Fast355

Quote: Originally Posted by flaming-ford damn that afr was downright scary. I thought it was just my tbi car that had that problem. Seems they were all tuned horribly fat....... whats with that? I mean i understand running fat up top for a safety margin but, 10 to 1 is just plane dumb, **** another couple points and it would be too rich to burn at all......... i remember mine dyno'd at high 10 to 1 ratio to mid 11 to 1 ratios. I also had a few bolt ons so i figured mine if anything should have read lean???? It did seem to dyno right on with what other people are showing though, to bad it reached its demise or i would have made my regulator adjustable and tried again. are tpi cars the same in this aspect? because, i have a 89 maf 305 5 spd car now and it seems to run with the same overall rich condition (dark plugs black tailpipe) Even a little smoke from the pipes sometimes. It also should if anything run lean as it has all bolt ons, other than msd box and roller rockers.... sometimes you just gotta scratch your head as to y an engineer would detune something for no apparent reason........ Actually, the GM engineers go rich for two reasons. First is to protect the exhaust valves from overheating when running continuous WOT up say a mountain. Second they dump in ALOT of added fuel to choke out the oxygen to the catalytic converter. That keeps the catalyst brick from melting down. Also the rich mixtures is also a safety net, if something in the fuel system becomes weak, the engine won't lean out and destroy itself, ultimately creating a warrenty claim. The rich mixture also helps fight damaging detonation. MOST GM vehicles run that rich, Carb, TBI, TPI, MPFI, LTx, LSx, etc. EDIT- Just read the line about the AFPR and the mods, that WILL NOT lean out the system after the closed loop fuel trims have become active. The ECM will see that the engine has leaned out at part-throttle and add in additional fuel at WOT by increasing the pulsewidth to the injectors. Even if you cut the fuel pressure back down to 9 psi, after a few miles the ECM would drive the BLM numbers through the roof and it would go back just as rich.

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flaming-ford

Actually, the GM engineers go rich for two reasons. First is to protect the exhaust valves from overheating when running continuous WOT up say a mountain.

yah but, isn't this just way over the top rich???? i can't imagine anything short of a big shot or nos or high boost applications that would need this kind of safety window.

+ the egr valve does kool the exhaust temps greatly.i'm amazed the lt and ls engines arestill doing the same thing.

Second they dump in ALOT of added fuel to choke out the oxygen to the catalytic converter. That keeps the catalyst brick from melting down.

i always heard that the overly rich conditions are what cooks a converter. Then again i guess your right that if you run it super rich that, that would kill that argument, being that if theres little to no oxygen u certainly cant make it burn.+ wouldn't that make the airpump quite useless?

Also the rich mixtures is also a safety net, if something in the fuel system becomes weak, the engine won't lean out and destroy itself, ultimately creating a warrenty claim. The rich mixture also helps fight damaging detonation.

definetly won't disagree in any means here.

MOST GM vehicles run that rich, Carb, TBI, TPI, MPFI, LTx, LSx, etc.

EDIT- Just read the line about the AFPR and the mods, that WILL NOT lean out the system after the closed loop fuel trims have become active. The ECM will see that the engine has leaned out at part-throttle and add in additional fuel at WOT by increasing the pulsewidth to the injectors. Even if you cut the fuel pressure back down to 9 psi, after a few miles the ECM would drive the BLM numbers through the roof and it would go back just as rich.[/quote]

This makes sense, that is afterall the idea behind close loop operation, sorry for posting that misinformation about backing it down.

1 question though why is it that most tpi/tbi applications tend to gain a few horsys from bumping the fuel pressure up if they are already overly lean? Better atomization, or could it just be that basically everyone who is doing this has some mild bolt ons creating a mildly lean condition?


sorry for so many questions, and i don't mean to argue whatsoever i respect your opinion by far more than most just curious as to why they would do this.

BMmonteSS

10-1 isn't really that bad, it's hurting power a bit but it's not causing misfires. The guys who are adding fuel and saying it's adding power are basically full of ****.

I've tuned a few combo's for guys who got in over their heads, once I take out the extra fuel they added and back the timing back down from the 36 degrees that they all think is necesarry to make power the motors run pretty darn good.

This just further illustrates why tuning is so necesary on these cars.

flaming-ford

no i didn't mean 10-1 is terrible just thinking that it seems like it's highly wasteful at least.....

Thats a good bit of gas milage i'd be saving haha.

yah i kinda figured that about adjusting the fuel pressure, i've tried to do so on my full bolt on tpi car and it only seems to get worse and use more gas, i put mine back to specs lol.

BMmonteSS

Just to clarify, they only used a rich mixture at WOT. At part throttle it's 14.7 to 1