I can hardly believe I'm asking this, but at what point is it too much HP on a Subaru conversion? I'm having my engine rebuilt now, and while I had everything open and at the machine shop, decided to go with forged pistons, rods, new valves and springs as well as all the seals and whatnot. Basically, I'll have a pretty "built" motor.

Last night my builder/mechanic was asking about what Turbo I was thinking. Now, this is a shop that works on Subarus and Nissans all day long. They build 600hp WRX motors weekly, and an occasional 800hp monster. So there are a ton of options for a turbo. The motor that I'll have will support just about whatever the hell I want to bolt on.

The turbo I found that and was about to buy would put me at way north of 500. The question is...do I WANT that? Keep in mind that the turbo (AMR-CXR550) puts about 450 to the wheels on a WRX (driving 4 wheels on a car that's 1,200lb heavier.) He thinks that in the 914 it'd likely put 500+ to the wheels. I can pick that turbo up for $600 (normally about $1,500) which is the same price as a decent VF39 STi turbo. (350-ish HP)

So now I'm starting to wonder at what point I'm going to have too much HP and the "Summer Daily Driver" becomes a monster that's no fun to drive.

Opinions?

IMHO 914's over 250-275 are not so much fun. Unless you've got some serious meat in the wells, it's hard to hook up, then it's just a missle with a sloppy guidance system. Dangerous in curves, deadly in the mountains, one blip of the throttle and you're facing the wrong way

For the rest of the picture: I've got welded flares, 17x9.5s in the back, spaced out 2" each. I'll also have sway bars. Boxster brakes, and a pretty beefed up suspension & chassis.

...but I hear ya.

According to what Cobb Port told me, with the stage 2 reflash was suppose to add another 26% to the mix, so I should be about 300 ponies, but don't seem like adding more would be a problem for me, but then I've been told around 325 is where you need to start to beef things up, or things may start to fly apart with the added ponies? Just more expense is the problem.

So what turbos are people running?

I just have the stock one.

built but stock, it sounds like.

what hp would it put out without a turbo installed? 250hp

my understanding is that smaller turbo's spool up quicker and come on sooner than big turbos. that is the extent of my turbo knowledge : )

i'd talk to your builder and ask him what is involved if you go small (stock) and want to go bigger in the future?

You want to take drivability into account. I had a 2 liter turbo with a larger than stock turbo in mine. It put out a lot of power when stomping the throttle, but had little low end power. I now have a n/a 3.3 six which is nicely balanced for my car.

Stock on mine is suppose to be 250.

If the car is setup correctly, 300hp is a sweet spot. I had 500+ and it was too much IMO. In your case, look at a GT30 turbo. 350-400hp. Plenty fast for a 2200lb car.

A few months ago, I picked up an 2013 STI rated at 305 hp. Based on that car's weight and the teener's - Mike is dead on with the HP range.
Good luck with your build.

I am going to run a G20. that should be good for about 300 at the wheels. I may change it out later, but, considering all of the weight I lost off my car. I seriously have to think about putting weight back in (low).
I will be running 11's in the back and 9's up front. So, lots of meat, lots of motor and lots of brakes.

I will also be building two maps. One for the wife (economy mode) since she drives with both feet firmly planted on the floor. And one map for having fun on the hills.

thrills on the hills.

I agree with Mike. I think 300-325 is a sweet spot. Of course anything over 150hp in a 914 is a blast. My stock suby I love & it only has 160hp with no turbo. Could I use more power? Sure but I'm content for now. Will I go to a six at some point or do a turbo . I just may but I'm in no hurry. Love my setup just the way it is

I'm going to look for a VF39 then. I think that CRX550 would be way too big for what I want.

