High Octane?

[smooth_eddy]

I have a 74 914 with a 75 2.0 engine. What octane gas should I be buying?

[Jason Porter]

In an air-cooled car, you should only be running premium. 91. 92 93 whatever (depending on where you are)

These things aren't Chevys, and they run hot anyways compared to a water-cooled car. Then take into account the lack of a knock-sensor or variable timing system, and you have a possible grenade on your hands. Use all the cheap insurance you can get.

And yes, I said cheap. A full tank of premium is only about $3.00 more than the cheap *****, and octane is a good thang.

Run premium only, get rid of your 75 exhaust if your using it, switch to something less restrictive, pull off all that emissions crap, plug your EGR holes, and go!

[914helo]

My '73 2.0 has a factory sticker saying to get at least 91 octane fuel. Of course I don't speak German, so it could be saying rust will form in '91 or you will have at least 91 rust spots...
Kent

[Jason Porter]

They use a different rating system, which translates to around 87 octane

RON or something. Just run the premium.

[smooth_eddy]

The 75 exhaust is long gone. Must have rusted out. Gone also it all the emissions garb. In Wahington, we don't have to emission test a 30 yo car. lucky us! Eddy

[Dave at Pelican Parts]

The US-spec 1.8 and 2.0 motors are spec'ed to use 91 RON (Research Octane Number) fuel. This is equivalent to our 87 AKI (Anti-Knock Index) that US pumps are labeled in. I believe that putting anything of higher grade than that is a waste of money. But if it makes you feel good to put super in it, go ahead!!

I have gotten conflicting information about the 1.7s. The 1973 CA-spec 1.7 definitely used regular-grade fuel. The early 1.7s were definitely spec'ed for premium. But I'm not sure about the 72 cars (and non-California 73s). They still had the high compression of the 70-71 1.7, but a friend who owns a 72 says the octane sticker on her car says "91 RON"... Which is regular-grade fuel.

--DD

[Scooter311]

'Sup y'all
My 73 1.7 (stock rebuild, 60,000 miles) ran fantastic on 87, however my 2.0 (actually 2056, little higher CR and cam, 800 miles on it) only runs on 93. I tried $5 of 87 (I was in a pinch) and it ran like a bucket of crap. It was only a little over 2 gallons worth, but it scared me- pinging, rough idle, whoa I'll never do that again. It purrs on 93
I dont' know if that's because of my mods or what, but all motors are different - you may not need super like DD says, but maybe something in between?
Whatever you use, gas prices suck eggs anyway.
Ciao,
Jeff

[norustscott]

Listen to Dave... Know your CR....Don't waste money. I set my euro spec piston stock 73 2.0l to have 7.5:1 CR runs on 89 octane fine.

BTW, I have put 43K on my engine in two years...I can't seem to stop driving it!

[lawrencedesigns]

Hey guys! I am totally confused.
Dave's signature indicates he is Pelican Parts Tech Support
Jason's signature indicates he is Pelican Parts Custormer Svs.

And yet there is conflicting, totally opposite advise on the the octane issue.

Who represents company policy and advise?

[lapuwali]

Completely agree with Dave here. Only use the octane required, and no higher. Putting premium in a late, low-compression 914 is wasting 20-30 cents per gallon, or a good $5 a tank at today's prices. No reason to pay 15-25% more for gas if you're not gaining anything from it. SOME brands of gas have more detergents and other additives in premium that they don't put in regular, but many don't change their additive packages from grade to grade. These additive packages aren't universally good, either.

The only stock 914s that need premium are the early 1.7s, the switchover being sometime during the '72 model year.

[Jason Porter]

Originally posted by lawrencedesigns
Hey guys! I am totally confused.
Dave's signature indicates he is Pelican Parts Tech Support
Jason's signature indicates he is Pelican Parts Custormer Svs.

And yet there is conflicting, totally opposite advise on the the octane issue.

Who represents company policy and advise?

Nobody really represents company policy or advice. We just have our own opinions on the matter. I'm driving my roommate's '73 1.7 today, and it prefers premium. So did my '75 2.0

It's not that it's required, but it's inexpensive insurance against bad gas. Even if you get bad premium, it's still probably gonna be 90 octane at worst.

My feeling is that our engines, although very average in terms of performance, are in the middle-upper class in terms of cost to rebuild. Why not spend a couple of extra bucks to ensure yourself and your valvetrain a little extra support?

