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

[Knox]

Hey guys I still haven't solved the problem, power will still come in good up to around 4,5k then just fall flat. I've since chucked my ignition module and coil and replaced it with an msd cdi box and blaster coil, pretty much eliminating any chance of spark breakdown, but it didn't get rid of the wall. I also got soft mounts for the carbies and that helped with the fuel frothing issue and it now hits the wall at a more consistent rpm.

 

I'm currently running my a87 head with the 290Deg cam, springs, etc. But I'm looking at doing up my open chamber u67 head, maybe chucking in some 44mm intake valves, sourcing some bigger exhaust valves and taking out the ports, particularly the exhaust. I also have a spare complete stocker l20b I recently got which I'm considering running as is just out of curiosity but I think I'll end up building a better motor out of that while I have it on the stand.

 

At this point I think it's just running out of breath with the a87 head I'm running now, it just doesn't act like a very peaky motor, I can get it to idle pretty good below 900rpm and pull up hills fairly well below 2500rpm despite the 290Deg cam, oversized chokes and bigger intake ports. I think this could have something to do with the exhaust ports on the a87 head, the ports on the u67 head were a fair bit bigger, when I ran that head it didn't pull as well down low but picked up a little better up top but I think I was still having slight troubles with the ignition and carb mounts which might have held it back slightly.

 

But there is still a huge chance this just another glimpse of false hope and won't resolve anything but to me it's worth a shot doing up this head to see what happens.

[banzai510(hainz)]

should hit 7 k ez in first gear

 

5th gear I could never get past 7K.

 

I dont think its the head and bigger valves isnt going to do this. 42mm to 44mm isnt going to do it

 

 

sure the venturis are not loose inside the carbs?

[datzenmike]

This thread is so heavy with posts and conflicting info it's almost impossible to even guess what might be wrong. Too many things have been changed and tried I don't know where we are. Seems like everything has been swapped at one time or another so what's left???

 

Hits wall at 4,500-5,000 RPMs won't rev past. Does this literally mean it gets to this RPM and then just stays there and won't go higher? Or is this just an expression and acceleration has peaked and now just drops off dramatically?

 

If it absolutely won't rev past 4-5K what does it sound like???? I imagine it should sound all broken up like a rev limiter... popping and snapping.

 

Is your tach even working properly? Has it been tried on another engine? Is it reliable? Could it be reading 6,500-7,000 but displaying 4,500-5,000?? Do you have another tach to try???

[Knox]

The problem pretty much hasn't changed from when I started the thread, except for eliminating a few other problems that made it a lot harder to diagnose. But I'll try and describe in depth what it does (I might try and post a video later on)

 

The engine will pick up pretty well at around 3000rpm give or take a couple hundred rpm, it'll pull well and sound smooth until 4500rpm, from here the motor takes on a really buzzy, whiney, ringing sort of sound and starts vibrating like crazy, but it's NOT misfiring or popping or anything like that. In 5th gear it'll only get to 4500rpm if I'm lucky. There is absolutely no power more beyond this rpm. In lower gears I can squeeze it out to 5000-5500rpm, 1st can sometimes go out to 6000rpm.

 

In neutral, foot flat, revs will climb to 6k, then slow a bit then climb out to 7200rpm (the rpm I set the cdi ignition limiter at). At this rpm it is so unbelievably loud, it sounds like it's revving at 10,000rpm, but it's not misfiring or popping, it just buzzes and vibrates like crazy, it doesn't have any real engine tone it almost sounds like white noise, it's pretty hard to explain.

 

Oh and btw I compared the tach to a digital timing light and it was spot on.

 

I don't know whether I touched on this before or whether you guys are going to hate me for saying this now, but the engine itself is really sensitive to temperature, on hot days it runs real rough and just goes 'flat' when you open it up; in 5th gear it won't even go past 3800-4000rpm sometimes, but on really chilly nights or mornings it'll go like a rocket (comparatively) it runs a lot smoother and sounds crisp, but still hits the wall at 4500rpm in 5th. It could just be rich jetting though.

 

Also for some reason it hates thermostats; at the moment I'm just getting by with a higher flow thermostat with a few coils off the spring so it opens earlier just so it doesn't go past operating temp. With normal thermostats it overheats after about 5mins of driving. I've gotten a new alloy radiator and water pump and it does the same thing. So not sure what the deal is there and whether it's related to the rpm wall.

 

Sorry if this comes across really confusing or misleading, it's hard enough trying to troubleshoot a problem that shouldn't really exist given the circumstances, but hopefully someone can make sense of it.

