6.2 dyno and power peaks early

Badass69 · March 14, 2016

I have found the only dyno sheets of these L86 trucks on this forum. Both stock and tuned my truck went flat for horsepower at around 4900 rpm.... held that to 5100 and then started falling. By 5600 rpm I was down 20 hp from peak or so. This was all measured on an older Mustang dyno. The truck makes alright power but the horsepower number was a bit lower than I would have thought it would be in relation to the torque and with it falling shy that might be why. With the tune it picked up decent gains but something seems to be holding it back.

We did the tune with the stock air filter in the stock airbox and an Airaid MIT with a 3.5" MBRP exhaust. I am almost wondering if the cam isn't retarding correctly at higher rpm or if its something dumb like a plugged up cat..... or air filter. I didn't even look at it but it's not very old either. That should have been evident though and the truck seemed okay. Truck has like 16000 miles on it. I need more data logs to see about this stuff but my torque is peaking bang on 4100 rpm... so I am betting it's phasing okay...... but then maybe not?

The numbers I made are pretty meaningless.... the dyno isn't reading right and the guy knows it..... an over 1000 hp Duramax blew up one load cell the day before I went in for my tune lol.

I saw the same tuner did a Hemi Ram yesterday and even it carried making power to 5700 or so.... mine is a nice gentle slope but peaks at about 5100 rpm and falls off..... something isn't right.

Here is my data sheet:

Jon A · March 14, 2016

I agree, that looks a bit suspicious. Here's my 100% stock dyno:

It doesn't climb much after 5000, staying within about 3 HP, but technically it is climbing, certainly not dropping like yours. Do you have scans/logs of the runs? Here are some things to check:

Was there a bunch of KR on top?

The cam should be retarding 8-10 degrees by 5500.

Intake restriction can be checked by your MAP--stock air intake will drop around 6 kpa from the beginning to the end of the run. A good CAI will reduce that to around 3 kpa. If it's a lot more than 6 you've confirmed an intake restriction.

Plugged cats could also do it but I don't think you can isolate that from the scan.

And of course if you're suspicious of the dyno that can't be discounted. Trying a different dyno may save you a bunch of hair-pulling. Inertia Dynojets aren't as nice for tuning, but they're very precise and consistent in their measurements and would confirm or refute the issue.

Badass69 · March 14, 2016

Thank you! Your truck is one of the dyno sheets I was referencing in my first post. No I don't have any copies of the logs he was taking as he was tuning the truck so I can't comment there. I asked him about it and he really didn't reply lol. I will keep bugging him but in saying that I do own HPT myself and can just do some logs on the street. I am no expert but I can make changes myself and this guy is really good about that.... he gave me a copy of both my tunes in HPT files, as well as his datalogger he built in HPT for himself so I thought that was cool. He also said if I have any questions just ask and he will help me out too. And hey.... this tune cost me a grand total of $150 in my pocket..... lol. I sold him my EFILive software because I don't use it anymore lol.

Things I do know. I have no KR and even in stock form there was minimal to zero knock. I was running 94 octane premium that was from a known high volume station so it should have been fresh and that showed( has ethanol up here so that's my freshness concern). My spark advance is at 22 degrees with the tune and we have minimal to zero knock.... anymore and it started pulling timing.

I don't know what the camshaft was sitting at any given rpm so I need to log to figure that out. I have read many accounts that the Corvette tables for the camshaft is a nice bump for the trucks so I might try that out.

I am suspicious of my intake though and 6 kpa is a lot especially if an aftermarket one will halve that.... I got looking at it and the opening into my fender is actually smaller on these new lower boxes than the old GMT900 airbox base was. Those the entire side is open.... this one in my truck is almost like my original GMT800 boxes with one smaller opening. With this engine that might be a problem..... so I might order an aftermarket complete intake and see if that helps. I will datalog and confirm my map readings though first before I do anything. I pulled the intake off and the filter is spotless so it's as good as it will get.

The truck runs good.... so I would hope at this low of miles the cats wouldn't plug up.... but I dunno. Doesn't really seem like it though.

The dyno is another one.... but as I mentioned I saw the run of a 2013 or 2014 Hemi Ram that he did the day after my truck and it pulled right to where you would think which is around 5600 or 5700 rpm making power.... so I don't think it's the dyno itself. The Ram made less HP tuned than me and the same torque value once tuned as I did stock so it seems about right.

My thing too is not the raw number but the split. Stock was 321/356.... that's pretty damn close to the HP/TQ split stock being 420/460. Now tuned I gained almost 40 ft lbs at peak.... but like 15 hp? That doesn't seem right at all.

