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wind & fire = guides to power
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Discussion Starter #1
I have "learned" some things on this forum...or at least some things I'm trying to learn. Very smart people with years of experience here.


Some time back there was a "carb size" thread and now the vac advance thread.
In both of these I have read some things I'm having a hard time believing, although everything i read most certainly backs up these statements.

Here is what I'm having problems with>

1) a bigger carb increases cylinder pressure(even though it reduces throttle response?)

2) the same carb on a smaller engine needs bigger jets(even though a too big carb smokes black?)

3) a leaner mixture burns slower than a rich mixture(even though a lean mixture is more likely to ping?)



so let me apply these theories..or facts

1) my low compression 305ci will benefit from a larger carb by increasing cylinder pressure, if not why not?

2) If i pull my 850 dbl pumper off the 454 and put it on my 305 I will need to jet it up

3) my 11:1 350 has a 13:1 air/fuel ratio but pings. I can lean it out so as to allow a slower burn and prevent ping.


I am not trying to be difficult, but trying to learn by using "real" world examples. The engine is a system and must work as one. I need to fully understand this system to fully benefit from it.
 

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If you put that 850 on your 305 it wont pull away from the curb. A friend built a buick v6 motor for a toyota truck several years ago. We hooked it up on the garage floor and ran it for 30 minutes to break it in. He had a 650 holly and headers. It had a nice cam all the goodies. Sounded really bad on the floor. Best sounding v6 I ever heard. Sounded more like a small block. When he put it in the truck it didnt even want to move. It would just bog down. Went out and bought a 450 carb and it would chirp those 44 inch monster mudders when it hit second. A bigger carb allows more flow but if the engine cant pull that much flow the speed of the air going through it is slower. I would think this would mean less vacuum and vacuum is what draws the fuel out of the carb. The ping is caused by the fuel/air mixture exploding before the piston gets to the top. It harder for a richer mixture to explode. Higher octane raised the flash point. I hope I explained some things now the rest of you guys can straighten me out.
 

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wind & fire = guides to power
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1,529 Posts
Discussion Starter #3
Let me clarify please.

I do not have a 305 or 454, i said "real", not real!

I know a 850 will not run on a 305..a 302 ford it will, but only after 3500 rpm, lol!

I'm just trying to merge my experiences with these stange "facts" i read!
 

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489 Lemans
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carbs

on cheaper carbs the air bleeds are factory set on a flow bench to work the best it can.
a large carb on a small engine will not receive a strong signal as air passes by the venturis. thats why it doesn't work.
a small carb on a large engine will receive a strong signal but will lean out at high rpm.
 

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Bracketeer,

I am glad to see that someone agrees with me on the carb size and jetting. I have argued this point with so many people, but noone seems to get it. Been called an idiot several times for suggesting that you might have to use larger jets on a larger carb to get the desired mixture and vice versa.

As for the cylinder pressure thing, I must say that is complete BS. No way on that one.

A lean mixture will not burn slower. Rich mixture will. Lean mixture will certainly increase detonation. 13:1 is too lean at WOT anyhow for most engines. I suppose the detonation theory with a rich mixture might be supported if you throw weak ignition in to the equation. It is important to understand the difference in preigntion and detonation. Preignition is what it sounds like and usually from hot spots in the chamber. Detonation being incomplete, irratic combustion.

Chris
 
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