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DIY High Flow 8V Head

I certainly am not an authority but I have spent a lot of time researching and testing 8V 951 heads in a quest to develop a low cost solution for larger motors.

Obviously the 16V is the best solution but the cost is significant and in many cases not practical. I wanted to do a head that would perform well and keep in
line with the spirit of low cost Hybrid Stroker motors. Outlined in this thread is my current progress. Much thanks to all who have helped me along the way, especially Sid and MM.

The results and the total cost of the effort are also outlined below:

951 Head.........................................$0 (head from my 2.5L)
47mm +2 Valves..............................$108 (set of 4, see here)
Valve Guides....................................$34
Valve Seals......................................$36
Valve Springs...................................$84 (set of 8, see here)
Install Guides...................................$160
Remove Valve Seats.........................$48
Install New Seats.............................$100
Surface Cut......................................$60
Competition Valve Job......................$265
Total Cost................$895

I started with the 8V 951 head from my 2.5L. I disassembled the head, cleaned it, and carefully inspected it. I inspected the ceramic exhaust ports, inspected the deck for pitting in the seal ring areas, inspected how much the head had previously been decked. Some may laugh but below is a picture of my valve spring compressor. It consists of an 8" C clamp from Harbour Freight and a modified socket (total cost $9 )



The next step was to do the initial porting. I did much of the porting before the new guides or intake seats were installed. In this way I did not have to worry about damaging the guides or the seats while removing much of the port material. The approach I took to porting was two fold. One, to clean things up especially in the throat area. I found on the flow bench that cleaning up the bowl area right above the throat resulted in improved flow. Secondly, to increase the size of the intake port to accommodate the bigger intake valve. My approach was to maintain the port shape while making it bigger. The intake valves I used were 47mm which are 2mm bigger than the stock intake valves. Therefore my approach was to remove 1mm from all the walls of the intake port as shown below.


Below is a picture of all the tools I used for doing the porting. All of the tools were purchased at Harbour Freight with the exception of the inside calipers and the carbide bur (McMaster 4324A32). My porting technique was slow and careful. I took A LOT of initial measurements using the inside calipers. I also used a technique in which I used a drill bit to make several 1mm deep holes as guides for how much material to remove. I removed quite a bit of material from around the guides. Be careful not to remove too much material in the lead up to the guide (see yellow circle above). I probably spent over 20 hours porting the intake ports. It is very important to make the ports as similar as possible in order to promote equal flow. My ports flowed within a few cfm of each other on the flow bench.


Once the initial porting was complete, the head was taken to the machine shop to have new guides and intake seats installed. I had the machine shop bore out the seat throat to within 0.005" of the final throat dimension. I had them bore down into the bowl as shown below as a guide for porting the bowl. At this stage I completed the porting of the intake ports.


I also cleaned up the exhaust ports both around the seats and at the header interface using sanding rolls as shown below. The ceramic often does not line up with the casting and this can be smoothed out to a large extent.


I also did some work to the chamber to de-shroud the intake valves. My bore size is 102.3 mm and therefore I could remove some chamber material. I used the head gasket to determine how much material could safely be removed. I marked the deck with a Sharpie as a guide then used sanding rolls to remove material as shown below. I was very careful not to damage the seats.


Once this work was completed, the head was send back to the machine shop to have the valve job done and to be assembled. The valve job is SUPER important. Choose a shop wisely. The intake dimensions I used were developed by blown 944 (Sid) and I used them with great results.


The intake valves are one piece valves and were purchased from SI Valves for $27/each. SI has stock intake valves (45mm) and +1 (46mm), +2 (47mm), and +3 (47mm). I used 47mm valves due to my bore size (102.2mm). On my flow bench I found very little improvement in flow was obtained above 47mm for my bore size. The exhaust valves are the stock sodium filled valves.


Shown below are some basics with respect to valve springs. The first head I built, I was pretty ignorant to these details. Do your self a favor and get familiar with this diagram. Do not assume the shop you use will get the details right. Verify EVERYTHING.


I was intending to run a high lift cam (0.525" intake lift) and using the formula above it became clear that the stock springs were going to bind. In an effort to find a low cost solution I was able to find some springs for a Datsun 280Z that fit perfectly in the stock retainer and spring cup and provided a bit more seat pressure (138 lbs vs 130 lbs) while having 0.065" more spring travel. The springs are made by Isky Cams (ISK7005-8). As an added bonus, the springs are half the price of the stock springs.


I was able to measure combined coil bind length using a vise and calipers as shown below. Coil bind clearance would be defined as the amount of spring travel remaining before coil bind at the minimum spring height. A safe minimum coil bind clearance would be 0.060". Some have run as low as 0.030" coil bind clearance in race environments. Running these low of clearances requires real precision in determining the physical dimensions of each valve. Also, keep in mind that as clearance is reduced, spring life is also impacted.


I had the head decked a few thousands just to clean things up for the Cometic MLS gasket.


The completed head was flowed on a Superflow flow bench at 28 inwc and the results are shown below. The results show that cleaning up the exhaust port and having a proper competition valve job makes a huge difference in an already outstanding exhaust port. Also, the larger valve size in conjunction with proper seat and throat dimensions resulted in significant improvement in intake flow.


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