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MN47 Head vs shaved ZN47


bernie lomax

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to boost CR to achieve better low-mid torque on a budget, would it be preferred to swap a MN47 head on a pretty much stock L28E or shave the existing ZN47 head? the stock dished pistons would stay, budget.

 

how much shaving could occur before cam tower shimming becomes a concern? would shaving of .050 reduce combustion chamber volume to 40cc? is there a rule of thumb?

 

given torque is the objective, would replacing the MN47 stock 42mm intake valves with the N47's 44mm valves be a good place to spend money?

 

thoughts & opinions are appreciated

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As you probably know, the best way to increase CR is by changing pistons. ITM L28 flat tops (part number RY6134) are $33 each (~$200) with rings and pins. This is route I would go using your Z N47 head. Use a stock head gasket, and your CR is around 10:1. I've been running these in my race car for three seasons now, and they are holding up fine.

 

As far as milling the stock head, I would not go more than 1mm using a stock head gasket. As far as the MN47 head, since you are not looking for big HP numbers, you can use it as is to increase CR to around 9.22:1 with a Felpro gasket.

 

Pete

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to boost CR to achieve better low-mid torque on a budget, would it be preferred to swap a MN47 head on a pretty much stock L28E or shave the existing ZN47 head? the stock dished pistons would stay, budget.

 

how much shaving could occur before cam tower shimming becomes a concern? would shaving of .050 reduce combustion chamber volume to 40cc? is there a rule of thumb?

 

given torque is the objective, would replacing the MN47 stock 42mm intake valves with the N47's 44mm valves be a good place to spend money?

 

thoughts & opinions are appreciated

 

 

 

i have been running the mn47 head for 2 years and it has its ups and downs depends if its efi or carb i think it would be cheap to go with the mn47 head if its easy to get to here in SD california we have JY full of them

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  • 1 month later...

As you probably know, the best way to increase CR is by changing pistons. ITM L28 flat tops (part number RY6134) are $33 each (~$200) with rings and pins. This is route I would go using your Z N47 head. Use a stock head gasket, and your CR is around 10:1. I've been running these in my race car for three seasons now, and they are holding up fine.

 

As far as milling the stock head, I would not go more than 1mm using a stock head gasket. As far as the MN47 head, since you are not looking for big HP numbers, you can use it as is to increase CR to around 9.22:1 with a Felpro gasket.

 

Pete

z-ya can you give us your source for the RY6134 ITM pistons?

Thanks,

George

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