L28 Dyno Results - Bad Cam Timing?

[ThaPimpShrimp]

I got the chance to put my 240z and new motor on a dyno (Free of charge!) today, and got some bad news. I peaked at 148ft/lbs and 124hp to the wheels. Both sad and odd numbers right? Well, the guy let me check my AFR's on the second run, and lo and behold they lean out dangerously after 3500 or so.

 

This is my first build/swap, and I've never dyno'd a vehicle before, so I'm sure some of you will have a bit more expertise when reading these graphs so I'd love some input. It's looking to me like my cam timing is way off, I can't really think of any other way to explain what's going on here. I didn't set the cam timing myself, I had someone who knows what he's doing do that, but it's possible he made a mistake.

 

Engine Specs: F54 Block, P90A, Stage III Isky Cam (.490 Lift, 242* @ .050), flat top pistons, ZTherapy SU's (SM needles) tuned pretty well which you can see initially on the AFR chart, E12-80, timing set properly, I believe 14* initial to a total of 37*, headers, 2.5" exhaust, etc.

 

So with that said, take a look and let me know what you think. Hopefully I'll be able to fix this and pick up some major power. Motor feels super strong right up till about 4,000 so I'm excited what it'll do when setup and tuned right.

[Leon]

I wouldn't run it WOT above 3500RPM until this is fixed. Seems like a float valve or fuel pump issue. If you can't keep the floats full, you'll eventually run lean which seems to be what's happening here.

[ThaPimpShrimp]

I wouldn't run it WOT above 3500RPM until this is fixed. Seems like a float valve or fuel pump issue. If you can't keep the floats full, you'll eventually run lean which seems to be what's happening here.

 

I considered fuel pump, but discounted it because I figured through one run it shouldn't be emptying the float bowl.. Also what could be wrong with the float bowl that could cause this, just the floats being set wrong?

 

And yeah, definitely won't be hitting the throttle anymore, I'm glad I discovered this now before I blew the engine.

[madkaw]

Timing numbers don't add up. E12-80 usually is 17 degrees worth of mechanical, so you would only be at 31 total.

[ThaPimpShrimp]

Timing numbers don't add up. E12-80 usually is 17 degrees worth of mechanical, so you would only be at 31 total.

 

Apologies, I took a look at my paperwork for the timing curve (Had a guy rebuild and change the distributor curve a bit) and I believe I have it setup so it goes from about 18-19* to 35-36*. It's been a couple months since I set it, so I couldn't tell you exactly. When I get to solving this problem I'll definitely take a look at timing, but honestly that is the part I'm least worried about and wouldn't cause a super lean running condition anyway.

[NewZed]

Power comes from the fuel.  No fuel, no power.  You actually start going lean at 3500 RPM, and it's a straight line up and leaner.  Pretty dramatic.

 

There are two tests for the mechanical pump in the FSM.  Pressure and capacity.  You can do the same with an electric pump.

[ThaPimpShrimp]

Power comes from the fuel.  No fuel, no power.  You actually start going lean at 3500 RPM, and it's a straight line up and leaner.  Pretty dramatic.

 

There are two tests for the mechanical pump in the FSM.  Pressure and capacity.  You can do the same with an electric pump.

 

Yeah it's bad. I'll take a look in the FSM for that test, thanks!

[johnc]

Float levels are too low.  Way too low. 

[ThaPimpShrimp]

Float levels are too low.  Way too low. 

 

I never have checked the float levels in these carbs. I bought them new from ZTherapy and just assumed that they were good to go.. because that's what I paid them for. Hopefully that's not my mistake.

[Xnke]

Not enough compression for that cam, either...flat tops and an uncut P90A are 8.8:1, and that cam will want 10:1+ for best performance. You're right at the bottom edge of the compression ratio range, it'll run and can probably make good power, but there is still cheap power to be had in compression.

 

Set the intake valve closing event to 76*ABDC and try it again, that cam should start pulling from about 3500 and pull cleanly to 8000, making peak power somewhere around 7000RPM or even a little higher...will depend heavily on your intake runner diameter and your fueling.

[ThaPimpShrimp]

Not enough compression for that cam, either...flat tops and an uncut P90A are 8.8:1, and that cam will want 10:1+ for best performance. You're right at the bottom edge of the compression ratio range, it'll run and can probably make good power, but there is still cheap power to be had in compression.

 

Set the intake valve closing event to 76*ABDC and try it again, that cam should start pulling from about 3500 and pull cleanly to 8000, making peak power somewhere around 7000RPM or even a little higher...will depend heavily on your intake runner diameter and your fueling.

 

Raising compression was something I struggled with, and was eventually convinced not to do. I have been thinking about removing the head and having it shaved a bit though, luckily doing that isn't a super tough job. I'd just need to find shims for everything.

 

Thanks for the tips.

[Xnke]

With that much cam, you should be bleeding off enough compression to not have preignition issues with proper fueling. But KEEP YOUR EARS ON! Check your plugs regularly for detonation signs until you're convinced it's safe!

[ThaPimpShrimp]

With that much cam, you should be bleeding off enough compression to not have preignition issues with proper fueling. But KEEP YOUR EARS ON! Check your plugs regularly for detonation signs until you're convinced it's safe!

 

Most definitely. For now I'll get this fuel issue solved, then we'll see about upping that compression!

[JMortensen]

Don't up the compression on that cam. That cam really isn't that big. I ran a similar .490/280 cam on a stock short block with 8.3:1 compression and everyone was telling me it would be a dog, no low end, etc. The low end loss wasn't even noticeable, but it was MUCH better on the top end. I then moved to a higher compression bottom end at about 11:1 and had massive pinging and needed 96 octane in order to run the full amount of advance that I wanted (mid 30's). 

