Current Setup:
Piston
SUM-2999273810-2 (3.81 Bore, 1.299 C.H., 2cc dome, std stroke 6.124 rod) Has valve reliefs cut
Head
PRC 2.5 5.3L milled to 58cc chambers
2.02" intake valve / 1.575" exhaust valve
Crank
Standard gen 3 truck crank
Rockers are standard 1.7 ratio stamped things

Okay.... so, head is on, currently running TSP 228R cam. I didn't swap it when I upped compression and did all the other engine work.
I'm considering SUM-8709R1 cam.

With the heads on the car, I did a 'valve drop' test. Got piston to TDC using piston TDC tool. I am pretty sure it's TDC, but would like to keep a slight margin for error here.
In the valve drop test, I found:
Intake @ TDC - 0.376"
Intake @ 10BTDC - 0.413"
Intake @ 10ATDC - 0.408"
Exhaust @ TDC - 0.359"
Exhaust @ 10BTDC - 0.394"
Exhaust @ 10ATDC - 0.389"

Do these seem reasonable? There is some room for error here, where crank position may not be exactly at 10 degrees, or maybe 1 degree off for TDC. Do the valve reliefs from summit add that much?

So, I started using a cam spreadsheet found online, from PCM OF NC Inc.
https://www.pcmofnc.com/2013/01/10/p...ce-calculator/

According to the spreadsheet, the cam would be closest to the valve for exhaust at -3 d crank, and says MIN FLAT TOP P2V 0.257 in. Now... this seems to be that this is the closest the valve will get to the piston.
For the intake side of things, with all numbers for the cam put into the spreadsheet, I see closest is 3 d crank and MIN FLAT TOP P2V being 0.262 in.

I have read that I should account for heat expansion as well.... how much?

Additionally, engine revs to just under 7k. Redline set at 6800. How much 'room' does this clearance give me in terms of any valve float? I am guessing minimal or none. haha!

Any information would be greatly appreciated!

 

It does sound excessive. Are you using a solid lifter to check? A hydraulic will leak down even with checking springs due to rocker ratio pressure increases. Sum-8709R1 is designed to be the biggest that fits without valve reliefs and that’s with a 2.165 intake valve. I need to look it up but it’s slightly over the .060 intake .090 exhaust threshold we use as a minimum. This is with a piston to head clearance of .045 so net without a gasket simulates zero piston to head under running conditions and you may find yourself with as little as .015/.045. The 15 degree valve angle is a factor too but you see the thought process. At any rate, if our pistons have .200 vertical valve reliefs, that would be something just a little over the .260 .290 but adjusted for the valve angle. You should find minimum piston to valve at 8 degrees btdc exhaust and 8 atdc intake. I’ve never seen much variation from that. Please come back with a little more and we can get further in depth. Thank you.

 

Great, thank you!
The test of valve clearance was done using valve drop and a dial gauge. I removed pushrods and attached rockers. I have helper springs in, and took a measurement from extended, to with the rocker pushed down.
.200 valve reliefs make sense. These measurements were done with engine assembled. So, it includes head gasket.
I was glad to see the valve reliefs cut for the larger valves.

Overall, it looks like the Summit stage 4 will fit the build without issue. Even with expansion from heat, there would still be plenty of clearance.

​​​​

 

Attached a picture of first measurement setup.
I took 12 more measurements, but using rockers for those, with pushrods removed

 

With the above method of testing, dial gauge on top of the rocker, valve side.... took initial measurement, pushed down, took second. Subtracted, and that's how I got the measurements mentioned above.

I'm thinking... if the SUM-8709R1 should clear stock without milling, than mine w/ milling, but with .200 fly cuts... should be more than enough, and that's why the measurements are so large.

I suspect I could fit an even bigger cam if I wanted to because of the Summit pistons w/ reliefs.

Sooo, any considerations I missed with this method of testing? I suspect I'm close TDC wise, because when I got -10 one direction, the measurement is pretty close to the same as +10.

 

With the proper springs your should have plenty of room in terms of valve float. I spun mine to 7000 with a Torquer V2 and TSP 660 springs with solid stem stainless valves more times than I can count. I daily drove it and I ripped it to 7000 every chance I got.

 

Thanks for the confirmation.

The more I think about it... the more I feel sure it would be okay.
Summit says the cam fits unmilled stock setup. My heads were milled ~0.030" (or, I am guessing to reach 58cc). So, subtract that from clearance... but, the summit pistons add +0.200" clearance.

With summits response above, and them shooting for .090 for exhaust, and .060 for intake.... using the spreadsheet calculator, I see at 3 degrees it would be the closest at 0.256" P2V. Thinking about this number... without that 0.200" extra clearance from the pistons, it would be .056". Which would be too little for their threshold. So, it make sense why the number I'm seeing is so great.
I suspect with these valve reliefs, I could probably go bigger, but I think I'll stick to the stage 4 max performance cam, due to being lower displacement and only LS6 intake.

 

With this method you are not taking the intake /exhaust valve overlap into consideration. You have to have solid lifters and checking pushrods installed to zero lash to get a truly accurate reading. Next you need to be taking this reading around TDC but it has to be when the exhaust valve is closing and the intake is opening. Not on the firing stroke.

 

The problem is, with your heads installed, you will not be able to put the solid lifters in place for the check which makes things difficult. As others have stated, even the light checking springs can cause the lifter to collapse when the engine is not running. I suppose you could put the dial indicator on the pushrod with the rocker not installed and determine the lift of the cam at various checking points. Then times that by the 1.7 rocker ratio and subtract that number from your previous recorded measurements.

 

Thanks for the input Aston.
I'm not sure I fully understand what you're trying to say. I'm measuring Piston to valve clearance without regard to the current cam I'm using, so I'm confused why solid lifters would be required, in addition to zero lash.

Mentioned in my original post, I had:
In the valve drop test, I found:
Intake @ TDC - 0.376"
Intake @ 10BTDC - 0.413"
Intake @ 10ATDC - 0.408"
Exhaust @ TDC - 0.359"
Exhaust @ 10BTDC - 0.394"
Exhaust @ 10ATDC - 0.389"

Showing that I did test at TDC. But you're post is saying I need to be taking it at TDC with the exhaust valve closing and intake opening? It doesn't make sense to me, as I'm doing this without regard to the current cam in the vehicle. Instead, just measuring total P2V distance.
Once I have that distance, I use a spreadsheet and calculations that include rocker ratio, to determine if the cam would fit, and if so, how much clearance I would have, and at what degree I would have it at.
Some testing was done with the rocker on, but no pushrod. This was done to make it easier to push the valve down, without my fingers interfering with the readings.

I've included a screenshot of the spreadsheet I used.