340 Intake on 273

[MObarracuda]

I just purchased a 1967 Barracuda with the 273, AC, PS, PB, 904 Auto with 2bbl carb. I have the opportunity to purchase 340 4bbl intake and heads off of a 1971 340. Can I install the intake on the 273 w/4bbl carb (500-600cfm) and enjoy it now or do I need to wait to find the 360 motor down the road?

I know I will need a longer kick down rod (2bbl and 4bbl different locations) but have read differing opinions on the bolt diameter and the intake angles between 273 and 340. Will the 1971 340 intake fit on my 273 and it this a worth while performance improvement? The discharge ports are much larger on the 340 intake vs the 273 heads, will this cause any problems without grinding the 273 heads? My plan is to swap engines this winter but I want to leave the 273 stock for the next person but enjoy the car this summer without taking it down for the full engine swap.

I'd appreciate any assistance I can get from the Forum.

 

[rumblefish360]

There is insufficient room for the increased valve size so they will not operate.

 

[JBurch]

I just purchased a 1967 Barracuda with the 273, AC, PS, PB, 904 Auto with 2bbl carb. I have the opportunity to purchase 340 4bbl intake and heads off of a 1971 340. Can I install the intake on the 273 w/4bbl carb (500-600cfm) and enjoy it now or do I need to wait to find the 360 motor down the road?

I know I will need a longer kick down rod (2bbl and 4bbl different locations) but have read differing opinions on the bolt diameter and the intake angles between 273 and 340. Will the 1971 340 intake fit on my 273 and it this a worth while performance improvement? The discharge ports are much larger on the 340 intake vs the 273 heads, will this cause any problems without grinding the 273 heads? My plan is to swap engines this winter but I want to leave the 273 stock for the next person but enjoy the car this summer without taking it down for the full engine swap.

I'd appreciate any assistance I can get from the Forum.


View attachment 1714936931

View attachment 1714936932

View attachment 1714936933

To answer your first question, yes you can bolt down 340/360 heads on a 273, been done before; however it's gonna take ALOT of work! Cylinders must be notched for valve clearance, best done with engine out of car. The installation of pop-up pistons; bigger than the Hipo 235 hp 10.5 to one slugs; to compensate for compression loss due to larger chambers is highly recommended, otherwise turbo/supercharge your compression ratio is right where you need it.

Look up back issue of "Mopar Action" with article "Darn Dart", it's about a 340 headed 273.

As stated it can be done, it would be different, the $64,000.00 question is cost/benefit. It's your car, do what makes you happy.

 

[66fs]

Actually, if you are not changing cams you should be OK, but not really worth the effort for a few months. I've run milled to min cc 72 340 1.88 intake valve heads on a +.04 273 with great results, but also used a 71 340 intake carb cam and exhaust manifolds. If you want more power, I'd just add a 4 barrel intake, Carb, throttle bracket, and linkage. Then tune it. Should run great with just those mods.

 

[mguner]

You can upgrade the intake now and get your linkages sorted out. The linkage is not only longer, the bracket is wider to the drivers side as well.

 

[nm9stheham]

IIRC, the intake bolt angles on the '67 273 were the same as the other LA engines. I'd forego the 340 head for sure; besides the possible valve to cylinder bore interference, the combustion chambers are much bigger and will drop the compression ratio and you will really feel that on the low end, especially starting with the lower compression 2 BBL 273 pistons and with newer thicker-then-original head gaskets. You CR will be in the toilet.

Put on the intake and 4 BBL but do not be surprised if you do not see a huge increase in power. What there will be will be at the upper RPM ranges. The stock cam will not be able to take full advantage of the larger carb and intake. (And would not take advantage of the large ports on the 340 heads.)

Are you buying the 4 BBL new? That may take some thought to get the right one for use on the 360. What is your expected long term use of the car? Daily driver? Street cruising? Pure drag racing?

 

[4spdragtop]

What rumblefish said. Without clearing the block for valves on 340 heads I was going to do the same thing.

 

[rumblefish360]

The 2.02 will not clear.
The 1.88 needs a valve notch cut into the cylinder as I am told by the MP books.

 

[rumblefish360]

JBurch, you need to put your answer outside of the quote tags.

 

[340 demon 72]

JBurch, you need to put your answer outside of the quote tags.

The combustion chamber or the cc's of the heads are bigger on a 340 the motor will most likely have low compression and not alot of power

 

[Inertia]

The 2.02 will not clear.
The 1.88 needs a valve notch cut into the cylinder as I am told by the MP books.

^^^^^^ Xs2

 

[318willrun]

you can get your 2bbl linkage to work. I've done this multiple times. Got to bend a little.... In fact, you can see it in my dual exhaust video in my 318 thread

 

[dibbons]

I ran 12.72 at 108 MPH in my 273 (.060 over) with stock heads. Converted to 340 heads and vehicle never broke out of the 13 second bracket. Why did it run slower? Probably the loss in compression.

