You must have missed half of the nissan members arguing with me the exact opposite.

 

Ask those idiots why bmw's 335i has a c/r of 10.2:1 WITH direct port fuel injection, yet people cant get more than 400whp out of the 3L because the pistons are uniquely shaped for the direct port fuel injection, and afaik, no aftermarket company makes aftermarket pistons for that car yet. Vishnu's world fastest 335i runs 12's Martin is an idiot. When it boils down to it, he doesnt know very much about engine dynamics. He buys expensive shit, throws it on, makes good power, and expects people to respect him. I can dig up some of our old posts if you want a good laugh

It boils down to this. Run the highest compression ratio you can for the amount of power you want to make with the octane you are running. If you want to make the most power on pump gas, you will be running a very low c/r. End of discussion.


cliff notes: Martin isnt very bright.

 

Finally someone with some damn brains. That's exactly what I was saying in the last thread. You can run higher compression on 93, but you're not going to be running as much boost as a low comp motor. Again, a 10.3cr SR20 would rock on 93oct and 13-15psi. Yes, that is a valid setup. It's not for everyone, but it does work, and well.


I completely forgot that you're effectively reducing the displacement of the engine with the Miller cycle. Bah! You do get a full expansion, though. With this VCR system you get full(er) displacement. Can anyone find a better drawing of what's going on? It's really hard to see exactly how things are articulating during rotation at the limits of both modes.

That VCR main rod member doesn't look like the most robust piece I've ever seen. I'm willing to bet that this will be directed towards small displacement (in the 1.5L range) engines that will need the turbo to make enough power to propel a larger, Sentra/Altima sized car. That would keep the max torque figures manageable for the new rod arrangement. With high CR's off boost, something like that would make killer mpg's, too. They do this (small boosted engine in big car) in Europe with a 1.8L supercharged E-class, which does not make good mpgs.

 

And as I said, you arent going to be able to run much boost, and its not going to make as much power as a similar setup with 9:1 and 22 psi.

It would be more responsive, yes, but with your limiting exactly what you were saying in those posts, now you've got half the board around here swearing 12:1 + 25 psi will work just peachy on pump gas.

 

I'll go with you on that one. My 9:1 3071r setup will likely make less power at 10.5:1 because I'm limited to less boost (even less than I'd make up with that 6%/pt efficiency gain due to CR). Going back to the original debate, just because someone is selling pistons that are 10.x:1, doesn't mean that they're not for a DET setup. Can we agree on that?

And just because everyone thinks that I said high comp and high boost are fine on pump gas (which I didn't), doesn't mean we shouldn't be able to talk about technical topics. That'll only dumb the place down.

Where'd that Vertigo guy go? This VCR thing is getting interesting!

 

Thing is those pistons were for 11:1, yes you might be able to run a thick enough gasket to bump it down a bit, but then you run into quench area problems, and end up back where you started.

The quench thing makes me wonder how the vcr setup is going to work with that, because from what it seems, it lowers the piston at tdc to decrease the comp...

 

Define responsive? if you mean vacuum response then yes. If you mean turbo lag, then maybe... maybe not. There are some well known tuners in the z32 community that insist lower c/r spools the turbo faster, and they have dynos to somewhat back up their claim. The problem is, none of them were controlled tests so take it for what it is.

 

Well, that wouldn't be a problem for me then. I had my quench pads CNC'd off at Mazworx.

The other thing about those pistons that you might not know is that Wiseco had a brain fart when it came to the SR20 and couldn't get the head volume correct when it designed the pistons. Their marketing and ads say they're 11.0 but they're really as I stated earlier: 10.7:1 with a 1.1mm headgasket, which is the stock thickness on a DET motor.

The quench pad thing is less of an issue. To get a 14:1 motor (at max cr) you'll have a pretty damn small head volume. So, the difference in piston heights to min CR won't be as big as you'd think. I "shortened" a rod once by .030" and lost something like 1.5pts. If you make a piston that matches quench pads and throw it at the head for a stroke of 75-90mm, stopping 1mm shorter than usual isn't going to make a hell of a lot of difference if you're already at a low CR / on boost.

 

Chiropractor :]

Upon second look of that page, it looks like the c/r can vary from 14:1 down to 8:1 which is awesome. Too bad the rods are weak, the rotational mass is increased significantly, frictional losses will go up due to the increased journal surface area, and the fact that this car will not be cheap at all. When you add in the cost of turbo, and machining all of those parts, thats going to be an expensive, low revving engine. Say it gets 30mpg over its conventional counterpart's 24mpg. Average person drives 12,000 miles per year. Thats 500 gallons of gas vs 400. At todays gas prices, that is $400 / year. If that engine costs $4000 more (being conservative), it would take 10 years or 120,000 miles for it to pay for itself. Its a cool idea, but it has no performance market, and its not economically feasible.

 

I was really hoping for a larger photo of the acutal rod, you can barely make anything out from it.