4.8 block - want more compression

bigjimmyv3 · August 1, 2015

07 silverado extended cab , I have done some mods already I put a howards cam in it all ready jba longtube headers and borla exhaust an superchips tuned it ,but I want higher pompositon any idea?

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bigjimmyv3 · August 1, 2015

I was thinking the 317 6.0 may work to get the pompositon up a little any ideas

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Chris · August 1, 2015

I was thinking the 317 6.0 may work to get the pompositon up a little any ideas

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317 heads will not fit on the 4.8/5.3 block. They are made for a 4" bore.

bigjimmyv3 · August 1, 2015

Well what can I do to 4.8 heads to get so power, I have the 706 heads on there now and I put a Howard cam .525

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Chris · August 1, 2015

Well a custom tune for the cam instead of a general out of the box tune from superchips. Raise the converter stall. It's a 4.8 no matter what way you look at it. You wont get big power unless you add boost.

bigjimmyv3 · August 1, 2015

Maybe a port a polish and stiffer valve spring , and possibly bigger valves what u think?

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bigjimmyv3 · August 1, 2015

I hear people talking about how they get the power out of the 4.8 is that just bullshit

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Chris · August 1, 2015

The bog power from the 4.8 comes from boost. 4.8 and 5m3 are the same except the 5m3 has a longer stroke. For the cost of what you want to do, it will be cheaper to junkyard swap a 6.0 and be starting with a better base. My truck came with a 4.8. Stock for stock the LQ9 has 60 more HP. All my 6.0 has now is a tune. Runs great.

MichaelJT · August 2, 2015

I hear people talking about how they get the power out of the 4.8 is that just bullshit

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I heard someone say that the 4.8 is the same as a bored .090" over 283 (292) and he made big power with one of those drag racing in the late 1950's.... There are so many things wrong with that statement I don't know where to start. Lots of lore and mythology associated with Chevy engines new and old.

MJT

Chris · August 2, 2015

The 4.8 is nowhere near identical to the 283. It is a Gen 3 LS based engine. Same as the 5.3 and 6.0. They share architecture with the LS1 but have an iron block.

BlackZ71Silverado · August 3, 2015

I hear people talking about how they get the power out of the 4.8 is that just bullshit

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..........well what do you hear? What are they telling you they are doing for power & what numbers are they telling you?

Unless these you are talking to have forced induction engines, the gains are not going to be drastic. If HP & TQ is what you want, get yourself a 6L and start building.

You can try going with a higher lift cam from LS6, LS7 but you will also need new valve springs and a retune for it to run properly. Those off the shelf cookie cutter tuners aren't going to get the job done.

There are also direct fit LS cams offered that work with your 4.8L valve springs.

The factory heads flow really well on the 4.8L and should be good to around 400-450HP. You should not need different heads on the smaller engine. Having them ported is an option but it needs to be done right or your low end will suffer.

There are a million different combinations of heads, intake, valves, and the like. It really comes down to what you are looking for and how much money you are looking to spend. You can build a high revving screamer, a low end torque machine, or a middle of the road daily driver.

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ifixedit · August 3, 2015

There's an old saying that goes something like this: There's no replacement for displacement. If you're really looking for more juice, start with a bigger foundation and pay a visit to the local wrecking yard and pluck a 6.0.

BlackZ71Silverado · August 4, 2015

OP, can you post 'what you hear' so you can be pointed in the right direction?

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Duelin · August 4, 2015

I heard someone say that the 4.8 is the same as a bored .090" over 283 (292) and he made big power with one of those drag racing in the late 1950's.... There are so many things wrong with that statement I don't know where to start. Lots of lore and mythology associated with Chevy engines new and old.

MJT

The most you could safely bore a 283 was .060 over and be safe. And big horse power back in the 50s is not big horse power today. The biggest horse power 283 in the 50s was the fuel injected model which produced 283 HP. and topped out at 315 HP in 1961(if I remember correctly). And your 4.8 is producing 295. So if you were in the 50s you would have a screamer.

Badass69 · August 4, 2015

317 heads will not fit on the 4.8/5.3 block. They are made for a 4" bore.

Incorrect. 317 heads fit just fine on the smaller bore block. It's just the 71 cc chambers killing compression that make it undesirable for pretty well anything. A 243 or 799 casting beyond having more quench area making the chamber drop from 71 to 64 cc is identical.

The op could do worked 243 or 799 heads and the newer intake... but i would mill them first. Stock gen iv 4.8 engines only have 8.8:1 compression.... great for boost and thats about it lol. If a person wants big power from a 4.8 turbo it. Otherwise whatever you throw at it will always be inferior to either a 5.3 or 6 liter.

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