timing and wastegate question

[justin0469]

first off i know these arent related. I looked around on here for awhile but i cant quite follow the things i have ran into and im not quite sure what to search for because just "timing" or "wastegate" produce a ridiculous number of threads as im sure you can imagine. I also looked in the keyword index on 1000q.dsm.org but didnt find what I was lookin for. Basically im looking for general info of how they work and why they work, how to adjust and why, and what the affects are. I know that wastegates can be internal or external but dont know what the differences are or which is "better" (although it seems like opinion dictates that rather then fact) or what the advantages and disadvantages are and why you would choose one or the other. When I see 38mm, what is that refering to? I know that timing affects knocking but thats about it. I dont know how cams or cam gears change it or the general idea of timing. Im guessin it has some control over the timing of when the cylinders are fired or something to do with that. I know its alot of questions and pretty broad subject but if someone has sometime to spend, id appreciate it.

 

[justin0469]

and maybe explain the difference between engine timing and ignition timing

 

[NOSLO2PT0]

www.howstuffworks.com

 

[justin0469]

thanks for the link, under what category is timing? in the engine section they have alot of catergories, i dont know enough to know where to look. sorry

 

[NOSLO2PT0]

www.vfaq.com

 

[justin0469]

from what i see vfaq is how to install stuff with a link to the 1000q page. i dont mean to be a pain, i just want to learn

 

[iwantawd]

ill give it a shot but im sure someone can explain it better than me....

you want cylinder pressures to peak when the crank is about 15degrees after top dead center. in order to achieve that you need to ignite the mixture beforehand because it takes time for the flame to spread across the area inside the cylinder (it moves at about 900ft/sec). having to much advance will cause the piston to have to fight its way up to top dead center and having too little will result in poor power and throttle response because of the lack of pressure available to push the piston back down the cylinder once it reaches top dead center. in extreme cases, at very high engine speeds, the piston can actually run away from the expanding flame front. Larger bores need more advance to get the flame all the way across them and smaller bores typically need less.

*some of this is directly from Building and Tuning High-Performance Elctronic Fuel Injection by Ben Strader

as for wastegates, internal wastegates work great and are cheaper overall. external wastegates can tend to have better response plus BLING BLING.
ex: an internal gate set to 15psi will slowly start opening a few psi earlier than 15 because if it opened immediately at 15psi you would actually spike a few psi above and then it would settle back down.
external wastegates can be placed on the o2 housing, the turbine cover itself, or anywhere on the manifold even though its best to place it on or near the collector if it is on the manifold. i like the idea of an external on the turbine housing like the fp30 series turbo but at a little less harsh of an angle than 90 degrees. these are better at opening closer to your desired boost and not overshooting which helps spool up. they are also more expensive because you need to buy the wastegate, weld it on, and either reroute the gate to the downpipe or buy a dump tube. when searching for an external you see sizes like 38mm, 40mm, 44mm. if your turbo is pushing a lot of air and you have the turbo set at a low psi you want a larger wastegate because more air will be bypassed through the wastegate in order to hold that low psi. if its not large enough then you'll start to creep just like an unported internal gate.

i hope this helps and someone make sure i didnt say anything stupid

 

[justin0469]

you want cylinder pressures to peak when the crank is about 15degrees after top dead center. in order to achieve that you need to ignite the mixture beforehand because it takes time for the flame to spread across the area inside the cylinder (it moves at about 900ft/sec). having to much advance will cause the piston to have to fight its way up to top dead center and having too little will result in poor power and throttle response because of the lack of pressure available to push the piston back down the cylinder once it reaches top dead center. in extreme cases, at very high engine speeds, the piston can actually run away from the expanding flame front. Larger bores need more advance to get the flame all the way across them and smaller bores typically need less.

First off I want to say thanks for takin the time to explain it for me. Now i wanna see if i understand this right. Top dead center is when the crank is when the crank is in the center of the crankshaft (maybe the crank isnt what im thinking). but overall timing refers to when the ignition takes place before the crank reaches TDC. advance timing for bigger cylinders because it takes more time to fill it. what does degrees refer to?

