For those of you who don't know, I've been working on this engine for more than 3 years now....something I won't go into other than DO NOT BUY FROM MIDWEST ENGINES!!!!
To get this JDM VGT in shape, had to endure a complete rebuild. Rebuild included 20over bore, larger pistons, shaved heads with port/polish, valve job, and balance crank. FYI: engine not together, however based on my mechanics figures, the VG will have 10:1 compression using flat top pistons. I communicated to him that such numbers were unacceptable when using boost. I don't anticipate going over 14psi with my T3 as it should max out around that number. But, he's telling me that the info he has states that the VGT can handle such compression dependably at 14psi.
I'm running JWT program and 370cc injectors with a Apexi AVC-r controller and Stillen rising rate FPR and recirculating BOV (Greddy). Either way, I'm pushing for compression no more than a standard VG of 9:1 and would like to go lower (as I know VGT is 7.8:1). I figure going back to turbo pistons (which I'm not sure why he didn't get these to begin with!) will pull me back down to 9.5:1. I would hate to go with a metal head gasket as I recall they run $500.
Are there any other options I have? Can I get some help as to how to run the numbers to ensure I'm running where I need to be as this engine finally comes together? If I were not going boost, I wouldn't be as concerned about the ratio as the VG's are nearly indestructable. Pervis? Matt? Some knowledgeable feedback is much appreciated!

 

im sure they make cosmetic head gaskets for the VG. probably more like $250 for them.

 

id just run 10:1 almost every VQ and VE turbos have 10:1 and they dont have any problems

 

Anyone else have some feedback to add? I've continued to do some checking and it looks like I can get a 1mm or even 2mm Head gasket from Courtesy Nissan for around $150-200 bucks. I can also install the dished pistons like should be in a turbo anyway.
My concern is fuel management. I don't have a laptop or emanage or anything like that. I'm concerned about knocking at such high Comp ratio even with a FPR and 370cc injectors. I have concerns even if I upgraded to a Walbro (which should do anyway). For certain I'll be stuck running 93-94 octane all the time.
Am I truly being too paranoid about this guys? As tough as the VG's are, will it withstand 10:1?

 

I don't think it's a wise idea to run 10psi (or more) on your stock compression without doing something for timing and something more for fuel, let alone higher compression. Ultimately I wouldn't worry about 10:1 compression, but I wouldn't go cutting corners on tuning. With proper tuning I don't believe you'd have a problem. With your current setup I think you are pushing it.

What's your stock headgasket thickness.

 

I've not been able to find information about stock thickness of VG head gasket. Common sense says that it is less than 1mm given Nissan upgrade options of 1mm or 2mm. I agree, with my setup I feel that it is pushing it, especially given I want to be capable of boosting over 10psi. Of course, stock compression on this engine is supposed to be 7.8:1 for the VGT. Locating a factory H Gasket upgrade that is not as outrageous in price as I previously believed, it looks like I will just break down and get either the 1 or 2mm gasket and install the dished pistons.
I still welcome further thoughts and appreciate the responses thus far.

 

Im pretty positive the VGET has 8.2:1 compression. Some one else did a VG30ET swap and he said he lost alot of bottom end with the really low compression. I would get 9:1 like the stock VG30E as being low boost it would be fine, obviously better then 10:1 and still retain the bottom end of a VG. Maybe if you got slightly dished pistons and used the stock head gasket you should be close egnough.

I wonder why you had the heads shaved if you didnt want the higher CR?

~Alex

 

Alex, thanks for input. Reason is not so simple and referrenced to in the opening thread. To sum it up, Midwest Engines sold me a VG30ET, JDM with "less than 35k miles." Got engine and in going through the normal checks one does before installing an engine (replace timing belt, check compression, inspect water pump, etc), the engine was found to be destroyed. It had little to no compression depending on cylinder, valves bad, water pump rusted out and rust poured from coolant channels. That was just surface stuff. Midwest REFUSED to replace the ENGINE as that was all I was asking, I would hate to have heard their comments had I asked for money back. All they did was send me an aftermarket water pump and SAY they sent valves (which I never recieved). So, in my dedication to the build, I had it completely torn down. Cylinder walls were out of shape which is why it REQUIRED to be bored. As well as the heads, were slightly off as well and is why they were shaved. The pistons that I have now was a mistake by the mechanic, but not too late into the build to fix by obtaining larger turbo pistons. So, that's the story in a nut shell. BBB did nothing and I feel was a waste of my time, knowing now that the only real power they have is to document complaints. That was my niavety though.
So, now I have essentially a brand new engine that I just need to make sure gets put together right.

