No_jdm_fanboys

Hey guys I've posted before about turbo stuff still piecing a setup together. Just wanted some feed back from you turbo guys.

My question: is it unrealistic to want some better hp numbers then stock and expect 20-25 mpg on hwy?

The motor it will be goin on is my hybrid b18a bottom b18b head with a overhaul when turbo is installed. I've looked around but no one really talks about mpg when They turbo I would like to retain stock rev limit (as I never rev to red line ever) and as much of the stock motor as possible money is no issue.

That being said I don't want to be dumping 10g into a motor one could get an impressive dc5 for that anyways thoughts?

2kdrift

...so money is an issue

F22Master

With a good tuner, and the right setup, some have seen great MPGs, both city and highway.

BUT, there are MANY factors that come into effect here. Just a few are:
Gearing (=rpm @ cruise speed)
Turbo size
Compression ratio
Turbo spool rpm (when the turbo creates boost)
Engine efficiency
Injector efficiency (older style injectors wont get the same MPG as the newer designs will)
and the list goes on...

wantboost

iTrader: (2)

That isn't really a hybrid motor... It's still a straight ls...

justYncredible

iTrader: (1)

Co-sign
When I saw the word hybrid I thought it was half electric.

turbomaniac

with n/a mod and +20 hp, it is possible even lower consumption than stock.

meny people wants power and low petrol consumption. Thats only possible with direct injection petrol engines

wantboost

iTrader: (2)

i could care less about mpg, when it goes empty I fill it back up. That's the way it always works. It's not so bad on the cars that take 87 but when you're filling up multiple times in one day with 100+ octane it kind of sucks but that's what it takes to make power sometimes. Don't even get me started filling up on diesel, meh.

if you stay in boost all the time obviously you'll have **** mpg.

m4xwellmurd3r

I feel the same way. I only watch my milage to know if somethins up like an o2 sensor going bad and cause I don't trust my fuel gauge. Ill be usin e85 so ill be keepin a close eye on that gauge once I make the switch. (Got a pump like, 2 blocks from me)


And turbomaniac, what you said is absolute bull.
High power and lower fuel consumption is absolutely possible.
Out here in az we have a tuning shop called forced air tech. They built a subaru with an amg supercharger and a twin turbocharger (twin charged with electric clutch on the super+bypass valves) they were able to tune it well enough that they were pulling better than stock mpg and making some awesome power
(Yes, twin turbo and supercharged. These guys are nuts. I wanna post a link but they changed their site)
Its all in the tune, and your right foot.

wantboost

iTrader: (2)

**** our 650rwhp c6 z06 still gets over 25mpg on the highway.. running 93 or oxygenated 100 octane and it's a 7 liter v8. it's all in the tune and gearing.

m4xwellmurd3r

Exactly. Its all in the tune, gearing, and driver.

I hate all this nonsense of power=crap mpg and high comp=bad for boost.

Sometimes you can have your cake and eat it

wantboost

iTrader: (2)

I still like to put street tires on the z06 and go trolling, when we street drive on our road course slicks people don't even mess with us lol.

no matter what we drive on we get decent mpg even though street driving is rare now since it's 100% a track car. although there is an mpg decrease with the slicks, given their much bigger contact patch and stickier compound... even though they weigh less than our street tires/wheels.

Schister66

My old turbo GSR used to manage 25-26mpg highway on E85...i think its realistic to expect the same or better with pump 92-93oct. As everyone else said, it comes down to the driver, the setup and the gearing. I was running an S256 on a 9.8:1 LS/VTEC and it would hit full boost ~38-4000rpm which was my cruising rpm on the freeway. On a previous setup with the same car on pump gas, I had seen nearly 30mpg on straight interstate.

wantboost

iTrader: (2)

Yea it really comes down to trans gearing (forward gears and final drive) on top of that you need to consider wheel diameter and weight as well as tire size, weight, and compound. by default a stickier tire like an R888 will lower mpg slightly because the tire has a large contact patch for its size (typical of most sticky dot rated tires) and its compound means a higher coefficient of friction which also means more rolling resistance.

a b series using a b16 trans will have much lower mpg than one using say an ls trans due to the differences between the forward 5 gears. you can change this a bit by playing with the final drive and tire sizing but there's no real way to get around the physical gearing.

m4xwellmurd3r

Thats one of my reasonings for keeping the ls trans when I go turbo. I do a lot of highway driving so those long gears will help.
Also the twisty roads I drive on put me in upper 2md gear. Even with a shorter ratio I would end up in a worse situation by having to shift between 2 and 3 even more

mangina

31mpg on the hwy. for me

kyden

i can get over 30mpg if i baby it. ls/vtec, gsr transmission, pro1s. i suspect i can do better if i had cams with smaller primaries.

turbomaniac

check the consumption of audi TTRS 350 hp at highway and you will understand what i mean...

TheShodan

iTrader: (14)

Not really. Its about the amount of injector duty cycle and more importantly engine load for a given driving style. one can have a GS-R or B16 transmission and get fine gas mileage. (Drove my older EM1 daily for 8 years, at 70 miles per commute before semi-retirement) and even when turbocharged with small turbo, there was slightly lower, but good gas mileage.

Crusing hwy commuting speeds are not the best test for mileage because the engine is barely under engine load. When we switched from the B16 5th gear to the LS 5th gear, we found very little change in hwy mileage. In fact, we took it out because we were tired of shifting up to a higher gear just to pass someone when we didn't want to "blow by them". Which is why the whole LS transmission is "better for boost" argument rarely ever held water unless you had a full LS in which the rest of the short block was catered to lower rpm torque.

So what does this all mean? 1) If you want over 300whp one way or another, forget your OEM gas mileage; get another car as a commuter if you're so concerned about that. 2) smaller turbochargers that are being utilized in hwy driving can positively effect mileage; if the purpose is not to gain power and just to keep the turbo in its usable range of lower end torque. Which is why you see so many newer cars with smaller turbochargers.

When you get over 300-400whp, MPG is the last thing you or a tuner would really worry about. .

Muckman

iTrader: (2)

Are people under the impression that you're in boost all the time? No. When you are driving at low load at hwy speeds you are in the same part of your vacuum map as you were without the turbo. It can be tuned the same, or even leaner.

F22Master

That is false. My friends stock ls turbo, gsr trans, t3/t4, is at atmospheric pressure @ 80mph. And any twitch of your foot sends you into boost. Where as my b16 was well in vacuum.

TheShodan

iTrader: (14)

Exactly. Engine load plays a BIG part in the partial throttle tunin.

Again, its because he went from 0 load into positive pressure. Do it with a small enough turbo like most 50/57/60 trims and you're going to be using fuel. especially at 80mph. that's to be expected. If he were at 70mph with no load, his MPG would go up.. just like in an NA car, because he's lower in engine load, thereby, less vacuum.

Anyone can go 90mph and the car will be in load since he'll be over vacuum.. You've actually proved our point here. Morning WIN.

wantboost

iTrader: (2)

That's the price of being a rockstar

wantboost

iTrader: (2)

I know when I get my 11:1 gt2871r lsvtec done that I'll spend most of the time on the highway in boost... that's just the nature of the beast. mpg never even crosses my mind.

F22Master

This is the part I am disagreeing with. Even at 70mph, his LS turbo has less vacuum than it would NA. We have tested that.

F22Master

No, at cruise, at anything over 75mph, he is at 0 vacuum. Even at 70mph, he has much less vacuum with his turbo than he does with his turbo disconnected (disconnected intake pipe).