Questions About Turbocharging

[91GranSport]

I have two quick questions about turbocharging:

 

1. What is a "diverter valve"?

2. What is a "wastegate"?

 

Thanks for your help. By the way, I did search using Google but all I came up with were these bullshit website with too many damn pop-ups.

[timbit_69]

a waste gate is used to let access pressure out of your turbo system. it helps regulate boost.

 

to my knowledge a waste gate is the same thing as a BOV(Blow off Valve).

[Aaron]

true. after you "spool up" and let off the gas, a turob car will hold the pressure inside it self, cuz it has no where to go. this is bad for all of your turbo selas among other things, so the bov is the loud [soundfx]pish[/soundfx] noise you hear when the spool then let off the gas, it is a valvee letting all of the pressure out since he let off the gqas and no longer needs it to be pressurized. they also sound cool too

[brian89gp]

the wastegate is on the exhaust and routes exhaust around the turbo, no exhaust no spooly. The BOV is on the intake and works on a pressure differential, low manifold vacuum but high intake pipe boost, it opens up and releases the excess pressure (when you close the trottle) to prevent the shockwave from hurting the turbo

[TGPilot]

to my knowledge a waste gate is the same thing as a BOV(Blow off Valve).

 

No a BOV is not the same thing as a wastegate. There are internal and external wastegates...this may be where you got confused. BOV's only job is to release pressure in the clean charged air that is going into the intake stream when the throttle body closes.

 

Wastegates are (as a few have said) to regulate the amount of boost being produced and sent to the intake stream via a bypass in the exhaust stream. It is the "point of least resistance" theory that when a turbo is producing boost it must go through the exhaust fan (wheel that drives the turbo shaft) with the force of the exhaust gases. When the wastegate opens it bypasses or limits the flow of exhaust gases driving the Turbo shaft... 8)

[timbit_69]

thanks for the clarification "Pilot"

 

more known stuff is better.. thankx for the info...

 

when i was refering to them being the same thing i ment they are both boost regulators and work on the same principal...

[91GranSport]

Thanks for the info guys. I'm more of a "supercharged" dude myself, rather than turbos. Turbos seem too damn complicated.

[brian89gp]

na, just a little different

[topless94style]

Do superchargers rob u of any power because they are belt driven? Or does the boost just make up for it?

[Redfox340]

Do superchargers rob u of any power because they are belt driven? Or does the boost just make up for it?

 

Yes, they do take some power at the low-end because it is belt driven.

But, like you said, it'll make up for it when the positive boost is made.

 

- Erik

[topless94style]

Im lookin at turbo and supers too my friend wants one on his Z28 when he wasnt pulling very hard away from the new neon srt at 130mph. that was from a rolling race though off the start he whopped its ass. the Z is no where near stock either.

[Redfox340]

Im lookin at turbo and supers too my friend wants one on his Z28...

 

I want to force induce my MK3.

I know exactly how you feel...

 

- Erik

[topless94style]

I guess he can only put about 4-6psi through the LT1 but still that will add alot of damn power.

[Redfox340]

I guess he can only put about 4-6psi through the LT1 but still that will add alot of damn power.

 

Um... I'm no engine builder expert, but 4-6psi will see average results.

Why can't he go higher on boost? High-mileage? No rebuild? Poor compression numbers?

 

- Erik

[topless94style]

100K miles he said thats all the LT1's can handle i guess.

he has..

full lenght racing heads

straight pipe exhasut

cold air intake

HUGE cam

bigger valves

elec. water pump

and he customized the computer with his laptop

so hes makin good hp already but i dunno why he cant go more

[supreme_style21]

Thanks for the info guys. I'm more of a "supercharged" dude myself, rather than turbos. Turbos seem too damn complicated.

 

[god910]

A supercharger @ 6 psi is like a Turbo @ 12

positive displacement 6 psi, will show around 30% HP increase (mods depending obviously) Most SC's come w/ a ~6 psi pulley from the factory.

[Guest TurboSedan]

100K miles he said thats all the LT1's can handle i guess.

