Low comp. pistons vs. head shim APEX

87gtNOS · Mar 3, 2017

which would be better when doing rods and pistons....head shim or low compression pistons?
I'm doing rods and pistons this summer in my 2012 Apex....
Thanks

up-high · Mar 4, 2017

If you are doing pistons anyway, do low comp. Going to run big boost? Do upgraded rods as well. Had Apex with both and think throttle response was better with pistons. Could have been trying to justify the purchase.

roughrider99 · Mar 6, 2017

Also headshim is less reliable compared to low comp pistons in terms of the head gasket, headshim has potential for 2 sealing surfaces for sale while low comp pistons leaves the original sealing surface and single head gasket.

kinger9 · Mar 6, 2017

Headshim is just fine for reliability. I was more scared to do low CR pistons and re-nikasil the cylinders to do it 'right'. Also pick your pistons carefully and rings so they don't knock or burn oil. Stock with headshim is hard to beat up to about 15 psi. Over 15 psi you need rods and pistons and take the trade off of some possible slapping and oil consumption.

Octanee · Mar 6, 2017

kinger9 said:
Headshim is just fine for reliability. I was more scared to do low CR pistons and re-nikasil the cylinders to do it 'right'. Also pick your pistons carefully and rings so they don't knock or burn oil. Stock with headshim is hard to beat up to about 15 psi. Over 15 psi you need rods and pistons and take the trade off of some possible slapping and oil consumption.

I ran 17-18 psi on my apex regularly, odd spike to 20#, elevation ~5500feet all she had was a head shim, absolutely no issues

M5- · Mar 7, 2017

If you use a head shim which IMO is fine up to 17 lbs on an Apex, use a stainless steel one, I've blown out an aluminum one before.

M5

87gtNOS · Mar 7, 2017

Thanks guys for the input.

I was thinking CR pistons from Hurricane which use the stock Yamaha rings.
Along with Carillo Rods...

I assume the pistons he sells for this (10 to 1, I think) are suitable for NO headshim and a 290 kit? I know he can answer that when the time comes I guess....

87gtNOS · Mar 7, 2017

M5- said:
If you use a head shim which IMO is fine up to 17 lbs on an Apex, use a stainless steel one, I've blown out an aluminum one before.

M5

I have whatever headshim it is that comes with the MCX 290 kit in it right now....I didn't install it, so I'm unsure the material.

87gtNOS · Mar 7, 2017

I have run about 13.6 psi....on 91 octane (with maybe some Shelbourne fuel additive, not sure if it works!) and that 13.6 could also be a spike from letting off the gas....but anyways, I just want to build this motor with rods and pistons ready for C12 and about 16 psi boost for grudge racing!

sledfvr · Mar 7, 2017

I have heard that the 2011 and newer apex motors are not as durable. Something with the pistons coming apart at mid-high level boost. Check on ty4stroke. I wanted to build a 174x3 turbo apex with eps, but the rumors of weak motors scared me off.
Just and fyi. Might be better to do a built motor in that case.
That being said I have 5500 hard miles on my 06 apex motor 15-17psi.

HANDSOME · Sep 14, 2017

sledfvr said:
I have heard that the 2011 and newer apex motors are not as durable. Something with the pistons coming apart at mid-high level boost. Check on ty4stroke. I wanted to build a 174x3 turbo apex with eps, but the rumors of weak motors scared me off.
Just and fyi. Might be better to do a built motor in that case.
That being said I have 5500 hard miles on my 06 apex motor 15-17psi.

Keep us posted , I'm trying to get a 2011 apex. I will do pistons if I go to a 290 kit

gunnerthesnowman · Nov 19, 2017

87gtNOS said:
I have run about 13.6 psi....on 91 octane (with maybe some Shelbourne fuel additive, not sure if it works!) and that 13.6 could also be a spike from letting off the gas....but anyways, I just want to build this motor with rods and pistons ready for C12 and about 16 psi boost for grudge racing!

I have a engine built by OSP that has stock pistons, stock compression,has rods and the block is decked, the head and valve train is all stock, clutched to run at 11600-11800 rpm,s, 3076 turbo external waste gated, I have a tune to run 22-24 psi of boost on C-12, The thing is crazy. I have a full ported and polished head with 1mm oversize valves with dual coiled tie springs with hurricane race cams sitting in a box for years now, hard to pull a engine a part that has tons of UN-usable power now to install the modded head

87gtNOS · Nov 20, 2017

gunnerthesnowman said:
I have a engine built by OSP that has stock pistons, stock compression,has rods and the block is decked, the head and valve train is all stock, clutched to run at 11600-11800 rpm,s, 3076 turbo external waste gated, I have a tune to run 22-24 psi of boost on C-12, The thing is crazy. I have a full ported and polished head with 1mm oversize valves with dual coiled tie springs with hurricane race cams sitting in a box for years now, had to pull a engine a part that has tons of UN-usable power now to install the modded head

Stock pistons? Awesome, good to hear that.
I think for one more season I will run the stock rods and pistons at 12 psi (91 octane, sea level).

Thank you guys for your input. Thanks to Mark of MXC USA too for the quick chat on FB.

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Low comp. pistons vs. head shim APEX

87gtNOS

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up-high

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roughrider99

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kinger9

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Octanee

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M5-

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87gtNOS

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87gtNOS

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87gtNOS

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