I have a 346ci LS1.

238/242 @ 108lsa, 0.603" 0.605" lift

Heads are 241 casting, have not been milled yet

Pistons are Mahle -4cc valve relief

Checked PTV with a dial indicator, checking springs installed and pushing down on the retainer. The dial indicator was mounted onto the rocker arm above the valve.

The figures I have just seem too big to me, and I cannot figure out why. Is it just because of the valve reliefs?

Intake
5BTDC - 0.435 "
TDC - 0.427"
5ATDC - 0.390"
9ATDC - 0.374"
10ATDC - 0.378 "
11ATDC - 0.380"

Exhaust
5BTDC - 0.325"
TDC - 0.309 "
1ATDC - 0.307"
2ATDC - 0.316 "
5ATDC - 0.321"

So my minimums are 374 intake / 307 exhaust

 

Cam in correctly?
Decimal point in the wrong place?

 

I got similar results on my build and never figured out why (was in a time crunch to get car done). I'm very interested in seeing what you figure out.

 

Sounds like you did it correctly. I'd rest easy.

 

Hi thanks for the reply guys.

I am pretty sure the cam is in correctly, I had a friend check the cam as this is my first time assembling - he told me it was good but I am going to double check myself for good measure (he has built a couple of BBC motors to 1000+hp)

Yes sure did get that decimal place in the right spot, hence why I am pulling my hair out.

I'd like to think it is just because of the valve relief's in the pistons, but I want to be very very sure.

 

I checked the cam is degreed properly this afternoon and it certainly is.

Checked by putting dial indicator on the lifter bowl, and using the centerline method. Came back at 108 so is spot on.

Only other thing I can think of is pushrod length, so I am borrowing an adjustable pushrod checker for this weekend.

 

The valve reliefs in these aftermarket pistons are massive.

You could probably run a 280/280 cam and still have clearance.

 

Thanks, I am almost now certain this is all it comes down to, -4cc of valve relief.

But I will grab the pushrod length checker just to be sure.

 

I'm running these pistons with an ms4 and 5.3l heads. They give you plenty of PTV clearance.