Quote:
Originally Posted by MF Doom
I know if you tune a ls motor it runs a hell of a lot better and stronger than factory. not sure if these are relatable in anyway but just throwing it out there. What's the main benefit of tuning in a carb this much? HP gains? sorry if you already explained the purpose of this lol read 70% of it tbh
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actually this is not tuning it much at all, I am just going very slowly and documenting everything even my mistakes and struggles, once you know what you are doing and assuming you have a fully tunable carb (which mine is not, non of the Holley street carburators are, Demons are more tunable and Quick Fuel are fully tunable) you can be done in an hour
there are benefits to tuning both types of engines, carburated and fuel injected ie throttle bodied, the fuel delivery system does not matter
the newer engines such as the LS are able to run leaner I think (at cruise 17 maybe 18 AFR) but I know nothing about them (yet) so that's why I focused on what I had and began with a carb motor, if I did an LS swap on this truck I would be doing the same thing to tune it, plus these types of DIY diagnostic tools did not exist in the 70s and 80s unlike the LS motors that come with ODBII computers and Oxygen Sensors from the factory.
in my case I have a scenario where I bought an "aftermarket" Holley carburetor, (like most or many Hot Roddres go out and do) in all fairness a very good one but as most manufacturers do, it is pretty much designed to do all things to all cars, ie run on as many different cars as possible, which equals more sales (I am not a synic here just saying) so Holley tunes it to do so
also Holley don't want some dude to run it too lean and blow up his engines than go on some forum and complain about a bad Holley carb, so out of the box they come out a bit on the rich side to keep the engine from overheating and bad things happening
for a carb small block chevy I like heuristics ie rules of thumb, and over the last few months maybe years I read enough to sort of have these fuel ratio guidelines (have I tested them on a dyno yet, no, but its coming up very soon)
Idle should run at 14.x AFR Air Fuel Ratio (13 is acceptable)
Cruise should run at 15.x AFR Air Fuel Ratio (16 is acceptable)
Power should run at 13 (not 13.5) Air Fuel Ratio (though my old dyno guy said SBCs generate the most power at 11.5) well we shall see
I hope I am answering your question.
So who am I who do I think I am?
I am just a guy who likes to get his hands dirty but not fly by the seat of his pants, ie I don't believe you tune an engine by saying yup that sounds about right, or by putting your hand against the exhaust pipe and going oh yeah that feels right. COME ON MAN, have guys tuned their trucks like that for decades, yes sure absolutely, does that mean they were tuned properly, I strongly doubt it as there are some such subtle differences in the air fuel ratios that you can make that they do not change the RPMs where the human ear can pick the differences up nor the exhaust pulse yet the ratio can change by as much as a point
Yes AFR gauges are still very expensive but they are invaluable,
- not only for fuel efficiency
- but health of your engine (I may have discovered that the passenger side bank on my engine runs richer than the driver side - is one spark plug fouled up and missfiring, is there some other issue?) I would not find this other wise
- And Yes finally for power, but I say finally not firstly as it is super important to have everything else in order first, a lot of youngsters [ahem] and oldesters, ha ha, skip the idle circuit and head right for the power valves right for the squirter ie accelerator pump - hewk I know of many cases where going smaller jets and smaller fuel pump nozzle improved the performance of the vehicle not the other way around