2020 LT1 SS, super weak on dyno trying to figure out issue

Car was previously tuned, has BTR stage3 cam 34% fuel lobe, LT4 injectors/pump but is dooky at WOT (410hp 410 ft lbs 11.7:1 air fuel) First headache was figuring out some spacer plate was used (less than 1mm) on the NW TB and MSD Atomic combo with a hole too small and the blade was hitting it putting into REP. Then it was throttle shutting up top, got it bit better with changes from run4 to run5 but still seems real wonky.

Knock sensors going wild (not like it has much timing in it) hi pressure rail is on target and doesnt have wide inj pulsewidths (3.2ms?) so I wouldnt think its SOI backing it up into spark area and pulling timing away from it. Not seeing why the throttle stays open for much longer but it made LESS power up top (timing some but why) and showed rando misfire flashing that run

Ive ran into a few cars that acted like this... and couple times figure out the thing has 87 octane in it. Starting to think that may be the case its a SS with ZL1 everything on it outside and tons of carbon fiber and it always seems to be those types that will spend thousands on appearing to be $$$ and letting a dime hold up a dollar being a cheap ass in the worst place :doh:

I assume compression has been checked? Usually when they don't dyno right, it's mechanical. If it's good mechanical then start playing with soi and maybe even lower rail to spread that injection out some more. Might want to lean it up a bit too. Some cams like rich, while others like lean.

Have you seen pulsewidth too narrow be a problem? As long as pressure isnt dropping I wouldnt think it would matter if it gets enough fuel in the cylinder

Believe it or not injection can be worth several ponies on these. I started ignoring the exhaust valve closing and started focusing more on intake valve after some things I found out even most recently with idle that I had never even considered. Get your pulsewidth back closer to 5 if you can. Lowering rail and supply will take care of a lot of that. Again, this is if nothing is mechanically wrong. Put it up in the 12's to 13's and see what that does for you too.

These cars will knock if they are too rich. 11.x AFR on an NA motor will knock. Lean it out and start adding timing. SOI should be around 350-360 for that cam at WOT and EOI shouldn't fall past 160. Make sure your throttle body isn't closing and the TCM isn't throttling torque.

If you still have a terrible dyno then you likely have a mechanical issue somewhere. Could incorrect valvetrain geometry or broken springs, busted rings (would be smoking), bad torque converter(would likely have drive-ability issues).



I didn't check your log, but these are the things that came to mind.

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Originally Posted by GHuggins

Get your pulsewidth back closer to 5 if you can. Lowering rail and supply will take care of a lot of that

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I did find that some injector data was wonky and made sense that the airflow model need bunch of fuel pulled out at first. Still waiting on word from the guy if he puts 87 in the thing lol (or maybe just bad 93) I was thinking it be best to leave pressure up so theres lots of headroom for E85 later the PW will have to get wider for that - but if it cant get happy with 3.2ms PWs and 12.8 A/F on pump then no point

15-17 degrees of timing is all Ive been able to get into it up top so far ven in the mid upper 12s A/F

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Originally Posted by TriPinTaZ

These cars will knock if they are too rich. 11.x AFR on an NA motor will knock. Lean it out and start adding timing. SOI should be around 350-360 for that cam at WOT and EOI shouldn't fall past 160. Make sure your throttle body isn't closing and the TCM isn't throttling torque

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Best run now has .86 or so lambda, SOI 310 in middle rpm - 300 up top, EOI only as low as 180. Still little soft up top and has a harsh dip at 6200 you can see/hear/feel although knock sensors dont match it always

If I pull pressure supply out of it and get the injector pulse wider, then Ill have to start SOI earlier. maybe with 4+ms PWs that SOI number will need to be earlier and everything happier Just was hesitant to take pressure away, for headroom on E85 later

Dip you can feel and flat up top. No TPS closure, no kPa showing vacuum, timing at 15 degrees and KR isnt spiking right there making a dip

Something is wrong if it will only take 15 degrees of timing. Did you try any Torco or Octanium to see if it's crap fuel? Fwiw I would shoot for .88 and a SOI of 360. You are going to see power fall off running below 350 imo.

The dip and description (you can hear it) looks and sounds like valve springs.

You know Id tend to go there, but new spring/cam kit from BTR or TSP I think the guy said

Even lowering low side pressure from 72 to 58psi, and hi pressure all the way down from 2900 to 2100psi - the injection pulsewidth doesnt change nor does the SOI/EOI or injection duration always starts around 70 degrees and max up to 120 degrees. Still 3.1is ms PW? That doesnt make sense does it?