[datzenmike]

Not at all. After so many pages it's really hard to remember what was said or tried.

 

A rev limiter? I don't like the sound of that as this is basically what our problem IS. Any way to get rid of it and just run a normal points distributor system to try it???.

 

 

 

Odd that it runs so hot so how about checking things that can cause an engine to run hot?

 

Extremely retarded timing will dump huge amounts of heat onto the exhaust ports and from there into the water jacket around them. Can you re-check the timing is 10-12 degrees or what ever the L18 is???

 

Very lean mixtures will also do this and the pedal goes to the floor with no increase in RPMs. You could run it at the 4,500 RPM limit and then shut off and inspect the plugs. A lean mixture will over heat the plugs and the porcelain tip will be bright white. Normally they are light brown or tan.

[Stoffregen Motorsports]

 After so many pages it's really hard to remember what was said or tried.

 I was thinking the same thing.

 

Not to be difficult, but could you give a basic outline of the engine, carb, exhaust and ignition again?

[datzenmike]

Yeah, like a fresh look.

[Stoffregen Motorsports]

Zackly.

[datzenmike]

 

 

A rev limiter? I don't like the sound of that as this is basically what our problem IS. Any way to get rid of it and just run a normal points distributor system to try it???.

 

 

 

Odd that it runs so hot so how about checking things that can cause an engine to run hot?

 

Extremely retarded timing will dump huge amounts of heat onto the exhaust ports and from there into the water jacket around them. Can you re-check the timing is 10-12 degrees or what ever the L18 is???

 

Very lean mixtures will also do this and the pedal goes to the floor with no increase in RPMs. You could run it at the 4,500 RPM limit and then shut off and inspect the plugs. A lean mixture will over heat the plugs and the porcelain tip will be bright white. Normally they are light brown or tan.

[KoHeartsGPA]

If you live several miles from the freeway, take your tools with you and when you get off the freeway find a safe spot as quick as possible and check your plugs then, this should tell you if your issue is mixture.

 

 

Keep us posted!

[Knox]

Alrighty the block is a semi recently freshened up l20b with stock internals, 11cc dish pistons, ect. The head I'm running at the moment is the closed chamber a87 head off my l18, valves are stock 42mm/35mm and exhaust ports are stock as well, I've taken the intake ports out to 36mm and put in the crow 290deg cam and matching springs that were on my u67 head. At the moment I'm running the cam a tooth retarded in I think the no.2 dowel position.

 

Carbies are twin dhla40 dellortos (emission type) running 36mm venturis, mounted on soft O-ring style mounts. I'm also running a stock fuel pump. My afr gauge stopped working probably a month ago, but last time it was running it was in the high 12:1/low 13:1s at the limit rpm, with the same setup.

 

The headers are 4 into 2 into 1 (haven't checked pipe sizes, but I think the primaries are over 1-1/2") all mandrel bends, into a 2-1/4" exhaust with a resonator at the end.

 

Ignition is run off a Bosch electronic dizzy found in some 200b's, I've now removed the module and replaced it with an msd cdi box, the coil is a blaster 3 coil. Plugs are BP6ES I think.

 

I think that's about it...

[Knox]

Oh and timing is around 8 degrees idle (I'd imagine it shouldn't even idle with this timing and cam duration - but it does!) and 35-36 degrees max.

[datzenmike]

Trying to get a sense of what has never been changed and is common. 

 

You did have a different head on it at one time? Were the valve springs used the same on both heads? Thinking valve float....

 

Did you have two different distributors? The modules may have been changed but maybe the stator or reluctor coil inside is the same??

[Stoffregen Motorsports]

Alrighty the block is a semi recently freshened up l20b with stock internals, 11cc dish pistons, ect. The head I'm running at the moment is the closed chamber a87 head off my l18, valves are stock 42mm/35mm and exhaust ports are stock as well, I've taken the intake ports out to 36mm and put in the crow 290deg cam and matching springs that were on my u67 head. At the moment I'm running the cam a tooth retarded in I think the no.2 dowel position.

 

Carbies are twin dhla40 dellortos (emission type) running 36mm venturis, mounted on soft O-ring style mounts. I'm also running a stock fuel pump. My afr gauge stopped working probably a month ago, but last time it was running it was in the high 12:1/low 13:1s at the limit rpm, with the same setup.

 

The headers are 4 into 2 into 1 (haven't checked pipe sizes, but I think the primaries are over 1-1/2") all mandrel bends, into a 2-1/4" exhaust with a resonator at the end.

