cruising rpm

[dumbucket1]

is 1375 rpm's at 65 mph too low for a stock 350 in a 84 gmc? In other words is that lugging the engine too much? thanks

[Lt.Del]

I don't know what too much is, but, that is really low rpms.  You must have a 2.50 rear with overdrive or oversized tires.  I guess if it starts to jump abruptly, it may be too low, sort of like when on a standard tranny, you throw her in high gear too quickly. 

[eventhorizon66]

My 3.08s had my engine at 1650 at 65.  I considered that too low.  The engine would do it no sweat, but I would have to drop it down into third to pass or make it up steep grades.  It now gets slightly better fuel economy with 2000 rpms at 65 (3.73s) and highway passing is much easier now.  In fact, I never have to leave OD gear once I'm above 60 to pass just about anyone; the only thing my trans has to do is unlock the TC from time to time.  I almost feel like I'm abusing it now when I force it to downshift into third at highway speeds...almost.

[chrpmaster]

Do any of you have over sized tires?  I am wondering because I am looking at the same issue on my c10.  I have the stock tires on mine with a th350 tranny. 

Andy

[chrpmaster]

bump

[Stewart G Griffin]

There's a good possibility that 1375rpm is too low at 65mph.  Especially with big truck aerodynamics.

But it's easy to get confused because it happened to me-----are you sure you are really going 65mph?  It sounds like you've got larger than stock tires and that plays havoc with the speedo readings.  What are your rear tire sizes?

There was an article on the then new corvette ( i think zr-1?) where the engineer---Zora Duntov did not want them to drive it in 6th gear on the test track because he felt it would lug the engine.  i don't remember the exact rpm but it was below 1500 at a high speed--over 100.  i will try to find the article.

But let's verify that you are indeed going 65 first.