Hmmm, I really don't think you "have" to go with lower compression pistons. It will lower your effective compression, and make you more dependent on boost for your power. If tuned right, and with the right amount of boost, stock compression should be OK. But it is safer to run those pistons, and that might be what you are looking at right now.

 

Thats true to, but you want to do it to safley run the boost. If you can get someone to tune the car, which I think is next to impossible unless they make an LS1 edit type software for the 350Z, your asking for future problems.

The best thing to do if you are running high compression is run low boost to help slow the process of negative effects. And try to run higher octane fuel like 104, or race gas. If you can find higher octane fuel then it is a little safer to run more boost.

 

I'm pretty sure SGP told me the rods are good for like over 1000 hp. I can't wait too long, need this stuff asap so my order goes in on Monday for rods, pistons and cams. I'm going to also look at the J&S safeguard, I've heard really good things about that unit.

I'm going to run 8.5:1, no doubt about it. I just think it would be my safest option, especially because I'm going to run higher boost one day, that is if my engine doesn't go again, plus my engine will be pulled out of the car anyway. Does anyone else on this site or anywhere else with a Z run 8.5:1?

 

The choice of using 8.5:1 is a good one, with quality parts behind it. You will gain power potential by using these pistons as well. You are opening up the volume of space which can be packed with more fuel and air at your specified boost pressure. More fuel and air equal more power potential. But, you will also need to make sure that the ignition system will be able to fire off the added volume of air and fuel completely and in a timely fashion. You will probably want to be able to control your timing with an aftermarket product.

You may also need to use a 9 lb. pulley to get your 7 lbs. of boost, though I have done no math to figure that out. Remember that the pulley only decides what volume of air can be moved through the supercharger at a specific rpm over a certain amount of time. The cars that are not reaching full boost with the 7 lb pulley normally have mods which have been effective at increasing the flow potential through the engine, and the pulley can't make enough air volume pass through it to get the boost pressure back up. Well, you will experience a certain amount of this by simply having a larger void to fill in each cylinder with the use of a lower compression ratio piston.

The downside to all of this is that to get the boost level back up will mean spinning the supercharger to higher speeds, which may be a problem for reasons of longevity of the unit (still a bit suspect, as we look at Dr. Bonz situation), as well as the creation of additional heat from doing so. Just like a turbocharger, you really need to know the efficiency range of the C2 unit, to see if it will be making more heat than power at these elevated compressor wheel speeds. Hotter air is less dense, and you reach a point where the trade off is inefficient enough not to warrant the additional boost.

Because our project car sees so much track time, I am going to investigate the use of a 5 lb pulley for it (waiting for our ProCharger to arrive so we can evaluate it first hand to consider the possibility of selling them) so that we might get more life out of it. Of course we want more power for the road courses we visit, but we need it to be reliable over a long period of time, and you can attack speed from angles other than peak HP on a road course, like suspension tuning. Five intercooled pounds would probably still provide a nice power increase for us. Time will tell if we do this, and what the results will be.

So, you have a lot of things to consider with your choices, and if you do your homework correctly, you may find a nice level of power increase is buried somewhere in there. Good luck with this.

 

I am wondering if you would have been better off going with a twin torbo set up now that you are going with a lower compression? I know you are doing this because of what happened to your motor but one limitation of a SC to me seems to be it is not able to vary boost as easily as a TT. This will be intersting to see what happens. You are going somewhere I think most of us were not expecting to go with a SC set up.

 

All I know is right now, my head hurts alot. I've had alot of time to think about this whole situation this weekend, I don't know what to do. I'm just praying and hoping that this extra $3300.00 I'm spending on rods, pistons and cams, I hope it's really worth it and I don't run into this mess again. I think after I get this all completed, and my installer tunes it once again, I'm going to take it to one other place locally and let them have a look just for a second opinion. Last thing I want is for this to happen again, I'm just really nervous, and I'm sure that everyone here understands and agrees.

