Turbo 4 cylinder?

[Racer-X]

What is the advantage to a turbo 4 cylinder? Our team runs an N/A f4i and we make about 90 peak horsepower and are already at the choke flow of the restrictor. I don't see how it would help a whole lot, especially when you figure the turbo doesn't spool up until 7,000 RPM and then it has maybe 3,000 RPM of usable gain before the motor hits the choke flow anyway.

Is it for a bit more bottom end?

[RaceCatt69]

torque, efficiency, sexiness

[Racer-X]

I can see torque and cool factor. But I don't know how it can be more efficient.

[AxelRipper]

It exploits the rule regarding only introducing one fuel into the combustion chamber by introducing oil into the A/F mixture, thereby allowing you to use less fuel.

[Rex Chan]

More complexity, more weight, less reliability for more power you can't use and don't need. Win-win!

Turbos aren't worth it at FSAE-A from a power standpoint, regardless of costs (track is too tight), and probably not worth it overseas from a laptime/points gain vs team effort cost. Too much hassle to tune as well.

[Racer-X]

Rex, that's what I was thinking too.

[Jon Burford]

Rex, your right in a way...

[Jon Burford]

You can radically change the way you use the engine. It's up to you if you decide to do that.
you could for example increase torque at lower rpm's, change your final drive ratio and reduce your max rpm.
there are many possible options. but they basically boil down to being able to control the saturation of your restrictor.
It's up to you to evaluate if it's worth doing.

I will not comment as to my own opinions with regards to Turbocharged 4cyl engines in FSAE. but you can probably work it out.

[jlangholzj]

Originally posted by Rex Chan:
More complexity, more weight, less reliability for more power you can't use and don't need. Win-win!

Turbos aren't worth it at FSAE-A from a power standpoint, regardless of costs (track is too tight), and probably not worth it overseas from a laptime/points gain vs team effort cost. Too much hassle to tune as well.

for a 4-cyl yes...maybe worth it on a single....but I just want to argue with you rex http://fsae.com/groupee_common/emoticons/icon_smile.gif

you do bring up a point that nobody seems to get though....you don't need it! Has anyone who's looked at putting a turbo on their car actually looked at where they were traction limited? does the added power really gain you anything or does it just cause a bunch of tire spin?

hmmmmmm......

[Charles Kaneb]

The old Cornell turbo fours had it all - an extremely broad powerband to shove it out of corners in endurance and autocross, enough peak power to win acceleration, and mapped so well they didn't suffer much in economy. The turbo reduced pumping losses and allowed that broad powerband.

They were heavy, which didn't matter as much on old, hard 13" tires as they do on the sticky 10s.

[Jon Burford]

Our car is turbocharged and does not suffer from wheelspin. A difference of situation I guess.

[MCoach]

It seems that, from a reliability stand point, isn't one of the best choices, especially if you are considering E85. From a "dyno queen", both of these would make a great combo. However, this is FSAE and there is more to life than be the guy on the forums who can brag "I make 105hp out of a turbo f4i" or "I make 60hp on a N/A single."

There are trade offs in the way things are used. You can do an analysis on the engine with respect to competition points and what measures would need to be taken (lap sim?).
Does it improve how easy (or difficult) it is to drive the car? Does it increase oil consumption to two-stroke levels? Again, it doesn't matter to have a strung out engine if no one can drive it, keep that in mind as you are chasing that tune. Does it integrate into the concept of whole teams car well? Was the car built like Maryland's old car (massive wings and a 4), their new car (massive-er wings and a single)?

Just the start of the questions to ask yourself.

It's not all about horsepower, the engine is not the one godly thing that cannot be compromised.

[Rex Chan]

As an engine guy, I'd go so far as to say the most important things about an FSAE engine are:

1. Reliability (starts, runs without question in testing and comp)
2. Driver control (should be reponsive, must be controllable)
3. Fuel economy
.
.
.
10. Power

[Jon Burford]

I agree perfectly with Rex and MCoach. Which is why we have a turbo.
Our enduro restart fail was down to a mistake I made when tweaking before comp accidentally resetting some of our start comp cells to zero. The single most stupid mistake I think I have ever made and I will never forget. That aside we have had genuinely no reliability or starting issues. Just a mistake.
My genuine opinion on turbocharging is that as MCoach says, it has a time and place. I believe our car would suffer heavily without the additional torque the turbo provides and the CVT needs to work. The CVT operates in a very slim RPM band, the point at which I have peak torque and power. It make the car brilliantly drivable, and fairly fuel efficient, estimated 1.5 litre saving over the CBR we used to use (although it was overly thirsty.)

It is what it is. I would not go and try and justify it though, I think it's a long road to go down if your going to get minimal gain.
As for oil consumption. I don't know about other teams, but we don't really use any. obviously there are oiling issues with the turbo seals. but everybody sorts that out pretty quickly I would think?

[Mbirt]

Jon, how much CVT work was required to match the ~3000 rpm engine speed reduction?

[Jon Burford]

The genesis engine has a 2:3 internal reduction. Output shaft speed is less than crank speed.
With regards to shifting, thus far we have changed the primary and and secondary springs, flyweights and cam.
The engagement is low at the moment ~3000 rpm and shifting is up to 8500.
we then have a single chain reduction onto the diff.

[Racer-X]

Jon, I wonder how much the CVT changes how you tune. I talked to the UNM (New Mexico) guys and they said they just shoot for peak power and tune the CVT. Which sounds like my kind of deal.

Right now we are looking for more mid range torque. We were actually thinking about running a turbo but then realized the complexity offset the gains over a good cam. So I was poking around to see how other people felt.

[Jay Lawrence]

Racer-X,

Wollongong ran turbo F4 for several years with great success, but it's not a simple thing to do and it's extremely hard to justify (unless (like Jon) you run a CVT and tune for a certain efficiency peak that you don't stray too far from, which we didn't). With some tricky turbo management you can get it spooling well before 7000rpm and as efficient or more so than N/A, but as Rex said, you just waste it all in wheelspin (or traction control).

Be careful with cams. They will gain you nothing like a properly done turbo, but if you can find a California spec F4 cam you're on the right track... Then tune your runners to suit your lower RPM goals and you will have far more power than you need in a simple N/A package.