A half a point of compression won't be noticed.
Engine Advice Needed
- Thread starter rugbyjon112
- Start date
IMHO, I don't think that it means that much, especially in the world of C-bodies.
The problem with that relates to the way Chrysler Corp designed their cars . . . when one part (engine) gort more power, so did other parts of the car get upgraded to better handle the power (think brakes, suspension, transmissions, rear axles, for example). If you were starting with a 383 or 400 car, those upgrades would already be there, so just some tweaks would be needed (i.e., a transmission rebuild with a shift kit in the 727).
About a year ago, I was surprised when Nick's Garage (on YouTube) rebuilt an alleged 340 in a '73 Cuda, to discover it was a LA stroker motor. Cam was not disclosed, but that 408 stroker made 425 horsepower without sounding radical and was good in the street driving segments after the rebuild. "HEMI power from an LA motor", or something like that. Doint something like that is a much less invasive way to get more power and CID from an LA block and car. Rotating assys are available for such upgrades.
As somebody mentioned, a LA360 motor would be a good "drop-in" replacement, too. After a general freshening-up of the rotating assy, though. A future owner would probably go for that rather than a "hot rod stroker motor", I suspect, as this was a factory engine option in that car. Similar in concept to replacing a Chevy 305 with a Chevy 350 (to which new rings and bearings were added).
Telling a future potential owner the engine was replaced with a later-model 318 can be good to do, but with the commonality of repair parts from the 1968 model year forward, would not make much difference in which normal maint items the new engine would need. If the engine was taken in for a rebuild, the machine shop can check these things as a matter of course . . . as the casting date would be in plain view with the engine on the work bench. Similar if you go with the LA stroker route or a LA360.
In the middle '70s, a friend was driving a '68 Polara Fasttop. Neat looking car. An original 383 2bbl car. Something happened to the 383 and a '68 318 was installed. Yuk. That is when I realized that so much under the hood between an LA engine car and a B/RB engine car is different! As to location of items and related wiring that had to be changed. I don't think they ever got the wiring issues fully fixed before scrapping the car (from TX, no rust issues, just wiring issues "that somebody else can deal with"). Almost every engine-related harness had to be altered. THEN also consider that a B/RB engine single exhaust is on the rh side of the car and an LA single exhaust is on the lh side of the car . . . not a really big deal if a dual exhaust is planned.
Can a B/RB engine be swapped-in, as it was a factory option when new? Certainly. All things being considered, can it now be really financially justified with the new stroker LA rotating assys, as to added power? Not so much, to me.
There is a YouTube channel done by a guy that likes 318s. "318 Will Run", or similar. Lots of little things than can be done for little $, including modifying a factory spreadbore intake to take a non-spreadbore carburetor. Easier done than suspected! The engines are from the post-1970 era, so they are "emissions engines".
It might be a bit convoluted to follow, but David Vizard, in conjunction with Uncle Tony and somebody else did a 318 2bbl build over a year ago. All low $ modifications, generally, but with Vizard involved, I suspect some head porting was involved. I have never checked that series out, though. Seems like the finished engien was going to be raffled off to benefit St. Jude's Hospital or similar?
Your money. Your time. Your car. Your desires.
Enjoy!
CBODY67
Especially on a "drive around" street engine. Much more cam, then it might. But even the later 360HO police motors had the lower CR, too, and still made power.
CBODY67
Maybe but 8.5 to 9.2 is a bit more than half a point. I think the 69 318 was rated at around 200HP and everything after 72 was around 150. I think you would notice that. I'm just looking at factory ratings on the 318. The only experience I have as a comparison is a 68 satellite we had with a 318 2 brl, and a 76 Dart Sport with a 318 2 brl. The Satellite was much quicker even thou it was heavier than the Dart. I know making this change on big blocks makes a difference. I have build many RB engines from the smog era and just swapping in pre 70 pistons gave them a very noticeable increase in seat feel. Now some of those engine's had pistons that were .090 to .100 in the hole and after the swap were .025 to .040 in the hole, but just that change did make a difference.
You have to remember that in 1972, they started rating horsepower differently. Gross HP became Net HP. It wasn't unusual to have drops of 50HP when they changed how it was rated.
"To understand the dynamics at play, let’s first start with what many concern themselves with: horsepower. That number sells cars. That number gives the end-user perspective on what that vehicle can do for them, and we aren’t talking just speed, either. Horsepower sells trucks, sold station wagons, you name it. Prior to 1972, manufacturers rated their engines using a gross horsepower figure, which measures the theoretical capability of the engine. To determine gross horsepower, a basic engine was bolted to a dynamometer, tested at the crankshaft, and that number was the end result.
