Hope everyone is well.

I have a 71 with a newly rebuilt engine - 350. I upgraded the postion heads to flat top hypereutectic pistons and swapped the stock Holley in favor of an Edelbrock. I now have about 700 miles on the engine to break it in.

I have been running 93 octane with ethanol. The service station dwn the road is now selling 90 octance without ethanol. My preference is to use the non-ethanol gas to save the fuel lines, seals, gaskets etc. So....I filled up the tank completely today with 90 oct / no ethanal gas and it is running just a bit rougher.

Question: Should I do another tune on the engine or should I just commit to adding octane booster from here on out when I am using the lower octane fuel. If the suggestion is octane booster for every tank - what is the best brand? I was looking at Torco - but i have bveen reading about an orange build up on plugs.

Thanks for the help.
David

 

what heads? what compression ratio? 69 and 70 with some having 11;1 need high test. and most cars you can retard timing a bit for lower octane. higher octane numbers actually burn slower. so you can run more advance and increase cyl pressure.

 

Flat top Pistons you likely don't have more than 10+1 compression you could back it off a couple degrees on timing.id run 93 and maybe a fuel stabilizer.

 

Having no idea of your current timing specs. I would have to agree with above that your compression ratio is likely be around 10-1 or maybe a tad less.
So with the correct timing specs it should run well and make very good power on the 90 octane.
I vote for a retune. Putting in octane boost all the time is a real hassle. Not to mention the cost.

 

I should probably add. My engine is also a rebuilt 350. Hyperunetic flat top pistons, 64cc chambered aluminum heads. A fair bit of cam, etc. And with shim style head gaskets (.015) I'm right on 10-1.
Octane readings are measured differently over here. but basically our 95 is much the same as your 91.
Mine runs great on midgrade 95. Close to your 90.
I do run a custom curved distributor and fuel delivery is very precisely monitored with a wide band O2 sensor and metered with throttle body EFI on a single plane manifold.
Still, many argue that a carb setup properly will easily match EFI. Although, I run EFI as I am not one of those people.

 

define rougher? pinging? i vote the 90 non..due to longer storage periods vs daily driver where it would matter less..

I filled up the tank completely today with 90 oct / no ethanal gas and it is running just a bit rougher.

 

I am running about 9.1:1 for compression. I ma thinking of trying to advance the timing

 

No pinging - just rough idle now. I would like to stay with the 90 non ethanol - storgae is one of the reasons as well. I ordered some BOOSTane. The math works out to about 96.5 octance if I add one can to a full tank of 90 octane non ethanol. Going to see what that does before I mess with anything.

 

I am about 9.4:1 for compression. I have that full tank of 90 non ethanl now - orderd some BOOSTane which should get to me around 96 octane with one full can per tank.

 

I would think that going from 93 to 90 should not have affected your idle. as far as idle goes the only thing that could be different would be if the car is possibly running richer due to the fuel being 100% gas with the 90 octane. If that is the problem adjusting the mixture screws should fix it. Either way the actual octane number itself should not have any effect on the idle quality.

Pat

 

At 9.4-1 you probably cold save the money on any additives as your engine will probably not need the extra octane. Higher octane will not make extra power so it becomes a waste of money unless your engine NEEDS it. I run 12.25-1 compression in my BB 427 and can survive on 93 octane but need more in the warmer months.

Contrary to popular belief the higher octane will not help or make any more power in a lower compression engine. I still see people with Honda's and other Asian cars filling with higher octane and they are wasting a lot of money. The only benefit they are getting is that the higher octane fuels have more or better detergents in them which helps keep the engine clean internally. Some gas station owners are making a lot of money on the premium grades around here, who keeps that myth alive? Higher octane burns/explodes slower than lower octane fuels. There are other factors that come into play on this like the Open Chambers in the cylinder heads on the 1970 LT1's makes pinging much more of a problem. My 427 has closed chambers which are more resistant to detonation.

I had a 1970 LT1 and it was 11.1 and would ping like crazy on anything but the better grades of premium. My 427 has a Water/Methanol Injection system to assist in times when it gets warmer or the engine gets hot. The water cools down combustion chamber temperatures and the Methanol makes the gas equivalent to 115 octane which my 427 really likes. When I need more of it I use plain old windshield washer fluid to replenish the fluid levels. $.99 a gallon makes a lot of very high octane fuel and sure beats dealing with tetra-ethyl lead additive or race gas.

 

if you are running rough i don't think it is fuel or timing. i think it is time to do plugs, wires, etc. you want to chnge the timing? you need to know your timing curve first. you may already be at the edge and can not safely advance farther. you could also be way retarded and NEED to re-time. that is why...

 

VP Madditive Octanium is my fav octane booster. It pretty close to the numbers you’ll get with boostane and it’s $7 cheaper

 

At the current compression it very likely can be using E15/UL88 when tuned correctly, (Approx 1% - 2% richer jetting and equal to regular gas 91 to 93 octane rating as far as compression to anti-knock tolerance), it will cost less at the pump than Reg 87 !! As said it may need to be a few percent richer in jetting (etc), ( 94 octane E30 is only approx 10% to 12% additional fuel required and has the potential of a min 96 octane).
Even with most 64cc chamber heads added it would likely use the same fuel - even iron Vortec heads, but especially with any aluminum version.

Cap your carb bowl vents and vented tank's cap - if you're worried about storage.

Edit: E15 octane tolerance comparison is based on a blend of low grade gasoline to equal only an 88 pump rating - such as current 87 pump gas is 84 octane "gas" and 10% ethanol = 87, (84 octane with 15% ethanol = 88, but acting higher).

off the soap box

 

I still have several gallons of "Tetra Ethyl" lead additive I bought years ago up at Corvettes@Carlisle. It is the real thing to making your own higher octane gasoline. Unfortunately you need to wear a rubber apron, eye- protection and rubber gloves to work with it. If you happen to get any of the treated gas on your paint it gets damaged very quickly. You also don't ever want to get it on your skin as it is easily absorbed.

For me the water/methanol injection seems to work well enough allowing me to enjoy my 427 all year long. It is certainly the cheapest way to get the octane your engine needs IF your engine "really" needs it.

 

The only '71 Vette that came with a stock Holley was the LT-1. If you removed the 780 cfm LT-1 Holley and installed a POS Edelbrock AFB clone, you took a massive step backwards and that is likely the source of your problems. Throw that AFB carb in the trash and install the stock carb- set it up right and it will run well.

Lars

 

Same.. I run 90 in the states with a very similar setup and 10.1:1 with a carb