bernie lomax Posted December 30, 2008 Share Posted December 30, 2008 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 Quote Link to comment Share on other sites More sharing options...
z-ya Posted December 31, 2008 Share Posted December 31, 2008 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 Quote Link to comment Share on other sites More sharing options...
PurePontiacKid Posted January 1, 2009 Share Posted January 1, 2009 In response to the Fel Pro gasket, how thick are they? I have one on my car, but I never measured it, since I was just trying to get it running at the time Quote Link to comment Share on other sites More sharing options...
z-ya Posted January 1, 2009 Share Posted January 1, 2009 1mm Quote Link to comment Share on other sites More sharing options...
datsun 1/2 dozen SD Posted January 2, 2009 Share Posted January 2, 2009 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 Quote Link to comment Share on other sites More sharing options...
giorgio61 Posted February 26, 2009 Share Posted February 26, 2009 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 Quote Link to comment Share on other sites More sharing options...
z-ya Posted February 26, 2009 Share Posted February 26, 2009 You can get them from Black Dragon auto, or Northern Auto Parts: http://www.northernautoparts.com/ProductModelDetail.cfm?InventoryId=90529 Quote Link to comment Share on other sites More sharing options...
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