Hello everyone. As a lot of you already know from my posts of old I want to SuperCharge my NA motor. Since almost every other part number other than the pistons is the same for the VG motors and other than a few other minor differences I will mention in a moment any VG motor should be able to be boosted if done correctly and cheaper than the popular TT conversion methods mentioned here so far. After seeing a fair number of people boost other NA cars, either by turbo or supercharger, and keep their reliability in most cases im almost convinced this can be done easily and moderately cheaply if done correctly. To do it correctly one needs to understand the maths involved. After reading up a bit I found this to be some common numbers NA standard head gasket thickness: 1.0mm TT standard head gasket thickness 1.2mm Here are my questions. Is the pin set at the same height for NA and TT pistons? (When held together are the piston pins at the same height on the piston?) TT pistons are slightly concave and the head gasket is slightly thicker making the decompression for the motor? If this answer is yes, what is the depth of the concave on the TT piston so I can calculate a swept volume? Has anyone used NA pistons on a boosted motor before and if so how much boost did they take before BOOOOM? Assuming some of these questions come out the right way then the following can ensue . . . Using swept volume calculations one would be able to have a copper head gasket set made for a specific thickness to allow for some decompression on an NA motor. This itself can present some problems. The best example being the valley cover (in our case, the lower plenum) The maths are, assuming that a 45 degree angle is being used, everything that goes up 1mm will go out 1mm. Calculations can be changed depending on the actual degree that the heads sit at. Using this calculation one can also get lower plenum gaskets made slightly thicker (to whatever calculation you came up with) thus having everything still match. (remember we are only talking POINTS of millimeters here so nothing else should really be an issue). I could SC one of these motors and have it run GREAT for a year then end up with an expensive paperweight with no modifications. However if I can do it correctly I can boost the motor and have it run great indefinitely assuming that I keep up maintenance on it. I dont want to run ridiculous boost through it, like strapping a centrifugal vortech to it and run 20psi. I just want to try and calculate how much boost I would need to have it achieve 100% volumetric efficiency or close to it. A simple supercharger running at about 7 to 10 psi should do this and even that boost estimation is probably high. I know I could just strap one on and run it at lower boosts like 2 or 3 psi and be fine for a while until the motor starts to bleed from here and there . . . but thats not what I want to accomplish. If done right even a TT conversion should be cheaper and easier than the popular and expensive methods explained here. Thanks . .
Rightyo... You have some facts wrong here... What I reckon is in red below. Use a TT bottom end and save yourself the dramas. There is just no point in going this way. You priced up custom gaskets yet? You will probably find that you have to buy 10 sets.
It cant "just have" a lower compression ratio. There has to be something that creates it. I know it does not depend on the shape of the piston. However since the blocks are essentially the same (as I understand it, I could be wrong here) then the concave piston plus the 1.2mm gasket would make a different swept volume in total. I know that they are both 3.0ltr motors and they take that from the cylinder volume but swept volume includes the added volume of everything else also (clearance, gasket thickness etc). The VG30DE motor makes higher compression because it has flat top pistons and a thinner head gasket. All other relevant part numbers are the same for both motors. So, rather than getting into a debate about stuff as I know you are quite knowledgeable in these areas and have beaten me in debates before I will make the question different instead. If I were to supercharge an NA motor by slightly decompressing with a copper gasket set (I know someone in US that will make them for me) Can I boost it via supercharger safely and by how much PSI? Also, the other boosted NA's that you have seen, are they just strait NA thats been boosted or did they swap the bottom end? Thanks
I can't say 100% but I think you'll find that the NA piston crown will have more meat in it and possibly a lower pin location, I'm sure Erik will chime in and say one way of the other. I've never looked at an NA VG30 motor, but that's how I'd do it if I was reusing the same block between NA and TT variants. BUT really, for what you want to do, you don't want to drop the static compression ratio at all. 10.5:1 is good. What you want to do is research ways to effect your dynamic compression ratio's through the use of cams and valve overlap. That way you harness the potential power of longer duration cams and increased overlap without compromising the compression of the cylinders. Static compression ratio's are for brochure's.
