Poston NH500/NH600 cam questions

One of the many problems the ole "Nail" suffers from is the actual rocker arm itself. It is so short & stubby that it actually loses ratio quite rapidly with a lobe lift of anything over .250". To the point the ratio can get to be 1.1-1 or less. In other words adding, say, .050" to lobe lift actually gives you at the valve less than .050".

 

Hey, have any of you that installed a hotter cam get their pistons valve reliefs cut deeper?
I had to do that when I put the Isky 310 cam in.

 

Walt
What was your clearance before and after the pistons were cut?
Roger

 

I don't recall...it was 1978!

 

I am running power brakes with the NH 400. No problems there. I read the car craft article about 5 years ago that it was worth 15 HP at the rear wheels. I am still not sure if it is a regrind.

 

Bob, any idea what issue that was in???
Was it the white 4 speed vert that Tony had, or another car?

 

I have the issue but will have to look for it. Yes it was his car, white 4 speed vert. If I remember right what sold me on useing it was at 5000 rpm it held on to 50 HP more than the stock cam. Now I see there are a lot more options than I knew about at the the time.

 

But I do have to say that cam with Toms rockers and I have not hit that out of air spot like I use to. I have had it to 5000 so far. More to come this summer. hehehe

 

Poston's catalog for the NH400 says notched pistons are NOT required. Do you guys have info that say other wise? I am thinking of buying this cam and just want to be sure I know what I am getting into.

 

If you are getting the Telesco's you probably need to check valve to piston clearance with the better rocker ratio anyway.

 

A friend of mine tried th NH400 on a rebuild, but was not able to use it due to lack of v-p clearance.
If you have the thicker 0.040" composition head gaskets, that will help.
You might be able to make minor adjustments by advancing/retarding the cam a few degrees to help v-p clearance on either the intake or exhaust.

 

Never even considered valve piston clearance on my rebuilt 401 with the Poston NH400. Maybe I just got lucky, or like Walt suggests there is no problem with the thick head gaskets. I was going to use the thin shim gaskets on the wagon, but maybe not now with this info.
Mike

 

I am running .30 over cast pistons, NH 400, thin steel gaskets and telesco rockers. I looked at V.P. clerance when putting heads on and I was OK. So far so good. every one should check there situation though.

 

I'm glad I asked. I'll make sure I check it. Thanks

 

So I guess my buddy Marty was the only one that couldn't fit the NH400 cam. I'll get more info from him.
Let us know how you make out.