Octane for a "standard"(?) 1776

[KatzeBus Driver]

Recently got my first bus, a '71 with a 1776 duel carb engine. One of the things I'm still not certain about is the octane for the engine. I've been using 93 (with choices locally of 87, 89, or 93), but what with prices for 93 about to head over $2/gal here, I'm wanting to make sure I really shouldn't run on anything lower. The peril of not being a gearhead. Advice?

(Oh, and if you want a bit more info about my bus (mainly pics) I found it has a webpage from the guy who restored it at http://www.revolks.com/dink.html)

Thanks.

[bmx2c4me]

That link won't work for me ^
The bus looks awesome, you're lucky to have bought a 'complete' bus as your first. Unless you have some kinda hopped up motor with higher compression, which it doesn't look like if you have a single carb, you should be able to use 87-89 octane without problem. I use 89 because it does have better detergents etc. but VW street motors are NOT high compression motors and usually run ok with lower octane gas.

[KatzeBus Driver]

Oops, sorry about the link. Silly of me to put the ")" right at the end of it. This one will work better, I think:

http://www.revolks.com/dink.html

Actually, it's a dual carb engine. How much does that change things?

[KatzeBus Driver]

And, yeah, the bus does look cool, is a sweet ride, and I do realise how lucky I am to get a complete one for my first bus. Was extremely fortunate to find one in the Classifieds here within my budget and fairly nearby (3 hours away or so).

And, if anyone could point me in the direction of a good source (web site/page, book, whatever) on the 1776, I'd appreciate it. Or, failing that, giving me an idea of how the engine differs from the stock 1600. Whenever the Owner's Manual or Muir (14th Ed, though I'm getting the 19th Ed mail order at the end of the month) talks about the engine I'm never sure what does and doesn't apply.

[gbsmallie]

Actually, "cool"s got it wrong. A 1776 uses 90.5mm pistons as opposed to the 85.5mm ones used in a 1600. Thats the only difference. You very well may need to use 93 octane in your bus to avoid detonation which you may or may not here. A larger piston compresses more air, raising compression ratio. If your engines compression ratio was not set below about 7.5 to 1 when built, you risk detonation, which will be worse with lower octane fuel and a stock carb. Larger carbs allow you to get away with somewhat higher compression. Basically, if you dont know the compression ratio of your engine, Id stick to the 93 octane for longest engine life.

[KatzeBus Driver]

Thank you. I'll do that.

However, now I'm curious as to how/if I can go about finding my engine's compression ratio. Unfortunately, while I emailed the person who restored the bus and installed the 1776, he has never replied. And me with so many questions, as I do want to take good care of the engine.

[gbsmallie]

Theres really know way to tell without taking apart your engine and ccing the heads, checking deck height, yadayadayada. If it runs cool on 93, your always safe. If your engine is suffering from too high compression and detonation, it will run hot. Dont listen to people that tell you "you can here it pinging if its detonating". Thats BS. Most detonation you will never here. Good Luck with your bus

[KatzeBus Driver]

Danke. I'm not about to pull apart the engine since that would be like having a chimp work on my computer. OK, sounds like I'll just stick with 93 as it is running tops at about 140F driving around town in 40 to 50-something F weather.

[Aussiebug]

To test for detonation, run the tank almost dry and put a couple of gallons of low octane fuel in it.

Then get the engine warmed up and drive it, flooring the throttle at the lowest rpm in 4th gear you can without the engine shuddering (about 30mph or so).

If you hear a harsh uneven clicking sound from the engine - that's detonation. Add some higher octane fuel and it should stop.

You CAN drive safely on lower octane fuel (which would normally detonate) if you keep the revs up - don't load the engine at lower rpm.

For more info on the topic
http://www.geocities.com/aussiebug1970/octane1.html

Rob
Rob and Dave's aircooled VW pages
Repairs and maintenance for the home mechanic
http://www.geocities.com/aussiebug1970/

[gbsmallie]

For the compression ratio bible, check out the info available from Gene Berg. Not everyone agrees, but the fact is, most people dont get 200,000 miles out of there 2006cc motors either. The above mentioned test is dangerous at best, you CANNOT here all detonation in 4th gear at low rpm, or any gear at any rpm for that matter. Better yet, just be safe and run the 93.

[chabanais]

I have a 1776 Type 1 engine and have used 87 octane on it for over 4 years and never had a problem. It is stock in every way, except for the displacement of course.

