engines from different eras

Hello. I am interested in buying an engine for my car. my question is: what is the difference between buying a, let's say 350, from 1969, than a 350 from a 1982 camaro? i hope my example works out with what i'm trying to ask.

i know that manufacturers peaked their engine performances around 1970, and from then on the engines were detuned. does this mean i should look for an engine that is from the high performance era for that particular enigne?

for another example, a 440 in a charger in 1968 would be considered a good performance engine. but does a 440 in a dodge van in late 70s or 80s have the same capabilities as a 440 from a charger in '68?

if this isn't a clear question i can help try to define what i'm trying to say. thanks.

there is a big performance diference. like for your example of the 440, fyi they stopped making tthe 440 in 77, the compression ratio was dropped big time. in 68 it was 10:1 and in 74 it was 8.2:1.also you have to think about the emissions systems that were starting to be installed. another fyi in the late 70's you could only get the 440 in trucks and some cop cars. so if you think of the difference between a 69 350 and a 82 350 it is just as bad if not worse. you also have to think about the machining differences like the heads, the valve sizes, the cam size there is alot that is different between the years. to help you further here is a page with the 440 info. http://www.lhmopars.com/engines.htm since your trying to buy an engine a couple of questions have to be asked. is it going to be a crate engine or out of anthor vehicle? if out of a vehilce are you going to rebuild or just throw in? if your rebuilding it the year of the engine matters to the point of cappabilites of the year block and heads. if its crate you can are you getting a long or short block? i could keep going but i think i answered your question already.

Mischa, don't make the mistake of buying the crap about "you can't make a Pontiac run, you MUST use a Chevy". If you do, in a car as heavy as that Tempest, you'll get your doors handed to you nearly every time you run against a similar car with either BBC or a Pontiac (400 or bigger). This is especially true with streetable cars.
Or are you considering a 350 Pontiac? I recommend against it, as it does not respond to high performance modifications as well as the 350 Chevy, or the 400 Pontiac. Internal geometry is completely different. A 350 Pontiac is NOT the same as a 350 Chevy (or Buick, OR Olds..).
A '69 350 Chevy was available anywhere from 220 (2-bbl) horsepower to 370. These are "gross" numbers, not to be confused with the later rating of "net" numbers. Rule of thumb is to multiply "net" numbers by 1.2 to get "gross" numbers. Of course, you can go the other direction, too. An '82 350 Chevy is useless as delivered, from a performance point of view. The heads, cam and induction MUST be modified to gain anything from it.
The '71 model year is the "line in the sand" for performance engines, with only a couple of notable exceptions, until the late '90s when LS-1 came around. That was the year ('71) when the government mandate for use of "regular" fuel was implemented. The result was horsepower falling off the table for years to come.
The 440 question is valid, but there's an important point missed. The earlier 440s with higher compression and more aggressive cams, were for high performance, period. The later (and earlier low compression) version is for trucks and full-sized cars. The power output and RPM range are aimed at a completely different purpose. Don't confuse power for trucks with power for hot rods...

On your 350 question. A 350 block is a 350 block. The casting is the same. On the newer 350 the Heads cc's are probably not as effective so your compression will be lower than that of lets say a 69 block. You can change all that yourself. For the block though it is the same thing. If you change the internals you can make the engine anything you want it to be. Dont get all caught up in the 2 bolt main and 4 bolt main arguements. Either one is good plus a 2 bolt is usually cheaper to buy. The 80's block would be just fine to build.

Mr. Horsepower, at the risk of opening an arguement, I must disagree. First, that all the 350s are the same. The pre-79 blocks are a bit "harder", containing a higher amount of nickel alloy. Some of the "performance" blocks are said to have even more.
The distick tube installs on the driver's side (left) up to '76. After that, it was on the other side (exceptions here and there, but in general...). There are factory "warranty" blocks with the tube provision on BOTH sides.
Also, for a stroker, a 4-bolt is highly recommended. Considering the majority of early (pre-77) blocks are 4-bolts, it would be prudent to get one. We have seen main bearing issues with nos. 2 and 4, when 2-bolt blocks were used, and the engine was used in a performance application.
We have also seen significant problems with the cast steel cranks out there, on nos. 2 and 4. We suggest either the factory 400 nodular crank be turned down to fit, or go with a high quality forged steel crank. These have shown to live in an engine designed to make power.

