Honda D Series Forum banner

1 - 20 of 44 Posts

·
Registered
Joined
·
79 Posts
Discussion Starter #1
Sup everyone,

Im researching for my DD turbo build (D16z6 w/ s20, 94 eg), I was looking into a quick spooling t25/t28, but would this mean I would be in boost cruising on the highway at 65mph or would I be better off with a bigger t3/t4 hybrid that spools later??. Since it will be a DD i dont wanna pushing too much boost just cruising (I dont want like 15mpg) but at the same time want something that spools quick. If that makes any sense. Any input appreciated.

thanks
 

·
B-series Destroyer
Joined
·
912 Posts
Turbo's spool under load. So unless you are holding the brake or using the tiniest turbo ever you should not be boosting.
 

·
Registered
Joined
·
3,720 Posts
You could have the smallest turbo possible (within reason) and you wont be boosting while cruising.
That being said, with a T28, as soon as you start to crack the throttle you will start to build boost.
 

·
Registered
Joined
·
79 Posts
Discussion Starter #4
oh ok that makes sense, but would you reccommend one over the other as far as fuel economy is concerned? I know alot of other factors are involved (tune,injectors,etc) but I do alot of highway driving. thats my only concern.
 

·
Registered
Joined
·
253 Posts
i had a t25 on my DOHC ZC and i got 39mpg highway in my 2400lb eg sedan with AFRs tuned to 15.5:1 on the highway. from what i've seen, smaller turbos tend to get better mpgs because they create more heat promoting better fuel atomization and creating a less dense intake charge which requires less fuel. you will definitely not see boost during cruising unless you cruise at 90mph. if memory serves me right, i was cruising at 14 inches of vacuum at around 65mph.
 

·
Registered
Joined
·
79 Posts
Discussion Starter #9
i had a t25 on my DOHC ZC and i got 39mpg highway in my 2400lb eg sedan with AFRs tuned to 15.5:1 on the highway. from what i've seen, smaller turbos tend to get better mpgs because they create more heat promoting better fuel atomization and creating a less dense intake charge which requires less fuel. you will definitely not see boost during cruising unless you cruise at 90mph. if memory serves me right, i was cruising at 14 inches of vacuum at around 65mph.
this is exactly what i needed to know. I looked through your build thread, looks nice. Im going to be going with a similar route. thanks
 

·
Registered
Joined
·
6,365 Posts
No boost while cruising. Turbo size does not effect mpg the way your thinking. Its more of hp and your foot. But mpg is all n the tune and driving habits.

Also buy yourself a boost gauge(reads vac and boost). Install it and drive around. When that gauge hits 0inhg, thats when boost will start to build. Turbo size to rpm tho, small turbo will start when at 0ingh and like 2.5k rpm, while bigger turbo will sit @ 0inhg till the rpm get to like 3.2k then it builds pressure.
 

·
Registered
Joined
·
1,757 Posts
i had a t25 on my DOHC ZC and i got 39mpg highway in my 2400lb eg sedan with AFRs tuned to 15.5:1 on the highway. from what i've seen, smaller turbos tend to get better mpgs because they create more heat promoting better fuel atomization and creating a less dense intake charge which requires less fuel. you will definitely not see boost during cruising unless you cruise at 90mph. if memory serves me right, i was cruising at 14 inches of vacuum at around 65mph.

You have it somewhat correct. Somewhat.

The smaller turbos dont create a better atomization of fuel. You are pretty much correct that a less dense intake air charge requires less fuel.

Any air in the motor getting compressed is going to make heat, especially when you add addtional pressure to atmostphere.

But atomization is controlled by where your injectors are placed, the fuel pressure itself, the injector design/spray pattern, and the way the a/f is drawn into the cylinder.

Your mpg is going to be tied (like was said)to your tune and driving habits. How lean they run it and the timing at little/no load. Your gearing will also make a difference in Mpg.

There are guys out there with large turbo's that are getting high MPG's as well.
 

·
Registered
Joined
·
6,966 Posts
You can get great mpg with the biggest turbo. Just because you have a big turbo doesn't mean the mpg goes down while cruising. It will acually stay out of boost more so it should get better mpg than a small turbo setup would unless your always in boost.
 

·
()*#$(*$
Joined
·
11,404 Posts
I got 35+MPG untuned with my DOHC T25 setup. The only time you get into boost on the highway is when you open the throttle up. At normal cruising, even at higher speeds, you don't need to keep the throttle open past the point where the engine generates enough energy to spool the turbo so that it is pressurizing the intake. This is true even at triple digit speeds, though, above a certain point, the car's aerodynamics takes over, and you will eventually get to a point where the drag on the car forces you to open the throttle enough to make enough power to overcome the drag, and you might get a little bit of surging. Might.

Also, for the record: Almost every small turbo engine I've tuned (T25/T28/T3) has a boost threshold under 2K in most gears.
 

·
Registered
Joined
·
361 Posts
just turn the boost down to 5 or 7psi and it should help with your gasmilage. your motor will just flow easier making it more efficient
 

·
Registered
Joined
·
79 Posts
Discussion Starter #17
that makes sense thanks for all the help everyone, this is one less thing i have to worry about.
 

·
Boost Gets You Laid
Joined
·
4,402 Posts
As stated above, my car does not spool unless there's load put on it(i.e I pass or a decent hill). Running a TD05H 14g greddy kit, 2.5in DP, no cat, 2.5in Skunk2 cat-back, RC 650s, DX trans.

32.96MPG if I drive like a sane human, 28.5MPG driving like an asshole
 

·
Registered
Joined
·
79 Posts
Discussion Starter #20
As stated above, my car does not spool unless there's load put on it(i.e I pass or a decent hill). Running a TD05H 14g greddy kit, 2.5in DP, no cat, 2.5in Skunk2 cat-back, RC 650s, DX trans.

32.96MPG if I drive like a sane human, 28.5MPG driving like an asshole
thats good to know, how are you liking the 14g?
 
1 - 20 of 44 Posts
Top