273 with stock 340 cam ?

[toolmanmike]

There's probably 150+ years of Mopar experience trying to answer your questions. Tell us what you're up to and have some respect.

 

[64whiteghost]

Yes and no...

The commando cam came in engines with 10.5 compression... Putting the 4 bbl commando cam in a 2 bbl engine may not make as much power as the 4 bbl because of the lower compression...

The commando cam was designed for engines with higher compression and had more overlap, the 2 bbl piston may not make the 4 bbl cam happy because of the longer overlap of the commando cam and lower compression pistons won't make as much cylinder pressure... Cams have a recommended minimum compression requirement for them to work efficiently.... The more overlap, the higher the compression you will need is a rule of thumb...

Also keep in mind that the early 273's had solid cams and lifters where the 68 - 69 273 had hydraulic cams and lifters...

The 273 I have is a 66

 

[64whiteghost]

Really? I'll "answer" any questions I prefer to.....keep twisting **** around dummy.
You were the one that stated "no 2bl pistons" lol wrong.
Then 273 heads ported to match 340 intake, so I assumed you were hoping for 340 head flow seeing as how you're talking 340 cam....



View attachment 1715649934

View attachment 1715649935

No sir, I have a 340 and spare 340 parts. So i will used the extra 340 parts for my 273.

 

[krazykuda]

The 273 I have is a 66

It's a good start...

Stock compression was rated at 9.0, but all chrysler engines were less than advertised... It's a solid lifter cam and adjustable rocker arm engine... Most importantly, it's the first year of the standard intake bolt diameter and angle in the heads so most LA intake manifolds will fit....

You can make it run good, just do some research on cams for the compression that your engine is...

You can see where your engine is at currently by following this thread:

How to Check Compression

 

[64whiteghost]

It's a good start...

Stock compression was rated at 9.0, but all chrysler engines were less than advertised... It's a solid lifter cam and adjustable rocker arm engine... Most importantly, it's the first year of the standard intake bolt diameter and angle in the heads so most LA intake manifolds will fit....

You can make it run good, just do some research on cams for the compression that your engine is...

You can see where your engine is at currently by following this thread:

How to Check Compression

Yea, Im confident it will run well. Im not trying to go crazy and pump all this power out of it. I just want it to have a more power

 

[str12-340]

If you are going with a stock 340 cam, there were several over the years. I would suggest the one for a 1968 4 speed, just a tad more than the automatic cam and it should work well with your 4 speed.

I don't think anybody asked this directly... is this a street car, a drag car, something in between??? I wouldn't pick a cam for drag racing if you'll only take it there a few times. Living with an over cammed engine as a driver can be a *****.

 

[64whiteghost]

If you are going with a stock 340 cam, there were several over the years. I would suggest the one for a 1968 4 speed, just a tad more than the automatic cam and it should work well with your 4 speed.

I don't think anybody asked this directly... is this a street car, a drag car, something in between??? I wouldn't pick a cam for drag racing if you'll only take it there a few times. Living with an over cammed engine as a driver can be a *****.

Its a 66 valiant convertible with sub connectors and no it wont be dragged lol.
its a weekend warrior. but I just want more power

 

[krazykuda]

If you are going with a stock 340 cam, there were several over the years..

The stock 340 automatic cam was the 'go to' cam for the small block with a factory 4 bbl for years... They even put that cam in the Lil Red Express pick-up trucks from the factory.... 268/276 duration .429/.444 lift... That's the basic small block 4 bbl cam for Chrysler...

 

[66fs]

First off, is the Valiant an automatic transmission? Second, don't try to make a small port head a large port head. The Stock Class racers will tell you to just use a 340 intake, as they will work fine with the smaller port window. If ported, by someone who knows what they are doing, your 66 heads can indeed flow what stock 340 heads do. Ask Moparofficial. Since you have a solid cam valve train, I would go with that. 2 barrel pistons will work just fine with today's gas. Make sure you check you timing marks for TDC and centerline your cam. I have run a 340 cam, but I also had 10.5 pistons, the rest of the 340 top end including heads, and a 4 speed. It was very fast, and my daily driver. Not sure if someone else would enjoy it as a daily driver though. A 273 should be a very efficient, quick motor, but it is small. It works best with a smaller, less than 260, duration and less than .50 inch lift cam for most people.

