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Right something i havent seen covered before and i just happend to have both in bits on the bench so here we go.
The difference between the usual PR3 b16a/b, b18c5/6 and the P72 GSR, b18C4/1 head designs.
Difference between the combustion chambers.
P72 C4 HEAD (GSR/C1)
[/IMG]
PR3 B16a/b, B18c5/6 Head
As you can see the C4/C1/GSR head has flat face either side of the pairs of valves giving that extra CR when used on other B series Bottom ends. Where as the usual B16a head has a complete round shaped combustion chamber. The flat parts of the combustion chamber is called the Quench Area. Having these there aids swirl and combustion of the mixture as it rises up into the chamber. But the PR3 may have the advantage when it comes to volumetric efficiency as with the rounder more open shaped chamber I would have thought it better for the air entering and exiting the cylinder. Flowing smoothly out into the cylinder and back out into the exhaust ports, where as the P72 quench area's might to be as friendly to the air flow having the flat face and sharper edge's
Edit: Thought I would add some usefull info I forgot to put in.
The difference in compression between either head is around 0.25-0.3:1. So if you say fitted a PR3 head onto a GSR/C4 B18C then you would actually loose almost 0.3:1 of compression.
Difference between the intake ports:
P72 C4 Intake port
PR3 B16a Intake port
As you can see the P72 head takes a more direct downward port path witch in turn is larger.
The PR3 is more sticking with the conventionl "S" flow path through intake manifold to port and then cylinder. But in turn looks smaller in size.
It seems as the P72 port is more direct and bigger at the entrance. this shows how it would give better throttle response and more torque in the mid range. But then become restrictive as it doesn't have as much of a refined flow path as the gasses get faster in the higher RPM. Where the PR3, which has the more natural S type design of gas flow path witch in turn allows smother flow in the Higher RPM. This is usualy show as B20's with PR3 heads tend to have peak power higher up the rev range than the ones with P72 heads. (or so from what i have heard and seen so far)
(nothing here is fact except the picture's. Its just my conception of my thoerys from engine tuning that i have read up on. Im not 100% on how acurate my description is. But hope im somewere near the mark and making sense )
Oh and also got the coolant jacket hose difference.
P72 C4/GSR
PR3 B16a/b, b18c5/6
Could Be Helpfull as a STICKY
The difference between the usual PR3 b16a/b, b18c5/6 and the P72 GSR, b18C4/1 head designs.
Difference between the combustion chambers.
P72 C4 HEAD (GSR/C1)
PR3 B16a/b, B18c5/6 Head
As you can see the C4/C1/GSR head has flat face either side of the pairs of valves giving that extra CR when used on other B series Bottom ends. Where as the usual B16a head has a complete round shaped combustion chamber. The flat parts of the combustion chamber is called the Quench Area. Having these there aids swirl and combustion of the mixture as it rises up into the chamber. But the PR3 may have the advantage when it comes to volumetric efficiency as with the rounder more open shaped chamber I would have thought it better for the air entering and exiting the cylinder. Flowing smoothly out into the cylinder and back out into the exhaust ports, where as the P72 quench area's might to be as friendly to the air flow having the flat face and sharper edge's
Edit: Thought I would add some usefull info I forgot to put in.
The difference in compression between either head is around 0.25-0.3:1. So if you say fitted a PR3 head onto a GSR/C4 B18C then you would actually loose almost 0.3:1 of compression.
Difference between the intake ports:
P72 C4 Intake port
PR3 B16a Intake port
As you can see the P72 head takes a more direct downward port path witch in turn is larger.
The PR3 is more sticking with the conventionl "S" flow path through intake manifold to port and then cylinder. But in turn looks smaller in size.
It seems as the P72 port is more direct and bigger at the entrance. this shows how it would give better throttle response and more torque in the mid range. But then become restrictive as it doesn't have as much of a refined flow path as the gasses get faster in the higher RPM. Where the PR3, which has the more natural S type design of gas flow path witch in turn allows smother flow in the Higher RPM. This is usualy show as B20's with PR3 heads tend to have peak power higher up the rev range than the ones with P72 heads. (or so from what i have heard and seen so far)
(nothing here is fact except the picture's. Its just my conception of my thoerys from engine tuning that i have read up on. Im not 100% on how acurate my description is. But hope im somewere near the mark and making sense )
Oh and also got the coolant jacket hose difference.
P72 C4/GSR
PR3 B16a/b, b18c5/6
Could Be Helpfull as a STICKY
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