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You are correct that if you lower compression, you need to boost more to compensate, but, because the compression is lower, you can boost more+more, if you will. Here's a rough estimate of how this works. CR ------10.5:1---------8.5:1----------8.0:1
0psi----- 222HP ------ 179HP -------- 169HP
9psi ---- DT ----------- 300HP -------- 282HP
23psi --- Nowayinhell -- DT ----------- 721HP DT=detonation occurs
No way in hell = No way in hell The reason the engine will detonate is because maximum pressure that the cylinder achieves is great enough to ignite the fuel before the plug fires. PV=NRT explains the relationship between pressure and temperature very well. You can only pressurize the air and fuel so much before it spontaneously ignites due to the temp/pressure. By lowering the compression ratio, you are not squeezing the air/fuel mixture as much during the compression stroke as compared to a higher compression engine. Because of this, you can cram more air and fuel into that cylinder which means more power. If you look at the rough table above again, you will see that I put a DT in the NA column for 9psi of boost. You'll only squeeze about 4 psi or so out of that compression ratio before you detonate. Each PSI is worth more power at 10.5:1 CR, but in the end, you lose the ability to up it any more. As the compression ratio decreases, you can put increasingly more air and fuel in there and ultimately make more power. Dont take this statement to the nth degree though, if you try to run a compression ratio of 2:1, you'll run into several problems. The first being that you wont get it to start. Good luck finding a turbo for this application and good luck actually trying to make your VG 2:1 compression ratio. LOL I did math on this about a year and a few monts ago which show how the pressures build up with respect to boost pressures and compression ratios. There is a critical pressure in the combustion chamber at TDC that you dont want to exceed and you can see in my explanation how the larger quantity of air and a lower compression ratio actually makes more power than higher compression and lower boost. Additionally, it allows you to boost proportionally higher with lower CRs.
: "Becuase it lowers the chance of detonation, you can up your boost and make more power than you would have before."
: say compression is "1.00" and you can boost 16 psi and get 400 rwhp (yes, i know...just hang in ther).
: if you lower compression to "0.90", you will need 19 psi to get the same rwhp. : by doing this, you lose alot(!) of torque, especially low end. : I personally would only recommend lowering compression if you are running insane amounts of boost. but for our normal bolt on turbos, i don't believe it is a big issue. (IMHO!) (IMHO)
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