that drawing looks like a transformer...or maybe a monster...sorry off topic.

 

The effective compression with the atkinson is WAY lower than 13:1.

you start putting otto ICE cam timing in there... and it's a race motor... and if you don't detonate... you'll stress the rods from the extra power!

I'm a bit srprised that no one has put 13:1's in this car... because it'd be SO CHEAP to do... but you'd have to run on race fuel... and one good ping = buh-bye motor.

 

Octane rating was my only question. And that is why I said that you would definitely have to run a piggy back like e-manage ultimate to keep everything in line.

And yes 13:1 sounds crazy high, but is it really? Sure the effective compression ratio under the Atkinson cycle is lower due to the valve being left open. But you also have to look at what is being done EVERY DAY to the 10.5:1 Otto cycle 1NZ-FE.

Guys are throwing 6 psi+ of boost at them. Using an online calculator that computes to an effective compression ratio of 14.79:1 at sea level. Hell, ZPI is running something like 7.5 psi on the stock 10.5:1 pistons. That bumps the effective compression ratio to 15.86:1. Far more than the 13:1 that would be seen in the 1NZ-FXE with the FE head.

And those forced induction guys are handling all of this with standard e-manage. And IF I were to try this I would probably go with e-manage ultimate. You would have the ability to retard timing, and adjust the duty cycle on the injectors. If you were raising the duty cycle too much you can always switch out to larger injectors as well. Just like the forced induction guys. Oh, and of course swap out to a colder plug.

Again, this is all just the wild ramblings of one nut job. I have no idea if it would work. And I am probably in way over my head. But until someone tries it, we'll never know for sure.

 

While 6psi of boost may calculate to a 14+ compression ratio, you're not operating at 6 lbs boost that often. When you build in 13+, it's continues as long as the engines running. That makes all the difference.

 

there is no point in running 13:1 comp pistons if you just retard the timing super far to elim. ping.


I doubt it'd be driveable at 94 octane... but by all means go for it!

The 1NZ-FE retards timing like MAD on 87 octane... there is a very sensitive knock sensor...

Altho the coolant flow in the head is VERY good at pulling out heat... at 13:1... even on 94... it'd pop IMHO.

 

And this is exactly why I am asking the questions in here. I don't know if it will work. I just want to know if anyone thinks it might.

And I understand that the high compression ratio that results from boost isn't constant. I know that it increases as the boost does. I have no doubt that the rods, crank and pistons would be more stressed by a naturally aspirated 13:1 than by a forced induction 15:1.

Then again, ZPI claims they had no problems hitting 12 psi of boost in their xB. Internals were fine, as far as they knew. The first failure came in the form of a sheared axle due to too much grip. That means at PEAK their little 1NZ-FE was seeing over 19:1! And no doubt saw greater than 13:1 quite a bit of the time.

Now what about the octane? 91 is the highest commonly available fuel here in California. I can get 100 through VP near here, but that definitely isn't something I would want to have to do on a regular basis.

Do you really think you would have to retard the timing so far to use 91 octane that the bump to 13:1 would be useless? What if machine work was done to the stock FE head to increase the size of the combnustion chamber? What compression ratio would have to be acheived in order to use 91 octane fuel and not retard the timing so much as to make the modifications useless?

I still think that this would still be a budget alternative to a typical n/a build. And IF it could work, you could probably do it for less than any of the forced induction kits out there.

 

my SC'ed box hits 12psi everyday.
i cruse with it at 8psi (4k rpm). been two years and no issues.
i can use 87 with out knocks or pings (yes the timing is retarded enough to rob me of power) using 92-94 (common super fuel grades in NJ) it runs at factory timing.
so running 13:1 on pump grade fuels is not an issue.

 

Thanks for the comment DG.

I would love to give this a shot when I get my xB, but doing an unproven swap on a BRAND NEW car just isn't my idea of fun. I have to many other things I want to get done first. But if there is some brave soul out there willing to give it a try first, I would love to see it.

Even if it meant pulling out a lot of timing to get it to run on 91 octane, I still think it would be worth it. Say you can ONLY put down 130 whp. Where else can you make that kind of power for under $1500 including install and tuning? No where. And I have a feeling with the knock sensor and some really good tuning with e-manage ultimate you will see more power than that. Throw in the typical i/h/e setup and you could free up a couple more.