There goes pbody forcing his opionion on everbody else. If you ran a mopar you dont need 4 bolt mains they are for 600hp and constant 8000 rpms. Maybe in a GM product which probably would blow up....Tool!

No forcing here, Soxs, just observations over several years of experience.

Wasn't it you that insisted I only post when I have something constructive to add?

In response to soxs post, i have never seen a factory 2 bolt block that cant turn 8000 rpms, maybe you will take me for a ride in your dodge dart and bring it up to 8000 rpms, i would really love to hear what that sounds like. For one, the opinon that a GM product will blow up if you bring it to 8000 rpms is extremely biased, if you want some proof ask redneck383, he has a freind that has a GM 454 turning 9 grand, now if it is a GM shouldnt it of blown up before it could turn 9 grand. And also i would take Mr.pbody's word for gold if i where you, he is a engine machinist for christ sake. So when will you be picking me up in this dodge dart of yours?.

I said, or meant to say, 4 bolt mains were only required for units running over 600hp and turning 8000 rpms for an extended period of time such as road racing or oval...A street/strip does not need 4 bolt mains to survive...except your bowtie units. :screwy:

Oh thats what you meant to say. Well my bowtie unit 402 is in and it is still running strong, and guess what the kicker is, yup thats right its a 2 bolt main. Its not like there is any difference between the iron that a mopar block is made with and the iron a chevy block is made with, other then the nickel alloy content all the blocks are the same. I think you are just angry at chevy because the engines cost less then your mopar, or have you got your ass handed to you by a chevy?. You should love all muscle cars, i dont have a biased toward any one. But yes i own a chevy.

My ass was handed to me a few times back in 70' but not by any bowtie unit, when i had a 69 350 SS camaro....and it was first of all beaten real bad by a 70 340 Duster, then about two weeks later a 70 340 swinger schooled me....Now i have a 69 340 Swinger. :nono:
As far as 4 bolt mains they are overrated at least in mopars. I do happen to have a bit of bias. I remember when the mopars came out in in the 70s and all the chebby and fird guys were laughing...didnt take long for me to see the light. Mind you i'll take any american muslce over rice anyday. I'm just an old fart that went through the muscle cars wars and it was great. As for pbody i still call BS on his goat. :screwy:

Well so far i have found two mopars that wind it over 8 grand with 2 bolts johnboy...oddly enough ones handle is PBody....the real one. Not bad for 10 minutes of lookin.

I dont know, maybe you had a bad experience with chevy because you couldnt or didnt know how to tune it. The one reason i like chevy and choose to buy it is because the engines in them are really cheap to build, and you can get insane horsepower numbers for very little cash.

Did you read my post????....Your reply is typical knot head shit. You said there is no way a factory block can spin 8000 and live with 2 bolt mains. Your dead wrong buckwheat. But you keep going with the flow, dont ever dare to be different. :screwy:

I have no problems spinning my 340 base 395 ci to 8200 on every pass
and its been doing it for 7 years now
:2cents:

Yes, i did read your above post, and yes i do still maintain my opinion that a stock 2 bolt main block will not last to 8 grand, there is just to many parts that are to weak and that will break, that is just way to much reciprocating mass for the stock rods and crank not to mention main caps and bearings to hold on to. Now if you would like to prove me completely wrong take a video of you revving your dodge dart to 8 grand. Then i will give it to mopar.

I had heard that there was another Mr P Body over here and wanted
to see what he was running?
I'm new to this forum so I will tell you real quick what I run. Its a 88
Plymouth Sundance with a full tube / moly chassis, I used to have a
340 in it but bumped it up to 395 ci, W-2 ported heads, roller cam and
rockers, with basicly a low 10.5:1 compression, the last couple of years
I have been running 9.47 @ 142 with 1.25 60 ft
Thanks guys

LOL how many p body guys are there here now? Is this a joke?

LOL how many p body guys are there here now? Is this a joke?

No, no joke, I am not normally on this board but I heard of another
P body and came in to talk with him. I can say that I have had the
name on the side of my car for 8 years now and never heard of any
other till now
Have a good holiday
:)

You that guy with that blue Shadow? I saw one on Moparts...

Yes thats me

Ah, Sundance. Sorry about that. I like the idea.

I thought maybe you were some guy that just made a name like this to mimic the other pbody guy, or something...

