Hey guys. So I have had my cobra for about 2 years now. Bolt ons so far are 2.93 pulley and 100 idler, offroad x and magnaflow mufflers, JLT cai and a killer chiller system. Its no longer my DD so want to turn it 8000 rpm and outrun corvettes with a stock looking setup. (So I can actually get races obviously) I'm a machinist so I'm going to port the heads, eaton, and plenum. Get some better cams. Higher pressure springs and retainers. I'm not afraid to turn the stock short block 8000 so it'll just get a bit wider clearances and a set of low tension rings. Bigger injectors and maybe a fuel pump are also on the list if necessary. The real question I have is the eaton. Right now I make 450 rwhp at about 6200 and right about there the blower runs out of juice. What can I do to bring the rpm range up on the blower? Smaller lower pulley? Is there anything internally I can do to make it more efficient? Thanks in advance and sorry for the rambling. Haha. Cheers.
Raise the rpm range on my eaton
- Thread starter HardRockinAmigo
- Start date
Shifting at about 5k RPMs is optimal for a 2.9/4# or 6#. You are going to build a LOT of heat going to 8k. If you really want to shift at 8k, get a whipple 2.3 or something else more efficient in the upper RPM range.
Like I said I want it to look stock. If I put a whipple on it nobody is going to race me that I want to race. The point is taking people's money dude. Shifting higher lets you run more gear. The car with more gear always wins. And if I can turn it higher I can hopefully just have the boost come in later. Maybe a larger than stock pulley? Would that help the eaton come in when I want it to?
Did you try doing a search? You are going to need more power and less weight along with the machining your going to do.
8K RPM on an overspun M112 Eeaton just is not going to happen bud, you will cook your engine. Seriously, you will lose worse than shifting at 5K. Past 6.3K RPM ish, the boost drop off and heat due to inefficiency will kill your horsepower. Let me know how your IAT2s work out.
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Port the blower and hide a nitrous kit. No need to spin the engine/blower to the moon.
Paint a whipple grey:shrug:
Turning the blower with stock pulleys to 8000 engine rpm = the same supercharger rpm as you get with a smaller pulley turning 6500. I don't understand how it would make more heat if the eaton isn't turning more rpm. I understand that the motor will be sucking more air at 8000 so I will lose some boost but I feel that the good the rpm is going to do will offset the lower boost numbers. Any input?
And the port will help efficiency so I might be able to pull off the same boost numbers at the higher rpm.
Another option for a more OEM looking install but higher power is the cobra engineering adapter plate and a M122 gt500 blower. OEM looks and people make ~600whp with a port job and pulley.
If I had the money to change superchargers I probably would. I'm really looking for input on my idea. Where is all this extra heat coming from if the supercharger is at the same rpm? Right now my iat temps are 78 degrees at 6500 rpm. At 6500 rpm with my 2.93 pulley and stock lower the supercharger is at 16,638 rpm. If I put the stock 3.6 pulley back on it and turn the engine to 8000 the supercharger rpm will be 16666. Please check my math and numbers and tell me if I'm wrong. I want to understand why this won't work.
So then where is your boost at with a stock pulley? 7-8psi. Spin it to 7K rpm, boost drop off will only be a pound or so. So what, my ported pullied Eaton is pushing 16.5 and I already PASSED YOU with over 500hp even though you are winding in out to 7-8k RPM and making 425 - 450hp at the most. See how it works?
The best idea was the hidden spray kit.
At 6500 I'm sure it'll be lower boost but with the motor turning more rpm the boost will be on par with the smaller pulley I'm thinking. Low end Torque isn't what wins you races which is what you have when you turn 6000 rpm. Gear and top end horsepower win races. It's silly to turn a DOHC engine to 6500. Silly little pushrod LS cars turn 7k all day long and Will outrun you with 100 less horsepower. There's a lot more to going fast than dyno numbers. I've seen plenty of motors that were faster on a track with dyno sheets that you wouldn't even compare.
It's not just about the blower. Your engine at 5 or 6k is not going to make power the same way it would at 8k. I don't think the 4.6 can do 8k anyway. Not without a bunch of cash, time, and good engineers at least. I know some people do 7k. Even if you could just increase the RPM the torque you'd be making would probably be pretty low at that speed.
make sure youre looking at IAT2 for post blower temps, IAT is just ambient air temp pretty much
What kind of hitch do you have on the back bumper? You must have a nice racecar to afford to pull the trailer with your cobra. That's all it's good for when you're worried about torque and horsepower that low.
You have a interesting concept that you are toying with and potentially could have good results. The thing I am curious about is at what rpm will the eaton become a restriction for the needs of the engine. If you can get the car in a sweet spot where both are within their efficiency range you might have some decent gains. If heat becomes an issue you could always change things like the heat exchanger and possibly add a killer chiller. I have a feeling that the gains from the increase in rpm might be lost due to the lowering amount of boost trying to spin the blower slower. Overall though your power band curve might be more desirable for top end tho! Good luck keep us posted with the results if you move forward with this!
Not sure about your area but switching to E85 might also help out for your goals!
Not sure about your area but switching to E85 might also help out for your goals!
It already has a killer chiller with no heat exchanger. I'm not too worried about heat. I don't see a supercharger ever becoming a restriction. It's always going to be making boost. Not that I'm a genious when it comes to superchargers. Haha.
Thanks for the input. I'll have to punch some numbers once I get my heads on a flow bench and see what they'll do. Along with the eaton. And see where they'll be most efficient. For the rpm range I want that is. I'll also have to do some research on e85. Cheers.
Thanks for the input. I'll have to punch some numbers once I get my heads on a flow bench and see what they'll do. Along with the eaton. And see where they'll be most efficient. For the rpm range I want that is. I'll also have to do some research on e85. Cheers.
True the supercharger will always be making boost but the amount of CFM or air that it pushes into the motor will vary from blower to blower. At the upper rpm's your engine might want more volume to eat. I an no expert with the flow rates of the M112 but with people maxing them out spinning their engines less RPM you might be fighting different variables with the project in motion.
also OT where did you come up with the 8k RPM number? Is it just a theoretical value you want to shoot for?
8k is just the max rpm I would feel comfortable spinning with the stock bottom end/ valve train with only springs valve job and cams. This is all only theoretical right now I'm just looking for input on the idea. I feel that they're maxing it out early because they don't realize what rpm does to they're little pulleys that look good but don't function where this motor wants to make power. It's DOHC. That means rpm is its friend.
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