PEZi720... the build thread

[damn]

Advancing the timing too far with the emission set up is what is causing the idle problems you all have. Remember the engine is designed to operate with 3 degrees BTDC to about 5 degrees ATDC. Too much advance and you'll get either post ignition or the cylinder fires too early at idle.

Thats what i was thinking...In the manual it say's the ecs read's various sensors like the water temp sensor,knock sensor and oxygen sensor to determine the amount of fuel and timing to use.....Not sure how that work's with a carbutated engine..

[PEZi]

it runs awesome under throttle tho

[flinterman2000]

In the carb version the fuel is controlled by you the driver. The venturi in the carb causes vacuum to draw the fuel through the jets, the wider open the throttle the more vacuum, except when the throttle is first activated. Then the power valve forces fuel through for initial acceleration.

[jtbenfie]

seems like part of the solution would be to disable the second set of spark plugs and set the timing again. That way there is no second delayed spark to cause knocking or pinging. It even says in the nissan/datsun 720 dealer manuals that some of the engine controllers in the later models shut off the second set of spark plugs during full acceleration to cut down on engine noise.

Really, i think the trick to unlocking a lot of the performace after switching to a weber would be to eliminate all the emissions components, and switch to some aftermarket ignition

[PEZi]

what i want to know is exactly when the second plugs fire... i have all my emissions equipment removed and pulstar plugs so it runs like a charm as is (except the idle of course)

but one thing i do know is that certain other automakers have used dual plugs in the past as performance gain... under throttle with both sets firing with the timing advanced... wouldn't the Z24 be doing the same thing as these other cars and gaining performance?

[seang]

The second plugs fire 10 degrees after the primaries.

Above 3000rpm, and at full throttle, the second plugs shut down to allow more advance, and more power. How much more, I don't know.

With the naps-z twin plugs, you have two flame fronts flying at each other from opposite ends of the combustion chamber at incredible speeds, and then they slam into each other, just like two waves in the ocean running into each other. With the performance minded dual-plug setups you mentioned, I wonder if the plugs were positioned near each other instead of being on opposite sides of the head, then the flame fronts wouldn't be slamming each other head-on, but going in the same direction instead.

And just in case you missed this, Pezi, here is something I posted a few posts back.

Pezi, here is an old post from 2004 that made me think of the possible engine build you were talking about:

Quote, originally posted by DeviousKA » The first nap-z head is actually a decent flowing one, the z20, after that top end performance was sacrificed due to the nap-z being used solely in the trucks.

I wonder, if the above is true, if the early naps head would qualify as a stock head in autocross.

Modified by seang at 2:56 PM 1/10/2010

[PEZi]

And just in case you missed this, Pezi, here is something I posted a few posts back.

yeah i did see it... its something i'm looking into but i don't think it works... it says it must be the head that came on the engine and since the Z24 never came with the Z20 head I'm thinking no

[damn]

The second plugs fire 10 degrees after the primaries.

Above 3000rpm, and at full throttle, the second plugs shut down to allow more advance, and more power. How much more, I don't know.

With the naps-z twin plugs, you have two flame fronts flying at each other from opposite ends of the combustion chamber at incredible speeds, and then they slam into each other, just like two waves in the ocean running into each other. With the performance minded dual-plug setups you mentioned, I wonder if the plugs were positioned near each other instead of being on opposite sides of the head, then the flame fronts wouldn't be slamming each other head-on, but going in the same direction instead.

And just in case you missed this, Pezi, here is something I posted a few posts back.

Modified by seang at 2:56 PM 1/10/2010

Does the computer shut the plug's off?

[seang]

Does the computer shut the plug's off?

I'm not sure exactly how it works. I don't have my Haynes manual to reference anymore. It's been a while since I read about it, but I'm pretty sure that's where I read it originally.

[jtbenfie]

Does the computer shut the plug's off?

My 86 dealer manual says the computer shuts the plugs off on the carbed z24 under full throttle.

On some of the older models given the way they are wired i don't think its possible for the computer to do this.

Nissan change so much stuff thru the production run of these trucks that its hard to just say they are do something specific, when it reality it changed year to year....

