Turbo 4.8L questions

Ok, I dont have a truck but since this motor comes in the trucks I figure this is the best site to get the info I am after. First off the car is a 92 Z28 that I swapped a LS1 into and have recently pulled the motor to go another route. I have a 4.8L and am going to turbo it but I want to keep it as "sleeper" as possible unlike it was before with the cammed LS1. I was thinking after doing some research looking at a few other 4.8L turbo builds of going with a LS6 cam, 241 heads (since I already have those off my LS1) to drop comp. and my LS6 intake. Then I will build a kit using truck manifolds and my question is which turbo to go with, the car has a fully built RMVB with a brake and will have around a 3K or so stall once its restalled. The car is LIGHT as with the LS1 in it weighed around 2900lb raceweight. The only plans to do anything to the 4.8 is a simple rebuild with rod bolts then later down the road when I get the extra money I will build my LS1 to handle boost or go with a 370 6L. Any help would be greatly appreciated!

Thanks, Nick!

You've explained your plans but what exactly are you asking? I'm running a turbo'd 4.8L and I think I can help but I'm not sure what information you're after.

Sorry, my question was in the middle of all that guess I should have proof read better before posting. I mainly want to know which turbo would be a good turbo, I would like one that can make good power but not lag like crazy and have a useless short powerband. I'm kinda new in the turbo field so I dont want to waste money buying one thats doesnt work properly. I guess a reasonable power goal would be 550-600hp if that helps. And also what kind of boost levels can these motors handle safetly?

In that case I'd say run about a 70mm. It'll spool pretty quick and you'll be able to squeeze about 600 out of it with a good tune and low enough IAT's. If you're new to turbos, then you may want to research a bit more before taking the plunge because there are a lot of "little things" that need attention. I can fill you in on a lot of it if you'd like - I've learned a lot since I first went the turbo route. These engines can handle more boost than you might think. I've ran 14psi a number of times with no problems and the only reason I didn't turn the boost controller up further, is because I'm still running the stock 1 bar MAP and I doubt my injectors can support more than 14psi.....even with both meth nozzles. An LS6 cam is a good boost cam though.

Thanks for the info. Thats around what size I was leaning towards so I am on the right track. As far as the little things, I know fuel system if the most important thing to keep the motor safe so that'll be taken care of with twin 255's in tank. I'm pretty sure the stock fuel lines can handle that much power without a issue as its a 3/8 supply line if I recall right. I know there are other things I am either overlooking or forgetting right now but I wont even be starting the turbo side of the build untill I get most of the parts I need and get the fuel system taken care of. Which will be a few months away once It cools down around here since welding in 110* heat index sucks! If you can help with anything or see anything I may be looking at wrong please let me know, I would rather know first hand then learn the hard way!

Oh, and as far as tuning and any other things I may need I have Allan at Futral right down the road who takes care of all that for me so tune will be good. I just dont like bothering him while he's working making him a living with my little questions that someone can easily answer on there free time. I'd say if I can get that 600hp out of this setup I will be happy since that'll be faster than the LS1 was NA so that sounds good! BTW what is the record in the 1/4 for a 4.8 anyways?

Yes, the fuel lines will support 600rwhp, but I don't think you'll need TWIN 255's. If you're going for a lot of boost though, then why not? When I say little things I mean stuff like:

- proper PCV setup so the turbo doesn't pressurize the crankcase
- oil restrictor for the turbo so you don't blow the turbo's seals
- keeping your IAT's cool enough (possibly running water/meth injection)
- running colder spark plugs

I might be forgetting a few things but just a little food for thought. And I have no idea what the 4.8L record is

Ah, yeah those things I overlooked but they make sence. I am going to go ahead with twin pumps mainly for personal comfort since to much is never enough to be safe. I knew about the PCV system but not sure of how to go about setting one up. I'm guessing there is a certian restrictor for the setup so once I figure which turbo I'll know more there. And I personally dont like the Idea of having to rely on Meth or water inj. since I've seen what happens when a pump goes out on a buddies car. But if I have to I will. Plugs I know about, I have a few different sets for on motor and nitrous plugs so I'm used to having to use colder plugs. I'll be doing some more research tomorrow and see what else I need to learn. Thanks for all the info!

