4.8 NA build

alright many things have changed in my life in the past year since being on the site. rather not get into that as its not important.
now to the build:

2005 gmc rst 4.8 5 speed

just finished my t56 install with stock ls1 clutch and flywheel. looking to get an ls7 clutchsoon also, i just installed my new cam yesterday and yes its huge for a 4.8 but thats the plan. 236 242 .580 .590 @ 050 on a 112 with patriot gold springs and comp pushrods. Getting a live tune tuesday. The cam is so large in fact that it wont even idle on its own. just lovely:ma: alright heres the plan some 4.88's a strong clutch with udp. also looking into heads and intake. Im looking for bang for the buck. Looking for direction on intake and head choices id like to stick with factory castings and have them ported fully and decked to bring compression up. What would be a good combo on the 4.8 with my setup to bump compression and have more flow. Id like to stick with all factory parts such as head casting and intake to make it look as stock as possible. ideas on which casting/intake and how much to take off so i can still drive this everyday and run on pump gas... i want the motor to look like a sleaper and put the 4.8 to its full potential N/A thanks guys i know you guys will say go 6.0 but i want to do something a little different

Woot woot go 4.8!

go for 243 heads down, mill them a little bit, wont need to do a lot since the 4.8 has flat tops already, gen 4 intake and spin it to the moon

how much would you say to take off of the 243's theres a local machine shop that does big name high end motors. i was thinking of getting some 243's ported and decked and 07+ intake port matched to it. how much would you say to take off by decking? im gonna run a stock headgasket. also should i have them machined for bigger valves? im looking for a magic combo to make it scream to the moon

anyone care to answer the question above? guess no1 cares about the 4.8 until i post track times!

have the machine shop cc the heads and the piston in the bore then they can mill the heads and get a head gasket with the appropriate compressed volume to get the compression where you want it.

taking the motor out of the truck isnt really an option. but i do understand exactly what your saying.
since they are flat tops, does anyone know the actual compression with a stock headgasket/243 head combo. and also by milling off every.005 how much it would increase the compression? im gonna start googling this to see what i come up with

came up with stock headgasket, stock 243 comes out to 9.2:1
so to bump it to 10.5:1 how much should be taken off? could i get away with 11:1 on pump gas? thoughts suggestions?

so i came up with this calculation:
at .050 off the head it creats roughly a 10.5:1 ratio
at .060 off it creats roughly a 10.7:1 ratio

is this too much to take off? am i wrong with my calculations? would i run into PTV issues with my current cam?

i respect you alot for building the 4.8 cause everyone always says 6.0 and its always nice to be different. tell me how the build goes

main reasons as to why a 4.8:
1. people underestimate the 4.8 and use the old no replacement for displacement theory
2. not many if any have gone the route im taking
3. i cant justify tearing out a motor that runs so strong with only 60k on her
4. im 20 years old, in college, and have a baby due in september so im on a tight budget.
5. i personally want to see what this motor can do.
and finally 6. it will be a COOL!

sounds like it should be sweet......not picking on 4.8s but we had a guy brag that he could get more power out of a built 4.8 than u could out of a 6.0 lol then he got outrun by a fully bolted 4.8.....guess it just depends on how u build it

good luck

Don't mill the heads more than .020 IMO.

Is that because it would make the deck of the head to weak? Possibly thinner headgasket? Looking to get a safe but increase my compression here. Best headgasket/ milling to get the most compression without compromising durability

any takers for the best head gasket / milling combo?

guess no1 cares to bother since its a 4.8.... anyway update! got the truck tuned tonight. runs good. got it updated for the cam and t56. all the dash lights went away and the truck runs awesome. i need gears badly! thing wouldnt idle any lower than 1200rpms. guess im gonna have to live with it. (because of how large the cam is in reference to how small of cubic inches i have). also tuner told me hes buying a dyno mid april so hopefully by may ill have numbers by then as well

there should be no reason why that cam cant idle at 850-900 in that motor

Quote:

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Originally Posted by SNEEKY

taking the motor out of the truck isnt really an option. but i do understand exactly what your saying.
since they are flat tops, does anyone know the actual compression with a stock headgasket/243 head combo. and also by milling off every.005 how much it would increase the compression? im gonna start googling this to see what i come up with

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You don't need to take the engine out to cc the piston volume. It can be done in the car.

Things like head volume are not exact. These are just cast aluminum heads you are working with. I have seen CNC'd chambers that cc to a spec other than advertised. This is why I say to have the machine shop check this and mill accordingly.

Keep in mind you can't add 2 points of compression by cutting the heads. you can only mill the heads so far before bolt holes and intake ports won't line up anymore.

hmm well the motor didnt want to cooperate with the tuner i guess...unless someone wants to live tune it for me :) think im gonna do some gears and an ls7 clutch before i do heads and intake. but they are in my future sometime this summer.

in not sure if a 4.8 has gone 12's n/a, go for it. a 6.0 can hit that cam only, it all depends on the money you have to spend. i started out with a 4.8 im now a 6.0 with a t76 fm turbo will see how it goes

id love to touch that on motor