best turbo for fuel milage

[Nellie]

any thoughts for a 03 thanks nellie

 

[rbattelle]

Probably the one that came with the truck.

Ryan

 

[WoodChuck]

The stock one is best if all you want is MPG, though a nice upgrade at a modest price would be a 04. 5 and up "600" turbo. It'll give you more air and might be the same MPG but it could give more or maybe less, I wouldn't know for sure one way or the other.

Anyone else do this mod and have MPG stats?

 

[Kubotaorange76]

i Think having a larger exhaust housing over the stock 9cm will help on the highway cruising... especially over 2200 rpm

 

[Nellie]

yes that was what i was thinking about the 9cm stock turbo housing is very tight

that crusing above 2100 that drive pressure is higher than the boost my97 12valve

had a12cm housing and i was going to go for a16cm housing but bought an 03 ho

 

[ENafziger]

I'm not so sure that a larger exhaust housing helps with mileage. Going from stock to a SPS66 turbo has shown to decrease mileage by 1. 5 - 2 mpg. Since the exhaust housing is not as tight, much of the available energy is not being utilized.

The most efficient turbo will be the smallest one you can go with and still maintain adequate cooling on the top end.

The SPS66 is an efficient turbo, as long as you're making 500 - 650 hp. However, go cruising down the interstate at 70 mph and 105 hp or so, and you're so far out of its efficiency range that your mileage will suffer.

Thus, to have enough cooling for big hp, and yet efficiency for daily driving, you are forced to go with a properly paired set of twin turbos.

Just something to think on...

--Eric

 

[cerberusiam]

yes that was what i was thinking about the 9cm stock turbo housing is very tight

that crusing above 2100 that drive pressure is higher than the boost my97 12valve

had a12cm housing and i was going to go for a16cm housing but bought an 03 ho

The housings on the CR's are equivalent in flow capabilities to the dual port 12cm on the 2nd gen trucks. Larger housings tend to waste more energy than they save and the net is usually a mpg loss.



Mileage on the CR trucks is all about speed and rpm's. Lower the rpm's to certain degree and mpg trends upward a bit, as does slowing down.



Mpg's is fuel and timing not air, the fuel curve and timing is what will give you the biggest gains in mileage.

 

[WoodChuck]

Out of all the mods I've done the two things that dropped my MPG are (1. ) 35" x 12. 35" Toyo MT (2. ) High Tech 62x65/14 turbo.

A bigger exhaust housing only helps the motor breath better on the top end where you don't want to be if your looking for MPG. For max MPG you want more boost at cruising speeds which is normally a very low load. Cruising 60-63 with a empty truck might be a 7% load. Not much fuel required to do that.

The 62/14 did give me a huge boost in performance (maybe 50 HP) and allowed sustained full power output. No MPG gain driving that way I assure you.

Your sig doesn't list any mods so I'm assuming you're stock. If that is the case I would recommend a tuning box like maybe the Edge MPG max or the Juice with Attitude. Another route is a downloader like maybe a Smarty. If you do any of the above and want to run over 50-60 HP at a minimum you'll need a Pyrometer to monitor your EGT.

 

[WoodChuck]

Forgot to add that I upgraded to the SS 13cm housing and raised my cruising boost and MPG a bit.

 

[Nellie]

hey wood chuck nellie here the only mods to my truck are a fass & rocteck milled

timming senneser. my road trips from ny to ga and western pa and run the 2100 -2200

rpm when the traffic is fast. nellie

 

[WoodChuck]

2100 RPM is supposed to be the sweet spot for fuel efficiency on the CR but drive pressure and boost have more to do with load than RPM. While cruising on the highway with the 14 cm housing you will end up with less boost and higher EGTs. If you go with the bigger turbo go as small as possible 62 x 65 with the 12 or SS13 cm housing.

A new hi performance turbo is not cheap and it also requires supporting mods to really make it effective, such as free flowing exhaust and and intake. For a truck like yours upgrading to the 04. 5 turbo (just a little bigger than the one you have now) with the full 4" cast elbow (yours necks down to 3. 5"), 4" downpipe and free flowing muffler (Borla makes a nice quiet one) would probably be a better choice.

You could start with the 4" cast elbow and complete exhaust and decide on a turbo later unless you have the money for both now.

Another problem no matter which way you go is that the ECM will detect the boost is building quicker and higher than it's programed to see and you could end up with less peak power as it backs off fuel to get boost numbers where it expects to see it. So that means at a minimum a boost fooler to lie to the ecm as to what boost actually is. Another thing that would help MPG is a pressure box like maybe an Edge EZ (go easy on pressure so you don't do damage to your injectors). Higher pressure fuel atomizes better so it can burn easier.

