I have a 1993 del sol SI. What is the normal rpms in 5thngear at 80 mph

 

Need wheel and tire specs, but approximately 3700 rpm.

 

I have a 1993 Honda del sol SI. What should my rpms be at in fifth gear at 80 mph

 

Fronts are 195/50/15 backs are 205/50/15
​​​​​​​it is running between 4000 and 4300 in 5th gear at 70-80 mph

 

And depends on final gear ratio...

The way it works is you have engine RPM x 5th gear ratio x differential ratio x circumference of your drive tire, which is 2(Pi)r, so you need the radius of your wheel and tire. Ideally the true radius while the tire is at pressure and loaded with the vehicle weight.

And don't forget unit conversion; inches to miles, minutes to hours, etc.

 

it's bugging you so much, you had to make 2 separate threads.

 

What trans do u have. I have a 4.7 it and I'm at 4500 at 80mph

 

I hate math so I just went to zealautowerks.com/transcalc.php

It says that he should be around 3800 rpm at 80, but his speedometer could be off, his tach could be off, or someone might have swapped his engine/transmission...

OP, do you have the stock single cam engine or a dual cam swap?

 

If you are indeed running 15" wheels, it will be off because those wheels are a bit larger than what was on the car from factory; 14" You may not think it to be that much different, but yeah.

 

Outside diameter of the tire matter, not the rim size.

 

And the overall diameter will change as the rim size does. Math 101

 

That depends entirely on the tire size.

a 195/45/17 tire is smaller in diameter than a 195/74/14 tire.

 

And the overall diameter still changes just as drastically lol. Even though he's still same tire height and diameter; 50/15, there is actually still a difference in their overall revolutions.
The difference in stock rotation vs what he has equipped is pretty near a wash in terms of revolutions/mile. There's more math to go into figuring that part out and breaking down to where he should be on the tach, but my brain hurts today.

https://tiresize.com/calculator/

With about a 300-500 RPM difference where he is vs where he "should" be; 1- I wouldn't sweat that in the least as it is actually probably on the nose since i'm in a D15B7 with a stock trans, stock wheels/tires, and at 3300 RPM @ 80mph and he's got the shorter gears so it'll be higher.. 2- Si trans has a history of high rpm at freeway speeds anyways.

 

Overall diameter will not change as rim size does. Or more accurately, it does not HAVE to change. By getting different widths/sidewall heights, you can increase the overall diameter to offset changing to a smaller wheel, or decrease the overall diameter to offset a larger wheel. Overall diameter is the only thing that matters.