273 commando Build

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stroker402 said:
update .... update
My 273 commando is still running strong . seems to get fast and faster every year with more miles put on it .
I tried tweaking a couple afb carbs for more power but the one carb that really turned the 273 commando on , was a holley dp 700 carb . It just loved it in All rpm ranges . I jetted down a couple sizes on each end and it loved it . throttle response is awesome and the top end power pull is just a rush. it screams ! haven't taken it over 5900 rpms yet , cam peak power is 6400 rpms . just keeping it there so the engine last longer .
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LOL, don't you know that a 750 cfm is too big for a 273? Good 273's are freaky aren't they. My 340 is still on the stand waiting it's turn.
 
all I can say is.......... don't believe everything you read here what people are saying about the 273 . I've been wrenching on these old mopars for 50 years .
 
Stroker, Well that doesn't tell me anything. What timing do you see: static, mechanical and total with vacuum advance? How do your plugs look?
Richard
 
Richard Sweet said:
Stroker, Well that doesn't tell me anything. What timing do you see: static, mechanical and total with vacuum advance? How do your plugs look?
Richard
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Richard ........... my 273 runs the best with 16* initial 18* mechanical 24* total curved with fob plate . don't remember what number arm is in vac adv can . hooked up to vac source .
mopar electronic dist with pertronic ignitor III , high volt coil . rev limiter set at 5900.
 
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Stroker,
I don't understand how total can only be 24* at the crank? 16+18 = 34. If vacuum is added, it will be even more. What is an fob plate? Do you use a dial-back timing light to see advanced timing? What am I missing? Is the timing not additive?

A page from a Sun manual specifies: 10* @ 500rpm (vac disconnected); 11-15* Centrifical only @ 2500 rpm; and 28-38* total @ 2500 rpm, at the crank, for a 273 w/ 4 barrel.

Does your carb have adjustments available, other than the jets?

Don't you read your plugs, or do you go by how it runs and performs?

Thanks, Richard
 
stroker402 said:
Richard ........... my 273 runs the best with 16* initial 18* mechanical 24* total curved with fob plate . don't remember what number arm is in vac adv can . hooked up to vac source .
mopar electronic dist with pertronic ignitor III , high volt coil . rev limiter set at 5900.
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34° total.
 
Richard Sweet said:
Stroker,
I don't understand how total can only be 24* at the crank? 16+18 = 34. If vacuum is added, it will be even more. What is an fob plate? Do you use a dial-back timing light to see advanced timing? What am I missing? Is the timing not additive?

A page from a Sun manual specifies: 10* @ 500rpm (vac disconnected); 11-15* Centrifical only @ 2500 rpm; and 28-38* total @ 2500 rpm, at the crank, for a 273 w/ 4 barrel.

Does your carb have adjustments available, other than the jets?

Don't you read your plugs, or do you go by how it runs and performs?

Thanks, Richard
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sorry................ meant 34* total timing
 
Richard Sweet said:
Stroker,
I don't understand how total can only be 24* at the crank? 16+18 = 34. If vacuum is added, it will be even more. What is an fob plate? Do you use a dial-back timing light to see advanced timing? What am I missing? Is the timing not additive?

A page from a Sun manual specifies: 10* @ 500rpm (vac disconnected); 11-15* Centrifical only @ 2500 rpm; and 28-38* total @ 2500 rpm, at the crank, for a 273 w/ 4 barrel.

Does your carb have adjustments available, other than the jets?

Don't you read your plugs, or do you go by how it runs and performs?

Thanks, Richard
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no other carb changes but 2 sizes smaller on jets .
 
FBO Ignition sells a limiting plate used in the distributor that allows you to set initial higher while limiting mechanical timing. You can always weld up the slots and file, but the plate is plug and play.

I ran one on my 273 and have one on my 5.9 Magnum. Both wanted lots of initial.

Here's the link. I emailed Don a question about using the plate in my 273 and he called me back to discuss. Unbelievable customer service.

FBO Ignition - Home of the HRR688
 
66fyssh, That's a good site and it has some articles that helped me understand electronic distributor settings. I don't have an electronic ignition so I am relatively ignorant about that tuning. Thanks for the info and the reference.
 