Cool...

Hey, the new mr.pbody. Nice et's by the way. 9's are very hard to pull off. I was wondering if you had any pictures of your car, i would like to see it.

It catwalks, it's cool.

Yes, i did read your above post, and yes i do still maintain my opinion that a stock 2 bolt main block will not last to 8 grand, there is just to many parts that are to weak and that will break, that is just way to much reciprocating mass for the stock rods and crank not to mention main caps and bearings to hold on to. Now if you would like to prove me completely wrong take a video of you revving your dodge dart to 8 grand. Then i will give it to mopar.

Well johnboy? MR P BODY does it and he is not alone. :twak:

Yes, he does it. But as we all know that this is a discussion about a 2 bolt main spinning 8000 rpms. Mr P Body, is your engine a 2 bolt main or a 4 bolt main?. If he says 2 bolt then there you have it, if he says 4 bolt you counted your eggs before they hatched.

Yes, he does it. But as we all know that this is a discussion about a 2 bolt main spinning 8000 rpms. Mr P Body, is your engine a 2 bolt main or a 4 bolt main?. If he says 2 bolt then there you have it, if he says 4 bolt you counted your eggs before they hatched.

Well it is a 2 bolt main among other Mopars at moparts.com. Check out the thread "RPMs and 4 Bolt Mains" from yesterday. Heres a reply from CruisingRam and i quote " I have spun my SB mopars to 8k with no problems hundreds of times with 2 bolt mains and forged crank-You have to tell your chebby guys that SB mopar bottom ends and valve train are WAY stronger than stock chebby pieces-SB chebby is not even in the same category. I used to race SB chebby's-and I discovered that they were actually more expensive than mopars when it came to holding together-sure you could find cheap parts for them, but having to buy those parts over and over again when they grenaded made the chebby more expensive. You dont need 4 bolt mains(for the most part) or stud girdles(like a chebby) to make a mopar race motor hold together".........end of quote......need more? :smokin:

Hey, the new mr.pbody. Nice et's by the way. 9's are very hard to pull off. I was wondering if you had any pictures of your car, i would like to see it.

I can post a pic IF someone can give me a quick leason on how to post
in here, I dont see a place for posting a pic

To the other post pertaining to a 2 or 4 bolt block its a 2 bolt, but I
do have other engines (blocks) with 4 bolt mains
1 engine I have is a 340 base 395ci with W-5 heads
1 engine I have is a 340 base 405ci with W-9 heads
both of these are 4 bolt blocks

No i dont need any more, thanks for all of the information you have given me and the new knowledge that you have bestowed upon me. I will take P bodys and your word that you can spin a mopar to 8 grand without it letting loose, but that is to big of a gamble for me (even if i was in a mopar) for me to take. Well, it was a good debate and maybe there will be another some time. Best of luck with the mopars.

:biggrin: At least its not about rice, I saw a Yenko 427 Nova at Mission raceway last summer. Grenaded in the first round. I got schooled long ago about mopars and fell in luv with them but to each his own. :thinkerg:

Mischa, don't make the mistake of buying the crap about "you can't make a Pontiac run, you MUST use a Chevy". If you do, in a car as heavy as that Tempest, you'll get your doors handed to you nearly every time you run against a similar car with either BBC or a Pontiac (400 or bigger). This is especially true with streetable cars.
Or are you considering a 350 Pontiac? I recommend against it, as it does not respond to high performance modifications as well as the 350 Chevy, or the 400 Pontiac. Internal geometry is completely different. A 350 Pontiac is NOT the same as a 350 Chevy (or Buick, OR Olds..).
A '69 350 Chevy was available anywhere from 220 (2-bbl) horsepower to 370. These are "gross" numbers, not to be confused with the later rating of "net" numbers. Rule of thumb is to multiply "net" numbers by 1.2 to get "gross" numbers. Of course, you can go the other direction, too. An '82 350 Chevy is useless as delivered, from a performance point of view. The heads, cam and induction MUST be modified to gain anything from it.
The '71 model year is the "line in the sand" for performance engines, with only a couple of notable exceptions, until the late '90s when LS-1 came around. That was the year ('71) when the government mandate for use of "regular" fuel was implemented. The result was horsepower falling off the table for years to come.
The 440 question is valid, but there's an important point missed. The earlier 440s with higher compression and more aggressive cams, were for high performance, period. The later (and earlier low compression) version is for trucks and full-sized cars. The power output and RPM range are aimed at a completely different purpose. Don't confuse power for trucks with power for hot rods...
You state the 350 Pontiac does not respond to performance mods as well as a Chevy 350. WRONG! check out rock n roll engineering for there pump gas 350 buildup. 87 octane and over 530 HP

