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Flat top pistons : do they need a valve relief in I6 4.0 

 

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 Post subject: Flat top pistons : do they need a valve relief in I6 4.0
Posted: Sat Jan 06, 2007 8:33 pm 
Getting Side Ways
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Hello people The question is do you need a valve relief in the crown of the pistons (flat tops, with same deck heights as OE.) ?
The cam has 0.500" lift at the valve and is 282/292 in/ex.
The OE pistons had a valve relief, but did they really need it?
Any help appreciated.

 

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Posted: Sun Jan 07, 2007 12:21 am 
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could try and put the head together turn it till the valve is fully open and see if it will hit buy lookin how far into the chamber it goes? if it will clear then it will be ok :wink:

 

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Posted: Sun Jan 07, 2007 1:57 pm 
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hope someone knows this (stockstandard?)
as i have a very similer problem.

 

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 Post subject: Re: Flat top pistons : do they need a valve relief in I6 4.0
Posted: Tue May 31, 2011 11:14 pm 
Oompa Loompa
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I'm digging up this post again because I'm interested in fitting Intech (flat tops) into my EL block.
It's ready for a rebuild and I'd like to up the compression as much as I can.
Obviously I will be shaving the head and thinning down the gasket.
I could possibly machine the valve clearance at work but if it isn't required then even better.

Anyone done it yet?
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 Post subject: Re: Flat top pistons : do they need a valve relief in I6 4.0
Posted: Wed Jun 01, 2011 12:14 am 
Smokin em up
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They certainly do from my measurements, but maybe not as big as they were on the EA to EL. I did one the same size as the AU relief which is alot smaller as I did not want to take out more than necessary. I measured valve to piston clearance with the AU relief size cuts (I used BA forged pistons) and whilst there was enough clearance, I wouldn't say there was heaps. Cant remember what lift the cam was but nothing extraordinary.

 

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 Post subject: Re: Flat top pistons : do they need a valve relief in I6 4.0
Posted: Wed Jun 01, 2011 12:48 am 
Oompa Loompa
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Sweet!
Definately need to get it checked with a dummy assembly anyway but at least I know it's been done before.

I'm wanting to roll a 1673 wade cam (0.512" ex, 0.485in), shave the head and AU gasket. It's gonna be very close I reckon.
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 Post subject: Re: Flat top pistons : do they need a valve relief in I6 4.0
Posted: Thu Jun 02, 2011 11:31 pm 
Oompa Loompa
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I've been informed the AU Piston Compression Height of 30.88mm/1.216in
is way different to EL 25.5mm/1.004in

Not such a good idea after all. :?
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 Post subject: Re: Flat top pistons : do they need a valve relief in I6 4.0
Posted: Fri Jun 03, 2011 1:07 am 
Getting Side Ways
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fitz wrote:
I've been informed the AU Piston Compression Height of 30.88mm/1.216in
is way different to EL 25.5mm/1.004in

Not such a good idea after all. :?

AU run a shorter rod too.

 

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 Post subject: Re: Flat top pistons : do they need a valve relief in I6 4.0
Posted: Fri Jun 03, 2011 8:02 am 
Getting Side Ways
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fitz wrote:
Sweet!
Definately need to get it checked with a dummy assembly anyway but at least I know it's been done before.

I'm wanting to roll a 1673 wade cam (0.512" ex, 0.485in), shave the head and AU gasket. It's gonna be very close I reckon.


How much compression do you want? If you are rebuilding get pistons to suit rather than shaving the head, leaves you little room to play with if you do a headgasket and need a skim (ouch if a worked head) and you can get chain play.

AU rods are 6" (or 6.060") from memory, and E series rods are 5.88". If you are going for an N/A build use an AU rod/piston length combo, as will be your cheapest/best option to rev with.

 

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 Post subject: Re: Flat top pistons : do they need a valve relief in I6 4.0
Posted: Wed Jun 15, 2011 5:54 pm 
Smokin em up
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I was just looking thru some photos. THis will give you some idea

 

 

Attachments:
File comment: Weisco Forged BA, stock ED and Stock AU
millcrest3 004.jpg
millcrest3 004.jpg [ 318.25 KiB | Viewed 62 times ]

 

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 Post subject: Re: Flat top pistons : do they need a valve relief in I6 4.0
Posted: Wed Jun 15, 2011 5:56 pm 
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close up of a stock AU piston

 

 

Attachments:
File comment: stock AU
millcrest3 013.jpg
millcrest3 013.jpg [ 313.96 KiB | Viewed 32 times ]

 

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 Post subject: Re: Flat top pistons : do they need a valve relief in I6 4.0
Posted: Wed Jun 15, 2011 11:06 pm 
Oompa Loompa
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Cheers for the replies.
Looks like it's easier to just use an AU bottom end with bellhousing and alternator into an EL.

Sump mod is easiest option too.
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