If you all have been watching on my 273 commando engine build I have replaced the head gasket 3 times in the past two years on the pass side ... searching my posts you will the details on different topics ....
So.......... I put on approx couple hundred hard miles since I installed the mr gasket1112 head gaskets this past fall 2023 this last time and had the heads milled so they were flat . Now I have another issue... It is huffing smoke/ exhaust pressure out the valve cover filler holes. both sides . Just happened so will do compression check on it today . either that head gasket pupped again or broke a ring or hole in piston. this is the 3rd time with issues. it's a 273 commando engine. I very seldom ever had to mat it to the floor and open the secondaries but the every time I gave a quick stab to the floor is when I always popped a head gasket. and now this issue. what is going on ? times already. I just blew another one the other day .
 
ok A few hours ago I did a compression check most cylinders were 150-160 # 2 cyl had 50# dead cyl. so took valve cover off check valve gear looks all fine . bumped engine over.... looked thru the drain back areas in the head seen the head gasket pertruding out Buldging .. when cranking engine it will blow compression out where head meets block with antifreeze seeping out also . both # 2 and #4 cyls are popped ...... under the valve covers looks like a milkshake.
 
Plymouth 65 said:
That's correct, I'm not certain if there's a difference between the 315 head combustion chamber cc's and the 920 head combustion chamber cc's. 65'
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920 are around 67 cc, maybe a smidge less.
315,920... same closed chamber.
The pistons were designed to work with them.
Use a performer intake if you can't find a ld4b
 
MOPAROFFICIAL said:
920 are around 67 cc, maybe a smidge less.
315,920... same closed chamber.
The pistons were designed to work with them.
Use a performer intake if you can't find a ld4b
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this 273 has all the good stuff in the engine. 920 heads ld4b intake
 
Darn...are you thinking the head gaskets re to blame or the head gasket on that side ? Has to be something there.....sorry for your issues .....
 
65Val said:
Maybe its the block on that side, not the head?

Also…smoke coming from both valve covers???… not running PCV then?
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Yeah thanks guys !! that's what it appears like.. warped block .. I check it with a straight edge that last two times the head was off and appeared to be in tolerances. this time it it blew on #2 and 4 again. last time was on #6 .I have another good block to start over with .
 
65Val said:
PCV should be sucking all that smoke into the carb base….valve/hoses/carb port plugged?
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no nothing wrong with pcv set up.. engine is puffing exhaust out the valve cover inlets. internal block pressure from the head gasket blown .
 
stroker402 said:
Yeah thanks guys !! that's what it appears like.. warped block .. I check it with a straight edge that last two times the head was off and appeared to be in tolerances. this time it it blew on #2 and 4 again. last time was on #6 .I have another good block to start over with .
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A long time ago I made up a rule. And that rule is if a head or a block comes into the shop and the customer says pressure test and check the surface or something similar I never ever bother checking the head or block for flat.

A feeler gauge and straight edge are very crude measurement tools.

So the rule is I don’t bother checking the **** to see if it’s flat. It’s not. They never are. So they get pressure tested or mag’d and then surfaced.

You’d be surprised what a feeler gauge will miss.

It isn’t cost effective to waste time with measurements. Sometimes you can skate by without decking the block but never the heads.

I’d pull it down and deck the block and start over.
 
Newbomb Turk said:
A long time ago I made up a rule. And that rule is if a head or a block comes into the shop and the customer says pressure test and check the surface or something similar I never ever bother checking the head or block for flat.

A feeler gauge and straight edge are very crude measurement tools.

So the rule is I don’t bother checking the **** to see if it’s flat. It’s not. They never are. So they get pressure tested or mag’d and then surfaced.

You’d be surprised what a feeler gauge will miss.

It isn’t cost effective to waste time with measurements. Sometimes you can skate by without decking the block but never the heads.

I’d pull it down and deck the block and start over.
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Thought I'd bring this up for concerns .. look at the block deck and you can see it has rough cut and not perfectly flat. could this be why it keeps blowing head gaskets? the other block I'm thinking about using has a smooth flat deck surface .

my 273 block pistons pass 2023.jpg
 
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