 

What a terrible ordeal!

Well... what was wrong with the stock engine that's eather in it now or was in it? I've got over 207,000mi on the stock bottom end of my Maxima. I"ve been putting 12psi to it daily for over 20,000mi.
I would not be afraid to use the engine that's in your car now if it's good.
If not, your in a hell of a situation. Already having pistons that are wrong a block that's been bored for them and a rotating assembly that I assume is also ballanced with those pistons.. eeeks. You'd have to have a custom set of pistons made for your setup to attain 9-1 or 9.5 or so. I'll bet all the turbo pistons are going to be too low. 10-1 isn't going to require race gas it will just limit the safe amount of boost you can run on pump gas because your that much closer to detonation with the squish. I would not run a extra thick headgasket... too much loss of quench area.

Cometic does not make gaskets for the VG.. I called.
Nissan or Felpro are the only two that I found Around 200.00! The only way your going to hurt the gasket is from detonation.

I use the "Pocket Romulator" to tune the fuel/timing curves because I refuse to pay Wolf 500.00 for a program that they "think" is good and I can't change anything on! Get a Walbro 225 or 340 in the tank. Double feed your fuel rail Got pictures if you need them on how to do that. Depending on how your going to run your up-pipe the plenum needs ballanced.
lots of info to shair mail me anytime I'll send you pic's or programs from what I"ve done.
~Scott

 

I'd run 9:1 compression personally. Anything lower just kind of sucks. I think a lot of Z31 guys think the same too (especially the earlier 7.8:1 compression engines... that just plain sucks). Then engine you have should be the later W block VG (longer crank snout, a few changes in head and block design like oil and water gallies i believe). The W block turbo engines had a 8.3:1 cr, which is what I have.

I definitely noticed a loss of low end power which made for a tougher time off the line just driving normally. I think 9:1 should be plenty low enough for quite a bit of power.

If you need some custom pistons a lot of Z31 guys suggest BRC pistons (www.brcperformance.com). They can make a set of custom pistons for a very reasonable price.

 

Thank you for the clarification mtcookson. I should have the "w" block as well. I'm concerned about the ceiling for boost given my limited JWT engine managment system, despite upgrading fuel pump, 370cc injectors, and rising rate FPR. I wonder if having higher compression will really just equal out the peak horsepower of the engine? I mean, the horsepower gained from the increased compession will take the place of the power gained higher up in the band from the increased boost? My concern is that with increased low end power, what is going to be the actual daily drivability as compared to lower compression (and HP) and being able to bump up boost when I need/want it (racing)? Removing the adjustable power gained in boost and applying it to the higher compression engine seems to reduce daily drivability in my mind.

 

If your worryed about your engine management i would recommend switching to doing your own tuning. Basically chipping/emulating your own ecu. the same thing that JWT does but you do it so it can be more fit for your Specific car. This is what im running in my car along with Boostedmaxima and a few other VG turbo guys. It works Perfect once your learn how to use the software. the best part is... it is pretty cheap to get up and running.

 

With the higher compression and boost you'll have all around higher power output as well as quicker spooling and most likely better throttle response. Really the only limit is that you'll reach your peak power output with lower boost than you would with lower compression.

Lets say for instance with the build the engine will handle 600 hp. Lets say that with the 10:1 pistons alone it is making 250 hp. It will take less boost to reach the 600 hp than if you had 9:1 compression making 200 hp.

In the end, its all in the tuning. I've seen race car setups with 15:1 compression running 50 psi reliably. If you can tune it to perfection you can run pretty much whatever you want. Going with the lower compression route will be a bit safer and will give you a broader power margin (using the explanation above, lets just say with the 9:1 cr you'd have between 200-600 hp capability so to speak).