 

boost is boost isn't it? add an aftercooler and i would assume you could run more boost than 6psi. the LT1 would be a great motor to turbocharge or supercharge, unless he raised the compression i would think he could run at least 10-12psi.....? i really don't know actually. and for a newer small block chevy like an LT1, 100K miles means it's just been broken in. superchargers are easier to package in an engine bay, and also produce instant boost since the drivebelt directly spins the supercharger. they also aren't as efficient as a turbocharger, ecspecially the screw or 'roots' style supercharger (aka blower) like the Series II Buick 3800 motor uses. turbochargers don't rob power via a drive belt, but there is the problem with turbo lag and all of the exhaust plumbing like crossover pipe, downpipe, upper & lower charge pipes going to & from the intercooler, oil & coolant lines running to/from the turbo for lubrication and cooliing etc. superchargers also aren't very efficient; they heat up the charged air quite a bit (at least the screw types do, i dunno about centrifugal superchargers).

 

i'd like a '95 Caprice Wagon with the SPO '1A2' police package and LT1 motor, swap in a T56 6-speed, then twin turbocharge it using two Garrett T3's on each bank. heck i'd even do it to a Buick woody '95 Roadmaster wagon! those cars are cool

joshua

[91GranSport]

If a supercharger produces the same amount of power at lower boost than a turbo at higher boost then why the hell do manufacturers use turbos? I know you have to take "parasitic loss" into consideration since superchargers are driven off the engine's horsepower but they're less complicated than turbos and they can run without intercoolers. Strange, huh?

 

A supercharger @ 6 psi is like a Turbo @ 12

positive displacement 6 psi, will show around 30% HP increase (mods depending obviously) Most SC's come w/ a ~6 psi pulley from the factory.

[topless94style]

I know turbos are supposed to have a better increase in power than superchargers so im told. But they also sound more complicated and more work. So how do IC's work? I know turbo lag is a bit of a problem and even more if you want to go with a bigger turbo. Hence the creation of twin turbos using two smaller turbos and creating less lag. And dont usually turbos kick in around 2500rpm? If this is so there isnt much lag i mean if your ripping through the gears at full throttle that split split split second wont matter much would it? Another question. If they kick in at 2500 rpm does that mean they go when ur doing regular driving and just accelerating nicely from a stop light? Or is it just the speed of the exhaust coming out that gets em going? And with superchargers dont u need higher/lower compression? I got more questions but i think thats enough for now.

[Aaron]

a turbo, on an average application, will not make ANY more power(it might even lose some) befor about 3000-400 rpm. now the supercharger will increase power all of the way, making more boost as rpm's go up. overall, the S/C doesnt give as much of a igh end, but still helps your low end. the turbo doesnt help, and even hurts, the low end but will help the hgih end even more than the S/C

[Guest TurboSedan]

I know turbos are supposed to have a better increase in power than superchargers so im told.

 

But they also sound more complicated and more work. So how do IC's work? I know turbo lag is a bit of a problem and even more if you want to go with a bigger turbo. Hence the creation of twin turbos using two smaller turbos and creating less lag. And dont usually turbos kick in around 2500rpm? If this is so there isnt much lag i mean if your ripping through the gears at full throttle that split split split second wont matter much would it? Another question. If they kick in at 2500 rpm does that mean they go when ur doing regular driving and just accelerating nicely from a stop light? Or is it just the speed of the exhaust coming out that gets em going? And with superchargers dont u need higher/lower compression? I got more questions but i think thats enough for now.

 

 

intercoolers are basically just radiators that cool the charged air coming out of the turbo so it will become more dense and give you more power. the air coming out of the turbo is usually hot for two reasons: 1. the turbo itself is part of the exhaust system and obviously it will heat up the intake air by going thru it. but mostly 2. air heats up as it gets compressed. the TGP uses an air-to-air intercooler like most turbocharged cars, but some are water-to-air like the Sy/Ty's. even alcohol or water injection is a way of intercooling really, since it cools the charge entering the engine. the alcohol can also serve to 'steam clean' your combustion chambers so it has other benefits too.

