esprit's 11.5:1 piston claim that the piston is the same size as normal bore diameter, it is possible to replace with the normal piston.
which means no other internal work need to be done ?
can some one explani this to me?

 

You would probably also need new rings for the pistons, the associated bearings and personally I would have the cylinder bores honed to ensure the best fit and longest engine life.

The higher compression from those pistons can come from one of several areas, there could be a slight dome to the piston, or the ringland could be moved up higher. I'm not familiar with what type of pistons come stock (flat top, dished, domed). The higher compression is most likely acheived in one of the two ways I mentioned above (ringlad or dome) or a combination of the two.

They work without too having to bore or resleeve the cylinders (I assume the block is sleeved) because they are the same bore size (diameter) as the stock pistions. The bore size has very little to do with actual compression ratio. Going with a larger bore however will yield some more displacement, but will require block machining and new sleeves (if they're sleeved). This gets expensive, but could potentially yield more horsepower through more cubic inches (or cc's) and through further unshrouding of the valves, etc. (if applicable).

hope that answers it for you.
Don

 

i "think" i am getting this!
thanks for the help!
then wat is the really difference between a piston that have the same size as normal bore diameter and a piston that does not have the same size as norma bore diameter?
thanks for ur tine

 

I'd reccommend other things to get more compression than just changing pistons!

 

Regarding the Espirit pistons...

First, shop for a different brand. I think they are just imported from the states and sold under the Espirit name (but I am not sure). CP, Arias, and a few others make pistons. You can also purchase directly through sgpracing.com.

Second, the VQ35DE essentially has a flat top piston. 11.5:1's have a dome and the ring may be moved up (not sure on the rings). 8.5:1's have a dish out. At least, the ones at sgpracing.com are like this.

Third, you asked about over-bored pistons, or ones that are larger than stock. They are available. The VQ35DE has a 95.5mm bore. I am not sure if that is the bore or the piston diameter, but it is one or the other. There are piston in 95.5mm and I believe 96mm sizes. I cannot remember whether I read this at Arias or somewhere else. At any rate, pistons are sometimes sold a slight bit larger so that you can hone the block to get a perfect match to the piston set. Yes, it get a tiny bit more displacement, but it is usually about higher compression and perfectly "blueprinting" the engine (higher design specs and perfect matching parts).

Hope this helps. You will need to double check a little of my info, but I think you get the bigger point. Take care.

 

To give you a direct answer as simply as I can to this question it's this.

A piston that is the same as normal bore diameter will fit your engine with no additional machine work required (it's a piston swap) though this is not a simple operation.

A piston that has a larger bore may require a small or large amount of machining, mainly resleeving the block or reboring and resleeving, in some cases you may be able to get away with just a fresh honing of the block. This will dependant on the difference in size from stock.

Also a larger than stock piston will yield some more displacement. A good example here, my old 302 (5.0) Mustang had a 4.00 inch bore. Bored .030 over (or thirty thousandths of an inch), it displaced 306 total cubic inches. So an increase in bore size of just .030 yielded 4 more cubic inches of displacement.
The Z makes approx. 1.34 HP per cubic inch (61cubic inches per liter of displacement, 287/(61x3.5)= 1.344 ), so until you get into a signifgant increase in cubic inches you're probably not going to notice a great difference in power with a larger bore piston.

Unless you have to have the pistons, for a big power adder application, I'd reccomend maybe looking at other mods first. There is a lot of labor and parts cost as well as downtime involved here and if you're going to do this much work you might as well do it right and put higher strength rods in there too. If you're sticking to a naturally aspirated setup, the stockers will probably be fine, the difference in power may not be worth it to you at this point in time. (keep in mind I have no idea what your plans or current mods are)

Just my .02, hope that helps.
Don

 

thanks for the help, from my knowlegde, i dont think esprit just just other brand's piston(since i dono any other brand's piston has the same normal bore diameter as stock's!
but i will double check anyway!
so which piston will u recomand for?
the piston i want will be the one that is the most safe ones(it doesn't have to be a large increasment in hp)
thanks

 

a higher compression ratio piston will be my last step to my car,
exhaust, test pipe, CAI, cam, lightend flywheel, headers. and then the valve spring, forged rods, amd a/f ratio tuning along with a higher compression ratio piston.
so it will take more risk for a larger bore diameter piston than a same bore size diameter piston?

 

Hey Guys

I need you opinion on this. I am thinking of swapping in 8.5 ppistons and forged rods (probably from SGP) for my TT setup. Do I NEED to resleeve the block, or is it safe to just swap it in? A very good mechanic at PErf Nissan told me "no, if it's stock size - just drop it in" He recommended against boring, etc. I have 30K miles on my G and do drive the car pretty hard.

So if the right diameter is 95.5mm, do it just order those, or do I need to resleeve the block?

Thanks
Gurgen

 

Ok, a lot of questions here that I will try to answer:

First for GY-Z:
If you are going with nitrous or a naturally aspirated setup get a higher compression ratio piston, and you can go Forged or Cast (hyperutectic) on this as long as you're not running a power adder. If you plan to run nitrous which is the only thing you should ever run with a higher compression ratio then get a Forged piston. You can ask when you call the manufacturer what HP these pistons will handle with the rods you're choosing. I would reccomend a piston that can handle more power than you're planning to throw at it, so you stay on the safe size. Additionally as long as you don't have too many miles on the engine you can get away with just a stock size piston, however I would highly reccomend a fresh hone on the sleeves to ensure the best fit, a light hone to make some fresh cross-hatch marks on the cylinder walls will help with sealing and won't increase the bore size.

For gurgenpb01:
As long as you use a stock size piston the block should not need to be resleeved, granted that there is no damage to the sleeves from something like driving while overheating or piston damage, or a jack a** mechanic doing the teardown.
Much like GY-Z, I would reccomend that you have a fresh hone put on your cylinders (sleeves) to get the best ring seal possible, you may need some machining on the crank to get the rods to work right and have the longest bearing life as well as the best oil pressure. You can have the mains align honed, then the crank turned, and compensate for the size difference with the appropriate size bearings. Cylinder walls and water jackets I bet have some tight clearences on this engine and overboring the block could cause some hot running problems.
You should be able to call and order the pistons and tell them you wanta a 8.5 piston with stock bore size.

Hope that helps you guys out.

 

DynoDon

That helps a lot, you're the man!

A follow up if you don't mind, and it's about the rods/crank. You mentioned machining the crank - is that that the usual routine? Also, I understand that machining the crank will allow for a a better fit of the rods, but you would be machining the part of the crank that sits in the bearings? (sorry if I didn't get the details right here, but I am imagining the bearings sitting a teh ends of the crank).

As far as the bearings are concerned, i thought stock ones are my only options. Are there "stronger" ones out there?

Also, is there a thinkcer head gasket to lower compression for the time being (until I go with the full internals work).

Sorry for the multitude of questions.... I appreciate your help.

Gurgen