These are just generalized figures but should hold true to whatever power you do end up making.

Daily driving wise, you might actually like the higher compression a bit more simply because you'd have better low end making it much easier to take off from a stop. It will also reduce turbo lag to next to nothing, depending on the turbo you use, which should make the power feel almost seemless.

 

On pump gas, 91-93 octane, the lower the CR the more boost you can get away with before the onset of detonation, however as previously stated, off boost and low boost performance suffers.

I'd have to say 8.5-9:1 is probably ideal for <25psi on pump gas. You can get away with 10:1 CR and 10psi on a VQ anyday, but not sure on a VG...check their boards. Once you get go past 10psi on a VQ, you really need to have your timing under control and know what you're doing.

I'd look into the VG websites, since there is a wealth of information on this subject I'm sure.

 

I'm not sure he'll find anything on high compression boosted VG's unless its the VG30DE. The VG30E came with 9:1 compression and I've not seen anyone modify them to a higher compression engine except for maybe that Hekimian racing group. It only makes about 250 hp, which is decent but nothing compared to what a simple boosted VG is capable of... oh yeah and that engine is over $8,000.

Internal limits wise, the most we've seen out of a stock block VG is a bit over 500 whp to my knowledge. Some claim around 300 whp max since the internals are cast but it has been proven they'll handle a bit more than that.

Detonation wise... its all up to the tuning. If, however, you have it tuned to perfection and are still detonating on pump gas you'll then have to back off a bit or run race gas.


Personally, if it were me in this situation I'd get some custom made pistons and run it at 9:1 compression. That'll retain good low end power and have some awesome top end with excellent spooling of the turbo (if you get a decently sized turbo).

 

I meant VG30DETTs, since they're the same/similar and have many different CR pistons available.

Tuning is a tradeoff. If you're starting with 91-craptane, you'll either A)have to lower CR or B)severely retard timing. You can run super rich AFRs to combat detonation to a point, but that's just a bandaid.

Lowering CR vs. retarding timing, in the example below...lowering the CR meant a 1-2 percent torque loss vs. not lowering the CR and just retarding timing, which caused a loss of 5-6% in torque.

Here's the example:
http://www.streetrodstuff.com/Articl...ion/Page_4.php

 

Well since pump gas is now at raceing gas prices who the hell cares what we put in the tank it all costs the same!!!!!
Good information in above posts.
Simply put... lower compression.... more boost to make XXX hp.
Higher compression lower boost to make same XXX hp.
We are only talking one point of compression and having a allum. head. It's totaly different with cast heads. You'll be fine eather way.
Hey Mark... how the hell are ya?
~Scott

 

The VG30DETT has forged pistons to help maintain a stable and reliable block. You might be able to find a set of stock VG30DETT pistons and run the 10:1 CR. I believe the VE?VQ engines use forged pistons already. I may be wrong on that last statement though.

 

They had forged rods and a crank but cast pistons. Most stock vehicles use cast pistons that I know of. The heads of the VG30DE(TT) and VG30E(T) are different so the CR's will be quite different between the two engines if you use the pistons of one in the other. (the VG30E(T) heads have a larger combustion chamber so the cr will be lower using DE(TT) pistons).

I'm doing pretty good. Just turned 21 yesterday.

 

I appreciate all the input. Since this is my daily driver, I'm shooting for the lower compression to lower my base (non-boosted) hp on the engine, especially for rainy and snow/slick weather. Courtesy Nissan emailed me back about the Head gaskets. They said that the thicker gaskets don't seal well and are not recommended. Therefore, I'm looking to use the stock turbo pistons and see where the CR lands.

** With all this talk about horsepower and trading off increased base HP with increased compression versus lower base hp with lower compression and gaining overal hp output through boost there is still a HUGE lingering question. On an engine, assuming everything is the same, boost is said to equal about 10hp per 1 lb of boost. So, what does every .1 of compression (or .2 - whatever) equal in hp gain?

*** One more question. When I began this project there was only JWT that I knew of for ecu modification and engine management. Now there are all these programs that I'm hearing about and the number of turboed Maximas is unreal (there were only about 4 total when I began my project). Where to go to explore these systems, cost, reliability? Just curious. Previously I thought these could only be used on the newer Maximas.

