How to De-Tune a Z

[jmortensen]

Those '40 over flat top pistons' would raise the c.r. about 1.5 points by themselves. Add in the 'Head shaved' and it climbs even more depending on how much it was shaved. That cam might not work well with EFI, though Schneider says it will, but it's the same cam they recommend for carbed cars. It's the mildest L series grind they sell but the duration seems a little hign for basically stock fuel injection. A 60mm, probably 240SX, throttle body won't work well with a stock AFM. I'm assuming the AFM is stock since there is no mention otherwise. I see no mention of larger injectors either. It might just be that all this engine needs is a stock throttle body, a stock fuel pressure regulator, and a milder if not stock cam. I would be a little concerned about the compression ratio possibly creating the need for higher octane gas, however.

.040 over changes compression from 8.29 to 8.46 according to the lengine.exe program. I'm pretty sure the cam she has is the Stage III, which is the hottest cam that Schneider recommends for EFI as far as I know, even though in reality it is still a really small cam. http://www.thezstore.com/page/TZS/PROD/PEM01/10-2003

My feeling is that the head shaving is an unknown. Could be shaved .040, could be shaved .120, we really don't know, and that will change the compression ratio quite a bit, but it's still hard to imagine it being over 11:1. It's somewhat obvious to me that someone monkeyed with the FI to try to get it to run right since it is getting 10 mpg.

The fixes that I see are either return to a stock head and stock FI, or figure out what was F'ed up on the FI to make it run so bad and fix that. I still see no way that 109 octane gas could "fix" any of this.

[sblake01]

.040 over changes compression from 8.29 to 8.46 according to the lengine.exe program.

True. But I was thinking stock dish pistons to .040 over flat top pistons. Which is 8.29 to 10.03.

[jmortensen]

Good point. I wasn't thinking about swapping dished for flat tops.

[Zrush]

Please help all.

Zrush is doing what I say I have no reason to lie. The injectors are not stock. The web site on Suncoast is old many mods have benn done since then.

If I had the money I would pay a 280Z pro to come down here and help me "De-Tune" this monster (pain in the AZZ).

Tony D the car is not what she appears to be. This is my whole point Scott did things to the car when I wasn't present.

Please keep all suggestion/help/advice comming.

I just want to cruise in the FLA sunshine without having to deal with these mod issues.

Vicky

[hls30.com]

Vicky,

Getting with Jim and letting him test a few things with the O2 meter and his other bag of tricks would be my first move-too many unknows in terms of mods means at this point all we know is the color of the smole and the bogging down-both indicate problems. Jims tests would tell us what the engine is doing, and the problem could be solved backwards letting the perforance guide the changes.

Will

[Zrush]

OK Will

I'm so depressed, I should have paid more attention to the engine. Maybe I'll just let Zrush sit and rot ( not rot as in rust, but rot as in idle mode)

Help me pleae with this car.

Vicky

[hls30.com]

Vicky,

All of these little issues are purely temporary!

No reason to be depressed over them.

In a few weeks, you will be cruising in the car with a big smile on your face, decent gas mileage, and no bogging or smoke from the exhaust!!!

Treat this just like your favorite desert, finish ot off one bite at a time!

Will

[Tony D]

I'm telling you, I've heard this car run at the MSA event four years ago--unless something seriously radical (and from the description it's not, other than possibly a bump in compression) had been done, some basic detective work should figure this out. I am on board with the suggestion of the O2 sensor.

But using Stock EFI with these kind of components is a recipe for something that won't run well, but that you can spend a lot of money putting together. In many cases you make more power with lower compression and a stock cam when using the stock ECU. Sine you say the injectors have been changed, I'd probably say that is why you are getting 10MPG...

It's a poor mismatch of parts. I see this all the time. With a standalone you can make a lot more power and not have these problems, but you will have to do some diagnostics first to determine where you are. Sticking a standalone on something not running right in the first place is another receipe for disasterous results.

Bogging/Smoke form the exhaust form this setup will be traced to AFR's in the 9's when the O2 Sensor is put to it, my prediction.

Megasquirt would be sooo nice to make it fuel correctly according to demand and load, as opposed to what's on it now. That cam is mild enough to give decent idle vacuum and resolution for a MAP based standalone. But for a stock EFI setup, that kind of idle vacuum will make you run RICH...fuel pressure too high for the load on the engine...just a function of how the FPR works. Adding bigger injectors will exacerbate the problem.

Like said above, don't get depressed about it. It's all fixable. I just think some red herrings were being chased initially.