PI Swap and 268 Cams

[kenny150r]

Good evening!

I'm planning on doing a PI swap on my engine this weekend. I sent some used pi heads I took off a donor motor to the machine shop to get rebuilt, they'll be installing some Comp 268 cams with upgraded valve springs and retainers. I thought I had read that the 268's would work with the stock PI bottom end without PTV issues... however I read one article that said that any upgraded cam with the NPI stock short block would have issues... can anybody tell me if I will have PTV issues? I most likely will degree the cams myself.

Thanks!

 

[96blak54]

Youre going to be really close! Ask the machine shop to cut the overhang lip off the intake valves...about .060". This will gain you comfort. Also a $100 tool with a gutted head as a fixture could gain you some valve reliefs without taking pistons out.

 

[Musturd]

Notch the pistons

 

[DropTopPony]

268 is an NPI cam set isn't it?

 

[D3VST8R96GT]

If they are degreed you shouldn't have an issue...... if the motor is apart you could add a cushion for future growth and north the pistons.

 

[kenny150r]

So I called Comp Cams and they said since it's the xe268h and not the AH it is indeed a NPI cam, so even without degreeing there should be no PTV contact problems. However, I would still like to degree it in to get the best performance... I understand the process on how to find the actual intake centerline, but how are you supposed to adjust the centerline?

 

[D3VST8R96GT]

You mean how do you degree to that center line?

 

[D3VST8R96GT]

Others have ground the key way off to get to the exact degree. I haven't tried that yet

 

[96blak54]

I would just replace like stock. Your not upping the compression to utilize the new found valve timing and youll only gain a tiny bit, if that, by degreeing them in. Basically,.. not absolutely necessary but degreeing them in is good practice.

 

[D3VST8R96GT]

I think the stock teeth are like a 8.15 degree window

 

[ScottyDsntKnow]

You buy the TFS adjustable crank gears to adjust the chains. Degreeing is NOT OPTIONAL when you install new cams. Unless you like your car to run like a bag of dicks and have possible PTV issues. Not degreeing is like not lining the dots up on a pushrod cam install and just saying "**** it" and throwing the cam in to where you think its close. Although you should always degree the single cam in the pushrod too, there has been more than one instance where the "dot to dot" was off a tooth from the factory.