4.8L Turbo Build

[1bad396ss]

Moving along with my 4.8L / 4L80E Turbo project for my 68 Short Fleetside.

I have a couple of questions for anyone who has picked up a nice drop out LS type motor for these builds.


1. Top Ring Gap: researching this topic; many people open up the stock top ring a bit to allow for more heat expansion under higher boost levels. What is the recommended range for this gap? At what power/boost level is this necessary?

2. Rod Bolts: when going for high revving/boost I understand many folks swap out the stock rod bolts for ARP. Do you simply remove the stock bolts and swap in the ARP's to their recommended torque (not worrying about end size etc)? At what power/boost/RPM level is this necessary?

3. Head Studs/Gaskets - it seems like a lot of people are throwing in studs and new gaskets without any machining of the head/block. Is it common practice to ever just swap the bolts for studs without lifting the head and gasket (although that seems risky). I understand the LS9 cam is a good choice / any other good turbo cams with street-able manners recommended. Are the guys just swapping without machine work just cleaning mating surfaces and moving on? At what power/boost level is this necessary?

4. Fuel Rails - I am running an in-tank Aeromotive A-1000 pump etc. Can someone please recommend a good set of rails to use on the truck manifold and what injectors are being used (not worried about flow ratings / just what companies' products are preferred for quality etc)


I have the motor/tranny/harness etc all cleaned up and ready for the next stages. Power goals are kind of open ended. Currently looking at Borg Warner S475 as well as a Precision unit (sticking around 76mm on the turbo). I would like to throw down 500 rwhp daily and crank it up just when I feel like it. 99.9% of the time, I just want a nice driver that is a bit ignorant when the go pedal is mashed.

I always appreciate anyone's help or advice. If you have any good links, feel free to pass them my way.

[69trk]

Similar to what im doing...
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[wgeyer88]

I'm in the process of doing a very similar swap to yours, with the exception of a 6.0 LQ4 instead of the 4.8. I'm leaning towards a S475 as well!

I do a TON of reading over on LS1TECH.com, they have a forced induction section where many people use the 4.8, 5.3, 6.0 engines. I would suggest doing a search on that site, you will easily find answers to those questions. What you're doing has been done there many times. You can probably find a build to use as a guideline, that way you know everything works well (well...maybe).

Don't quote me on any of this because I'm still fairly new to the LS FI world but this is the best I have:

1. If you only want 500 hp at the wheels, I wouldn't even worry about the ring gap. Most of the higher mileage engines have enough of a gap already. Many people seem to be running 600+ rwhp without touching the gaps. I personally won't be touching mine (for lack of knowing any better I guess).

2. There seem to be many different opinions on rod bolts. Most people say the rods will bend before anything happens to the rod bolts. Again, I'm not changing mine out.

3. For lack of knowing any better, I'm just swapping out my gaskets to LS9 gaskets and head studs, no machining.

4. Can't help you on this one, but it seems the stock truck fuel rails are capable of much more than 500 rwhp so I'm not sure if they need to be changed out. The Siemens Deka injectors seem to be popular, probably 60# or 80# injectors if you want room to grow.

There are quite a few people on this site that are very knowledgeable on the subject as well. I know Wasted Income has a pretty sweet FI build and a few others as well. I'm sure they will chime in soon to give you some better answers.

You should post some pics of the build!!!

[BR3W CITY]

Take a look at the Junkyard Turbo section of TheTurboForums
There is/was a member pushing like 8xxhp on a stock bottom end, and the only thing he did was gap the rings. I believe he lists his tolerances on his thread. At 500 tho, Wgeyer is pretty correct about the stock setup being ok.

Rod bolt are a good idea if your gonna open it all up and disassemble, but just like the ring gap, it isn't 100% needed. There are many followers of the "throw a turbo and some fuel on it and walk away" strategy of turboing these, especially at only moderate power levels. I'd say its a bigger concern at high rpm's than it is at middle boost levels.

Head studs; you've got high goals if you really think you need them. You won't be lifting a head or pushing coolant at ~10-15psi most of the time.

I like FIC for injectors, most of them are on the Deka body, you'll want to have them setup with the Ev1/ev6 plugs instead of the MultecII plugs the truck injectors use. Since your fine with an aftermarket rail, this shouldn't be a problem (it would raise the stock rail about 1/2"). 60# would be the comfortable minimum, bigger couldn't hurt, just don't throw 120's or something huge on there or it'll be so scaled down in the tune it won't want to run. All an aftermarket rail really ends up being is a ported aluminum tube Any of them made by a decent company should be fine, just skip the ebay stuff. You'll end up needing an FPR of some type as well, since the stock truck setup was built into the rail.

