L24 lacking HP

[rayaapp2]

I have a basically stock L24, SU's, and a 6-1 header. The exhaust is to big at 2.5". I have a Delta mild cam in the engine as well set straight up with a new timing chain and timing components.

I would not normally have issues finding a problem with something like this, but you know how it is when youve smashed your head against a problem for too long and your 'fuzzy' headed.

Please give me an outsiders perspective on this.

 

I have a pertronix pointless ignition with an MSD blaster2 coil. My fuel system consists of the OE style lift pump and a Mallory 110 electric fuel pump set at 4psi. The SU's are in good shape, but without a exhaust gas analysis I do not have a concept of were I am with my AFR's. Ive checked the float bowls and Im good with where the level is set at and with 4psi of fuel pressure Im sure the fuel volume is more than adequate for the engine. The timing is set at 12*btdc.

 

The car exhibits good low end torque but a total lack of power beyond 2K rpm. Its just flat and slow. It sounds great driving down the road but just does not pull at all. I mean it revs out and I end up having to keep it in a lower gear just to stay moving. I tried adjusting my main jet nozzles to sort out any lean/rich issues and I have hit both rich and lean walls. Ive changed the spark plugs out as well to try and get some reaction out of the engine and nothing. Its almost as if Im not getting any advance though I know I am as I can see the timing go up to 28* or the cam was retarded even though I have more than quadruple checked the cam timing. This engine was recently rebuilt and I did not have an issue with the old components. The new components are basic things like timing chain kit, gaskets, etc. so Im baffled. There has to be something very simple that Ive overlooked and am now blind to.

 

Without just replacing a bunch of components Id like to come up with a strategy to diagnose this engine issue. Im pretty stuck on it being some kind of timing issue as Ive all but eliminated the fuel system from the equation.

[johnc]

I don't think its a mixture issue. It sounds like the timing is retarded or cam is too advanced. Typically the L series is a bit doggy under 4000 and then starts coming alive above that. Your distributor advance should take it to 36 at 3000 to 3500.

[WEBEZEEed]

Cyl. p.s.i. ? still got all the lobes on the cam? B T W I have 2 1/2 on my stock L24 & it runs quite well.

[rayaapp2]

I don't think its a mixture issue. It sounds like the timing is retarded or cam is too advanced. Typically the L series is a bit doggy under 4000 and then starts coming alive above that. Your distributor advance should take it to 36 at 3000 to 3500.

 

I was pulling that number off the top of my head.

Here is the specs I pulled off this distributor:

Idle @ 750rpm 12°

1350 still 12°

1500 17°

1700 22°

2000 27°

2300 33°

2600 37°

above that it stays around 37° but gets occasional flux above

 

Those were my guesses as well, but after I could find nothing wrong with the timing cam or ignition I moved on the fuel. So now Im back to timing. LOL

I guess I will pull the valve cover off again and check the cam timing. I cant conceive I looked at it that many times and somehow got it that wrong. If it were the cam timing I would suspect it to be off by less than a link but still a good bit for this much performance robbing. Im not great with setting up cams as I have only basic knowledge of cams. My guess was the cam was retarded, but I guess advanced makes more sense in this case now that I think about it. Worse comes to worse I guess I could retard the cam and see what that gets me.

 

 

 

And cylinder compression is even all across and cam lobs are in good shape.

Another bit of information I will throw out there just to muddy the water here. I started with a "C" cam in this car and it was doing the same thing with the "C" cam after the rebuild. I suspected a cam issue and went as far as trying a different cam I had around. All that changed was a bit of low end torque or so says my uncalibrated butt dyno. I cannot find the common link for some reason unless Im installing cams wrong all of a sudden.

Edited May 8, 2012 by rayaapp2

[Leon]

I don't think its a mixture issue. It sounds like the timing is retarded or cam is too advanced. Typically the L series is a bit doggy under 4000 and then starts coming alive above that. Your distributor advance should take it to 36 at 3000 to 3500.

