azriel_strife

Looks like the Isky stage 2 or 3 cam is what i will want. coupled with springs and thicker lash pads. While i'm doing this i plan on having the head ported out more. I'll also replace the valve guides and seals (she smokes a bit on decel) so i'll just have the shop install all the replacement parts since the stock stuff will be removed anyway. Probably looking at about a grand for the job I'd imagine. but she should go like a raped ape after shes done.

Hi guys, I have a 72 240 with a 2.9 stroker. F54 flat top block and N42 head. Dual Z Therapy SU's with SM needles, nismo motorsport 6-2-1 header, 2.5 inch exhaust all the way, port matched intake and exhaust. its got a stock l28 cam in it however, and it falls on its face around 5500rpm, and has a nasty flat spot right around peak advance (3000rpm) that might have something to do with my static compression ratio from what I have read. I have also read that with my compression (should be over somewhere just over 10:1) i should be running a cam with somewhere in the neighborhood of 270-290 duration on this build. is this about right for this engine? and will i need better valve springs and lifters as well? or will the stock ones do the job? Also, i'm not sure if I need an oil bar, I believe my n42 is from a newer engine, so I will need a cam that is right for my head i believe. or does it matter what type of cam you use? I'm in the market for a cam as we speak, so if you have a combo that is suitable for the car, please let me know.

It still does it with vac advance enabled, but i got ping under low rpm high load conditions with it in use, so i disconnected it. probably the high compression combo causing this as well.

I figured the floats were fine with the SM needles being so rich. I could go a half turn richer on the fuel screws too i guess. but i want to change one thing at a time until it goes away, to be sure what the problem was. but from what i have been reading, my static compression is over 10:1 at least. and the compression in the chambers with the stock cam will reach around 200psi. this leads to knock or poor burning. a hotter cam will bring the compression down to around 160 or so, and should move my power band farther up. It's possible my old stock coil was just old and tired, and couldn't produce a strong spark past 3000rpm anymore. so we shall see!

I just ordered a 1.5ohm 12v petronix 40,000v coil, it's made for electronic ignition so it should be fun running at 12v on the hot spark module. Also gapped my plugs up to .45 to take advantage of the hotter spark i'll have when the coil is in. I really hope this will do the trick.

floats have been rechecked twice, they are exactly on spec. plug gap is at .35 across the board, i run with no vac advance

it has an LD crank in it. it's definitely a stroker motor. wish i could nail it down, advancing or retarding timing doesnt seem to have any effect on the flat spot. but retarding does kill my torque and idle.

I've been reading and it seems that this flat top block and n42 head bump the compression up too much for a stock cam, this might be my issue, as the mechanical advance maxes out around 3000rpm where i start to see this lack of power appear. thoughts?

the z thereapy dvd says to set the needles against the jets (at zero turns out) by holding up on the choke plunger and pushing the slide down until it stops, then completely tighten the needle set screw. basically it ensures the the needles are set perfectly on the slides. once this is done you set at 2.5 turns out and go from there. not sure if i explained that clearly?

I would have to buy a wideband, I don't know of anyone that will loan me one. If i remember correctly the cam is a factory n42 cam, making it an "a" grind. I want to get a stage 2 cam for this car if i can't find a turbo motor, but I dont want to spend that money if there's some other underlying issue.

anyway. I'm pretty sure this is fuel related. can anyone else recommend good needles for a 2.9 stroker build with a free flowing exhaust?

I see that, but it also states that if the coil is getting more then 14v when the engine is running that you need to either install a 3 ohm coil, or a ballast resistor. It is definitely getting more than 14v, since my battery terminal voltage is over 14v when the car is running, and the coil supply wire is switched battery power.

I agree, but if the coil is not supposed to be getting 12v because it is a stock coil, this could be a problem. I know the coil is getting 12v, and this coil was on the stock points distributor, so I should be getting a 3 ohm coil regaurdless, just because that is what should be int here with no ballast resistor. I don't think it is an ignition problem. But I was asking if it could cause this problem. I moved my needles up about 4mm in the slides (so the seats of the needles are flush with the slide bottom, and set my fuel screws to 2 & 3/4 turns out, the bog is definitely reduced. It occurs right around 3000rpm and it will remain there until I give it more pedal. the bog doesn't go away really. But to go any faster than 3000rpm on the highway, i need more pedal anyway. I can feel the bog come on in every gear if i let the car accelerate without increasing the throttle input. it just doesn't seem happy above 3000rpm unless i have it at 3/4 throttle or more. I tend to agree. I think it is fuel related because moving my needles up in the slides has helped the issue, but it is a bit rich at idle now. I was hoping someone had a suggestion for other needles, because I have heard bad things about the SM needles i am running now.