 

turbos are just more efficient because the engine's waste (exhaust gas) is what drives the turbo shaft, not an accesory drive belt which obviously robs power. i guess the turbo produces some backpressure, so it's not completely free power. turbos & superchargers are just two different parts that do the same thing: create boost. so both will need lower compression; i'd say around 8.2:1 is what i'm going for in my TGP engine, even tho it's an 8.8:1 engine right now (i'll need custom pistons). turbos are definately more complicated because of all the plumbing needed for exhaust gas, boost pipes, turbo placement, oil & coolant lines etc. your right that a bigger turbo usually produces more lag, but the benefits pay off if you get the right turbo for your application (trim, A/F ratio for example).

 

my brother iTurbo has an '89 Dodge Shadow with an intercooled turbo 2.5 that came with a small mitsu turbo (mitsu TEO4H turbo) and that thing spools instantly. it's hard not to spin the tires in that car even when your hardly on the gas from a stop. my '89 GTS by comparison has an intercooled turbo 2.2 (same engine; just de-stroked) which came with a much larger Garrett T03 from the factory. it has ALOT more lag, but when you hit full boost the car REALLY rockets forward and will reel the 2.5/mitsu turbo car in no problem.

 

i don't know much at all about twin turbocharging but it would obviously be more complicated. besides that, turbos are expensive and you'd need two of them.

 

IMO i think turbos are GREAT with 5-speed cars, and other people like them better with automatics. there are pros & cons to each i guess. if you have a turbocharged engine and are using a 5-speed, i would highly reccomend a BOV, because you have to let off the GO pedal at each shift (throttle blade completely shuts) and that creates a 'shockwave' (boost has nowhere to go) that can slow down the turbos shaft fast, wear it out quicker, and slow you down more in a race since the turbo will have to spool up again. with a BOV, the excess pressure is vented (it opens via a vacuum signal from the plenum) when the throttle blades shut, so the turbo keeps spinning quickly and it won't need to spool up so much when you get in the next gear. and we all know they sound cool i would even run a BOV in an automatic equipt car, even tho it wouldn't be as important with a 5-speed car cuz your foot would be on the floor during an entire street race. it will definately help the turbo live longer anyway.

 

sounds like other people have covered what a wasegate does - basically just controls the amount of exhaust gas that spins the turbos turbine shaft (which is solidly connected to the compressor shaft of course) and usually uses a computer controlled wastegate solenoid to operate it. when the wastegate opens, it lets exhuast gas flow out into the downpipe (gas isn't being used to turn the turbine shaft) and that way boost is controlled. with my CS turbo project, i am not going to use the stock wastegate solenoid (i guess i'll *try* it); instead i am using a grainger valve that will probably be set @ minimal boost while i break in the clutch, then work my way up to about 13psi later down the road. a grainger valve will keep the wastegate completely shut until a set 13psi, which is when the wastegate will start to open and be controlled by a spring inside the grainger valve. i bought my grainger valve for $25 from M & M racing. i'll have to have a custom burnt chip to do this tho without setting a trouble code/SES light i'm sure.

hth,

joshua

[Guest TurboSedan]

a turbo, on an average application, will not make ANY more power(it might even lose some) befor about 3000-400 rpm. now the supercharger will increase power all of the way, making more boost as rpm's go up. overall, the S/C doesnt give as much of a igh end, but still helps your low end. the turbo doesnt help, and even hurts, the low end but will help the hgih end even more than the S/C

 

if you just get the right turbo for your application (learn how to read compressor maps) you won't have problems with turbo lag. it'll be a compromise, but your saying a turbo hurts power below 3000-4000 RPM? that just isn't true.

joshua

[Aaron]

you have never riden in a Talon or an eclipse. they whipwash you at 3500, nothin till then. and they die off at 6500.

[brian89gp]

Well, mine will build at least 6psi below 2000 if the wastegate is unhooked, so that statement about no power below 4000 is false.

 

Few things:

-a turbo does create a parasitic loss to the engine, 15+ psi of exhaust back pressure does that to things, but still that loss is less then a belt driven s/c setup

-a properly sized turbo is key

-a custom turbo is easier to make then a custom s/c, turbo all you need to do is weld up tubing, a s/c you need a hell of a lot of bracketry which is hard to say the least without decent metal maching equipment.