l20b hits wall at 4500 - 5000 rpm, won't rev past help!

[Knox]

Stoffregen, It really feels like it should be a fuel issue, but I've seen several times the afrs are in 12s to low 13s at the limit rpm, and it makes no difference whether it's under load or not. Are the nismo soft mounts similar to the Volvo ones BRE used in their trans am 510? At the moment I can can actually move the carbs by hand relative to the manifold, before I literally couldn't, so I'd say its an improvement.

 

I haven't been able to adjust the valve lash properly for awhile since I lost my good set of metric feeler gauges and I've had to use a weird set of imperial feeler gauges with huge gaps between gauges so I've had to settle for I think cold lash 0.203 inlet and 0.279 for exhaust. Would it be worse to have excessive valve lash compared not enough for high rpm? Either way I've gone out and bought a set of metric ones with 0.20, 0.23, 0.25, etc gauges. I've adjusted them to 0.20 inlet and 0.25 exhaust, but I don't feel much difference at the limit.

 

The symptoms you described are spot on, as soon as it approaches 5k the engine manages to buzz, scream and hum all at the same time and you can almost hear it vibrate through the chassis, it sounds like a car without a limiter that's at its actual limit.

 

I have tried swapping the coils but I haven't tried any hei type coils yet.

 

Datzenmike, I tried the jumper wire, I ran it through into the cabin with a switch just for safety, still didn't notice any difference :/.

[datzenmike]

Valve clearance is almost half what you have set. Should be 0.008" intake and 0.010" exhaust cold.

[ggzilla]

A big cam like that will need more valve clearance than stock. Although probably not as much as 25 thousands.

[Knox]

Oops sorry I meant metric, over here in Aus pretty much everything is metric, the manual spec for lash are in mm, so 0.20mm should be 0.008" and 0.25mm should be 0.010"

[Stoffregen Motorsports]

A big cam like that will need more valve clearance than stock. Although probably not as much as 25 thousands.

Not necessarily. It depends on the take-up. If a cam is ground with a "hydraulic" profile (not necessarily used with hydraulic lifters) you can run a much tighter valve lash. It's not uncommon to see .006" at the valve clearance on a big cam.

[Stoffregen Motorsports]

Stoffregen, It really feels like it should be a fuel issue, but I've seen several times the afrs are in 12s to low 13s at the limit rpm, and it makes no difference whether it's under load or not. Are the nismo soft mounts similar to the Volvo ones BRE used in their trans am 510? At the moment I can can actually move the carbs by hand relative to the manifold, before I literally couldn't, so I'd say its an improvement.

 

I haven't been able to adjust the valve lash properly for awhile since I lost my good set of metric feeler gauges and I've had to use a weird set of imperial feeler gauges with huge gaps between gauges so I've had to settle for I think cold lash 0.203 inlet and 0.279 for exhaust. Would it be worse to have excessive valve lash compared not enough for high rpm? Either way I've gone out and bought a set of metric ones with 0.20, 0.23, 0.25, etc gauges. I've adjusted them to 0.20 inlet and 0.25 exhaust, but I don't feel much difference at the limit.

 

The symptoms you described are spot on, as soon as it approaches 5k the engine manages to buzz, scream and hum all at the same time and you can almost hear it vibrate through the chassis, it sounds like a car without a limiter that's at its actual limit.

 

I have tried swapping the coils but I haven't tried any hei type coils yet.

 

Datzenmike, I tried the jumper wire, I ran it through into the cabin with a switch just for safety, still didn't notice any difference :/.

Yes, the Nismo mounts are exactly like the Volvo style. They come in two varieties: offset and non-offset, meaning the manifold side has two different bolt patterns. The offset mounts are thinner with not as much rubber in between. The non-offset mounts flex better, but they pose a problem when mounting them to most intake manifolds. The nuts on the manifold side of the non-offset mounts tend to ride on the radius of the casting between the runner and the flange. It may sound confusing, but it's easy to fix with a mill by spot facing the area around the stud opening. If you can't find the non-offset mounts, you can modify the offset ones to flex well by chucking them up in a lathe and cut into the rubber with a parting tool removing a bit of the rubber.

