Cam and Ignition timing issues?

[acador]

I having a few issues with my freshly built L28 that I would like to get some opinions on. My setup is a 240z with a stock 90k mile F54 block, cleaned up P79, Isky 480lift/280duration regrind, round-top SUs, header, E12-80 ZX dizzy (mechanical advance only) with a 5speed and 4.11s out back. The carbs are balanced and my wideband says the A/F idles at 11, cruses around 14, and is low 12s at full throttle. The car runs great but I am getting some unexpected results.

1st oddity - According to my Gtech and seat dyno, the car is making max power at 5200rpm. 5200-6500 is flat and drops off a bit. The advertised cam power band is 2500-6500 so I expected the peak power to be closer to 6k.

2nd oddity- My base ignition timing is as far as I can twist it at around 25 degrees and it doesn’t ping a bit. I know the mechanical advance is working because I can see it advance with the light, although I’m not sure how much. The vacuum advance is blown and not connected.

I suspect that my cam timing may not be ideal. I placed the reground stock cam on the #2 sprocket position per the recommendation of an experienced Z engine builder. His logic was that 90k mile stretch should go on number 2. Could my cam be too advanced/retarded causing the lower than expected power band? Could that also cause the extreme base ignition timing? If so, what direction should I move the cam in?

[ozconnection]

I having a few issues with my freshly built L28 that I would like to get some opinions on. My setup is a 240z with a stock 90k mile F54 block, cleaned up P79, Isky 480lift/280duration regrind, round-top SUs, header, E12-80 ZX dizzy (mechanical advance only) with a 5speed and 4.11s out back. The carbs are balanced and my wideband says the A/F idles at 11, cruses around 14, and is low 12s at full throttle. The car runs great but I am getting some unexpected results.

1st oddity - According to my Gtech and seat dyno, the car is making max power at 5200rpm. 5200-6500 is flat and drops off a bit. The advertised cam power band is 2500-6500 so I expected the peak power to be closer to 6k.

2nd oddity- My base ignition timing is as far as I can twist it at around 25 degrees and it doesn’t ping a bit. I know the mechanical advance is working because I can see it advance with the light, although I’m not sure how much. The vacuum advance is blown and not connected.

I suspect that my cam timing may not be ideal. I placed the reground stock cam on the #2 sprocket position per the recommendation of an experienced Z engine builder. His logic was that 90k mile stretch should go on number 2. Could my cam be too advanced/retarded causing the lower than expected power band? Could that also cause the extreme base ignition timing? If so, what direction should I move the cam in?

Fresh build with 90K? Huh?? Do you mean just the head has been freshened up? Did you talk to the Z mechanic after the instal to ask him what your asking here? What did he say? Did he suggest a new timing chain? Does your head have new valve springs?

Sounds like a nice combination of parts. If you put all this together yourself, then you should know that you can't advance your timing that far and expect good results. Bang it up to 30 degrees mate, if 25 is good, more is better right?....WRONG! Total mechanical advance for your combination if the compression is stockish and the fuel is the best from the gas station is around 35 degrees. With 25 degrees static, you'll be well over this. Try 15.

I can see that you have a wide band. Now spend some more and get a decent timing light like a Innova professional unit that will advise what your timing is versus engine revs on the guns LCD display.

New cam? Should've been supplied with a cam card. Who did the instal? Do you have a multiholed cam sprocket or the stock 3 hole jobbie? For the best possible results you should use a better cam sprocket. I don't because I have a stock cam, but I do have one ready for my next engine combo because that engine will have modified parts! Modified cams need a cam card, with a proper cam sprocket and someone who knows what they're doing. Get someone who knows this stuff to help you out the next time you check things out. Take written notes or record it on a camcorder or something.

Then you'll be able to refer to your notes later on for whatever reason.

Good luck

[Diseazd]

Acador.....Did you use Isky valve springs and retainers to handle the lift of the new cam? Dave Rebello sells outter valve springs that you use with stock inner springs and stock retainers that will work with up to .500 lift and .240 lash pads.Did someone set up the rocker geometry with the thicker required lash pads? In other words,tell us in detail what exactly was done to the head. I don't think that maximum power at 5200 is abnormal for an L28 with longer stroke. Just shift at 6,000 rpm and go for the next gear!

[acador]

Fresh build may not be the correct term, however the cylinders did look brand new. I did the build myself. I ported the runners a bit, lapped the valves, used the Isky valve springs & Lash pads, and ford valve seals. All the geomety is to spec.

The cam did come with a cam card but an adjustable sprocket wasn't in the budget so I decided to trial and error with the three possible adjustments on the stock sprocket. I totally agree that degreeing would be best but that is not an option at the moment. This trial and error method is how I got here. I guess what I am really asking is if I should move back to position 1 on the sprocket to raise the power curve, or If I would need to move it to position 3? 5200 peak may be normal for this setup, I just want to make sure i'm not leaving any power on the table.

