Compression question
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Compression question OK, last night I became disappointed with the stock LQ4 in my S10 when I went to the track for the first time. Soo, its time for some work. I have never run a turbo. Don't really know a lot about them or the setup needed to run one. BUT, I like compression and big cams. Nitrous guy. If I were to rebuild this engine for a lot more power right now and then add a turbo setup later, whats the max compression recommended? Its not a daily driver. I could care less how it acts on the street, but it will be driven on the weekends from time to time. I would like to keep the stock crank and rods. And to be totally honest, I would like to shoot for 800+ rwhp. 1000 would be my optimum goal. I know these engines can do this. And I hear some turbo cars with higher compressions. Will it last forever? nope. But that's ok. I don't want to spend the money I used to in my drag cars to go fast.
Thanks for the advise in this first step of my turbo future.
Thanks for the advise in this first step of my turbo future.
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Big cams and turbos dont go well together, so keep in mind youll have to do something about that later.
Compression depends on what fuel youll be running. Pump gas and water/meth I would stay below 11:1. E85 or race gas you could go 11.5:1, and a little higher on pure methanol.
Compression depends on what fuel youll be running. Pump gas and water/meth I would stay below 11:1. E85 or race gas you could go 11.5:1, and a little higher on pure methanol.
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Yea, I knew the cam would be different and that's not a huge deal. Cams aren't too expensive so I would swap that out. Its the rotating assy and heads that I don't want to have to do twice.
As for fuel, I have always just run race gas depending on the compression. We have E85 gas here at some stations. I am clueless on the water/meth injection so I would most likely run race gas or E85. My 565 in my dragster had really high compression and I loved it.
So with this in mind, I guess 11.5 is the number for a turbo engine?
Alcohol is an option since we have its available here pretty easily. But I really don't want to worry about the lube issue and the problems it causes with pumps, lines and other parts. Too much maintenance for my taste.
As for fuel, I have always just run race gas depending on the compression. We have E85 gas here at some stations. I am clueless on the water/meth injection so I would most likely run race gas or E85. My 565 in my dragster had really high compression and I loved it.
So with this in mind, I guess 11.5 is the number for a turbo engine?
Alcohol is an option since we have its available here pretty easily. But I really don't want to worry about the lube issue and the problems it causes with pumps, lines and other parts. Too much maintenance for my taste.
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You would likely have to run methanol specific ful compnents anyway because of the demand it puts on the fuel system. It requires about twice the amount of fuel flpw as gas does, so 1000whp on methanol would require 2000whp worth of a gas fuel system. In comes pump, regulators, and filters compatible with methanol from the start.
Dont stress on the heads. Stock casting with even a light port job flow enough for boost. LS9 headgaskets are a favorite as well.
As for compression, I would still try to not to go above 11.5:1 with race gas.
Dont stress on the heads. Stock casting with even a light port job flow enough for boost. LS9 headgaskets are a favorite as well.
As for compression, I would still try to not to go above 11.5:1 with race gas.
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Yea, we used to run alky on a super stock many years ago. And it does take about 2 times the volume as fuel. That's another thing I don't like about it. But it does help keep the engine cool, which is the biggest benefit in drag racing with the fast turn around times.
Ok, So 11.5 it is.
I don't think I want to mill the heads down to get there since I want to keep a thick deck. I would be ok with cutting them down as long as I know how far is safe on them. And I will need to search a good piston. I also don't want to increase the cubic inch other than what might be needed for cleaning up the cylinder walls. I have heard these engines actually wear really well most of the time so they don't require a lot of boring.
Now this gets into more of a component question. Intakes and TB. What would be a good choice that will work now and with the turbo? Oh, I also want to do a single turbo for space under the hood. I have the stock manifolds from the truck and heard they work pretty well too along with the 317 heads.
Ok, So 11.5 it is.
I don't think I want to mill the heads down to get there since I want to keep a thick deck. I would be ok with cutting them down as long as I know how far is safe on them. And I will need to search a good piston. I also don't want to increase the cubic inch other than what might be needed for cleaning up the cylinder walls. I have heard these engines actually wear really well most of the time so they don't require a lot of boring.
Now this gets into more of a component question. Intakes and TB. What would be a good choice that will work now and with the turbo? Oh, I also want to do a single turbo for space under the hood. I have the stock manifolds from the truck and heard they work pretty well too along with the 317 heads.