[69trk]

I also used the holley injectors. Pretty fair price. I also think the truck intake and rails will work fine.. what do u plan on using for exhaust manifolds?
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[tinydb84]

Originally Posted by 1bad396ss

Moving along with my 4.8L / 4L80E Turbo project for my 68 Short Fleetside.

I have a couple of questions for anyone who has picked up a nice drop out LS type motor for these builds.

Disclaimer. All my input is just from hanging out over on the LS1tech forums

1. Top Ring Gap: researching this topic; many people open up the stock top ring a bit to allow for more heat expansion under higher boost levels. What is the recommended range for this gap? At what power/boost level is this necessary?

I wouldn't bother until 600-700 hp. Many people run stock short blocks higher with no changes


2. Rod Bolts: when going for high revving/boost I understand many folks swap out the stock rod bolts for ARP. Do you simply remove the stock bolts and swap in the ARP's to their recommended torque (not worrying about end size etc)? At what power/boost/RPM level is this necessary?

Some people will swap and just torque them down. I have seen pics of ruined bearings after doing so. Some people have no problems. I would guess 750hp is where I have seen people making the change. My brother's 6.0 will likely be in the 500hp and he is swaping the bolts.

3. Head Studs/Gaskets - it seems like a lot of people are throwing in studs and new gaskets without any machining of the head/block. Is it common practice to ever just swap the bolts for studs without lifting the head and gasket (although that seems risky). I understand the LS9 cam is a good choice / any other good turbo cams with street-able manners recommended. Are the guys just swapping without machine work just cleaning mating surfaces and moving on? At what power/boost level is this necessary?

I am in the air as to whether or not I will turbo my 5.3 (whenever it finally gets in the truck). I got a LS6 cam because it is turbo friendly 116 LSA. The LS9 cam will require some changes to the sensors. If you are going to rev high go with LS7 lifters and trays. I would never just swap the head bolts our without changing head gaskets. I am going to mill my heads and use the ebay studs (they have a lot of decent reviews on the board).

4. Fuel Rails - I am running an in-tank Aeromotive A-1000 pump etc. Can someone please recommend a good set of rails to use on the truck manifold and what injectors are being used (not worried about flow ratings / just what companies' products are preferred for quality etc)

The A-1000 should be good for a whole lotta power. I would guess 80lbs injectors. Don't know which rails though.

I have the motor/tranny/harness etc all cleaned up and ready for the next stages. Power goals are kind of open ended. Currently looking at Borg Warner S475 as well as a Precision unit (sticking around 76mm on the turbo). I would like to throw down 500 rwhp daily and crank it up just when I feel like it. 99.9% of the time, I just want a nice driver that is a bit ignorant when the go pedal is mashed.

That is a bit big for a 4.8l and will take a bit of time to spool.

I always appreciate anyone's help or advice. If you have any good links, feel free to pass them my way.

Hopefully that helps. I was researching a turbo for my build for awhile but kinda back burnered it as I have a ton of other work to do first.

[1bad396ss]

Thanks all for the info. I'm liking the leave it alone and boost it thinking; however, I know how I am.... More Power!!!!

If I decide to keep it around the 500 to 600 at the wheels range:
1. Is a valve spring swap necessary if the cam is left stock?
2. Can a boost reference fuel pressure regulator be adopted to stock rails? I'll probably just swap out to nice rails, but doesn't hurt to have options.

I had seen several 4.8's running S475's with good results. I'll keep searching.

I've always liked the overbuild and dial back approach... That can get expensive quick.

I'll get some pics up on this thread soon.

Thanks again.
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[BR3W CITY]

If you leave stock valve springs in it you can risk floating them. The truck FPR runs off vacuum, so it already is one. Its not like on an import where you would run something like an aftermarket 1:1+ Boost reference FPR and use it to deliver more fuel. The FPR just needs to keep 58PSI to the injectors, and the injectors themselves do all the work (with the computer) to keep the right amount of fuel in the engine.

The thing your talking about would ramp FP to the rail effectively giving you a blanket of "more fuel at X boost", for cars that didn't have something like HPT to tune the fuel issues of a boosted car.

Spend some time in the forced induction section on ls1tech (or yellowbullet, but that just gets ugly sometimes)

[tinydb84]

^^the forced induction section of LS1 tech has some really smart people also check out the turboforums.

