6 replies to this topic

[viz139]

Trying to figure the details of a modified head I acquired.

Is there any handy DIY method to work out the valve spring pressure .

[nicklouse]

More to do with the cam design.

The springs should state their pressure and free and fitted length.

[unburntfuelinthemorning]

Yes.  Here's one way:

 

[slidehammer]

From memory you want to be able to stave off valve bounce around 500 rpm past the engines redline. The springs should give an indication of where valve bounce sets in. Too much pressure wastes hp and would add to the wear rate on the valve train. Too little and you won't get to peak power without valve bounce.

[viz139]

The video above is on the lines of what I'm looking for.

To be clear what I'm looking for.

I got a fully built engine of unknown components including valve springs of unknown pressure rating.

I removed the head, 12G940 , 12g1805  and a large R ( beside the 12g1805), 11 stud. Well ported and polished, valves 29.5, 3 collot and 35 single collot. Roller tip, roller rockers.

Initial measurment of the cam point towards a 649.

 

If my cam lift was 10mm and I'm using 1.5 rockers should I messure the pressure at 15mm compression? as per the video.

[nicklouse]

Spring pressure is measures in lbs per inch. So measure and scale.

[unburntfuelinthemorning]

If my cam lift was 10mm and I'm using 1.5 rockers should I messure the pressure at 15mm compression? as per the video.

You need to measure the installed height of the springs in the head and then compress the springs to that height to test.  This gives the on seat poundage.  Then compress, in your case, a further 15mm and that will be the over the nose poundage. 

 

Ideally you'd do a dry build with the head, cam and rockers and measure the valve movement directly to find the maximum lift as it takes things like valve clearances into account.