Ryde _Or_Die

I was wondering how much boost I could run safely. I am going to have all the mods in my sig. I should have plenty of fuel and a good intercooler so could I run to 15psi or is that too much?

hIGGI

iTrader: (7)

From what i heard u should not go more than 14psi on stock or hybrid turbo..as long as u will be using center housing u are limited to those numbers..

NRA T2

if you want the turbo to last I wouldn't run more than 12 personally

Ryde _Or_Die

Hmm, what if I just went to 15psi for runs at the track? Just like a couple runs a month? I am going to buy a S5 turbo in not too long but don't want to be forced to buy a new turbo. Would rather be ready for it.

TBoost

Why do people ask this question? You very rarely overspin your turbo. The main problem is the fuel for the turbo. Running on pump gas with a turbo running high boost is the biggest cause of engine failure. You can run 20psi of boost safely if you have the fuel. The HT18 is capable of that.

You will run lean way before you overspin the turbo..

-M

Ryde _Or_Die

Oh ya? I was hoping so. I can get some 100 octane leaded gas at a gas station nearby so that wouldn't be a problem. And I believe with the walbro, fcd, s-afc and 720cc secondaries I have plenty of fuel.

TBoost

Yea, especially on a stock turbo.
Take the boost up a little...make sure you have an air/fuel ratio meter just in case.

One of the main concerns is the oil seals in the center section. These seals should hold up (if they are new) at very high speeds. Most blown turbos are because they have had miles on them before. I run an HT18 center section with T04E compressor housing and wheel at 15psi consistantly with no problems of leakage.


-M

Ryde _Or_Die

I won't have an a/f gauge but I'll have my egt gauge and will have been on a dyno to know what particular e.g. temp.= in a/f ratio.

BlackRx7

you lucky man I got a shitty a/f gauge, man you always have the best wish list of mods for money straped fools like me and you, I run 10-11psi at the track on 103 octan with stock injectors and s-afc

Ryde _Or_Die

Are you talking about me?

Tec

Drop your skirt, grab your *****! and turn the boost up! I'm not going to tell you " your turbo might blow because is's old and can't push 16psi" you just bought a ******* awsome I\C thats could eat a small child! Your at the next level! **** the mustangs,or whatever rice rolls around your town, go blow the doors of some **** FD or better yet!! some other TII with 720's,Safc walbro pump but still running 7psi!

I'm tired of seeing all the FD guys running 20+ psi and making 450+hp!! where's all the mean FC's??????????

DaleClark

iTrader: (55)

OK, now we got all the misinformation out in the open...

A *stock* turbo will do MAYBE 14-15psi with the wastegate disconnected - that's as much as it can put out. It physically can't do any more. About 13psi of boost is about as far as you want to *reguarly* run it and still keep the bearings in one piece.

A hybrid turbo is a whole 'nuther story. Remember, with turbos, QUALITY is as important if not more important than QUALITY. A good upgraded turbo can make the same amount of boost with lower shaft speed than a stock turbo.

Trying to run more than 12psi or so on the stock turbo really won't get you much - you're just whipping the donkey at that point. The turbine becomes the restriction, and the engine can't get out all that extra air you're pumping in and starts to choke.

Regardless, the stock turbo is going to top out around 250-270hp. That's all you're gettin'.

Geez, seems like more people around here would know this kind of stuff - "YO DAWG BOOST THAT JUNK" has gotta go.

Dale

DaleClark

iTrader: (55)

Uh, yeah.

The FC's with 450hp are out there DOING it, not sitting in a forum going "BOOST THAT SHIZNICK FOO".

Grrrr....

Dale

TBoost

You are wrong about this scenario.

Its not the fact that the turbo can't push anymore air, its the fact that the engine can't produce enough exhaust gas energy to spin the turbo faster. You notice this phenomena when you get upgraded exhaust. The car's back pressure if freed up so much that it produces more power which makes the turbo spin faster which in turn produces even more power. Small turbos can definitely spin upward 20psi. Look at the DSM turbos. Their T25s are much smaller than the HT18 (stock turbo) and yet they can get 22psi with no problems.

