Bigger cam, ignition timing question

[olie05]

I recently put a bigger cam in my daily. It is a crane 272/282 split duration with .480" lift.

 

The problem is that I lost most of my low end putting-around-town power and it has killed my around town mileage.

 

The one thing I can adjust (as of now until I go with megasquirt) Is the ignition timing. What would be a good initial number to run? I seem to think that giving it more advance will give me a better around town car, but the question is how much?

 

thoughts?

 

-Oliver

[Pyro]

20 initial.

 

36 total mechanical.

 

Plus 15 from the vacuum advance at light engine loads (high vacuum).

[Zmanco]

Not sure which dizzy you have now, but a late 280zx dizzy has less mechanical advance than the early 240s. That means you can set your timing for more initial advance without exceeding 35-36 total advance. Usually you can't go beyond that without detonation.

[JMortensen]

Are you running the stock FI? It doesn't like big cams. With a slightly larger cam I was able to get mid 20's mileage on the highway with triple Mikunis.

[BRAAP]

As Jon pointed out, the OE EFI will NOT tolerate larger than stock cams and there is no “reasonable” way around it. I’m sure someone could hack the resistors and caps in the ECU, but with Mega Squirt being so inexpensive and readily accessible...

 

The OE EFI will barely tolerate extreme exhaust mods and minor head work, (those two items with the stock cam and stock EFI intake manifold don’t alter the VE curve too much and what they do alter the VE curve, we are able to compensate for with a variety of methods). The OE EFI will not tolerate freer flowing intake manifolds nor will it tolerate aftermarket cams. Both of those alters the VE curve so drastically and there is no reasonable way to keep the part throttle cruise AND WOT in balance. You will have to sacrifice one for the other and at that, if you spend too much driving around in the compromised area of the tune, it can be bad enough to foul plugs, which means that it wont work right when you start driving in the region it was tuned for due to fouled spark plugs I.e., if you have stock EFI, and you want to drive it, either put the stock cam back in or swap out the EFI to Mega Squirt.

 

Also, because you now have a more radical cam, it is common that you will loose some low end torque and mileage, though it all really depends on how well tuned it was to begin with. You might get some of the lower end power back with an ideal tune using mega squirt and getting rid of that AFM from the air stream, though you wont be able to take full advantage of the top end power that the bigger cam is capable of due to the restrictive intake manifold, in particular its runners. The throttle valve is not really restriction compared to the runners. . Sure, you will see “some” gain up on top, but not as much if you uncorked the runners, i.e. freer flowing intake manifold.

 

Hope that helps..

 

Paul

[olie05]

I just came back from a 4hr road trip. This was the first road trip I have been on with the cam. I noticed no difference in this cam and the other one in highway mileage.

 

I am only getting poor mileage in city driving.

 

Wouldn't it be pointless to open up the intake manifold runners without opening up the intake ports first?

[Daeron]

 

Wouldn't it be pointless to open up the intake manifold runners without opening up the intake ports first?

 

I have no numbers to back up my "internet parroting" here, but the stock manifold intake runners are MUCH more of a restriction than the intake ports themselves are. manifold runners are 32? mm in diameter (low 30s at least)

 

Now, think about that 32? mm, and think about all the posts people have made that discussed the high HP limitations of the 40mm diameter triple carburettors... and think some more. A new manifold is more important than opening up the ports on the head.

[BRAAP]

Great analogy Daeron.

 

Olie,

As Daeron pointed out, in regards to allowing the engine to breath, manifold runners need attention first. Then if you plan to port match, take the time to unshroud the valves as well.

 

Because you now have a larger cam than stock, in my opinon, it would be pointless to do anything to the manifold or head ports, (including installing a larger than stock cam), while you are still running the stock ECU.

 

Good luck,

Paul

[JMortensen]

Because you now have a larger cam than stock, in my opinon, it would be pointless to do anything to the manifold or head ports, (including installing a larger than stock cam), while you are still running the stock ECU.

Agreed. That stock FI is crap. Get yourself a decent FI setup or some good carbs and you'll find out how much power you've paid for but aren't getting.

[Daeron]

Agreed. That stock FI is crap. Get yourself a decent FI setup or some good carbs and you'll find out how much power you've paid for but aren't getting.

