Sparks03Max

iTrader: (1)

I'm in the planning stages of an engine build and making sure I buy the right components. The first thing I want to be sure of is that with ~280ish duration/~12mm lift intake cams, I will still have full travel of intake CVTC. I know this means valve reliefs in the pistons, and the Z1 rebuild kit allows custom pistons for ~100 bucks extra... so I want to make sure I get the right thing.

Maybe this is a stupid question and there's an easy way to determine how much clearance I'll need, but I haven't found any easy answers. Is this something I can tell Z1 when ordering the custom pistons and they will know what to do?

Initial ideas on cams for this setup is GTM stage 2 NA (282/272) or a tomei 280/272 setup. Since they're so similar in duration/lift, and since if I go with any other cams, they will be less extreme than this, I feel that I can go ahead and have valve reliefs cut that will suit one of these.

In any case, help would be much appreciated... I may put a build thread up on here (if you guys want to hear about Maxima NA builds) when things start rolling better.

str8dum1

iTrader: (11)

get up with SgSash.
https://my350z.com/forum/search.php?searchid=13388549

They used C10/C9 cams in their build. lots of clearancing and custom cam sprocket adjustment

Sparks03Max

iTrader: (1)

Yeah, they could only use 27 degrees of intake cam travel because the pistons didn't have enough relief cut for the intake valves, thus the custom cam sprocket adjustment to mechanically limit travel, but I believe they're working with some 12:1 dome topped pistons with very little in the way of relief cuts.

I went ahead and emailed GTM and will try to get in touch with SGsash if that doesn't work...

SGSash

iTrader: (3)

You need to put in a tester valve spring and make or get a tool to compress the valve bucket. This is the normal procedure for checking piston to valve clearance.

We know that as we advance the intake cam the piston to valve clearance is reduced right - so we must artificially advance the cam to measure piston to valve clearance at the fully advanced position.

The easiest way to do this is to test the intake cams only (timing chain installed but NO secondary chains and NO exhaust cams installed), and install the cams 1 tooth advanced. I can't remember right now how much angle each tooth changed, but it was around 12-14 degrees. The math to figure it out is:

Number of teeth on the cam sprocket = X

360 / X = number of degrees of cam movement PER TOOTH. Times that by 2 and you get the degrees AT THE CRANK. So if 1 tooth is 5 deg at the cam, it's 10 deg at the crank. 2-3 teeth is pretty close to the full advance of the cam.

Safest to do one tooth at a time and measure your P:V clearance as you approach TDC, the P:V is closest right at and just after TDC, when the valve is being pushed open by the cam and the piston is still "floating" at the top of the head.

If at your max advance you don't have acceptable clearance you must put a stopper in the sprocket like I did to limit mechanical advance!

It's much easier than it sounds.

In my case, going the full 40 degrees caused the valve to hit the piston right away!

Sparks03Max

iTrader: (1)

Thanks a lot for taking the time to respond!

I understand what you're saying. What I really want to do before this engine is put in the car is have it set up so I can have full advance for the best low/midrange power possible to help (at least a little) to make up for such a big cam choice and highend oriented intake manifold.

I'd been looking for a theoretical approach before purchasing, but pretty much what I'm going to have to do is go ahead and buy all the parts that I want and continue with the build, maybe asking them to exaggerate the intake valve reliefs when ordering (or how much I can exaggerate them while maintaining strength), then get everything assembled and test. Then, if I do have piston to valve contact, take the pistons back out and have them machined further?

edit: I'm looking at wiseco 11:1 or 11.5:1

Z1 Performance

iTrader: (564)

simply contact Wiseco, they will give you the info as to the max lift their off the shelf piston will accomodate

an 11:1 piston is an off the shelf unit, 11.5 is not and would be custom built

Sparks03Max

iTrader: (1)

Good to know, and the custom is +100$ on your level 2 rebuild kit, right? That's what I was looking at doing since I've seen so much evidence that raising static compression with long duration cams helps to increase the dynamic compression that is lost from higher overlap and retain more lowend/midrange power and drivability. I can live with using less timing on 93 and using water/meth and/or 104+ at the track to get the most power and tractability.

MREDDLE

I too wished that there was a way to figure valve clearance. But, I dont think it is possible. Claying the motor is the best to really know.

Z1 Performance

iTrader: (564)

I think you're confusing us with someone else

the difference between 11 and 11:5 in the big picture is not even worth spending an ounce of time thinking about. It takes relatively large changes in compression to have any meaningful impact

Sparks03Max

iTrader: (1)

Z1 motorsports, Z1 performance... guess you can see where I got mixed up.

Everywhere I go I get different advice about compression vs the cam/heads/IM/headers that I'll be running. Guess I'll just keep reading

Z1 Performance

iTrader: (564)

it is all inter related yes, but a difference between 11 and 11.5, or even 12.0:1 is not going to amount to a hill of beans, particularly on pump gas

Sparks03Max

iTrader: (1)

I was planning on running a conservative street tune on 93 then another on 104+water/meth that I will use at the track. If the 11.0:1 is acceptable for a 280ish duration cam setup, then I'll just go with that for simplicity.

tuko316

iTrader: (6)

Why wouldn't 11:1 compression be enough for a 280ish cam? Wouldn't that mean the engine has to rev a lot higher?

Z1 Performance

iTrader: (564)

I would doubt you'll see much change in overall power with race gas either. From what I've seen on these engines, they need a lot of compression (~13+) to benefit from octane changes, and the timing changes you can then make