Sorry, didn't elaborate enough As I said somewhere above, the compression ratio is the swept volume divided by the volume of the combustion chamber. I'm including any concave section of the piston, volume of the head and clearance volume in the total combustion chamber volume. Both the head gasket thickness and the shape of the crown of the piston have a effect on the CR. What do you mean by shape? Yes, blocks are practically the same. Swept volume discussed below. Swept volume is only the cross sectional area of the cylinder (the bore size) and the stroke. It is the amount of air that is displaced when the bore is 'swept' by the piston. This is the same as displacement. The shape on the end of the piston doesn't effect the swept volume as it is the same at the start of the stroke and the end of the stroke. Here is the Wiki link, it's quite good if you haven't seen it already. Clicky Bang on the money Yes, you can boost a standard NA VG with a thicker headgasket (or without, stock ones are very good). How much boost? I don't know, I can't give you a 'safe' number. You would have to run it up on the dyno and see how it runs. If the charge air gets hot (which will be the major issue) then that will restrict the amount of boost, water/meth injection will help a lot to keep the temps down at a safe level. If you are supercharging then I would start with 5-6psi and go up from there. It's a bit of a PITA with a Supercharger though, you have to change pulleys to increase boost level The NA's I have seen boosted have been standard NA's with standard pistons, they had just had turbo's banged on the side. I've seen it done with Zeds, Skylines, Honda's MX5's and Corolla's. Varying degree's of success. Most that fail seem to have detonation problems. I haven't seen a NA+TT Z go bang, but there hasn't been a lot of them. Edit Listen to Andy
Compression is calculated like this, Swept volume + clearance volume divided by clearance volume. Changing the piston height will not alter compression, you need to change the clearance volume. Reducing the piston height without a rod length increase will reduce the squish area and cause a very cold flame front resulting in low power output. Running thicker head gaskets will need to be compensated with the use of adjustable cam gears, and increase in plenum height will change the cam timing between the 2 banks and also between the 2 banks and the crankshaft. This also reduces squish. The Na heads have a smaller combustion chamber and a slightly less dish the crown. The problem boosting an NA is high dynamic compression, this needs to be offset with less timing advance, less advance will increase exhaust temps, higher exhaust temps will make the turbo spool earlier, more airflow into the engine means taking more advance out. Eventually you have taken so much advance out, you no longer have enough time to burn the fuel you need to make the hp. An Na also has thinner gudgeon pins, thinner piston crowns and different conrods. The safe limit on a boosted Na bottom end is 14psi, this will give around 400hp at the flywheel, or around 330hp at the wheels. But the torque characteristics of TT'd na will be much greater than a similarly boosted TT. Unless you have all the parts to TT an NA, it isn't worth it. It certainly isn't worth supercharging the NA only to achieve the same results as a very mild TT. Time permitting, our NA will be getting TT'd this week, 10psi max boost, TT injectors and water/meth with no intercoolers. I am only doing this because it will cost me almost nothing as I have all the parts and ability to do everything myself.
I've done testing on both NA and TT heads...all volumes on ports and chambers are the same between like variants of the heads. Meaning 90-93 cathedral and 94-96 Boxed heads are the same within each family of design. There are no differences.
Both the port and chamber volumes are different between series 1 TT and NA heads. I have also CC'd both. Have not measured series 2 TT heads. Also the bare casting numbers are different, which is good indication the heads are different.
Got any values Eric? Maybe there is a difference between US and Jap zeds? And are these 'boxed' heads any good? Any real benefit or drawback of them?
Numbers are at work, somewhere around 20cc in the exhaust ports and 5cc in the chambers, both lesser ammounts are NA. Boxed are the later heads, probalby a improvement to overcome the loss of VTC.
Loss of VTC wasn't until ~'96 and was only the US market IIRC. You still got my heads out of my slicktop? The ones with the mashed valves? Might be worth a look. They had S2 cams and gears, but S1 injectors. Might be S2 heads.
So basically everyone is saying that if I had the bits on hand I am better off using the 1.2mm comtec (whatever the name is) gasket and TT it and keeping it under 14psi? 1 question: Is this still keeping the 10.5/1 ratio (obviously the .2mm difference will drop it VERY slightly but not much) ? I wanted to supercharge one just because it would be a unique thing. A lot of people have an NA EVERYONE and their dog has a TT, would be nice to have the only supercharged 300zx in the club. LOL. This was my only reason for wanting to supercharge. I am not after huge power, I dont want the best Zed on the road, I dont want to outrun every possible porsche I see on the highway. I just wanted something unique. Being a slicktop makes it a "little" unique already though there are quite a few here in geelong now . . . . so I have to do something . . lol On another note, thx for the wiki link Crispy. thx
Perhaps off topic but by the sounds of it the information would be handy for samurai as well Can someone please give me a basic description of how water/methanol injection works and whats involved in setting it up? Cheers,
How can lowering the height of the piston not change CR? Swept volume remains the same, head volume is the same, but clearance would now be larger correct?
I got identical numbers for both. I measured the Cathedral 90-93 heads. The heads you checked were they pulled off a stock engine with no machining done to them? I checked free drop on the valves, chamber volume and port volume. I even went as far as checking valve angle and they were both the same. My only guess as to why Nissan made two different heads was that they used the same engine in countless other vehicles while that engine was in production (much like they do with any manufacture).
The boxed intake flange on the 94-96 heads have a better approach at fuel distribution. It allows boost to give a better mixture motion through the port allowing for a better burn in the chamber. The volume of the 94-96 heads is less than the 90-93 and I favor the 94-96 (10Y/48P) heads over the 90-93 (30P/40P) heads.
you sure those are the correct numbers? I get 55cc on the combustion chambers and 150+ on the intake port volume. I'll have to reference my notes when I get home as I'm at work right now.
Thats part of what I dont understand too. Anything that changes the distance between anything else in the chamber HAS to affect the CR. On another note . . . . If I could get stockies and the rest of the bits rather cheaply is it advisable to just TT it and run 10psi or so? Intercooled or WM injection? both? Peace
