Hey guys,

So my car has recently started burning oil and from what im told its from the Valve Covers and Piston Rings that are leaking oil into my engine and F***ing it all up. What im concerned about is i have 4 years left in my loan to pay on this car.

Would this "rebuild kit" fix my piston rings and possibly give me a performance boost? If not, what would you recommend?

this kit:
http://www.z1motorsports.com/350_g35...oducts_id=3546

 

First isolate your problem. Is it the valve cover leaking or are the piston rings leaking? It could be both or neither. Perform a compression test as well as a cylinder leak down test if necessary. For the valve cover, clean off the oil and do a visual inspection after a bit of driving to pinpoint the leak.

The kit you linked to will definitely give you a performance increase if coupled with the right tuning and supporting mods. It will also fix your leaky piston rings if they are actually leaking. Then again, so would a set of stock rings. If fixing a set of leaking piston rings is your real goal then maybe just save the money and go the cheaper route. Either way a rebuild alone will set you back a pretty penny if you have to pay to get it done. I would explore some of your other options before I set myself back 1K on parts alone.

 

Dang silver tiburon that was actually really helpful! Thanks for your input, what type of supporting mods would i need that your reffering to?

Im looking to fix an issue and then also get a little performance out of it too. Idk if you know this but ill ask, whith leaking valve covers how long can a motor last?

 

Well....

Ok 10.3:1 is the compression ratio for the VQ35DE motor. Go to the kit you linked and look where it says available options:

First you can select bore size. You can select stock, .020" and .040" over pistons. Bore will be the diameter of the piston. The larger the diameter, the more you will boost your compression.

Now look where it says compression ratio. There are 2 options: 8.8:1 and 11.0:1 compression ratio piston kits. The 11.0:1 will give you a slight boost in compression over stock. This could probably be run fine on the stock fuel system with a tune (Osirus perhaps). You would need to get it on a dyno after the upgrade to tell for sure if the stock fuel system could meet the performance requirements of the higher compression pistons all throughout the power band. Upping your compression ratio is not something you can just do alone. It will change the dynamics of combustion substantially and will have to be accounted for somewhere. The 8.8:1 option will actually lower your compression. This would be used in forced induction applications and won't do you any good. A lower compression ratio is needed in forced induction applications so that you can maximize the potential space in the combustion chamber and allow more room for air that is forced in via turbo or supercharger.

So to answer your question, with this kit you would probably at the least need some sort of computer and fuel management, as well as some dyno time to really get the full potential out of the new high compression pistons. It all depends on what pistons you get. If you get a 11.0:1 compression piston which is stock bore size, then you won't be boosting your compression much. However if you get crazy and get a 11.0:1 piston that is .040" over then you will be boosting your compression significantly and will need many more supporting mods to balance things out. Keep in mind an over sized piston will require an over sized bore, which means the block has to be bored out. You are talking about very expensive precision work when it comes to engine rebuilding. Make sure you are conscious and familiar with all the details associated with engine building. If this all sounds like Spanish to you, I would consider doing something besides rebuilding your motor. Simply replacing it with another motor would actually be much more simple in the scheme of things.

As far as your leaking valve cover problem, it won't affect your motor really at all. What WILL affect your motor is low oil levels, which are a direct result of leaking valve covers. As long as your oil level is where it should be, you won't be destroying your engine any time soon as a result of leaking valve covers. I would have it fixed though so you aren't buying oil every day. The leak will only get worse, and it's an easy fix. Additionally the wet oil attracts dirt which could lead to other components getting oil soaked, dirty, and potentially damaged.

 

I'm a complete engine newbie but wouldn't it be fine if he bought that kit but kept the stock compression ratio?

 

Yes indeed, but it looks like that kit only offers two standard compression ratios, 8.8cr and 11.0.cr. It looks like you can opt for them to send you pistons with the stock compression ratio, but they might charge you more for that (as a custom cr). I would just opt for the 11.0 cr unless forced induction is in the future.

 

Lol not to be mean but engine newbie indeed....

None of the pistons offered in the kit will leave you with an end result matching the stock compression ratio. It can only be higher or lower than stock with the piston options offered.

If what you meant to say was that only replacing the stock piston with an 11.0:1 piston will not work well on a stock car, then you are right. However that's not what I said to do. I said a 11.0:1 piston coupled with engine management and a good tune will work very well as long as the stock fuel system can keep up. After you get the car on the dyno you will know exactly what is lacking weather it be fuel, air, timing or whatever. Either that, or find someone who has already been down this road and see exactly what supporting mods they needed.