In 1972, SAE ratings (also known as SAE net horsepower ratings) were introduced. Unlike the gross horsepower ratings, which was the engine in it’s purest form with no accessories whatsoever, SAE ratings added production belt-driven items like the alternator, water pump, exhaust, air cleaner, and emissions controls. This provided horsepower and torque figures that were more in-line with what the consumer was actually getting. The measurement was taken at the crankshaft and like the gross horsepower ratings, did not take into account parasitic driveline losses. The result was a variance of figures that could be as little as 40 horsepower or as much as 150 horsepower. A Chevelle with the 454 might have claimed a horsepower rating near 450 under the gross rating system but in reality was only pushing out 288 horsepower. Chrysler’s 425-horsepower (gross) Hemi was rated for 350 (SAE) horsepower."
Taken from:
https://www.hemmings.com/stories/what-killed-horsepower-in-the-1970s-and-1980s/
230 horse
Last edited:
Seems like the normal 318 2bbl was ("Gross") rated at 230 horsepower for ever. With the stated 9.2CR Good, reliably and economical power for many drivers.
When the CR dropped, the cam and head/valve size specs did not change. Just the pistons and emissions-related tweaks to the fuel curve and ign timing. Aas always, deactivating the EGR and upping the base initial timing amount could increase drivability such that the minor difference in power at the rear wheels was not worried about.
AND, the later "Net" power ratings also included the full exh system, too?
End result? What actually hit the pavement was not that much different than before, IF it had the 1968-era tuning. But the lower CR would have more of an affect on road fuel economy, I suspect.
CBODY67
duke7112001
New Member
Put it in might not be as strong but it will work. paint it the right color and let her rip.
jim almond
New Member
what did it come out of? If it was in a van or pickup accessories, mounts, oil pan, exh manifolds etc are different, but yours will fit
Just Carbs
Senior Member
What I don't remember for sure about my 75 318 Dart to 85 four-barrel carb 360 Volare motor swap into the Dart.
The 360 heads have bigger valves and flow better but have bigger chambers that would reduce compression if used on the 75 318 motor. Don't know about the 69 318 motor.
I changed the 360 cam to increase the compression before installing the 360 motor into the Dart. The cam used is a hydraulic roller tappet that allows a very long duration with a very short overlap that increased the compression (according to the cam supplier) to 9.8.
Other notable changes to the 360 were Edelbrock PERFOMER (not Torquer) intake, Edelbrock/Carter 4-barrel carb, and Chrysler Imperial single exhaust muffler. That's it, no other changes.
The 75 Dart very much resembled my 69 Dart GTS (3.15 rear gear) in overall performance. Big improvement over the 75 318 Dart motor. A little more bottom end torque with 360 Dart swap than the GTS had and a little less top end rpm than the 69 340 GTS had.
If I needed a motor for a C body 318 car, I would put that 360 in it before I would do a big block conversion. And I would not put a 318 back in a C body.
The 360 heads have bigger valves and flow better but have bigger chambers that would reduce compression if used on the 75 318 motor. Don't know about the 69 318 motor.
I changed the 360 cam to increase the compression before installing the 360 motor into the Dart. The cam used is a hydraulic roller tappet that allows a very long duration with a very short overlap that increased the compression (according to the cam supplier) to 9.8.
Other notable changes to the 360 were Edelbrock PERFOMER (not Torquer) intake, Edelbrock/Carter 4-barrel carb, and Chrysler Imperial single exhaust muffler. That's it, no other changes.
The 75 Dart very much resembled my 69 Dart GTS (3.15 rear gear) in overall performance. Big improvement over the 75 318 Dart motor. A little more bottom end torque with 360 Dart swap than the GTS had and a little less top end rpm than the 69 340 GTS had.
If I needed a motor for a C body 318 car, I would put that 360 in it before I would do a big block conversion. And I would not put a 318 back in a C body.
A camshaft change cannot change "mechanical compression" BUT it can increase "cylinder filling" to increase "dynamic compression" to a higher number than it would normally be. Past a certain rpm level. BUT with longer duration, more lift, and minimum overlap, it might also result in poorer higher-rpm breathing capabilities? The lift curve of a roller-lifter cam would be needed to maximize these things (morfe area under the curve), too.
Just my suspicions,
CBODY67
Just my suspicions,
CBODY67
Just Carbs
Senior Member
Correct.
Similar threads
