Have you confirmed that your electronic timing matches your true engine timing? I am not sure if you are able to see via a timing light on these engines but I would start at that point. Also, what is your target A/F ratio at WOT and what is it at your peak torque? You could run it a couple points richer at peak torque (ie-12.9 down to 12.6)--this would most likely be a VE adjustment in your pcm and it could give you more power as well as curb detonation. If the above physical timing checks out and you add fuel and are still getting pinging then you will need to run a race fuel pump gas mix. Let us know your findings.

 

Lots to think about here haha. Thanks heaps for your input.

Cam was setup dot to dot and double checked with a degree wheel and engine builder said it was spot on with the cam card. Very well known cam grinder here in Aus. From memory the head gasket was slightly bigger and chamber slightly smaller so pretty much what you came up with. As for ground in advance im not sure I don't have the specs on me atm unfortunately.

I'm starting to lean towards transient fuel as it would explain the tip in knock and could cause other problems as well. I have a mechanical gauge on my rails and its always watched when doing power runs on the dyno so I would say my fuel pump is ok. Come to think of it most of the pinging is when I "surprise" the engine like stabbing the throttle or dropping back to 3rd and flooring it. Seems to ping in the space before WOT but just after applying pedal pressure. Rapid changes in engine load is probably a better way of putting it. Could be PE delay as it may be taking a little time to go into PE causing a lean spot. LOTS to think about...

 

yeah, the 4800 RPM peak torque really pretty much means the cam is right. It takes a lot of effort to make an LS NOT have peak torque at 4800 and peak power at 6300. i wasn't trying to throw the installer under the bus - just observating that on the surface it looks right.

You've done the preliminary diagnostic work, so that's good.

Lean transient tip in is very tricky, and honestly I'm not sure how to help fix that. Some guys can do it. Typically, if there is no PE delay and the VE table is spot on, lean tip in is very minimal. Even if you have to artificially bump the higher map rows of your VE table up a smidge to calculate more tip in fuel, along with getting rid of any PE delay, it might help.

FWIW, on the stock tune (98-02 F body) The PE delay is set to 5000 RPM. below that RPM, there will be a delay in when you get full PE fuel. Above 5000 RPM, there would be no delay. Lots of people will set the RPM to 1 to get rid of it.

If you have a larger throttle body, here is something else to consider... The 102 TB has almost 2x the area of the 78mm TB. In the lower RPM ranges, you might see 64% Throttle position to even enable PE. 64% on a 102 is feeding almost as much air as WOT on a 78mm. So, You might look at your PE TPS enable points and multiply that table by 0.6. This way, on some of your throttle stabs, you'll hit PE earlier and get your fuel.

Just some suggestions for you to consider. if someone better at this than me chimes in and says I'm all wet, i probably am

 

Darth you know valve events are one of the most important things in depicting where the power band will be. Right away the size of the cam got me. That much duration with 29* overlap. I seriously wouldn't think the motor would be happy at much under 5k rpm. Tony Mamo documented all the tests on his 383. With a cam a nice bit smaller, with 17* of overlap, his tq peak was around 5600rpm. Hp peak still 6300 I think. Carried well past peak. There was a pretty big tq loss at lower rpms.

 

You are not wrong. But intake runner length also boxes it in. Since op is running a stock style intake, it’s going to want to peak at 4800/6300.

You can cheat this with valve events, which will typically get double and triple hump torque curves, which is where the higher peak torque often hits - the second hump peak. But you can only cheat it so far. At some point, the intake runners and exhaust design kick in and force the power curve back into the box. The 4� stroke also will tend to pull the peak power back down in the rpm band a little.

As to the cam size - yeah, it’s big, and likely causing some low end tq losses. But it’s NOT causing high DCR. DCR is calculated off the IVC at 006. His IVC is late, so DCR is low.

 

I have definitely given up some low down torque. It starts to come on at 3.5k and hits really really hard at 4k and screams on from there. It's mainly a strip car now so it doesn't see revs below 4k anyway. The loss isn't really noticeable going from a big cam 5.7 the cubes sort of make up for it. Defiantly not a daily driver though

 

Definitely right. The intake manifold is another main factor in where the power will want to be. As he has the fast 102 it probably isn't causing much of a restriction on the stock heads. Coming down to how much they have been worked I guess. Also how the exhaust is setup as you stated.

I love that 20 LS manifold test. The Fast 78 had the longest runners at 12". Made it's peak tq close to one of the highest rpm at 5600. As that test was not on a 383, was on a 6.0l, that info can't really be apples to apples with this motor. The information is great though.

Your also right about the 4" stroke. As a cam spec'd for a 383 will adjust the events for the stroke & bring it back to say, where it was. To me the cam is huge & I don't see any benefits to it in the combo. My 383 peak tq is 4800 & I spin to 7k. Although I do have things that are not normal per say that help my powerband. Maybe the 241 heads are holding it back? Just really seemed odd with that big of cam & the tq peak where it was. Even with the plastic manifold.

