I.D. these pistons!

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Beatnik

Beatnik

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So I got my heads off finally, and these are what I found. Look like fairly simple flat-tops to me? Just looking for opinions. My car was advertised as having "11.1 slightly domed forged pistons". Well...looks like "probably cast, flat tops" to me...

Interestingly these look alot like the stock 318 replacement pistons Hughes sells w/ the 4 valve reliefs!

Let me know what you think! The funny thing is this engine hates 93 octance, it will run on it, but runs WAY better on 110 race gas.

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I'd say that they were these pistons, Speed Pro Part# ZH405CP30. They are Hyperutectic, not forged. No way to know for sure until you push them out and find a part number on them.

stl-h405cp30_w.jpg
 
If the large chamfer around the perimeter is any indication, they are old TRW 11.5:1 slugs.

What is your deck clearance at TDC?

A fair number of OEM 318 pistons had 4 valve reliefs.
 
C130 may well be right. The pistons that I show are for a 360 and do not have the chamfer.
 
Thanks guys!

ramcharger - Those Speed Pro's look identical! I would not be surprised if they were those (except for the chamfer)

C130 Chief - I have not yet gotten a piston to TDC to verify if they come above deck. I dont think they do. It would also make sense if they were the TRW 11.5:1 slugs you mention, based on being advertised as 11.1 and it running better on 110 than premium! Plus the chamfer on the edge. I've not seen those TRW's but they had that chamfer?

Unfortunately I'm not planning on popping them out, just swapping heads on it so I wont get a part# before it goes back together! At least I'll know if they come above deck or not...and that they are indeed flat-tops.
 
If you are planning a head swap you had better run one to TDC to check clearance, especially if you are running a closed chamber or heads which have been milled.

Also, you may find a number stamped in the tops of these. A little Gumout and a rag may answer a lot of questions.
 
Thanks! Yes, I'm planning on swapping heads, but only from stock J's to ported X's with stiffer springs and a good valve job (not milled either). So the chambers should be the same, I dont expect any issues.

I did rotate one to TDC yesterday evening. It came up flush with the gasket, but when I remeoved the gasket, it came up just barely above deck. I've yet to measure how much though specifically. I'm betting they are the TRW pistons you mentioned...
 
And if thats your plan, you'll be well under 11.1. Make sure you have no sharp edges anywhere in the chambers and pump gas shouldn't be a major issue.
 
hey ramcharger are those"hyper"pistons for a 318 or 360 im lookin for a set of 60 over ''Hyper" for a 318 build
 
65DrtGT said:
hey ramcharger are those"hyper"pistons for a 318 or 360 im lookin for a set of 60 over ''Hyper" for a 318 build
Click to expand...

They're for a 360, 4.030 bore. Have you checked out what KB has availible? What's you're plans? Measured comp ratio means everthing in combo with your cam plus head chamber style.
 
C130 Chief said:
And if thats your plan, you'll be well under 11.1. Make sure you have no sharp edges anywhere in the chambers and pump gas shouldn't be a major issue.
Click to expand...

I think the chamber on my X's is the same as my J's I took off...so if compression was around 11:1 to start..what makes you think it would be lower? Or are you thinking it was lower to start? If so, then I'm wondering why it ran rough on 93 but nice on 110? I know comp. ration isnt everything when it comes to detonation etc...but the engine ran good otherwise...maybe a little rich but that's it.

Thanks for the feedback!
 
Compression should be the same between X and J heads. Maybe run a little thicker head gasket to lower it some?
 
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