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Zrush

How to De-Tune a Z

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After reading through this entire thread a few times, let me ask if I have this right. This engine was not built with the intentions of being a daily driver. There are probably enough mods done to this engine to make it economically unfeasible to tone down for practical street use. That does not mean there isn't someone who would be interested in buying outright or trading/upgrading engines with you. I agree, it is a pain in the azz & you would be better off swapping out engines so you end up with something more enjoyable to drive. I'm sure that engine was built as a complete package and never intended to be detuned. Fun toy but not a good driver.

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Vicky,

Can you bring Zrush to the August event over at Jimbo's house? I have the factory EFI analyzer for Nissan fuel injection. I also have an innovate wideband that will tell us exactly what your car is doing. I'm sure we can get you on the road with pump gas.

Jim

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After reading through this entire thread a few times, let me ask if I have this right. This engine was not built with the intentions of being a daily driver. There are probably enough mods done to this engine to make it economically unfeasible to tone down for practical street use. That does not mean there isn't someone who would be interested in buying outright or trading/upgrading engines with you. I agree, it is a pain in the azz & you would be better off swapping out engines so you end up with something more enjoyable to drive. I'm sure that engine was built as a complete package and never intended to be detuned. Fun toy but not a good driver.

How True, How True,

I just don't want to open the engine and replace to stock parts. Funds are a problem, but so is $9.50 a gallon for a Z that MIGHT get 10 mpg.

Truly sucks for me now. I love the car but can't afford to drive it.

Z Painz in the wallet .

Vicky

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Swapping engines isn't so bad. (My Z takes less than 2hrs to swap) Just have a few people handy to help keep from scratching when moving engines in that beautiful Z of yours. Not being able to enjoy such a fine ride is a crime.

These cars can get you plenty of tickets and enjoyment with the stock motor. I almost lost my license twice when I first got the Z. My worst nightmare was coming home through Georgia doing 110-120 and seeing my ENTIRE rear view mirror consumed by a tailing state trooper. (Roads were entirely clear at 5AM where I was.) I was screwed and wondering how soon I'd be making my "one phone call" but then he passed me up!

Dropping a few hundred for a spare motor makes good sense to me.:)

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How True, How True,

I just don't want to open the engine and replace to stock parts. Funds are a problem, but so is $9.50 a gallon for a Z that MIGHT get 10 mpg.

Truly sucks for me now. I love the car but can't afford to drive it.

Z Painz in the wallet .

Vicky

There is NOTHING you can do to an L28 that should make it get 10 mpg while driving casually. If you're getting 10 mpg, something is WRONG.

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I have to agree with JM on that last point! Well....maybe with Webers. Mine got 12mpg routinely, but admittedly it was not driven 'casually'...

But my Triple Mikuini Blowthrough setup in my 73 averaged 17mpg being hammered through Carbon Canyon to and from work in Brea from Corona every day for three years+ That car had 350 RWHP, and on open-track events could get as low as 5mpg when actually USING 350HP on a consistent basis. Hard daily commuting the mileage was 17...

I would say something is wrong if 'casually' driving it the thing is only getting 10mpg.

From what I am reading here, it's a mix of gasoline formulation incorrect for the carburetion---that will cause you to run with more throttle to get the same acceleration over the stumbles.

And this 'black smoke out the tailpipe' : Air Fuel Ratios in the 9's or worse. 10:1 AFR's will not puff black out the tailpipe from my experience, and with the fuel mileage I'd say something was seriously wrong with the Carburetion. My guess is there was a lot of overjetting to cover transient flat spots, or other bad manners. "Fat is Driveable" was the axiom, but it's not right from a serious tuning standpoint.

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Tony if you look at that webpage with the description of the car, it says 60mm throttle body is one of the mods. It's still running stock injection with a larger cam. My guess is that someone put a RRFPR on the thing and has it cranked up way too high...

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"Carburetion" "Fuel Delivery System"--tomato tomatoe...same series of things affect it.

I somehow missed the website. But if it's puking black, and it's EFI, then fueling is definately incorrect---and ditto again for the mileage!

"Stock Injection with Larger Cam" is a recipe for terrible drivability. They don't work well together at all. That would go hand in hand with the drivability issues...possible injector swap there overfueling and the typical Bosch Band-Aid approach to fueling something not-stock.

Sure you can drive it, but it's nowhere near 'right'...

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Oh, this is 'Scott from Florida'---I found the post. I have seen this car, firsthand, in the flesh.

This car should NOT need anything other than regular pump gas, without a doubt!

This is a problem in the EFI system dealing with mismatched components or a sensor that has failed...the typical old stock EFI stuff.

"BOG" in these EFI Cars can be as simple a matter as misadjusted AFM causing a delay in the throttle response.

But the 460 Cam is not the friend of the Stock EFI system.

I'd suggest trying Megasquirt (programmable EFI) but at this point it may just be compounding a situation based on inexperience/unfamiliarity with the EFI systems as a whole.

This car is 'not' built so radically as to 'need' anyting but pump gas.

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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.

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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.

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.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.

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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

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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

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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

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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

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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.

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