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diesel_john · 03-31-2008, 11:21 PM

in regard to the efficiency of a WOT(wide open throttle) sweep, i am of the opinion, that the most efficiency throttle opening should be vacuum controlled (or ECU) like the secondaries on the old quadajet carb. especially on carb engines.
Fly by vacuum or fly by wire.

The pedal would allow the throttle to open if there was a little vacuum present(high velocity). refering back to post 4. the part where i want the engine to "catchup" with the throttle opening.
I am thinking that all the BSFC(brake specfic fuel comsumption, i think) curves are based on a controlled sweep or even steady state points.
So i am suspicious that a WOT sweep is the most efficient.
Another way of saying it is, the most throttle it will take without getting into fuel enrichment.(old term but still programmed in many fuel maps) In a previous life, i ran an engine test cell and what i observed (although i was not testing for it specifically) was, that, as the engine vacuum dropped to zero in of Hg, opening the throttle all the way up to WOT did not increase the efficiency. (Some engines went into enrichment at 5 in of Hg.) As engine management advanced in the 90's this became less of an issue because the ECU was doing this "feathering" for you. But for a carb'd engine, i don't think you want to get too far ahead of the engine RPM. Now with VVT variable valve timing, lean burn, high swirl HS, fly by wire and all the rest the ECU is able to dial in much closer to the optimal mixture. On the new engines the exhaust temperature would peak when the ECU found the best mixture for each RPM. What is the best way to determine if the ECU is keeping up with the sweep rate?, i don't know. Wide band o2? If it stays in closed loop and vacuum is close to zero? But i think i am close to optimal if i can just see a little vacuum left on the gage as i sweep. BTW.by the way. The highest ex. temp. i ever recorded was 1850 F on a modular truck engine with aluminum heads

So to make a long story short, i couldn't say that a WOT sweep is the best for most engines. Nor would i say that WAI is best for most engines. I think it depends on how technically advanced or retarded

the engine management system is.

03-31-2008, 11:21 PM	#14 (permalink)
diesel_john MP$ Join Date: Jan 2008 Location: SW Ohio Posts: 595 Thanks: 5 Thanked 19 Times in 14 Posts	in regard to the efficiency of a WOT(wide open throttle) sweep, i am of the opinion, that the most efficiency throttle opening should be vacuum controlled (or ECU) like the secondaries on the old quadajet carb. especially on carb engines. Fly by vacuum or fly by wire. The pedal would allow the throttle to open if there was a little vacuum present(high velocity). refering back to post 4. the part where i want the engine to "catchup" with the throttle opening. I am thinking that all the BSFC(brake specfic fuel comsumption, i think) curves are based on a controlled sweep or even steady state points. So i am suspicious that a WOT sweep is the most efficient. Another way of saying it is, the most throttle it will take without getting into fuel enrichment.(old term but still programmed in many fuel maps) In a previous life, i ran an engine test cell and what i observed (although i was not testing for it specifically) was, that, as the engine vacuum dropped to zero in of Hg, opening the throttle all the way up to WOT did not increase the efficiency. (Some engines went into enrichment at 5 in of Hg.) As engine management advanced in the 90's this became less of an issue because the ECU was doing this "feathering" for you. But for a carb'd engine, i don't think you want to get too far ahead of the engine RPM. Now with VVT variable valve timing, lean burn, high swirl HS, fly by wire and all the rest the ECU is able to dial in much closer to the optimal mixture. On the new engines the exhaust temperature would peak when the ECU found the best mixture for each RPM. What is the best way to determine if the ECU is keeping up with the sweep rate?, i don't know. Wide band o2? If it stays in closed loop and vacuum is close to zero? But i think i am close to optimal if i can just see a little vacuum left on the gage as i sweep. BTW.by the way. The highest ex. temp. i ever recorded was 1850 F on a modular truck engine with aluminum heads So to make a long story short, i couldn't say that a WOT sweep is the best for most engines. Nor would i say that WAI is best for most engines. I think it depends on how technically advanced or retarded the engine management system is. Last edited by diesel_john; 04-01-2008 at 12:45 AM..