Decompression Plate Benifets.
04-03-2005, 08:44 PM
#1
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I know this sounds like a dumb post but i need to know if i should purchase the decompression plate from kspec and install it when i boost. i know it will lower my compression ratio to 8.5:1 from whatever the stock compression ratio is. What are the benefits of getting the decompression plate? and what can i do differently with the turbo if i have the decomp plate. I know the betas are boost friendly and we have seen tim run 12-17 psi on his stock internals for like that last year or so,, and everything was fine. i will eventually upgrade, but shall i purchase the decompression plate or not, and why?
thanks guys. sorry for the dumb post.
thanks guys. sorry for the dumb post.
04-03-2005, 09:13 PM
#2
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With a lower compression ratio, an engine can safely handle more boost, everything else being equal. Similarly, if the temperature of the compressed air is lower, an engine will have a much higher detonation threshold (the point at which fuel ignites without a spark), and will be able to safely handle more boost.
Depending on how much psi you want to run, but if you are going for anything over 8-10 psi, I would suggest lowering compression to 8.5:1. If I was boosting, I would lower compression no matter what psi I plan on running to be on the safe side.
Depending on how much psi you want to run, but if you are going for anything over 8-10 psi, I would suggest lowering compression to 8.5:1. If I was boosting, I would lower compression no matter what psi I plan on running to be on the safe side.
04-03-2005, 09:14 PM
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benefits, you can run higher boost safely. with high boost and high comp, the air/fuel can explode without the spark, due to the super high pressure(knock). also, a lot easier to install than low comp pistons.
i would get it. tim has been tweeking cars for long time. he knows what hes doing. id say the plate is definately worth the added peice of mind. you can play around with numbers a little more safely. just keep in mind, your car will be a bit more sluggish in low revs.
i would get it. tim has been tweeking cars for long time. he knows what hes doing. id say the plate is definately worth the added peice of mind. you can play around with numbers a little more safely. just keep in mind, your car will be a bit more sluggish in low revs.
04-03-2005, 09:29 PM
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I dunno how Tim does it. I bet he's just lucky or running a crapload of fuel so its safe to run 17PSI on stock internals. tongue.gif
The stock Tib is 10.3:1 compression ratio. That is pretty high, and is why its fairly responsive down low along with its gearing. Its also the bane of turbocharging. Tibby01 tells deh truth.
If you plan on going anywhere near 15PSI, buy some low-comp pistons. Decompression plates are band-aids, not fixes. Best to invest in the best if you plan to be the best (Bwaha I made a rhyme lol.gif).
The stock Tib is 10.3:1 compression ratio. That is pretty high, and is why its fairly responsive down low along with its gearing. Its also the bane of turbocharging. Tibby01 tells deh truth.
If you plan on going anywhere near 15PSI, buy some low-comp pistons. Decompression plates are band-aids, not fixes. Best to invest in the best if you plan to be the best (Bwaha I made a rhyme lol.gif).
04-04-2005, 12:44 PM
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Decompression plates are very undesireable. They nearly totaly remove the quench/squish that is built into the pistons/combustion chamber.
That Quench/Squish is important for 5 different reasons.
#1. Combustion chamber turbulence/Mixing. While you may want smooth laminar airflow in your intake and Intake manifold runners, you WANT turbulence in your combustion chamber. Turbulence ensures a proper mixing of air and fuel, and evenly distributes the air/fuel around the combustion chamber.
#2. Combustion efficency. Proper squish/quench forces nearly all air/fuel towards the center of the combustion chamber. Squish/Quench clearances are VERY tight/small. There is very little unburned air/fuel left in the little crevace that remains between quench/squish areas. This allows a more efficent combustion event, as there is little wasted air/fuel out on the edges of the cylinder/pistion/head interface.
#3. Power production. That proper squish/quench that forces all of your air/fuel into the center of the combustion chamber also produces more power. You've got 90-95% of your air and fuel in about 70-75% of the Available space. This promotes a FAST and nearly Complete burn which = more power
#4. Emissions. Yeah, I know 99% of us don't give a rats butt about emissions, but, if you could make 200 WHP and still pass emissions tests, nearly everyone would go for it. The way to do that? Squish/Quench. As described above, since 90-95% of your air/fuel is in the center and burned, you are putting out fewer unburned hydrocarbons. That's one of the things they test for in emissions testing, and it's also one of the things that makes your exhaust "stink". If you've ever been behind a car running overly rich... you know that smell. It's good for the environment, it's good for power!