I was thinking the exact same thing as John, your timing is way too retarded. Advance your timing to 34 or so degrees with mechanical all in. Low speed cruise and transition will be slightly weak if the vac advance is broken or disconnected.

 

BTW, 2.5" exhaust is definitely not too big. There is no such thing, take a look at the exhaust sticky. I'm running twin 2" pipes on my L24 without a hitch. That is 100% not your issue, unless someone stuffed a banana in your tailpipe.

[Tennesseejed]

Did you or someone else time the cam when you installed the new timing chain?

 

I think one link equals 20degrees on the cam sprocket.

 

If you have a mircometer, that is what I would rule out first.

[madkaw]

Do your plugs look normal-do they have any color?

Does the engine sound flat like it's running out of gas?

Adjusted nozzles to hit lean and rich walls???? This sounds beyond a nozzle adjustment.

I've got an adjustable sprocket on my L24 and minor degree changes didn't exibit the symptoms you see. I've played with as much as 6-9 degrees and the changes were noticable, but they were small.

It almost sounds like your floats are lean. That would make it flat, but it would still rev out-just no power. You could try tweeking them to high side and see what that does.

If you were off a tooth on the cam, that would be a different story. Sure you counted the links exact from sprocket to sprocket? You said the cam was installed straight up-did you degree the cam in or just set it on the first hole. My schnedier installed on the first hole showed up retarted on the degree wheel. Variances in the rocker arms will show up on the wheel. And of course-valve adjustment is crucial.

Igniton timing looks good for power. Running proper impedence coil for the pertronix?

Alternator putting out a strong 14 volts for your ignition?

Edited May 8, 2012 by madkaw

[rayaapp2]

I was thinking the exact same thing as John, your timing is way too retarded. Advance your timing to 34 or so degrees with mechanical all in. Low speed cruise and transition will be slightly weak if the vac advance is broken or disconnected.

 

BTW, 2.5" exhaust is definitely not too big. There is no such thing, take a look at the exhaust sticky. I'm running twin 2" pipes on my L24 without a hitch. That is 100% not your issue, unless someone stuffed a banana in your tailpipe.

 

 

Of course there is such a thing as too big. I do not have an open header. I have a full length 2.5" exhaust system on the car. The exhaust isnt tuned for this engine at all. Not to drag this on, I will agree its not the issue, but its almost certainly to big for a mostly stock L24. I would guess this engine would be much happier with a 2-2 1/8" system with a nice 'turbo' style muffler at full length and a stock RPM range. Between velocity drop off/lack of scavenging and skin effect in the tubing this exhaust does not match up well with the mostly stock L24 I have. Unless you want to tell me that Hondas with 3 and 4" exhaust systems on stock motors are suddenly making gobs of power. If I had more access to neat tools like a dyno and a lot of time I could make the 2.5" work and well. Between the volume in the pipe mostly because of its length there is no way Im scavenging anything during the valve events and the mass of air stagnet to the pipes surface is most likely a huge restriction to flow. Id bet if I cut it off within 1' of the collector Id pickup a significant amount of power. Id also expect the same thing from a smaller tube diameter full length, but it would be a trial of test fitting sizes with mufflers to get it correct. I dont have dyno results to back it up, but I have played with exhaust systems on a few L series. I will say this, Id love to be wrong. I like the sound it makes.

 

BTW Plugs look good with good tanning, but not overly rich.

 

I built the engine. The timing chain assembly was installed by me.

 

I installed the cam straight up using the stock timing marks not with a degree wheel on the rocker and that may be my issue. The marks were dead on for once and I verified it after 4 rotations of the crank the first time and Ive checked it multiple times since then. I do not have a cam card for this cam. I wonder if its cut to be setup retarded. I will give it a shot when I have some free time to find out. That is DEFINATELY a possibility I completely looked over.

