Hello everyone, I have an 91 Z32 TT that I am waiting to do a compression test on as I’m slightly doubtful towards this motors health. It’s a JDM motor that was in the car when I purchased it almost 3 years ago. It’s always ran fine, however it has also always produced low oil pressure - even with Mobil 1 15w50. It has a tendency to tick if the oil is even a couple drops low, like not even visibly low according to the dipstick. I eventually found that out when I just added a little bit of oil when it would start ticking even though the dipstick wasn’t low and it would magically stop. Anyways it idles with like 15 psi of oil pressure and never goes past 45-50 driving. Even at wide open throttle at redline. Cruising is usually between 25 and 30. No misfire though. Anyways, I am waiting for my compression tester to arrive before I determine this motor’s fate.

Now, onto the question I have for you all. If this motor is bad, I intend to replace it with an NA block and use MSP manifolds and rebuild my stock twins and use them on it. I will be running 2 massive eBay sidemount intercoolers, 2” piping, 93 ethanol free gas since I have old style 555cc injectors, and methanol injection. How much boost do you think I could safely run on this setup? On the track I would just run C16 and meth injection, but I want this car to be streetable as well. I read an article about NA-TT guys being able to make about 400 horsepower on just 93 with 10-12 psi, and the article mentions that you can stretch that with meth, but does not say how much because the writer was clearly e85 biased. Just to be clear, I do not have e85 readily available where I live so that is not an option. Closest station is 50 miles away.

Sorry for the long read everyone, just had a lot to explain. Thanks

The blocks are the same, what will hurt you are the NA higher compression pistons.
We have had a few boosted NA long blocks here the they run 375ish WHP on 91 pump gas that are dyno tuned by SZ. The 2" pipe will require more boost to create the same flow as 2.5". Higher boost plus higher compression pistons(10.5:1) make thinks go boom. The meth injection will help, but I do not have any experience with that. I you have the NA block, why not upgrade the pistons before installing; you will need to swap TT heads over too.

Also, are you relying on the OEM oil pressure gauge for the readings? You know that this gauge is not very accurate right? Is the oil pan dented at all, this can cause your oil pressure issues too?

I wish we had a E85 only 50 miles away, my closest is 200 miles away

itsa300zx wrote: ↑

Thu Nov 07, 2019 11:28 am

The blocks are the same, what will hurt you are the NA higher compression pistons.
We have had a few boosted NA long blocks here the they run 375ish WHP on 91 pump gas that are dyno tuned by SZ. The 2" pipe will require more boost to create the same flow as 2.5". Higher boost plus higher compression pistons(10.5:1) make thinks go boom. The meth injection will help, but I do not have any experience with that. I you have the NA block, why not upgrade the pistons before installing; you will need to swap TT heads over too.

Also, are you relying on the OEM oil pressure gauge for the readings? You know that this gauge is not very accurate right? Is the oil pan dented at all, this can cause your oil pressure issues too?

I wish we had a E85 only 50 miles away, my closest is 200 miles away

I am aware of the 10.5:1 compression and thought it would make for a pretty big power setup on race gas even with small turbos. Spooling instantly and all. I am not opposed to putting a different piston in the motor to reduce compression if absolutely necessary. I was planning on dropping my current motors heads off at the machine shop and having a valve job done on them and putting them on the new motor. The reason I would buy the NA motor to replace mine with is because used TT motors are generally about double the price and I don’t need the turbos or anything off of them.

I replaced the stock gauges sender originally but even after that my gauge still stayed at only the first line on the gauge no matter what rpm. I also had a glowshift gauge that was wildly inaccurate and read whatever it wanted to. I have since replaced both gauges senders with an auto meter gauge that is accurate. My oil pan does not have a dent in it. Motor just straight up makes not so great oil pressure.

I am also playing with the idea of just making the drive to the E85 station and filling up many containers with it at once and just storing it. This car does not need to be driven on the street much, I would just like it to be able to enjoy it when I want to on nice days and whatnot.

The weak point of the stock NA bottom end are the NA wrist pins. There are people that have made 600+ on NA blocks on E85 but those did not last long. The VG30D engines are not adapt at running high compression and boost. Generally the best results on these engines have come from stock TT or slightly raised compression (~9.0) and 30+ psi. Seek out BaneZ (Matt Fenton) and also speak to Dane Miller of SZR Pro if you want to know about high hp VG30D engines. If you want instant spool AND big HP on a VG30DETT I'd recommend big turbos and a small shot of nitrous to get you going. If you want an autoX capable quick out of the corner car then antilag and smaller turbos will be your friend. This is after all a 3.0L engine so you can't really have your cake and eat it too.