 

LiveEdit, ZEMulator, and other Romulators only works on 3rd gens (and older maybe too) it doesn't work on 95+.

This depends on the efficiency of the engine, but 10hp per 1psi boost is very low. On VQs its more like 20hp / psi boost.

 

91Maxima and I both use "Live Edit" it is a FREE downloadable program from the internet and all you need to use it is a "Romulator" which is 150-175.00.
You can change all your fuel and timeing tables along with rev-limits,injector size, MAF changes and more. It's definatly the way to go. I've got a good base program for 370cc injectors and a Z32MAF to get you started.
Hope it's going well!
Scott~

 

One thing I forgot about that I remember over the weekend... one thing you'll probably notice different between lower boost with higher compression and higher boost with lower compression is torque. The lower compression engine with higher boost will most likely produce more torque.

 

Still the question whether there is any estimate about what .1 (etc) of compression equals out to? VG increased compression to ____, what is approximate HP increase? Boosted, ygm.

 

From the information I've read, A "General" guide is that when adding 15psi to a engine your "theroeticly" doubleing your cubic inch.
I'm sure there's a million variables to that "theory" but it's definatly possible to attain those numbers or better.
I sent you a e-mail about the specifics of Live Edit and the Romulator.
If I can be of anyother help let me know..
Scott~

 

not-shameless-plug: www.aquamist.co.uk (water/methanol injection can fix many of these problems), Summit also has a very affordable water kit, as well.
there's some Buick GN sites out there that have very good info on boosting, too.

 

Theoretically doubleing your Cubic inch and therefore also theoretically doubleing your HP...that also what ive always thought. but.... i over doubled my whp with only 11 psi boost on a VG. soo.... ya what im guessing is that when your under boost... your moter burns fuel as if it has higher compression therefore makeing more HP per volume.

 

Also if your interested in Liveedit.. im up for helping you get it working to.

 

Run the stock engine config. go to www.devilsownonline.com and buy the progressive alky kit. You will have NO problems running stock timing and 10+psi with an alky kit. I run my l28et with 36deg's advance with ww fluid and 91 octane. Afr's are 12.0 from 0 psi to 20psi. It's absolutely amazing what methanol/water can do. Also if you need any help with the ecu let me know.
Bernard
(I am in no way affiliated with devilsown, I made my own progressive kit, I just think it's the best bargain out there.)

 

Bernardd is the real man to talk to about live .... he knows his stuff

 

lets start this back up...&...whats different today?

 

It's been THREE YEARS... why?

 

dig, dig , dig em up!!

 

 

well just building mine now....and wondering what, if anything, should i change about the internals? i wanting to build a daily driver turbo max.

 

Unless you're looking to put down more than 500whp there is no need to open your motor up. You should know that VGs are easily capable of 500+whp on stock internals.

 

Nealoc pretty much said it. But, if I'm my old question is being resurected, I suppose I should have some say. I decided to go with dished pistons for a couple reasons. First, if I ever decided to run a bigger turbo. Second, the mechanic told me the heads had been shaved slightly, so I wanted to provide some additional clearance for the valves in case I wanted to upgrade to a more aggressive cam. I did end up going with a more aggressive cam. As far as internals, I did nothing. I only purchased new, oversized (because of 20 over bore), dished pistons straight from Nissan. So, effectively, the engine is bone stock except for the cam. This is also an "A" block as opposed to the "W" or modified blocks that most others have built. No difference you should concern yourself with though.

Currently biggest issue is a shotty tune. This car is my daily driver.

Feel free to email me anytime. Maxmaxima is definately someone to speak to. There are many good names both posted and referenced in this thread as well.

 

why should i not be concerned with the difference?

 

I just meant for the purposes of this thread, explaining the difference is irrelevant unless you have the "A" block. If you do, you just need to be aware of what you have given you will need to do just a couple of things differently, nothing major. The biggest difference you would need to know is that the older "A" block has a lower base CR. Knowing that is important in terms of tuning and setting up your system to achieve the goals you have for the car. I got your email, we can talk more specifics there if you like.