5.7 vortec mpg

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L31MaxExpress

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I'm not doing a tune ive bin thinking of buying a HP tuner as my truck Is 98 and I could make money on the side working on freinds trucks. My truck is a 98 Z71 Silverado with 350 000km on it it was gutless truck from factory it's even more gutless now with age. All I would like to see is more mpg highway my engine finally came on the other day it to buddy's shop asap and it's coming up fuel pressure but when fuel gauge is hooked up fuel pump is still well in spec so we're set it's the spider injectors and or the fuel pressure regulator. Disconnected the battery for few hours no more engine light I'm sure it'll be back I ordered a mpfi AC Delci mpfi with regulator will be installing it over the Christmas holidays. Hope to gain some mpg and some power it's embarrassing trying the pass I drop it to the floor and it just falls on its face takes forever to pass anything I'm sure not a fan of these vortecs my 5.7 TBI was way better powerwise and mpg.5.7 vortec to 5.7 TBI swap

Have you pulled the code?
 

1ofthesedays

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Now a lot of people dont get very good fuel economy in a full size 4x4 truck, and being that you've already done a lot of work to it, it sounds like you may need to think about a tune on the ECM.

I believe blackbear makes an economy tune that they can throw onto a black box and send to your door, and also my 96 vortec 5.7 felt like a dog as well, until I actually changed to a larger throttle body.
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As shown here, the factory throttle plate actually has a restrictor on it that actually makes a huge difference in performance and drivability. You can either knock this restrictor off, or move up to a throttle body from a 454 vortec. Either way, your throttle response will greatly increase.

Another thing to look at is your air filter, it's a small thing that's commonly overlooked, and also replace the PCV while your under the hood, they are cheap, and can effect fuel economy, and I've found that I need to replace mine every other oil change to keep it working properly.

If you have access to a scanner, or even a bluetooth OBD dongle, go ahead and view your O2 sensor data as well as your long term fuel trims. They can tell you a lot about your engine, and how its performing. A negative fuel trim may indicate a leaking injector, while a positive fuel trim can indicate a vacuum leak. The fuel trim should be around 0%+/- 5%

And lastly, you said you replaced your plugs/wires/cap/rotor/fuel filter. What was the condition of them? How did the plugs look? And was the filter clogged? Anything fall out of the filter?
Have not heard of the throttle body modification before, is it a simply bolt in or? Very interested to know. Thanks, Ron
 

Hobie

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I did the mod already with no difference. But there also is something wrong with my truck a said healthy truck I could see it helping
Throttle body upgrades wont show a direct improvement with CFM increases, but what this will do is increase throttle response due to the restrictor that the 350 TB have. As shown
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So in other words. The factory 350 TB needs a lot more throttle input for the same acceleration as one without this restriction.

From.what I hear, the same idea can be achieved by knocking this restrictor off, but as I'm planning on a new cam, exhaust, and injectors at some point, I wanted the little extra CFM of airflow
 

L31MaxExpress

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Throttle body upgrades wont show a direct improvement with CFM increases, but what this will do is increase throttle response due to the restrictor that the 350 TB have. As shown
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So in other words. The factory 350 TB needs a lot more throttle input for the same acceleration as one without this restriction.

From.what I hear, the same idea can be achieved by knocking this restrictor off, but as I'm planning on a new cam, exhaust, and injectors at some point, I wanted the little extra CFM of airflow

The lip on the blade does alter CFM. Whether or not you will notice it at WOT on a bone stock engine is hard to say for sure.

My 97 Express van had the lip pictured above.

My 99 Tahoe had a different lip on it that was 2x as wide.

The 99 Tahoe also had 6-8° less timing in the spark map in the high load/low-mid rpm area.

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Hobie

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The lip on the blade does alter CFM. Whether or not you will notice it at WOT on a bone stock engine is hard to say for sure.

My 97 Express van had the lip pictured.

My 99 Tahoe had a different lip on it that was 2x as wide.

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Yes, the lip will alter CFM, but the 454 TB have a larger diameter bore, 1/2" larger if I'm remembering it correctly. So that's the biggest gain in CFM along with removing the restrictor/lip.
 

L31MaxExpress

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Yes, the lip will alter CFM, but the 454 TB have a larger diameter bore, 1/2" larger if I'm remembering it correctly. So that's the biggest gain in CFM along with removing the restrictor/lip.

I had a 454 TB on my marine intake. Have also run the BBK on a marine intake.

It is the same size blade but the housing on the small block TB is necked down smaller than the blade.

I have also run the BBK unit. I epoxied up a stock plastic upper plenum where the stock rubber o-ring sits, opened up the opening to match the BBKs larger bore and ran the BBK with a gasket I cut out of gasket paper.
 

L31MaxExpress

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Since I tune I also did a once common LS1 mod to a spare MAF I had laying around. Once the tune was dialed in with the epoxied/ported upper plenum, the modified MAF and a K&N in place my stock at the time engine had noticeably more top-end power.

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Compared to a stock MAF.

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The 1K ohm resistor recalibrates the ported MAF back to the ballpark of a stock MAF but it still requires datalogging in MAF only mode to get the MAF table and thus fueling accurate.

I went from the stock setup dropping down to about 92 kpa @ 5,000 rpm to staying at 98 kpa @ 5,000 rpm. Barometric pressure here is about 100 KPA. So very little loss in the intake system on a stock engine after doing these mods.
 
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