 

"Crap" is a strong word to use, I think!! Just like "There is no 'best'" I would think that to simply bash the stock FI is a little harsh. For performance applications, the stock ECU is certainly limited, but is anyone expecting 21st century performance out of a computer designed in the 70s? The ECU is the key to the "crappy" stock FI, other than that the flapper AFM is the single worst part of the FI system's design, and again that is simply dated.

 

Antique, yes, short on power potential, yes.. (and I am not trying to convince you, I know you know this as well as anyone else would.. I am just putting this up there to go beside your statement for posterity's sake) BUT for stock performance, the stock FI is wonderfully easy to understand, and despite what many have problems with, all it takes is patience and the EFI bible to fix ANYTHING with it. Many of the components are servicable (try to "fix" a hotwire MAF or a MAP sensor, or a potentiometer style TPS.)

 

Once again, Jon, I am not trying to explain anything to you, and I agree that the stock FI leaves NO room for real performance improvement, (MS is one of the first investments I plan to make once work begins on my car, before intake, before engine work, before everything but my exhaust) but "crap" is a slightly strong word and I wanted to make this post to make sure that nobody decides to scrap their stock FI because "its a bum system," yanno?

[z-ya]

The only way to know for sure what the EFI us doing is to get it on the dyno with a WB O2 sensor. Doesn't matter if it is carb or EFI, you still have to freakin' tune it. Anything else is pure speculation.

 

With the stock EFI you can adjust the AFM, and fake out the coolant sensor with a potentiometer to get the mixture close across the power band. Put an adjustable fuel pressure regulator in there to tune the top end. Once you have the mixture as close as you can get it, start advancing the timing.

 

If the motor has a stock compression ratio (8.something:1), then you should be able to run in the mid 30s in total advance. Don't expect huge power gains by adding a cam to a stock long block. As you noted, it will most likely fall flat on it's face under 3000RPM. Higher compression ratio + performance cam will yield the best power gain.

[Thumper]

Hey olie in response to your question you can now advance the timing alittle bit more due to the fact that you were only detonating at low rpm high load before. And since the cam reduces pressures at low rpms you should be able to advance the timing a couple of degrees to help out your low end. Good luck

[JMortensen]

Once again, Jon, I am not trying to explain anything to you, and I agree that the stock FI leaves NO room for real performance improvement, (MS is one of the first investments I plan to make once work begins on my car, before intake, before engine work, before everything but my exhaust) but "crap" is a slightly strong word and I wanted to make this post to make sure that nobody decides to scrap their stock FI because "its a bum system," yanno?

We can disagree if you like, but I really think the stock FI is crap. If you want to keep your car bone stock like you said, then we could talk about the disintegrating connectors and all that, the restrictive AFM and manifold, etc. If a person doesn't mind dealing with all those issues, then OK, stock can be made to function correctly. That's about the best I can say for stock FI, that it can be made to function correctly but probably isn't now, because of the crappy connectors they came with. If you want to modify the car we can talk about how a cam install will render it basically retarded. To me, that's crappy, since I don't tend to leave things in stock form.

 

Every once in a while someone will say something about how bad carbs suck and that ANY FI (including the crap L series FI) is a step up, carb is a metered fuel leak, old technology, blah blah blah, yadda yadda. I wholeheartedly disagree with this opinion. Carbs in all common cases for the L, even dual Webers or 4 barrel setups, can be tuned to work with a bigger cam. They might not be the best carb setups that you can get for your L, but if you're installing a cam I'd rather have either of those than stock FI. But when you compare properly tuned SU's or triples to stock FI with the intention of making power, there's just no comparison. You can go WAY beyond the limitations of the stock FI and make a lot more power with good carbs.

 

I will grant you that in a turboed application the FI makes more sense and is easier to get and keep running, although again I'd say that for peak performance, turboed carb setups have more potential than the stock FI (think turbo setups with triple Mikunis from the 80s).

[Daeron]

We can disagree if you like, but I really think the stock FI is crap.

 

Call me sentimental.

 

Glad to know I was understood, thanks for the response.

[olie05]

I suppose I left out a few details about my engine. I have 10.3:1 static CR and I have been driving around with that for a while. I had to retard the timing *slightly* to make sure I didn't blow head gaskets under heavy acceleration. Now that the cam is in the engine runs WAY better than it did on 10.3:1 and the stock computer, in the top end.