I think the bigger question should be about turbo lag!!!! The first time in my life I turned down a chance to drive someone elses car was DBCopper's car. Its a narrow body with the 2.0 in it I believe it to be a somewhat stock STi. The LAST thing I would want is a huge hit from a turbo to unbalance the car. I wish now that I had not pussed out and took him up on the offer to drive the car. I have an 06 WRX and I can only dream of the problems I would get into if the car weighted dam near 1k less. And that's only 230+

I have a stock turbo on the WRX and I feel drivabillity is a big issue.
With 7'' and 8" x 16" tires the problem I feel is with reasonable power on the low end but you have to be careful punching it out of a corner.
First when I want it to come on, I get a lag, when it does come on, it's too much like a on off switch.
One day, I would like to get back into the ECU and see if I can make the boost curve more user friendly.
If someone makes a new map for the WRX / 914 conversion, please post it.

I also just picked up a complete SVX that I'm transplanting and was thinking of a turbo more for the top end range since the 3.3 has good grunt on the low end. Should pull fine from a stop and thru 2nd, then come on strong from 40-50 on up to redline. Thoughts?

To quote, or maybe paraphrase, the late, great Mark Donohue, "When you can burn rubber from the exit of one corner to the entry of the next, THEN you have enough horsepower!

The Cap'n

So with my Hydra EMS ECU, and an electronic solenoid on the wastegate, I can control the boost curve a little better than normal. The stock WRX TD04 turbo has a curve that puts the boost in at about 3,600, while the VF39 starts at about 2,800. I'd rather have boost earlier than later. (like the TD05 turbos are known for.) If I keep the hot-side under 8cm, that'll make it spin up a lot quicker too.

the good news is, this is a relatively easy thing to swap out, and there are literally hundreds of options, so I can tweak it over time if I feel the need. If the stock turbo I have now didn't have shaft-play, I would just put it in there. But since I'm literally having every-other-thing done to the motor...now is the time.

With great power comes great responsibility....

This video is relevant and I think demonstrates two interesting points:

1. If you're gonna over-do it, don't hold back.

2. It's okay to over-do it if it's over done well.


https://www.youtube.com/watch?v=KB1Wrv0SiyQ

The great thing about the VF39 or V43 is they are a dime a dozen used. All the STI guys are selling them to upgrade. You could argue a Tomei ARMS turboN7760 is far superior, but not 4 x the price superior.

For me the decision would depend on the use of the car. For track only I might go big on horsepower, but for a street driven car my decision would be dictated by the ability to run pump fuel. Regular gas would give one answer and premium fuel another answer in possible horsepower. With a turbo car (I have owned 5), you can make lots of additional horsepower by turning up the boost and have the proper mixture, of course, but at some point you are going to have to run race fuel - very high octane rating and very expensive.

With a small displacement engine, producing high horsepower can be relatively cheap ($)(to a point) by turning up the boost, after that your options are spinning the engine higher ($$) and/or increasing the volumetric efficiency ($$$).

Steve

Turbo cars are like hot women. A little edgy, every guy wants one, some guys can't handle them, and if you throw a little alcohol in them they'll rock your world

I would say that anything over 250 starts getting into the truly dangerous territory in a 914, but with the right restraint, it is a hell of a ride.

Also, over 200hp, I'd start looking into chassis weakness abatement. I'd tie the rear inner semi trailing arm mount to the firewall, I'd reinforce the semi trailing arm, i'd look into a 914 GT stiffening kit or something to deal with the inherent weakness between the hell hole and the shock tower in the rear.

An engman long kit would also help greatly.

Good luck, have fun and don't kill anyone else if you f' up.

I've just done a fair bit of reading on the td05 range for Subaru setups. Seems the common call is for 18g on the street and 20g on the strip
The 18g is good for 20 odd psi which is probably going to have trouble in a stock type setup in a 914
I'd go small and pull boost on early
I've just ordered a td05 16g for my daily car and its still rated for 300hp max

That would be my advice too. Big turbos and big dyno horsepower are great for bragging, but a balanced car is more fun to drive. And unless you're a seasoned racer on a track it's probably faster, too. Mine will do a high 12 quarter mile, which translates to spinning through second and a good part of third. When you're traction limited (and not Mark Donahue) more power only shows up as top speed, which isn't the 914's real strength anyway.

