Help! 4000 RPM's at 65mph . NORMAL?

[Vettehead Mikey]

I have changed the rear end gears and have had 4:11, 4:56 and 4:88. I think the car may have 4:88. A good all around final ratio is a good topic for discussion. I would say he should change it to something in the 3s, like 3:36. Another factor is the type of manual transmission in the car - close ratio or normal ( don't know what they call that). The normal transmission has a much lower first gear so that cars with 3:36 have an easier start.

Both the close ratio (M21) and wide ratio (M20) have the same 1:1 ratio in top gear, so the transmission type makes no difference in highway RPM.

 

[Crimson Thunder]

First thing I would do is make sure your speedometer is correct using a GPS or a smartphone.

 

[njlouc]

Welcome!!!
I agree with the comments. As you can see you cant have it all. IF you want to spend some quality highway time you must get a reasonable ratio.
Even a 6 speed will have drawbacks. The engine revs will be lowered but that poor rear axle will still be screaming. changing tire sizes is also limited and expensive.
Take your pick.