Turbocharging and Knock problems

[HowlerMonkey]

I drove my turbocharged L24E for 50,000 miles and it did the same thing.

 

Does your car have the N47 head?

 

Does your setup use the trigger straight from the pickup coil or does it pick up the signal from the ignition module or are you using something other than the distributor for crank reference?

[Robert]

Put the damn iat on there. If you're to lazy to do that that than your to lazy for anything.

 

Seriously dude you cant take advice and say that's not it if you have not tried it. After a few hard pulls under hood temps probably just increased 50 degrees or more.

 

 

I said maybee, and I stick by that. But again, I dont think its that easy, just speeking from experience, 2 hard pulls with an intercooler rearly increases temps by much more then 1-5 degrees, of which pulling 1 degree of ignition timing or so should fix it, and it DOES NOT. And it seriously sounds like the pistons are banging the asphalt, worst knocking ive heard since.. Well, the last time we turboed an L engine actually Must have been the same thing there.. These engines must be indestructable..

 

Oh, and I wont tune it another second until I get a water wetter and higher pressure in there.. Im convinced this has to do with the #5 hot spot, or possibly a spark plug going hot (dont think so).. While at it, Ill connect the IAT, Ive just waited for the bloody connector to come in my mailbox.. Slow progress though, so much to do, and so little time

[Robert]

I drove my turbocharged L24E for 50,000 miles and it did the same thing.

 

Does your car have the N47 head?

 

Does your setup use the trigger straight from the pickup coil or does it pick up the signal from the ignition module or are you using something other than the distributor for crank reference?

 

 

Hi!

 

I think these engines are indestructable, Ive never seen a engine hanle as much Knock as the previous L24E we turbocharged..

 

I have a N47. I can get my hands on a N42, but I really enjoy the bottom end pull of my engine, so I wont go there. I suppose thats what you use as well?

 

I use a 36-1 trigger wheel on the crank wheel, with a Megasquirt controlling ignition timing and fuel injection. I use the dizzy for the moment, but Im planing to install a wasted spark system in time using SR20DET CoilOnPlug. The COP system should allow about .6mm spark plug gaps, 3 times what I use today, resulting in a much better combustion.

 

Do you use fuel only, or did you manage the "impossible" and trigger of the stock VR sensor?

[Xnke]

Robert, You really need to take some of this advice to heart, rather than blowing it off.

 

First, get your IAT hooked up and working, you may be surprised at what is going on. More data is better, when it comes to tuning. You already know that.

 

Get a laser thermometer and measure spark plug temps, that'll tell you if you have one getting hot. just point it at the base of the plug. Check exhaust temps too. These buggers can be fun too, point it at someones skin and piss them off, some people get noticeably warmer, it's fun!

 

If it was me, I'd drill the head on ANY turbo L for the extra coolant ports at 4, 5, and 6.

[Six_Shooter]

Intake temps can rise a LOT more than 5 degrees.

 

During some short runs I've made I have seen the intake temps rise from about 100*F to over 150*F, then return to around 110*F, that one run.

On a particulary hot day a few weeks ago I saw intake temps over 180*F!

 

I've seen one engine that is is possibly more indestructable than the L-series, and that's the GM 60* V6 (with the large journals). I had one that I built from a bunch of parts kicking around for my 1985 GMC Jimmy, and the knock would get so bad (too small of an injector and not enough control of tuning), that the truck would literally fall on it's face because of all the timing being pulled by the ECM, then lift the front end again when timing was put back in. I tore it apart after a few years of abuse, and the pistons still looked like new. Crabon on them obviously, but no indications of pre-ignition or detonation!

 

You'll be surprised just how much can change is a short amount of time, when it comes to temperature and related parameters.

[yetterben]

You might also have excessive carbon buildup in that cyl. Pull plug and look in there. If you have knock you are gonna see it on the piston dome. Look for irregularities between cyl. What rpm is this happening at.

[Robert]

The knock comes mid range, but probalby at any RPM with boost.

 

I live in a cold place, 70F out temperatures. The highest EVER datalogged IAT temp Ive seen here is ~95F (35C). Big intercoolers that get air is the best

 

Btw a water injection system is currently being assembled as another anti knock solution.