Also, upgrading to a bigger compressor wheel while still retaining the stock center section and turbine wheel will still allow your supposed boost "limit". Since the compressor wheel is driven by the exhaust wheel, your limit of 14psi is still there. More air may flow into the engine, but this will make the turbo spin faster since the engine will produce more exhaust gas energy. Right now with *no* boost controller and an upgraded T04E compressor wheel on the stock center section and exhaust wheel, my car can creep up to 15psi overcoming even the ported wastegate which still opens at 5psi of boost. That's some tremendous energy coming from the engine!! You notice this when you punch the car at low rpms. The boost stops at 5-7psi, but as the car builds up rpms, the boost slowly begins to go toward the 15psi mark. This is because the engine is producing more and more power as the rpms go up which, in turn, produces more and more exhaust gas energy, which makes the turbo spin faster..

Hope this clears some things up..

-M

Tec

"BOOST THAT SHIZNIC FOO" Nice dale! that must be a North west FL thing? and we get a bad rap in west palm or all the dumb ***'s down south. next time i come down to the vacation house we should get together and cap so bitches,and pull the wastgate line on the daily driver! show all them busta's how to keep it real with low boost button on the profect b

Supermac 7

Id like to add my $.02:

The Stock HT18 is perfectly CAPABLE of making 20 psi. Unfortunately, I have seen it in my own car (yes, my boost gauge is dead on). My wastegate actuator line happened to pop off one time, lets just say I was one lucky SOB.

Ive got a walbro, 720 secondaries, and an S-AFC for my fuel compensation.

Sure it's Capable, but that doesnt mean that it's efficient up in that range. The compressor housing is too small to make that amount of boost all the way through the powerband, and the turbine housing is waaay too small. The HT18 is basically the size of a big T3; the rotary's exhaust pulses are plenty strong enough to spool it, or even a bigger turbo.

I would like to tell you that the FD guys who are making 450 hp are NOT doing it on the stock twins. Ive seen it, im not saying it's not possible, but it's very rare that this setup works perfectly reliably. The more dense your air is, the hotter it gets; and when pushing that much boost through such a small compressor housing, you have the potential to create major heat issues. with a bigger intercooler it would help, but there is no comparison when switching to a bigger compressor wheel/housing just because your efficency range changes so much.

As far as the stock hot side: Those of you hitting around 12-13 PSI without a boost controller, you probably notice that boost drops off to around 5 lbs by redline. This is a good example of the stock hot side choking the engine. The engine has PLENTY of power to spin the turbo that fast, but since the exhaust passageways are so small, it chokes the engine. If the engine were not able to produce the necessary force to spin the turbo, there is NO WAY IN HELL that it would spool a bigger turbo. Correct me if im wrong, but i don't believe that the force of the exhaust pulses decreases as you move up in engine speed; this is evident by all the cars running huge turbos that make power from 5-6k to 9k. The extra inertia required to spin the bigger turbine/compressor wheel causes the turbo not to achieve full boost until later in the rpm range, shifting the entire powerband. This shift of the powerband and delay of the boost is what we call Turbo Lag.

In Closing,
Sure the HT18 is CAPABLE of making 20+psi, but it doesn't mean that it will last long doing it because of all the extra heat that is created. It also doesn't mean that the person will see any extra benefit, because the turbo is inefficient past 13-14 psi. It's just extra hot air blown into the engine. So my question is, why would you risk it, and why would you want to? Buy a bigger turbo.

Jameson

Tec

Why would you risk it! Well more boost is free! it's hlding me over intill my project motor is finished. With a FMIC, race gas and smoking tires, it 's just fun to go out and run them hard!

I forget about the guy that rely on there tII to get them to work every day! mine is just a go fast toy.

Supermac 7

Did you read ANY of my above post?

Sure you can crank the boost up for free, but you will not see much of, if any, a gain above 14psi or so, just because the compressor housing is inefficient up to that point. The extra heat from the density of the air is also killer on both your turbo and your engine.

If your hobby is replacing your motor/turbo every few months, then that's fine, but I guess I dont understand the obsession.