 

[toolmanmike]

The 340 cams are borderline too big in a 318 (without a high stall converter and higher ratio rear gear). 273's are worse yet. With a low compression 273 you are already starting off on the wrong foot. Do what ever you want to it. Good luck.

 

[67Dart273]

2 barrel pistons ? i dont think there is such a thing my friend, but thank you for your advice

Check this thread

273 Commando Piston Dome Volume

 

[AJ/FormS]

its a weekend warrior. but I just want more power

Hugo; yur in trouble. Big trouble.
Lemme spell it out for you; keep in mind that I am not a 273 hater.
What you propose to do has been contemplated for well over 50 years, and every guy who ever did was wrong.
Yur thinking; the heads will add 50 hp
the cam will be 30.
the headers 25 and
electronic ignition will get you 5,
so that adds up to 110hp, am I right?
Well, it will never work that way, never, never, never.
Firstly;
putting the 340 heads on is +72cc versus 57cc. Put that on a 2bbl 273 and you instantly make a lawn-mower engine out of it, because the compression ratio has dropped to 6.9/1 . Next, you swap a 340 cam in there and change the Ica from 48* to 60*, and the Dynamic Compression Ratio falls to 6.6/1

So what you have built is a slug off the line to say 4000rpm, when it finally wakes up, and then the 340 parts finally kick in. Great,
But here's the deal, even running 3.91s, 4000rpm with 24.5 tires comes to 24mph in first gear with a 3.09Commando 4 speed. So, there is no warrior in that combo.
But wait, the Advertised duration of that cam is 268/276/114 making the Ica to be 60* at plus 4* install. But that is at .008 tappet rise so the valves are still open by .012 inch; and your engine cannot begin to make pressure until the intake valves are on the seat and not leaking. When this is factored in, your Dcr falls even further, to perhaps 5.8/1 and this will turn your 273, at low rpm, into a total lazy dog. The laziest dog ever known to man...... until around 4000/24mph with 3.91s. But if you have the more typical 2.76 ratio, 4000 will be 34mph.
The guys above are trying to tell you this, but you are NOT listening.
But Ok I get that you added a few nuggets, but it will still NOT be enough..
To do it right, with the 340 parts, you will spend a mountain of money in machining, and in the end, have less performance, than a 69 318 with a 4bbl and dual exhaust.
You said;

its a weekend warrior. but I just want more power

You're going about it all wrong.
BAR NONE; the cheapest fix is a bigger engine.
But,you can build a fun-to-drive 273, if you do it right. Just ask the 273guys, right here on FABO, how much money they spent on their 273s, and what the results were. Then decide for yourself which way to go.

Ok, just to wrap it up; for your 273 to be fun with all the 340 parts on it, the Scr will need to be raised to about 11/1, and it will still be a slug at below 3000 rpm as compared to that 69 318, gear for gear..
To get to 11/1, the total chamber volume will have to be reduced to 56cc; that ain't gonna happen with 340 heads, and 2bbl pistons. I think, not even with 4bbl pistons. And even if you were able to; everything will have to be custom machined and custom fitted. Your talking multiple mock-ups, multiple trips to the machine shop, and multiple re-machinings. You are likely looking at months of test-fitting.
IMO, there is absolutely NOTHING right about putting a 340 topend&cam into/onto a 273. What I mean is; there is not a snowball's chance in hell, for a streeter, that I would ever consider it. There are just too many easier,faster,better, cheaper solutions .
Sometimes; just because a thing can be done, does not make it the thing to do.

