Hey guys, new here so bear with me. Wanted to get some opinions on how to handle the parts selection on a new build im doing. Its a B20Z/P8R supercharged motor. Goal here is to keep this as budget oriented as possible as this is not a high hp, high boost build. Looking at anywhere between 7-10psi in terms of boost and about 250-275hp.

I have a P8R head i purchased with 33mm valves, this head will be getting sent out for a mild port and polish and 3 angle valve job with your standard issue machine work to get it ready for use. Gonna be using supertech valve springs to accommodate for some mild/moderate FI cams in the future. Thats it for the head.

Im having a dilemma here about compression though. I have been targeting around 10:1 compression for use with the supercharger, however with the P8R head now being used, my combustion chamber volume has increased to 47cc. So i need a way to raise the compression slightly. The B20Z pistons will need to be fly cut, and the block with need to be decked when it hits the machine shop, taking all of this into account, i have calculated this.




Now 9.4:1 is not where I want to be, ideally i want to be between 9.5:1 and 10:1 compression to have suitable compression for supercharger use. Couple things I need to figure out....

1) can i use a 2 layer head gasket with the supercharger, and on this application, and where would i find one?
2) after the pistons are fly cut to match the 33mm intake valves, what is the maximum lift these pistons would be able to accommodate in terms of cams before I have to worry about the valve hitting the piston?

1) what kind of supercharger are you looking to use? you wont get 250whp out of a JRSC (roots style) you will have to go centrifugal which the kits are costly. most i have seen from a JRSC on nonvtec motor is like 220whp

2) 9.4:1 is not that bad for forced induction...the higher you go in compression the more risk you have at blowing your motor up cuz there is less room for error regarding the tune and idk who you are planning to tune it.

3) what do you mean by fly cut? the b20z pistons should have valve pockets to accommodate the 33mm valves b/c the b20z P8R motor came with 33mm valves stock. and a 2 layer headgasket will raise compression, but good luck finding a 2 layer headgasket for a non vtec motor.

4) pretty much what i have concluded is you want to have a f/i setup on a stock b20. my advise is go turbo just because the power potential is a lot more and a supercharger is just not as efficient. you could forgo the p&p and head work, and just put in a f/i cams and put the rest of the money towards a turbo kit

i appreciation the suggestions but this is a budget build like i said, i picked up an entire motor, and jrsc kit last year for 950 bucks, i have no intention of investing 3 grand in a turbo build on a car i drive on a daily basis.

to answer 3) fly cut means to recut the angle and size of the valve reliefs on the piston to accommodate bigger valves, the P8R head and block combo that came on the japanese motors is a low compression motor, i only have the head, not the actual block or set of pistons that went with it, the b20z short block im getting is from a USDM crv b20z, with PHK pistons, the valve reliefs on those only fit 31mm valves.

the whole purpose to running higher compression on the supercharger kit is to make up for the lack of CFM that the blower produces, often people relate psi or boost pressure to be the deciding factor on how to tune the motor, i tune around CFM produced. Typically superchargers are run between anywhere from 9.5:1 and 10.5:1 compression. GSR and Type-R motors do this just fine with the JRSC, im looking to do the same to give it a little extra power to turn the supercharger itself.

oh ok so well if you get the valve pockets redone then i bet you could use up to a stage 3 cam or so...i have seen ppl use the crower turbo stage 2 cam or the stage 3 all motor cam in boosted setups with good results.

i understand where you are coming from as far as higher compression...the only other thing i could suggest is mill the head, but then you should prolly clay the motor (depending on how much you take off) just to make sure the piston and valve clearance. Milling the head can raise compression a decent amount if done correctly