NolimitZ32 wrote: ↑

Sat Nov 09, 2019 1:15 pm

The weak point of the stock NA bottom end are the NA wrist pins. There are people that have made 600+ on NA blocks on E85 but those did not last long. The VG30D engines are not adapt at running high compression and boost. Generally the best results on these engines have come from stock TT or slightly raised compression (~9.0) and 30+ psi. Seek out BaneZ (Matt Fenton) and also speak to Dane Miller of SZR Pro if you want to know about high hp VG30D engines. If you want instant spool AND big HP on a VG30DETT I'd recommend big turbos and a small shot of nitrous to get you going. If you want an autoX capable quick out of the corner car then antilag and smaller turbos will be your friend. This is after all a 3.0L engine so you can't really have your cake and eat it too.

I see, thank you for the information. I would be using this car for mostly spirited street driving and drag racing at my local track. I get that about the small motor not really making that much torque out of the hole without nitrous. But you don't think that stock turbos with the msp manifolds on 93 octane with meth injection could make around 450 horsepower reliably before going boom? Like I said, on the track it could run C16 and still use the methanol to cool the IATs down, but I would like a somewhat usable street car as well. I know a few other motors have been able to run 10-15 psi with high compression ratios and aluminum heads on pump gas with an intercooler, so why not the VG? I would really like to shoot for at least 12 psi since I know the stock turbo's efficiency range is about 12-16 psi. This is just the motor I would opt to throw in the car and run for a while if my VG30DETT is indeed worn out as I kind of suspect. I would just wanna keep the car on the road and making decent power while I save the money to rebuild the VG30DETT with forged rods and pistons and I would probably shoot for a 9.0:1 CR on that motor. I would also probably wait until I had the money for nice bigger turbos before bothering putting that motor in the car. I just want something fun for a while that doesn't break the bank while I wait for that to come together.

There is a YouTube channel called overboost that has a couple twin turbo Z's they work on and base the channel around, and one of them has a junkyard VG30DE with custom manifolds and larger turbos on it that runs on E85 and has made over 600 rwhp on 23 psi for quite some time (about 2 years or so) before it eventually started bending rods. It was on 36 psi when it bent the rods so who knows what power it was putting out when it gave up. It actually still ran when they bent, was just slightly down on compression on those cylinders. I believe he simply found the torque limit for the stock rods, however one piston did crack a ringland when all that went down. That build was actually what gave me the idea to swap in a VG30DE for a bit while I rebuild the likely worn out VG30DETT.

https://www.nickelperformance.com/300zx ... -your-na-2 - This is the article I referenced in my original post. It claims that the wrist pins are capable of holding the power with proper tuning, although admittedly I do not know entirely how credible it is, but it seems pretty legit. I really don't want to go through all this work to build something that simply blows up after a short while running though, so I am trying to do as much research as I can to see how much power I can safely get away with.

Also, my compression tester arrived yesterday as I was leaving for work. I was not able to perform the compression test this morning before work though due to not so great weather conditions. Hopefully tomorrow before work I will have the opportunity. If not, then I will surely get to it on my weekend (I work Thursday-Monday, Tuesday and Wednesday are my weekend). The suspense is killing me lol. If it has good compression, but the oil pressure I reported in my original post, do you guys think I should just send it and pop my 555cc injectors in with the appropriate chip and turn the boost up to about 15 psi? Or is that oil pressure too low to play around with? At the moment it has 370cc injectors and I keep it around 12-13 psi being conservative with it.

As an update, I was able to perform a compression test on my motor before leaving for work today, although I made the dumb mistake of forgetting to warm the motor up before I started taking it apart. Anyways, I found some not so great results although the it actually runs surprisingly well considering. Doesn’t have a noticeable misfire, every cylinder still makes the car run significantly worse upon unplugging the coil pack.

#1 - 70 psi
#2 - 130 psi
#3 - 150 psi
#4 - 140 psi
#5 - 140 psi
#6 - 140 psi

Granted, these were all on a completely cold engine so they should be a little higher if I actually warmed it up first. I then poured a bottle cap full of oil into #1 to see if the compression jumped, and it only jumped to about 88 psi so this leads me to believe I have a bent valve on #1. What do you guys think? Not sure what the deal with #2 being a little lower is though, but I’m much less concerned about that than #1.

These engines are fully capable of making 450 on 93 octane with stock turbos and all supporting mods. A better choice would be some updated turbos like the 530/550bbs which are larger and have better spool characteristics than the factory journal bearing units. If 450chp is your goal than there are plenty of t22/t25 housing options. 450whp you may have to step up tot he larger t25 based units. I''m running GT28RSs, I haven't dynoed my car but it will break some 265s loose at highway speed, the torque comes on quick. As you quoted, can big numbers be pulled out of a stock NA block on boost and juice? YES absolutely. It all depends on what you are building the car for, when i built mine I went with a build that should theoretically handle 700+ at the crank while only planning to get no more than 600 so I could have a healthy safety factor built in. My car is a weekend fun car, I won't even take it to the track, its more for smiles and putting the occasional dbag in his/her place with a little 3rd gear pull on the freeway.