Mr. Fulper has been known to "fudge" numbers over the years. He has also found himself on the outside, looking in, in the Pontiac community. If you're looking for ACCURATE and non-selling information on Pontiac V8s, I suggest you look elsewhere. He bragged about that POS Ventura for a long time. I saw it in Charleston in '02, and it left a trail of blue smoke and knocking sounds everywhere it went. I also submit, if you pumped a 350 Chevy to the same level of tune, it would STOMP the 350P. And that's coming from a Pontiac man! BTW, nobody really cares about an 1/8 mile "record".
Mr. Fulper and RRE are also conspicuous by their absense, in Jim Hand's recent book "How to Build Max-performance Pontiac V8s".

Now to this other "Mr. P-Body". I have never seen or heard anyone using the moniker before this post! It's okay, I have no legal ties to the nickname. Mine comes from an affection for the Fiero. (GM "P" body). I've been using it online for about 6 years, mostly on the Pontiac sites. Where do you get yours? BTW, welcome aboard! You'll find some crying and whining about personal taste versus reality here, but in general, after sifting through the BS, you'll gain some good information. Watch out for the snipers in the bushes. If you step on their personal brand or style, they'll come at you with insults and diversion. And above all, DON'T CONFUSE THEM WITH FACTS!

Comparing the small Dodge to the small Chevy, as to the need of 4-bolt mains, is apples-to-donuts. First, the VAST majority of the small Dodges are/were 2-bolt. The main saddles and bulkheads are more rigid than that of the Chevy. Some of the 340 T/As and MAYBE 6-Packs were 4-bolt. I've only seen a few over the years. On the flipside, the VAST majority of 350 Chevys, made before '87, WERE 4-bolts. From a shop's perspective, probably 70% of 350s we see are 4-bolt. That includes the restorations and truck applications, as well as the "hot rods".
The Chevy block has issues with cap walk and distortion, the Dodge simply doesn't share. Also, the Dodge performance engines (360s, in stock form, don't qualify as "performance") were virtually all forged steel crankshafts, as well, where the steel cranks in Chevys are a real "prize". The crank is another reason for the 4-bolt caps. The iron crank is much more rigid than the forging, and the block can't take the distortion from harmonics usually absorbed by the steel crank.
And how did big blocks get into this mix? ZERO of the MOPAR B and RB blocks are 4-bolt from the factory. ONLY the Hemi, and it is a "cross-bolt" system, not similar to other 4-bolt arrangements. We're in process of upgrading a 440 block right now, with ProGram Engineering "cross-bolt" caps. It will be a 700-plus HP "street" (more like PRO street...) 499 CID "wedge". AWESOME engines, these RBs.
BBCs have 4-bolt caps on ALL "high performance" and "heavy duty" blocks. While one can build a very stout 402 or 350-hoprse 396, 4-bolt caps are unnecessary until power output exceeds 700, and RPM exceeds 7,500. Bring that down about 1,000 RPM for 454.

The "other" Mr. P-Body (I think we're BOTH "real")

Jim

Mr P
Thanks for the welcome, its funny that use use it also, I hadnt heard of
anyone before that used it. The reason that I use it is that I race a
Plymouth Sundance and here at Chrysler where I work its refered to as a
P body(body line, pre production) same type of thing over at GM
Well I tried to put a pic in here but it doesnt want to play, I'll see if I can
at some other time
Have a happy new years

Race a Sundance? A SUNDANCE??? I suppose there are as many variations on the theme, as there are guys doing it. Is that a drag car with a V8? Or a road racer, relatively stock? I'm curious. There was a man here (Richmond, VA) that ran a Sundance for a while, but he broke an axle and bounced it off the guard rail. It has a Dodge Challenger (the Jap one) body now. Good runner. 346 CID and it goes low 10s. It's a "foot brake" bracket car.
Where do you work for Chrysler? Again, just curious. From your answer, I assume (always a dangerous proposition...) the "P" designation refers to any pre-production car? The Fiero is a "P" body, like Firebird is an "F" body. Fiero is the purist form of Pontiac since the corporate overlays began in the '50s. That is, no other GM division built anything on that platform. As a "Dodge" guy, you probably don't care. It's okay, I just like to share...
Best of the New Year to you (and to ALL reading this!).

