round port heads
Thread Starter
Registered User
Joined: May 2005
Posts: 330
From: sacramento california
round port heads
im sure this has been asked before, is there a way to remove the exaust rings from the round port exaust heads? is it difficult and will it really make that much of a differance? thanks
zakk
zakk
The Good Twin
Joined: Aug 2005
Posts: 20,639
From: Wild Wild West, UTAH!
There's no reason to remove them... but if you feel like you must, grab the vice grips, lock on, and pull. 
http://datsunzgarage.com/p79/
In 1977 Nissan added cast-in liners to the outer exhaust ports to heat red-hot and reduce emissions. They used them from 1977 through 1983 on both the N47 and P79 heads. Some people claim the liners are restrictive and a poor choice. And you can hack them out but I've been told it's a lot of trouble and leaves the port airflow ragged. The larger valve P79 flows better than the smaller valve E31 and E88 but few people pick on those older heads. So for the street enthusiast it's not really worth losing sleep over. I have used P79 on my carburetor L28 and pulled a 13.9 1/4 mile.
HOWEVER:The P90 turbo head has square exhaust ports like the E31/E88/N42. Nissan apparently "did it's homework" on the exhaust runners on this head. The intake port shape/size is identical to the P79.
http://datsunzgarage.com/p79/
In 1977 Nissan added cast-in liners to the outer exhaust ports to heat red-hot and reduce emissions. They used them from 1977 through 1983 on both the N47 and P79 heads. Some people claim the liners are restrictive and a poor choice. And you can hack them out but I've been told it's a lot of trouble and leaves the port airflow ragged. The larger valve P79 flows better than the smaller valve E31 and E88 but few people pick on those older heads. So for the street enthusiast it's not really worth losing sleep over. I have used P79 on my carburetor L28 and pulled a 13.9 1/4 mile.
HOWEVER:The P90 turbo head has square exhaust ports like the E31/E88/N42. Nissan apparently "did it's homework" on the exhaust runners on this head. The intake port shape/size is identical to the P79.
i felld offa mai trike
Joined: Nov 2008
Posts: 827
Leave the liners in. They flow extremely well for how small they look.
If you've ever seen a cleaned round port head, you would know that you simply cannot just yank the liners out, they go all the way to the valve seat, they are NOT just a simple round tube in the runners
If you want to do port work, just smooth the back of the valve seat into the port, and you'll have a very nice flowing head (on the exhaust side, at least).
If you've ever seen a cleaned round port head, you would know that you simply cannot just yank the liners out, they go all the way to the valve seat, they are NOT just a simple round tube in the runners
If you want to do port work, just smooth the back of the valve seat into the port, and you'll have a very nice flowing head (on the exhaust side, at least).
Registered User
Joined: Oct 2004
Posts: 92
From: Portland Or
Leave the liners in place , they are not restrictive at least in a P-79 head. They are there to smooth the flow but also to help burn the unused fuel as it passes out into the exhaust system. On a P-79 , if you mill the head .030 it will bring the compression to 9.5 to 1 and you don't need to shim the cam towers. With the combustion chamber shape you can still use regular gas. by the way the P-90 has the same shape chambers.
Gary
Gary
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