 

I'd go after the fuel issues first. FWIW, I know a couple people who put together motors with that cam that were sorely disappointed with the results. One guy built a pretty stout engine and ended up with 180 whp on triples. Kinda sad. Only guy I've seen have good results with it, and they were pretty damn good, was MONZTER. He figured out a way to get something out of it, and that made me wonder what he could have done with a better cam...

[ThaPimpShrimp]

Don't up the compression on that cam. That cam really isn't that big. I ran a similar .490/280 cam on a stock short block with 8.3:1 compression and everyone was telling me it would be a dog, no low end, etc. The low end loss wasn't even noticeable, but it was MUCH better on the top end. I then moved to a higher compression bottom end at about 11:1 and had massive pinging and needed 96 octane in order to run the full amount of advance that I wanted (mid 30's). 

 

I'd go after the fuel issues first. FWIW, I know a couple people who put together motors with that cam that were sorely disappointed with the results. One guy built a pretty stout engine and ended up with 180 whp on triples. Kinda sad. Only guy I've seen have good results with it, and they were pretty damn good, was MONZTER. He figured out a way to get something out of it, and that made me wonder what he could have done with a better cam...

 

Well, this certainly won't be my last L series build, so what's your opinion on the best cams/grinds/etc. I built this engine pretty mildly and I got a few recommendations for Isky so I went with him, good price and a nice guy to deal with. In the future I'd like to do a build around Rebello's 63di, I know a guy with that cam in his motor (Similar build to this but with higher compression and more head work) and it's a monster.

[madkaw]

Get the fuel issue fixed first . Like said- no fuel- no power .

CR isn't too bad and it should make more power with it like it is.

Tune it !!!

[JMortensen]

Well, this certainly won't be my last L series build, so what's your opinion on the best cams/grinds/etc. I built this engine pretty mildly and I got a few recommendations for Isky so I went with him, good price and a nice guy to deal with. In the future I'd like to do a build around Rebello's 63di, I know a guy with that cam in his motor (Similar build to this but with higher compression and more head work) and it's a monster.

Ya know, it might help if I correctly read what you wrote. You did the ISKY cam, not the Schneider cam that I've seen the lackluster results with. I'd keep what you have, tune it, and see what happens. Not a fan of the Schneider cam. Don't know much about the ISKY one, but my impression is that ISKY does a pretty good job on their Datsun cams. Rebello obviously knows his stuff. BRAAP has a favorite Rebello cam, want to say it has .520 lift. That was the one that I was eyeing before I decided to go V8.

[bradyzq]

I agree with Jon above. Don't give up on the cam til the car's running right.

 

What transmission and diff do you have? And what gear did you run in on the dyno? I'm asking because I can't come up with 4.30 overall ratio no matter which diff gear and tranny I mix and match.

 

The Dynapack dyno measures torque at the hubs then divides it by the overall gear ratio the operator types in, in order to come up with the torque on the graph. It also uses the same ratio that was typed in to calculate engine RPM. It multplies the measured hub RPM by the 4.3 factor.

 

So, if the ratio is wrong, both RPM and torque numbers will be wrong. Peak power will be correct, but at the wrong RPM.

 

I had an L28 on my dyno awhile ago that had a simillar problem with torque dropping off. But he had a stock cam and advanced cam timing, with the resulting pinging problem.

 

Which makes me wonder: did you hear any pinging during the dyno pulls?

[ThaPimpShrimp]

What transmission and diff do you have? And what gear did you run in on the dyno? I'm asking because I can't come up with 4.30 overall ratio no matter which diff gear and tranny I mix and match.

 

The Dynapack dyno measures torque at the hubs then divides it by the overall gear ratio the operator types in, in order to come up with the torque on the graph. It also uses the same ratio that was typed in to calculate engine RPM. It multplies the measured hub RPM by the 4.3 factor.

 

So, if the ratio is wrong, both RPM and torque numbers will be wrong. Peak power will be correct, but at the wrong RPM.

 

I had an L28 on my dyno awhile ago that had a simillar problem with torque dropping off. But he had a stock cam and advanced cam timing, with the resulting pinging problem.

 

Which makes me wonder: did you hear any pinging during the dyno pulls?

 

To be honest, I'm not 100% sure on the diff or transmission. If the PO is to be believed, the transmission is the earlier 280z 5 speed, and the diff should be a 3.36 R180. I also don't know what gear he ran it in, this was sort of a freebie quick event for people who came to the meet, since my numbers were so off he quickly checked the AFR's for me as a favor. I'm not so worried about the numbers, more the AFR. This solidified what I thought I had been feeling since installing the engine, and have been trying to fix through tuning alone.

 

No pinging while on the dyno. The top end didn't sound good, but I'd say that's due to it running so lean.

[Xnke]

The big thing on the L28 is timing advance, and compression/cam comes into that. With that Isky grind, you should easily be able to run 10:1 compression if you set the valve events properly.

 

I ran 9.7:1 with a smaller cam for several years at 36* advance and had zero pinging issues on 87 octane. Set your intake valve closing event properly, don't run it lean, and make sure you use the correct plug heat range, and you will be rewarded with a ping free engine. Cylinder pressure makes power...too much cylinder pressure at low rpms results in pinging, and too much heat in the chamber makes it worse and even more damaging. Manage cylinder pressure to make power without pinging.