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P90A with solid lifters!


AydinZ71

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Hi guys! People said they existed, but honestly never saw one in the wild. I pulled the valve cover from the 71’ SCCA car today, and low and behold it’s a P90A with solid lifters. Am I crazy, or are these rare? 
 

I also can’t make out the cam. The fire-wall side is blank on the end, but it does have an “A” on the casting. 🤷🏽‍♂️
 

the block is an L24. Curious what the CR is for this setup, but for now the best I can do is run cylinder pressures. Will do when I get the bat back in. 
 

has anyone else seen this setup before? Curious what you all think. I think I’m going to steal this head for the L28et so I can install an upgraded cam into it. Currently, it has a P90a with hydraulic lifters, which will not allow for aftermarket cams. 

 

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1 hour ago, jonbill said:

P90A is quite common in the UK and all have solid lifters.


Hmmm interesting! Well That’s good to know! I wonder why the previous owner Mounted this on an L24 block. I heard the P90’s flow well, but really no idea compared to thier predecessors. 

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2 hours ago, AydinZ71 said:

 pulled the valve cover from the 71’ SCCA car today, and low and behold it’s a P90A with solid lifters. Am I crazy, or are these rare? 
 

the block is an L24. Curious what the CR is for this setup,

 

 

Just saw jonbill's reply.  This is just a follow-on, below, that I was writing.  Seems like an interesting motor.  The other thing people like about the P90 is that it has the square exhaust ports without liners.

 

 

The block has probably been bored or modified to allow the bigger valves to miss the sides of the cylinder wall.  And there is a very common Timesert modification that people do to get rid of the hydraulic pivots.  They're not actually "lifters".

 

The P90 with flat top pistons would be similar to a ZX engine except that the swept volume would be less if it hasn't been bored much and still has the L24 crankshaft.  Probably about 8:1, but hard to say for sure.  Check the bottom of the P90A letters to see if the head has been shaved.  That would up the CR somewhat.  There are engine calculators out there too that you can play with.

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Ah cool!!! What is the stock measurement from the bottom of the letters to the deck? I can use a caliper to check. I don’t have a Spare head gasket or chain tension tool To pull the head at this time. I should be able to next week. This was an SCCA car, so I’m hoping the previous owner knew what he was doing. I doubt the CR from a flat top piston L24 block and stock P90a head would be very attractive 

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Yeah... I don’t know if it was common to put these heads on L24 blocks for racing 🤷🏽‍♂️. The CR alone doesn’t make much sense. I picked up an N42 from a local guy, and will swap it after cleaning it up. the guy I bought it from ran mega squirt and blew a head gasket, but he thinks it was from improper ignition timing At high rpm. I don’t see any valves bent, but I will spray some lightweight oil down the runners and see if it leaks past the valve/seat when closed. 


When I pull the P90a, I will use a syringe and plastic plate to estimate the chamber volume. Then il know if it’s appropriate for the L28et. Fingers crossed. It might still be OK with the dished JE pistons, but id prefer if I settle on a CR sub 8 for the ~16psi I was running. Otherwise, I will need to use a 2MM gasket (if they still make those), or turn my boost down. I’m going to need to look into a knock sensor. It’s hard to hear over the wastegate dump. 

Edited by AydinZ71
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