Here's a little quote from Mamo on his 383 when he went to a bigger cam:
TEST 4

Same 225 heads....Swap to larger 239 / 243 Hyd. roller. (.650 / .660) 114 LSA

NO other changes versus Test 3

Final Results 594 HP / 505 Ft/Lbs. (10-10.5" of idle vacuum)

TQ output @ 3500 RPM's : 432 Ft/Lbs.

Note: TQ peak occured @ 5600 RPM's....Power Peak @ 6500 RPM's

Summary:

Before you guys start cheering about the extra power, make sure you take a look at the area under the curve. While this camshaft certainly showed its stuff upstairs (it was still making 590 @ 6700 RPM's), the lower part of the curve took a good hit, and even the peak TQ figure was almost down 20 Ft/Lbs. If you were purely concerned with drag racing and sidestepped the clutch at close to 6K or better, this cam would perform well, but as I was trying to feature a more balanced package here, this cam would not be the cam of choice. I think it also would have worked better with a little more static compression, but for that matter, so would all the other combinations I featured as well. This was a good test in the sense it shows clearly that there is a point you reach when you have chosen a cam that's just a bit too big. The smaller 234/238 made close to the same power and was simply far more efficient on average which was also clearly evident by the better V/E #'s and stonger TQ for the better part of the power curve. I will do my best to try and get some actual curves in this thread when I have some time.


You have stated that it is mainly a drag car. Like you say lower rpm doesn't mean much anyway with your use. I think I stated earlier that cam would be more at home, I think, with a big single plane intake & revving to 8k maybe. With the LS manifold on it & spinning to 7k I just think that cam doesn't fit the combo well. Not bashing your combo or saying that is the root of your problem with the pinging. Just opinion. Can't wait to see a dyno graph.

 

I'm looking forward to the graphs as well as I have only seen one briefly on a computer screen when the motor was first built. I will have a pump fuel and race fuel graph so that will be interesting. The cam size did scare me a little when the engine builder suggested it but I was actually very surprised how well it drives down low considering its size. Drives like it did when it was 5.7 with 238/240 112 and with 3.73 rear end. Now it has 4.11 rear end to help it get off the line. Maybe I've been driving on big cams for so long it doesn't bother me and I have nothing to compare haha

Aftermarket heads will come in the future when budget permits along with some valve train mods to help it rev. Atm the heads seem to be limiting air at peak so no point revving past that at this point. As far as the pinging goes it should be all sorted in the next couple days and will have some dyno graphs to drool over and some good track numbers to back it up.

 

I tend to find that stroke absorbs cam duration and overlap quite a bit.
So I'm not too surprised that cam is driving OK with a decent tune. Curious why you say there's no point revving past peak? Or are you just thinking along the lines of the build not being fully complete yet?

That's a really good point. What so you think about the cathedral MSD with its shorter runners? probably make a better match to the cam events, i'd think.

 

Right on. If you're happy with it, & it runs good, that's what really matters.

The motor will love some aftermarket heads. I still have a couple other things on my mind but I'll wait till the dyno sheet comes in. I'd say the track performance(11.9@124 on low timing?) is pretty darn good considering things. It's not even all happy yet.

Your right. As we know with the cathedral MSD you may take a hit on the numbers below 5-6k or so. The return is better power in the higher rpm range witch I would also think would be a better match with this cam/use of engine. Although I'm not too familiar with the feedback on the cathedral MSD out of box. I know your results of coarse were great for top end power. Although that is a Mamofied MSD. I know 98 has one on his 383 also.

 

yeah, that 124 means there is a TON of quickness in there to gain. Just sorting things out you'll drop 3/4 second off.

 

Ok guys hoping some of you could have a look through a couple of my logs. I have been trying to tune my VE table using AFR error with my wideband (speed density open loop tune). I can get my error percentage around 5% rich and just about all of my knock retard is gone now. I then log a short normal drive and my wide band says I'm running lean and bank 2 o2 flat lines lean. I have no idea what is going on here any help would be greatly appreciated.

Long Drive Part Throttle VE Table 3.hpl
Short Drive Lean Bank 2 o2.hpl

 

Possibly bad o2s

 

I have swapped o2s and the lean condition stays on bank 2. The weird thing is if you look at the logs it mainly happens at 2500 ish rpm when cruising. DFCO, COT, STFT, LTFT and Lean Cruise are all disabled

 

I have just looked over the logs again and it looks like both o2s read stable when the IAT is low. In the second log the IAT is around 60* C and bank 2 leans out. Seems to be heat soak causing the problem. Any ideas anyone?

 

It may just be your open loop EQ ratio table. When you're logging for VE, are you using all the data or only the fully warmed up data? If you are using all the data - while it is warming up - you are artificially trimming it lean. I'm pretty sure you're doing it right, but it's worth asking.

It does look like your O2 sensor is lazy, BUT it actually matches your WB. I assume the engine is cammed? You mind posting the tune?

 

I am Going to start a new thread on the issue because its becoming really big problem. I'll post a link when it's up