HR pistons in VQ35DE block.. no go without mods..

[TurboS13Hatch]

I'm starting a new thread, and hoping that a mod will sticky this.. so you guys can avoid the same problem that I've encountered.

Stock HR pistons, with VQ35DE rods/crank will not work, without either slightly fly cutting the edges of the pistons, or, by using a slightly thicker Cometic head gasket.

Without mods, and with clearances set a little on the loose side (any performance built engine), the pistons just barely make contact with the quench pads in the cylinder heads.. So, I would recommend fly cutting the edges on each piston, up to about 1/8" from the valve reliefs. I would cut it around .010" deep, to avoid any/all potential contact.

Here's a pic to show what I'm talking about..



The area in the rectangle, shows how contact with the quench has cleaned the piston of carbon. We're not talking much here, but, there's enough contact to cause noise. By cutting the area shown with a mill, you can increase clearance by about .010", just to be safe, and get away with putting HR pistons into your DE block. You should be able to get this done at any competent machine shop for around 100.00 for 6 pistons. Or, you could spend a few more bucks, and get Cometic gaskets that are a little thicker, and avoid having to cut the pistons alltogether.

Anyway.. just wanted to share some useful info..

Travis

[TurboS13Hatch]

Ok, so I did some research.. and found that the HR pistons have the same dome volume as Rev-up pistons. The difference in compression ratio between the two, comes from changes in the combustion chamber volume. So, we know that HR pistons have a 5cc's of dome volume. We can get pretty close in guestimating that the .010" of material removed will equate to roughly .5cc.. MAYBE 1cc.. max.. So here we go..

Bore- 3.759"
Stroke- 3.204"
HG thickness (compressed)- .028"
Deck height- -.007" (after removing material/splitting the difference with the rest of the remaining (taller) material where we didn't take .010" out)
Piston dome volume- -4.5cc (with material removed)
Combustion chamber volume- 56cc's

This give us a static compresion ratio of 11.53:1. I would say that it will be plus/minus 1 tenth, depending on the exact dome volume, but, it's safe to say that it'll be within .5cc's of my estimate. So, betwen 11.4:1 and 11.6:1 static compression with this HR pistons, fly cut .010", in a DE block with DE heads/rods/crank.

Travis

[sparks03max]

Originally Posted by TurboS13Hatch

Ok, so I did some research.. and found that the HR pistons have the same dome volume as Rev-up pistons. The difference in compression ratio between the two, comes from changes in the combustion chamber volume. So, we know that HR pistons have a 5cc's of dome volume. We can get pretty close in guestimating that the .010" of material removed will equate to roughly .5cc.. MAYBE 1cc.. max.. So here we go..

Bore- 3.759"
Stroke- 3.204"
HG thickness (compressed)- .028"
Deck height- -.007" (after removing material/splitting the difference with the rest of the remaining (taller) material where we didn't take .010" out)
Piston dome volume- -4.5cc (with material removed)
Combustion chamber volume- 56cc's

This give us a static compresion ratio of 11.53:1. I would say that it will be plus/minus 1 tenth, depending on the exact dome volume, but, it's safe to say that it'll be within .5cc's of my estimate. So, betwen 11.4:1 and 11.6:1 static compression with this HR pistons, fly cut .010", in a DE block with DE heads/rods/crank.

Travis

Seems like you're still having alot of fun with those vq swaps in the specs, travis. Are the HR pistons forged?

[nismology]

Originally Posted by sparks03max

Are the HR pistons forged?

They are still hypereutectic cast.

[nismology]

Stuck.

[TurboS13Hatch]

Thanks Nismology..

I snapped a few pics of a piston that has been cut down .010" to clear the head..




The piston's edges are now flush with the bore.

Travis

[nismology]

Thread closed. Will consider reopening if the OP has something new to add or if someone has a legitimate question that has not been addressed.