Hey guys, It seems that time and time again I see people (including myself) posting up questions looking for difference between the OBD-1 Pr4 head and OBD-2 P75 head. I have a couple of each laying around, and decided to take a quick looksy.

As we all know, the b18a/b/b20 heads can be switched out with no modifications necessary. This is with the exception of the p8r head, but Im not including that.

On with what I found,

First thing I looked at was inside the valvetrain casting in the head. Overall everything is the same. The only difference I can see is that the p75 head has a 4th oil return to the pan, while the pr4 has more of a vent hole.

Pr4 on the right, p75 left


Picture of the p75 oil return


Pr4 oil return Vent


The next thing I did was take a quick measure of the intake and exhaust ports to look for any noticeable differences. It has been brought up before that the p75 has bigger ports that flow better, but I failed to see nythign different. I measured quite a few different surfaces, and everything was identical between the two. Im no professional, but if there is a difference I didnt see it.

Intake Port


Exhaust Ports


Next up, I took a look at the head surface of the two heads. This is where I found the most difference between the two. As can be seen from the pictures, the p75 has much larger coolant ports than the pr4. However the pr4 has on additional port on the return side of the cooling system, the p75 does not have this. The chambers in both appear to be identical.

Pr4 left, p75 right


Pr4 head


P75 Head


P75 Center Cooling Jacket


Pr4 Center Cooling Jacket



The last thing I looked over was the cams. Once again, there have been claims of slightly bigger cams in the p75. From what I found, the lift on both appears to be the same. I had no good way to easily test duration, but if there is a difference it is minor

Pr4 on the right


Overall, an easier to give to someone is that the heads are identical. If your really worried about cooling, the p75 appears to be a bit better, but deck rigidity may be sacrificed a very small amount. The ports also appear to be identical. When it comes down to overall performance, they should be the same.

Hope this helps answer someone questions.

 

good [freak]en write up... real interesting

 

good write up on this topic.

 

faq worthy i would think.

 

was that the sec gen pr4 head or first?

sec gen pr4 cams are the the same as the p75

first gen's pr4's are not

 

B18b1, so second Gen. This head in particular was a 1995.

I tried my best to make it clear that this is between the B18b1 heads. Its common knowledge that the B18a1 heads (and cams) are different.

 

Sorry I actually searched, you mean to tell me that if i have a B18b1 block with a p75 head it is obd2? but it's had an obd1 dizzy the entire time, running good also........back from the dead so hopefully someone can answer.

 

no the 94-95 ls integra I believe has a p75 head and is obd1.