1973 flat tops?

[Sjc311]

New to the site, I've done a lot of Google but can't find the answer I'm looking for anywhere. 

Basically I'm rebuilding a california 1973 datsun 240z it has a e88 and p30. As far as I'm aware it hasn't been rebuilt. 

I purchased some new pistons however these came with no valve reliefs whereas the ones in the engine do have valve reliefs. 

I'm guessing that the valve reliefs are there for a reason. Maybe due to the 73s having bigger valves? (If I read correctly). 

I was effectively wondering if there's any chance I could run without valve reliefs. Quite expensive getting hold of new pistons here in the UK so thought I'd ask whoever unlikely 

[Chickenman]

Apparently the P30 engines came with valve reliefs for some reason. Maxima L24's had them:

http://forums.hybridz.org/topic/72440-are-these-parts-stock/

You should be OK though with a stock cam. Valve reliefs aren't needed with a stock cam and some mild cams. However, if a large duration and lift  camshaft was put in the owner you may need valve reliefs.

My 280Z with F54 Flat Tops and N47 head does not require valve reliefs. It has a .480" lift 280 duration cam... or so I've been told. Don't trust that though. Cam timing figures make a big difference. Stock cam...you should be good.  Modded cam... measure twice cut once.

Valve reliefs can be machined into the piston if needed. 

Here is a picture of the factory Ampco FT pistons out of a P30:

 

 

Edited February 19, 2017 by Chickenman

[siteunseen]

The '73 motor I bought and disassembled had the bigger rods and bolts but the pistons were flat. American car though, maybe there's a difference? 

[Sjc311]

38 minutes ago, Chickenman said:

Apparently the P30 engines came with valve reliefs for some reason. Maxima L24's had them:

http://forums.hybridz.org/topic/72440-are-these-parts-stock/

You should be OK though with a stock cam. Valve reliefs aren't needed with a stock cam and some mild cams. However, if a large duration and lift  camshaft was put in the owner you may need valve reliefs.

My 280Z with F54 Flat Tops and N47 head does not require valve reliefs. It has a .480" lift 280 duration cam... or so I've been told. Don't trust that though. Cam timing figures make a big difference. Stock cam...you should be good.  Modded cam... measure twice cut once.

Valve reliefs can be machined into the piston if needed. 

Here is a picture of the factory Ampco FT pistons out of a P30:

 

 

Thanks for the replies, unsure on the Cam, shall have to check tomorrow on what size lobes it has. I've attached pictures of the pistons, they have AMPCO stamped on the inside so by your attached link I would have thought they are original.. Hopefully its the standard cam in there, it certainly didn't look like anyone has been in the engine since it was manufactured. Although I'm bit of a noob at this so I could be wrong. 

[Sjc311]

30 minutes ago, siteunseen said:

The '73 motor I bought and disassembled had the bigger rods and bolts but the pistons were flat. American car though, maybe there's a difference? 

The car is originally from California. However I believe they had extra emission regulations to pass? I figured a lot of the extra stuff this car has (such as possibly the valve reliefs) were an attempt to lower them or something. 

Edited February 19, 2017 by Sjc311
spell check nazi

[Diseazd]

I have built several L24 engines using the Nissan or ITM 73 notched Pistons. One thing I do notice about those Pistons is that that come out of the bores about .025 to .030 inches above the deck. The original L24 Pistons don't do this. I've tried on numerous occasions to find out why Nissan designed the 73 pistons with a different deck height ....to no avail......anyone know why? The head on the 73's are about as worthless as they come and maybe it was designed that way to at least increase C/R some. On the other hand, maybe they were fly cut to decrease compression ratios to meet stricter standards.....or maybe because they come out .025 inches, they are closer to the valves and therefore are flycut.  Whatever, I would be very surprised with the stock camshaft, if you would have any clearance problems using the flat tops that you have.....however, used heads are a dime a dozen so why not get an E31 or early E88 and use them with your flat tops.....makes sense to me....you'll have a much better engine!

Edited February 19, 2017 by Diseazd