 

[MObarracuda]

I appreciate the posts. I need to clarify. I have no plans to use the 340 heads on the 273. I just want to put the 4bbl intake on the stock 273. What I am hearing is the following:

Can I fit the intake on the stock 1967 273
1) it will bolt on
2) the 2bbl linkage will work but may require manual bending to accommodate the 4bbl

Now….the next question Should I put the large intake and 4bbl Carb on the stock 273
3) The stock cam will be the limiting part and will not take advantage of the increased flow of the 4bbl carb and intake

My goal is a street cruiser but with more power than the 2bbl stock 273 with the goal of achieving 280-325hp. I think I will purchase the 1971 heads and intake and hold them until I find the 360 since the performance gains will not be substantial on the 273. Does that sound like a prudent plan?

 

[66fs]

... the bracket is wider to the drivers side as well.

It is also farther back to fully allow the secondaries to open fully. Stock 340 bracket will work for most manifolds.

 

[66fs]

The 2.02 will not clear.
The 1.88 needs a valve notch cut into the cylinder as I am told by the MP books.

I've run 1.88 intake valves, stock on 72 up 340's and 71 up 360's, without notches. 273 Commando with stock 340 cam. Ran great. Daily driver for years and about 100k on the Odometer. 2.02 Intake valves require bore notches on a 273.

 

[66fs]

I appreciate the posts. I need to clarify. I have no plans to use the 340 heads on the 273. I just want to put the 4bbl intake on the stock 273. What I am hearing is the following:

Can I fit the intake on the stock 1967 273
1) it will bolt on
2) the 2bbl linkage will work but may require manual bending to accommodate the 4bbl

Now….the next question Should I put the large intake and 4bbl Carb on the stock 273
3) The stock cam will be the limiting part and will not take advantage of the increased flow of the 4bbl carb and intake

My goal is a street cruiser but with more power than the 2bbl stock 273 with the goal of achieving 280-325hp. I think I will purchase the 1971 heads and intake and hold them until I find the 360 since the performance gains will not be substantial on the 273. Does that sound like a prudent plan?

1, Yes

2, See my post above.

3, Yes it will not run like a 340 but will wake that 273 2 barrel up nicely. Are we talking TQ carb? What number?

280 -325 HP is 340 360 HP territory, stock. The 273 can make that, but not with the stock 2 barrel cam. That HP range is easily doable and streetable with 318, 340 or 360, especially since you will already have the good Heads, Intake and Carb.

 

[66fs]

The combustion chamber or the cc's of the heads are bigger on a 340 the motor will most likely have low compression and not alot of power

There is only about 8cc difference between minimum cc'd chambers between closed chambered 273 heads and early 340 heads. That means I can easily get to 273 unmilled chamber size with 340 heads simply by milling .040 off the heads. 273's have a stock Compression Ratio (CR) of 8.8 to 9.0 with the piston .020 down in the bore. Not like 318's or 360's by 1973 most of which have a CR of 8.4 to 8.6 or lower with the piston way down in the hole. The 67-69 318's are the exception as their CR is about 9.2. Anyway the lowly 273 pretty much runs very efficiently with good power. It was never a smog motor.

 

[toolmanmike]

Hey guys, let's quit talking about the 340 heads. MO BARRACUDA just wanted to know about the 340 intake on his 273. Please read his original post.

 

[toolmanmike]

MO, you should edit your title. That's what is confusing us.

 

[nm9stheham]

Now….the next question Should I put the large intake and 4bbl Carb on the stock 273
3) The stock cam will be the limiting part and will not take advantage of the increased flow of the 4bbl carb and intake

My goal is a street cruiser but with more power than the 2bbl stock 273 with the goal of achieving 280-325hp. I think I will purchase the 1971 heads and intake and hold them until I find the 360 since the performance gains will not be substantial on the 273. Does that sound like a prudent plan?

I have put 4 BBL's on 2 BBL cams wiht poor results, but not on a 2 BBL 273 cam. So, I can't really answer on this particular cam. For the cost of a few gaskets and a bit of other work, it would not be much trouble to find out. I'd do it just to find out.

 

[toolmanmike]

The 2 barrel and 4 barrel cams aren't that much different.

 

[toolmanmike]

Here's some 65 273 specs.
2 barrel= 240° 240° .395 .405
4 barrel=248° 248° .420 .430
1966 4 barrel lift was increased to .420 .430

 

[krazykuda]

I would go with the 68 - 70 340 intake which is square bore and use a Holley 600 Vacuum secondary. Yes, there will be a slight port mismatch, but you will still get a performance increase...

The 71 and later 340 intakes were for spread bore Thermoquads that had 800 cfm, which is a little bit much for a 273...

Or you can get a Wiand Stealth new, which will run great on there, a little better than the stock one....

Weiand 8022WND Weiand Stealth™ Intake - Chrysler Small Block V8 - Holley Performance Products

 

[66fs]

I would go with the 68 - 70 340 intake which is square bore and use a Holley 600 Vacuum secondary. Yes, there will be a slight port mismatch, but you will still get a performance increase...

The 71 and later 340 intakes were for spread bore Thermoquads that had 800 cfm, which is a little bit much for a 273...

Or you can get a Wiand Stealth new, which will run great on there, a little better than the stock one....

Weiand 8022WND Weiand Stealth™ Intake - Chrysler Small Block V8 - Holley Performance Products

71-73 TQ's were rated at 750 cfm, but because of the adjustable air valve it is quite streetable even on a 273 2 barrel. I've done it on a couple 273 daily drivers with no problems. Easily out performs a Holley 600.