 

Ignition is run off a Bosch electronic dizzy found in some 200b's, I've now removed the module and replaced it with an msd cdi box, the coil is a blaster 3 coil. Plugs are BP6ES I think.

 

I think that's about it...

Great, thanks for refreshing my (our) memory.

 

Two things that jump out at me are both cam related and can certainly cause the "hit the wall" feeling you describe.

 

1st - the "matching springs that were on my u67" - Were these springs checked for pressure? How old are they? Who set them up? What brand are they?

 

2nd - "At the moment I'm running the cam a tooth retarded in I think the no.2 dowel position." - Have you not physically checked the cam timing? I mean without guessing you're in the right hole? It would be nice to know what the difference is at split overlap.

 

 

If the springs are too soft, worn out or impropery shimmed, that can cause valve float which feels like hitting a wall. Valve float is not necessarily audible so don't think you're alert enough to catch it by the sound.

 

If the cam is not properly degreed, the obvious result is that the power curve will not be where it was designed to be.

 

Conclusion: I think you need to have someone have a look at the cam and how it's set up. It may be that you need new springs, an adjustment of the cam timing, but it may be that the cam you have is just not right for that motor and needs to be replaced altogether.

[datzenmike]

The L20B was sent out from the factory in the #2 hole but this is just the cam/sprocket and has nothing to do with the chain and does not prevent you being one, two or more teeth out on the sprocket. The chain can be set anywhere.

 

After checking the valve springs try moving the chain ahead or back one tooth on the sprocket. If better, try another tooth. It's laborious but each tooth is 9 degrees of cam change. L series will run with cam way off, not well but will run, they are very forgiving. But when the cam is right, hang on!

 

 

 

 

Now we're getting somewhere!!!!!

[banzai510(hainz)]

Does Baz at Datsport recommend having a tooth off? 

 

Never heard of this

[datzenmike]

Each of the three holes on the sprocket moves the cam 4 degrees. Each tooth moved is 9 degrees.  Thus you can move in +- combinations. Like one hole back and one tooth ahead -4, +9 = +5 degrees. On an L16 that come on the first hole 3 holes ahead and one tooth back for +12 , -9 = +3. Can't see this being significant on a street engine, maybe racing but then you'd get one of those $550 Kalamari adjustable sprockets.

[Stoffregen Motorsports]

The thing about cam timing is it's either right or it's wrong. You can adjust a bit either way, but cams are generally ground with a certain spec in mind.

 

There are a lot of factors that can make adjustments in the cam timing necessary, like changes to the carburetion, exhaust, etc. If an aftermarket cam is purchased, it should be installed according to the spec on the cam card and only adjusted to fine tune it. But we're not talking a lot, maybe one or two degrees.

 

One trick commonly used on Datsuns is the eccentric cam adjusters as used on small block Chevys. Crane makes them http://www.summitracing.com/parts/crn-11991-1/overview/. Just drill the dowel hole in the Datsun cam sprocket to get them to fit.

[620Turbo4X4]

I don't know whether I touched on this before or whether you guys are going to hate me for saying this now, but the engine itself is really sensitive to temperature, on hot days it runs real rough and just goes 'flat' when you open it up; in 5th gear it won't even go past 3800-4000rpm sometimes, but on really chilly nights or mornings it'll go like a rocket (comparatively) it runs a lot smoother and sounds crisp, but still hits the wall at 4500rpm in 5th. It could just be rich jetting though.

 

Also for some reason it hates thermostats; at the moment I'm just getting by with a higher flow thermostat with a few coils off the spring so it opens earlier just so it doesn't go past operating temp. With normal thermostats it overheats after about 5mins of driving. I've gotten a new alloy radiator and water pump and it does the same thing. So not sure what the deal is there and whether it's related to the rpm wall.

 

Sorry if this comes across really confusing or misleading, it's hard enough trying to troubleshoot a problem that shouldn't really exist given the circumstances, but hopefully someone can make sense of it.

 

No, This is all making sense to me now...

 

Sounds like the A/F ratio gauge you were using may have been lying to you, or getting false readings. If it's running better on cold mornings with a cold engine, that's telling you something... it's running pig rich... The heat range of plug (believe I asked before), and overheating is another issue that would have been nice to know....