[flinterman2000]

The distributor can't do this for itself. The computer is what shuts off the second set of plugs, but the actual power difference is not noticeable when the computer is off and both plugs fire all the way to maximum RPM.

[bracktheron720]

My 86 dealer manual says the computer shuts the plugs off on the carbed z24 under full throttle.

On some of the older models given the way they are wired i don't think its possible for the computer to do this.

Nissan change so much stuff thru the production run of these trucks that its hard to just say they are do something specific, when it reality it changed year to year....

quick question since were one the subject...i drive an 84 with the z24 and was told the computer was under the passenger seat but there's nothing there....just a little light relay/delay or sumthin like that..idk...does mine just not have one????or if it does any other idea where it is and does anybody have a pic of this thing so i know what im looking for????and if not im assuming the plugs fire the same full throttle or not???

[jtbenfie]

86 dealer manual says its under the seat....dunno thou on an older one....never looked for it on my 83

[PEZi]

it IS under the seat... but its also beneath the metal of the floorboard... you can't see it just by taking out the seat

[bracktheron720]

hmm how do i get to it???

[PEZi]

ummmm.... i think you get to it from under the truck... been a while since i really cared to look for it but i think you just go under and then boom... its there

[flinterman2000]

and if not im assuming the plugs fire the same full throttle or not???

Once there is no computer or its disconnected, both plugs fire through out the RPM range. The only thing is that you do not get the full advance timing for maximum power, but there is sustainable power for the vehicle.

[85NIS720]

Pezi, what kind of wheels are you running?

[PEZi]

the wheels are american racing outlaw II's in 15"x7"

the ones i'll be getting for the next autocross season (autocross only) will be diamond racing wheels in 15"x10"

[85NIS720]

Thanks, did you have to alter the bore on the AR's?

[PEZi]

nope

[dogred]

quick question since were one the subject...i drive an 84 with the z24 and was told the computer was under the passenger seat but there's nothing there....just a little light relay/delay or sumthin like that..idk...does mine just not have one????or if it does any other idea where it is and does anybody have a pic of this thing so i know what im looking for????and if not im assuming the plugs fire the same full throttle or not???

My 83 has it under the driver side seat right after the hump. It is a black box about 3"x4" inside the cab.

[PEZi]

^ i don't think that thing is the actual computer... i ahve that thing too... can a larger actual computer on the other side... you'd honestly never know it was there until you pull the carpet

[PEZi]

ok... slight update time

at the last event in denver my truck was 'too loud'

the sound regulations at 2 of our 3 sites are as follows:"sound meter will be placed 50' away and perpendicular to the vehicle in a location where it is expected to be at full throttle and high RPM. 90+ decibels measured from 50' away will be issued a warning. 93 decibels or higher will be DNF'd for their run, and required to fix the issue before they are allowed to continue"

my truck was at 94.1 decibels we had to stuff steel wool in the pipe in order to quiet it down for the rest of my runs and it killed the power

so... a new muffler will be going on soon... instead of running a resonator... i'll be switching to an actual muffler. it'll be a Magnaflow XL turbo muffler

[flinterman2000]

. it'll be a Magnaflow XL turbo muffler

These flow a lot better than the stock muffler and the sound aint that high either. With no resonator you should get about 85 decibels.

[PEZi]

with the headers and test pipe and with how i have the exhaust setup.... i'm thinking this will take it down to 90-ish with the way they measure it

but my intake (induction roar) may also be too loud which will be another headache in its own

[85NIS720]

What kind of test pipe do you have? Also, how much did it change the power and noise? I'm running a Flowmaster Super 44, single-in double-out, with 2 3/4" piping from the manifold back, no converter and 3" tips.

[PEZi]

custom made test pipe.... the sound went up quite a lot, thus the need for a new muffler now

the power wasn't as noticeable down low... it didn't give me much of an advantage over my high flow cat.... but up high it helped quite a bit and allowed for the revs to keep climbing

[85NIS720]

Oh, gotcha. Any tips on making one? I might have to try that out.

[marleyone]

Hey pezi when you installed your weber did you run a line from the fitting on the upper passenger-side of the carb? I can't figure out if I need to run it somewhere or just cap it?