Piston to valve clearance issue????

You should always measure PTV clearance, otherwise it's mostly a guessing game.

I'm just wondering how "custom" can it be?

You would have been asked to provide what pistons, what heads, what valves, springs, rockers, compression, deck clearance, transmission, chassis weight etc., and the camshaft designer would factor all that in.

Not to mention what 90blacknight already suggested... which is absolutely correct.

That that large of a duration, I could see some issues with stock pistons.

Do you have the intake centerline? 107? 108?

5spd GT said:

That that large of a duration, I could see some issues with stock pistons.

Do you have the intake centerline? 107? 108?

Click to expand...

What duration is too much and creates interference? What is the lobe proflle under the nose? Does that not matter... or does just duration? What about index of the camshaft in relation to crank?

If the cylinder heads are installed, you do not need to clay!
Do the necessary steps to remove both valve springs and install checking springs. Then put the piston at TDC and measure the clearance using a depth mic which is measured on the retainer. However much you can depress the valve... that's your clearance.
The neat thing about this method... you can check PTV throughout the camshaft events.

347HO said:

What duration is too much and creates interference? What is the lobe proflle under the nose? Does that not matter... or does just duration? What about index of the camshaft in relation to crank?

Click to expand...

No.

Those are all good questions. I asked a couple questions to get at the valve events @ .050".

I said he COULD see issues. I did not say he will, and I did not say he will not run into issues. I said he could...

A stock lift camshaft (.444") with an early intake opening, a late exhaust closing, and a steep ramp rate (steep lobe) would hit.

i ran into ptv clearance probs with my crane 2020 with the stock 87 bottom end. they are 530 lift an gtp heads with 1.84 valves.

lang williams said:

i ran into ptv clearance probs with my crane 2020 with the stock 87 bottom end. they are 530 lift an gtp heads with 1.84 valves.

Click to expand...

PTV has very, very little to do with how much lift is on a camshaft lobe.

This is what 5spd was leading into... and I wanted to ensure you cannot judge PTV by a camshafts duration because anyone reading events @ .050" tells you absolutely nothing about lobe ramp.

If you have an intake opening at 5* BTDC, and an exhaust closing at 5* BTDC, and you compare it to an intake opening at 10* BTDC, and an exhaust closing at 2* BTDC, assuming same lobe lift, duration, etc, could one not see that a steeper ramp rate is being used with the later one?

The intake is opening up at a sooner degree and the exhaust is closing closer to TDC all by using numbers at .050" for the valve events.

Using a Trickflow Stage 1 lobe lift as an example, you can see that lift is nothing to worry about with piston to valve clearance.

At peak lift, a 107.5 ICL (TFS-1 camshaft) is 2.156" down the bore, when the valve is open .499".

Lobe Lift - 1.6 RR - 1.7 RR - 1.8 RR

0.010 - 0.016- 0.017 - 0.018
0.020 - 0.032- 0.034 - 0.036
0.030 - 0.048- 0.051 - 0.054
0.040 - 0.064- 0.068 - 0.072
0.050 - 0.080- 0.085 - 0.090
0.060 - 0.096- 0.102 - 0.108
0.070 - 0.112- 0.119 - 0.126
0.080 - 0.128- 0.136 - 0.144
0.090 - 0.144- 0.153 - 0.162
0.100 - 0.160- 0.170 - 0.180
0.120 - 0.192- 0.204 - 0.216
0.130 - 0.208- 0.221 - 0.234
0.140 - 0.224- 0.238 - 0.252
0.150 - 0.240- 0.255 - 0.270
0.160 - 0.256- 0.272 - 0.288
0.170 - 0.272- 0.289 - 0.306
0.180 - 0.288- 0.306 - 0.324
0.190 - 0.304- 0.323 - 0.342
0.200 - 0.320- 0.340 - 0.360
0.210 - 0.336- 0.357 - 0.378
0.220 - 0.352- 0.374 - 0.396
0.230 - 0.368- 0.391 - 0.414
0.240 - 0.384- 0.408 - 0.432
0.250 - 0.400- 0.425 - 0.450
0.260 - 0.416- 0.442 - 0.468
0.270 - 0.432- 0.459 - 0.486
0.280 - 0.448- 0.476 - 0.504
0.290 - 0.464- 0.493 - 0.522
0.300 - 0.480- 0.510 - 0.540
0.310 - 0.496- 0.527 - 0.558
0.312 - 0.499- 0.530 - 0.562