Big Bore throttle body for MPG?

[johnmyster]

Air doesn't flow like that.

[Formula413]

Originally Posted by hondaguy72

The only thing I can think of where that statement might be true is that the TPS values vs airflow would be different than stock causing a potentially dangerous lean condition.

I was wondering about that. Lots of people on LS1tech have their TBs ported, shaving off as much excess material as possible. But like you said, that means more air is coming into the intake manifold at any given TPS value. Although it probably is true that the O2 sensors can easily compensate. People who have this done talk of improved throttle response. Well of course, there is more air coming in for any given throttle position.

[jonr]

All this intake airflow stuff pertains to WOT and maximum output. Generally not applicable to moderate output operation and FE.

[Vanner]

I would think a SMALLER bore throttle body would help at moderate throttle positions, given that the air restriction would then "be" at the bore and allow the throttle plate to open up more for a given demand. Nascarnation nailed it: your restriction is at the throttle plate unless the plate is open.

jonr touched on this: for WOT there is no throttle plate and fuel economy should increase with a big bore. Great.

I see this argument as in a similar vane to CAIs, they say if you can reduce intake restrictions the engine doesn't have to "work as hard" (whatever that means) to cruise at some speed. Seems like rubbish, the throttle plate just chokes off whatever progress you make upwind.

Anecdotal evidence is evidence, I know, but there a hundred factors that go into fuel economy. And no one yet has installed a throttle body trying to save money.

[Christ]

Noone (that I saw) mentioned that adding a larger throttle body will do nothing but impede airflow...

Considering that the plenum it's bolted to is milled specifically for the size of TB that you were already running, and adding a larger bore without port matching it just adds frontal area inside the throttle bore, which will create a separate flow characteristic, which actually means that you'll ultimately have LESS air coming in at the same throttle position.

Using that throttle body without port matching the manifold for it will do absolutely nothing for you... at least nothing noticeable. You might lose power at high throttle angles though, due to the flow restriction.

[Coyote X]

On my ls1 camaro smoothing and porting out the throttle body made it get better mileage at wide open throttle so I think it went up to 3.1mpg or some other equally meaningless number. It didn't change the mileage at all overall, but it did let the engine rev quicker so it was even harder to launch the car off the line.

I suppose under an ideal situation you might get better mileage. But for the most part at partial throttle that big throttle blade is 99.9% of the intake restriction. Smoothing it will help very little unless your tps sensor is now reading a bit off and making the computer do something different.

Porting them is much easier than it looks so if you want to do it I would say just get a dremel and do the one you already have and save your money.

[ATaylorRacing]

All of this depends on the car itself. I mentioned earlier from a post I made on 9-12 that improved air flow made every one of my cars go quicker and get better FE....I was shocked that this was NOT the case on my 96 Geo Metro 3 cyl! Going from the stock air filter to a home made CAI and fine wire mesh for a filter made the car consistantly loose nearly 2 mpg on the hiway!!! Using the stock air filter but keeping the CAI made the FE worse than the stock set up by about 1 mpg too!

[Christ]

The idea is that even if you're at partial throttle, and have that huge restriction in the way, you're still flowing more air at the same throttle angle, meaning less VE (pumping) loss. Technically, this would give SOME improvement in both HP and MPG.

The fact still stands that a larger throttle body is never a bolt on procedure... you need to portmatch the manifold or you will get LESS airflow overall than the OEM config does, because you're introducing flow reversion at med-high throttle angles (due to the original TB port sized hole in the plenum.)

Reversion is worse than restriction, because restrictions slow down flow, but it's still positive... reversions attempt to "Reverse" flow, which isn't possible, so it creates a large area of turbulence in the flow, thus making the flow's cross sectional area smaller than the OEM config.

I still maintain that without matching the plenum to the TB, that "bolt on" mod will net you a loss of whatever it cost you, and probably less power/mpg as well, if there is any change at all.


ATaylorRacing - did you try just using smooth pipe and the stock airbox/filter? Or even using a smooth pipe w/ the stock airbox and a higher flow filter?

AFAIK, the most restriction present in the intake tract of most vehicles is the filter, second the airbox itself, and third the piping.. smooth piping sometimes helps, but isn't usually necessary. Filters are usually the best single piece to the puzzle.. so maybe a K&N or a Green filter will help out instead of hurting?

Putting a short ram on Granny did nothing but improve high-end HP... I have not noticed a lower MPG or less seat-of-the-pants torque at all, and the filter is right behind the radiator's flow path on the cooling fan side.

[Peter7307]

Originally Posted by cfg83

hondaguy72 and Daox -

I think a lot of HP mods are just adding the "saves gas!" claim to all their stuff these days.

CarloSW2

Having been around the car modifications business for more years than I care to admit to I have seen more than a few items come back again relabeled to claim greater fuel efficiency.

"Shrouded" spark plugs are one example.

Previously they were touted to boost power (1960's) or reduce pollution (1970's) and from time to time they claimed both !

The packaging and marketing slogans have changed but little else has...apart from the warning dating back to the days of the Roman chariots racing around the Collusseum in Rome : Caveat Emptor = Buyer beware !

Cheers , Pete.

[jazzie604]

Originally Posted by ATaylorRacing

From my own experience I can tell you that a slightly bigger TB can give more HP and FE. The TB in the E-bay add would do both, but NO WAY are you going to gain 12 HP! The throttle plate is the same as stock and all they are doing is cleaning up the air flow going into the TB.

On a bone stock 3.0 liter V6 Dodge Shadow/Plymouth Sundance from the early 90s going from the stock 42mm TB to a 52 or 56 one off a 87 mini van with the same, but older motor picks up about .25 seconds in the 1/4 mile and from 1.2-1.8 mpg (1.7 in my case).

On my 98 SOHC Neon I went to a HUGE Indy Cyl Head intake and the FE stayed the same and I lost torque, but gained higher rpm power...no improvement in the 1/4 either (advertised a 25 hp improvement with a bigger TB.....So I bought the AF/X 60 mm TB and picked up a bit over 1/2 sec in the 1/4 and FE became nearly 2 mpg better.

On EVERY car I have owned.....if I was cruising, any air flow improvements into the motor made more FE and power....on MOST a better flowing exhaust did the same thing, but not on the V6...a better flowing exhaust made it have worse power and FE until I did a lot more mods....the stock set up worked the best initially.

What I have found is that with the extra power you can drive up to your speed easier and maintain it with less throttle = better FE.

Originally Posted by jonr

All this intake airflow stuff pertains to WOT and maximum output. Generally not applicable to moderate output operation and FE.

Taylor, are you sure that you just didnt change your fuel trims whel you were adding the high flow stuff? Several of the cars you listed were very archaic(sp?) computer systems that didnt have much compensation room built in. A properly functioning system should automatically adjust for minor changes.