Jim

I am aware of the pissing match between Pontiac rivals, and you are right mr. P-body. I have never personally owned a fast 350 Pontiac, I did have a 71 Lemans sport 350, here is the specs. 68 block and heads, comp 268h cam, performer intake, holley 600. It really was not all that responsive, as I remember. I was taking that of other people's (Fulper's) word. You are right about a 350 being able to make power cheaper than anything though, but parts need to be selected carefully. There is a vast aftermarket just waiting to gobble up people's SBC earning dollars. As far as 340's go, I can speak with some experience, since I have owned a few. No 340 ever came with four bolt caps stock. The T/A block as you refer to has provisional material for that so Trans Am racers could machine them for that. Also the cylinder head or 1970 "J" heads use offset rocker arms do to casting differences inherent with the TA head. I know because I have a set on my 70 Swinger right now, and let me tell you they are the best heads you can get. I am a big 340 fan, not much so for the 360. I realize that with certain parts a 360 will run, but the 340 was oversquare, had forged pistons, with full floating pins stock! Try to find that with a 350 Chevy! Anyway it is cool to see there is so many people on here with so much knowledge on cars.

This is his picture from his signature on Moparts:

http://files.automotiveforums.com/gallery/watermark.php?file=/503/155239pbody.JPG

And underneath it says:

9.47 @ 142.5mph, 1.25 60 ft,395 ci, W-2 heads
2400 lbs

All production 340 pistons were cast. They were the heaviest at 719gr per. Actually the 360 piston at 584gr was lighter than the 318 at 592. This from a smaller bore and a longer stoke with the same lenth rods as a 340.
Also there is no performance advantage to T/A heads as cast. The intake rocker was offset and the pushrod hole was elongated to provide provision for porting.
Any J,U,X,O or Z head has a poor flowing exhaust port. T/A heads could have any stampings of the above. The 360 "308" heads will outperform any of the earlier heads due to a far superior exhaust flowing port.
I am currently looking around for a stock bore 360 short block for a stroker. Putting the 340 on the shelf. What the details of your Swinger Wedge?

The "308" head as you described, has a potentially better exhaust flow fully ported. The stock 308 head will not outflow the 915, I guarantee that if I swapped bone stock heads right now, I would see my top end performance decline. As far as the heavier piston, of course it does. it's 40 thousandths bigger, and also taller than the 360. The bottom line is if you took Identically prepared w-2's and I put them on a 10.5 340, and you put in the same with the 360, the 340 is going to outperform the 360. Make more horsepower, rev higher and last longer. The only advantage a 360 has over a 340 is the larger crank diameter, but you can negate that due to it's cast design, except for 71 360's. -70 Swinger 340 #s match, keith black hyper pistons (.030) TA heads 284 cam stock intake with edelbrock carb headers, elec ign 4-speed orig 3.91 sure grip FY1 yellow car, bench seat - best 1/4 time 13.71 @ 102. very reliable, nothing like a 4-speed!

For street-performance, and not max-power, I like the longer stroke of the 360 better. Keep the revs under 6,500, and the cast crank is not a liability. The low-end torque is the desired performance quality sought by most street-oriented customers. This is especially true when car weight exceeds 3,500 lbs.
Floating pins are desired for engines revving above 6,000 for extended periods, or over 7,500 for short bursts. All the 273s and early 318s (both head styles) were floaters. So were the earlier 340s. I've done 2 340s (one '73 and one '74) with the 360 heads (factory emmission stuff) in the last couple of years. Both were pressed pins. All the 360s (that I've seen) are pressed.
Chevrolet was one of the earliest V8s without floating pins. A 302 can rev well past 7,500 without issue. We use pressed pins in most of the lower level circle track engines, including the Dodges. Pressed pins are not a liability if everything is done correctly, and much less failure-prone. Bushing the rod and adding the locks complicates things, and adds more parts to fail.
Don't misunderstand. This is not to say floaters don't have their place. They most certainly do. But they are not necessary for a street machine, under most conditions.
Soxs, please stop trying to compare features across engine families. Apples-to-donuts. Each engine family has advantages AND disadvantages. None are exactly alike. An example would be to figure a way to install small block Chevy race heads on your Dodge small block. The SBC head is where the advantage is, and nobody makes a better design for a smaller cubed race engine. As much as I like to see Chevys lose, I'm not stupid about them. They are the MOST popular race engine for many good reasons. And it isn't the lower cost. The lower cost is a by-product of the popularity.

