I recently aquired a 55' CJ5(M38A1) w/ a 68' SBC 327 V8 w/ a 3 speed TH350 Auto Tranny... Motor runs strong but sometimes ticks(see other posts), but other than that I am having a blast cruising it around town...

Motor, while 37+ years old, has been rebuilt in 90's (still has fresh paint) and I don't see how anyone could of put more than 25,000 miles on it - so while not beat up, it certainly isn't fresh...

I like to cruise it on the country roads in my little farm town here, but havent had it over 3k RPM's in 3rd gear (about 45-55mph - I don't have a speedo)... wondering what a safe cruising RPM is? (and by safe I mean not going to blow up the engine) Can I cruise faster than 3k RPM or is that bad for the motor? At 3k RPM's I am getting about 35-40psi of steady oil pressure...

What about when I manually shift the auto tranny driving around town (I have one of those B&M mega/ratchet shifters)... I currently wind it out to NO MORE THAN 3k RPM's and then bang it into the next gear, is it okay to wind it up higher than 3k RPM's for a quick couple secs before shifting into a higher gear??? How high is too high???

Also - is it bad to manually shift an Auto Tranny? It is a FRESH TH350 (B&M Shift Kit) with a B&M mega shifter... The package on the mega shifter had directions for manually shifting the tranny, but is it hard on the tranny??? When I shift from 1st to 2nd, you can feel it - which I like - but I have a feeling it is probably hard on the tranny... Besides taking a little off the lifespan of the tranny, is it doing any damage???

I like to cruise it on the country roads in my little farm town here, but havent had it over 3k RPM's in 3rd gear (about 45-55mph - I don't have a speedo)... wondering what a safe cruising RPM is? (and by safe I mean not going to blow up the engine) Can I cruise faster than 3k RPM or is that bad for the motor? At 3k RPM's I am getting about 35-40psi of steady oil pressure...

for a v8, 3k is a little on the high side for me personally. anything over about 2500rpm just doesn't seem like cruising. however, i dont see you doing any damage at 3k.


What about when I manually shift the auto tranny driving around town (I have one of those B&M mega/ratchet shifters)... I currently wind it out to NO MORE THAN 3k RPM's and then bang it into the next gear, is it okay to wind it up higher than 3k RPM's for a quick couple secs before shifting into a higher gear??? How high is too high???

manually shifting is fine, although i'm not sure i understand the facination with manually shifting an automatic. i buy vehicles with manual transmissions because i enjoy them... however i don't manually shift the wifes vehicle when i drive it. :D

anywho... you can run it past 3k while accelerating. i'd say max rpm should be somewhere around 5000-5500rpm with that old ass valvetrain.


Also - is it bad to manually shift an Auto Tranny? It is a FRESH TH350 (B&M Shift Kit) with a B&M mega shifter... The package on the mega shifter had directions for manually shifting the tranny, but is it hard on the tranny??? When I shift from 1st to 2nd, you can feel it - which I like - but I have a feeling it is probably hard on the tranny... Besides taking a little off the lifespan of the tranny, is it doing any damage???

i read somewhere that a hard shifting automatic will supposedly last longer because the clutches aren't slippng, trying to give you a smooth shift that you can't feel.

"read somewhere that a hard shifting automatic will supposedly last longer because the clutches aren't slippng, trying to give you a smooth shift that you can't feel."


Wow, that is surprisingly interesting! (in a good way)

My fascination with manually shifting the automatic comes from only owning manual transmissions!!! I never really liked the automatic, although I must say that now that I have the automatic I could see myself getting another in the future...

Something about shifting gears just gives me a small but enjoyable adrenalin rush!!! (especially when my old ass M38A1 smokes rice rockets off the line!!! Greatest feeling in the world...)

So as a safe rule of thumb I shouldn't take it out much over 4500RPM because NO DOUBT my valvetrain is definitley "OLD ASS"... And I am not trying to snap a timing chain or anything like that...


So am I also to understand that 3k isn't really a great cruising RPM... When I am cruising at 3k the thing sounds like a NASCAR so I enjoy it - and I am probably more likely going about 55-65mph (can't really tell because the speedo is so old and just jumps anywhere from 45-70mph)...

I guess if I was worried about a really long drive I would drop them down to 2500rpm or so and just cruise at 50mph !!!

Shifting manually increases the line pressure and does less harm than letting it shift itself. Most transmissions won't downshift into first or even second if you're going too fast though...which isn't a bad thing. Cruising a 3k rpm is nothing, before the 80's when OD transmissions started to become standard equipment...all the cars had were 2 and 3 spd autos with 3 and 4 spd manuals. Cruise rpms were typically 3000 or more. Get used to it, you're just spoiled by OD. I would rather cruise at 2500 too but you'llget used to the sound. Cruising at superlow rpms is just as hard on your mill. I would set the rev limit on that 327 at 5600 just to be safe but it could surely go higher.

Ya, I am DEFINITLEY NOT COMPLAINING ABOUT THE NOISE AT 3000RPM's on the contrary I think it is VERY COOL! It seriously sounds like a nascar (Im running longtubes out straightpipe-glasspacks)...

I haven't tried to downshift my transmission yet, I thought that would be REALLY BAD!!! , because one time by accident at about 20mph I pulled it down to first from 2nd (I don't know what I was thinking) and it made the car jerk and I was thinking "OH $HIT - that just took 6mos off the life of the tranny!!! " but I guess that it was okay then??? The car didn't make any funny noises other than the tranny winding up and the shocks etc... jerking...


"Cruising at superlow rpms is just as hard on your mill"
What does that mean? Mill???

THANKS FOR THE HEADS UP ! Now I can cruise with confidence!!! (once I get a working tach! :p )

He is refering to the motor as the mill.

"Cruising at superlow rpms is just as hard on your mill"
What does that mean? Mill???



Reason: At a lower rpm it is forcing your motor to work harder to pull the weight of the vehicle...to a certian extent. The best place to drive your motor is where the peak torque and horspower is. But the only way to know this is to get it dynoed. Don't worry a sbc will last, if maintained.

u can run that 327 at 4000 all day and not hurt it, had one in a 55 chevy pick up hit 8000 rpms before the valves started to float. that ingine will last a long time if serviced

i read somewhere that a hard shifting automatic will supposedly last longer because the clutches aren't slippng, trying to give you a smooth shift that you can't feel.

I think that only applies if you've done some work to the vavlve body to increase the hydraulic pressure on the clutches.

wasn't the 327 built as a high revving engine?