 

I make my own feeler gauges by snipping them to fit inside the lash pad with a tin snip, then smoothing out the sharp edge with a file or a grinder. Otherwise, Snap-On makes a good narrow feeler gauge set, but they only go down to .010 (inches).

 

Are you sure you have the right valve springs? Are you sure you have the rocker geometry properly set?

[datzenmike]

So much has been changed on this engine that it's hard to imaging the cause hasn't been touched on.

[Stoffregen Motorsports]

You're right Mike. It would be a lot easier for us to be there and see/hear/drive it to find out for sure.

[datzenmike]

Well not saying this is the case.... but it wouldn't be the first time that someone has described a problem that didn't really exist. Again, not saying this is the case here. Hits wall at 4,500 is very definite and should have been an electrical problem or runs out of fuel.  Carbs, heads, dizzys all changed (probably more than  this in 3 pages) still the same? 

[Knox]

To be honest it feels like the cam isn't behaving the way it should, for example, if I tweak the idle I can get it to idle at around 700rpm quite easily (not sure if that's easy to accomplish with anything around 290 degree), and although it lacks power anything below 3000-3500rpm, I think that's just due to port size. I'm wondering if I should invest in a valve train setup that I know should work. What some good cam/valve train component companies and grinds I should look at?

[620Turbo4X4]

 

Im sticking with my original diagnosis. Coil.

 

 

- spark jumps about 15mm if I hold a spark plug near the valve cover in the open

 

My lawnmower can do better than that.

 

 

 

 

Even with the points distributor the previous owner had fitted, he said he it always seemed to lack top end. I guess this car has never properly 'worked'.

 .

These two statements would lead me to believe that he's been using a 3 ohm coil this whole time.

 

Tried to get him on target on page 2 by recommending using a coil suited for electronic ignition, but was quickly discredited by several members stating that a high resistance coil and ballast resistor is a proper setup for EI. I disagree. With that much resistance there is no at the coil can get the proper current to create adequate flux (magnetic field) for high RPM. Sure I might work, and could get you home in a pinch, but it's far from ideal. There seems to be confusion and misunderstanding here on how coils work, so I'm including a couple links I found that will hopefully clear up some confusion

 

http://www.dtec.net.au/Ignition%20Coil%20Dwell%20Calibration.htm

 

Take note of the statement that says " you need to use a coil that's comptable with the module"

 

This article s also informative, but seems to be written by a MSD salesman (not a huge fan of MSD)

 

http://www.hotrod.com/how-to/engine/ignition-coil-tech/

 

So, to sum these articles up. I'm thinking that coil crash and clipping of the spark is occurring. Re-install the electronic ignition with the RIGHT coil and open your spark plug gap back to where it should be... That's my 2 cents.

[datzenmike]

I hate after market coils. Have no history with them and can only say with assurance what the stock coil will do.

 

Agree the points coil and ballast will have the same output with a matchbox or points set up. You need the lower resistance EI coil for the higher spark potential.

[datzenmike]

To be honest it feels like the cam isn't behaving the way it should, for example, if I tweak the idle I can get it to idle at around 700rpm quite easily (not sure if that's easy to accomplish with anything around 290 degree), and although it lacks power anything below 3000-3500rpm, I think that's just due to port size. I'm wondering if I should invest in a valve train setup that I know should work. What some good cam/valve train component companies and grinds I should look at?

 

What sprocket number is the cam on???

[Stoffregen Motorsports]

I'm wondering if I should invest in a valve train setup that I know should work. What some good cam/valve train component companies and grinds I should look at?

I would call Rebello Racing and get a cam from them. Dave is the only engine builder on the planet still developing the L series motor and over the past few years has come up with some really cool cam grinds that run well on the street and produce lots of HP.

[Stoffregen Motorsports]

I hate after market coils. Have no history with them and can only say with assurance what the stock coil will do.

 

Agree the points coil and ballast will have the same output with a matchbox or points set up. You need the lower resistance EI coil for the higher spark potential.

 

Im sticking with my original diagnosis. Coil.

 

 

My lawnmower can do better than that.

