Air Fuel Ratio Gauge

Engine discussion.

Re: Air Fuel Ratio Gauge

by hcap » Thu Jul 09, 2015 4:22 pm

Harv extremely pleased with how car is running .......idle is a little rich but far less angry ....also cooler when stopped in traffic here is what I am getting with 380cc main jet
Cold start with choke 11.7-12.0
Idle 13.9-14
Freeway constant 15.2
Full throttle 12.9
3/4 throttle highway 12.1
Haven't pulled a plug to see how it looks :)
 
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Re: Air Fuel Ratio Gauge

by Harv » Thu Jul 09, 2015 7:43 pm

Much nicer values... now sounds well tuned.

Highway still lean, but OK. Run it up to 110km/h, and hold it there for a while on a long, flat stretch of highway. Don't put your boot in (you want the power bypass valve shut), just cruise it at 110km/h at part throttle. If you get an intermittent miss, you know you are still a poofteenth too lean on the main metering jet.

As long as it doesn't do that, and plugs look good after a run like that, I'd leave it.

Cheers,
Harv
 
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Re: Air Fuel Ratio Gauge

by hcap » Thu Jul 09, 2015 10:32 pm

As an adjunct to this discussion I leant the ute to someone with a full tank and surprise surprise it came back near empty. I always use 98 octane in all of my cars but the only servo I could get to was all out except the cheap unleaded with up to 10% ethanol..... How much diference does good fuel make ????? I discovered a huge amount huge huge amount
 
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Re: Air Fuel Ratio Gauge

by Harv » Fri Jul 10, 2015 7:33 am

Different fuels have a pretty big effect on a Strommie. Oxygenated fuels, particularly methanol and E85 (both forms of alcohol-base fuels) are common ways to squeeze in more power from a given engine combination. Both fuels are oxygenated, and can deliver significantly more power provided the engine is tuned to use their respective capabilities. For early Holdens, this is normally by taking advantage of the increased octane (pump fuel is typically 91RON, whilst E85 is 105RON and methanol is 109RON) by increasing compression ratio and/or advancing ignition timing. As a very rough guide…
Compression Ratio RON Required
5:1 72
6:1 81
7:1 87
8:1 92
9:1 96
10:1 100
11:1 104
12:1 108

There are however some things to be wary of when running alky in a carburetor. The most pronounced issue is that E85 requires 25-30% more fuel flow (1.25 to 1.3 times your current pump petrol flow), whilst methanol requires 100-150% more fuel flow (2 to 2.5 times your current flow). Provided your fuel pump is up to it, the carburettor itself may not be. Whilst running methanol is nothing new to the early Holden racing fraternity, running E85 is. Part of the difficulty in examining what has historically worked is that a common way to tune methanol is to run the carburettor way, way rich ("block the power valve, wind out the idle screw and double the jet size", i.e. flow much more fuel than is required). This has little downside on power, and is OK for short duration track work. However, for those hunting efficiency a the same time (say for a daily driver on E85 or for distance circuit work) a more logical approach is warranted. I took a good look at both E85 and methanol in the Strommie Guide Addendum 1 here: http://www.scribd.com/doc/238223610/FB- ... Addendum-1.

E10 is a bit more subtle. Typically you will get away with running it with no dramas. A lot of guys piss and moan about it, with no understanding how E10 (or modern fuels) are different from 1960's fuels. Everyone whinges that modern fuels are crap, though no-one complains about the steadily increasing octane at the pump (amongst other things). Generally, moving the main metering jet up 1-2 sizes will provide more than adequate fuel to account for the change to E10... little other carb changes are needed.

Cheers,
Harv
 
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