I believe the blaster 2 coil is setup correctly for the pertronix ignition, but Ill double check. It hasnt been an issue and Ive driven the car for several years before this with this ignition setup.

 

Thanks guys

[madkaw]

Ray

What part did you think you might have overlooked. Not trying to be a jerk, but your response was a bit convoluted:)

 

Even though my cam set up retarded- straight up- it was still plenty strong.

Not sure how you did a degree wheel on the rocker??

 

By the way, I run dual 2" and dynoed 150/150 running too rich

Edited May 8, 2012 by madkaw

[Leon]

Of course there is such a thing as too big. I do not have an open header. I have a full length 2.5" exhaust system on the car. The exhaust isnt tuned for this engine at all. Not to drag this on, I will agree its not the issue, but its almost certainly to big for a mostly stock L24. I would guess this engine would be much happier with a 2-2 1/8" system with a nice 'turbo' style muffler at full length and a stock RPM range. Between velocity drop off/lack of scavenging and skin effect in the tubing this exhaust does not match up well with the mostly stock L24 I have. Unless you want to tell me that Hondas with 3 and 4" exhaust systems on stock motors are suddenly making gobs of power. If I had more access to neat tools like a dyno and a lot of time I could make the 2.5" work and well. Between the volume in the pipe mostly because of its length there is no way Im scavenging anything during the valve events and the mass of air stagnet to the pipes surface is most likely a huge restriction to flow. Id bet if I cut it off within 1' of the collector Id pickup a significant amount of power. Id also expect the same thing from a smaller tube diameter full length, but it would be a trial of test fitting sizes with mufflers to get it correct. I dont have dyno results to back it up, but I have played with exhaust systems on a few L series. I will say this, Id love to be wrong. I like the sound it makes.

 

BTW Plugs look good with good tanning, but not overly rich.

 

I built the engine. The timing chain assembly was installed by me.

 

I installed the cam straight up using the stock timing marks not with a degree wheel on the rocker and that may be my issue. The marks were dead on for once and I verified it after 4 rotations of the crank the first time and Ive checked it multiple times since then. I do not have a cam card for this cam. I wonder if its cut to be setup retarded. I will give it a shot when I have some free time to find out. That is DEFINATELY a possibility I completely looked over.

I believe the blaster 2 coil is setup correctly for the pertronix ignition, but Ill double check. It hasnt been an issue and Ive driven the car for several years before this with this ignition setup.

 

Thanks guys

I don't want to drag this on either, hence why I posted the link. I'm assuming you haven't had a chance to really look it over.

 

In a nutshell, the long pipe to the back of the car has nothing to do with scavenging, that's the job of the header and collector. You want the pipe to be as big as possible as to not create more losses, post collector. Therefore, the bigger the better. A smaller pipe will not make for less losses. You make a lot of assumptions about exhaust dynamics that are just not true (explained in sticky). I don't want to take this off track, and we both agree that this is not your problem.

 

As far as your running issue goes, start simple. Check the charging system and make sure it kicks out the proper amount of voltage. Then check each ignition component for proper operation, checking timing is the last thing you'll do here. After that, and maybe a valve adjustment, go to fuel and carburation. Cam timing would have to be way advanced to cause such a seemingly huge hit on performance. Retarding the cam will shift your power curve to higher rpm.

 

Also, make sure to check throttle linkage and the pedal stop.

[rayaapp2]

Ray

What part did you think you might have overlooked. Not trying to be a jerk, but your response was a bit convoluted:)

 

Even though my cam set up retarded- straight up- it was still plenty strong.

Not sure how you did a degree wheel on the rocker??

 

By the way, I run dual 2" and dynoed 150/150 running too rich

 

To be honest I have no idea. Ive been just dealing with the problem for so long even a break from working on it has not allowed me any insight into the problem and I do diagnosis for a living. My only guess is that its something simple that Ive overlooked as that tends to be my kind of mistakes in the past.