 

Like stated before, Ill check back in when Ive tried the cap and water wetter. Shure, IAT will be connected, Ill datalog a bunch of gears for you.

[yetterben]

Is your fuel pump up to the task? and are you sure!

[kolonelklink87]

Put the damn iat on there. If you're to lazy to do that that than your to lazy for anything.

 

...lol...

 

also, i'm not fully up to spec on these engines but isnt the compression on an l24E something like 9:1???

 

if that is the case, no matter your cooling, detonation control is going to be an issue. it seems like you're force-feeding this thing a diet of steak, eggs and steriods... cardiac arrest?:icon15:

[Noddle]

also, i'm not fully up to spec on these engines but isnt the compression on an l24E something like 9:1???

 

Depends what pistons it running, my L24 (240K, and my R30 skyline) both has dished pistons as standard, and with the N47 head (small chamber), it's about 8.3:1

 

Nigel

[Six_Shooter]

...lol...

 

also, i'm not fully up to spec on these engines but isnt the compression on an l24E something like 9:1???

 

if that is the case, no matter your cooling, detonation control is going to be an issue. it seems like you're force-feeding this thing a diet of steak, eggs and steriods... cardiac arrest?:icon15:

 

Stop reading turbocharging info from the '60s.

 

9:1 SCR is not very high at all, even when it comes to turbocharging, these older L-series engines. I'm currently running 11 PSIG at max boost non-intercooled, on an 8.8:1 L28, and no "problems" with knock. The only time I seem to get any knock right now is when I A) turn up the boost to 14 PSIG (Highest I've ran so far), get the intake temps up real hot, 150*F+ (directly related to A)), even then I only get a couple degrees and C) When I get real agressive with the tune, to try and squeeze more out of it.

 

With the better controls (EFI) available today, the engines can be run closer to the "edge", witout ever going over, with better driveability, and manners than ever before.

[Robert]

Is your fuel pump up to the task? and are you sure!

 

AFs are down to low 12s and 11s without maxing the injectors out, so YES!

[Robert]

...lol...

 

also, i'm not fully up to spec on these engines but isnt the compression on an l24E something like 9:1???

 

if that is the case, no matter your cooling, detonation control is going to be an issue. it seems like you're force-feeding this thing a diet of steak, eggs and steriods... cardiac arrest?:icon15:

 

Nope. If we go extreme, you probably cant run a 600bhp engine with 40PSI, but Im tempted to try close to 30 on this ~8.5:1 if I can fix my cooling.

[wigenOut-S30]

AFs are down to low 12s and 11s without maxing the injectors out, so YES!

 

If you are running 23psi and your AFRs are 12's thats just too lean for the L motor. I would maybe try backing the boost down to 20 and riching your fuel up to like 11.5- 11.7. See if that cure's your pinging problem.

[Robert]

If you are running 23psi and your AFRs are 12's thats just too lean for the L motor. I would maybe try backing the boost down to 20 and riching your fuel up to like 11.5- 11.7. See if that cure's your pinging problem.

 

First off, as said before, the problem is not there when the internals are cool, first after some hard runs.

 

AF VS Knock depends greatly on spark advance. Less spark and less fuel can give the same power.

 

Knock is simply that the "peak" of the detonation comes before TDC. A lean mixture burns faster, so you would need less spark. Add more fuel, and you can add more spark. If it gives more power has been discussed for ages. I think so though.

 

Anyways, hope you see my point. Theres no "the rich or lean for that engine". I cant pull any boost, but I can add fuel. AF goal table is added as an attatchment. As you can see, Im trying to get 11.5, Im just not there yet, cause Ive only had a few miles of tuning before this knock problem came to my attention. If you read the whole thread, youll understand more.

 

Also added is my spark table. You may review it, but again, thats probably not where the problems are though, cause then the knock would be instant, not only after emptying one or two gears, and even if it was after emptying some gears, and the IAT went sky high, it WOULD NOT be as extreme (it sounds like the pistons hit the ground!! Worst Ive ever heard!)

 

Edit:

 

As you can see from the AF table, the AFs are richening up more and more from 12-11.5 from 180 to 260KPA (~12-28 PSI). This should be good. IAT retard will be enabled if needed. Ill start looking at my problems today, and see where I end up.

