando. Yes?
If so what changed the compresion? The piston?
Is there any other differences? (Besides valve covers and air cleaner.)
 
Barracuda67 said:
Whats the difference?
I know compresion is something like 8.5 in the 273 and 10.5 in the 273 Commando. Yes?
If so what changed the compresion? The piston?
Is there any other differences? (Besides valve covers and air cleaner.)
Click to expand...


The 10.5 compression commando motor has domed pistons to raise the compression ratio and a slightly hotter mechanical cam.I think the specs are something like 248 degrees and .425 lift so nothing too serious.
Not sure if the heads are any different but apparently some 273 heads are better than others but don't know if the commandos used their own heads.


ps hope you checked your anti-freeze before that pic was taken.
 
The compression was in the pistons. The HP engines had a slightly hotter cam, a Carter AFB 4-barrell carb, and a dual point distributor. It also had balck wrinkle finish valve covers with aluminum heat sinks and chrome oil fill cap and pcv cap. It also had a chrome unsilenced air cleaner. The cars had a HP exhaust with a 2 1/2" y and intermediate pipe feeding into a low restriction Hemi style muffler and exiting the car through a 2 1/4" over axle pipe and a chrome tipped resonator.
 
My 273 was not a Commando but i've done alot of upgrades to it.
4 bl 500cfm edelbrock carb. sitting on a Weiland stealth intake. Mopar electronic orange box ignition. Heads port, polish, shaved 20 and matched to dome. Mech. Comp Cam , lifters n springs with .468 lift. and exhausts out thru a set of '70 340hp exhaust manifolds and dual 21/4" stainless. The block was bored 40 over. The only pistons available to me at the time were 4-valve relief and a slight concave to the top. I'm guessing low compression now with these pistons.
The car runs good, sounds good, but just doesn't have the 'stuff' that I think it should.
Can I get pistons somewhere or do i have to have them made or something?
Thanks.
 
So if I am able to locate correct pistons and up my compresson from 8.5 to 10.5 ....
What kind of gains and or loses am I going to encounter?
 
I can't say how much more hp you will get, but the response and power should be a big improvement.

My 273 with the newer cast pistons calculated to 7.8 to one compression. Heads cc'd to 65 and pistons were down .050. It was a real turd. I milled .045 off the decks and .032 off the heads for about 9 to 1 with .045 quench. It is much better now. I also installed the comp 272 .468 solid cam and a 65 273 single plane 4 barrel intake with a Holley 600 vac sec. Balanced the assembly as well. It has stock manifolds and a single 2.5 inch exhaust with a chambered muffler. I also pocket ported the heads. It has 2.76 gears now but with some lower gears it would really wake up. The 8 3/4 rear with 3.55's is laying in the garage yet to be cleaned up and installed.
I was going to get the dome pistons, but money was tight. Milling cost me nothing at my job. If I was to do it over and spend the money I would have Ross make me some custom light weight pistons and get it just under 10 to 1 with good quench.
Nothing really kills an engine like too low compression.
 
I just contacted Flatlander racing. The forged 273 pistons in their engine kits can be ordered in any overbore size and any compression ratio. Lead time is 3-4 weeks and the engine kit price is around $1000. Use the link below and scroll down the parts list on the left and cllick on engine kits.Then click on HPengine rebuild kits then click on Chrysler. The 273 listing is down about a page. toolmanmike
http://www.flatlanderracing.com/index.html
 
I have looked at the flatlander site and have emailed them cocerning pistons.
I dont need their rebuild kit, just the pistons.
Thanks for the link.
 
The higher compression dome tops dont mean beans with todays lower octane pump gas. You can gain more hp for less coins using the stock pistons. OOPs you already did most of those things.
On to the 360 :)
 
RedFish said:
The higher compression dome tops dont mean beans with todays lower octane pump gas. You can gain more hp for less coins using the stock pistons. OOPs you already did most of those things.
On to the 360 :)
Click to expand...

If his compression is as low as mine was, pistons would help a lot even with pump premium. That little engine with good quench should be able to run in the upper 9's for compression with pump gas.

And yes, a 360 would definitely solve the no power problem!
 
I run 93 octane BP in mine with an occasional splash of 90 gasohol (10%) with no problems in my stock 273-4 toolman
 
Layson's Restorations
They have 40 overbore pistons to fit my car. $620 + shipping is the best price I've got so far.
When I inquired on their pistons this is what they told me.

"QUOTE"
"" These say "commando" which back then was the domed pistons that are the high compression ones. These are pistons only. They are factory replacements pistons. Dave Layson
Layson's Restorations Inc. ""

So has anyone had any experience with them? Whats thier product like?
Thanks
 
I noticed on my '67 Barracuda that the factory 273 Commando exhaust had a better "Y" to it, more intelligent, free-flowing bends than the usual goofy 2 barrel style single exhaust. I didn't know the cams were different than stock.....is there a link that shows that?
 
Barracuda67 said:
Layson's Restorations
They have 40 overbore pistons to fit my car. $620 + shipping is the best price I've got so far.
When I inquired on their pistons this is what they told me.

"QUOTE"
"" These say "commando" which back then was the domed pistons that are the high compression ones. These are pistons only. They are factory replacements pistons. Dave Layson
Layson's Restorations Inc. ""

So has anyone had any experience with them? Whats thier product like?
Thanks
Click to expand...

I dont know about "factory replacements" . Most mfgrs run pistons at stock, .010 over , .020 over and .030 over and thats all. Anything beyond .030 over is aftermarket. This has been the case with boat motors, refridgeration compressors, everything I ever dealt with.
 
I would not buy 10.5 to 1 Pistons. I'm redoing my 273, just to replace my 10.5 with 9.0 2 barrel Pistons. You can make more power with full Timing advance and lower compression, than high compression and back off on Timing advance. The differences from the 2 barrel and Commando engines are:

1. 10.5 to 1 domed pistons
2. higher rate valvesprings
3. .425 lift camshaft (Isky makes one that is real close)
4. 4 barrel intake and Carter AFB
5. 2.25 Straight Through single exhaust with muffler and resonator (Accurate Ltd makes a real close system).
6. cast iron Prestolite dual point distributer
7. Engine Dress items such as valve covers crome breathers air cleaner and PCV adapter
8. Special 904 automatic transmission
 
Redfish is correct. I thought it was a bit strange that they would have +.040
slugs. Dave doesn't know or doesn't want you to know who made them. If you're planning a stock rebuild the Egge pistons would be fine. They make them
themselves and they have been in business for decades. An all out race motor needs high dollar custom made pistons and they are not necessary for a street motor. toolman
 
Redfish and Toolman
Back in the day... when Chrysler still had some stock remaining for the 273. 40 over pistons were available for this engine from the dealer. (which have been long sold out) I have access to a 1968 parts manual and the pistons are listed up to 40 over with part #'s.
Joesnow
Thanks for the link... Layson's sounds like a place I should stay away from.
I will have to take another look at egge
Thanks everyone for your input.
 
I have a 273 in my 67 Dart-wanted to keep the original engine. It's .040 over, 224/468 mechanical cam. I ported and polished the heds (great heads on a 273). 500 CFM carb, 9 1/2:1 flat head pistons, 2 1/4" X pipe with Imco exhaust, 904 auto trans with a shift kit and Electronic ignition. I just replaced my 3:55 with a 2:76. When the 3:55 was in it-she would burn rubber in all gears. Advance is 12-14 degrees. I am not racing it so it is just fun to drive.
Not so great on gas milage though.

Dave
 
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