78 SC Cam help

[5.7 GT1]

I’m currently rebuilding the top end on my 78 sc. I’m excited to finally have another Porsche project again since my last build

Taking the EFI Plunge

In the process I decided to upgrade to L&N 3.2 SS cylinders and JE 9.5:1 CR pistons.
Here are the other changes being made to the engine (most being induction and exhaust) in the process:
-964 cams
-ssi’s
-dansk 2 into 1
-xfaktory Itb’s
-coil on plug ignition
-xfaktory ecu

My question is: can some tell me if my valve clearance is ok running the above?

I have already purchased all of these parts and won’t be making any changes if I’m fine on valve clearance. I’m also curious on recommended cam timing?

Thank you!

[jac1976]

You likely will get more traffic in the technical forum. Reaching out directly to KNIGHTRACE, icarp, and jpnovak will get you what you need. Not an exhaustive list, but it’s where I first would turn. Sorry I’m not more help.

[5.7 GT1]

Thanks jac

[dannobee]

You'll have to check P2V clearance to be sure, but JE's usually have pretty deep valve reliefs. There should be tutorials here on how to check if you're not familiar with the procedure.

Set 964 cams at 1.25mm.

[5.7 GT1]

Thanks for your advice dannobee. I was hoping someone has the same build specs and can chime in to help me understand if I don't need to worry about checking the valve to piston clearance. I guess I'm being lazy. Once I get started on assembly next week I most likely will be checking v to p clearance before setting the cam timing.

[boyt911sc]

GTI,

Assemble your motor and do a visual test inspection using a dial indicator. You also need P7E/P7I valve compressors. If you don’t have these compressors, simply remove the valve springs from the cylinder head prior to partial engine assembly. Then measure the actual valve clearance with the crankshaft @ Z1 TDC and no cam tower installed.

Tony

[jpnovak]

964 cams will easily clear JE pistons.

but, If you are going with those pistons you should seriously think about changing cams to something else. A DC40-108 would be my choice. more midrange torque, more top end. Just better matched to ITB/EFI setup.

['78 SC]

I ran 9.5 CR JE pistons (95mm) with the stock cam re-ground to 964 profile and had no clearance issues, just as Jamie says.

I still suggest you check the clearances, especially if you have done anything that could change deck height. I used the technique described in Waynes's rebuild book. Be sure to check throughout a full cycle (720 degrees of crankshaft rotation) since the point of closest approach between the piston and valves is not at TDC.

[5.7 GT1]

Originally Posted by boyt911sc

GTI,

Assemble your motor and do a visual test inspection using a dial indicator. You also need P7E/P7I valve compressors. If you don’t have these compressors, simply remove the valve springs from the cylinder head prior to partial engine assembly. Then measure the actual valve clearance with the crankshaft @ Z1 TDC and no cam tower installed.

Tony

Thank you Tony! This is really helpful.

[5.7 GT1]

Originally Posted by jpnovak

964 cams will easily clear JE pistons.

but, If you are going with those pistons you should seriously think about changing cams to something else. A DC40-108 would be my choice. more midrange torque, more top end. Just better matched to ITB/EFI setup.

Thanks Jamie, I would jump on a set of DC40-108 cams if they were available. Unfortunately, it seems to take months to get anything these days and I will have everything ready to assemble next week.

[5.7 GT1]

Originally Posted by '78 SC

I ran 9.5 CR JE pistons (95mm) with the stock cam re-ground to 964 profile and had no clearance issues, just as Jamie says.

I still suggest you check the clearances, especially if you have done anything that could change deck height. I used the technique described in Waynes's rebuild book. Be sure to check throughout a full cycle (720 degrees of crankshaft rotation) since the point of closest approach between the piston and valves is not at TDC.

78 SC, That is good advice. I used Wayne's book to build my last motor (and will use it for this one as well), but it was a low compression 930 motor. I know that with a 9.5:1 CR I need to be careful with valve to piston clearance.

[RDM]

There is a lot of good buzz around William Knight's M1 cams, and he may have them in stock. He's very generous with advice after making you clearly identify your goals.

knightrace911@hotmail.com
615.969.4917

[5.7 GT1]

Originally Posted by RDM

There is a lot of good buzz around William Knight's M1 cams, and he may have them in stock. He's very generous with advice after making you clearly identify your goals.

knightrace911@hotmail.com
615.969.4917

Thank you!
I’ll reach out to him.