16v Head on 3.0 8v Turbo
10-22-2007, 06:43 PM
#1
Burning Brakes
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16v Head on 3.0 8v Turbo
What are the technicalities involved in switching heads on my 3.0 8v turbo. I have a 16v head an understand I need a custom intake and exhaust manifold to make the external bits work. I have Motec which is perfectly capable of controlling the variocam and the hall sensor on the head. Really the question is can the Mahle 8v pistons work with the 16v head and if not will the Carillo rods I have work with the 968 pistons and either a thicker head gasket as in Marcus car or machining them? Apart from uprating the exhaust valves are these my only issues?
10-22-2007, 11:09 PM
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Your compression ratio will go up .... a bunch. 16v heads have a lot smaller combustion chamber. If you are going to run it hard you may want to upgrade to a more heat resistant exhaust valve. The piston bowl shape is not a perfect match but the 16v head is pretty forgiving.
10-23-2007, 12:28 AM
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[QUOTE=nick_968;4702294]Really the question is can the Mahle 8v pistons work with the 16v head and if not will the Carillo rods I have work with the 968 pistons and either a thicker head gasket as in Marcus car or machining them?QUOTE]
Nick, You seem to have a wonderful car. I would consider enjoying it for a bit longer, as is, and saving up to do the 16v head the right way, instead of mix matching parts. Mix matching 8v pistons and 16v pistons is not wise. You may have to get the fuel rail and cooling bits too.
Nick, You seem to have a wonderful car. I would consider enjoying it for a bit longer, as is, and saving up to do the 16v head the right way, instead of mix matching parts. Mix matching 8v pistons and 16v pistons is not wise. You may have to get the fuel rail and cooling bits too.
10-23-2007, 07:25 AM
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10-23-2007, 07:27 AM
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Ah, shucks Dave. I appreciate it. One day you may be great. No worries, mate. Just don't get your hopes too high.
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10-23-2007, 07:43 AM
#10
Burning Brakes
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I am in no rush to do this, but it is the next logical step having invested in the Motec and also having a complete 968 engine which no one seems to want to pay much for. I would be better off selling the 8v head and manifolds and possibly the pistons (if I cant make them work) and using my 968 head and exhaust manifold welded to the 951 crossover pipe. It shoudnt cost a whole bunch to do, the only stumbling block being the intake manny which has been done before.
Exactly what would the comp ratio go up to with out the use of a thicker head gasket?
I am sure I can get away with 9.5:1 up to 18psi with the Motec running things. I have closed loop lambda control and can also run EGT as a trim to keep things safe.....
Would be so much more tempting if I know I can try it out without changing anything in the shortblock.
Exactly what would the comp ratio go up to with out the use of a thicker head gasket?
I am sure I can get away with 9.5:1 up to 18psi with the Motec running things. I have closed loop lambda control and can also run EGT as a trim to keep things safe.....
Would be so much more tempting if I know I can try it out without changing anything in the shortblock.
11-29-2008, 07:17 AM
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hey did the answear ever appear about 8v pistons and 16v valves rushing toward each other ?
the valves dont come much out of head it may be OK with thick gasket but you can get the pistons relieved to but it is a pul down some one needs to dummy it it up with plastisene.
I think I bigger cam thrown in you 8v is an resonable comprimise and will only take a single day .
the valves dont come much out of head it may be OK with thick gasket but you can get the pistons relieved to but it is a pul down some one needs to dummy it it up with plastisene.
I think I bigger cam thrown in you 8v is an resonable comprimise and will only take a single day .
11-29-2008, 09:15 AM
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Excuse my ignorance but isn't the relief on a 16v vs an 8v appear to be quite different?
11-29-2008, 11:49 AM
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yeh but I think that with say a 3mm cometec gasket and the conservative cam timing the relives may not see any action until you break a cambelt. the inlets only stick out perhaps 4mm from the head at full lift wich is midstroke not TDC some cams with harsh asymetrical profils open inlets fast from tdc this is when the relifs are genrally needed this is acceleration along with valve chain mass is how we calulate valve spring pressure.
there is also a phrase interfernec and non interference .
an interfernce set up is the horrible sandard 951 rig when a belts fails its bent valves and dinged pistons .
the proper set up is no inerfernce wich i imagine a 16v is so you can never get a valve to hit a piston
as much i'm excited about having a 16v i would never bother sacrificing a good working 8v 3.0 turbo to get one.
also in a 968 you can make a nice 968rs replica pretty and one day get decent coin for the car .
its kind of proven that an 8v makes more sense up to 500 hp so unless thers a turbo and all the 600 hp stuff there .
if you have a good engine like that thers plenty of other good things that can be done to a car .
there is also a phrase interfernec and non interference .
an interfernce set up is the horrible sandard 951 rig when a belts fails its bent valves and dinged pistons .
the proper set up is no inerfernce wich i imagine a 16v is so you can never get a valve to hit a piston
as much i'm excited about having a 16v i would never bother sacrificing a good working 8v 3.0 turbo to get one.
also in a 968 you can make a nice 968rs replica pretty and one day get decent coin for the car .
its kind of proven that an 8v makes more sense up to 500 hp so unless thers a turbo and all the 600 hp stuff there .
if you have a good engine like that thers plenty of other good things that can be done to a car .
11-29-2008, 12:39 PM
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