#5 Pre-ignition/detonation resistance. Ah...here's the one that get's everyone's attention. By mixing all of the air/fuel in the combustion chamber into a turbulent vortex, you're keep the air moving very fast, and very erraticly. If you've got a "hot spot" in your combustion chamber, that would promote pre-ignition, turbulence prevents "hot spots" from locally pre-igniting any air/fuel, since the turbulent air is simply flowing over the hot spot, cooling it, not stagnant over the hot spot, picking up heat untill pre-ignition occurs. Since the flow is "chaotic" and not cyclical, the air doesn't flow over the same hot spot again and again, so it has a chance to dispurse the heat it picked up from the hot spot before it passes it again.
There are a lot of things you can do to make a Forced induction engine work, but one of the guarantee'd ways to f-it up is to remove the quench/squish area.
That Quench/Squish is important for 5 different reasons.
#1. Combustion chamber turbulence/Mixing. While you may want smooth laminar airflow in your intake and Intake manifold runners, you WANT turbulence in your combustion chamber. Turbulence ensures a proper mixing of air and fuel, and evenly distributes the air/fuel around the combustion chamber.
#2. Combustion efficency. Proper squish/quench forces nearly all air/fuel towards the center of the combustion chamber. Squish/Quench clearances are VERY tight/small. There is very little unburned air/fuel left in the little crevace that remains between quench/squish areas. This allows a more efficent combustion event, as there is little wasted air/fuel out on the edges of the cylinder/pistion/head interface.
#3. Power production. That proper squish/quench that forces all of your air/fuel into the center of the combustion chamber also produces more power. You've got 90-95% of your air and fuel in about 70-75% of the Available space. This promotes a FAST and nearly Complete burn which = more power
#4. Emissions. Yeah, I know 99% of us don't give a rats butt about emissions, but, if you could make 200 WHP and still pass emissions tests, nearly everyone would go for it. The way to do that? Squish/Quench. As described above, since 90-95% of your air/fuel is in the center and burned, you are putting out fewer unburned hydrocarbons. That's one of the things they test for in emissions testing, and it's also one of the things that makes your exhaust "stink". If you've ever been behind a car running overly rich... you know that smell. It's good for the environment, it's good for power!
#5 Pre-ignition/detonation resistance. Ah...here's the one that get's everyone's attention. By mixing all of the air/fuel in the combustion chamber into a turbulent vortex, you're keep the air moving very fast, and very erraticly. If you've got a "hot spot" in your combustion chamber, that would promote pre-ignition, turbulence prevents "hot spots" from locally pre-igniting any air/fuel, since the turbulent air is simply flowing over the hot spot, cooling it, not stagnant over the hot spot, picking up heat untill pre-ignition occurs. Since the flow is "chaotic" and not cyclical, the air doesn't flow over the same hot spot again and again, so it has a chance to dispurse the heat it picked up from the hot spot before it passes it again.
There are a lot of things you can do to make a Forced induction engine work, but one of the guarantee'd ways to f-it up is to remove the quench/squish area.
04-04-2005, 02:54 PM
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Like everyone says... buy the 8.5:1 pistons..... kspec is your best option. I bought it from them.... It's looks really nice and I trust more in the pistons than the decompression plate...
Nice Reply Random.... I learned something new today thanks
Nice Reply Random.... I learned something new today thanks
04-04-2005, 03:17 PM
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BTW...Tim was able to run elevated boost levels becasue he KEPT his Squish/Quench area. (he left it alone). I'd rather see you run 10-12 PSI on stock compression than see you try to run 15-17 psi with a de-compression plate.
The De-Compression plate is one of the reasons that the Alpine Turbo kit had such detonation issues. They install a 3mm thick decompression plate and an extra head-gasket. That added thickness screwed up the quench/squish.
The De-Compression plate is one of the reasons that the Alpine Turbo kit had such detonation issues. They install a 3mm thick decompression plate and an extra head-gasket. That added thickness screwed up the quench/squish.
04-04-2005, 04:20 PM
#9
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thanks alot for the information random. i dont plan on running any more than 12psi with my stock internals. i will run 8-10 daily. I guess i will save up for the pistons for more boost. i have just heard so many failures after piston install, from faulty rod installation and such things. i just didnt want to tear her open and start replacing things if it was not neccessary. as i want the tib to be a beast, i think running 10-12psi will be good enough, since its safe for stock internals, as shown by tims beatings.
04-04-2005, 05:11 PM
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Squish/Quench is something I didn't even know... I just knew the gaskets were sucky and caused problems inside the combustion chamber because of the way the air came in, but I never knew why. Mucho props, I learned something today. B)
Remember Tim's beatings weren't for an extended period of time... he only had it setup like that for a few months before he tore into it and did it the right way. I wouldn't recommend 10PSI on stock internals if you plan on keeping your car at 8-10PSI for the rest of its existence and never tear into the engine.
Remember Tim's beatings weren't for an extended period of time... he only had it setup like that for a few months before he tore into it and did it the right way. I wouldn't recommend 10PSI on stock internals if you plan on keeping your car at 8-10PSI for the rest of its existence and never tear into the engine.