I am sorry, there is no answer to this question

Driveability is why I went with a Factory Motronic 7.5 ECU and drive by wire. When tooling around town the car runs like a stock Audi/VW motor should. I have no jumpyness or peakyness at all. Perfect idle. Just an all around great running motor.

I had the tuner (his recommendation) remove my electronic boost control AND my manual boost control. The ECU controls the boost but is re-mapped for higher boost levels. This keeps the boost stable and the ECU can then compensate for any variables. It works great! The boost ramps up to 20psi and stays there. I get full boost by 3000 rpm and it holds 20 psi all the way to redline.

I went with a Garrett GT2860 "Disco Potato" turbo. This is the smallest of the "Big Turbo" options common to my engine. I also have a 4" exhaust so there is no turbo lag. the boost comes on quick and steady WHEN I WANT IT. I could have gone with a bigger turbo but that would be more than I needed for my HP goal; 300+ hp.

A turbo is most efficient right before it maxes out. My turbo is rated for about 350hp. So the 2860 is perfect for my setup.

Your setup is a personal choice. My recommendation is put the smallest turbo that will suit your needs. Find a turbo that is in common use with your engine. Find a tuner that is familiar with both your ECU and turbo choice. Install a good intercooler or meth injection system. I have both.

300+ HP in a 914 will either put a smile on your face or terrify you every time you drive. Make sure your chassis is setup for the power. My car was a former road racer so the suspension and brakes are designed to go fast and stop. I also have a roll cage to stiffen everything up. My 930 turbo brakes are overkill for most 914's but not overkill for my HP level. doesn't matter how fast you are if you can't stop. I also run 245/50/16's in the rear and 225's in the front. You must have grip or you won't go fast or slow down.

Hope some of this helps...

Seems like you could adjust a throttle curve to handle anything. If you are in 5th and want to pass, how is there insufficient power? It's in the delivery IMHO.

The pro's about a large turbo would be that you can start small with your boost and slowly up the power. Especially if you get a turbo that can be run at really high boost.
I have a Comp Turbo tripple ball bearing that efficient to the upper 30's PSI range.

I have full boost between 3500 and 7500rpms giving me 4k rpms of working range, on the wastegate it makes 10psi and about 275-300hp. On 35psi with some good gas I'll probably be making 550hp. Out of a 1.8 Audi engine...

I would say only get the turbo if you dont mind a little bit of lag.

You can also get an electronic boost controller, lower the boost in first gear(subaru trani, dont use first on a 914 trani) all the way down, and slowly raise it each gear so that you have enough power to just barely spin the tires in first and have just enough grip in the rest of the gears to keep it going, but each gear will be more and more powerful (Basically making the car as fast as your tires will allow it)..


Something to consider.

Not so much throttle cure as boost control. With a proper ECU controlling the boost levels, you could dial up or down the boost levels for a given load or rpm.

I can pass in 5th without any problem. In fact, I can pass almost anything in 5th without a problem.

In many cases, the driver runs out of ability before he runs out of power.

The key is to have smooth power. Then it is controllable and somewhat safe.

I don't have boost lag. Smooth from start to finish.

I think around 400hp is perfect.

Your also capped at around 160hp without head work or lots of boost

^This was the reason why I liked that particular turbo in that car... It was simply amazing at autox courses. Come out of a corner and stomp on the gas, and it was like I was driving a v8.

i was gonna ask how turbo works then found this video.

https://www.youtube.com/watch?v=zenMEj0cAC4


OT - nitrogen - I did not know.

https://www.youtube.com/watch?v=SJs_64Aj4Ho

Just so everyone has the rest of the picture:

Chassis: GT Flares, GT Stuffening Kit, Engman Long Kit, firewall to Trailing arm bars, Trailing Arms tube'd.