 

[toolmanmike]

Hugo; yur in trouble. Big trouble.
Lemme spell it out for you; keep in mind that I am not a 273 hater.
What you propose to do has been contemplated for well over 50 years, and every guy who ever did was wrong.
Yur thinking; the heads will add 50 hp
the cam will be 30.
the headers 25 and
electronic ignition will get you 5,
so that adds up to 110hp, am I right?

Well, it will never work that way, never, never, never.

Firstly;
putting the 340 heads on is +72cc versus 57cc. Put that on a 2bbl 273 and you instantly make a lawn-mower engine out of it, because the compression has dropped to 6.9/1 . Next, you swap a 340 cam in there and change the Ica from 48* to 60*, and the Dynamic Compression Ratio falls to 6.6/1

So what you have built is a slug off the line to say 4000rpm, when it finally wakes up, and then the 340 parts finally kick in. Great,
But here's the deal, even running 3.91s, 4000rpm with 24.5 tires comes to 24mph in first gear with a 3.09Commando 4 speed. So, there is no warrior in that combo.
But wait, the Advertised duration of that vam is 268/276/114 making the Ica to be 60* at plus 4* install. But that is at .008 tappet rise so the valves are still open by .012 inch. and your engine cannot begin to make pressure until the intake valves are on the seat and not leaking. When this is factored in, your Dcr falls even further, to perhaps 5.8/1 and this will turn your 273, at low rpm, into a total lazy dog.
The guys above are trying to tell you this, but you are NOT listening.
But Ok I get that you added a few nuggets, but it will NOT be enough..
To do it right, you will spend a mountain of money on this 273 project, and in the end, have way less performance, than a 69 318 with a 4bbl and dual exhaust.
You said;

You're going about it all wrong.

Ya, what he said. I was torn between the like, thanks and agree buttons. You get the like. It ads to your count.

 

[RustyRatRod]

Ive read that Isky makes a good one. do you have a part number of the one that you recommend ?

Yes. I told you in my first response.

 

[4spdragtop]

 

[64whiteghost]

First off, is the Valiant an automatic transmission? Second, don't try to make a small port head a large port head. The Stock Class racers will tell you to just use a 340 intake, as they will work fine with the smaller port window. If ported, by someone who knows what they are doing, your 66 heads can indeed flow what stock 340 heads do. Ask Moparofficial. Since you have a solid cam valve train, I would go with that. 2 barrel pistons will work just fine with today's gas. Make sure you check you timing marks for TDC and centerline your cam. I have run a 340 cam, but I also had 10.5 pistons, the rest of the 340 top end including heads, and a 4 speed. It was very fast, and my daily driver. Not sure if someone else would enjoy it as a daily driver though. A 273 should be a very efficient, quick motor, but it is small. It works best with a smaller, less than 260, duration and less than .50 inch lift cam for most people.

Its a 4 spd and yes Mopar official is the one that will be working on my heads

 

[Dartsun]

Just get yourself the E-4 Isky cam, it’s proven on here by many of guys to be great for the 273.

 

[64whiteghost]

Hugo; yur in trouble. Big trouble.
Lemme spell it out for you; keep in mind that I am not a 273 hater.
What you propose to do has been contemplated for well over 50 years, and every guy who ever did was wrong.
Yur thinking; the heads will add 50 hp
the cam will be 30.
the headers 25 and
electronic ignition will get you 5,
so that adds up to 110hp, am I right?
Well, it will never work that way, never, never, never.
Firstly;
putting the 340 heads on is +72cc versus 57cc. Put that on a 2bbl 273 and you instantly make a lawn-mower engine out of it, because the compression ratio has dropped to 6.9/1 . Next, you swap a 340 cam in there and change the Ica from 48* to 60*, and the Dynamic Compression Ratio falls to 6.6/1