 

[CToney]

Nellie you have some of the same thoughts that I have had. In my opinion the turbine housing is too small. My cruising boost levels should be at 4-5 psi not 8-10 psi. Also when I downshift my boost goes up. Joe Donnelly has said that boost is restriction to flow. I definitely have restriction to flow even at low rpms. Going to a 12cm housing with a slightly larger compressor would probably be what you and I would both want. I have seen adds saying that a 62mm turbo with a 12cm housing improves milage by 3-4mpg. I wouldn't get too crazy about changing your exhaust, the numbers that I have seen are only small improvements not much bang for buck. Maybe change out your muffler. We don't have a cat so we're better off than the newer trucks. I like my smarty jr, it does dynamic timing which will provide better results than your rokktech. Drop me a pm if you like.

CR Toney

 

[Kubotaorange76]

After i installed my helix 2 camshaft... my cruising boost numbers were insane. WIth my G-56 truck my rpms are higher cruising than most already. With the cam and stock turbo i was seeing 12-14psi on flat ground doing 70mph (2200rpm)... 80 mph (2550 rpm) i was seeing 20-22 on flat ground. Now with my 62/65-12 at 80 mph i see 12-14 psi... much better... mileage over 70 mph seemed to pick up about 1 mpg from what i can tell so far.



I think the cam made a huge improvement in air flow through the cylinder and drive pressure went through the roof with the stock 9cm housing. I could hit 30 psi with stock fueling at 1600 rpm in 6th gear with no load.

 

[ENafziger]

My cruising boost levels should be at 4-5 psi not 8-10 psi. Also when I downshift my boost goes up. Joe Donnelly has said that boost is restriction to flow. I definitely have restriction to flow even at low rpms.

While boost in a sense is resistance to flow, that does not mean it's a bad thing.

What is the reason for a turbocharger in the first place? Obviously, it is to boost the engine's efficiency (no pun intended ) by extracting thermal energy from the exhaust that would otherwise be wasted. Thus, the more of this energy that can be "captured", the more efficient the engine is running.

Say your cruising boost levels are the aforementioned 8 - 10 psi, and then you change to a larger turbo and can cruise at just 4 - 5 psi boost. Does this mean you're running more efficiently? No! No restriction to flow has been altered, other than the turbo. This simply means that the larger turbo is not as effective at harnessing the available exhaust energy and turning it into useable work.

If lower cruising boost meant more efficiency, a normally aspirated engine would be the ticket because there would be no restriction imposed by the turbocharger! Boost is a good thing, and can only be used as a measure of engine load when talking about the exact same charger. Therefore, it's not accurate to install a larger turbo and think the load on the engine is so much less because the boost is lower.

Rather, it takes a certain amount of power to move the truck down the road regardless of what turbo is on the truck. Higher boost numbers would indicate that more available energy from the exhaust is being utilized... and less boost with a larger turbo simply means you are operating way under the turbo's efficiency range, and much of the available exhaust energy is being bypassed due to the large exhaust housing.

If you want to lower cruising boost, the more efficient way to do this is to reduce restriction to flow in the intercooler, piping, intake manifold, exhaust manifold, head, etc. This way, you are still utilizing as much of the exhaust flow as possible with the tighter housing.

This in effect is one reason for most newer vehicles employing variable geometry turbos... so much more energy can be extracted at low power levels, and yet still be able to cool well on the top end.

There's plenty of good information around on people who have done mileage comparisons regarding multiple turbo changes... and almost exclusively, the larger turbos hurt mileage.

--Eric

 

[WoodChuck]

I have seen adds saying that a 62mm turbo with a 12cm housing improves milage by 3-4mpg.

If you really believe that you should have done it a long time ago.

In my experience ads are usually hyped up and written by marketing departments who don't really do research and slaes people will tell you what you want to hear just to sell their product.

 

[JamesStevens]

I have read that the super B turbo is a good replacement for the stock ones. They are said to be more efficient then stock and good for towing. I do not have any first hand experience, am just considering upgrading like yourself.

James 07 auto

 

[CToney]

No doubt that you are right Woodchuck about the ads. Boost does not necessarily mean power or efficiency. The exhaust manifold is a choke point and flow improvements are made by changing it. A small housing with a wastegate bleeds off an excess of energy in high boost situations no energy is obtained from this. You have to stay in the effiency map of the turbo. A slightly larger compressor (not a 64 or 66) and a slightly larger exhaust housing would be an improvement. The Cummins engineers have to design things with emissions and cost at the forefront of their decisions. People who buy aftermarket turbos most likely do so for egt reduction and power increase. They probably use that added power that takes more fuel and obtain better milage. I don't drive in the city much at all and tow most of the time. My needs are different than most I guess. I've had first gens, second gens (12 and 24) and HPCR trucks I know the power that they had and the milage that they obtained. My '03 probably has the most power but not by much over our '01 with EZ. It would get better milage though. Lighter, front axle disconnect, lower emissions, and bigger exhaust housing.