NolimitZ32 wrote: ↑

Mon Nov 11, 2019 7:15 am

These engines are fully capable of making 450 on 93 octane with stock turbos and all supporting mods. A better choice would be some updated turbos like the 530/550bbs which are larger and have better spool characteristics than the factory journal bearing units. If 450chp is your goal than there are plenty of t22/t25 housing options. 450whp you may have to step up tot he larger t25 based units. I''m running GT28RSs, I haven't dynoed my car but it will break some 265s loose at highway speed, the torque comes on quick. As you quoted, can big numbers be pulled out of a stock NA block on boost and juice? YES absolutely. It all depends on what you are building the car for, when i built mine I went with a build that should theoretically handle 700+ at the crank while only planning to get no more than 600 so I could have a healthy safety factor built in. My car is a weekend fun car, I won't even take it to the track, its more for smiles and putting the occasional dbag in his/her place with a little 3rd gear pull on the freeway.

Awesome, thank you for the information. So far I think that my current VG30DETT is actually healthy except for having a damaged valve on cylinder 1. I won’t know the extent of things until I have the opportunity to pull the head of course sadly. I do believe I’m probably gonna be spending at least $2k having the heads rebuilt, getting new head gaskets and bolts, and the timing kit which is at a minimum what I’ll need to do. But I figure this beats spending $3k on a used JDM motor that could potentially be even worse. I imagine that on a warm comp test my numbers would all be 150-160 except for my hurt cylinder. As long as that piston isn’t all beat up from hitting that valve then I think my shortblock is worth building. I honestly don’t even know if it bent during my ownership of the car since it’s always ran pretty good and still does in the almost 3 years I’ve owned it, but I never compression tested it before so who knows when it happened. Either way, pouring oil in the cylinder only caused a slight jump in compression, still nowhere near the others so this leads me to believe I have a valve issue. I just hope that the piston is okay or else this may be snowballing into a full on engine rebuild.

I had hoped that the NA block with the higher comp would be capable of making 450 on the stock turbos haha, thanks for confirming that it cannot. I know the TT motors can generally make between 380-410 with stock turbos once you have bigger injectors, downpipes, exhaust, intake, etc. Honestly I think even with the low compression in cylinder 1 my car is still making around 320 horsepower on 12 psi. Now that I know the compression is low though I’m definitely turning it down to wastegate pressure until I can check it out. Gotta pick up a daily again since I had been using just the Z for the last year or so.

Also, it sounds like you’ve got quite a well built Z and more than accomplished your goal with the car. Pretty awesome

I think you misunderstood me, the NA block is capable of making 450 on stock turbos, so is the TT (we're talking CHP here). It the longevity of the stock NA block that will be in question. As a rule of thumb the VG30DETT bottom end is good for 500 chp in stock form (I've never heard of an upper limit for the heads). Not much data on the NA version so a "rule of thumb" doesn't really exist especially when boost is brought into the equation.

NolimitZ32 wrote: ↑

Mon Nov 11, 2019 9:01 am

I think you misunderstood me, the NA block is capable of making 450 on stock turbos, so is the TT (we're talking CHP here). It the longevity of the stock NA block that will be in question. As a rule of thumb the VG30DETT bottom end is good for 500 chp in stock form (I've never heard of an upper limit for the heads). Not much data on the NA version so a "rule of thumb" doesn't really exist especially when boost is brought into the equation.

Oh no, I’m sorry, I did understand you. I meant rwhp, I realize now that I did not include that in my response to you. But yeah, I realize that the growing availability of better fuel today can make a lot more power safely on the NA blocks than had been realized in the past so there is not much fresh data on our 30 year old motors.

Honestly it seems that my current thread topic is no longer useful to me as I do not believe I will be attempting to use the VG30DE shortblock as I was planning on doing if my motor had low compression across the board. I was actually quite shocked at how high the healthy cylinders read for the motor being cold as this was a JDM replacement motor with unknown miles on it that was put in the car before I bought it. Did have a fresh timing belt service too. But that was almost 3 years ago now, however I’ve only driven the car 13k miles in the time I’ve owned it.

Once I get the heads off this motor and can inspect the piston top to cylinder 1, I will decide what to do from there. I imagine that if the piston was bad then the car would probably smoke, no? But time will tell I suppose. Also cylinder 3’s plug was wet with oil, which may be why it’s compression read 10 psi higher than the others. At the moment I think the best idea for my car would be to pull the heads and see if I can get this motor back up to healthy compression levels without a full rebuild. If the piston is bad, then I will probably be swapping in an NA block while I fund a proper rebuild of this motor with forged pistons and rods, block decked for MLS head gaskets, etc. For now I’m just in a “prepare for the worst but hope for the best” kind of mindset. Hopefully it’s just a valve that isn’t sealing correctly, be it slightly bent/burnt/whatever. The motor isn’t noisy so I don’t think it is continuing to make piston-valve contact. I think it probably floated the exhaust valve at some point and got smacked a little bit.