[softballnrd27]

For your power goals the stock rails should be fine. If you can try and find some fuel rails without the FPR on the rail, they make them I have a set on my truck currently. I am not sure on the years but you can search it to get your answer(returnless rails). If you plan to keep it under 6800 then there is no reason to change the rod bolts. LS9 gaskets and ebay studs are the way to go. Yes upgrade your valvesprings to have more seat pressure to avoid valve float.

[1bad396ss]

Looks like I have more research to do!!!!

For some reason I thought a boost referenced regulator was the way to go. I can also see how keeping proper flow and letting injector opening and closing events control the rest makes sense. Fuel stays at 58psi at all times, injector hangs open longer at that psi, more fuel enters cylinder, fuel pump and rails have to support the volume/flow rate to keep pressure consistent. I

I also thought a boost referenced FPR allows you to get more out of a said injector size given the rating is at a lower static pressure effectively lowering duty cycle through increased pressure instead of hanging the injector open too long.

Understood that studs and gaskets are a good idea.
Springs seem to be a must, which I figured would be the case. Appreciate some recommendations considering a stock cam at this stage (or near stock).
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[tinydb84]

Understood that studs and gaskets are a good idea.
Springs seem to be a must, which I figured would be the case. Appreciate some recommendations considering a stock cam at this stage (or near stock).
Posted via Mobile Device[/QUOTE]

I believe tick makes a couple "blower" cams. The LS6 or LS9 if you want a stock(ish) cam. Remember to buy springs that meet your cam needs.

[tinydb84]

http://www.tickperformance.com/tick-...1-ls6-engines/

[tinydb84]

Here is something you might be interested in:

http://www.lsxtv.com/news/video-twin...e-walk-around/

[Wasted Income]

Originally Posted by 1bad396ss

Moving along with my 4.8L / 4L80E Turbo project for my 68 Short Fleetside.

I have a couple of questions for anyone who has picked up a nice drop out LS type motor for these builds.


1. Top Ring Gap: researching this topic; many people open up the stock top ring a bit to allow for more heat expansion under higher boost levels. What is the recommended range for this gap? At what power/boost level is this necessary?

I've built several turbo LS setups, and the only one that I've opened up the ring gaps on, is the only one I've broken ring lands on...it might have had something to do with the fact that I've leaned harder on this one than any other turbo LS.

The general consensus is that if the motor is "old and tired out" with high miles, you're generally ok to leave the ring gap alone. A newer, tighter motor would probably benefit from some extra clearance. There's no downside to gapping them larger, as long as you do it correctly....however you are also disturbing a perfectly good running engine, so there are risks there. For 500-600 rwhp I personally wouldn't bother.

2. Rod Bolts: when going for high revving/boost I understand many folks swap out the stock rod bolts for ARP. Do you simply remove the stock bolts and swap in the ARP's to their recommended torque (not worrying about end size etc)? At what power/boost/RPM level is this necessary?

How high are you planning to rev it? I understand that it's a 4.8, and you'll probably want to rev it higher to make up for the cube deficiency...lol. I've had good luck simply swapping out stock bolts for ARPs without having the rods re-sized...lots of guys swear it's necessary to re-size, but I've got lots of emperical data that says otherwise. I don't torque them, I use bolt stretch to determine torque. What year is your engine? The 2004+ rod bolts are stronger than the earlier bolts, so if you have a 2004+ engine, i'd leave them alone.

3. Head Studs/Gaskets - it seems like a lot of people are throwing in studs and new gaskets without any machining of the head/block. Is it common practice to ever just swap the bolts for studs without lifting the head and gasket (although that seems risky). I understand the LS9 cam is a good choice / any other good turbo cams with street-able manners recommended. Are the guys just swapping without machine work just cleaning mating surfaces and moving on? At what power/boost level is this necessary?

After pushing water at only 14 psi, I'm a firm supporter of studs/MLS gaskets. I've NEVER done any machine work on a junkyard LS...kind of defeats the purpose of a cheap junkyard bullet. Clean the head and deck, and slap on the 7 layer LS9 gaskets, some studs, and go have fun. It will run for awhile on stock TTY bolts, but WHEN it does push water, while you're pulling the motor again you'll be cussing yourself that you didn't do it to start with.

4. Fuel Rails - I am running an in-tank Aeromotive A-1000 pump etc. Can someone please recommend a good set of rails to use on the truck manifold and what injectors are being used (not worried about flow ratings / just what companies' products are preferred for quality etc)

I made around 500 rwhp on my old turbo 5.3 with a single Walbro 255, -6 feed, and stock fuel rails with 60 lb/hr injectors. I like the siemens 60s. They're cheap and work well. Could even step up to 80s if you want some head room.