 

I was in a rush when I wrote that. I did not use a degree wheel with a dial gauge on the rocker arm to set the cam up. I do no have a cam card for this cam. As I said I tend to miss the simple things like making sure this cam is setup at zero. I have not had the chance yet to even check on it. I set the cam up using the stock markers like an idiot.

 

Yes Leon I did follow that thread long ago and I did re-read it. I still stand by my statement. To my knowledge the volume in the pipe is the restriction in more than one way. There is a reason behind twice pipes out there. I know dual 2" works well. 50mm twice pipes work really well on a stock L24. Much better than 2.5" single... and its not because its 'bigger'. I guess I should never have used to "big" as my description. My biggest problem with my exhaust is that its a one size fits all 6-2-1 header with almost no length secondaries and the entire 2.5" exhaust system is really the collector. At best all it is, is a silencer.

[Leon]

Yes Leon I did follow that thread long ago and I did re-read it. I still stand by my statement. To my knowledge the volume in the pipe is the restriction in more than one way. There is a reason behind twice pipes out there. I know dual 2" works well. 50mm twice pipes work really well on a stock L24. Much better than 2.5" single... and its not because its 'bigger'. I guess I should never have used to "big" as my description. My biggest problem with my exhaust is that its a one size fits all 6-2-1 header with almost no length secondaries and the entire 2.5" exhaust system is really the collector. At best all it is, is a silencer.

"Volume" is not a restriction. I could see volume as a capacitance, but not resistance. A dual 2" pipe is close in area (and hence volume) to a single 3". I'd argue that dual 2" pipes are worse than a single 3" since there is more friction when using a smaller pipe. I did the twin 2" because I wanted the sound of twice pipes. It may seem counter-intuitive but that's how it works, if you follow what was presented in the sticky.

 

I actually dyno'd my Z with a single 2.25" or 2.5" exhaust but have yet to dyno with the twice pipes. Unfortunately, those results are not going to be conclusive since I installed my header when I did the twice pipes.

[rayaapp2]

Well, I played with the car a bit more. The cam is definitely dialed in as good as I can get it with my current setup. ~1* retard.

After playing with the ign timing I found that the car picked up a small amount of top end by setting the base timing at 15* BTDC. I also found that my stock balancer was shifted a few degrees. I replaced it with an L28 balancer and timing mark indicator which from what I can tell shifted TDC to the old 5ATDC mark which is why I used the corresponding timing mark indicator. I verified TDC with an old spark plug tapped out and a 5/16" rod fitted with a dial indicator. Any more ign timing and the car exhibits other drivability issues. I did try retarding the cam some more, but I have a stock cam gear so Im somewhat limited in my adjustments and the result was just backfiring through the carb at around 4K rpm and power again dropped off worse than the current cam setting.

 

I just had one of my other cars toss a nice set of issues at me as well which is not cool.

I thought it developed an exhaust leak on my 150mile trip back from sacramento. Its an original 260Z with the stock carbs and EGR. I found that the flange to head pipe gasket was blown out, and the EGR tube finally gave up and cracked right in half. So I pulled everything off, ordered my carb rebuild kits from MSA, and put it all back together. The car wont restart due to something I did(most likely the replacement of the old vacuum lines and such as well as the fact that I installed an early non-egr balance tube on these carbs), but during crank I can still hear an exhaust leak. So I know that my exhaust is not leaking. Im betting after reading through the recent post by johnc head gasket burn through and remembering what that sounds like that Ive lost compression in #3 or #4 and the head gasket has blow out under the exhaust manifold... and I had just listed the car on CL for sale, sigh.

 

So none of my Z cars are road worthy at the moment. 1971 240Z current post issue, 1972 240Z sitting for over a year with a multiple minor issues that need dealt with, 1974 260Z with blown head gasket, and 1974 260Z rb25 hit while parked & going to court with the insurance company. Murphy is an ice-hole and he doesnt like me or Datsuns.