So what you have built is a slug off the line to say 4000rpm, when it finally wakes up, and then the 340 parts finally kick in. Great,
But here's the deal, even running 3.91s, 4000rpm with 24.5 tires comes to 24mph in first gear with a 3.09Commando 4 speed. So, there is no warrior in that combo.
But wait, the Advertised duration of that cam is 268/276/114 making the Ica to be 60* at plus 4* install. But that is at .008 tappet rise so the valves are still open by .012 inch; and your engine cannot begin to make pressure until the intake valves are on the seat and not leaking. When this is factored in, your Dcr falls even further, to perhaps 5.8/1 and this will turn your 273, at low rpm, into a total lazy dog. The laziest dog ever known to man...... until around 4000/24mph with 3.91s. But if you have the more typical 2.76 ratio, 4000 will be 34mph.
The guys above are trying to tell you this, but you are NOT listening.
But Ok I get that you added a few nuggets, but it will still NOT be enough..
To do it right, with the 340 parts, you will spend a mountain of money in machining, and in the end, have less performance, than a 69 318 with a 4bbl and dual exhaust.
You said;

You're going about it all wrong.
BAR NONE; the cheapest fix is a bigger engine.
But,you can build a fun-to-drive 273, if you do it right. Just ask the 273guys, right here on FABO, how much money they spent on their 273s, and what the results were. Then decide for yourself which way to go.

Ok, just to wrap it up; for your 273 to be fun with all the 340 parts on it, the Scr will need to be raised to about 11/1, and it will still be a slug at below 3000 rpm as compared to that 69 318, gear for gear..
To get to 11/1, the total chamber volume will have to be reduced to 56cc; that ain't gonna happen with 340 heads, and 2bbl pistons. I think, not even with 4bbl pistons. And even if you were able to; everything will have to be custom machined and custom fitted. Your talking multiple mock-ups, multiple trips to the machine shop, and multiple re-machinings. You are likely looking at months of test-fitting.
IMO, there is absolutely NOTHING right about putting a 340 topend&cam into/onto a 273. What I mean is; there is not a snowball's chance in hell, for a streeter, that I would ever consider it. There are just too many easier,faster,better, cheaper solutions .
Sometimes; just because a thing can be done, does not make it the thing to do.

Cool thanks !, Just asking questiotns. I have a 69 340 complete and have extra parts from it. but Its for another car. So thats where the question comes from.. Thanks for your time

 

[64whiteghost]

Just get yourself the E-4 Isky cam, it’s proven on here by many of guys to be great for the 273.

Awesome, thats why im thinking. Thanks !

 

[toolmanmike]

Just get yourself the E-4 Isky cam, it’s proven on here by many of guys to be great for the 273.

And use the stock heads. Massage them if you wish. Look through my build thread. The link is just below. Save the 340 heads for your 340 that you mentioned you had. Rebuild it and put it in. That would be a screamer.

 

[64whiteghost]

And use the stock heads. Massage them if you wish. Look through my build thread.

yes my intention was always to use the stock heads. Moparofficial is going massage them. I have a 600 cfm AVS edelbrock.

 

[Dartsun]

I have a 66 273 with the hipo pistons LD4B with an automatic dual 2” exhaust, with and Oregon cam grind on the original 4 barrel cam. It’s a great engine but far from a screamer. It’s a joy to drive around on the highway 8.75 3:23 open.

 

[64whiteghost]

I have a 66 273 with the hipo pistons LD4B with an automatic dual 2” exhaust, with and Oregon cam grind on the original 4 barrel cam. It’s a great engine but far from a screamer. It’s a joy to drive around on the highway 8.75 3:23 open.
View attachment 1715650647

Very nice ! what intake is that ?

 

[64whiteghost]

And use the stock heads. Massage them if you wish. Look through my build thread. The link is just below. Save the 340 heads for your 340 that you mentioned you had. Rebuild it and put it in. That would be a screamer.

I looked at your thread. Are you running the 340 performance exhaust ?

 

[Dartsun]

Very nice ! what intake is that ?

Edelbrock LD4B. 600cfm edelbrock carb.