 

Oh yeah Z-YA... i have the little coolant fuel trimmer

[JMortensen]

I suppose I left out a few details about my engine. I have 10.3:1 static CR and I have been driving around with that for a while. I had to retard the timing *slightly* to make sure I didn't blow head gaskets under heavy acceleration. Now that the cam is in the engine runs WAY better than it did on 10.3:1 and the stock computer, in the top end.

 

Oh yeah Z-YA... i have the little coolant fuel trimmer

Retard the timing to prevent blowing the head gasket(s)? Not sure what that means. Do you mean you had to retard it to get rid of pinging? Do you actually have more than one headgasket on the engine? I know Norm did that on his motor. I'd suggest that you probably don't know what you're missing out on by running the stock FI, and that the last little bit of timing can make a pretty huge difference in power, so if you've got timing backed down in the 20's or around there you're losing a significant amount of hp. Even if you have it at 30 you're likely losing a bunch.

[Zmanco]

I have a similar setup and am running MS fuel only. I have a 280zx dizzy and MSD 6AL and have no noticeable issues with spark. But, Jon's comments have me wondering if by not letting MS control spark (and vary it) that I may be missing something. Perhaps I'm not getting as much advance across the rev range as the engine could tolerate? In other words, I can never advance more than the worst case rpm.

 

I do notice that when I add too much advance, I hear pinging around 4500 rpm. It's usually gone by 5k. I've tried richening the VE table in that region but haven't been able to go past 35 degrees total. I am wondering if I had MS controlling spark if I might be able to add some more advance above 5k? Anyone have an idea how much additional power might be gained?

 

FWIW, I am currently running with 35 degrees total advance - all mechanical, no vacuum.

 

PS. Hope this isn't a thread hijack as it seems to me to be a continuation of the discussion.

[Tony D]

I'd ask 'Did you degree the cam'? I have seen cams that were off several degrees from their cam card specifications.

On our Bonneville Car, installing the cam in the '#1' hole had a torque curve that started at 6000 rpms, and went on flat as a table through 8500. Tweaked the cam 2 Degrees, and that same torque curve was now available and present at 4000 rpms! If the difference wasn't so dramatic I would not have remembered...but only a 2 degree adjustment in the cam location relative to where it originally was installed made almost a 2000 rpms difference in useable torque band!!! The top end power did not change one bit...power peak was still at 8250rpm. We ended up running the cam a total of four degrees in each direction from 'straight up' to check the 'best' location. For the $200 we spent on the dyno...I would say it was the best $200 we ever spent in regards to the payoff returned.

 

So if you have the time and money, take it to a dyno and check exatly where your cam produces the most torque and horsepower. If you can, take the time to install either the Arizona Z Car, or Tomei Adjustable Cam Sprocket. Changing the timing on the cam is a SNAP on those compared to the Nissan Motorsports "Multi-Hole Abortion"!

 

After that experience, I started degreeing my cams religiously and that is when I started noticing some cam manufacturer's specs may not be right on to what their cam card says opening events need to be...the profile and the differential between intake and exhaust lobes are pretty much correct, but where that operator starts grinding the cam may float about a bit. So I always now check, and if you are 'loosing power noticably' on the bottom end, you may want to make sure you are optimized for what you have.

 

Now, on to the EFI.... 40mm Triples restrictive, sure, they usually run only 32 or 34mm chokes as well. Same as the Stock Intake Manifold. The EFI is not so much 'junk'---it works really well for what it does, and if you had access to the Bosch (NECS Actually) Setup for the Triple Nissan 45MM ITBS that were in place on the European Rally Cars in the early 70's your thoughts may change about how "junk" they really are... The Megasquirt is really nothing more than the stock box set up so you can EASILY adjust what happens in reagards to inputs and outputs.

 

In the same vein that the stock box is "junk" for a mildly or highly modified system, so would be the Megasquirt be classed "junk" by someone running a full-on Motec controlling variable cam timing, etc etc etc.

 

It's just not what it was designed to do---if something is "junk" because it doesn't work in a misapplied situation....then there is a LOT of "junk" out there: A Geo Metro at a Monster Truck Competition, a 240Z at LeMans entered in the Prototype Division...

 

I won't disagree, the Stock Box is unsuited to the application with the modifications as described but it most definately is not 'junk'--a stock vehicle is very well served by a Stock Box. Let's see how many MS units are around running these vehicles 30 years down the road. Durability and Longevity go a long way towards debunking the "junk" misnomer, IMO.