 

BTW, I installed a straight through 18" long by 2.5" ID anti-drone pipe in the center of the 240Z 2.5" exhaust. I have a Thrush 2.5" "Turbo" muffler at the end. It sounds much mellower now and gives a crisp note in the upper rpm range. The center 'anti-drone' muffler was from a mid 90's v6 camry I believe or possibly a lexus es300(same thing). The MSA 2.5" I have was either not assembled correctly by the P.O. or like the twice pipes I have from MSA were not designed well as it does not give you much clearance to install things like mufflers. I had to scrounge around my exhaust pile for 2.5" mandel piping with the proper bends to locate that camry anti-drone muffler in the center of the trans tunnel under the driveshaft and again to the left to clear the differential cross members.

 

Ray

Edited May 20, 2012 by rayaapp2

[madkaw]

I guess I am still confused on how you set up or dial in a cam without a card?

 

What numbers are you referencing?

 

I wouldn't even know where to begin without the card in my hand. Any numbers in a FSM for a stock cam wouldn't work for an after market cam. Most cams, if not all that are sold are usually dialed in using measuremnts based on .050 lift on the valve. Nissan used an arbitrary number like .020 or .025 lift to dial in there cams in any published numbers. I remember reading this from a Racer Brown article.

 

As far as the statement about the L24 not coming on until 4k rpm, My engine feels very strong(torquey) starting at 2k. In fact I am always impressed at the amount of low end grunt the little booger has. Maybe I haven't driven enough Z's to make that statement, but I feel power is very even across the rpm band-and the dyno showed that.

 

Anyway, I realize it's frustating, hope you find something.

[Tony D]

You use a dial indicator and profile the cam. From there it's veritable child's play to make your own cam card detailing opening and closing events, determining lobe separation angle, etc...

From there there are general rules of thumb regarding opening events of the intake valve, and you can go from there.

 

As for the exhaust -- ray if it's the "new" exhaust with three bolt flanges on it, that is exactly right: t hugs one side of the tunnel. The older exhaust with slip fit pipes apparently was the source of complaints, so they "idiot proofed"" it with the flanges and a relocation of the pipe routing.

 

I no longer use that exhaust, I replicate the earlier one with mandrel bends out of bends and straight tubing now.

Edited May 21, 2012 by Tony D

[madkaw]

Maybe Childs play for Tony D, but for an average mechanic - very average like me, basic valve geometry is beyond my ability. Not that I don't understand that timing of the events is crucial, but to dial in a cam without specific details to go by- no way.

Maybe Ray can do that and I am under estimating his ability, just thought I would throw it out there.

[BlueStag]

Just a guess, and certainly I have no reason to say that it means anything, but when I got my car running last summer, it would randomly bog down.

 

The front fuel float was sticking closed. Are your needles working? Are your floats working? Easy enough to check.

[Tony D]

I can't go to the first page to see what can he's using or degreeing, but simply reading the dial indicator and noting vale lift is pretty basic skillset.

Same one you use to determine TDC.

 

Understand something: this isn't a DOHC so there is ONE event you can set. Intake opening or intake closing. Reading the indicator tells you this point. Make that point according to the stock chart in the FSM... Or some other spec. Most cam manufacturers post the events online. There's your reference...

[madkaw]

After re reading the thread, it's hard to believe you have had the same issue with two different cams. I'm with the float issue. Insufficient fuel in the bowls with show up under heavy loading, but otherwise drive decent. Maybe time to revisit the floats and bump them up a bit and check out the needles and seat closely

[BlueStag]

After re reading the thread, it's hard to believe you have had the same issue with two different cams. I'm with the float issue. Insufficient fuel in the bowls with show up under heavy loading, but otherwise drive decent. Maybe time to revisit the floats and bump them up a bit and check out the needles and seat closely

 

I suspect those things can go wrong pretty easily. I want to buy the sight glass concept from ZTherapy to see how mine are doing.