sparks03max

iTrader: (7)

Considering there is no scoring on the stock cylinder walls, how much risk would I be running installing a set of fly cut HR pistons in place of my stockers? I'm guessing I would have to reuse the stock piston rings, considering they fit (guessing they should).

I'd consider doing this while installing rod bolts, as total investment would be roughly $450 for a 1.2ish bump in compression. 350ish for a set of stock HR pistons, and probably 100 to have a shop fly cut them.

If I have to pull the block and have any machining done, it would become far too expensive and labor intensive to be worth my trouble at this point. I'd may as well wait and do a full bottom end build with forged parts in that case.

I'm looking for responses that are on topic of this thread from you guys who have experience, please!

98SEBlackMax

iTrader: (9)

I think you have to remove the cylinder heads to replace pistons. I've never heard of anyone pulling the pistons from the crankshaft side on any engine build.

Also I thought VQ35HR piston rings were different that VQ35 ones?

sparks03max

iTrader: (7)

Heads would be removed regardless. I'm not sure on the rings, was guessing they would be the same. Could use info on that, as well.

Weimar Ben

iTrader: (5)

Why would you need to build the bottom end? If you're NA, the bottom end can easily handle whatever you can throw at it.

Putting a set of hicomp pistons into a untouched bore is asking for trouble. New slugs should mean new bores. At a minimum, you should have a light hone done.

98SEBlackMax

iTrader: (9)

Oh ok. I misunderstood seeing as you only mentioned replacing rod bolts, which can be been done with the bottom end installed.

I have heard of people replacing rods and using the stock pistons with new rings, this was for a V6 TT S4 engine. But I would be concerned with different pistons on a stock bore.

Last I checked Nissan VQ pistons come in 3 different sizes and a overbore size as well. Not to mention if the flycutting will distort the pistons at all.

I would say that is an overstatement. This engine is going to rev alot higher than stock I'm guessing. A N/A VQ35 reving to 7500 rpm likes to have upgraded rod bolts. Beyond that better rods and oil pump are in order IMO. About the only thing that a N/A VQ bottom end can take at very high revs (Beyond 8K RPM) is the crankshaft.

sparks03max

iTrader: (7)

I would build the bottom end if I was getting bottom end work done because I will not only be running N/A and because if I'm spending the money, time, and effort to pull the block and have it machined, I would go ahead and spend more for forged internals.

Weimar Ben

iTrader: (5)

Umm, upgraded rod bolts are a given. Revving above 7500rpm is ridiculous anyways since the VQ35 doesn't make any power above that.

98SEBlackMax

iTrader: (9)

Bear in mind my use for a VQ is probally different than yours. On a roadcourse the VQ30DEK I have spends most of it's time at 4000 ~ 6600 RPM which is to low, I need a 7200 - 7500 rev limit with a balanced/built bottom end that can survive several hours in that situation. One reason why I've kept my stock rev limit to keep me out of trouble until my built motor is done.

It sucks to be that guy who's car throws a rod and pukes oil all over a turn. I've had to drive thru some oil slicks and it's not fun. So when I suggest an engine build it's usually overkill for the 1/4 mile guys.

asand1

iTrader: (1)

Im not familiar with HR pistons, but new standard bore pistons in a worn standard bore would be better than worn pistons in a worn bore. And never re-use rings, that's just begging for blow-by and smoke.

t6378tp

iTrader: (69)

if the mileage is low, get out the mic and measure it, hone it if in spec and throw it stock bore pistons with new rings

don't forget to measure ring gap also. musclecar guys do it all the time. make sure you double check and measure everything

SteveB123

iTrader: (2)

No scoring does NOT equal no wear.

Measure, hone/bore as required, install new rings or new rings and pistons.

Rings are a wear part, as they are the piston "bearing" and, more importantly, the seal.

Poor seal equals poor power, and for a good seal you must prep the cylinder walls, and install new rings.

sparks03max

iTrader: (7)

Thanks. Mileage isn't low, so I'll just wait until it's time to do more work to the block. I'll be doing topend work, first.

In terms of all the side chatter about RPMs, I'm going to tentatively (depending on power dropoff) have a redline of about 7700 with valvetrain, cams, rod bolts, oil pump.

nismology

iTrader: (8)

Just measure the bore roundness and taper and if these check out you should be fine. As mentioned there are three different pistons grades so use the bore diameter measurements plus the piston diameter info in the FSM to tweak the clearance. I will, however disagree with the suggestions to rehone the stock bore, provided the OEM crosshatch is still intact. A hone should only be done a fresh bore otherwise it's almost impossible to get the old and new patterns to match up consistently. Very easy to end up doing more harm than good. New HR rings should also be used
but there's no real reason to set the gaps as they are factory rings and not file-fit.

sparks03max

iTrader: (7)

I was hoping you would respond. That makes me a lot more likely to do this, then. When I have the engine torn down for other stuff, I will do the measuring as you've suggested and order a set of HR pistons/rings in the proper size provided there isn't excessive wear. I doubt fly cutting .010" off of the edges for head clearance will distort the pistons, as this is exactly what Travis did and had no problems.

Honestly, although labor intensive, this is a very cheap way to gain a good deal of N/A power. I'll definitely spray water/meth, and run 104 octane at the track so I can still run plenty of timing. Higher compression will also mean I can run a more aggressive cam with less detriment to lowend and gain more power topend. Just theoretically speaking, going from 10.3 to roughly 11.5 could gain around 8-15whp throughout the powerband.