1994Vmax

iTrader: (4)

I am kind of curious if other Gen V 6.2 guys have dyno sheets kicking around. I had my truck tuned on a Mustang dyno and I found it odd my horsepower peaked at just over 5000 RPM..... and then started falling lower instead of carrying to 5600 RPM like I would expect at least. 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 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.

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.

Vortec350ss

iTrader: (20)

This is with the tune?

Do you ha e logs of it? Do you know where timing is set? Stock tune files drop timing a lot at high RPM. It really makes power drop off earlier than it should.

A clogged up intake will show as excess vacuum at higher RPM and a clogged up exhaust would show as airflow and injector duty going flat or declining earlier than it should.

Where is max hp based on factory ratings?

1994Vmax

iTrader: (4)

I know where everything is set and the data logs look normal. With or without the custom tune the truck did the same thing. Factory hp peak is at 5600 rpm...this truck is already declining rapidly by the time it reaches that... makes me think it's related to the vvt.

Vortec350ss

iTrader: (20)

Very well could be. Is the torque peak early as well? The cam should be phasing before the tq peak, and if its not moving the tq peak should be shifted lower as well.

1994Vmax

iTrader: (4)

Hmm. Well that idea might be out then.... which isn't bad I guess. The torque peaks both stock and tuned and nearly bang on 4100 rpm which is where GM rates them. My HP on the the other hand peaks at around 4900 rpm.... carries flat to around 5100 rpm or so and then drops off. By 5272 rpm on the graph I am already losing power and by 5674 I have dropped by about 20 HP from peak. The graphs are identical stock or tuned in that regard.

He picked me up close to 40 lb ft of torque at peak and in other areas significantly more than that...... but horsepower peak was like 16 HP...... that's it. Something is killing it's top end here.....

I just read an old thread in here about some Lance Atkinson and his truck pulling to 6400 RPM with no real mods...... I have the same camshaft as the LT1 Corvette ( LT1 and L86 longblocks are part number for part number identical) so I should be pulling harder than this. The truck feels okay but maybe I wouldn't know any better lol. When I bought it this was easily the fastest new one I drove so something isn't right.

I guess I can log when I have time..... and I will pull the air filter and see what it looks like.

I checked on gmtruckforums too as a couple guys posted stock graphs and they are pulling hard to 5600 rpm or more completely stock. So...... something is wrong with my truck even if it doesn't really feel like it lol.

Here is my pic of my graph:

Vortec350ss

iTrader: (20)

Maybe it is cam timing. Check the tune to see when phasing starts. It does seem to make sense as the right answer.

1994Vmax

iTrader: (4)

Maybe yeah. I guess I could load my tune and one from the repository to see if they are the same and then log it to see what it's actually doing. The only thing I changed recently was I flashed it with efilive to remove the limiter and afm... then the tune was redone with hpt. The stock file is my efilive tune and that was the base run. I did go to 5w30 weight oil too instead if gm's recommended 0w20... but if anything if it's like the older trucks it should just retard the cam earlier if oil pressure has anything to do with it. Gm specs 5w30 on the vette too so I doubt that has anything to do with the problem as guys seem to like loading the Vette's cam phaser values as an upgrade for the trucks..

Vortec350ss

iTrader: (20)

Interesting... I didnt know they spec'd 5-30 on the vette.

1994Vmax

iTrader: (4)

Yep... wet sump or dry makes no difference. They spec water in the trucks on the sole goal of slightly better fuel economy lol.

Pulled the air intake and no surprises.... filter looks new still. So unless mine is choking and we didn't notice and other trucks don't.... probably nothing to do with anything.

MINK

Have you witnessed other vehicles on this Dyno ? If your trucks feels good...maybe it is! lol.