4.8 swap?

[T/A Addict]

Nah.... I wasn't going to work the heads. Don't plan on doing much to the motor right now other than maybe a cam.

[68Formula]

Nah.... I wasn't going to work the heads. Don't plan on doing much to the motor right now other than maybe a cam.

You'll want a different cam for boost versus N/A. But you could at least pick some decent springs that will work with either type if you plan ahead.

I'd also recommend upgrading the stock rocker arms with something like this (example, but there are others out there):

https://www.briantooleyracing.com/bt...kit-37642.html

If the stock needles let go due to the higher loads from more lift, rpm, boost etc. ;it can have catastrophic problems.

[68Formula]

Duplicate post

[F-Body International]

Dont put $1 dollar into the 862 heads. The best bang for the buck are some 799's. PM me contact info, will help you build a combo and give some insight. The typing kills me, lol.

Why not?

4.8 heads are high compression heads but the only downside is a slightly smaller intake valve....if I recall off the top of my head.

The main ones I’ve heard to stay away from are the very early perimeter bolt LS1 Heads.

[Schwartz Performance]

We've done a couple 4.8's.. It'll put over 300hp to the tires with a stock LS3 cam.

[DualQuadDave]

Why not?

4.8 heads are high compression heads but the only downside is a slightly smaller intake valve....if I recall off the top of my head.

The main ones I’ve heard to stay away from are the very early perimeter bolt LS1 Heads.

It's just a bang for buck issue. Porting/VJ/springs all cost the same. Why put all that into a head that is not that great? The $$ difference is minimal, just sell th 862's and go 243/799. If you go bigger later, you dont have to buy heads again, either.

[F-Body International]

It's just a bang for buck issue. Porting/VJ/springs all cost the same. Why put all that into a head that is not that great? The $$ difference is minimal, just sell th 862's and go 243/799. If you go bigger later, you dont have to buy heads again, either.

Why not? From what I’ve gathered, most cathedral port LS heads flow roughly the same air once ported out. Any other stock GM head will cause a 4.8 to lose compression.

I don’t want to come off sounding like I’m an engine pro. Is there something that stops the 862 from being able to accept a larger valve? I just don’t see why someone would want to drop compression.

[andrewb70]

Valve size is limited by bore size. The 243/799 heads have better ports. They are easy to spot because they have a D shaped exhaust port. The 243 castings were used on the LS6.

Andrew

[F-Body International]

Valve size is limited by bore size. The 243/799 heads have better ports. They are easy to spot because they have a D shaped exhaust port. The 243 castings were used on the LS6.

Andrew

So let me get this straight, you’re saying the 4.8 862 heads can’t run a larger valve due to the 4.8 block bore but the 4.8 engine can accept other GM heads with a slightly larger valve? Is there a different valve angle built into other LS heads that allow for the larger valves to be used on the 4.8?

I’m just curious to see why one can’t get some stock LS1/LS6 valves and install them on the 862 heads. I have a 4.8 with 862 heads myself.

Please inform!

[DualQuadDave]

So let me get this straight, you’re saying the 4.8 862 heads can’t run a larger valve due to the 4.8 block bore but the 4.8 engine can accept other GM heads with a slightly larger valve? Is there a different valve angle built into other LS heads that allow for the larger valves to be used on the 4.8?

I’m just curious to see why one can’t get some stock LS1/LS6 valves and install them on the 862 heads. I have a 4.8 with 862 heads myself.

Please inform!

Hi, yeah there seems to be some confusion on the 4.8's. I never said you could not run a bigger valve on the 862's, just that cost wise , it's not worth it to upgrade them. Bore is same as 5.3 and GM put the same 243/799 heads on those in some applications(LC9 for example) from factory. Shrouding is a non-issue, they work just fine, same valve angle. As far as swapping valves to make a lesser head work, why? I can see if there were some mitgating factor that forced a better solution, but I do not know of any in this case. The 243/799 heads are still cheap per what you get(although price is going up), they are way to go vs making something try to perform "as good as" . Any questions, let me know

EDIT: Part of this discussion should mention intake manifolds, as well. The very hardest thing to make in a tiny motor is torque across a range. For that reason, any sheetmetal ebay intake is out. The Dorman LS2/FAST 90 or maybe MSD Atomic for low profile, the TBSS if you have hood space would be best by far over any of them torque wise. Keep in mind, 400whp is not that hard to do with a 4.8, just making it something that you want to drive is the trick.

[T/A Addict]

TBSS intake referring to the stock intake?

[T/A Addict]

Since I will not have any form of intake or pcm right off I am considering intake/carb setup.

[DualQuadDave]

Since I will not have any form of intake or pcm right off I am considering intake/carb setup.

Yes, TBSS is stock Trailblazer SS. Carb intake, go dual plane all the way. As far as carb size, not even sure what to recommend, either 650 or 750 and see which has the better driveabilty. My $$$ is on the 650 and should be close in peak power.

If you need an intake, my buddy might have a carb dual plane LS intake for sale. Will check with him.

[andrewb70]

Since I will not have any form of intake or pcm right off I am considering intake/carb setup.

This makes zero sense. Assuming you have a carb, you still need an intake and an ignition box. You can use that money towards an aftermarket ECU, which will be very flexible in terms of tuning. Use the Holley HP with all of the stock EFI hardware.

Andrew

[F-Body International]

T/A Addict,

To go along with what the other guys are saying...you will still need a computer to tune timing on an LS engine if you’re using a carburetor. It could even be more expensive if you use a carb setup on an LS engine. Nothing wrong with a good tuned carburetor but make sure you weigh your options. Again, you will still need a computer for timing control because LS engines don’t have distributor based timing.

[T/A Addict]

Computer tuning is actually not required. The MSD ignition controller has different timing chips that are used.

Intake and controller would cost about 650 new and almost all that is needed while an intake, injectors, harness, ECU will be substantially more.
Not that I have decided one way or the other yet, I may just take time and build the turbo build and go Holley ECU and not even spend the time/effort on carb setup.

[T/A Addict]

I have decided that I will, for now put in one of the Pontiac 400s I have and enjoy the car while I buy what's needed and prep for the 4.8 build/swap. No carb setup... FI only and probably turbo, if I can hit at least 500 rwhp with a reliable, fun and moderate boost build I will be more than pleased.

[AU Doc]

^^^^ If there was a thumbs up, I'd click it.

[Beantown]

I'm building a nova with a 4.8 right now with plans to upgrade to an aluminum LS later and put the 4.8 in my girls jeep. With my car needing EVERYTHING the budget is tight. The 4.8 will outperform a stock or mild 350, I'd say that's a fun street car. If you're not looking to get every 10th of a second or stand on any podiums I don't see why you shouldn't pull the trigger.

What do you have for brakes and suspension? You can never have too much handling or brakes, but you can have too much horsepower. If your car is running stock brakes and suspension high horsepower shouldn't be your priority upgrade.

I've always focused on chassis before Horsepower, you can upgrade power once you can stop and turn

[Shawn0331]

Also building a 4.8 for a high rpm low torque road race motor. Just to clarify on the 4.8 and other gm heads. The 4.8 has the shorter stroke like other have mentioned which makes it requires a dedicated head with smaller chamber. the 5.3 has a normal stroke so you can throw 243 and other heads on it no problem. if you did that with the 4.8 you would loose a significant amount of compression. Regardless you would need to grind down the heads to around 58cc to get compression on par with the other high performance motors making the head worthless for other ls engines down the road. Just food for thought. Also stick to FI and see if you can score the oem harness and ecu for free. There is tons of shops you can send the harness and ecu out to convert it to stand alone for sub 500$.