^^ Not what I want to hear, HA! Kind of tired of working on it at the moment, but I'd be looking to correct the cam and turbo in the future.

Valve springs are the isky single beehive 165A's shimmed .030 (130 seat pressure @ 1.8", 330 open pressure @ 1.2") on the intake side at the recommendation of stock48. They've been in there for about 3 years now of abuse, spinning to 7200rpm on countless occasions...

 

Your cam is fine, your intake is totally wrong for your setup


Replace the valve springs and see if that helps...valve springs have a life span to them

Increased boost could be causing valve float

 

Ok, I suppose the springs could be wore out - and I've said (since all this started) that it seems to not rev, or run through the rpms, very quickly imo.

So, is a high ram ALWAYS wrong for a 4.8l? Would a s475 utilize the benefits of the high ram more/better and make the combo more inline with what it should be? Reason I ask is because I'd be considering an s475/83 1.0 A/R if/when I upgrade the turbo.

 

Stock 4.8 will never use a holley to fullest..it may dyno but never et....youll need a transbrake with 5000 stall and steep gears with a large cam that pulls 7500 8000 rpms



Youll go faster keeping motor normal....holley works ok on a 6.0 but better for a 4xx cube motor


You have alot of members out there going very quick with a stock 78mm intake and some using a gmt900 intake


Fastjew is 11.0 with a mp70mm stock intake...something to consider and hes 120mph amd foot brakes 1.5s or 1.6s

 

Stock 4.8 will never use a holley to fullest..it may dyno but never et....youll need a transbrake with 5000 stall and steep gears with a large cam that pulls 7500 8000 rpms



Youll go faster keeping motor normal....holley works ok on a 6.0 but better for a 4xx cube motor


You have alot of members out there going very quick with a stock 78mm intake and some using a gmt900 intake


Fastjew is 11.0 with a mp70mm stock intake...something to consider and hes 120mph amd foot brakes 1.5s or 1.6s

 

Ok, good to know. Thanks! Yes, fastjweb's truck is a beast!

I may throw the stock intake back on. Before I do that, I'll get the current issue figured out first (more boost, slower ET - which isn't the intakes fault) so at least this issue is figured out.

 

I dont think the current intake is hurting you any, so I wouldnt spend any money on a replacement.

I would put a pressure gauge on both sides of your intercooler, willing to bet you have a lot of pressure drop across it. I know with an old setup of mine I couldnt run more than about 16psi on an 80mm, but the turbo was putting out about 25psi. Better intercooler picked up a ton of power.

Also very easy to add a pressure gauge to the downpipe as well.

 

Valve springs

If you do youre own logging setup the air mass and torque...make a pull and see where power is falling off and watch for odd fluctuation in air mass

 

Im running my 376 engine blow through carb with the 88/83 right now as you know, but am building another harness to swap back efi soon and will be throwing a stock intake on it aswell just to see how it works. They always tell me to never fear the stock intake!! haha

 

Truth is the turbo really doesnt care about what intake you run, unless you run big cubes or want every last bit of power at high rpm. For 95% of the trucks on here and in general, the stock intake will work just fine. Just looks stupid.

I always like running dual springs with boost, but thats just me.