shifting with no tach:(

[95dx]

i have a 95 protege dx(z5) i hate not having a tach. besides the fast that my car is as slow as all get out, not knowing when to shift doesnt help. i've been shifting from 1st to 2nd at 30mph and 3rd at 55mph. am i close? it feels like the engine is working pretty hard(aka about to blow up haha) before i shift. i'm mostly worried about 1st to 2nd, the car seems to fall on its ass.

Anyone with a tach wanna help me out?

[Pox]

Sounds like your revin the **** out of the motor. Stop being in such a rush and slow down lol.

[95dx]

i have a z5 motor, if i go any slower i'll be going backwards.

[1Mazda323Fan]

Here's a tip: if your engine sounds like it's about to explode right before you shift, you should consider shifting sooner. Seriously, you shouldn't need a tach to know when to shift. Hell, I taught myself to double clutch without one, so they're not really a necessity. Handy, but not vital. As to when to shift, I'm guessing you're looking to maximise your acceleration, not fuel economy (which you can find shift points for in your owner's manual, helpfully listed in mph/kph instead of revs). You should probably be shifting out of 1st at around 25 mph, as you're losing power at the very top of the rev range. Also, it's less bad for your engine.

[KAinjection]

Here's a tip: if your engine sounds like it's about to explode right before you shift, you should consider shifting sooner. Seriously, you shouldn't need a tach to know when to shift. Hell, I taught myself to double clutch without one, so they're not really a necessity. Handy, but not vital. As to when to shift, I'm guessing you're looking to maximise your acceleration, not fuel economy (which you can find shift points for in your owner's manual, helpfully listed in mph/kph instead of revs). You should probably be shifting out of 1st at around 25 mph, as you're losing power at the very top of the rev range. Also, it's less bad for your engine.

So....does your transmission not have synchros or what?

[tehstocker99]

z5 ftmfl!

that's my contribution lol

i shift at 3k-4k rpm range...never brought the motor past that, so not sure what you're comfortable, but those speeds are a bit high for me

[goldstar]

How Calculating Can You Be?

Here's a tip: if your engine sounds like it's about to explode right before you shift, you should consider shifting sooner. Seriously, you shouldn't need a tach to know when to shift. Hell, I taught myself to double clutch without one, so they're not really a necessity. Handy, but not vital. As to when to shift, I'm guessing you're looking to maximise your acceleration, not fuel economy (which you can find shift points for in your owner's manual, helpfully listed in mph/kph instead of revs). You should probably be shifting out of 1st at around 25 mph, as you're losing power at the very top of the rev range. Also, it's less bad for your engine.

Exactly as 1Mazda323Fan states.

However, just as a technical exercise, it's easy to calculate mph as a function of rpm, or the reverse, if you know a few of the variables involved. The formulas are:

rpm = mph(overall gear ratio x 336.31)/tire diameter, inches

The terms in the formula can be easily transposed to solve for mph:

mph = rpm x tire diameter, inches/(overall gear ratio x 336.31)

336.31 is a constant whose derivation I will not go into, unless forced.
Reference:
The Design and Tuning of Competition Engines, Fifth edition, by Philip H. Smith; Chapter 27: Definitions, Constants and Formulae, page 459

I used these formulas myself before I installed my digital tach.

The other required variables are easily obtained. Thanks to TheMAN's excellent FAQ, a listing can be found of the final drive and intermediate gear ratios of every Protege transmission ever built.

I don't know much about your model vehicle but according to the FAQ you should have the F25M-R transmission. This has a 1st gear ratio of 3.416:1 (2nd gear ratio of 1.842:1) and a final drive ratio of 4.105:1, yielding an overall gear ratio in 1st gear of 14.02268. The only other datum you need is your tire diameter which you can obtain from a tire calc or a manufacturers tire chart. Since I don't know your wheel/tire size, you have to provide the appropriate value.

So, you want to know your rpm at 30 mph?

rpm = 30(14.02268 x 336.31)/tire diameter, inches

You can now calculate the rpm for any combination of road speed and intermediate gear by plugging in the appropriate values.

In like manner, you can calculate the mph associated with any given rpm by utilizing the second formula. For example, what would be the mph in 1st gear at the engine's power peak of 6,000 rpm?

mph = 6,000 x tire diameter, inches/(14.02268 x 336.31)

Plug in 6,500 rpm in the above formula and you'll find the mph in 1st gear at redline, or calculate the mph associated with any other combination of rpm and intermediate gear ratios. As has already been pointed out, shifting above the power peak reduces performance as the HP starts to fall off above that value, as well as unnecessarily stressing your engine.

There are probably online calculators for these functions but I haven't specifically looked for any because it's so much fun using my calculator to do the simple arithmetic involved.

Happy Calculating!

[95dx]

Thank you Goldstar! this helped a lot. after calculating, i'm defininetly gonna shift sooner haha. you guys are right though, i should stop being such a ricer and slow down before it explodes lol. but hey, what are beaters for?

[goldstar]

You're welcome. I'm glad you found it useful.

Happy Motoring!

[1Mazda323Fan]

but hey, what are beaters for?

They're for beating on, of course. But they're less fun after the bearings have spun, or you punch a rod or two out. Trust me, you'll still have just as much fun if you back it off a hair. Beat it within two or three inches of it's life, and it should be fine.

So....does your transmission not have synchros or what?

No, it had synchros. Somebody showed me how to do it, and I was young and a nerd (now I'm just a nerd), and wanted to be like the cool guys, so I taught myself how to do it. Then I realised that rev matching was easier, and started doing that instead. Now it's just a habit. Like I said, nerd.