[kiwi303]

More advanced:

RD28 water pump with large impeller

LD28 Pump, I don't know if the RD series pump works, but in the #5 cooling thread it discusses the LD Pump, and they are scarce as hens' teeth

 

 

Really? I must have missed that in the #5 thread, through I admit I was scanning rather than studying it.

 

What specificly is rare about the LD28 pump? there were LD28 Maximas in the US market so surely pumps would be around, or is it a low-production numbers specialist application pump for something other than a Maxima that is fitted with an LD28?

 

A quick check of one supplier here in NZ shows 2 pumps available.

 

early:

Water Pump Nissan LD28 Z24 Pre-10/1986

66mm from base to top of flange WP754 FP1502 GWN-05A

 

Late:

Water Pump Nissan LD28 10/1984-86 Laurel

60mm from base to top of flange

[yetterben]

That is lean as ♥♥♥♥ but whatever not my ride. good luck.

[kolonelklink87]

First off, as said before, the problem is not there when the internals are cool, first after some hard runs.

 

AF VS Knock depends greatly on spark advance. Less spark and less fuel can give the same power.

 

Knock is simply that the "peak" of the detonation comes before TDC. A lean mixture burns faster, so you would need less spark. Add more fuel, and you can add more spark. If it gives more power has been discussed for ages. I think so though.

 

I don't see spark advance in being a magic bullet for power production - more advance does not equal more power. Greater advance is a band-aid effort for poor head design (i think i may have quoted someone there?). Greater advance is required to compensate for slow flamefront travel due to low swirl and gas velocity within the combustion chamber during the compression stroke. this is not news.

There is of course a point where ignition timing is optimised to capture as much useful mechanical energy during the power stroke and minimal mechanical energy during the compression and exaust strokes - you can see that advancing beyound this point moves your combustion phase too much into the compression stroke. Thus to make ideal power you ride the "knife-edge" between optimal mechanical(gas expansion) energy in both strokes.

 

To counteract this effectively employing modern EFI will help - greater control of AF is well beyond the capability of carb systems. Additionally, adding fuel has the added benifit of lowering the gas temperature inside the cylinders as the entropy of the intake gas is employed in vapourisation of fuel (yes fuel absorbs heat).

this will work to a point. However, ideally the better solution would be to use better quality head work on combustion chambers to improve the swirl in the chamber without adding extra temperature - big power/big boost means big dollars and big headwork. Have you considered ceramic coated chambers?- these would also assist with reducing heat dissapation into the cylinder head and the thus #5 problem.

Additionally, while you're at it you might want to consider some port work? greater manifold boost is required to push more air through tiny ports esp at higher RPM. Your turbo works harder and pushes less air when working against a high pressure differential - also contributing to exaust back pressure. If you increase the volumetric efficiency (filling) of you cylinders you negate the need for higher "boost" while still pushing the same amount of air more efficiently. remember - more boost in the manifold doesnt translate directly to more air in the cylinders. The greater component of laminar flow also means less gass is in contact wiht the port walls for less time - decreasing the temperature of the gas as it enters the cylinder (some people explore ceramic coating ports as well... i dont know about this one).

 

I think your explaintion of knock is perhaps a bit oversimplified... there are numerous factors relating to how the gases behave wihtin the combustion chamber and the formation of flame fronts which will result in "knock". Additionally, if hot-spots are your concern perhaps preignition may also be a contributory. Cooling would be a massive help in this instance - as would the removal of hot spot susceptable regions in the head, smoothing of areas of high friction and surface area which become flash-points.

Yes a lean-burn does so faster, however it is also more susceptable to preignition and irregular flame front formation than a richer slow-burn.

 

The point i guess that i'm trying to convey here is that there are numerous factors at play when trying to control ideal combustion. I'm sure you can tell I have some reservations about running massive boost on a stocker engine. Yes the L is versatile and impressive, but it isnt magical. A conglomerate of factors are contributing here and I think if you work at each little bit you may find the results more effective than a single magic bullet solution.

 

However, It appears that you have already decided how and what you want to do before asking advice (that being the case why not just read the sticky and not ask?).

 

There is another thread titled "the battle against detonation" where some of these factors are discussed at length (among many other threads). As well theres that old saying that always pops up around here about cheap vs power vs relability (pick two!).

 

Best of luck

Pete