Alright guys, I have been wondering what ALL of the differences between these heads were for a while now. I know a lot of them but I dont know if I know all of them… What am I missing??
Dont worry about specs and info on the cams, I just want information on the heads alone.
PR3
Found on the b16a (all generations), b17a and b18c5 (with minor port and polish out of the factory)
Better flow at high rpm's than the P72
[u][b]P72[/b][/u]
Found on all b18c engines except for the b18c5
Yields .2 higher compression than the PR3 head (smaller combustion chamber)
Sits higher than the PR3 head
Different bolt pattern for intake manifold than PR3
Intake ports are larger than PR3 intake ports
Better flow at low and midrange rpm's than the PR3
Thats about all I can think of off the top of my head. Am I missing anything??
What are the flow characteristics between the two heads??
This should be a good reference in the future as I will update the lists with new information as this thread grows.
You say the P72 head is taller and that is why only g3 gsr headers will work with it. My b18a header (DC 4-1) is supposed to fit on my b18c1 w/p72 head when I swap it in right?
teg92 - Those are some damn good articles. I am glad you posted them up.
Looks like each head is tailored to a different end of the powerband. P72 for low and midrange torque and the PR3 for the high end of the powerband.
Good read.
JOE - I havent tested this on anything yet but I have been told by very reliable sources that the P72 head sits taller than the B16 head and that is why they had to make different manifolds for each of the applications.
Originally posted by JOE You say the P72 head is taller and that is why only g3 gsr headers will work with it. My b18a header (DC 4-1) is supposed to fit on my b18c1 w/p72 head when I swap it in right?
You’ll be fine with that header. I first test-fitted a B17A exhaust manifold/A-pipe and it cleared with no problem. I’m currently using a Comptech for the ITR w/ no clearance issues.
Originally posted by B R teg92 - Those are some damn good articles. I am glad you posted them up.
Looks like each head is tailored to a different end of the powerband. P72 for low and midrange torque and the PR3 for the high end of the powerband.
Good read.
Glad you enjoyed them, I find them very informative.
Originally posted by LeftCorner You’ll be fine with that header. I first test-fitted a B17A exhaust manifold/A-pipe and it cleared with no problem. I’m currently using a Comptech for the ITR w/ no clearance issues.
Hey Jason, what block/head are you running right now??
I know that the b18a/b/c & b20b/z have a higher deck than the b16a & b17a. There is also the fact that the b18c head sits higher than any other b-series head…
Originally posted by B R
[B]Hey Jason, what block/head are you running right now??
I know that the b18a/b/c & b20b/z have a higher deck than the b16a & b17a. There is also the fact that the b18c head sits higher than any other b-series head. [/B]
'96 P72 on a '95 B18C1 block. I never even looked into this beforehand - good thing I didn’t have any trouble.
Originally posted by LeftCorner '96 P72 on a '95 B18C1 block. I never even looked into this beforehand - good thing I didn’t have any trouble.
Right on, that is some good news. I will have to change the information in the list then.
How does your teg run right now?? Just pretty much stock internals??
Originally posted by B R How does your teg run right now?? Just pretty much stock internals??
Runs pretty well aside from needing a valve adjustment and a couple dyno runs. Internals aren’t really stock, check out my Premier Profile for the details.
Originally posted by dillinger 4 if the p72 head has different bolt patterns on the intake manifold than the pr3, does the skunk2 intake manifold fit both heads?
Skunk2 makes 3 different intake manifolds. One for the b16,b17,b18c5 then another for the b18a/b and another one for the b18c1.
That is why when you order one you have to specify what head you have so you get the right manifold.
one comment about the headers…
i’m running a Greddy 4-2-1 SS header (ceramic coated later) that came off a 98 GSR motor… fits perfect.
this is my conclusion:
the p72 head may be taller… But, the exhaust port positioning is the same as the pr3/pr4 heads
i havent actually measured one. but thats what i’ve come up with since the 98 GSR header fit perfectly on my pr4 head.
as far as the valve sizes are concerned… the pr3 and p72 heads have same size in/ex valves… 33mm intake and 28mm exhaust…
the difference is the design of the valve back-cut (and thats only on the ITR that is different… as far as i’ve researched anyway).
so what can we conclude from this info. Can we say that one head would be better for one application over another? i.e. FI vs. NA?
Personally, I think the head itself both in the same condition and in stock form will not make much of a difference given a NA setup (most applications) and given the same valvetrain used. But this is just my thoughts, not anything concrete. The info on this thread is valid, but info alone without knowing the benefits is all but trivial.
If you look over the flowcharts that teg92 posted up you will notice that the P72 head has a better low/midrange flow than the PR3 head. In other words you will get better torque out of that head.
The PR3 head on the other hand really shines when it hits the higher RPM’s, as you can see by the flowcharts, especially the ported comparison.
In the end, there isnt that much of a difference between the two. Make what you want of the information and if you decide to go VTEC then hopefully this will help you out in your quest for the head that is right for your application if your really worried about flowrates and the like.
This is a bunch of information that 99.9% of the “import community” will never know, or even come to the point to where they can comprehend it.
what i’d like to know is this:
sure the flowrates differ a lil bit… and for my build up i’d prefer a p72 head because of the midrange…
i’d like to see the flowcharts done with the intake manifolds on…
the biggest draw back to the p72 head is that you’re limited to the stock IM or a Skunk2 IM… but for myself i’d prefer neither of these and go with a b16a2 IM… unfortunately that wont bolt on a p72 head… (without extensive mods anyway)
i’d like to see the p72 with Skunk2 IM flow charted. (i’m not a fan of the stock p72 IM)
I hear ya on that one. I wish they would do a flowchart with each head with the skunk2 manifolds on so I could see that comparison. Maybe one will come out someday like that.
I am curious why you would want to use the b16a2 manifold when you could bolt the ITR manifold right up to that head with no problems. It has better flow than the b16 manifolds and doesnt really cost that much, even when you buy it new.
Internals aren’t really stock, check out my 
