tahoe214

Ok guys ill start off by telling you what i have. Its a 99 tahoe obs. Its got a 383 stroker made to run on 87 vortec heads and intake. It has a 10 bolt and geared with 456 it has a built 4l60 stock stall. And a black bear tune. It has 33 inch tires 2 inch suspension lift and 3 inch body lift. im not impressed with the performance of this engine. Its ok but i get really crappy mpg. The most i can get on the highway is about 15.

now i have had a 98 silverado stock 5.7 stock trans stock tune 373 gears 9.5 axle 33 inch tires 3inch body lift 2 inch suspension lift. Almost the same. Only difference being the engine and gears. This truck had efans and the tahoe does aswell. I could easily get 20mpg on the highway. The power felt about the same save for the tune with the torque management. I want to get some realistic ideas about what i can do to solve this. It really gets on my nerves. My last truck was a 2000 silverado with 373 30 inch tires e fans and otherwise all stock it got 22 all highway.

my ideas.... swap the 383 for a 5.3 ls swap and or change to 373 gears with a 9.5 sf axle. Should i consider both or just go with the 5.3 and keep my 456 gearing. I have towed with the 98 silverado and it had plenty of power.
i have also towed with the 2000 and it didnt really struggle. I love everything about this tahoe except for the mpg and i think doing the engine swap would make a big difference. I will be doing all the work myself so i just need the engine and other few parts to make the swap work. I can get a decent mileage 5.3 for 400-800 complete harness and ecm. Basically everything i need for a drop in.

now to the question what do yall think. Let the opinions flow. Im determined to get better mpg im not looking for massive power i have a bullet bike for that. Let me know what yall think.

FFDP

iTrader: (2)

The 5.3 should net you better MPG with how well they perform right out of the box and the computers tune-ability.

A happy medium might be doing that and going to 4.10's instead of 3.73's. The 4.10's would be a better choice with the 33in tires and it will lower the cruising rpm a little bit to help with fuel mileage in most cases.

dsmmace

Going from 4.56 gears to 4.10 would change the engine rpm 400rpm lower at 60 mph (very rough guess, no actual math done). My 98 Tahoe with a vortec 383 setup and 3.42 gears would get 18mpg.

tahoe214

Ffdp i agree the 5.3 would net some gains it is a more efficient engine i think i will see a gain just from it. I say 373 because it is easy to find in the junk yards and i can just swap a 14 bolt sf and front diff into the tahoe. However even if i kept my 456 gearing i still think i would see a sizable gain just from the engine. Lot of decrease in ci and as far as im concerned atleast with this particular engine the same amount of power. Plus a better fuel management.

all in all a vortec 383 getting 18 on the highway is great. I barely touched 15all highway with my setup but 342 is just to steep for me. 373 is the most i want to go. Also because its easier to find. I could go 410 but it would probably cost me more.

which should i try for first 5.3 swap or 373 9.5 sf axle and front diff swap. I think the 3.73 axle and diff swap would be less expensive but the 5.3 swap might net better gains and really no loss of performance especially with a tune.

dsmmace

456 gears are great for off roading, however not great for a everyday/highway tow vehicle, they have no purpose other than increasing the rpm and reducing fuel economy. Isn't that your complaint?

Can't you just sway out the gears in your current diffs?

383 has 400 ft lbs of torque at 1800rpm. A 5.3 will never have that amount NA power until 3000rpm, therefore you will have to use more throttle to move the vehicle and it will use more fuel. It's your money and time however.

tahoe214

^ this is exactly my question. But which one would see better results. You say that a 383makes 400ftps of torque well every engine is different depending on the way it was built. I think this one has much less than that. I could be wrong but i dont think so. Im not looking to do heavy towing all the time just a boat and a small tractor from time to time. I feel i would be happy with 373 gears but cant help wondering if the 5.3 is the better option. Yea its my money and id like to spend it wisely thats why im asking for advise. I can get a 9.5 sf with 373 gears from the bone yard for about 4-500. Can get the front diff for about 200. So do you think the low end torque that this engine is supposed to make will handle nicely with the taller gears. I think with 33 inch tires it would bring me down to about 1800-2000 rpm from the 2600 rpm im at doing 70mph right now.

dsmmace

Factory in your Tahoe would of been 3.42 typically. 3.73 gears would raise your rpm by almost 200 rpm. 4.10 would raise it by ~250 rpm, 4.56 gears would raise your base rpm up by at least 700-800 rpm from the factory 3.42’s. Very roughly calculated. Please find an appropriate gear ratio calculator and do the proper math. No v8 will give you good fuel economy at 2600 rpm cruise speed. 1800-2100rpm max is a good target range.

tahoe214

So you think i should change gears before i think about an engine swap. I can see what you mean by higher rpms in general getting less mpg no matter what v8 were talking about. Just wonder if a more efficient v8 would see more gain than the axle change. However with the higher torque my engine is supposed to have with a taller gear it shouldnt work to hard and therefore get better mpg. My g80 in the 10bolt has burnt clutch packs and does not work. I was going to turn it into a full time posi but i guess ill pick up a 9.5 sf and run with it with 373 gears and change the front too. We will see how it works out
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