 

 

 

 

These two statements would lead me to believe that he's been using a 3 ohm coil this whole time.

 

Tried to get him on target on page 2 by recommending using a coil suited for electronic ignition, but was quickly discredited by several members stating that a high resistance coil and ballast resistor is a proper setup for EI. I disagree. With that much resistance there is no at the coil can get the proper current to create adequate flux (magnetic field) for high RPM. Sure I might work, and could get you home in a pinch, but it's far from ideal. There seems to be confusion and misunderstanding here on how coils work, so I'm including a couple links I found that will hopefully clear up some confusion

 

http://www.dtec.net.au/Ignition%20Coil%20Dwell%20Calibration.htm

 

Take note of the statement that says " you need to use a coil that's comptable with the module"

 

This article s also informative, but seems to be written by a MSD salesman (not a huge fan of MSD)

 

http://www.hotrod.com/how-to/engine/ignition-coil-tech/

 

So, to sum these articles up. I'm thinking that coil crash and clipping of the spark is occurring. Re-install the electronic ignition with the RIGHT coil and open your spark plug gap back to where it should be... That's my 2 cents.

Pertronix has some really good info on how to chose a coil. It's not info that's easy to find, but if you dig deep on their website, you can find it.

[620Turbo4X4]

Pertronix has some really good info on how to chose a coil. It's not info that's easy to find, but if you dig deep on their website, you can find it.

Pertronix is also a different type ignition module than the bosch. They use a "saturated" driver for ignition and thus require a ballast. The bosch works like a peak and hold injector driver and is able to sense the actual current and limit it once the thread hold is reached in addition to the ability to change dwell. This type does not use a ballast resistor. Apples and oranges.

 

The first link I provided is relavant to the actual BIM 024 module he was using.

[datzenmike]

So is he using a Nissan EI module or some other part because I have no faith in other 'stuff'. Thought he put a points dizzy in and it did the same thing.

[ggzilla]

Pertronix makes a high-energy ignition (needs no ballast) called Ignitor II.

 

But the one for Datsun is Ignitor I, which requires ballast. Some guys successfully use an EI coil with it, but others have burnt out.

[ggzilla]

Bosch was a Nissan OEM in some countries.

 

910 electronic distributor for L20B

 

Some say the module (BIM024 021) fail frequently. Used by many cars 1977-1996 e.g. VW

[620Turbo4X4]

So is he using a Nissan EI module or some other part because I have no faith in other 'stuff'. Thought he put a points dizzy in and it did the same thing.

Last I heard he was using point dizzy and had gotten a slight improvement. From the info I've gathered using a E dizzy with points coil and ballast actually reduces output due to a 2v drop that is a "common characteristic" of the Darlington transistor used in the bosch.

[Knox]

I did swap to the points dizzy and it did the exact same thing. My dad is an electrical engineer and we actually have an oscilloscope, we hooked up the other day to check the electronic dizzy's signal when the car was running, the dwell time is pretty consistent and the voltage spikes were up around 250v at idle and 150v at 5k, I'm not entirely sure what this voltage is when it comes out the coil, or whether the voltage spikes are in the wrong place value, but I assume 150v should be enough for a 15000v spark?

[620Turbo4X4]

Your dads a electrical engineer? He should be figuring this shit out for ya. :)

 

Dwell times should be consistent with points, but not with electronic. You should see a steady increase as engine speed increases with the E dizzy

 

250v spikes are pretty normal on the primary side. Only seeing 150v at 5k means a near 50% reduction in spark energy

 

Does your dad have a CT for his scope? Getting a visual and knowing how much current going through coil is helpfull too

 

So with the wires removed from coil how many ohms do you get across the primary?

[620Turbo4X4]

Also you need to open up your plug gap. .5mm is too small for a low compression, low turbulence engine. Try something in the .8-1.0mm range.

 

Sit down with you dad and read the links I posted above. The first link is relative to your module and has excellent info that a electrical engineer will have no problem deciphering.

[Stitebunny]

Anything new? Finding this interesting.

[scooter]

This thing should wail to 7000. My stock l20b did.

 

Maybe you have some weird voltage regulator issue fucking up your ignition?