P(b), I like the way that front end comes up! Nice looking car... Fast, too! Nice job.

mr pbody, I can understand where your coming from with the torque thing and in most cicumstances this would work. I just am speaking from my experiences with both engines. All of the 340 engines I had responded better with light mods, and that added torque you say was never enough to overcome the top end charge of the 340's. To understand this, in my experience 340 should not have less than a 3.91 gear out back, they love it. I have had 340 cars with 2.91's 3.23's, 3.55's and two cars with 3.91's. I know this is as you say "apples to oranges" but the cars without those gears just never responded that way. The two A-body 360 cars had 3.91's also, but didn't run that well this way. -Not all early SBC motors were full floaters. Yes Chevy definately has a lock on the amount of cylinder heads they offer, and designs are plentify, but most of the w series heads will keep up with these heads, although they are considerably more expensive. Yes Chevy heads will always be cheaper, and yes they are plentiful, but why isn't everyone buying them? Same reason a guy buys a pontiac, or Buick, or whatever. He feels there is pontential to be found in these engines that cannot be found in a chevy. A chevy engine isn't always the answer. I realize again that in this day and age you can make ANYTHING go fast, so that is why people don't pick Chevy. Bottom line is- you want to make power- buy a Hemi. You want to make power cheap- buy a BBC.

This is his picture from his signature on Moparts:

http://files.automotiveforums.com/gallery/watermark.php?file=/503/155239pbody.JPG

And underneath it says:

9.47 @ 142.5mph, 1.25 60 ft,395 ci, W-2 heads
2400 lbs

BleedDodge, thanks for posting my pic, it sure wasnt happening for me
thanks again
Thanks P (a)...LOL, I changed my IC around so that its not climbing
that high any more
:smile:

First of all the 308 heads will outflow and outperform any mopar sb heads before the magnum era. Thats a fact.
The 360 vs 340 debate will go on forever. For myself i'll stroke a 360 before a 340. I luv my 340 but i'm not interested in blowing it up somewhere along the line. A 360 buildup is cheaper and will produce more bang for the buck. The 20 extra cubes. the longer stroke at less rpm means more torque and it will live longer. As for my 69 Swinger I saw a timeslip from the previous owner and it was [email protected] you thats at very close to sealevel track. Mine is a stick also with 295s out back.
As far as the hemi thing....Most well tuned 440s would beat a well tuned hemi in the the 1/4. If the 1320 was 1520 the hemi wins every time.

so just slapping on a 308 head just outflows x heads and 915 heads? I have heard of people using the 308 before but it is not all that common I guess. Did you ever see that 68 Dart GTS 340 cross ram car, I think he has those heads and goes 11's and it's a 4-speed to boot!

How did you get the 295's to fit? My car has 235/60 radials on steelies and it barely fits. Did you massage your wheelwells?

First of all the 308 heads will outflow and outperform any mopar sb heads before the magnum era. Thats a fact.
The 360 vs 340 debate will go on forever. For myself i'll stroke a 360 before a 340. I luv my 340 but i'm not interested in blowing it up somewhere along the line. A 360 buildup is cheaper and will produce more bang for the buck. The 20 extra cubes. the longer stroke at less rpm means more torque and it will live longer. As for my 69 Swinger I saw a timeslip from the previous owner and it was [email protected] you thats at very close to sealevel track. Mine is a stick also with 295s out back.
As far as the hemi thing....Most well tuned 440s would beat a well tuned hemi in the the 1/4. If the 1320 was 1520 the hemi wins every time.

If you are just trying to save the 340 block thats one thing, BUT if you
are stroking either the 340 block starts out with a bigger bore and can
be bored out farther than the 360, so you would come out with more
cubes if you went with the 340 block, plus the 340 's have less dia. on
the mains so you end up with less drag on the crank

As in 416 as oppossed to a 408 Mr. P Body? I can see why someone would want to take out the 340 and swap in the 360 due to parts availability.