Dynamometer Results & Comparisons - What would cause this?

Every time I have had my truck on the dyno it has a weird drop right at peak boost. It only does it above 9psi so I guess it could be a few things but I wanted some opinions. Here is my setup and dyno graph.

stock 6.0L
STS kit, FMIC, Meth, TC 76 BB turbo w/.96 housing
z06 cam and valve springs
built 60e by performabuilt and Yank trt3000 stall

This dyno run was at about 13psi and 20 degrees of timing with no knock and the converter unlocked. The truck pulls good on the street and it has ran a best 11.81 on 11psi. Could it be blowing through the converter or trans slipping on the dyno? Any ideas are welcome. Thanks

valve float.

Yep, or a wastegate or blowoff valve problem.

Jim

valve float.

I was thinking that too. I'm also thinking that the meth might be blowing out the spark a little too. I closed my plugs down to .28 last night and I'm going to back the meth off a little and see if that helps before I mess with new valve springs.

Yep, or a wastegate or blowoff valve problem.

Jim

Can you elaborate? I am not seeing and boost drop or spike, it holds it's boost level nicely.

I had it back on the dyno today and it did the same thing again with the tighter plug gap so that wasn't it. It actually falls off right when it reaches full boost and the wastegate opens all the way. Could it be something with the wastegate or deffinitely valve float? It made 540rwhp today at 14psi but at 4800 rpms.

what dyno?

what dyno?

Dynojet

looks kinda similar to mine....

http://www.ls1tech.com/forums/dynamometer-results-comparisons/1195639-528hp-491tq-but-have-you-ever-seen-graph-like.html

looks kinda similar to mine....

http://www.ls1tech.com/forums/dynamometer-results-comparisons/1195639-528hp-491tq-but-have-you-ever-seen-graph-like.html

Yeah, I've been watching your thread to see if you figured it out. I put mine back on the dyno Saturday tried a few things but nothing worked. So far I have tried the following.

pressure tested all piping
pulled air filter
with and without meth
closed gap on my spark plugs to .27
locked the converter for one run to check for slipage
changed my wastegate to vent to atmosphere

Nothing seems to change on the dyno so I'm going to upgrade my springs and change to the 7.425 push rods. My problem gets worse the more I up the boost. At 8-9psi my power peaks and stays flat to 5500 but at 14psi I lose 50rwhp from 5k to 5500.

ya it sucks... I think im gonna break down and try new springs when i get the money for them.

What springs are you running? I am running PRC dauls with only 8000 miles on them.

Im really starting to wonder if its the ls6 cam... I posted a link in my thread to a thread in with a bunch of other dyno sheets where ls6 cams were used on several differnent motor setups and they all did the same!

kinda makes me wonder??????

ya it sucks... I think im gonna break down and try new springs when i get the money for them.

What springs are you running? I am running PRC dauls with only 8000 miles on them.

Im really starting to wonder if its the ls6 cam... I posted a link in my thread to a thread in with a bunch of other dyno sheets where ls6 cams were used on several differnent motor setups and they all did the same!

kinda makes me wonder??????

I'm using ls6 yellow springs right now. I looked at my dyno sheet again from Saturday and it looks like venting the wastegate to atmosphere did help some.

I read through that post and I don't understand why some people like Parish and WJMark have had great luck with the ls6 cam and a turbo but some people have trouble.

I installed PRC duals tonight and they didn't seem to help any. I did a few pulls and my fuel trims didn't change any and it still feels like it struggles above 5k. Any other ideas? could it be a back pressure problem since it is a STS kit?

This is a graph from a TC76 BB .68 AR on a 6.0. It's from the member Stock48. It peaks at like 4500. What size engine do you have? I think the turbo is choked up out top.

http://www.trickperformanceproducts.com/images/spec/jarod_dyno.jpg

This is a graph from a TC76 BB .68 AR on a 6.0. It's from the member Stock48. It peaks at like 4500. What size engine do you have? I think the turbo is choked up out top.

http://www.trickperformanceproducts.com/images/spec/jarod_dyno.jpg

Intersting...