There are a few ways to setup the PCV and it's not too difficult. I can give you all the details on PCV setup if you want. As for the oil restrictor, with a 70mm journal bearing turbo you would probably be fine with a 0.065" restrictor.

Sure, go on ahead with the info on the PCV system I'm more than willing to learn! I was thinking of a master power T70 to start off with since I'm trying to make this a budget build to start off with untill I build the big motor and spend big money on a good turbo. Which trim should I go with, they have P and Q trim and also what A/R?

The best way to setup a PCV system for boost is to swap in an LS6 valley plate. Once done, all you have to do is tie the valley plate into the intake manifold with an inline check valve and put filters on the valve cover ports. If your engine is not in the car this would be the best route. If the engine is in the car, you can use switch valves triggered by a pressure switch to vent the crankcase to atmo during boost. I'll have to draw up a diagram for it so if you'd like to see it, let me know cuz I don't have one drawn up. Oh, and here's the LS6 valley plate info

http://www.ls1howto.com/index.php?article=18

I'll go ahead and do the LS6 valley plate since the motor is still out the car, since thats the best way. Any opinions on a MPT70, P trim, .68 A/R? Said to be good for 700hp so that sounds right up my alley. Once again, I greatly appreciate the help!

I'm not too familiar with MP turbos but there is a guy on here that knows everthing about them. I think "KBracing" is his screen name and I believe he is a MP turbo dealer. A .68 A/R sounds good for a 4.8L tho. As for the LS6 valley plate, make damn sure you use an inline check valve between the valley plate and the manifold. It will prevent boost pressure from pressurizing the crankcase which is VERY bad with a turbo setup.

As far as check valves is there any better than others? I found the info on that turbo that I was needing and it made around the power I am looking for at a certian amount of boost so I think I'm going to try it out.

When it comes to little parts like check valves, I always get a migraine trying to find what I'm looking for. That said, there aren't any "good" check valves that I know of. I just use whatever I can find that will suffice. The only place I know of off the top of my head that sells check valves for PCV systems is STS. Be careful tho, STS has some TERRIBLE customer service.

A MP T70 with .68 a/r would be right on the money with a boosted 4.8 and LS6 cam ;)

NO pcv on a boosted motor!!!!!!!!!!!!! save yourself time and money and just vent each side of motor with -10 to a breather tank and be done with this. if this appilication works for 1500+ setups it will work for your 500 hp setup

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Originally Posted by kbracing96

A MP T70 with .68 a/r would be right on the money with a boosted 4.8 and LS6 cam ;)

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Awesome, just what I needed to know!

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Originally Posted by Quik

NO pcv on a boosted motor!!!!!!!!!!!!! save yourself time and money and just vent each side of motor with -10 to a breather tank and be done with this. if this appilication works for 1500+ setups it will work for your 500 hp setup

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Yeah after figuring a few things out thats what I came up with doing to make it simple and easy without headache. Impressive setup you have on your truck also! I bet that thing flys from a good roll!

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Originally Posted by Quik

NO pcv on a boosted motor!!!!!!!!!!!!! save yourself time and money and just vent each side of motor with -10 to a breather tank and be done with this. if this appilication works for 1500+ setups it will work for your 500 hp setup

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just checking but i only have one breather filter vented to atmoshpere on the oil cap side,is there soppose to be another one on the other side?

each side of motor should be vented, if you can pick up a LS6 valley cover and vent the valley of motor as well

interesting

I'm starting to agree with George. I had an improved STS PCV setup and even with the catch can I was still losing oil. I pulled all that crap off and just put filters on the valve covers. I'm hoping to at least see LESS oil consumption. From what I hear, oil consumption through the PCV increases heavily with a turbo'd engine. Hopefull the KISS solution will remedy the "dissapearing oil" problem

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Originally Posted by jetmech

You've explained your plans but what exactly are you asking? I'm running a turbo'd 4.8L and I think I can help but I'm not sure what information you're after.

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what heads will work on my 4.8l so I could boost it?