Hi,

my car is mostly used for a 30 mile commute on the 210 freeway at

5-45 am . hence , no traffic .


what is the ideal rpm range i should try to keep the engine at .

I'm referring to 5th gear when I say that the engine seems most smooth anywhere from

3100 rpm and up .

from an fuel efficiency and or efficiency stand point what rpm do these flat fours like to be at for extended periods of time ?

please consider ,

73- 1-7 / stock w/ d-jet , it is in proper tune ,, points plugs , filter , etc done recently

modern tires , fuchs wheels

super unleaded gas for the most

and pretty cool air at the morning hour ?


Tell me what rpm your teener likes ? too

I have the same car, same spec and it sits at 3800 all day

"the engine seems most smooth"

-you answered correctly .. that is it, good job, nothing else to be added.. also your probably right that under 3100 seems to dog it a little.. and probably somewhere over 4100 seems to hound it a bit..

they have made cars with shift dummy lights before..

on another note per manual says not to exceed 5,000 rpm for extended periods except for passing and as temporaryneed exsists ect..

3,800 with stockish tires is about 80mph ... You can cruise at that for a 1,000 miles no problem ...

3500 is the maximum full advance on the distributor, therefore I would argue that the true Volumetric Efficiency is designed right at 3500 for a stock motor.

Rich

I rarely use 5th, even on the freeway. Unless I am over 70mph, the engine is turning too slow for 5th gear.

Zach

Not here in SoCal, Zack. My 3rd week here, I had a middle aged women flip me off for going 70 in the #2 lane on I 15. Now I'm just as bad.
Your car will tell you what speed it likes to run. Just listen to it.

that is the zone 3500 rpm sweet spot.. I use rpm above that for accelartaion and jumping up a gear or holding high in a gear because I can't slow down or speed up out of the way ect.. ect though sure you can cruise 1,000 miles at 3800rpm, I have driven it at least that hard and long in above 100 deg. temps for part of it and hills for another and coastal sea level for the rest.. but the reality is your rpm is going to vary road depending, flow of traffic depending.. hills, curves ect.. acceleration/deceleration needs.. engine temps. .. ect.. so rule of day, you answered already.. "when the engine seems most smooth"

70? so. cal. O.C. you do that when ever you can or get out the way! Welcome to the suburban rush to nowhere!

when the engine is the smoothest "

and my new rpm sweetspot is

anywhere between the signal indicators on the tach . like[ 3100 to 4600 ] revs

it runs super smooth there , for like you said 1k miles plus

I'm sure it go smooth for 3 k miles if you keep gas in it .

At 70mph, my engine is turning 3050. my tires are 2%under driven which will make the rpms a little higher.

If I'm not mistaken, with stock tire dia., at 60mph you should be around 2700rpm.

For MPG sake this would be better. My 73 1.7 seems to like the 2700 to 2900 rpm range for cruising.

when I do my 5 lug conversion, I'm going with a taller rear tire to overdrive it a bit to get a little more MPG by bringing the RPM's down. then I can tune the cruise area of the fuel map with MS.

I believe you'll get the best fuel economy at 3000-3100 RPM. That's just about the limit the CHP will give you, maybe a little more than the limit. You should probably switch to mid- or even low-grade fuel. Premium is only lightening your wallet unless you have crazy compression.

The Cap'n

Will mid or low grade give better MPG?

No difference. Just less money. Go to 89 first, see if it pings. Mine runs fine on 89, but doesn't like 87 during warm weather.

I set my Cruse Control at 3,100 ( yes my 914 has Cruse ) and just let it go.

It is about 70 ish , 1 size tire size up from stock. Dave

Yea, that was not a middle aged woman that was me.




I want Cruise Control...

hey cap ,n

The reason I'm filling with super or 91 octane is that when i use 87 I notice a slight and infrequent back fire , when down shifting 5 to 4th .

after I switch'd to 91 . it never back fire's ever ! Also warm up time seems to be quicker .

I think i'll try mid grade -89- next time with a splash of marvel mystery oil and see what happens ?


and where you refering to the cal highway patrol when you said that 3100 is the limit of speed allowed ????

?????????


because I don't want to attract any chp attention

87 octane should be fine. If it pings under load, move up to 89. The backfiring is an exhaust system related issue. 91 octane burns slower and actually could affect your mileage. The chippies look for cute little sports cars going as fast as- or faster than- traffic. Generally speaking, 5 over the posted limited is "relatively" safe, unless the nice officer is having a bad day or he otherwise has issues with you, your car, or the general class of car you're in. With stock tires and gearing on a 914, 3000-3100 RPM is 5-7 MPH over.

The Cap'n

Dude I love Monrovia I lived there tell I got my house in Pomona, Still go by my son in law mom is on canyon north of foothill....we should hang out..

For best fuel economy, you want the slowest speed you can stand in the highest gear you have. You have less resistance from the tires, less air resistance, less internal losses, yadda yadda yadda.

The problem is that the engine usually won't be happy at 2000 RPM in 5th gear; head temps will likely be higher than are good for it after a while.

If the engine is happy at 3500, then run it there.

--DD

I run my 71' 1.7 at about 3200 all day long on the highway (about 30 mile commute each way), with one eye scanning the overpasses and pullouts for the CHP! My car is a little, uh, how do we say....paint challenged so I have gotten a little extra attention late at night...a deputy sheriff actually told me that when he gave me a warning about my license plate lights being burnt out

It just seems to want to run there so I let it

Jim