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Wow ok. I was thinking i might have to go to a differnet intake and elbow setup. I guess i can use my truck intake since i dont have any clearence issue with my hood.
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From: San Marcos, Tx
This is why I question this compression theory. And remember, I am learning about turbo systems as I go. But being an engine guy and a racer for many years I have to question some of this.
The turbo adds a ton of compression to make more power. And it increases pressure with rpm. So unless your wide open or running it on the heavy pedal side, your not pushing much psi. So why cant the engine have higher compression and just run less boost psi and end up at the same point at full boost? I really just don't get it. Why can you run 20psi with 8:1 and not 12 psi at 11:1 ?? I am not saying these have the same ending horsepower, just making an example.
This is part of the rod question too. They can handle and I know guys that are running over 800hp turbo engines on stock bottom ends. Will they last forever? nope, but they survive pretty well if built right and run right. And if the rods can handle 800+hp turbo applications, why cant they live with high compression which will be much less than 800hp? It just doesn't make sense.
I understand why there are cam differences. We ran different cams for our Nitrous cars.
The turbo adds a ton of compression to make more power. And it increases pressure with rpm. So unless your wide open or running it on the heavy pedal side, your not pushing much psi. So why cant the engine have higher compression and just run less boost psi and end up at the same point at full boost? I really just don't get it. Why can you run 20psi with 8:1 and not 12 psi at 11:1 ?? I am not saying these have the same ending horsepower, just making an example.
This is part of the rod question too. They can handle and I know guys that are running over 800hp turbo engines on stock bottom ends. Will they last forever? nope, but they survive pretty well if built right and run right. And if the rods can handle 800+hp turbo applications, why cant they live with high compression which will be much less than 800hp? It just doesn't make sense.
I understand why there are cam differences. We ran different cams for our Nitrous cars.
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The engine CAN have higher compression and run less boost, but it will typically make less HP than an engine with less compression and more boost.
In regards to the rods, there are a couple of factors here. Peak cylinder pressures and the chance of detonation being two of the big ones. You're a lot more likely to hit the rods harder even at less HP.
In regards to the rods, there are a couple of factors here. Peak cylinder pressures and the chance of detonation being two of the big ones. You're a lot more likely to hit the rods harder even at less HP.
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OK, I "kinda" get it a little. LOL Again, I am a turbo newbie so bare with me. So for me to get the best HP numbers I should go ahead and run less compression up front. So more like 10:1 .. I am ok with this. I just don't want to build the bottom end 2 times. So I want the most I can get right now that will be turbo happy later on once I get everything ready. again, I know I'll have to swap cams at that time and that's fine.
I want to start building my hot side now. I can get this done pretty cheaply doing it myself and I have truck manifolds to start with. So now my other questions come up. What size pipe should I run on the hot side and also which turbo should I be going for? This is going to be a race truck that will be legal to drive on the street. Auto trany and converter. It will be street driven but very little. So I am not worried about how smooth it is on the street. I don't mind a nasty high hp engine for street use. LOL I kind of like it really. I would like to be at 800+ rwhp with more room to get more by turning it up. 1000 wouldn't hurt my feelings at all for the track. So I need a turbo capable of these numbers without being overly big or taking forever to spool up. Stock bottom end isn't going to like a ton of rpm. Plus I want to keep budget in mind. Even a used turbo if its nice and a good deal works for me. I just need to be able to purchase the flanges and pipe needed to build the hot side. And it gets me the Turbo dimensions so I can place the mounting flange in the right spot so it all fits well.
I want to start building my hot side now. I can get this done pretty cheaply doing it myself and I have truck manifolds to start with. So now my other questions come up. What size pipe should I run on the hot side and also which turbo should I be going for? This is going to be a race truck that will be legal to drive on the street. Auto trany and converter. It will be street driven but very little. So I am not worried about how smooth it is on the street. I don't mind a nasty high hp engine for street use. LOL I kind of like it really. I would like to be at 800+ rwhp with more room to get more by turning it up. 1000 wouldn't hurt my feelings at all for the track. So I need a turbo capable of these numbers without being overly big or taking forever to spool up. Stock bottom end isn't going to like a ton of rpm. Plus I want to keep budget in mind. Even a used turbo if its nice and a good deal works for me. I just need to be able to purchase the flanges and pipe needed to build the hot side. And it gets me the Turbo dimensions so I can place the mounting flange in the right spot so it all fits well.