So with tank on E put 5 gal of E85 in, 67% on flex sensor, injector PW actually did jump up (but not enough, AF was 12.3 on gas and 13.12 on ethanol) usually i dont see that much discrepancy in air fuel vs target going from e10 to e70 what to do about that? Makes identical power still 477hp vs 474 best before same dip up top, knock sensors going haywire still seems to be led by cyl 2 usually... Theres no way should be knocking on ethanol at 20 degrees of timing when guys say they run 29 degrees (I dont, maybe more like 24-25)

I think theres multiple things going on with this car. I tried setting SOI at 360 or something across the board, but it made 35 less hp or something than where it is here

I would do a compression check quick. Really sounds like a piston issue. In fact do your dyno pulls have any squiggly marks representing a weak cylinder?

Then as you already discovered - lower pulse width means you need to run a lower soi and in doing so you'll fight yourself cause then you'll not only make more power but it'll get richer too causing more fuel to need pulling. So kinda a catch 22 sorta thing.

You should be making substantially more power on E. Somethings mechanically wrong. I've seen springs with less than 1000 miles break. These are also bad for piston skirts causing flop and rattle. You can maybe change the oil for the skirt. Haven't seen it on an LT1 yet, but exhaust valves stretch and pop.

I haven't looked at any of your logs yet. Just going by what you're saying. I need my other computer to go over the logs in detail and right now it's not with me. Still transferring all my maths over to this one.

I glanced at you last log. Again don't have everything in this scanner yet, but your injection is fine right now. Knock is killing your power. Cyl 1 has the most. Did the owner say why they did the cam swap? Are you sure a piston or cylinder wasn't damaged before hand? Something's mechanically off on this one causing the timing to be pulled.

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Originally Posted by GHuggins

I glanced at you last log. Again don't have everything in this scanner yet, but your injection is fine right now. Knock is killing your power. Cyl 1 has the most. Did the owner say why they did the cam swap? Are you sure a piston or cylinder wasn't damaged before hand? Something's mechanically off on this one causing the timing to be pulled.

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Run15 & 16 had same tune file - 15 first pull I made that day and was way lower (100hp) than it was the night before. Changed nothing and ran back to back and it made the best power it had Run16. if you look at run15 Cyl2 led the way with knock, as it did in run21 on ethanol, and most of the other pulls. The one run16 your talking about was the only time i think Ive seen cyl1 be the worse off? Trying to sanity check myself because it doesnt seem to repeat consistently i put the run15 tune back in it and did Run19 and it was 20 hp lower through the whole curve but still had same dip shape up top

Attachment 143588
Run16 and run19 same tune file, richer one actually made more power

You will get knock on the LT's if timing is too low or SOI is too advanced. Put 22 degrees in it and move SOI closer to 350 if you're sure there isn't mechanical issue. I've seen LT1's and LT4's show knock when you have timing down in the teens and SOI isn't optimized.

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Originally Posted by TriPinTaZ

You will get knock on the LT's if timing is too low or SOI is too advanced. Put 22 degrees in it and move SOI closer to 350 if you're sure there isn't mechanical issue. I've seen LT1's and LT4's show knock when you have timing down in the teens and SOI isn't optimized.

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I think I mentioned it, but ive tried SOI up in the 350s-360s. Lost like 20 hp I think?

Look at the dyno graph right above, the dip does not coincide with timing being pulled consistant either. Everything I do in tune can move curve up/down but dip is there whether it has 14 17 or 19 degrees in it at that spot. There gotta be some other things going on too

I'm telling you that's some valve train shit going on. I don't ever take customer's words for anything. And I tell them that too. I'd be pulling a valve cover and doing a complete inspection. I'd most likely be doing a complete compression, leakdown and bore scope inspection also. I would have stopped trying to tune out the ugliness in the dyno graph a long time ago.

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Originally Posted by GrannySShifting

I think I mentioned it, but ive tried SOI up in the 350s-360s. Lost like 20 hp I think?

Look at the dyno graph right above, the dip does not coincide with timing being pulled consistant either. Everything I do in tune can move curve up/down but dip is there whether it has 14 17 or 19 degrees in it at that spot. There gotta be some other things going on too

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I was mentioning about why you might keep seeing constant knock. As for the dip, it looks similar to when you have an air turbulence or stall issue due to the intake path, valvetrain geometry, head/valve work, incompatible cam(with head port), broken valve spring, cam phaser that isn't truly locked out, installing the cam and not having the cam/crank degree'd properly.

At this point I would start investigating physical issues vs tune issues. If you lost 20HP going to 350-360 SOI then that cam has a hefty exhaust duration and you may be better off in the 330 range. When the power dips on the dyno, the Lambda and Timing doesn't change....that only leaves airmass entering the engine as the variable in question. This is where I would investigate.

The cam is supposedly something recommended from TSP for no converter. 227/231 is the specs I was TOLD. That's not real big at all on exhaust closing side especially at 116 lsa but again I'm not sure. It doesn't ACT like it