Building new engine, cylinder head DIY..
03-20-2005, 07:05 PM
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Building new engine, cylinder head DIY..
I have had a stock 930 engine core lying around that I was planning on rebuilding as a test engine for the EFI kit and new HF2.. Since most people have "stock" engines the first tuning test will be run on this rebuilt engine..
I know of 2 recent engine rebuilds that required valve guides and topend rebuild. The dollars spent basically got the engine whole again with the only additions being ARP rod bolts, ARP head studs, and 964 cams.. I asked why they didn't do any porting to the heads and both owners replied they didn't have the funds..
I'm going to give some DIY steps to encourage people to "contract" the work done on there heads to provide excellent results for reasonable $$$. Here is my disclaimer, I am not in the business to rebuild cylinder heads.. Yes, I have done many sets of heads, working my way up from VW heads through the N/A and turbo 911 heads.. The machine work that I show done will be completed by recommended shops just like you would have done.. There are many publications out there that teach and show you the process, what I'm going to do, is show you the next steps...
The above picture show a "stock" mid 80's 930 head, that I sent and had two very important things done.. Twin plugging, and the next having the sealing surface cut for the addition of the C2 style head gasket.. This provides an added benifit for head sealing at boost higher than 1 bar and the head is trued up by being flycut..
This main goal for this porting job is to allow the average Porsche enthusist to get his hands dirty and get some awesome results.. I'm not going to go down the path of how to build the 10 sec 930.. But to offer some proven tips as to how to get it down without screwing things up.. I have seen many ruined heads over the years.. 930 heads are based on HIGH PORT VELOCITY, and yes, we are going to adhere to those lines of thought.. Yes, I'm restraining myself as to not bolting these heads up to the CNC and opening them UP... The black sharpie has identified the major offending air flow restrictions.. You see when the heads are cast, they are done in two pieces.. The casting halves are actually split right down the centerline of the ports.. When the heads are machined for the valve seats, the cutter will pass into the bowls and leave the transition from the casting to the machining.. Thus the line that I drew, to show this area..
This shows the look through the exhaust port towards the bowl.. Please note in the pictures the rough aluminum casting.. This will impede the airflow by increasing friction..
One can see the stock intake port.. The measurement of the port is 32mm, I marked the diameter in black.. Many people have taken the outside casting diameter or lip which varies from 33.75-34.00mm, however this is not the actual size or critical dimension. It is the 32mm..
Okay, I suggest that anyone trying to do this, go and purchase some machinist dye, I use Dykem blue.. What is does is show you the different casting ridges or imperfections between surfaces or low spots.. It is basically a guide coat.. And it will keep you from going overboard with your sanding rolls.. As you can see in the picture, the edge between the machined area and the casting in the exhaust port is quickly sanded away.. as I blend it out, the blueing will be sanded completely off..
I have pretty much finished the right side of the intake port.. All the rough casting is gone and the casting ridge or transition is gone..
I know of 2 recent engine rebuilds that required valve guides and topend rebuild. The dollars spent basically got the engine whole again with the only additions being ARP rod bolts, ARP head studs, and 964 cams.. I asked why they didn't do any porting to the heads and both owners replied they didn't have the funds..
I'm going to give some DIY steps to encourage people to "contract" the work done on there heads to provide excellent results for reasonable $$$. Here is my disclaimer, I am not in the business to rebuild cylinder heads.. Yes, I have done many sets of heads, working my way up from VW heads through the N/A and turbo 911 heads.. The machine work that I show done will be completed by recommended shops just like you would have done.. There are many publications out there that teach and show you the process, what I'm going to do, is show you the next steps...
The above picture show a "stock" mid 80's 930 head, that I sent and had two very important things done.. Twin plugging, and the next having the sealing surface cut for the addition of the C2 style head gasket.. This provides an added benifit for head sealing at boost higher than 1 bar and the head is trued up by being flycut..
This main goal for this porting job is to allow the average Porsche enthusist to get his hands dirty and get some awesome results.. I'm not going to go down the path of how to build the 10 sec 930.. But to offer some proven tips as to how to get it down without screwing things up.. I have seen many ruined heads over the years.. 930 heads are based on HIGH PORT VELOCITY, and yes, we are going to adhere to those lines of thought.. Yes, I'm restraining myself as to not bolting these heads up to the CNC and opening them UP... The black sharpie has identified the major offending air flow restrictions.. You see when the heads are cast, they are done in two pieces.. The casting halves are actually split right down the centerline of the ports.. When the heads are machined for the valve seats, the cutter will pass into the bowls and leave the transition from the casting to the machining.. Thus the line that I drew, to show this area..
This shows the look through the exhaust port towards the bowl.. Please note in the pictures the rough aluminum casting.. This will impede the airflow by increasing friction..
One can see the stock intake port.. The measurement of the port is 32mm, I marked the diameter in black.. Many people have taken the outside casting diameter or lip which varies from 33.75-34.00mm, however this is not the actual size or critical dimension. It is the 32mm..
Okay, I suggest that anyone trying to do this, go and purchase some machinist dye, I use Dykem blue.. What is does is show you the different casting ridges or imperfections between surfaces or low spots.. It is basically a guide coat.. And it will keep you from going overboard with your sanding rolls.. As you can see in the picture, the edge between the machined area and the casting in the exhaust port is quickly sanded away.. as I blend it out, the blueing will be sanded completely off..
I have pretty much finished the right side of the intake port.. All the rough casting is gone and the casting ridge or transition is gone..
Last edited by Kevin; 03-20-2005 at 10:12 PM.
03-20-2005, 11:04 PM
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Kevin:
This is excellent! Really appreciate the pictures and descriptions.
Approximately how many hours are required to polish the ports?
What is the easiest way to machine these?
This is excellent! Really appreciate the pictures and descriptions.
Approximately how many hours are required to polish the ports?
What is the easiest way to machine these?
03-20-2005, 11:36 PM
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Enclosed are the final pics.
It took me 45-55 minutes to rough out both ports and another 20 minutes to polish the ports. Yes, one can spend hours polishing them, however this was done to show you guys what can be done in a little amount of time.. Again the object was not to try to take metal out of the ports.. However, this doesn't mean that the work done won't yield results.. It is night and day between what I started with vs smooth as a babies butt...
It took me 45-55 minutes to rough out both ports and another 20 minutes to polish the ports. Yes, one can spend hours polishing them, however this was done to show you guys what can be done in a little amount of time.. Again the object was not to try to take metal out of the ports.. However, this doesn't mean that the work done won't yield results.. It is night and day between what I started with vs smooth as a babies butt...