Bill

 

I'd call every tuner in town and ask them if they've had experience with Aeromotive programmable FMU's for returnless fuel systems. If they say they have start asking them questions about the scale and slider settings ie what exactly do they do. If they sound like they don't know what your talking about or try to bullsh!t you, take them off the list. Believe it or not there are many tuners out there that will flat out lie to you about their tuning experiences to get your money. I had a couple tell me they've tuned an Aeromotive setup to cars that have fuel systems that aren't even compatible with our FMU.

Also, when you get it tuned insist that he tunes it to a fat AFR.

What's the duration and overlap of those cams? Higher performance cams designed for NA cars are generally not as good for FI as the stock cam believe it or not.

 

A lot of excellent post here, one thing you do have to remember is when you lower your compression the N/A part which is when your off boost will feal like ****. I personally would not lower your compression 8.5:1. its way to low. Unless you plan to boost 25psi which your supercharger wont do...

"little_rod "

Is correct, if tuned correctly you can have a very safe and reliable car even at high compression. One thing you have to remember when you lower compression is that you will also loose that much more power and you need to increase boost to compensate for the "dish" style piston. For example..

If you have 10.1 pistons and boost 7PSI and make 350whp tuned perfect. And than you change your pistons to 8.5:1. and boost 7PSI you will not make 350whp. You will probably be making 300whp. You would have to boost about 10-12 PSI to get 350whp. The only advantages a lower compression piston really has is it has more room for "screw ups" when tunning. But like "little rod" said a perfect tune 10.1 compression car running 7PSI is equivelant to a perfect tune car 8.5:1. running 12PSI. Because the metal you are extracting from the piston to lower the compression has to compensate with air... I think you should go more in the line of 9.5:1 excellent piston not to low yet not to high... Just my opinion from racing and building engines.

 

Ok, I am a novice but it seems to me that you have to keep in focus you purchased an ATI SC thus at this point, the SC is designed to boost at 7psi with the possibility of going 9psi later with a different pully. If you go with different pistons, you might give a greater window of error for motor but now you have to reconsider how much stress SC can handle and if it can even boost enough to get the result you want.

To me, if you want to go 8:1 compression, you should be thinking TT that gives you more range of boost control. It seems to me, the ATI set up is designed for stock internals but Greddy and other TT are going for low hp bolt on set up and to pass smog & then allowing for upgrade if internals are switched.

Do others agree or think I am off on this?

 

Yeah, zland and wicked, I agree with you. But we also have to see that he has a lot of money on the line here, and doesn't want to be hurt again. That is why I left my post at, he would be safer, which is true.

Now powerwise, yes, the lower compression pistons will cost you ravaz. Wicked mentioned some 9:5:1 pistons, but I am not aware of any manufactors making that compression for our engine yet. I don't think you would want different cams, that could cause more trouble for you.

Really, you are looking to answer your problem at a time when there are not many products out there for our engine yet. You do have some options though, and guys add some if you see anymore:

1. Go with the lower compression pistons (SGP), and try to run more boost. You may run into problems with trying to get the power that you want out of this setup, cause you might exceed the ability of the SC. You could still add headers and such to get more power out of this setup.

2. Go with stock pistons, and try to get it tuned better. This is the try it again approach. Now this would be hard to do, especially with the same installer. But this is really the way anyone else will go with a new SC, cause really, it only runs max boost at the redline, so you are seeing nowhere near 7 psi during regular driving.

3. Go with the higher compression pistons (SGP), and run with your same boost. Now this is far more daring and would take a lot of *****. But the new pistons should be able to hold up to more power than the stock pistons. Your effective compression wouldn't increase by much when going from 10:3:1 to 11:5:1, but the aftermarket pistons would be a lot stronger and could take the 7 lbs of boost. Of course, you would and should do a whole lot of research before even thinking about this.

Now with those 3, you could add retainers, rods, and whatever else makes you happy. But above all, do what makes you sleep at night. If that is going conservative, then do that.

 

jesse:

The cams have a duration of 264.

Wicked:

The C-2 can run up to 30psi. Will I ever run that? No way, but I know 100% I wouldn't stay
with just 7 pounds. I guess it's all up to ATI on what they will produce for us.