*some of this is directly from Building and Tuning High-Performance Elctronic Fuel Injection by Ben Strader

as for wastegates, internal wastegates work great and are cheaper overall. external wastegates can tend to have better response plus BLING BLING.
ex: an internal gate set to 15psi will slowly start opening a few psi earlier than 15 because if it opened immediately at 15psi you would actually spike a few psi above and then it would settle back down.
external wastegates can be placed on the o2 housing, the turbine cover itself, or anywhere on the manifold even though its best to place it on or near the collector if it is on the manifold. i like the idea of an external on the turbine housing like the fp30 series turbo but at a little less harsh of an angle than 90 degrees. these are better at opening closer to your desired boost and not overshooting which helps spool up. they are also more expensive because you need to buy the wastegate, weld it on, and either reroute the gate to the downpipe or buy a dump tube. when searching for an external you see sizes like 38mm, 40mm, 44mm. if your turbo is pushing a lot of air and you have the turbo set at a low psi you want a larger wastegate because more air will be bypassed through the wastegate in order to hold that low psi. if its not large enough then you'll start to creep just like an unported internal gate.

So obviously there is a difference between a BOV and wastegate. but it seems they accomplish the same basic job, letting off extra pressure. just at different points. when is the wastegate used rather then the bov? once again, thanks for your time and i know this is some newb stuff but ive looked and i cant get some straight info. some stuff i dont even know enough to know what to ask.

 

[iwantawd]

First off I want to say thanks for takin the time to explain it for me. Now i wanna see if i understand this right. Top dead center is when the crank is when the crank is in the center of the crankshaft (maybe the crank isnt what im thinking). but overall timing refers to when the ignition takes place before the crank reaches TDC. advance timing for bigger cylinders because it takes more time to fill it. what does degrees refer to?

whoa brother, you should really get onto how stuff works and read every chapter on engines and turbos. you'll feel so much smarter, i promise (but dont stop reading there either, get some books if you really plan on modding your car. these forums arent the end all be all of auto info). top dead center is when the piston is as far up the cylinder as it can possibly go, right before it starts coming back down. as far as degrees of rotation, its exactly that. the crank rotates a full 360 degrees of course and when i say 15 degrees after top dead center (atdc) think of the cranks position at tdc as 0 and then rotate it 15 degrees. the piston will have started moving down the cylinder bore at this point. a little movie in the howstuffworks site depicts this very well.

So obviously there is a difference between a BOV and wastegate. but it seems they accomplish the same basic job, letting off extra pressure. just at different points. when is the wastegate used rather then the bov? once again, thanks for your time and i know this is some newb stuff but ive looked and i cant get some straight info. some stuff i dont even know enough to know what to ask.

a blow off valve is placed between the compressor side of the turbo and the throttle body. when the throttle is closed the compressed air hits the throttle plate and a wave of pressure starts heading back to the compressor which is still trying to push air. this can destroy a turbo so a blow off valve is put in place to blow off the air or releave pressure in the system. a wastegate is placed in the exhausts path to release exhaust gas. by regulating how much exhaust gas goes through the turbine you regulate its speed which is pretty much directly related to the psi it produces. if you have no wastegate the turbo will just spool up and up till something blows up. the shaft in a turbo can spin up to 180,000 rpms and maybe even higher, im not sure.

both a wastegate and a bov should always be used but some think a bov is not needed when running low low psi like 5 or so.

youre lucky i kicked ass on my final today and im in a good mood. you need to do some big time researching and i highly suggest howstuffworks.com for newbs because the pictures they have are great along with the explanation.
how did you register in 03, mod youre car somewhat, and still not know this stuff?

 

[justin0469]

i know i know, i would get on howstuff work but the computers at work are messed up and the site doesnt work, and when it does it tries to install flash about 10 times but it wont install because i dont have admin rights. annoying as crap. but when i get a comp that work ill definately do that. believe it or not, i did think it was somethin like what you were saying about the crank position but i didnt understand how anything could be beyond TDC so i revised my idea but i understand now. once again thanks for your time and hopefully you didt feel like it was a waste, i did learn alot just from your two posts. i do greatly appreciate it. yeah i did register in 03 but in the middle theres about a yr without a dsm that i havent been around. i know more about electrical things then mechanical.