Brakes/Suspension: Boxster Front/Rear. 911SC struts, Sway Bar, all new bushings/bearings. 930 Tie Rods. 17" boxster rims (8" & 9.5")

Engine mods: Completely stripped, machined, honed. Wiseco Forged pistons. Mahle Forged Rods, King Bearings, Forged pistons, titanium guides, and all new seals. Lightweight crank and alternator pulleys. new oil pump, Water pump, oil uptake, air-oil desperate, fuel rods, 750cc injectors and alternator. Hydra EMS 2.7 ECU with a new custom wiring harness.

Exhaust/air: Perrin Equal Length Headers and up-pipe. (Both ceramic coated) Divorced down-pipe, TurboXS 3" inlet exhaust, and an air-water inter cooler.

The turbo is the only missing piece. I think the VF39 is likely the way to go.

I have 500+ at the flywheel and 476 ft-lbs at the wheels. My problem has been transmissions and half shafts. I ripped out 4th gear from four 901 transmissions and one Subaru 5 speed transmission. I have a Garrett GTX3071R Turbo which is working well with 25 lbs of boost I have little lag. Attached is a dyno & torque sheet.

Since the 914 transaxle is rated below 300 hp and even less torque(depending on the gear) I`d say your plight shouldn`t be unexpected. That`s power that, assuming you want to stay with Porsche boxes, 930 territory, with 108mm CV`s and custom axles.

Yeah, that's why he upgraded to the Subaru 5-speed, but then broke that too, which is impressive. And both were fourth and fifth gears, I think he mentioned going up the hill at Sears Point. One more reason for me to be perfectly content with half that much horsepower.

no such thing as "too much horse power"!

the key is drive ability!

if you cant touch the long pedal for fear of things going scary crazy then the engine isn't built right for your application.

but if you built the turbo motor and sized the turbo to be usable then you could build huge power.

put a big ass turbo on a set up that's wrong then you end up with a time delay monster. build a strong motor with a turbo sized right and the proper controls and you have a lady on the streets and a wild siren on the track.

the biggest factor of "too much " is the idiot that controls the long pedal!

Anyone in SoCal remember Crazyhippy?

He had a WRX motor in his a few years back. I did a search and couldn't find his posts.

He was running tests with ECU tweaks and different octane. Was putting out big numbers.

Got his car sideways somewhere and it bit him. I believe he was ok. I think he may have deleted the posts.

Let's be honest, even with ~100hp, these cars are better than most of the drivers here.

I'm going to err on the side of a smaller Turbo. Thinking the VF43 will be perfect for me. It's the same as the VF39 that's in the STI, but has a beefier hot-side so the waste crack isn't an issue. They only made it in 2007, before the upgrade to the 08 engine. I can get a fully rebuilt one for under $600 and be ready to rock-and-roll.

Nice. Looking forward to numbers!

I was going to ask about turbo lag.
seems like only way to minimize it is with smaller turbo.

video

https://www.youtube.com/watch?v=c_IFh_6bpUo

You're right, of course, but true or not the macho in me won't let me admit to 100hp. Lowest I'll go is 250.

And yes, the ex may have been right about that.

Turbo lag can be reduced by the following.

Ceramic ball bearing turbo's
Billet aluminum wheels and better metal technology
Better fin design technology
Twin scroll exhausts (two cylinders that fire at the same time feeding the same exhaust side giving more push per combustion)
Appropriate sized intercoolers, intake and exhaust piping.
More aggressive timing, and better gas

A combination of all that, with a smaller turbo that can be run at a higher boost more efficiently, IE if one turbo is efficient to 20psi but a smaller turbo is efficient to 35psi and therefore can make more power up there, you will have a gain in power and boost response.


Then there are antilag systems, but this is not something for a street car.

Variable vane turbos also