I have the motor/tranny/harness etc all cleaned up and ready for the next stages. Power goals are kind of open ended. Currently looking at Borg Warner S475 as well as a Precision unit (sticking around 76mm on the turbo). I would like to throw down 500 rwhp daily and crank it up just when I feel like it. 99.9% of the time, I just want a nice driver that is a bit ignorant when the go pedal is mashed.

Saying that you want a BW S475 doesn't really mean anything. T4 or T6? What exhaust A/R? What size turbine wheel? Those are all factors of how well that turbo will work. That said, I'm a HUGE BW fan...crazy bang for the buck, with OEM reliability (I work for a diesel engine OEM, and we put them on our heavy equipment and on-highway truck engines....million+ miles )

I always appreciate anyone's help or advice. If you have any good links, feel free to pass them my way.

A lot of your questions ask "at what power level, boost, rpm" etc....there is no way we can predict that for you.

A good tune will be your best friend....if you have way too much timing in it, it doesn't matter what your ring gap is, if you're cracking ring lands and knocking the rod bearings out of it.....you know? Start with a very safe and sane tune and slowly turn up the wick. You'll be able to tell what the truck likes....and datalog EVERYTHING. Good luck.

[kamikazekyle05]

What rear end are you planning on running, 12 bolt?

[1bad396ss]

Great info. If I go S475, I would stay T4 and on the smaller side turbine and a/r wise (.96 or somewhere in that area). I'll research some specs and reply. Looking at possibly going a bit smaller 70mm... So many decisions!

The motor is an 03 with 84,000. Looks to be very clean as far as I have been into it so far.

Not looking to rev it to the moon. Just looking for a fun streeter and conversation piece around town.

I think I'll stay with stock gaps/rod bolts and slap on the studs/head gaskets. Like you said, the tune counts before beating on it. May do a cam swap - looking at something along the lines of Isky Triple 12.

I'll never throw a sticky tire on it / sticking with a 12 bolt eaton 3:42's.
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[BR3W CITY]

No sticky tires? Roll racing is for imports.


If your set on doing the head studs and gaskets, then get a new set of lifters since the heads will be off. At higher rpm's there is always a risk of blowing up the stock lifters, which due to the needle bearing design means spraying your cylinder full of tiny needles. Its not the most uncommon failure in high performance builds, though I can't say its exactly typical. An upgraded set isn't the cheapest, but its cheap insurance compared to a failure (same mentality as doing the head gasket).

Skip the isky cam, its not 1970 anymore and that company is behind. I'd suggest either getting something like the Pat G or TSP blower cams (there are a few other good blower cam choices as well, but keep in mind not all are built the same, and some blower cams will not be as good on a turbo truck engine). OR if your more concerned with the budget, get a good set of hardened pushrods and a quality valvespring and pair them with either a used blower cam or a brand new (or takeout) LS9 cam.

On a 4.8 or 5.3 with a 70-76mm turbo, the ls9 cam should be money...on the cheap. lol Fwiw, GM loves the ls9 cam on its in house projects, and some major engine builders like Lingenfelter have switched the Ls9 cam as their "spec'd" blower cam.

[1bad396ss]

Not racing at all; from a roll or from the dig. Those days are over.

If I wanted a racer, Id pick a better platform. Just looking to have fun driver.
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[Wasted Income]

Originally Posted by BR3W CITY

Roll racing is for imports.

To paraphrase you....it's not the 90s anymore.

[t300]

1bad396ss how did this build turn out?

[Willie Makeit]

Originally Posted by Wasted Income

To paraphrase you....it's not the 90s anymore.

[1bad396ss]

Hasn't turned out yet!!! Coming along slowly but surely though. Body has been at the shop for a year (I told them to take their time and use it as filler work while I'm finishing the chassis). Engine, tranny, fuel system, turbo hot and cold are basically all finished. Working on mounting the fast rails to the truck intake now. Odds and ends from a drivetrain standpoint.

I should have done a build thread. Between family, work, and this hobby; there isn't much time to do much else.

Here are a couple pics of the chassis.

[1bad396ss]

A few more showing gate placement / the cab in the pic is just a spare for placement (cannot wait to offload some of these spare parts(trucks!) I have eating up space. Having that cab proved perfect for mocking up everything.

[1bad396ss]

Downpipe placement