I have a 5.3, 317 heads, 02 z06 cam, 7.425 pushrods (around 8.5:1 compression)

turbo is a MPT70/.96AR

I have a stock 6.0L with the z06 cam. I do have the .96 exhaust housing on my turbo and I think that dyno was with a smaller AR but you might be right. I wish I understood compressor maps so I could figure out if I am pushing to much air flow for this turbo.

I have a stock 6.0L with the z06 cam. I do have the .96 exhaust housing on my turbo and I think that dyno was with a smaller AR but you might be right. I wish I understood compressor maps so I could figure out if I am pushing to much air flow for this turbo.

Hey man im sorry... i was thread hijacking above. may bad, just realized i replied like that in a post that wasn't mine, lmao!

So you changed valve springs and it didn't help, now maybee i wont change valvesprings. This shit is driving me crazy!

Hey man im sorry... i was thread hijacking above. may bad, just realized i replied like that in a post that wasn't mine, lmao!

So you changed valve springs and it didn't help, now maybee i wont change valvesprings. This shit is driving me crazy!

That's cool man. I think we might be chasing the same problem. I hope you figure it out so I can stop spending money. This is driving me crazy.

That's cool man. I think we might be chasing the same problem. I hope you figure it out so I can stop spending money. This is driving me crazy.

LMAO here i am hoping you will figure it out, so i can stop wasting my time and money!!!!

lol, i figure mine out youll be the first person to know!!!

I have a stock 6.0L with the z06 cam. I do have the .96 exhaust housing on my turbo and I think that dyno was with a smaller AR but you might be right. I wish I understood compressor maps so I could figure out if I am pushing to much air flow for this turbo.

You may want to look into the TC78 BB 1.15 AR. That should give you more up top. That's the turbo I've got my eye on for my 6.0. I don't want to fall into the same trap you guys did. I want super quick spool and great pull up to 6k rpm.

LMAO here i am hoping you will figure it out, so i can stop wasting my time and money!!!!

lol, i figure mine out youll be the first person to know!!!

Hey man, I spoke to forcedinductions today and they are saying that it's a back pressure problem with my setup being that I have a butt mount. I did a little research and it seems like STS kits have this problem so I'm going to try a 1.15 exhaust housing to get a little more room up top. Is there any chance that you might be having the same problem with your setup?

Hey man, I spoke to forcedinductions today and they are saying that it's a back pressure problem with my setup being that I have a butt mount. I did a little research and it seems like STS kits have this problem so I'm going to try a 1.15 exhaust housing to get a little more room up top. Is there any chance that you might be having the same problem with your setup?

I have a 3" downpipe dumped right by my starter... i dont think there woud be enough backpressure there...

I was just reading a thread on some other site where they were talking about preload:

even with the smallest amount of preload, with high oil pressure, and especially higher RPM where the lifter is getting filled quicker, it has a tendency to overcome some of the spring pressure and leave the valves open

IDK seems interesting... im am running a 10/30 oil right now and oil pressure is like 60+ at 3000 rpm up... im gonna switch to mobile 1 oil and a lighter weight and see if it will help... also waiting on a pushrod length checker.

If my preload is not right then it can be causing some valve float also...

Mine really looks like valve float and alot of experienced people say its valve float. So im gonna try some things and if it doesn't help ill buy some springs.

O ya when i had an sts kit on my ls1 with the garrett T70/.86AR and I didn't seem to have a backpressure problem... but idk, hope it will fix your problem!!!!

I didn't have as much of a problem with back pressure on my setup when I had the mp70 on it either. What I was told is that with the bigger turbo I'm flowing more air at a slower turbine speed so the turbine isn't spinning fast enough to help blead off the back pressure. I'm going to order the 1.15 housing and see if that helps.