'38 Big eight - 91, 95, 98, E-10..what fuels are you running on?

[DBT]

Hi,

I have the 90L here in Singapore running on 98 octane fuel [unleaded] and all seems well but am faced with a fuel challenge on a big trip coming up.

I am taking the beastie up to Bangkok in a few weeks and Thailand has been pushing very strongly the use of Bio-fuels. This has meant that very few stations now stock high octane non-bio fuel. Thailand offers two octane levels 91 and 95. 95 would be fine for the car but not if its an ethanol mix which is now most often the case in Thailand.

The 91 is still being offered in non-ethanol form but is a bit of a drop from 98! Solutions thrown about so far have been jerry cans [on the assumption that the bigger towns still carry non-ethanol 95] to detuning the car for 91 to not bothering as its just a few tankfuls over a short period.

Views? What should I do? its a three day drive each way, about 2200 miles, 1200 of those in Thailand for the round trip. Gotta get to Bangkok in time for the Vintage Car club of Thailand annual drive to Hua Hin so right now the trunk of the car is going to look like a WW2 fuel dump.

Regards

David

[Guest Grant Magrath]

Hi David.

Here in New Zealand we have 91 unleaded, 95 unleaded, and 98 unleaded. My '39 Chevy does ok on 91, but I use a lead substitute called Valvemaster. A shot of that is $1.50. Our '38 Buick Special sedan goes great on that as well.

Cheers

Grant

[Guest imported_Thriller]

The compression ratio should only be 6.35:1, so lower octane shouldn't be a problem. If it were me, I'd carry come additives to raise the octane if needed on the 91.

The other thing is that the ethanol should really be fine, especially if you are driving up there. As long as it doesn't sit in the tank for too long, and likely your fuel lines have been upgraded in recent history, then it should probably be OK. I try not to run ethanol in my cars regularly, but have no qualms about running a tank, especially if I know that I will be burning through it (i.e. highway miles or on tour).

[DBT]

I agree fuel lines etc should be okay because it is only for a matter of days I will be using the ethanol

I am worried about the carburettor being affected and if this would manifest immediatley. I am basing this on some forum data from the Bangkok riders club where some bikes were immediately affected necessitating a trip to the mechanics. I want to avoid that whilst on the road as much as I can!

[Guest ZondaC12]

Shoot....the owners manual for my 38 talks about <span style="font-weight: bold">76 </span> or something on that order, octane as being HIGH TEST!! Haha

Ive always just but regular 87 in, no issues, and as mentioned with ridiculously low compression and the timing sure isn't anything crazy, sure shouldnt need TODAYS high octane, if back when they were new even 87 was unheard of.

[Matt Harwood]

I wouldn't worry about octane--my '41 owner's manual recommends 72 octane. In fact, higher octane fuel in these old cars might not work as well because of the higher ignition point of the fuel. These old ignition systems may not have enough juice for a good burn on that ignition-resistant stuff.

High octane fuel doesn't clean the engine, make it run better or make more horsepower. You aren't protecting it by using the high octane, and it isn't any gentler on the fuel system. The bottom line: If it doesn't ping on low-octane, it doesn't need high octane. Period.

The thing to worry about is the alcohol in the fuel. If your fuel system has been rebuilt in the past 10-15 years, however, I wouldn't worry that there are non-compatible parts in it. The only real problem piece is the fuel pump diaphragm, but most rebuild kits have long since had the correct materials, so if your pump is reasonably new (like within the past decade) it'll have the right pieces.

The internals of the carburetor won't mind as long as you have it jetted and tuned to run on the fuel. And as someone else pointed out, a few days' worth of driving with the fuel, even if you don't have the upgraded materials in your fuel system, probably won't cause a catastrophic failure.

Hope this helps.

[jeff]

Totally agree with you, Matt.

Higher octane is simply slower burning fuel, to reduce pre-ignition in high compression engines. With the low-compression of these engines, octane is not really an issue. I run just fine on 87 octane unleaded. The jury is still out on whether or not the lack of lead will hurt these valves or valve seats. Some say this is only an issue on higher performance engines as well. Others say that it may be detrimental, but will take 40,000 or 50,000 to have an effect. I guess I'll find out.

Biggest concern is the diaphragm in the pump - if you have a modern rebuild, you should be ok.

[DBT]

Thanks gents - the car is setup for unleaded so no conerns there and we have decided that we will run it now for the next few weeks on 92 to see how she goes.

I want to return however to the question of ethanol, any concerns there? This seemed to generate the most concern on the bike forums here in Asia with fears about this affecting the carbys especially.

Regards

[Mark Shaw]

Ethanol will cause some rubber and other elastomer compounds to swell and/or deteriorate.

Make sure your carb and fuel pump have been rebuilt within the last ten years and you should already have compatable elastomer seals and diaphragms.

[Guest ZondaC12]

Oh wow. And to think I rebuilt both of mine THIS year and was worried the materials would be damaged!

[carbking]

In 1938, Buick used two vendors for carburetors: Marvel and Stromberg.

Other than calibration, the Stromberg should be uneffected by short-term use of deathanol. Long term use would suggest that one periodically (maybe every couple of years) checked the chromate coating inside the bowl for deterioration. Deterioration could lead to holes in the bottom of the bowl with time.

The Marvel carbs primary used cast iron bowls, which should not be effected; however Marvel used a cork float which was coated with orange shellac. Deathanol will cut orange shellac like a hot knife will cut butter. If you have the Marvel, I would suggest removing the float, fabricating new pontoons, and sealing the pontoons with a substance such as POR-15. We have had no luck in resealing floats which have been in fuel, but the POR-15 works well on new material which has not been in fuel. Use of the original orange shellac will result in the jets being plugged with the orange shellac from the float, and the float absorbing fuel. I have been told by a customer that model airplane dope will likewise seal the floats, but I have not personally confirmed this report.

Jon.

[DBT]

Liked the term deathanol...

So Jon what of a quick run up and back - still too much for the carby? Will check but I think I have a marvel.

Regards

[carbking]

David - the experience we have had is that the orange shellac will dissolve almost overnight in deathanol. I would highly suggest the "preventative maintenance" if you have the Marvel.

If cork is not available to you, balsa wood may be used (hobby and craft store).

Jon.