Sure, crank the boost up, but make sure you have the fuel to go with it.

from someone who's been there,
Jameson

Roy James

Im not sure i understand why the boost drops at 5PSI near read line as "Supermac7" said. I mean, im sure it happens if people says it happens, but, i dont understand why exactly. You say the the turbo chokes the engine down as the passageway is too small, and im assuming if that happens, and as the revs go up the engine is sucking more than the turbo is pushing therefore the turbo is producing less PSI for that environment. BUT, if the intake is sucking, that would me the exhaust is pushing, and if the exhaust turbine on the turbo is being pushed then the intake compressor side of the turbo is pushing. Wouldnt it be in purportion? I KNOW for a FACT that i am WRONG in saying this, but i dont exactly understand. Is it the same argument as PSI vs CFM? Thanks and sorry so ignorant.

Number 1 Dumbass

Tec

I'm only running 13psi on VP 104! i have my new motor almost ready to go, my hobby is not replacing my motor every couple of months! i'm having a hard time killing the one i have, a huge FMIC like the greddy kit is going to do a dame good job of cooling the intake charge. your going to see good hp numbers from 7 to 14 psi on the dyno.

My car went from 187 RWHP stock with cone filter to 219 RWHP with a catback,FCD and 9psi. this was before all the other little mods.

Ryde _Or_Die

So can I run 15psi safely or no? For occasional runs at least? What kind of HP numbers should that get me anyways(250?)? Thanks.

NRA T2

Racing beat claims 270 w/their exaust and fcd, right

Tec

You should dyno now! whatever boost your running, than install your FMIC and dyno again then turn up the boost to 14psi and see what you get.

I would say it's safe! just watch your EGT's and your A\F when your on the dyno. you really need to dyno tune a Safc anyway.

TBoost

Boost is not directly dependant on compressor housing size.

This is absolutely wrong. The more dense the air, the cooler the air. Particles expand when heated due to excitment, not when they are cool where they are more dormant.

If the boost drops this much from 12-13psi, you have a boost leak.

Turbo lag is the time it takes for you to press the gas till the initial response of the engine. Therefore, turbo lag is not dependent on boost response - rather fuel response.

True, it is extra hot air being blown into the engine, but if you have enough fuel, you will get some HP out of it. Its just like cars running alcohol applications. Boost pressure doesn't even factor into it. Inefficiency is irrelevant. Fuel has a sort of "cooling" effect on the engine.

-M

Supermac 7

TBoost-

It's not directly dependent, but the compressor housing size largely determines the efficiency range of the turbo with the amount of boost it can produce comfortably.

As you said, particles settle down and become more dormant when it is cool. When particles start jumping around more because of the heat, it becomes much hotter because of the friction against other particles. Whip out your chemistry book, you will find this to be true. The more air you are packing into a space, the more particles there are. They start moving around more because of the increased density, not the opposite. Try playing with an air compressor. when the compressor is compressing the air, is the air hot? As soon as you relieve it, it becomes cool, because it expands once it leaves the tank, cooling the molecules off.

Not so. The boost drops off because the compressor housing chokes it; To be honest, I really dont know if it's some sort of turbulence because of the lack of space, or what not; but I know if you clip the exhaust wheel, it allows for more flow, and the reduction of boost in the upper rpm ranges is dramatically reduced. This is not the case witha bigger turbo with an A/R ratio of, lets say .96. This exhaust housing provides for enough flow for just about any engine in the higher RPM range. I have absolutely no boost leaks anywhere, i can guarantee that.

The engine responds immediately; it's just the turbo takes time to spool, especially a bigger turbo. Fuel is ALWAYS present. the turbo will make boost reguardless of whether enough fuel is present or not, otherwise people would never see their engine blow up. The turbo doesn't go "oh, i cant make boost yet, there isn't enough fuel". If there is enough pressure pushing on the turbine blades, then the turbo will spool. depending on where you are in the powerband depends on how quickly the turbo will spool. If you step on the gas @ 2krpm, then it's gonna take awhile, depending on the size of the turbo, to achieve full boost. however, if you are around 5krpm, then the turbo will spool much quicker and achieve full boost almost instataneously because of the greater pressure on the turbine wheel.

If you have the fuel, go for it. sure, you may get SOME hp out of it, but it's not worth having to replace your turbo all the time. Yes, fuel does have a cooling effect on the engine; as stated in an above post: If you have the fuel, crank it up. but not until then.

Jameson