 

[iwantawd]

not a problem, good luck with it

 

[justin0469]

ok now that my boss was gone for awhile and i could get on his computer, i do understand much better. howstuffworks.com went over why wastegates are they and how they work basically but how does an internal one work vs external? i know they both basically let some pressure out when it feels things are goin too fast but how do they differ in their operation and detection of this? also in reading thru other compression ratio threads , i get the idea that compression ratio is simply how much the mixture as a whole has been compressed by the piston. ie: 10:1 means that the mixture has been compressed to be one tenth the volume that it was during the intake cycle and that the smaller the first number the higher the compression and the last number will always be a 1. What is the third number sometimes shown in compression ratios? or am i seeing things or seeing typos and there is no third number?

 

[NOSLO2PT0]

but how does an internal one work vs external? i know they both basically let some pressure out when it feels things are goin too fast but how do they differ in their operation and detection of this?

A wastegate is very simple. An air signal opens up a diaphragm, allowing exhaust gases to pass through an opening (the wastegate hole) and bypass the turbine wheel. Internal gate has a small round plate, hooked up to an arm. Plate is called a flapper door. Arm is connected to the gold bell looking thing. That's the actuator. It has a nipple on it. When the air signal (boost) reaches a level that exceeds the amt. of pressure that allows the diaphragm to keep the flapper door closed, it pushes it open. Exhaust gas flows through the hole of the wastegate, instead of over the turbine wheel. That's how it keeps boost constant.

External gate is basically the same way. Except it's mounted separately from the turbo. An air signal pushes against the diaphragm in the gate, and the diaphragm simply opens. Very easy. Works the same way.

also in reading thru other compression ratio threads , i get the idea that compression ratio is simply how much the mixture as a whole has been compressed by the piston. ie: 10:1 means that the mixture has been compressed to be one tenth the volume that it was during the intake cycle and that the smaller the first number the higher the compression and the last number will always be a 1. What is the third number sometimes shown in compression ratios? or am i seeing things or seeing typos and there is no third number?

Compression ratio if defined quite simply as the volume above the piston at bottom-dead-center (BDC), divided by the volume above the piston at top-dead-center (TDC).

C.R. = V1 / V2

C.R.s are expressed as a ratio. 1G has 7.8:1 c/r, while 2G has 8.5:1 c/r. The ratios are always expressed in decimal to the tenths, even if it's an even #. Most piston manufacturers will advertise pistons to be 9.0:1, but saying 9:1 would still be correct. Maybe the decimal is the 3rd # you are talking about.

 

[justin0469]

10:1 means that the mixture has been compressed to be one tenth the volume that it was during the intake cycle and that the smaller the first number the higher the compression

ok thanks for clarifing and i think i do understand. really thanks for taking time. just to make sure, my quote above is correct according to what you said right?

 

[NOSLO2PT0]

ok thanks for clarifing and i think i do understand. really thanks for taking time. just to make sure, my quote above is correct according to what you said right?

Not really. It's still a ratio of the volume in the cylinder before the stroke and the volume in the cylinder after the stroke. If we used your example, we would have to assume that the volume of the cylinder while the piston is at the bottom of the cylinder (BDC, bottom dead center) is 100cc. After the piston travels upwards and reaches TDC (top dead center), the new volume is only 10cc. Dividing 100cc/10cc = 10. Your compression ratio is 10:1. And yes, it does happen to equal 1/10th of the original volume.

Now, change those numbers around. Let's say the original volume is still 100cc, but after the compression stroke, the final volume is only 25cc. 100cc/25cc = 4. Your compression ratio is 4:1.

The higher the ratio, the higher the compression. 7.8:1 is much lower compression than 14:1.

 

[iwantawd]

smaller first number is the lower compression ratio

 

[justin0469]

Now, change those numbers around. Let's say the original volume is still 100cc, but after the compression stroke, the final volume is only 25cc. 100cc/25cc = 4. Your compression ratio is 4:1.

The higher the ratio, the higher the compression. 7.8:1 is much lower compression than 14:1.

25cc is one fourth of 100cc. but i do think i understand more now, i kinda had it backward for the compression ratio

 

[iwantawd]

just think of it as pressure not actual size of the squish area. 1.0:1 is obviously a larger squish area than 10.0:1 but 10.0:1 will have a higher pressure so its a higher comp ratio.

 

[justin0469]

ok i tihnk i got it, hopefully i got it