 

As for spark advance: run as much as you see power gains. Running anything more is useless, and can be argued can be detrimental by putting more heat into the combustion chamber than is required. If you have MS controlling spark, you can play with your bins quite a bit to tailor the timing in each spot...but you have to see on a dyno where you are getting the power and at what point you stop getting a gain in power for more advance being run. There is not a 'magic number' that you need to run---it is all dependent on your power production at each given point. "Don't run more than you need to."

[BRAAP]

Here is just one recent example of the OE EFI not liking cams, local customer Mike Hintz, also a member here on HybridZ. This is the car;

http://forums.hybridz.org/showthread.php?t=119783

He previously had another local Datsun shop build his L-28 engine. The engine has the Euro flat tops, N-47 head, approx 10.4:1 compression ratio, Schneider dual pattern cam, 270/280, and they used stock valve springs?! DOH! The machine work and overall assembly of the engine looked real nice, other than not researching parts compatibility. He met up with us and talked to us about his previous Dyno experience at Torque Freaks with this set up. It was detonating audibly, he couldn't here it inside the car at all, yet the dyno operator was hearing it and told him no more pulls because of detonation heard outside the car. Any how, I talked him into letting us build him a lower compression head and going back to a stock cam because of the EFI doesn't like cams, (I've been there, done that, and seen it with SEVERAL others). He was VERY reluctant on the cam part. Once the new head and stock cam were ready I swapped the heads which is a P-79 head with a static comp ratio of 8.6:1, stock '81-'83 N/A ZX cam, spent some time road tuning the EFI and ignition timing for best power and drivability. I went back to that same dyno with Mike that next day. When we got to the Dyno facility, He wouldn't stop talking about how much smoother, more drivable, and more powerful it was now. The Dyno reflected exactly what he described. He gained Torque/power everywhere, from idle all the way up the RPM range, the car was MUCH smoother, faster, and got better mileage. Win, Win, Win, all around. So we went from 10:4.1 down to 8.6:1, and also back to a much weaker cam, and the engine not only ran smoother, but made more power. Sure some of it could have been that I took the time to dial in the new combination and the other builder didn't, maybe he did, we'll never know. But I honestly don't feel that I could've squeaked even 5 HP more over the stock set up and it still would have been nowhere near as smooth, flat spots in the power band, etc. The OE EFI does not like cams, at all. Now if he had the Wolf EFI in the car, then that bigger cam would've made more power and ran pretty close to as smooth as stock once dialed in, the key here being pin point fuel control under any condition. In tricking the OE EFI, we use the water temp resistance, AFM spring adjustments, grinding the floor of the AFM for fine tuning, (mostly for idle depending on many other factors such as the AFM already being at the end of the CO adjustment range in the AFM), and we have even employed a separate stand alone WOT switch that utilized a different water temp resistance value from the cockpit adjustable fuel adjustment dial. Not all of those tricks were employed on Mikes car, but you get the point. Even with all those "tricks" to get the OE EFI to fuel extra in certain situations and not in others so as not to compromise drivability or power elsewhere, it still isn't enough for big cams.

It is my belief from all the experience I've gained in playing with many OE EFI L-28s is that if the OE EFI is to be retained, the cam needs to be stock, and the intake can't be modified to heavily, and the OE EFI will work and can make OK power. Aftermarket EFI frees up so much and allows the tuner so many more options for more power.

From years of experience playing with, tuning, and racing the OE EFI, for a street car, the OE EFI simply does NOT like cams. Take it or leave it.

Ok, I'm personally done beating this very very dead horse.

[BRAAP]

Just adding my Timing $.02 while riding in on Tony D’s. shirt tail.

 

Now if an engine combination runs best at 37-40 degrees timing and with premium pump gas you are experiencing pinging at anything more than 34 degrees, you are giving up power. You’d be far better off with a little lower compression ratio to retain that ideal ignition timing.

 

The open chamber L-series heads seem to like the high 30’s, 36-and even as much as 40 degrees total ignition advance. Between 36-39 seems to be the sweet spot for most open chambered L-6 heads. The closed chamber head like the MN-47, prefer 32-35. The MN-47 chamber is more efficient and the flame front doesn’t have as far to travel.