4AGE - Advanced Specs

[wiso]

sorry bring up an old thread but having trouble finding some info that is very relevant to the thread.

i am looking for piston to head clearances. does anyone know the standard AND does anyone know what the minimum clearence you can run is?

obviosly the stock clearance is the headgasket thickness but i am not sure if stock the 4age has 0 deck height pistons or if they are proud or under the block deck.

the engine bloke has found my pistons are sitting 3thou over the deck height so is is a bit worried about the clearence with the TRD gasket

cheers

[bermy]

0.015" from the piston crown to the deck surface... your block got deck more than what I'd be confortable with. Normally I try to be between 0.040 and 0.045" but the lowest I'd ever go would be 0.035"... TRD head gasket 0.8mm is well... 0.0315" thick so if your pistons are above deck your well under that minimum... stock headgasket is ~1.2mm thick when compressed (0.047") so you'd be at 0.044" clearance which is pretty within the target area for squish clearance.

[wiso]

thanks bermy. so they are normally 0.015 under the deck surface? or is it the other way and above?

if under that would make standard squish clearence about 0.062" correct or wrong?

[bermy]

Exactly, 0.015" under deck so total squish of 0.062" with a stock head gasket.

[oldeskewltoy]

Exactly, 0.015" under deck so total squish of 0.062" with a stock head gasket.

some disagreement here... if you do the known math...
center line of crank to block deck is 191mm
stroke is 77mm
center to center rod length is 122mm
compression height is 30.5mm



stroke 77mm / 2 = 38.5
191 - 38.5 - 122 = 30.5 = flat deck.......

Are the numbers wrong????

[bermy]

I know math pretty damn well, but I also know how to use a thickness gauge... strip a bone stock bluetop or redtop (did it on both), get the piston to TDC and get a thickness gauge on top to have it flush with the deck... 0.015" is what you need. Don't believe me? Try it out

Oh and compression height is 30.68mm (just measured it on a bluetop 9.4:1 piston) so I guess the deck is a little taller than what we tought...

[Billzilla]

0.030" squish is about as low as you'd want to go.

[wiso]

I didn't even think of this but I measured my bog stock un-machined block with a piston in it. between the dial guage and the digital verniers it looks to be 0.001"-0.002" over the block surface.

I was using the TRD headgasket on this block and it wasn't contacting the head.

So my new block that was skimmed the pistons were 0.0024" over as measured by the machinist, and he measured the TRD gasket at 0.032". So its gonna be tight, about a 0.029" squish.

But that is also using aftermarket pistons that are 38g lighter than the stock ones. I could get the pistons skimmed to give me more room, but not sure if I its worth skimming a few thou off them.

[bermy]

I didn't even think of this but I measured my bog stock un-machined block with a piston in it. between the dial guage and the digital verniers it looks to be 0.001"-0.002" over the block surface.

Wait, are you measuring the dome there or the edge of the crown? Squish band is around the combustion chamber and both my 9.4:1 bigport and 10.3:1 smallport pistons had the edge of the pistons 0.015" below the deck surface.

[wiso]

measuring around the outside edge where its flat where you are meant to. i know its not the most accurate tools to measure with it was for an indication to myself. but it certainly is fractionally above the block deck. you can feel a step up when you run your fingers or a straight edge over the block then onto the piston.