Popping on a twin turbo carburetor truck

[dline]

My buddy has a twin turbo on his truck and it pops/shudders when it hits about 10 pounds of boost, and shuts down, he has lightweight springs in the wastegates, and its not going lean, anyone have an idea why it would do this? He has his floats like a blow thru carb also I think

think his air/fuel is in the 11s to low 12s.....he has a timing retard box also

don't know his spark plug gap

 

[OnyxSSS]

might be valve float, what kind of springs does he have?

 

[Sean]

Need to know alot more about the car. Tell everything. Leave no detail untouched.

 

[dline]

383 engine, oem stall converter, 727 trans, 3.55 gear i think, 4500 pounds max probably

 

[Sean]

Plugs,jets,carb,Fuel,Fuel pressure,Timing,Plug pictures. the more info you give the easier this is to diagnose.For instance I didn't know it was a chrysler product till just now. What heads ? Pistons Cr. Seriously this kind of info is incrediablly helpful in diagnosis.

 

[ctgreddy]

isnt that afr a little lean for a boosted engine? i always learned boosted motors to like 10.5/11.0:1 afrs. thats efi tho.

 

[Sean]

isnt that afr a little lean for a boosted engine? i always learned boosted motors to like 10.5/11.0:1 afrs. thats efi tho.

Observed AFR as seen on a wideband is really a trend indicator. the spark plug is really the final word on it. Now that siad getting a safe starting point with a wideband sure doesn't hurt.

 

[dline]

I know he is running a forged 383 (60 over), Basically stock heads (Upgraded springs/push rods - I think roller rockers) 9:1 comp. He is running a solid 8 psi with fuel (fuel is not the issue for sure). He has big Walbro pump with return. Summit Timing box, Billit dist, Dual plane Edelbrock intake, 850 holley with proform main body, Blow threw carb floats (not sure on jetting or Timing)

 

[Sean]

Big block chryslers like alot of timming. If he has stock iron heads hes in a bit of a pickle. Find out what he is running. If it is a pump gas engine I would expect a NA 383 to like around 38 total on motor. So 28-30 on 8 psi of boost isn't to far out there. Now the issue is with factory iron heads and the propensity of the chamber to hold heat. Might need to come down to 24-26 to work with pump fuel. Just some food for though.