Safely cruising speed with a 318/727 combo

-
L

limelight72

Well-Known Member
Joined
Apr 16, 2014
Messages
50
Reaction score
4
Location
San Antonio
Recently bought a 72 duster with a 318/727 combo with 3.55 rear gears.

At 55-60 it hits about 27-2800 rpms.

It has an aluminum 4 core radiator/functioning scoops and never goes above 160 degrees. The engine and tranny seem to be in good shape. Could the 318 withstand 3-3200 rpm cruising speeds?

Have not dated the engine yet, but I'm sure it's from a late 70's car.

Tires are 26 in diameter.
 
Try going to a 28 inch tire bring rpms down a bit ... Im at about 2500 -2600 @65 or so I believe with a 275 60 15 and 3:23 SG I know guys running 4:10 even 4:30 gears but of course they're not on freeway that often but still keep the rpms in the high 3k to 4k range but my opinion 3200 is doable with out damage
 
Ya, I'm going to have to do my suspension first. The fender is already destroying my tires when I hit a bump. Thanks for info.
 
I try and keep my RPM's right at 3K when cruising on the hwy. Even though it seems to be way slower then traffic at 65 mph ! 340 / 4spd, 3.55 , 255/60r15 rear tires ... So far no issues, I've crusied at 4K for short periods, very loud !
 
Back in the day I used to drive 80-90mph all day long on the highway with my 72 Dart , 2700 - 2800 is not a problem , think we are just getting used to the new OD cars cruising at 2000 rpm , but 3000 rpm should not be a problem . Put over 400,000 miles on my old 72 Dart , lots of highway back then 3000 - 3500 was normal cruising rpm .
These days with my 340 highway with 3:55 i'm seeing 3400 at 70 mph without overdrive , with overdrive it's 2300 rpm @70mph . Again I'm used to the new OD cars so 3400 rpm "sounds" like a lot , but it's not , my new car when not in OD revs 3300 rpm @ 70 , so if the noise does not bother you it's not a problem .
 
Jeez, really? Of course! That's how it was back before overdrive spoiled us. Keep fresh oil in the engine and roll.
 
PoisonDart74 said:
Jeez, really? Of course! That's how it was back before overdrive spoiled us. Keep fresh oil in the engine and roll.
Click to expand...

whoa calm down :p
Just didn't want my engine exploding all over the road lol.

Just put fresh oil in it though. I'd rather ask then be sorry.
 
PoisonDart74 said:
Jeez, really? Of course! That's how it was back before overdrive spoiled us. Keep fresh oil in the engine and roll.
Click to expand...

Actually that would be incorrect. Most cars did not come with 3.55's, 2.76's would have been more common which would lend to lower RPM's at cruise.


To the OP.
I run 3.55's in my car and it cruises around 2800 at 60. No issues yet.
 
Bad Sport said:
Actually that would be incorrect. Most cars did not come with 3.55's, 2.76's would have been more common which would lend to lower RPM's at cruise.


To the OP.
I run 3.55's in my car and it cruises around 2800 at 60. No issues yet.
Click to expand...

Thanks, ya from the factory it was really low gears. Just have to get these leaks fixed.
 
318's are super tough engines that don't mind spinning RPM's. As long as it's in good condition I wouldn't worry a bit about spinning it 2800 down the hwy.
 
Bad Sport said:
Actually that would be incorrect. Most cars did not come with 3.55's, 2.76's would have been more common which would lend to lower RPM's at cruise.
Click to expand...

Of course, I was generalizing. Those that had performance gears dealt with it. Have fun with it! :D
 
You can add OD if you wanna, check into some threads, 200r4 or 42/46RH come to mind. Theres a MA5 thread going on right now.
 
short stroke engines don't mind rpm's. especially the 318 which had a 3.31 stroke and a 3.91 bore which makes moderate rpm easy on the bores because of the slower piston speeds and low thrust on the sidewalls. also remember the rod/stroke ratio of 1.84 (just unreal when compared to other smallblocks) this rod/stroke ratio contributes even further to the 318 reliability even with moderate rpms. 318's are really tough, especially the old ones. I still see old dodge farm trucks running down the road with well over a 10 ton gross weight and under the hood is a 318 and believe me, they are spinning some rpm's with 513 gears (even with the 9-20's, which are 40 inch diameter). I remember once I read that the old poly 318's had so little wear that Chrysler had to change their test for the development of the engine. they had to increase the interval just so they could get the engine to wear enough to measure it.
 
You must log in or register to reply here.
-

Back
Top