1996 Mustang
- Thread starter wknwar
- Start date
Gonna need some additional info to help you out.
What is your list of mods already done?
What supercharger are you going to use?
How much boost do want?
Will it be intercooled?
Will you use water/meth injection?
What type of power/torque levels are you trying to attain?
Do you want it to have lots of low end torque, or are you trying to make high end power?
To give you a generalization:
If you are going to use a roots, a twin screw where boost is not RPM dependent, or a turbo that builds boost at low RPM, you want to be at a lower compression (relative to the alternative).
If you are going to use a centrifugal supercharger or turbo that doesn't build boost down low you can keep a high compression ratio...you can even go higher that stock.
In reality, you can use any compression level you want. But like most other power building techniques there is give and take. When you have a large amount of boost at low rpm in a high compression environment you are closer to pre-ignition conditions. To compensate you must add fuel, pull timing, or both.
If you need further info, or would like some suggestions, please give me the specifics and I will help you as much as I can.
What is your list of mods already done?
What supercharger are you going to use?
How much boost do want?
Will it be intercooled?
Will you use water/meth injection?
What type of power/torque levels are you trying to attain?
Do you want it to have lots of low end torque, or are you trying to make high end power?
To give you a generalization:
If you are going to use a roots, a twin screw where boost is not RPM dependent, or a turbo that builds boost at low RPM, you want to be at a lower compression (relative to the alternative).
If you are going to use a centrifugal supercharger or turbo that doesn't build boost down low you can keep a high compression ratio...you can even go higher that stock.
In reality, you can use any compression level you want. But like most other power building techniques there is give and take. When you have a large amount of boost at low rpm in a high compression environment you are closer to pre-ignition conditions. To compensate you must add fuel, pull timing, or both.
If you need further info, or would like some suggestions, please give me the specifics and I will help you as much as I can.
Your peak lift is not going to affect whether you need to flycut your pistons, it will be the amount of duration involved that will determine that. Contact your cam manufacturer and ask if they know if you need to flycut your pistons. In any case either you or your engine builder should double-check the PTVC just to be sure.
Given that you are at 10.1 compression, I would generally recommend a centrifugal supercharger over a positive displacement. That's not to say you can't use either one, it just seems to me that a centrifugal will be a better complement to your current mods. But that is just my opinion, take that for what you will.
One other thing to consider is if your tranny or even your clutch are still stock, a centrifugal will beat on them less than a eaton/twin screw will. Thats because they tend to have much more torque than a centrifugal acting on the drivetrain during a shift.
Sorry I can't be more help on the cam right at the moment. Please let me know if I can give you anymore help.
Given that you are at 10.1 compression, I would generally recommend a centrifugal supercharger over a positive displacement. That's not to say you can't use either one, it just seems to me that a centrifugal will be a better complement to your current mods. But that is just my opinion, take that for what you will.
One other thing to consider is if your tranny or even your clutch are still stock, a centrifugal will beat on them less than a eaton/twin screw will. Thats because they tend to have much more torque than a centrifugal acting on the drivetrain during a shift.
Sorry I can't be more help on the cam right at the moment. Please let me know if I can give you anymore help.
Fuel first, you can gap your plugs down to prevent fire blow-out. If you are staying under 450RWHP you are probably safe with 42# injectors, beyond that up to 600RWHP I would use a 60# set.
Any bigger and you need to go with a stand alone system such as FAST to support big injectors which have an incompatible impedence value with the stock fuel system, I can't remember off-hand if they are lower or higher impedence but anything bigger than 60 is where the change occurs. There is one new company that makes 71# at stock impedence levels.
The sacrifice of using a bigger injector is that you will burn a lot more gas at idle, coasting, and low load due to the injectors being used at less than 5% duty cycle at these points.
Go with the biggest in-tank fuel pump you can. You also need to upgrade your fuel lines if you go much past 500RWHP.
Once you have fuel right, then get an aftermarket ignition. You can open your plugs back up and see some top end gain at that point. Until you can get that ignition, keep your gap at .024" if you are less thant 10# of boost, for more boost go with .018". Once the ignition is in, you can open up your gap, maybe as much as .035" Use a dyno to see how much gap you can get away with. I would love to give you a solid figure but there are too many variables (combustion chamber shape, air velocity, boost level, ignition voltage, etc.) You will know if you have to much gap because the car will stop increasing power as you spin it up.
Anything else, let me know. If anyone reading this thread has better information than me, feel free to throw in your 2 cents.
Hope this helps.
Any bigger and you need to go with a stand alone system such as FAST to support big injectors which have an incompatible impedence value with the stock fuel system, I can't remember off-hand if they are lower or higher impedence but anything bigger than 60 is where the change occurs. There is one new company that makes 71# at stock impedence levels.
The sacrifice of using a bigger injector is that you will burn a lot more gas at idle, coasting, and low load due to the injectors being used at less than 5% duty cycle at these points.
Go with the biggest in-tank fuel pump you can. You also need to upgrade your fuel lines if you go much past 500RWHP.
Once you have fuel right, then get an aftermarket ignition. You can open your plugs back up and see some top end gain at that point. Until you can get that ignition, keep your gap at .024" if you are less thant 10# of boost, for more boost go with .018". Once the ignition is in, you can open up your gap, maybe as much as .035" Use a dyno to see how much gap you can get away with. I would love to give you a solid figure but there are too many variables (combustion chamber shape, air velocity, boost level, ignition voltage, etc.) You will know if you have to much gap because the car will stop increasing power as you spin it up.
Anything else, let me know. If anyone reading this thread has better information than me, feel free to throw in your 2 cents.
Hope this helps.
trinity_gt
10 Year Member
Midnight2V made some good points.
The crank will be fine if you keep the RPM sane but I wouldn't trust the rods. They're a weak point.
Seriously, you've got the motor in pieces now so think carefully about your combo and what you want to do. If you want to build a blower motor, start now. Consider trading your 10cc (?) KB pistons for some 17cc parts to get down to ~9.4:1. Get a set of Manley H-beam rods to match the pistons and your bottom end will be pretty much good to go. You're this far into it...get the right parts. A broken rod will trash the rest of the motor so don't skimp now on stuff like this.
If you've got good gas and are assured of always having a supply of it, 10:1 might work but it's going to be more detonation prone. With a blower, especially a PD one, you don't really need or want lots of static compression...
You'll need a custom tune to go along with whatever your combo ends up being (centri, twinscrew, intercooled or not etc, injector size.) A 75mm MAF will probably saturate long before you hit 400rwHP so you might consider upping to a 90mm Lightning part (for example.)
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