[NeverHadaBeetle]

A simple compression test will tell you if you have a high compression engine or a low compression engine. I have had a type IV engine a couple of years ago that tested at more than 150 PSI on all 4 cylinders and I suggested to the buyer that he should run higher octane gasoline for that bus, but that was a first. Premium fuel may have not even been necessary in that bus. Any engine that tests at 130 or lower is close to stock and you're simply wasting money with premium gasoline. As an engine wears and the compression naturally decreases you receive no benefit from premium fuel. I'm not advocating which compression necessitates which octane rating, but I'm certain somebody out there will have that information or at least an educated opinion. I usually stay stock and a stock VW engine or any engine with nearly stock compression simply does not need or benefit from high octane fuel. Bigger displacement (1776, 1835, or whatever) does not mean you have higher compression.

[NeverHadaBeetle]

"Actually, you should stick to kayaking, and not talk about things you know nothing about." GBSMALLIE circa 2/18/03. I just want to remind you GBSMALLIE why I'm back again and why I'm still perplexed about the contents of my original post that upset you so much. It's certainly noble of you to be concerned about KATZEBUS's engine, but your posts seem to have taken on a defensive nuance. I was born at night, but it wasn't last night so I'm beginning to have suspicions that you simply refuse to answer the question I have posed. However, rather than allow my suspicions to grow into full blown accusations I will give you the benefit of the doubt and ask you to please clarify your thoughts again. Please forgive me for being such a doubter, but your previous posts just haven't quite convinced me that KATZEBUS should be splurging an extra $0.35 per gallon for premium octane fuel. So.....you stated above, "However, I do know that elevation allows you to run higher compression, and/or get away with using lower octane." Why do you feel this way? Does your compression ratio change at higher elevations or could it possibly be something else? If you choose to answer this you are certainly welcome to take a few more playful jabs at kayakers, Phish fans, Grateful Dead fans, my "Sweet Pickles" bus, or me personally if you like, but what I would really prefer to read is an actual answer to my question. Thank you in advance GBSMALLIE.

[gbsmallie]

No, your compression ratio does not change at higher elevations, but wait, you already knew that didnt you. How bout this. How bout you buck up and purchase technical article GB 801-CR from Gene Berg Enterprises and get that answer for yourself. The number is (714) 998-7500. Then you can go ahead and disagree with someone that I assume you can believe. Go ahead yaker, its all right there. I could read it for you word for word, but Id rather you support the industry and buy a copy for yourself. Thank you in advance gokayaking.

[Aussiebug]

gbsmallie said... (2/17/2003 at 9:24AM PST)

>The above mentioned test (in my post - Aussiebug) is dangerous at best, you CANNOT here all detonation in 4th gear at low rpm, or any gear at any rpm for that matter. Better yet, just be safe and run the 93.

Dangerous huh - I've had the SAME VW since brand new in 1970 - 248,000 miles on it's original engine, which was changed from 1500 to 1600sp with it's one and only rebuild rebuild, and fuels are a specialist topic of mine.

So OK - you think it's dangerous to test for detonation - I don't. Sure you may not pick up incipient detonation, but if you hear ANY from the engine, then as I said - change to a higher octane - what's dangerous about that.

gbsmallie said... (2/18/2003 at 7:35PM PST)

>Actually, you should stick to kayaking... I speak from experience and have built several engines. The most recent was a 1776 ...compression ratio came out to 8:1. The engine ran super hot, and suffered from detonation like you wouldnt believe. I added barrel spacers to set the compression at 7.46:1, and the motor ran cool, had more power, and absolutely no detonation.

Maybe YOU should go kayaking mate - I went the other route with my engine rebuild - added 1600P&Cs to the stock 1500 heads and got 8:1 compression (up from the stock 7.5)

It was quite happy on 91RON (87AKI in the USA) with 7.5:1, but now runs just as happily on 93RON (89AKI) at 8:1 compression. That was about 100,000 miles ago, so that solution obviously worked too.

So it is quite possible to run higher compression ratios if you know what you are doing.


gbsmallie said... (2/19/2003 at 5:28PM PST)

>Theres some misleading info on this post that I thought I could shed some light on. Like I said, Im no expert,

I agree.

>but I can tell you that I nearly fried my own 1776 by running too high a compression ratio, even with 92 octane fuel

Then something else was wrong wasn't it! 8:1 is no problem at all if you burn the right fuel.