I will log when I can and see what my MAP and cam position values come back at!

muddkatt · March 14, 2016

I think the data is flawed, because the torque and HP should cross at 5250 RPM if I remember correctly. Jon's chart looks spot on. Don't go trying to fix something that is not broken, get another dyno run and see what the truck is actually making.

Badass69 · March 14, 2016

There aren't a lot of dynos around here and even less shops I want to talk too because they are run by sleeze bags. I agree because it crosses at 4500 RPM or so..... but I dunno considering if he shifted the axis at all that throws that theory out the window. It's a bunch of money for nothing if I get the same thing. This guy will dyno me again once the dyno is repaired for free so I will probably wait for that. In the meantime I can log the truck and see what is up.

I just looked at the Ram he did and it crosses below 5000 rpm as well...... but he can adjust that so I don't take it to heart.

Jon A · March 14, 2016

That's not an issue, look at the scales on the sides--you're at about 332 both HP/TQ at 5252. It's just the way it was graphed.

I agree you should log a couple WOT runs on the highway so you can see what's going on. It's not as good as a dyno but it's better than nothing. I go from a slow roll to whatever the speedlimit is + a bit.... Make sure your traction control is shut off--if you're spinning too much use auto 4wd.

If you'd like to send me a copy of your tune and any logs you do I'd be happy to take a look and compare them to mine to see if anything jumps out.

Badass69 · March 14, 2016

Jon A, on 14 Mar 2016 - 5:18 PM, said:Jon A, on 14 Mar 2016 - 5:18 PM, said:Jon A, on 14 Mar 2016 - 5:18 PM, said:

That's not an issue, look at the scales on the sides--you're at about 332 both HP/TQ at 5252. It's just the way it was graphed.

I agree you should log a couple WOT runs on the highway so you can see what's going on. It's not as good as a dyno but it's better than nothing. I go from a slow roll to whatever the speedlimit is + a bit.... Make sure your traction control is shut off--if you're spinning too much use auto 4wd.

If you'd like to send me a copy of your tune and any logs you do I'd be happy to take a look and compare them to mine to see if anything jumps out.

I will do just that. I would like a comparison to another truck like my own and see if there is something obvious. I know I can't load it quite like that dyno can but I will try my best lol. It spins like a bastard now...... I thought something was up in first gear as it felt almost like it was slipping.... couldn't hear the tires squeal ( and they kind of really don't), didn't feel like wheelspin and it revved out and jerked into second...... and yeah...... it's just spinning lol. Popped it into 4wd and that issue went away.... did a WOT dead stop on the highway and it's rubber into second.... the torque is great!

I am just not used to a gov lock anymore and this peg leg BS wheel spin lol. Where is my Detroit Locker I want for this 9.76" lol.

UplandPa · March 14, 2016

Very interesting Thread, please keep us up to date!

Jon A · March 15, 2016

it's rubber into second.... the torque is great!

Cool, I'll PM you my email.

Georgia1911 · March 15, 2016

...

The numbers I made are pretty meaningless.... the dyno isn't reading right and the guy knows it..... an over 1000 hp Duramax blew up one load cell the day before I went in for my tune lol.

...

You answered your own question. GIGO- do not think that just any data are better than no data at all if what little you have is not of known quality. There is no reason to believe that an unreliable dyno is reading linearly. If not, you cannot even conclude your torque curve is dropping, which is what has you concerned.

Badass69 · March 15, 2016

Georgia1911, on 14 Mar 2016 - 8:16 PM, said:

You answered your own question. GIGO- do not think that just any data are better than no data at all if what little you have is not of known quality. There is no reason to believe that an unreliable dyno is reading linearly. If not, you cannot even conclude your torque curve is dropping, which is what has you concerned.

Doesn't explain the drop in power before the 5600 rpm mark........ when a truck on the same dyno the next day pulled to rated rpm. Period, end of story.

Georgia1911 · March 15, 2016

Doesn't explain the drop in power before the 5600 rpm mark........ when a truck on the same dyno the next day pulled to rated rpm. Period, end of story.

Sure it does- the dyno cannot be trusted. An habitual liar may be telling the truth from time to time, but how can you tell? Stop chasing a ghost and get numbers that you can be sure are meaningful.

Badass69 · March 15, 2016

Georgia1911, on 14 Mar 2016 - 8:31 PM, said:Georgia1911, on 14 Mar 2016 - 8:31 PM, said:

Sure it does- the dyno cannot be trusted. An habitual liar may be telling the truth from time to time, but how can you tell? Stop chasing a ghost and get numbers that you can be sure are meaningful.

Right. Thanks tips lol.

None the less I am sure I will find out what this things issue is. The calibration effects the power..... and maybe even not then considering the one load cell allowing around 500 hp vehicles to be tested was functioning fine. Even if the calibration on the load cell is off it doesn't affect how it registers power versus rpm. End of story...... again!