Lurch2461 Posted February 3, 2006 Share Posted February 3, 2006 I am building an L28 turbo motor, using the F54 block. The eventual capacity is going to be 2949 using L24 rods and KA24E pistons & L28 crank & Felpro head gasket. Am I better off using the P90 head and 7.88:1 compression or an N42 head and 8.87:1 compression? Which head will give me better quelch zones, P90 or N42? Which will give me better torque, P90 or N42? And fuel will be 98 octane minimum. Sometimes 100 with the addition of 10% Toluol/Methyl Benzine/Ethanol/Toluene additive. Love to know your thoughts. Quote Link to comment Share on other sites More sharing options...
AK-Z Posted February 3, 2006 Share Posted February 3, 2006 The P90 should give you more quelch since the air/fuel is focused more toward the spark plug electrode due to teh chamber design. The P79 have the same chamber design but with high compression. The N42 has a domed chamber design. As for compressions, the more compression the higher the fuel volume to aire has to be, especially on force induction. The fuel curve for a turbo setup is a little diferent than the NA setting because the higher the RPMs teh more the fuel has to be put in because of volume compression due to the turbo. For torque numbers between heads, I don't know. I don't think that anyone on here has actually done a comparision on different heads. Quote Link to comment Share on other sites More sharing options...
Mack Posted February 3, 2006 Share Posted February 3, 2006 actually, the P90 and P79 have the same size combustion chamber. the only difference is the P90 has square exhaust ports and the P79 has round, linered exhaust ports. If I were you, I would find some more suitable pistons for this project. or find some 135MM rods, I think they came in some sort of L series engine in aus and japland. that -2mm deck height is going to KILL you when it comes to quench. that negates ANY qunch you will have from a P90 or P79 head. Quote Link to comment Share on other sites More sharing options...
Lurch2461 Posted February 3, 2006 Author Share Posted February 3, 2006 Yes! L20A engines have 135mm rods, but what if I deck the block by 1.0mm thats only about 0.040 off the top of the block. That would give me a negative deck height of less than 0.020, bring the comp up and still use the P90 turbo designed head. Penny for your thoughts! Quote Link to comment Share on other sites More sharing options...
Lurch2461 Posted February 3, 2006 Author Share Posted February 3, 2006 Also L20A rods create a 9.33:1 comp, bit high for an L series turbo motor I would think. Quote Link to comment Share on other sites More sharing options...
BlackBeaut Posted February 3, 2006 Share Posted February 3, 2006 If you deck the block by 1mm, then you'll need to shim the cam towers by 1mm otherwise the timing will be right off. The with the cam towers 1mm higher you'll have fun and games setting up the tappets. All gets a bit tricky! Also don't think the felpro gasket is suitable for 89mm pistons, you'll need the HKS metal gasket, 1 or 2mm thick. There's also not much love on this site for felpro it seems, I've no personal experience on that though. Sounds like you're after big hp if you're burning that sort of fuel so it makes sense to be going with some forged pistons. That way you'll be able to run whatever rod you want (longer the better it seems, L14 rod is 137mm for example). Then get the piston made up to give you the right deck height and adjust compression with the piston dish. Cheers, Rob Quote Link to comment Share on other sites More sharing options...
DAW Posted February 4, 2006 Share Posted February 4, 2006 P90. Quote Link to comment Share on other sites More sharing options...
Lurch2461 Posted February 4, 2006 Author Share Posted February 4, 2006 This is all gettin top messy for me, think I'll stick to the original plan so long as I can get the F54 to bore 3.0mm oversize and see what happens from there. As for the fuel comment, we have 98 octane straight from the pump here in Oz. Might get onto an N42 head just for afters maybe and compare. Cheers and thanks for your ideas Quote Link to comment Share on other sites More sharing options...
Lurch2461 Posted February 6, 2006 Author Share Posted February 6, 2006 Hi All, After speaking with the Nissan gurus here in Oz the decision has been made to use the P90 head with KA24E Pistons, but with the rim machined off which creates an 89mm flat top piston with the P90 head and about 8.3:1 Compression. Thanks again. Quote Link to comment Share on other sites More sharing options...
Mack Posted February 6, 2006 Share Posted February 6, 2006 if you are taking off a bit off the top of the piston, wont that make the compression ratio even worse? or are you going to run a longer rod? I thing that would be ideal, a longer rod with a flatter piston. If you are worried about compression ratio, unshroud the valves out to the 89MM firing ring. that will open up a CC or two...... Quote Link to comment Share on other sites More sharing options...
RB26powered74zcar Posted February 6, 2006 Share Posted February 6, 2006 I think you will be sorry you went 3mm over bore on a turbo motor.... I cracked two different F54 blocks (cyl walls) trying to go 120 thou oversize. You have to find the perfect block to make that happen w/o the cyl walls being to thin once over bored that much.... Quote Link to comment Share on other sites More sharing options...
zcarman1259 Posted February 7, 2006 Share Posted February 7, 2006 I think you will be sorry you went 3mm over bore on a turbo motor.... I cracked two different F54 blocks (cyl walls) trying to go 120 thou oversize. You have to find the perfect block to make that happen w/o the cyl walls being to thin once over bored that much.... JS: Can you elaborate on your experience? Did the sleeves crack? Was it simply after the overbore? Was it after hard engine use? How much PSI, or NA? Did you have sonic tested or pressure tested or anything like that? Thanks, SB Quote Link to comment Share on other sites More sharing options...
naviathan Posted February 7, 2006 Share Posted February 7, 2006 Use a N42 block. The walls are slightly thicker and it's the same block the pros use to build strokers. Quote Link to comment Share on other sites More sharing options...
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