[norustscott]

Whoa, how does an octane rating support your valve train? If you have a stock type four motor and it requires high octane gas ( you hear pinging or detonation) then something is not right. Timing, Cooling, Air Fuel ratio (lean).

A

[Jason Porter]

Higher octane gas is designed to help an engine run cooler, which is why you run higher octane with higher CR's. To compensate for higher temperatures. Have you read GB 801, Gene Berg's Book of Tech Articles? While it's aimed at the type 1, most of the principles apply to any air-cooled VW engine.

And since the valvetrain/heads are the hottest part of the engine, besides the ehaust ports/manifolds, then heat prtection never hurts.

[norustscott]

I will read 801 agian...but I don't think higher octane gas will make an engine run cooler... Under Heads or Deck height?

[lapuwali]

Scott, the early 1.7s had high compression from the factory, and did require higher octane gas, even bone stock. Type IVs are not all the same.

Jason, I've never seen any credible evidence that's there's a direct correlation between octane and combustion temperature. There's also no direct link between octane and combustion speed, which has also been claimed (higher octane burns slower is the claim, which doesn't appear to be true).

Octane is a measure of knock resistance ONLY. Some higher octane fuels MAY burn at a lower temp than some lower octane fuels, but octane is not a measure of this, and there are some higher octane fuels that burn hotter. Knock raises CHT, which is why CHT will drop with higher octane UNTIL knock ceases. Beyond that point, higher octane will have no effect on CHT.

Higher CR is one of many factors to raise the propensity for knock, so higher octane is used to resist that knock. Higher CR means higher cylinder PRESSURES, not temperatures, although higher pressures will mean higher temperatures if other measures aren't taken to reduce the temp. Higher temp from other sources besides CR (like reduced cooling) will also increase knock sensitivity, along with a zillion other factors.

[Jason Porter]

Read the chapter on CR. It's been a long time since I read it, but Mr. Berg did significant testing in regards to temps vs. octane.

[AaronM]

Originally posted by lapuwali
Scott, the early 1.7s had high compression from the factory, and did require higher octane gas, even bone stock. Type IVs are not all the same.

Jason, I've never seen any credible evidence that's there's a direct correlation between octane and combustion temperature. There's also no direct link between octane and combustion speed, which has also been claimed (higher octane burns slower is the claim, which doesn't appear to be true).

Octane is a measure of knock resistance ONLY. Some higher octane fuels MAY burn at a lower temp than some lower octane fuels, but octane is not a measure of this, and there are some higher octane fuels that burn hotter. Knock raises CHT, which is why CHT will drop with higher octane UNTIL knock ceases. Beyond that point, higher octane will have no effect on CHT.

Higher CR is one of many factors to raise the propensity for knock, so higher octane is used to resist that knock. Higher CR means higher cylinder PRESSURES, not temperatures, although higher pressures will mean higher temperatures if other measures aren't taken to reduce the temp. Higher temp from other sources besides CR (like reduced cooling) will also increase knock sensitivity, along with a zillion other factors.

Higher cylinder head temperatures increase the liklihood of knock. If your engine is running a bit on the warm side and you're only running low octane, then the pinging will start and spike the temps even more.

My personal feeling is that since the engine in my car tends to run hotter, I would prefer to put 93 octane into the tank and have the insurance against knock on a 90 degree day.

Aaron

[lapuwali]

If the engine in your car is running hotter than normal, then there's some other problem you're just papering over with higher octane gas. If you can't drive around on a 90dF day w/o pinging, there's certainly something wrong. Assuming an otherwise stock engine, of course.

How are you measuring "hotter", btw? Hotter than what? Do you actually get ping on hot days with lower octane gas? I'm not trying to be a hardass here, but you're handwaving trying to justify doing something you want to do, not something that necessarily NEEDS to be done. If you feel you need the extra insurance of higher octane gas, fine.

Frankly, if CHT is so high that you need to run 93 octane in any stock Type IV other than a '70-'71 1.7, then you need to fix the underlying problem, as you're NOT lowering the already too high CHT by running higher octane gas, you're just preventing some of the aftereffects of the higher CHT (ping), and preventing the CHT from spiralling out of control. However, the high CHT is still cooking your heads, and shortening their lifespan.

[Joe Ricard]

Hmm, I have a 70 1.7L with no head gasket and no base cylinder shims. Never measured the deck hieght but. CR may be slightly higher. I run regular 87 and have never heard 1 single ping. Stock FI and timing adjusted to spec. Port matched intake and exhaust but that should make any difference.

[Joe Ricard]

I mean not make a difference with porting.