Hi everyone. Just had my car tuned and not very happy with the results. Heres the set-up

GSR Block
LS Crank
LS eagle Rods
Arias 9:1 pistons

GSR Head
Supertech valve springs and retainers
Supertech Valves +0.5mm on exhaust side
Comp cams 57200

Top mount turbo manifold
Custom Garrett T3/T4 0.48A/R ex. 0.60A/Rcomp.
Tial MVR 38mm Wastegate
10.2psi spring but holding at 12.5psi
full 3" exhaust
magnaflow cat
Apexi ws2 universal 80mm muffler
wastegate recirculated back into exhaust

made a peak of 285.9hp but dyno graph shows mostly consistent at 260 from 6250 up to 7750, peak is at 8000 and the torque curve starts to drop consistently around 6500 as well

So here's the problem, my tuner says that the exhaust is getting choked up and because of the cams i'm flowing too much for the turbo. Watching the tune this does make sense. His advice was to go to a .63 a/r on the exhaust side of my turbo to let it flow more. However my thoughts on that is that the exit from the turbin is still the same size and that might not help much. I was talking to the turbo builder in my area (has a great rep and lots of experience) and he was suggesting to go to a bigger wastegate and run an open dump. Another suggestion was to delete the cat, and run an open dump on the current wastegate. Iv'e been in this for a long time and these options make sense to me but I'm hoping for another opinion from someone knowledgeable as well.

 

How did you set the timing? (Mechanical)

Maybe its off a tooth.

 

Engine builder set the cam timing. I asked about that too and it was straight up

 

What mm size t3/t4 do you have?
I would suggest going with a .63 a/r as well. Turbo's like free flowing exhaust. So your returned wastegate isn't helping by adding exhaust back in the pipe. That .48 hotside is small/choked up.

Don't know where you are located at. But would be nice to remove the cat!

Edited. Saw about having 3" exhaust. ...

 

Lol it is pretty quiet. So far what i was thinking was to delete the cat and open the dump and try that. if that doesn't work then change the exhaust housing. Reason for this is to keep the quick spooling of the .48 a/r for track racing. also being cost effective and isolating the problem without changing too many variables all at once

 

*dyno sheet added

 

What size turbo?? 57 trim Garrett? ?

 

ya 57

 

Do you have a boost graph? Looks like a leak or the exhaust is choked up somewhere.

 

Ya that's what I'm thinking. I don't have a boost graph unfortunately. My main concern is changing the exhaust housing. From what i understand it will have more volume around the turbine for flow to create more peak boost on the compressor side. However where the exhaust exits the turbine would remain the same size so changing that won't necessarily affect it being choked up. In my opinion I think my biggest problem right now is having the cat and recirculating the wastegate. But I can't say for sure because I've never had this issue before, nor can i find anything relative searching

 

I will still recommend changing the exhaust housing. You will build boost quickly with the .63 and have a very broad power band. I use to have a boost setup similar to your parts list. I used the stock gsr cams tho. Made 400whp/300+w.t...... on 93 octane. And remove the cat. You won't be disappointed.

I used a 57 trim on a sohc-t(d16z6) build that I did and still used a .63 hotside on it. It was 9:1 compression. I ported the head and intake manifold runners. And 93 octane as well. This is the dyno graph from it.




So I don't know why you are so attached to the .48. It seems like it's at its efficiency level where it's at for how you have your car set up.