And if I was running this engine on LPGas like my Ford (gasp!) uses - 104 RON octane - I could safely run at 9:1 compression ratio in the bug.

Read this for more info
http://www.geocities.com/aussiebug1970/octane1.html

Rob
Rob and Dave's aircooled VW pages
Repairs and maintenance for the home mechanic
http://www.geocities.com/aussiebug1970/

[gbsmallie]

By "dangerous", I meant there is danger in that you may not hear detonation occuring, but that doesnt mean it isnt taking place. Not dangerous as in, you might die if you perform this test. And I guess I shouldnt have assumed that pretty much all parties involved knew that higher octane fuel allows you to run higher compression. How else would drag bugs run 13:1? Since I shouldnt assume, they run 13:1 by using high octane race fuel. No brainer. Of course you can run higher compression if you know what you are doing, many have, obviously your one of them. Theres too many variables to argue your specific examples, elevation, hemi-cut heads, carburation, blahblahblah. I wasnt tryin to offend you. Smart ass jabs are fun sometimes, look how it gets people talking, throwin jabs of there own, "mate". And no, nothing at all else was wrong with that 1776, its still going strong today, but it wouldnt have been if Id left it at 8:1. If youd have read closer, youd have seen I was running the highest octane available in my area, 92, still detonating. I guess were both just "home mechanics" mate!

[KatzeBus Driver]

I'm back after not reading this thread I started for a few days. First, let me say, I'm dismayed to see that the level of discussion on my question and the related issues has deteriorated so much. Not actually very helpful to me. I certainly can understand some people being right, wrong, or just having a difference of opinion but it seems to have gotten a bit too personal. And, while I'm certainly not a moderator, but as the thread originator I would like to ask if people could try to restrain the personal comments about each other and just keep to opinions/facts/guesses/whatever. It'd help me understand much better. Thanks!

As to my original question, I was finally able to get in contact with the father of the man who restored my bus and put in the 1776 by phone. Since this was his son's first project he helped him quite a bit on it. Thus, I now know that I can run on any of the octane levels availble to me here in the US.

Now, in his opinion, a higher octane would give me more mileage, but otherwise the bus should have no problems. I'm curious as to the milage/octane relationship such as whether it exists and so on. I've seen nothing about it in the (admittedly few) places I've looked so far. So, what do people here think/know/etc?

And, BTW, thanks to everyone for, if nothing else, furthering my knowledge of engines as well as letting me see that I can't take everything I hear as true (which I admit to already knowing from other things in life).

[NeverHadaBeetle]

