'71 vs'72 340? High vs low compression?

[Super Blue 72]

Hi guys, a question if I may and thanks in advance.

A couple of us were wondering if there was a way (externally without taking the engine apart) to tell if the engine that we have is a:

- high compression '71 340 with 10.25:1 compression, 275hp

vs

- low compression '72 340 with 8.5:1 compression, 240hp.

My car and JRoss22 are early production '72 Challengers.  Manufacture date 8/17/71 and 9/22/71 respectively.  We both have found orange paint on the engine and for '72 the engine should be blue.  They are both original engines and at least mine has never been rebuilt.

Any ideas?  Thanks!

[JRoss22]

 

[Alaskan_TA]

This is a shot in the dark but.....

On the front of the engines, right below the drivers side head surface should be a string of stamped numbers. Can you both post what they are? I have a theory, but the numbers may tell all.....

T/Ake care,
Barry

[madness]

JRoss i see ur in roseville i am right down the street in granite bay what parts u need probley have it

[JRoss22]

Yes I am in Roseville.... Most parts I already have because my car was pretty solid when I bought it but I will get back to you on stuff I need.... now not to hijack this thread but Barry I will get back with those numbers tomorrow

[Super Blue 72]

Thanks for the reply, Barry. 

I have a feeling that mine is just a regular ol low compression 340 since mine says something like:

HM 340R,

 I believe "R" denotes regular fuel and not premium fuel, so I figure that it's a low compression engine . 

Whatcha think? 

[moparnut]

Thanks for the reply, Barry. 

I have a feeling that mine is just a regular ol low compression 340 since mine says something like:

HM 340R,

 I believe "R" denotes regular fuel and not premium fuel, so I figure that it's a low compression engine . 

Whatcha think? 

You are right,when i bought my chally a couple of years ago the guy thought the R was for Race motor,lol.He and his brother were all excited about it until i burst his bubble,lol.It is Regualr fuel.Its kind of like the 440HP2 thing people say it the best 440,we all know it was just cast the second shift at the assembly plant

[gichy]

I have the same issue with my 340.
On the Pass side below the head it reads 6  17  71  , which should be built June 17,1971

On the Driver side there is this #  2780930   340   5 or 6,  I been told that the # 2 means that its a 1972 block?

Or was this block made in 71 but use for a 72 car?

I would like to know if this is a high compression motor

Please help

[Super Blue 72]

I think all the '68-'73 340 blocks have the same casting #s (except the T/A and AAR cars) so possibly the difference may come down to:

-heads?
-pistons?
-cam?
-carb?

Any idea? 

[gichy]

I bought the engine about 3 years ago.
It already has 360 heads with adjustible rocker arms, with a Edlerbrock 340LD intake
No carb and I have no idea about the pistons

[cjm]

The casting on the block for the 340  is as follows:

2780930  All 340's from 68-73 except t/a & aar.
3577130TA  1970 (340-6) t/a & aar..

Intake manifold castings for 340's:
 
2531915    1968
3462848    1970
3418681    1970  (aar & t/a)
3512100    1971
3614025    1972
3671918    1972  (california emissions)
3671918    1973

Heads for 340:

2531894    1968 - 1970   (2.02  1.6)
3418915    1970 (aar & t/a) (2.02  1.6)
3418915    1971 - 1972 (1.88 1.6)
3671587    1973 (1.88 1.6)

[cjm]

Engine specs for the 340:

1968 + 1969
V8-340 4-bbl         10.5:1  275 @ 5000
1970
V8-340   4-bbl     8.8:1   275 @ 5000      
V8-340   3x2-bbl    10.2:1   290 @ 5000 (TA & AAR)
1971
V8-340   4-bbl    10.2:1   275 @ 5000
1972 & 1973
V8-340   4-bbl     8.5:1   240 @ 4800

      

[Alaskan_TA]

The 1970 & 1971 engines used in 1970 or 1971 model cars respectively should have the "P" stamped in for Premium fuel. Since yours has the "R" for Regular fuel it would have been a low compression 340.

The 1972 model year started in August of 1971, so a lot of 1972 cars will have engines cast in 1971.

You can decode the whole number and it will tell you the day your engines final assembly was. Look at the last two groups of four numbers each below the drivers side head surface, one set is from the 10,000 day calendar and the other 4 would tell you what engine it was assembled at that plant that day. As an example, 0146 as the last four digits would be the 146th engine assembled that day.

T/Ake care,
Barry

[Super Blue 72]

Thanks for the great info cjm and Barry!  Definately useful info!

Yeah, kinda figured it was a low compression engine.    Oh well...

Hey Barry, I was wondering about those #s you mentioned.  Are they the numbers after the HM 340R?

It's wierd because I understood there should be more #s but after the HM 340R there's nothing else.  Is that right???  Thanks!

[Bullitt-]

2 questions. 
1. Where are the casting numbers on heads? 
       I replaced my heads 20+ yrs ago w/ " EARLY MODEL WEDGE" heads from a guy that used them in drag racing.
2. Would my '73s compression be comperable to the early models now?