Rick B. and I were out driving our 2.0 914's today and comparing things. His is a '72, mine a '76.

I noticed at 2600 RPM I am indicating 52 mph, actual (GPS) of 51 mph.

Rick's 914 at 2600 RPM is indicating 60 mph......did not check actual with GPS yet.

Surprised at the difference.

I know the ratio between RPM and MPH will be wholly dependent on tire size.

His tires appear to be .6" less diameter (23.6" vs my 24.2") which would explain some but not all the difference. Yes - we need to check his speedo and see how accurate it is.

Someone have the actual gear ratios so I can calculate what actual RPM is for a rear tire that is 24.2" diameter/ 76" circumference? at 60mph?


TIA,

GN

You can try my gear chart app online although it uses tire width/section/diameter or revs/mile:

Gear Chart

If my calculation is correct, a 76" circumference is (5280*12)/76 = 834 revs/mile. While you are still required to enter the width/section/diameter, you can override the calculated revs/mile. The gear ratios can be pre-filled by selecting "1976 914-4 5-speed" from the dropdown.

run orig spec tyres. 165 15 michelin XAS.
in 5 (fairly sure i was in 5) at pretty much around 3000 rpm i am at 70mph.
gps check on phone said we were at 67/68 mph.
speedo was surprisingly accurate still after all these years with orig spec tyres.
(74 1.8 - think all 914s ran same ratio gear boxes, whether big or small engine but not sure?).




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There’s an excel file, where you can change the tire size and it will tell you the speed versus rpm for all the various gear sizes. There is also one for the 915 trans. I think I saw links to them on Pelican.

2600 RPM in 5th gear = down shift to 4th.

Yes yes yes yes

I HEAR YOU! And agree!

But I do shift to 5th if on level cruise on highway.......

GN

Steve -

Thanks - going to look for it.

GN

Steve -

Ok, got the spreadsheet.

https://www.pelicanparts.com/techarticles/m...anny_ratios.htm

Problem is I now need to know which GEAR I have in my 901 for 5th? Sheet lists many......

Which one was most common for 5th gear? Looks like it could be anywhere from R to ZD......

Next question is: anyone know of the tachometer being off?

TIA,

GN

According to the spreadsheet on Pelican, that means your 5th gear was a ZA.

So, I'm going to assume for now that the ZA was the common 5th gear.

GN

1st is A
2nd is F
3rd is N
4th is V
5th is ZD

You shouldn't, you need to run 3000rpm for proper cooling.
I'm fully gauged, you should see the head temps go up if you lug an aircooled engine.
Only time I'm under 3k is decelerating and going down a hill...while decelerating.

Steve -

All 914s have ZD for 5th?

It seems that either mine is a Z, or my tach is off.

At 3,000 RPM in 5th, I'm going 61 mph GPS/62 mph indicated on speedo.

Putting my new tire radius in the spreadsheet, 61mph at 3,000 RPM shows to be a Z gear.

Unless my tach is off.

If I have a ZD 5th gear, when my tach reads 3,000, I'm actually turning about 2,652 RPM.

GN

Mark -

New to me - as all things 914 were 4 years ago. No one has told me this before, and I will apply it to my driving immediately. I've been pleased with the torque I have from 2,600 up and have been shifting near the shift indicators on the tach for mild driving.

Thanks for the heads-up.

How would I know if cylinder head temps go up as thought my temp gauge was reading oil temperature? I know I do have a head temp sensor, going to white wire in bundle to the relay board. But I assumed it was only used by the D-Jet.

I will watch the oil temp gauge and see if I see a difference there.

GN

yep, never lug a vw, golden rule in aus back then when they were new.

interesting remark re 3000 rpm. i got my passenger to take this photo because that is what the car wanted to do. it could have sat there at 3K and 70mph all day. in 5 you really did not want to be under 70mph.

a couple of times i shifted down to 4 around cop radar/camera sites and when i spotted them come up in the mirrors. aus has strict 110 kmh/65mph speed limits with 0 tolerance in the interests of revenue collection. govt. orders are 1km tolerance. in practice cops are slightly more lenient. used to be 10k tolerance. nows its about 3k i hear. we were testing the accuracy of the speedo in the interests of wallet integrity.

The funny thing with head temp VS oil temps, if you lug an AC engine the head temps will soar, but the oil temp won't even move barely a tick.

We have long hills in my area, gearing down to keep the fan moving really makes a huge difference on head temps, you can see the needle swing. I'd rather be humming at 3600rpm than lugging at 2600rpm. Level ground is more insidious because the head temp creep up on you.

Moral to the story, keep that fan moving, / 4 or /6 you should do minimum 3K rpm as a rule.

Yep, unless it was changed…
http://www.914world.com/specs/regearing_901.php

Steve -

Ok, if I have a ZD for 5th, that means when my tach says 2,600, it's really doing 2,300.

I've been wrenching engines for over 50 years, and I have to say that when I'm seeing 3,000, it sounds like 3,000 to me. But how good is my ear tach? No idea. I know this - at 4,500 - 4,800 RPM my engine sounds like it's wound really tight and I don't want to push a 45 year old 65k mile engine any more than that.

My tach seems pretty accurate to me.

BUT - A top 914 wrench and VW expert drove my car, and told me my tach was reading way too HIGH. The owner of the Green Machine - the green 914 with the Chevy 350 that sold for $25k - a friend. So that concurs with what seems to be indicated here.

Sadly my bench tach is dead. Clearly I need to get my tach checked.

GN

914-6 had ZA for standard 5th gear.... That was to keep the air fan turning faster at normal freeway speeds for better cooling.

My bad. Tried to use your page/chart & things are not coming out correctly.

My tires are 859 revs/mile. Your chart shows 415.7 rpm (at rear wheels I assume) at 3000 rpm in 5th gear. 415.7 rpm x 60 = rphour = 24,942. 24,942 divided by 859 = 29.03 mph.

What am I missing?

Thanks for the help. Sometimes I'm dense. Please be patient with me. Oh - didn't see pulldown menu for 914/4 so I entered all the gear ratios.

GN

you are a font of information mate.
that makes complete sense.

it was always just a kind of unexplained rule in aus. don't lug a VW.
but now i really understand it properly.

Tire diameter: 24.5", rpm's:3,200, speed 70 per factory gauge

I am considering a 175/55-15 with a 22.5"

If I enter your 859 revs/mile in the chart, I show a calculated speed of 57.7 MPH at 2600 RPM.

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Here's me - running 195/55's (861 revs/mile) - I've had my speedo recalibrated by North Hollywood and it seems to jive with GPS. 2800=55mph



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