 

Your running stock plugs? If your engine is not stock, neither should be your plugs. as RPM's and compression go up, plug heat range should go down (FYI I'm running BP8ES plugs in my mildly modified L20b) The hot plugs could be acting as a glow plug and igniting the mixture prematurely. That could very well explain why engine is running hot and falling on its face...Pre-Ignition will lead to detonation, damage the engine, make it sound like crap, loose power., and overheat... Too much ignition timing will also increase engine temps (and lower EGT's). Not enough and EGT's rise, and cylinder head temps fall. Reading the color transition of the ground strap on your plugs gives the best indication of what kind of timing your particular engine likes, but only after the correct range of plug is used and A/F ratios are in the ballpark...

 

Here's a couple articles that might help you out...

 

http://www.dragstuff.com/techarticles/reading-spark-plugs.html

 

http://www.4secondsflat.com/Spark_plug_reading.html

 

 

Excessively rich mixtures will hurt power. The fact that it's running better on cold mornings and when engine is cold is a dead giveaway to what's going on. If your tuning the carbs using plugs that are too hot, your having to add a considerable amount more fuel to the mix to see any color on your plugs. (if your even seeing a tan color?) Were these carbs purchased second hand or new? Previous owner may have had these tuned to run E85 or something.... Which, from the sounds of it, might be a good thing to try if you have E85 available locally. Or, If you want to stick with regular petrol, I would step up the air corrector jets several sizes larger, and decrease the mains, but keep in mind the air correctors have the greatest effect at the upper RPM ranges where the trouble spot seems to be. If carbs were second hand, take a good look and measurement of the jets installed. Someone may have drilled them out,     instead of buying new jets.... 

[datzenmike]

Update?

[banzai510(hainz)]

There was a kid in New Zealand had this issue a long time ago

Find out he was 2 links off on chain.

[Knox]

No real update, been sick for the past week and haven't been bothered to fiddle with the car. But I'm pretty certain I did some experimenting with different tooth/dowel combinations at some stage. First time I ran this cam setup I went stock no.2 dowel, and didn't see any point advancing it any further it, made the power feel even flatter than it already was. Retarding the cam seemed to improve things a little, I think the furthest I went was a tooth retarded, in the no.1 dowel, it ran better than the stock timing but nothing magical happened. At one point I looked up the grind number I found on the back of the cam, but I couldn't find anything in the Crow catalogue, the stuff I found out about the cam was just from measuring open and close points of the lobes while it was on the engine. I also tried running it as close to symmetrical timing as possible.

 

I don't think valve float is the issue, I haven't tested the springs or anything, but I've ran both the stock and aftermarket valve springs and didn't notice any real difference, unless they're both crap. Does valve float create a sort of fixed rpm limit or does it not affect free revving as much?  -  I'll still try and post a video at some point.

 

 

No, This is all making sense to me now...

 

Sounds like the A/F ratio gauge you were using may have been lying to you, or getting false readings. If it's running better on cold mornings with a cold engine, that's telling you something... it's running pig rich... The heat range of plug (believe I asked before), and overheating is another issue that would have been nice to know....

 

Your running stock plugs? If your engine is not stock, neither should be your plugs. as RPM's and compression go up, plug heat range should go down (FYI I'm running BP8ES plugs in my mildly modified L20b) The hot plugs could be acting as a glow plug and igniting the mixture prematurely. That could very well explain why engine is running hot and falling on its face...Pre-Ignition will lead to detonation, damage the engine, make it sound like crap, loose power., and overheat... Too much ignition timing will also increase engine temps (and lower EGT's). Not enough and EGT's rise, and cylinder head temps fall. Reading the color transition of the ground strap on your plugs gives the best indication of what kind of timing your particular engine likes, but only after the correct range of plug is used and A/F ratios are in the ballpark...

 

Here's a couple articles that might help you out...

 

http://www.dragstuff.com/techarticles/reading-spark-plugs.html

 

http://www.4secondsflat.com/Spark_plug_reading.html

 

 

Excessively rich mixtures will hurt power. The fact that it's running better on cold mornings and when engine is cold is a dead giveaway to what's going on. If your tuning the carbs using plugs that are too hot, your having to add a considerable amount more fuel to the mix to see any color on your plugs. (if your even seeing a tan color?) Were these carbs purchased second hand or new? Previous owner may have had these tuned to run E85 or something.... Which, from the sounds of it, might be a good thing to try if you have E85 available locally. Or, If you want to stick with regular petrol, I would step up the air corrector jets several sizes larger, and decrease the mains, but keep in mind the air correctors have the greatest effect at the upper RPM ranges where the trouble spot seems to be. If carbs were second hand, take a good look and measurement of the jets installed. Someone may have drilled them out,     instead of buying new jets.... 

