OK, I want to be able to increase the compression in my engine with forged pistons and at the same time improve/upgrade all the appropriate support systems. Extra heat is created when the compression is increased.

Question 1:
What support systems should be upgraded? radiator? oil cooler? oil pump? oil pan?

And im in Australia so 98oct pump gas is easily available here, so the amount of compression I can run should be a bit higher than is possible in the US.

Question 2:
Does anybody know what would be a safe level of compression to run with 98oct fuel?

Any info on this is appreciated.
Thanks
Murray

 

As for the cooling system upgrades, I would upgrade the thermostat and the radiator. I replaced the radiator, hoses, and thermostat on my ITR when I bumped the compression. I'm not really sure about the oil system upgrades.

As for the second question, I was running just south of 12.0:1 compression in my ITR (stock is 10.5), however it was stolen before I could get any real feel for how it was running or how it would hold up. That compression is probably too high for the street gas here (94 octane), but you could safely run the 11.5:1 pistons for the VQ. Spoon Sports also made a metal head gasket for the ITR that raised the compression ever so slightly. Maybe there is a similar set of head gaskets for the Z.

Good luck.

Dan

 

Bump your compression up, that's fine. It's another mod that is not worth doing just to do. Unless you are doing forged rods, pistons, etc. then there is no point in going into the bottom end of the motor for 15 HP compared to the several thousand it is going to cost you unless you plan to use that for FI later, in which case higher compression would be a bad idea.

You need to know what the ECU is tuned for as far as octane. If it is already optimized for 98 down there then increasing compression will be the same for you as it is for us. You will need to reprogram the ECU to bump timing down to counteract the compression bump. If the ECU is tuned for 93 then you can probably safely bump the compression and run 98 and leave the timing alone.

A compression bump by itself really doesn't warrant any major cooling upgrades. Maybe it would be nice to run the cooler thermostat and reprogram the fans to come on sooner. The motor is already aluminum and does a good job at heat dissipation already.

A much better way to increase power is in the top end on the motor. The new NISMO heads that are out will also bump up compression but also provide a much better platform for power building. You can port them (probably don't need to), run bigger cams, turn higher RPMs, etc. You will make much more power for much less money (or much more depending on your wallet) up in the heads.

 

In theory, if all the cars weren't tuned for 91 or 93 octane or whatever, wouldn't Aussie Spec Z's be putting down more power due to the fact that you can run a more aggressive map with a higher octane?

 

I dont know how close they are in standard form but I dont want to increase the valve to piston clearance unless the pistons are far enough away or or designed with the eyebrows.

I think stock compression is 10.3

Thanks for that other info.

Murray

 

Not necessarily, they have different specs for the intake and exhaust requirements from their govts. They have to be quiter. They do pick up more HP than us from those types of mods. I remember a pic of their stock Z intake and it looked similar to our G35 intake. Little stuff like that. On a NA car I don't think there is very much HP to be gained in 4 or 5 octane points. In fact, their cars may just not run so close to the detonation level of ours since it seems like ours are always retarding knock and running close to the edge in that respect. My point is, I have no idea what their computer tune is, but I wouldn't rule it out.

 

Well, there are cams available that increase lift to 10.9 mm. I don't know if that is the maximum available but it is a lot more than stock. You could use a shorter lift and get compression from the gaskets or new heads (or shaved heads) but it would probably not result in much if any of a power gain. That is why I would go with modding the top end. Airflow is more important than compression when our compression is already as high as it is.

 

I would be doing the rods as well, im not going into FI, BUT I might want to get every possible HP out of the car, so this avenue would need to be investigated. This mod would give a good across the range increase, and give a percentage increase of whatever you had before, so that 15hp could be more plus the better fuel here that number could be 20hp??.

Its tuned for 98, on a 10.3 compression ratio do a google search to comfirm the compression.
example
http://350zmotoring.com/2003_nissan_...fications.html

So an ECU change is necessary.

I shall look into this head as well.

Thanks
Murray

 

Your right, we do have a diffferent output to you guys, but its LESS than yours. your have 214kw Standard and ours has 206kw.

Our exhaust is more restrictive, here if I upgrade the exhaust i get a 22KW increase or 30hp! Where you guys only get a little increase.

Murray

 

If you are not going FI then save your money from the bottom end and put it into the heads and intake and exhaust. You will never make enough power NA to warrant a fully forged bottom end. If you have the money to blow for a compression bump because you want the last 15 HP out of the motor then go for it. But you can save your 1K on the rods. You def. won't need any NA. I would save the other 1K on pistons. Then the 2K on labor you can save. Put that 4K into the other aspects and you will have a badass NA motor.

 

Yeah that's exactly what I was trying to say.

 

Yeah i know, thats why I said your right?
Or did I miss something... oh you were saying its lower as well, ok its all good.

Murray

 

I don't know. Maybe I read into your emphasis on LESS like I meant MORE. Either way, we're on the same page.

 

I will be doing the full exhaust, air, cams, ecu, and the compression increase, but I need to gather info on the compression. I've got everything else down.

Murray

 

Is the USDM compression lower? or do we have 10.3 as well? I could have sworn ours was 10.0.

The thinner head gasket is only going to net you 0.2 compression points at the most, if they even make one. N/A tuning is so damn frustrating. Sometimes I'm glad my integra got stolen. 9k rpm sounds sweet, but 5k rpm cruising on the highway doesn't.

If you have a big wallet, don't discount FI. You can do it safely, especially since you have excellent gas down there.

 

we have 10.3

 

I dont have a big wallet, but I am committed to my car, the thing with FI is you can't do it piece by piece!, this is the big difference for me + you cant keep your warranty.

I dont have the money upfront to blow on FI, and void my warranty. Not the logical step for me. NA is.

I can go pay cheque to pay cheque doing mods.

Murray

 

Tearing the engine apart and raising the compression will void your warranty as well. FI is a big initial expense, but N/A can go on forever and ever like a damn money pit, and before you know it, you paid through your nose for maybe 50 whp.

I'm biased though. I'm very bitter when it comes to N/A tuning.

 

NA is like that chasing every HP, but we bought a NA cars so this whole scenario was already forseen. At least we can get good gains from the NA mods, unlike little NA 4's etc. Im greatful for that! Im biased to NA because I paid X amount for a NA car.

I mean how much power do we need though, im sure I can be happy with 300hp at the wheels

Murray

 

I am not sure why someone would go through the hassle of tearing down the engine and building this N/A engine for 20-30SHP? When for $6k you can get a s/c and put down 100 extra at the wheels? Not to mention many of the FI companies warranty their products and your engine.