Has anyone actually put a set of these into a VQ35DE block successfully? These pistons stick up out of the bore a good .010", and the thickness of the head gasket, compressed, is around .026".. so, that's less than .020" clearance.

 

http://forums.nicoclub.com/zerothread?id=207033&page=7

 

I've seen that thread, but I just can't see how they wouldn't make noise.. The general rule of thumb is about .020" clearance between the piston and the head when cold. Especially when you're talking about the edges, where the piston can be higher/lower, depending on how far it rocks over in the bore.

 

I just finished pulling a DE apart that had HR pistons in it, and it looks like there is some contact between the piston and quench pads. I suspect that this is happening when the engine is cold, and the piston can rock in the bore a little more. I measured as much as .014" of piston sticking up out of the bore, with it rocked all the way over. That leaves .012" of clearance, and I can almost guarantee that it was hitting the head. The pistons were clean of carbon, with a line across the dome, showing the edge of the quench pad(s).

This engine had a slight noise when cold, and I suspected valve train noise, but, now, I firmly believe that it was the HR pistons, just barely touching the cylinder head.. just enough to make a little noise, until everything got hot and expanded. My sollution? Fly-cut the edge of the pistons about .010", to make them flush with the bore. If I've done my math correctly, that will give a max potential of about .004" sticking up out of the bore, with the piston rocked all the way over.. And, with a crushed height (head gasket) of .026", that will give me a minimum of .022" clearance between the heads and pistons.

I'll post a pic of the piston later on to show what I'm talking about, but, bottom line, is that you need to take about .010" off of the edge of the front/rear edges of the piston, up to about 1/8" from the valve reliefs, to insure adequate clearance for a HR piston in a DE block, with DE rods/crank. Or, you could buy thicker Cometic head gaskets..

Travis

 

Oh wow! That's excellent info. There are a few of us that are interested in sticking HR slugs in our blocks but nobody has actually gotten around to doing it. You save us a whole heap of trouble. Do you know what the resulting static compression is going to be after the modifications (assuming an OEM head gasket)?

 

Yeah.. the ONLY thread that I had found was the one on NICO, so, I went ahead and put HR pistons into a DE block for a Spec V swap.. The engine made noise on cold start, and got a little quieter at temperature, but, still made noise. I couldn't find anything, other than a few tighter than normal valves (lash), but, that wouldn't make noise.. I tore the entire engine down, and measured the piston to wall again.. all at around .001" or so.. and all of the bearings were perfect.

So, stumped.. I made a call to Clark over at JWT, to kick tires around with him.. He suggested that I check to make sure that I had adequate clearance between the heads/pistons. I knew that they stuck up, but, I didn't realize that you needed a good .020" of clearance.. I figured that ANY amount of clearance would do. However, I was wrong.. You have to take into account, stretch, piston movement (rocking), and thermal issues.

Sure enough.. I looked at the pistons/heads.. and they were clean of carbon, with a perfect line across all 6 pistons, showing the edge of the quench. It's gotta be just BARELY touching though.. and I imagine that with tighter piston to wall clearance, and maybe tighter rod bearing clearance, you could possibly get away with not modding them. But, we build performance engines on the loose side, typically, and that simply won't work without modding the HR pistons.

Static compression should be around 11.6 - 11.8:1, without doing some serious math to give an exact number.

Travis

 

So maybe the Weisco pistons would work better without any modification. I'm not sure about the 11.6 - 11:8:1 with this, but I don't know sheit so I could be wrong. You can get the Weisco with 11.1:1 and .020 over stock with no modification possibly more with a little headwork. Glad I didn't get them yet so I can decide what I will be going with now.

 

The HR pistons stick up, above the deck, so, the compression ratio will be higher than if they were in a HR block.. The only person that has put a set of HR pistons into a DE block with DE heads, reported 225psi of compression, which should equate to around 12:1 static compression. Removing .010" from the pistons edges, should lower it a little, so roughly 11.8:1.

Travis

 

His method of determining the compression ratio was less ideal, to be sure. Is the compression curve from BDC to TDC even linear? You would think that it's exponential since the more you compress air, the hotter it gets, which raises pressure even more. Furthermore, that graph ignores intake valve closing so I never put too much stock in it, personally. Thoughts?

 

You are correct.. however, his "crude" method is going to be close.. we're talking maybe +/- a few tenths.. I will have to make an impression of one of my pistons, with a fly-cut, then determine the volume, in order to get the last (6th) "unknown" in the equation to exactly determine the static compression ratio. I need, bore, stroke, combustion chamber volume, piston dish/dome volume (positive/negative), head gasket crushed thickness, and deck height, to figure out the exact static compression that this engine would have, with .010" fly cuts for clearing the quench pads. I'll pick up some clay tomorrow, and make an impression..