 

I'm definitely not seeing any signs of detonation on the plugs, after a power run they usually come up a nice, if a bit on the rich (sooty) side, rusty tan colour. 

 

The carbies are second hand, the guy I bought them off ran them on his 2ltr pinto engine escort, he said it got 86rwkw (115hp). He didn't run it on e85 or anything fancy, it had 32mm chokes and 145 main jets, 210 air correctors with fairly lean emulsion tubes. Haven't measured the mains or the air correctors if they're drilled out but I'd say they're untouched.

[620Turbo4X4]

You really need a magnifying glass to see any signs of detonation. Plus the soot you mention could very well be masking any metal particles from detonation. But anyways, a BP6ES would be considered a Hot plug for a "stock" L20b and a BP7ES cold, again for a stock engine. Perhaps the saving grace here is because it's running so rich. You shouldn't be seeing any color with "hot" plugs and correct A/F ratios with a modified engine... ( I would expect to see some electrode melting going on.) If it were mine I'd be trying the BP8's or a non projected B7ES, I had better results with the projected plugs as the insulator is more exposed which helped with low speed fouling and high speed overheating, but what works for me, might not be what works well for you.. At any rate, you'll need to get the carbs leaned out of all the excessive fuel, or the cold plugs will foul out rather quickly...

Have not tuned a set of dellorto's myself, but a quick google search and I found this;

http://www.aircoolednut.com/erkson/ttt/engine/carbs/dellorto.html

Which chokes are you currently running? You said they were 36mm in a previous post. 32mm chokes are too small for a 2L engine to be happy at 6K. You should be running 36's to get good power up to 6000RPM. Also, using the choke diameter X 4 = main jet size rule, 32's should be using 125-130 main jets to be in the ballpark. Not 145's. Those would be a good starting point for 36mm chokes. Air correctors should be somewhere around +50 to the mains.

 

[Stoffregen Motorsports]

I still think it's cam related. Do you know how to check the cam timing with a dial indicator?

[Knox]

Alright finally put together a little video, so hopefully it can give a better idea of what its doing:

 

 

Car was running pretty good when we did the shots, managed to wind it up to 6500rpm in second, but power was well gone after 5000rpm. Would've liked to film it at the limit in maybe a higher gear to see better where the power drops off and how the engine sound changes (you can still sort of hear when the engine stops making power and starts running rough above 5000rpm), but the road we were on was too short to do anything above 2nd/3rd gear. Also should've done a neutral free rev clip as well, but I might try and do another little vid at some point.

 

You really need a magnifying glass to see any signs of detonation. Plus the soot you mention could very well be masking any metal particles from detonation. But anyways, a BP6ES would be considered a Hot plug for a "stock" L20b and a BP7ES cold, again for a stock engine. Perhaps the saving grace here is because it's running so rich. You shouldn't be seeing any color with "hot" plugs and correct A/F ratios with a modified engine... ( I would expect to see some electrode melting going on.) If it were mine I'd be trying the BP8's or a non projected B7ES, I had better results with the projected plugs as the insulator is more exposed which helped with low speed fouling and high speed overheating, but what works for me, might not be what works well for you.. At any rate, you'll need to get the carbs leaned out of all the excessive fuel, or the cold plugs will foul out rather quickly...

Have not tuned a set of dellorto's myself, but a quick google search and I found this;

http://www.aircoolednut.com/erkson/ttt/engine/carbs/dellorto.html

Which chokes are you currently running? You said they were 36mm in a previous post. 32mm chokes are too small for a 2L engine to be happy at 6K. You should be running 36's to get good power up to 6000RPM. Also, using the choke diameter X 4 = main jet size rule, 32's should be using 125-130 main jets to be in the ballpark. Not 145's. Those would be a good starting point for 36mm chokes. Air correctors should be somewhere around +50 to the mains.

 

 

Might look into the plugs, but I don't think they're the cause of the main issue I'm having. The carbies still need some tuning, maybe playing around with different air correctors (running 210's at the moment) and emulsion tubes might help things, but the emission dellortos aren't really ideal, I'm thinking of leaning towards some dcoe 45s or maybe even an efi setup at some point. But again I don't think thats the cause of the main issue at the moment.

 

 

I still think it's cam related. Do you know how to check the cam timing with a dial indicator?

 

Never touched a dial indicator to be honest, I'm sort of considering getting a complete new setup that I know will work; cam with matching springs and lash pads, from a reputable place. I was thinking of looking at isky cams, but does anyone know some good places that do good datto stuff?