sc430blue
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I'm going to change my pistons and rods on my 3uzfe. I believe stock is 14.5. I have a supercharger running about 9 lbs boost. What do you think? 8.5? 9.5?.
Compression ratio?
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The 1UZFE EGR Delete Kit is available for sale here.
Compression ratio says how much that air get compressed on the compression stroke and nothing about what we se on a boost gauge.
Boost itself isn´t anything we want because pressure creates resistance. Flow in weight is what we want. a good enginedesign needs less boost for a specific flow of air.
Test:
VE 80%, comp 10.5:1 @ 0,5 bar boost gives wich compression?
VE 110% comp 8.5:1 @ 1,0 bar boost gives wich compression?
If we change the compression ratio with low comp pistons, the combustion chamber and gets an increase in volume, but the stroke and bore is the same, so the "work volume" of the engine is the same, but the engine can take more boost without knock, pre iginotion, detonation and so on.
An engine should have the highest possible compression ratio to atomize the fuel better and increase pressure in the early phase of combustion = more power.
If we step back to the supercharged engine in this thread - the extremly small drop that he may se on his boost gauge isn´t of any interest, the flow trough the runners/head is the same, so the combustionchambers will get the same amount of air as before or slightly more on the (intake stroke), than the intakevalve closes and the compression stroke begins and compression ratio becomes important.
Lextreme II
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14.5? I dont think so.... I would stick with stock compression for supercharged system.
sc430blue
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Sorry, 10.5 compression ratio.
Lextreme II
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Blue,
You should stay with stock compression pistons because if you change compression ratio, you will change pressure level. If you are running 9 psi at 10.5:1 right now, you might only get about 3 or 4 psi with 8.5:1 compression ratio.
You should stay with stock compression pistons because if you change compression ratio, you will change pressure level. If you are running 9 psi at 10.5:1 right now, you might only get about 3 or 4 psi with 8.5:1 compression ratio.
TundraEddie
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Since he's supercharged,isn't boost determined by pulley speed/size and not directly affected by compression?Lextreme said:
Lextreme II
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Yes its correct. However, since the speed/size will be constant. Therefore decrease compression ratio will increase chambar volume and pressure will drop. Since the 3uzfe crank pulley is about 5.00" its will be very hard to increase boost.
sc430blue
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Lex, thanks for the input. I was thinking the same thing about the pressure drop. Since I'm pulling the engine and tearing it apart anyway. Should I just go with the lower compression ratios and upgrade my supercharger? I believe the C2 unit is pretty maxed out.
Lextreme II
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C2 is not max out. Its max out because of our engines (1-3uz) have very small crank pulley. The goal is to have a large crank pulley and small supercharger pulley to make more boost. Its almost impossible to increase the crank pulley and supercharger pulley you can only go so small. I think 2.50" to 2.65" is the smallest supercharger available and anything smaller then that the belt will start to slip. I think you should get stock compression 3uzfe custom forged pistons with 1uzfe rods and boost it 9 psi all day long.
C2 i believe is pretty much the smallest supercharger ATI make. One of the example I would like to share with you is that when I was boosting 12 psi in my stock Cobra with ATI P600B. When i got my 8.5:1 compression pistons, my 12 psi became 4 psi. I was very dissappointed and need to spend more money on an upgraded head unit to F1SC. If you have C2 now, you should be looking at D1SC. (One way to make up small crank size pulley is to have greater step of internal gear ratio of a supercharger). However, the bracket from the C2 would not work on D1SC. Basically you have to re-invent another D1SC bracket for your SC430. Lots of work, engineering, dowtime and so on.
I would recommend two choices:
1. 1uzfe rods with 10.5:1 forged pistons (about $1,250-$1,500)
2. Pauter rods wtih 10.5:1 forged pistons (about $2,500)
3. Pauter rods 8.5:1 forged pistons with ATI D1SC and new a bracket (about $5,000-$7,000). However, the D1SC might be too big and you might not able to close the hood or not enough physical space for it.
I think the first choice is all you need. Stock 1uzfe rods are slightly stronger than 2 or 3uz rods. Below is an ATI Supercharger Headunit Specs.
C2 i believe is pretty much the smallest supercharger ATI make. One of the example I would like to share with you is that when I was boosting 12 psi in my stock Cobra with ATI P600B. When i got my 8.5:1 compression pistons, my 12 psi became 4 psi. I was very dissappointed and need to spend more money on an upgraded head unit to F1SC. If you have C2 now, you should be looking at D1SC. (One way to make up small crank size pulley is to have greater step of internal gear ratio of a supercharger). However, the bracket from the C2 would not work on D1SC. Basically you have to re-invent another D1SC bracket for your SC430. Lots of work, engineering, dowtime and so on.
I would recommend two choices:
1. 1uzfe rods with 10.5:1 forged pistons (about $1,250-$1,500)
2. Pauter rods wtih 10.5:1 forged pistons (about $2,500)
3. Pauter rods 8.5:1 forged pistons with ATI D1SC and new a bracket (about $5,000-$7,000). However, the D1SC might be too big and you might not able to close the hood or not enough physical space for it.
I think the first choice is all you need. Stock 1uzfe rods are slightly stronger than 2 or 3uz rods. Below is an ATI Supercharger Headunit Specs.
Cobolt
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Boost x VE (%) give us how much air that actually get´s inside the cylinders. (and intake temperature, but lets not complicate the matter for now)Lextreme said:
Compression ratio says how much that air get compressed on the compression stroke and nothing about what we se on a boost gauge.
Boost itself isn´t anything we want because pressure creates resistance. Flow in weight is what we want. a good enginedesign needs less boost for a specific flow of air.
Test:
VE 80%, comp 10.5:1 @ 0,5 bar boost gives wich compression?
VE 110% comp 8.5:1 @ 1,0 bar boost gives wich compression?
If we change the compression ratio with low comp pistons, the combustion chamber and gets an increase in volume, but the stroke and bore is the same, so the "work volume" of the engine is the same, but the engine can take more boost without knock, pre iginotion, detonation and so on.
An engine should have the highest possible compression ratio to atomize the fuel better and increase pressure in the early phase of combustion = more power.
If we step back to the supercharged engine in this thread - the extremly small drop that he may se on his boost gauge isn´t of any interest, the flow trough the runners/head is the same, so the combustionchambers will get the same amount of air as before or slightly more on the (intake stroke), than the intakevalve closes and the compression stroke begins and compression ratio becomes important.
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