Hi guys,

so a friend of mine is working on his project to build his beast G35 sedan with GTM stg 3 TT kit.

the parts going into the build are as the following:

- CP Pistons (For some reason, part number for the DE is the same as the HR)
- Carrillo Rods
- L19 head studs
- New Stock main studs (No aftermarket main studs available for the HR as per my research)
- HKS head gasket.
- New bearings.
- Stock cams.
- Springs/shims..etc for the heads
- Port & Polish for the heads.
- NGK 2 step colder spark plugs.

Now the issue we are facing is the gapping between the deck and the piston when its fully up.

I dont think its a normal practice to have sucha big gap. and the installer thinks the same.

any input guys ?!?!?


below are some info/tests we did that might help:

Compared Stock HR rods with the carrillo's : result ---> HR = Carrillo in length

Compared Stock HR pistons with the CP's : result ---> HR > CP pistons

based on those results, we suspected that the pistons we have are shorter than what they suppose to be, but after checking with CP, we found out that the pistons for the DE are exactly the same as HR


Below is the picture to explain.

CP psitons gap:






Stock HR : flush with the deck of the block

 

different position of the wrist pin ?

 

Lower cr pistons

 

i dont think its about low comp pistons.. cause mine was low comp but the gap was not that big..


pic of my piston ( wiseco pistons )

 

do a side by side with the cp and stock pistons and find out whats different

 

i did.

Stock > CP

installer says thats the reason. but CP confirmed that there is no difference. :S

anybody tried CP on HR ?!??!!

 

Look at how much machining the Wiseco has done to its surface VS the CP.

The CR is determined by the volume of the combustion chamber. The volume can be changed by taking material out of the piston top( relief for valve clearance as well as additional material) or lowering the top of the piston.

If the CP's have less machine work done then they must use an alternative method to lower the CR. Either lower the wrist pin centers or shorten the piston height from the wrist pin center..

 

aha.. so you mean that CP is keeping the material more and lowering the piston level in order to lower the compression !!!!

is there anyone who installed a CP piston who can confirm if thier engine looked the same ?!??!

 

i have cp pistons on my HR build and they sat flush with the top I'm using BC rods on the BC stroker though so that may affect it since it rises and lowers more...

And we had ARP fabricate mainstuds as well as headstuds when we built my HR

 

Possibly. After looking at the pictures again the CP still has a decent amount of machine work done to the surface.

It would be nice to know the piston heights for stock hr vs de ( height from pin centers) to know whether the pistons are 1 to 1.

 

Hmm... I say call CP and rule out the obvious first... get the correct part number.

Next were there any item replaced for wear and tear like the crank or the block? I believe the rods and block are longer on HR (about 8mm) so if there were some accidental mis-matching going on, you could get a gap like you're showing.

 

bump

 

+1 on verifying correct part numbers.

Are these lower CR pistons? Depending on what they are supposed to dro the CR too you could very easily calculate it to verify if its correct.

http://www.csgnetwork.com/compcalc.html

 

I used CP pistons in my build, but custom ones IIRC.

And I know that the DE and HR use the same pistons.

 

Wiseco's have like 10 or 16cc removed from the domes, not sure exactly but I do remember reading that on the box.

You guys need to call up CP and ask what clearances they recommend and have the machine shop go by that.
Even if it looks tight or loose, you simply can't eyeball these things for a forced induction build.
No offense but seeing as you didn't post up clearances, you need to take this to a pro and have them mic everything up/do the proper machine work.

Also don't cheap out and use a cordless drill+honer and slap in "oem spec" pistons. That's just asking for issues down the road, imho.
You really should get those sleeves honed/clearanced to the pistons properly, with torque plate and all that jazz.

 

He's not talking about cylinder wall clearances he's talking about how the piston doesn't rise all the way to the top of the cylinder.

 

I actually had to ask this same question to Wiseco on a set of custom pistons I had mad for a DE and this was their response

"Using a DE piston in a HR engine will not affect compression at all. They sit farther down in the bore on the HR but the HR also has a smaller combustion chamber so those 2 equal each other out. So whatever compression they use in the DE’s will be the same in the HR. The valve pockets are all the same and everything so they are good to go."

This is on a set of Wiseco's so I would assume CP would be the same but i would still confirm with them.