?

 

YES IT IS

 

Can someone explain what a high compression motor means?

Thanks,

MoZi

 

Then why is everyone putting FI on their 350Z's? It was always my understanding that adding FI to a high compression engine is a NO NO. That it kills engine life dramatically.

 

The volume of the cylinder before divided by the volume at the time the fuel explodes is called the compression ratio

 

Because it makes our cars fast

If the engine has the proper A/F ratio and timing is pulled to account for the even higher C/R of FI. Then it shouldn't be putting any more wear on our engine than FI would on a low compression motor.

 

You still will make more total power with a low compression, high boost engine than you will with a high compression, low boost engine. Plus it's safer.

 

What's your point? It's not like I could choose between a low or high compression motor when I bought the car. It's really about how the engine is built.

Explain how it's safer? With a improperly tuned low compression motor, it will blow just as fast as a high compression one. Maybe you don't have to worry about timing as much, but that's why I've taken care of that as part of my tuning. Like I said, as long as you take it into account it's not a problem.

 

Compared to other V6s yes its pretty high compression. GM 3.8L is like 8.5:1 I think? Lol

 

the supercharged 3.8 is 8.5:1 and the NA version is 9.6:1. Interesting that people think the Z is ok with FI and 10.3:1. This is one reason I am not going FI until my warranty is expired on the powertrain. I am not bulletproofing a motor that will be fixed for free right now if something happens. I won't run FI on a motor with this high of compression as it isn't safe. Pulling timing is a band aid and not a real solution. There have been a ton of blown motors with FI already. Not so many anymore as everyone is pulling timing. You will realize a very limited power potential with high compression and boost at a dangerous level of reliability.

 

fly by z, is there anyone who has purchased new pistons to lower compression on this board?

 

there are at least a few who have. probably more that don't post much. the only name I can remember at the present moment is something like abogado...something. you may need to click the members link up top to search for the exact name and you can PM her. she is from FL. she also has posts in the FI forum. i know there are others but some screen names run together and i can't remember the difference until they post. sorry. i think that even though she has a motor built to take big boost, the problem now is finding an adequate ECU solution to control everything.

 

Exactly

 

At this juncture in the vq35 aftermarket, low compression or high compression is in some ways a moot point.

People still seem to have problems with 8.5+ psi of boost (about 450 RWHP) due to ECU issues. The engine seems to be running fine up to those boost and HP levels, so until that issue is resolved there isn't much of a point in trying to boost even higher.

Also, keep in mind that with a high compression ratio you will have more power @ an equivalent boost level than with a lower compression ratio. Keep in mind that you will also have better performance when you are off boost.

So, even though you may be able to make more overall power with a high boost/low compression setup, it may not be necessary for most Z owners. In other words, if you are not looking for more than 450 RWHP anyway, then there may not be much of a point in chaging the engine internals to try and get higher boost.

People say "It's safer" to have higher boost and lower compression. What does that mean? You still will blow a poorly tuned motor. It's no safer than a high compression motor in that respect. I'd say that the main difference is that it gives you more margin for error when tuning, but if you run a high boost/low comp motor near the edge in terms of performance, you will still be using up most of your margin to extract that extra performance. On the other hand, if you tune a low boost/high comp motor conservatively, it can still be very safe.

Plus, there are tons of Turbo Diesels out there, and they have compression ratios of 20:1 or more. The point is that compression ratio is not all that matters. The entire system is what counts.

So, in the end, the obvious reason people run F/I on the Z is because they can do it reliably and still make as much power as they require. Once people start really delving into high HP/high cost systems, you will probably see more people look into the low compression internals, but whether it is necessary is really up to what you want to do with the motor.

-D'oh!

 

Thanks Very nice post

 

the question posted by the thread starter was obviously loaded but i'm still trying to figure out why.... how else can you explain first asking if the vq is considered a high compression engine, then a few posts later explaining to someone how to calculate compression ratios...

 

I don't think there is line of demarcation for "high compression motors". I'd think that anything about 10:1 is higher compression. The VQ motor is not High Compression when compared to many hondas and Porsche's, which have 11:1 and higher ratios.

 

Not really, only some rarley go above 10:, nsx only 10:, type r only has 10: the RSX-S has 11, only the Ferrari 355 F1 has 11, rest are 10 and lil above like 10.8. So yes the VQDE 10.3 is considered high comp. And its a pretty large displacement so its harder.