I just know the coil is getting 12v with the engine off and probably closer to 14 with the engine running., which means i don't have a ballast resistor. secondary resistance is from one of the power leads to the spark output lead i assume? I never did check that, I just assumed the coil was good cause the car runs well aside from the flat spot. I went to the local parts store today and they don't carry aftermarket coils that are 3 ohms. I guess i'll have to order one online. the only ones they have are like the blaster 2 with .7 ohms, far too low. Insurance is up on the car on the 30th anyway, it'll give me lots of time to give her the attention she needs, maybe new plugs and wires too, even though they look new. Here are some pictures of her for reference.

yeah 1.5 ohm for the 6, but thats also assuming you have the stock resistor in place. it says: "Check the voltage reading at the coil's + terminal, engine running, at 2,500+ RPM. If the voltage measures more than +14 volts, you'll need to replace the voltage regulator, install a coil with 3.0 Ohms or more internal primary resistance or install a 1.4 Ohm external ballast resistor between the ignition switch and the coil's + terminal." I think i see 9 volts because the coil is constantly discharging, that and the coil is getting an intermittent signal because of the electronic ignition box sending pulses. I also never tried this at 2500rpm, just at idle.

I have a hotspark conversion, it says to never use a a coil under 1.5 ohms. This is the unit I got. http://www.hot-spark.com/Installing-Hot-Spark-Hitachi.pdf It says I should have a 3 ohm coil with no ballast resistor. I overlooked this because I checked the voltage at the coil while the car was running and got around 9 volts, so I assumed the resistor was still in place. I checked without the car running today and I have 11.95 volts at the coil power wire. So i know now that i don't have a ballast resistor. I don't know for sure if this is a 12v coil or not, but it was working with the stock points when I got the car. So it is probably the factory coil made to run with the resistor. I know running a coil with too low of a resistance is bad for the coil, but the coil doesn't seem to get very hot, and it's within spec for the electronic ignition i installed. I can't see this causing a flat spot only at a certain RPM/load.

Well, I checked the black wire with white stripe on my coil (which i can only assume is my coil voltage feed/tachometer wire) an it is feeding 12v to the coil with the key on. My coil reads 1.4 ohms across the positive and negative terminals. So I have to assume this is a factory 1.5 ohm coil without the ballast resistor in place. I'm pretty sure I should have a 3 ohm coil if i'm running it at 12v shouldn't i? I don't think this will cause poor running though, if anything the coil will generate a hotter spark with the extra voltage. Will the coil deliver crappy ignition if it is getting more voltage than it's supposed to have? It doesn't seem to get hot, I can place my hand on it after a long drive and it won't burn me, but it is warm.

seems fine, maybe a little bit jerky on the throttle. there's no cam in the car from what i can tell, maybe it needs one.

OK, so i pulled a needle out, it says SM on it, no numbers that I can see. What am i after for a 2.9 stroker?

My timing used to jump all over + or - 5 degrees with the points, but now that i have electronic the timing marks are rock solid when i use the timing light. the stock distributor is solid, bushings are good. every time i have had the plugs out they looked to be a nice golden brown. but to get a real condition under that situation i would have to quickly shut the car down after a minute or so of that rpm/load range to get an accurate indication, once it settles back down to in town speeds the car runs and drives great, so the plugs would indicate proper mixture after a minute or so in those conditions. I have no idea what needles i have, I guess i should go have a look at one. the needles are properly seated as in the z therapy SU DVD. I first synched the carbs at idle, then at 3000rpm since that is where the car sits on the highway. they are dead on. I am convinced this is a needle/fuel problem. linkage is all brand new, there is some slack, but you sync the carbs with the slack taken up anyway, so it shouldn't be an issue.

I'm not sure where I read it but I think ATF is like 20 weight? I'm not sure thicker oil will help, because it feels like it's constantly bogging on the highway. not sure how to explain it. it;s like the engine just isn't smooth and happy when its in that range. A bit more throttle and the engine perks up and moves along just fine. the slides are stationary during cruise unless i change throttle position, so I'm not sure if adding thicker oil will make any difference. the throttle response is great, it never stumbles or sputters when i put it to the mad hard, i believe this would indicate that the oil is fine?

Sorry guys, its the stock 240 dizzy with an electronic conversion. it's also a stock 240 1.5 ohm coil with the ballast resistor in tact from what I can tell, but i don't know where the resistor is, the engine bay was cleaned up. I don't have the paperwork for the carbs because I bought the car from someone else, but I do have the "just SU" dvd.

I am running ATF in there now. the problem is a consistent flat spot where the car feels like it doesn't want to go any faster, it lacks response and torque unless you push the pedal through the trouble area.

yes sorry, fixed original post.

hi guys, I have a 2.9 stroker motor in my z. I have a flat spot under light throttle with load, it sings under WOT and idles and revs perfectly fine. the problem is a consistent flat spot where the car feels like it doesn't want to go any faster, it lacks response and torque unless you push the pedal through the trouble area. unfortunately, this flat spot is almost exactly where the car cruises on the highway, so it hates highway trips unless i'm climbing a hills and use more pedal than normal cruise. -Upgraded 240z dizzy points to electronic pickup, running stock 240z coil at 9v -F54 block with flat top pistons -N42 head Timing is set to 36 degrees total with vac advance disabled. Total advance is all in at 2800rpm. initial is 10 degrees. -z therapy SU's -I have synched and resynched the carbs -checked float bowl levels -seated the needles against the seats -atf oil in the dampers Highest idle achieved at 3 turns out on fuel screws. I read somewhere that the stroker motor is supposed to have a different needle profile? is this true? if the problem is just the needles i'l happily buy a pair. I have no idea what needles are in the car now.