 

You can get a custom compression ratio for $100 which you can ask them to do the stock numbers no? I'm just asking a lot of questions because my car is also burning oil and I'm just looking at different options other then getting a new engine because I think that would cost more at the end of the day. Thanks for the informative replies though.

 

No man it is +100. Meaning the price of the kit +100 for a custom compression ratio. Unless you are building it yourself, an engine rebuild will typically cost much more than replacing the engine with a used one. Assuming of course you are doing everything you are supposed to when you rebuild an engine (balancing, blueprinting etc.). I don't know how you feel about salvage or junk yard motors, but you could pick one up for under 1K and have it installed for about the same price. So for around 2K you could have another motor VS the $1100 you will spend on just pistons, rods and rings. Not to mention you will have to pay for all the labor and other parts you will have to buy, such as gaskets. You are definitely right in that replacing your motor with a brand new one would cost you wayyyy more than a rebuild though. Sorry man, there's no good options here, especially when it comes to cost.

 

I agree with most of this, but a few things.
A) Increasing the bore size will not increase the compression ratio. 11.0:1 compression pistons in a stock bore is the same as 11.0:1 compression pistions in a .020 or .040 overbore.
B) If you are replacing pistons and rods you should be doing a slight overbore and hone so you're starting with a clean slate. Slapping new pistons and rings in a cylinder that has a lot of miles on it is not a good idea.

 

A) Increasing the bore size will absolutely increase your compression. Increasing combustion chamber volume will affect compression.
The calculation for determining compression ratio works out like this:

CR=(D + PV + DC + G + CC) / (PV + DC + G + CC)

CR = Compression Ratio
D = Displacement
PV = Piston Volume
DC = Deck Clearance Volume
G = Gasket Volume
CC = Combustion Chamber Volume


B) Right. I agree 100%.

 

Actually, your part A is wrong, and a random equation you pulled off google doesn't prove you are right. I don't feel like taking the time to show you why the equation is wrong, but in short it's because the equation just simply uses "displacement" and doesn't account for bore and stroke. You can have two motors of the same displacement but one have a long stroke and small bore and one with a large bore and short stroke.

Going over-bore on the cylinders/pistons does not increase compression or alter it in any way, it only increases displacement slightly. Compression ratio is related to the difference between the combustion chamber volume when the cylinder is at top dead center and bottom dead center. You divide the two volumes. If you actually do the calculation the area of the cylinder actually cancels out here (there are some more complications here due to open valves and what not and the fact that air entering the pistons is actually under a vacuum but I forget whether these are accounted for or not in a compression ratio determination).

Secondly, in response to your prior comment about how a larger compression ratio will throw off fuel ratios and all that, that is incorrect as well. All you are doing with a bumped compression ratio is compressing the mixture further than it already is. If the mixture was proper at a 10.3:1 compression ratio it will not all of a sudden be overly-lean or overly-rich at 11:1. However, when bumping compression ratio you do have to worry about detonation and the increased heat since heat is created when you compress something (standard PV=nRT ideal gas laws).

 

Yes you are right that the actual compression ratio won't change from TDC to BDC. I edited my post to to reflect such. I said compression ratio when I actually just meant compression. The actual compression will change due to the change in cylinder volume. Simply put, a larger cylinder will allow in more A/F mixture.


The change in cylinder volume (displacement) due to a larger bore or dished piston will affect cylinder volume in that a larger cylinder will allow in a larger amount of air and fuel in. Thats all I was trying to say. A 11.0:1 piston will increase displacement and therefore increase cylinder volume, as will a larger cylinder bore.

 

Pretty much what I would have said


Silver tiburon:
Regardless if the bore is 77mm or 98mm if you place a piston that is designed with a dome to create a compression ratio of say 11.0:1 it is still going to be 11.0:1 compression. If you have a cylinder bore of 89mm and you increase that to 95mm while using a piston with the same dome specs of the piston from the 89mm bore ( irrelevant to compression ratio) you will lower the compression ratio slightly because the volume of the cylinder has increased with all other things alike.

 

Wow I feel like I've just read enough about compression and bores to equal a technical deagree and automotive mechanics lol.

This is really good information but now im a little confused.

If I bought this kit and had a shop install it, I would want the 11.0:1 compression for NA and what else would I need? Nothing or something?