I do agree with everyone that 8.5:1 will hurt me down low with no boost, but like I said, if I do take
these steps, no way am I going to stay with only 7 pounds. 9.5:1 sounds good also, but they aren't
made for our cars yet, and I'd have to get up with Je, and send them a piston and wait 8+ weeks to
get the new ones, plus who knows what the cost would be. I'm going to talk to my installer today
and see what they think the best solution is, and cheapest, being that I'm looking at getting parts
at cost, but again if I go with them, alot will have to be custom made and I'll have to wait and wait,
while SGP might cost me a little more, everything is in stock except the cams (3-4 weeks or sooner). The problem with my installer
is that out engine is still new to them and they are learning as well. I'm still thinking, but am ready
to purchase the new parts today if that's what has to happen. I'm in it this deep already with my
car, what's another $5,000

I'd love to get a turbo setup, but now we are talking about more money that I will be losing out of my pocket.
I'd lose money selling the procharger, then I'd have to install and tune the turbo. I might as well work with
what I have now, I've always liked superchargers, and yeah I don't see full boost every time I drive, but that's OK too.

We'll see what happens today. I've been very good about this, and been patient with my installer, so today is the last day
for that. Let's see what they say today. The truth is, I spent all this money with them already, for what, 300 miles and
a day and a half with it working on my car? I better be getting hooked up.

 

Is that intake or exhaust or both? What is the overlap, that's the most important thing.

Overlap is when both int and exh ports are open at the same time. Too much overlap and your FI engine will blow the intake charge right out the exhaust port, making your engine very inefficient. Although it does help with cooling the combustion chamber, it's not the way to go with an FI engine.

 

Here is all that I know on them.

http://store.yahoo.com/sgpracing-sto...64x10case.html

I'd have to call for more specs and info.

 

I'd call Tomei and ask them, but just from the description of lopey idle, I'd say it has a large overlap. Just want to warn you that it's going to be very inefficient. Although it will still work, it's going to be less of a daily driver IMHO.

 

It's not really my daily driver, more of my after work stress relief and weekend play car/track car. How do you mean it will be very inefficient?

 

Lots of air and fuel will be blowing out of your exhaust. In a normally aspirated car, it is good to have overlap because it allows more time for spent exhaust gasses to exit the combustion chamber and more time for an intake charge to be sucked in. With an FI car the intake is pressurized so with both valves open simultaneously you will get some of your boost and fuel blowing right into the intake port and then right back out your exhaust port resulting in wasted fuel and boost. Plus I hope you don't have to pass emmissions because you probably won't.

 

Last thing I'm worried about is emmissions. I can pass without a problem. I will speak with SGP today and see what they say about this. I told them keep in mind I do take my car sometimes daily to work, when it's nice out. I'll let you know.

 

This is not true. Did you read my post above? The supercharger will have to work harder, ie. different pulley, to make 7 pounds of boost, but that seven pounds will be a larger volume than with the 10.3:1 C/R, and power will be very good (read, comparable to the 10.3:1) and it will be more reliable. Low end off boost will be worse, for sure, however. But, the lower C/R is going to allow for higher boost levels more safely as well. I would run about 9 pounds with a C/R of 8.5:1, and have a ball...

 

Ravas: Sounds like you are well on your way to a wicked little ride. Could be on the running for one of the Highest HP Z's out there. Hmmm lets see. Low comp+Big boost=
ATI 7psi kit 56,000 blower RPM.
Blower Redline 80,000rpm

Looks to me you have LOTS of Room to grow.

Forget the 12's ravas, your going for 11's

EA

 

Oh, IM sure the blower is capable of doing 30PSI but I don't see ATI manufacturing a pulley or so to get to that level. Maybe custom? Anyhow, I know of a company and I can get you these pistons Weisco with 9.5:1 compression. But might take about 1 month So it all depends what you want to do. I still think 8.5:1 is way to low and if you ever decide to sell your car (you never know) these pistons on N/A form will make your Z feal like a dog which im sure will probably make 200rwhp if dyno "stock" I will investigate more on these pistons as I know the owner and he kept telling me the other day that they make pistons for any type of compression you wish...