Cam Selection and P2V calculations (sanity check)

[Rx7TyreBurna]

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/piston-to-valve-clearance-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!  

[Cobranut]

I did a similar test on my roadrace motor, a Ford 2.3 Duratec w/ 13.8/1 comp.
I measured every 2 degrees, and sent the data to the cam company, as they have access to the whole lobe profile, which isn't commonly available to the customer.

Of course, also measure during assembly to be sure.

[Rx7TyreBurna]

You got a custom ground cam?  Is there a significant benefits over something like the summit stage 4?

[Cobranut]

You got a custom ground cam?  Is there a significant benefits over something like the summit stage 4?

Not a custom grind, but they made a recommendation based on the engine specs and my intended use.
I went with Kent Cams for this engine, as they are highly recommended in Europe, where the Duratec is a very popular race motor.

[Rx7TyreBurna]

Ah okay.
I got a response on LS1tech from Summit.

Right now, it seems like the cam should fit without issue.
Which makes sense.... the fly cuts on their pistons are cut to give .2" extra clearance.
The cam says it works with stock heads / pistons, but just barely.  Given that I have had the heads milled to 58cc, which is usually .030" milled (I think), and the deck was done, but I think it's .001", not zero'd.
So... that .030" doesn't hardly touch the .2" fly cuts in the pistons.

I think when they do the calcs for the cam, they assume a .041" head gasket, but I have a .051".

Overall, gut feeling is that the cam should be fine, and actually the fly cuts are probably excessive, but give opportunity for a bigger cam if I wanted to go that route later.

It makes me think maybe I should get a bigger cam than the stage 4 summit cam, but.... i know it's a big trade for max power vs street manners.  So, I think the stage 4 cam should be a quality setup for a road race / spirited driving machine.

Cam is 238/246 0.625"/0.605" 113+3.

[jwvand02]

Ah okay.
I got a response on LS1tech from Summit.

Right now, it seems like the cam should fit without issue.
Which makes sense.... the fly cuts on their pistons are cut to give .2" extra clearance.
The cam says it works with stock heads / pistons, but just barely.  Given that I have had the heads milled to 58cc, which is usually .030" milled (I think), and the deck was done, but I think it's .001", not zero'd.
So... that .030" doesn't hardly touch the .2" fly cuts in the pistons.

I think when they do the calcs for the cam, they assume a .041" head gasket, but I have a .051".

Overall, gut feeling is that the cam should be fine, and actually the fly cuts are probably excessive, but give opportunity for a bigger cam if I wanted to go that route later.

It makes me think maybe I should get a bigger cam than the stage 4 summit cam, but.... i know it's a big trade for max power vs street manners.  So, I think the stage 4 cam should be a quality setup for a road race / spirited driving machine.

Cam is 238/246 0.625"/0.605" 113+3.

If you want some extra peace of mind you could always measure clearance directly with clay. It's not accurate to the thousandth but it sounds like you have quite a bit of clearance and in that case clay should make it obvious.

[Cobranut]

Ah okay.
I got a response on LS1tech from Summit.

Right now, it seems like the cam should fit without issue.
Which makes sense.... the fly cuts on their pistons are cut to give .2" extra clearance.
The cam says it works with stock heads / pistons, but just barely.  Given that I have had the heads milled to 58cc, which is usually .030" milled (I think), and the deck was done, but I think it's .001", not zero'd.
So... that .030" doesn't hardly touch the .2" fly cuts in the pistons.

I think when they do the calcs for the cam, they assume a .041" head gasket, but I have a .051".

Overall, gut feeling is that the cam should be fine, and actually the fly cuts are probably excessive, but give opportunity for a bigger cam if I wanted to go that route later.

It makes me think maybe I should get a bigger cam than the stage 4 summit cam, but.... i know it's a big trade for max power vs street manners.  So, I think the stage 4 cam should be a quality setup for a road race / spirited driving machine.

Cam is 238/246 0.625"/0.605" 113+3.

If you want some extra peace of mind you could always measure clearance directly with clay. It's not accurate to the thousandth but it sounds like you have quite a bit of clearance and in that case clay should make it obvious.

That's always a good idea as a final check, as it also reveals a case where the edge of the valve is too close to the valve relief.
I've found it works best when you clean the piston with brake cleaner, and wipe a thin film of vasoline on the valve head to keep the clay from sticking.

[freeskier7791]

FWIW I would also talk to Tick Performance, they have a lot of experience with LS and have a variety of Cams, but a little more expensive than Summit.