Forthcoming Valve Job - Recommendations??
01-11-2004, 12:28 PM
#1
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Forthcoming Valve Job - Recommendations??
I'm about to convince a fellow 930 owner to help me drop the motor in my 79 930 and have a valve job done. I'm also going to replace the existing clutch with a Kennedy Engineering Products setup (thanks to those of you who recommended this setup. Heads up ImagineAuto, I'll be calling you this week!). Given that I'm hearing some valve tap, my guess is that the guides are worn on the left side and will need replacement.
[list=1][*]Since I'm having the machining work done, does it make sense to go ahead and spend the money and replace all twelve valves? I can't say with any certainty what prior valvetrain work has been performed, since none has been done since I have owned the car (outside of normal adjustments).[*]If the recommended approach is to go ahead and replace the valves, springs, retainers and guides, can anyone offer some recommendations on these parts?[*]Are there other gotchas I need to worry about?[*]Is it worth changing out the camshafts from stock to something else (the bottom end is pretty benign, but the car comes alive at around 2500 RPM)?[*]If so, what would the recommended camshaft grinds be? I've heard about the SC cams and the 964 cams - which are better suited for this car and its projected driving regimen?[/list=1]
My car is a 79 930 with B&B headers, K27-7200 turbo upgrade and Kokeln intercooler. It's a street car that will not likely see the track. That said, I'm not against performance mods (just will do my track stuff in a dedicated car).
Thanks in advance to all for your suggestions and recommendations.
Toby
[list=1][*]Since I'm having the machining work done, does it make sense to go ahead and spend the money and replace all twelve valves? I can't say with any certainty what prior valvetrain work has been performed, since none has been done since I have owned the car (outside of normal adjustments).[*]If the recommended approach is to go ahead and replace the valves, springs, retainers and guides, can anyone offer some recommendations on these parts?[*]Are there other gotchas I need to worry about?[*]Is it worth changing out the camshafts from stock to something else (the bottom end is pretty benign, but the car comes alive at around 2500 RPM)?[*]If so, what would the recommended camshaft grinds be? I've heard about the SC cams and the 964 cams - which are better suited for this car and its projected driving regimen?[/list=1]
My car is a 79 930 with B&B headers, K27-7200 turbo upgrade and Kokeln intercooler. It's a street car that will not likely see the track. That said, I'm not against performance mods (just will do my track stuff in a dedicated car).
Thanks in advance to all for your suggestions and recommendations.
Toby
01-11-2004, 02:35 PM
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My $.02:
Before you brake up the motor, I'd readjust the valves. You can check guide ware by trying to move the stem from side to side. Also check the cam lobes as if you nloose oil to one it will ware down/off.
If you do It I would get a nice port job to 35-36mm and if I had the money spend a bit more for a very good flowing here.
The SC cams are concidered a great match with this motor and have a lot more ability to breath. They do by design reduce your "effective" pre boost compression ratio a bit and are not the RV cam like stock but once you start to get a bit of boost they should pull better.
Also concidered helpfull to fly cut the heads 1mm (.040") to add about 1/2 point to compression for better preboost pick up (same as 3.6 CIS turbo).
If you are going for max mid to top HP then the C2 cams are a good choice w a K27 7200 HF & fuel head mod for more fuel.
When changing cams best to find a factory Cam if you can as it will ware longer. Also best to replace arms or refurb. Sport springs are a good idea w higher lift cams especialy the C2's.
If you post a WTB for SC ore Carrera factory cams on the other board I think Geoffery has a set to sell.
I am not an expert just what I belive.
Keith
Before you brake up the motor, I'd readjust the valves. You can check guide ware by trying to move the stem from side to side. Also check the cam lobes as if you nloose oil to one it will ware down/off.
If you do It I would get a nice port job to 35-36mm and if I had the money spend a bit more for a very good flowing here.
The SC cams are concidered a great match with this motor and have a lot more ability to breath. They do by design reduce your "effective" pre boost compression ratio a bit and are not the RV cam like stock but once you start to get a bit of boost they should pull better.
Also concidered helpfull to fly cut the heads 1mm (.040") to add about 1/2 point to compression for better preboost pick up (same as 3.6 CIS turbo).
If you are going for max mid to top HP then the C2 cams are a good choice w a K27 7200 HF & fuel head mod for more fuel.
When changing cams best to find a factory Cam if you can as it will ware longer. Also best to replace arms or refurb. Sport springs are a good idea w higher lift cams especialy the C2's.
If you post a WTB for SC ore Carrera factory cams on the other board I think Geoffery has a set to sell.
I am not an expert just what I belive.
Keith
01-11-2004, 10:49 PM
#3
I have posted some info over on the 911 board.
To answer some of your questions, I would first make some very simple evaluations. Are you using and blowing smoke under vacuum overrun conditions. This is always a very good indicator if the Guides are worn. Typically the Exhaust guides wear more. As for moving them as mentioned above, I'm not sure you can do this without disassembly. The spring pressure is probably to much to do this. As for changing parts, the guides are changed if out of spec. The Valves are changed if the stems are worn out of spec, and the margins are very thin after surfacing is done. If the springs are old(if known) then change them. The Reatainers should be magnufluxed and if good, can be reused. Make sure the seats are high, as low seats kill low lift flow, which in a 930 really hurts low RPM off boost conditions. As for surfacing, you will probably need to surface the heads to get a good sealing surface. I would recommend installing sealing rings and Head Gaskets if you can, and consider Twin Plugging the Heads also. This does bring other needs with it. Running 2 plugs per cylinder is a great upgrade but the Ignition system becomes another matter. Any Cam change should be known before the Heads are assembled, so that the Springs can be set up correctly for the camshaft.
There are many shops listed on the 911 board, so give them a call, and ask questions.
To answer some of your questions, I would first make some very simple evaluations. Are you using and blowing smoke under vacuum overrun conditions. This is always a very good indicator if the Guides are worn. Typically the Exhaust guides wear more. As for moving them as mentioned above, I'm not sure you can do this without disassembly. The spring pressure is probably to much to do this. As for changing parts, the guides are changed if out of spec. The Valves are changed if the stems are worn out of spec, and the margins are very thin after surfacing is done. If the springs are old(if known) then change them. The Reatainers should be magnufluxed and if good, can be reused. Make sure the seats are high, as low seats kill low lift flow, which in a 930 really hurts low RPM off boost conditions. As for surfacing, you will probably need to surface the heads to get a good sealing surface. I would recommend installing sealing rings and Head Gaskets if you can, and consider Twin Plugging the Heads also. This does bring other needs with it. Running 2 plugs per cylinder is a great upgrade but the Ignition system becomes another matter. Any Cam change should be known before the Heads are assembled, so that the Springs can be set up correctly for the camshaft.
There are many shops listed on the 911 board, so give them a call, and ask questions.