Travis

 

Sweet. Looking forward to your findings.

 

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

 

That's alot higher than I figured it would be, that's for sure. But that's a good thing. Excellence once againt Travis.


This is of course assuming that no material will be removed from the block/heads correct? So if I wanted to remove a total of .006" I'd just add that to the .010"?

Also, once the cut is made, should the edge be radiused or is leaving it sharp fine?

 

A couple or three questions, if you don't mind. Is there any difference between the older cylinder heads and the HR heads? Are the HR rods a different length? Does the HR block have the same deck height as the earlier blocks? Can the HR piston/rod combo stand up to more power than the earlier parts?

I'm trying to put together a plan for a 500WHP engine for next year (presently running 405WHP), and I know I can buy forged pistons and rods from third-party suppliers, but I'm curious about OEM parts.

 

The HR heads are different indeed. They have more pronounced quench pads in the combustion chamber for a more efficient burn. As far as the ports go, they have the same shape as the DE but the valve included angle may be different to improve flow. To use them you'd have to use either an HR or a L32 altima LIM since the stud placement is different. According to the FSM the HR intake valves are smaller but it could be erroneous (wouldn't be the first time). The HR block is taller and the rods are longer (and stronger). Even if they weren't longer though, the HR rod journals have a larger diameter so an HR rod is incompatible with a DE crank.


I personally don't think the HR heads are completely responsible for the increase in top-end power. I think it has more to do with the LIM/UIM setup and higher rod/stroke ratio. Although I believe GT Motosports did discover that the HR heads flowed better, but I'm not sure by how much.

 

Correct.. this is assuming stock block and heads, with no material removed. You want to remove an additional .006" plus the .010"? Are you wanting to lower the compression further? You could fly cut the domes, to lower it further.. But, I wouldn't take another .006" off on the edges, on top of the .010".

You don't want a big radius on the edge of the top ring land.. as this may help the flame front travel over the edge, and to the top ring.. however, just knocking the very edge off will help to prevent hot spots from forming on a sharp edge. Think if it more like "deburring" than adding a radius.

Travis

 

The HR heads have different CC combustion chambers than the DE heads..

The HR rod length is longer, as is the deck height on the HR block. So, running HR rods in a DE motor isn't going to work.. They are much stronger, however.. It's a shame that we can't use them.

Travis

 

I wouldn't want to lower the compression. No way! Just wanted to remove .003" each from the heads/block to true them up so I was thinking that removing that extra .006" from the pistons to compensate would be necessary.

Gotcha. Yea hot spots was what I would want to avoid.

 

OH.. ok.. I gotcha now..

I suppose that you could remove a little more from the pistons if need-be.. but, unless your block/heads are warped badly.. usually, just a skim cut of .001 - .0015" will do it. Especially on the block.. Cut as little as possible and take as little as possible away from the pistons.

Travis

 

Thanks for the answers - not what I wanted to hear, but oh well...

So is this a HR motor ? - and it's from a 350Z.

http://i48.photobucket.com/albums/f2...HRa_112008.jpg

and

http://i48.photobucket.com/albums/f2...HRb_112008.jpg

 

Yup.. that looks like a HR to me..

 

That's actually a revup DE.

 

Yeah.. I sat there and looked at it for a minute.. I haven't really seen a complete HR out of a vehicle. These newer engines have so much crap on them, that they all start to look the same.

 

That engine was on eBay, ending yesterday - I was bidding on it since I could pick it up in Kansas City, but since it was declared a HR motor, I let the other bidder have it for $196. Oh well.... I have another set of heads I can use as exchange with GT Motorsports for a pair of their level-3 heads.

 

Good info Travis and very helpful for anyone going this route. I remember thinking there could be clearance issues with the HR pistons back in the day when this was first being discussed but since I wasn't using them on my engine I forgot about it/didn't follow up.

 

Thanks for making me feel like crap.. lol.. Sorry about that..

Travis

 

Added these pics to the sticky.. but, I'll post them here, too..

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

 

That looks scrumptious.

 

Very nice.

This is the stock 02 Maxima engine just for comparison:

 

I'm sorry - I wasn't slamming you - just a little disappointed I didn't follow through on the bid - and that was my choice. I was still really tempted to buy the thing, just to tear it apart.

You just keep carving new trails with the VQ35s and we all win.