k20civicsi

Building a PR4 head (b18a1) to compare to P8R head (b20 out of Honda Orthia).

PR4 Head:
bore=81mm
flows at 197cfm
combustion chamber volume=45cc
stroke=89mm
intake valve size=31.0mm
exhaust valve size=28.0mm

P8R Head:
bore=84mm
flows at 226cfm
combustion chamber volume=47cc
stroke=89mm I believe
intake valve size=33.0mm
exhaust valve size=28.0mm

Question about compression and air flow....
Have the PR4 head and putting 33mm vtec intake valves only in it (cutting the valve seats).
It's going into a head with a combustion chamber of 45cc. (Which would be a smaller space than the P8R head with the same intake valve size.) First question: since the combustion chamber size is smaller with the 33mm intake valves, wouldn't this be more compression and better air flow? Or not?
Also doesn't the dome size of the piston effect this as well? And how? Also the cam lobe size and lift and duration.
And then what about valve lift and valve relief? If you have 33mm valves instead of 31mm valves.....
I want to get technical with all the numbers but am not sure how to. Please help.

turbodcxbro

iTrader: (1)

Most likely the smaller combustion chamber is going to cause shrouding of your larger intake valve which is a bad thing. I haven't looked at these two heads too well but I would look very closely at the area around the intake valves or have a knowledgeable head porter take a look. Are you planning to port the head any? How about getting a multi-angle valve job? Both will help greatly and are fairly easy/inexpensive to do while you are working on the head.

k20civicsi

Honestly its my fiance and his friend that are doing this and I am trying to figure out what would be best because i was wanting them to go vtec, but they are wanting to stick to a cheap budget and go nonvtec. Yes my fiance will port the head. And no they will not do a multi-anlge valve job. I told them they should, but they are wanting cheap. But I still am trying to figure out the smart route whether cheap or not because I am interested. (Maybe i'll stump them lol)

kyden

imo its cheaper to just do a vtec head. a stock vtec head will still flow more.

k20civicsi

they claim its more expensive....hes wanting to go all motor....?????

k20civicsi

bump!!! need advice!!

killer_siller

That I remember, Non-VTEC heads are open face, meaning that valve shrouding should not be a problem. If you go flat-bottom valves, you will be losing combustion chamber volume, if you go dish, depending on the valve, you'll actually be gaining a little, but I don't think it's 2cc worth.
I'm wondering if the P8R head has a 84mm diameter combustion chamber...That'd make sense.

Piston dome affects a few things, but combustion chamber volume is not one of them. Cam lift and duration don't affect your combustion chamber volume either.

The big things (and you addressed them a little) are piston-to-head, piston-to-valve, and valve-to-valve clearances. All of which should be common knowledge to any machine shop.

I'd suggest a different machinist if they're talking single-angle valve jobs. Those are for dinosaurs. Hell, my machinist has to dig into storage to get the tools to do single-angle valve seats.

k20civicsi

so do you think p30 pistons would be better than p72-00 then? i was suggested the p30s over the p72-00.

p30=6.93cc dome/30.00mm comp height
p72-00=2.25cc dome/30.05mm comp height
stock pr4=-3.20cc dome/30.00mm comp height

So I see a pattern.....are you the p30's have a larger cc dome. Is this good for this setup I take it?

I also see that the p30 has 30mm comp height while the jdm gsr's has the 30.05mm comp height. Would it be best for the 30mm comp height as you said in the p30's? And why?

killer_siller

Piston choice affects piston-to-valve and piston-to-head clearances. While the Non-VTEC heads do have larger combustion chambers, I really can't say that there won't be interference problems. P30 pistons have a lot of dome. Make sure your clearances are checked before you run it!