"Actually, you should stick to kayaking, and not talk about things you know nothing about." GBSMALLIE circa 2/18/03. Just in case you forgot who I am and why IÆm back again. There's an old saying that the first thing you should do when your find yourself in a hole is not to start climbing, but to first stop digging. Although GBSMALLIE appeared to almost stop digging in that last post I don't seen any signs of climbing. As a matter of fact my previous suspicions have now grown into a full-blown accusation that you are refusing to answer my clear, concise, and properly worded questions. Actually, I am going to risk scorn and contempt by making an additional accusation that you simply don't know the answers to my questions and now you have resorted to selling Gene Berg manuals. Oh sure you got that question correct about whether or not high altitude changes your compression ratio, but I was just throwing you a bone. Apparently that bone didn't have enough meat on it for you because you just chewed on it a little bit and spit it right back out. Well I'm not going to waste any more femurs, tibias, or clavicles since you obviously don't have an appetite for them. Instead I'm going to digress back to the most important thing in this thread, which is providing KATZEBUS with the best answer I can for an honest, genuine, and sincere question. In KATZEBUSÆs last post a question was asked about running higher octane to get better mileage. I donÆt even know were to begin with that question and I canÆt imagine what the guy is thinking. I would certainly like to hear his explanation or see his test results, but frankly I would be suspect of anything advice he gave me after hearing that statement. But, since heÆs not here to explain his reasoning you could just run a few tanks of premium octane and then run a few tanks of regular octane and decide for yourself. With hopefully my final regards and posts concerning GBSMALLIE I'll start first with statements and ideas that are fairly mainstream in the VW world. VW engines were not designed to be high compression high performance engines. They were designed to be simple, low maintenance, economical, and reliable engines. To my knowledge the highest compression type I production engine was the pre-1965 type 3 1500-S. The 1500-S had a high compression 1500 engine based on a 1200 engine with a total compression of 164 PSI. The vast majority of stock production VW engines had total compression between 114-142 PSI. Most VW repair manuals even distinguish between the 1500s as "high compression" models or "low compression" models. The 1500-S was notorious for running hot. Compression ratio (CR) and total compression are not the same thing, but they are directly and positively correlated. CR is simply the volume of the combustion chamber at bottom dead center (BDC) verses the volume of the chamber at top dead center (TDC). By mechanical manipulations that enlarge the volume at BDC or lower the volume at TDC you are able to change the mathematical relationship and compress the air/fuel mixture at a higher total pressure or lower total pressure at TDC. Higher pressure implies more air/oxygen and a larger ôexplosionö while lower pressure implies less air/oxygen and a smaller ôexplosion.ö The CR is established when the engine is assembled and for practical purposes it does not change throughout the life of the engine. Ceteris paribus, all other things equal, lower CR results in lower total compression and higher CR results in higher total compression. Unfortunately, ceteris paribus is a hard standard to keep and all other things rarely remain equal or constant. Ring wear causes blow-by, worn valve guides or valves cause poor sealing, and cylinder wall surface to head surface can be warped by incorrect torque or heat and also allow blow-by. All these things happen as an engine wears, but poor quality parts or workmanship can cause these problems even in a newly rebuilt engine. Knowing what your CR is will give you an idea of what your total compression is, but it is only one of the variables. Regardless of your CR, quality of parts, or condition of your engine a simple compression test will indicate your current total compression. If you have a stock type 1 engine with a CR of 7.5:1 and a hopped up drag racing engine with a 13:1 CR they could both test at 130 PSI total compression. This would be fine for the stock engine, but it obviously indicates excessive wear in the drag racing engine. However, at this point the drag engine certainly needs a rebuild, but premium fuel would not be necessary because there simply isnÆt enough compression in the engine to cause uncontrollable pre-detonation. With regards to the late Gene Berg he was obviously a VW legend, but like all of us Gene was not perfect. I have read articles from many very knowledgeable people that point out exactly what AUSSIEBUG pointed out in his last post: octane ratings in Europe and Australia are not the same as octane ratings in the USA. Different calculation method results in different numbers. The 91 (or whatever number) indicated in older VW ownerÆs manuals or written on your older vehicle simply doesnÆt correspond with what your see on the pump in the USA. Gene BergÆs advice sometimes referred to the VW ôfactoryö requirements, which implies the number indicated in the ownerÆs manual or vehicle labels. He actually referred to 91octane fuel by the USA method in his compression ratio manual so maybe he did know there was a difference. Since he acknowledged there was a different octane calculation for aviation fuel then it would figure that he would have acknowledged a different octane calculation for Europe and the USA if he was actually aware of it. Since he is deceased we may never know. If you have near stock compression of 114-142 and especially 135 or under then I still contend you do not need premium fuel. The factory didnÆt indicate a need for it and many people have driven stock engines or larger displacement engines with near stock compression for years on 87 octane. If you have overheating or symptoms of pre-detonation in a near stock compression engine then the problem is likely caused by improper timing, running too lean, or carbon buildup on the pistons. Not low octane fuel. Improper timing and running lean can easily be corrected, but to completely remove carbon would require engine disassembly. These problems should be corrected rather than using high octane fuel to just mask the problem. KATZEBUS can get a local shop to perform a compression test or purchase a pressure tester and check it at home. Either option shouldnÆt cost more than $25. I canÆt speak for or against AUSSIEBUGÆs method because IÆve never tried it, but at least he seems to have a clue and he isnÆt taking jabs at everybody. You GBSMALLIE, on the other hand, seem to be taking jabs at everybody else and then trying to sell us some of Gene BergÆs opinions that you donÆt even understand. Your posts can be nice and polite and when youÆre wrong you have a little egg on your face or you can be a smart ass and when youÆre wrong you end up with the whole damn chicken on your face. Well GBSMALLIE you didnÆt like those bones I threw so how does that chicken taste?

[KatzeBus Driver]

Thanks, gokayaking. Since my bus is currently in the shop for the engine not turning over (and my use of John Muir's methods didn't find the problem), I'll ask the mechanic to do a compression test.

[gbsmallie]

I prefer fish, thank you. Looks like youve read up on your Berg manuals, good job! Wasnt that easy? It was all right there for you all along. I guess alls well that ends well. Good luck with your bus Katzebus!