Taper valve guids when porting/polishing 951 head?
02-01-2013, 06:22 PM
#1
Addict
Rennlist Member
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Thread Starter
Taper valve guids when porting/polishing 951 head?
I'm having my exhaust valves replaced when I rebuild my head in a couple of weeks.
I've seen valve guides treated three ways before on performance heads:
1. P&P the bare head, install new guides, walk away.
2. Install new guides, P&P nicking/tapering the guides a bit.
3. P&P the bare head, install cut/tapered exhaust guides and polish flat inside the ports so there's 0 restriction from the guides.
I've never done 3 but seeing it more & more on LS engines, was curious if anyone has done this to a 951. Not studying how long/short the guides are, does'nt hurt to ask.
Mark (pic, my last head install on my last TurboS)
I've seen valve guides treated three ways before on performance heads:
1. P&P the bare head, install new guides, walk away.
2. Install new guides, P&P nicking/tapering the guides a bit.
3. P&P the bare head, install cut/tapered exhaust guides and polish flat inside the ports so there's 0 restriction from the guides.
I've never done 3 but seeing it more & more on LS engines, was curious if anyone has done this to a 951. Not studying how long/short the guides are, does'nt hurt to ask.
Mark (pic, my last head install on my last TurboS)
02-01-2013, 07:01 PM
#2
Three Wheelin'
Shortening the overall guide length will allow more valve wobble. I've had some valve wobble issues in the past, with using cut down guides. There were some other factors, but the shortened guides did not do me any favors.
I would stay with options 1 or 2, especially since I would not expect a big gain with the cut down guide.
Also, I'm not saying streamlining the intake track is not important, but its not as important on forced induction vs NA
I would stay with options 1 or 2, especially since I would not expect a big gain with the cut down guide.
Also, I'm not saying streamlining the intake track is not important, but its not as important on forced induction vs NA
02-02-2013, 12:26 AM
#3
Rennlist Member
Why are you replacing the exhaust valves? Has someone looked at them? They only need replacing if the stems are worn, valves are bent, or they've had so many valves jobs that there's no margin left.
Proper porting is an enhancement for any engine; turbo or NA. The key is getting a proper job. Way too many heads are ported improperly which results in a reduction in power! It's not a home project, nor can just any shop show a gain. It's a very specialized process that takes experience and skill.
There's an area in the intake port that needs to be re-contoured in a 951 head. This work, along with the area just under the valve (the throat) will pick up power significantly if done properly. The port is not enlarged, nor is it polished. The exhaust port on a 951 has a ceramic liner, and it usually has a pretty pretty good shape, so no need to touch it.
There's no gain in altering the valve guide bosses in the 951. Leave them alone.
Proper porting is an enhancement for any engine; turbo or NA. The key is getting a proper job. Way too many heads are ported improperly which results in a reduction in power! It's not a home project, nor can just any shop show a gain. It's a very specialized process that takes experience and skill.
There's an area in the intake port that needs to be re-contoured in a 951 head. This work, along with the area just under the valve (the throat) will pick up power significantly if done properly. The port is not enlarged, nor is it polished. The exhaust port on a 951 has a ceramic liner, and it usually has a pretty pretty good shape, so no need to touch it.
There's no gain in altering the valve guide bosses in the 951. Leave them alone.