The crazy high base timing makes me think something is not right. I originally had the base at 17 but it wanted more. The more I advance it the more the engine likes it. I suspect that maybe my balancer has spun and my numbers are not accurate, however the dizzy is still fully advanced and there isn't any adjustment left. If my blancer mark is incorrect, is there a way to further advance my timing by repositioning the dizzy?

I have never seen a Innova timing light but it sounds cool. Is it able to read timing without using a timing mark?

[Zed Head]

Sounds like you don't trust that "Zero" = TDC on the compression stroke. Why do anything else until you know?

If you find that it's incorrect, but the damper is in good condition and you know why the mark is wrong, you could just make a new mark.

[acador]

You are correct, I do not trust zero, but I don't know of a way to verify it without a degree wheel kit. I guess I could line the sprocket marker up with the dots on the cam tower and then see where the balancer mark is in relation to the timing tab. It would not be exact but it should at least tell me if i'm still in the ball park. The cam is a regrind so I assume its timing in relation to TDC is similar to the pre-ground stocker. I researched online a bit and the common consensus is that advancing the cam lowers the power curve. I think I will try moving the cam back to the first position on the sprocket to see what that does the power band and to see if it changes the timing situation.

I will probably need to pony up and get an adjustable gear at some point but right now I need to spend my money in other areas to get the car track ready.

[Diseazd]

Remember.....there are two adjustment nuts on the distributor to adjust timing. You may be able to get more advance by loosening the second adjustment nut. Also, if you don't trust your damper, you can pull the number 1 plug , disconnect the coil wire and turn the engine over by pushing in 4th gear until the number one piston is rising on the compression stroke. Stick a long screwdriver in the number 1 spark plug hole until it contacts the top of the piston and bring the piston to top center. Then check your timing marker to your damper.

Edited March 27, 2011 by Diseazd

[Zed Head]

Another way to do it, in similar fashion is to bring the piston up to a known depth from the spark plug hold (like when something in the hole just starts to move), make a mark on the damper, then go over TDC and let the piston drop down to that same distance on the other side and make another mark. Split the difference between the marks and you'll have TDC.

The piston doesn't move up or down much around TDC but the damper does so you can be quite a ways off in crankshaft rotation trying to estimate when the piston stopped moving up or down.

[ozconnection]

Another way to do it, in similar fashion is to bring the piston up to a known depth from the spark plug hold (like when something in the hole just starts to move), make a mark on the damper, then go over TDC and let the piston drop down to that same distance on the other side and make another mark. Split the difference between the marks and you'll have TDC.

The piston doesn't move up or down much around TDC but the damper does so you can be quite a ways off in crankshaft rotation trying to estimate when the piston stopped moving up or down.

I'm glad you wrote this Zed Head, saved me from doing it!

You want race this car. Your not ready. The timing issue bothers me and that absolutely needs sorting from two aspects.

1) If your timing is that far advanced, it will hammer the rings, pistons and bearings and something will give...usually the ring lands but anything is possible. Just because you can't hear pinging doesn't mean its not happening.

There is no latitude either, get a stale batch of fuel or fill up somewhere else and it could spell engine expiry quickly. Back off the ignition timing to something sensible until YOU PROPERLY VERIFY what's going on.

2) If the outer ring on your balancer is lose, then racing the engine or spinning it with high revs means that the dampening effect will be greatly diminished and crank breakage is a real possibility. Take your balancer off, inspect it, check the keyways are aligned with the vertical centreline of your engine and ditch it with something better. Even a reco stocker is better than a suspect original. Change your chain whilst you're at it and even your guides. Spend hundreds now or thousands later, your call.

[acador]

Yes I definitly want to sort out the timing before running the engine hard. I'll get the balancer mark verified later this week. I'm pretty sure I noted its position as correct when installing the cam but I don't remember now so I'll double check. Another senario may be that the mechanical advance isn't giving me the full 17. I may be at 25 base with very little mechanical advance. I'll set my timing back to 8 and see how far it advances at 2500rpms using the factory tab.

[Zed Head]

One way to measure your mechanical advance is to hook up your timing light, start the engine, disconnect your vacuum advance hose, retard the timing to zero (once you've confirmed the damper mark), then rev the engine up until the timing stops advancing. Your timing tab probably stops at 20 degrees, so you should get a direct reading of total mechanical advance. You will probably have to adjust your idle up to keep the engine running with the timing retarded.

Then you can temporarily connect your vacuum advance hose to manifold vacuum,while you're set to zero timing, to see what your vac advance canister pulls. If your pulling over 14 inches of vacuum through the intake you should get the full vacuum advance at idle without increasing rpm. Since you're at zero, you'll get a direct reading off of your timing tab.

Some simple tricks for seeing what works and how much, if you don't have the nice timing light or degree marks on your damper.

[ozconnection]

Zed head has all the best tricks!!

Well done mate, perfecto.

Best part is it works.