Phatscion

as far as i understand, the 1NZ-FE has a compression ratio of 10.5:1. I was under the impression that this compression was too high for a turbo boosting over 8psi. I was also underthe impression that with the cylinder pressure being as high as it is with this engine that the supercharger would be usefull contrary to most low displacement engines. I guess my question is this.

With the scion, which route would be more beneficial regardelss of whether the car was a daily driver or not?

Im assuming that the compression does not need to be lowered in order to add turbo to the engine.


PJ

jackmott

Turbos and superchargers do exactly the same thing, in different ways.

They both force air into the engine at higher than atmospheric pressure.

The pros/cons of a supercharger vs turbo for the scion are the same as with any car.

roots/screw supercharger - boost at ALL rpms, instant throttle response
centrifugal supercharger - boost rises as rpms rise, instant throttle response
turbo - most peak power, but can get turbo lag/poor throttle response. also typically trickier to tune/setup

hard to say what the peak boost the engine could 'safely' handle. far more variables than just the compression ratio. But I can say, that 99% of the time, adding boost to an engine that wasn't designed for it is goin to cause something to fail not too many miles in the future.

its_ikon

http://www.speedoptions.com/articles/3682/

Phatscion

what about the compression on the scion though, are you saying that you wouldn't have to lower it. i own a 94 probe gt which is a 2.5v6 and i know i have to lower the compression on that car which is a 9.5:1 in order to boost anything above 6 psi. this is even a higher compression but a much smaller engine. does displacement have anything to do with with how much you can boost?

jackmott

hard to say, you could certainly run some amount of boost, the question is how much?

The danger with high compression is usually predetonation. When the air/fuel mixture gets hot and compressed enough, it will explode on its own without the spark plug starting it. That is BAD.

Fuel octane, compression, boost, spark timing, air/fuel ratios, cylinder head shape, intake air temperature, can all play a role in when that will happen.

The other concern is if you just plain start making too much power for the stock internals.

My guess - an intercooled 6psi setup would probably be fine if you ran 93 octane and had the cars timing and air/fuel ratios carefully controlled.

Keep in mind there is a downside to low compression pistons, and that is a loss of low rpm power.

scionxb04

they say a perfect turbo setup should do about 10hp per pound of boost....welcome to the real world....more like 7-8hp.....even so at 8psi thats more then a 50hp boost....more power then u need in this thing.....
my 2k civic si stock put 138hp and 118ftlbs of torque to the ground.....with I/H/E afc and obd2-obd1 conversion with p28(jun program) could hit 15flat on street tires and lower on slicks.....

Phatscion

whats the fastest you see this thing running with an 8-10 psi boost?

jackmott

who is they?
they would be a complete idiot if they said that.

The amount of horsepower you make depends on the volume of air, not the psi.
A better rule of thumb is this:

atmospheric pressure is approximately 14.7psi

when you add 14.7 more psi you have essentially doubled the pressure and hence the volume (not entirely true due to heat and such, but its close)

So typically a car running 14.7psi will make twice as much horsepower.

so around 8 psi youll make 50% more power.

so you would expect a scion at 8psi to make about 150 horsepower


whereas, a z06 at 8 psi would be making about 600horsepower. thats a 200horespower gain. Thats way more than 10 horsepower per psi

DibujoB

we're running about 5-5.5psi on our supercharged xB, and so far it hasn't blown up yet :D

I'm pretty nervous to up the boost much more than that though. These cars were not built to go fast, and unless you want to do a motor swap (let us know how it goes) or spend about $8000 rebuilding the engine from the bottom up, I wouldn't recommend boosting that much.

Phatscion

did you dyno the supercharged xb yet?

DibujoB

no, not yet. We were hoping to do it this week, but the store's been really busy. Getting time off to do anything, even if it's for work is impossible.

Phatscion

Has anyone run their car yet?... What would it take for this car to run 14-15psi...(turbo)

DibujoB

According to 1 theory I've heard, about $5,000 to beef up the motor.

Sevedd

Well this is my first post here. I don't own one yet but I am looking to get the XB for my wife. I own a 96 Integra LS/Vtec with a compression ratio 12:1 and I am boosting 8psi. My wife has a 98 Civic Ex SOHC with an Apexi BB Turbo pushing 9psi. Both cars are stock bottom end. Now I noticed that the XB has pretty high compression for a 1.5l so I was a little concerned about boosting it, however if you notice I am doing a lot more on my teg. The key is tuning. The only hold up I am assuming from TRD is what psi that they feel safe backing and if the psi is low then can they justify the price of the supercharger/turbo. The key will be tuning, and with the engineers that they have I am sure this will not be an issue..

jackmott

funny how not a single OEM produces a car with 9psi of boost and 10.5:1 compression ratio, despite their huge resorces.

they key isn't tuning, the key is that everyone does this stuff and it lasts about a year and in that year they tell everyone how safe it is =)

Sevedd

LOL :D Yeah I guess it's funny that way, so far it's almost 2years for my wife's car and the only repair is a walbro 190 fuel pump in order to take care of the 440cc injectors. I am sure they will probably not take a chance with 9psi, if we are lucky it will probably be the same as greddy recommended psi for other vehicles with the same compression which is 6 to 7 psi.. Not a lot but I don't think the kit will be for breaking records, just to give the XB a little bit more umph.

BigOrangeXb

Since no one makes internal parts for the engine yet, I'd say cryotreat the crank, pistons, and rods. Get the rods shotpeened and polished. Have the pistons Swain Tech coated with their Goldcoat top coating and PolyMoly skirt coating. That should help the bottom end live with the added pressure. You could have all that done under $500 (if you do the labor of tearing it down and rebuilding it).