I have a ls1 out of a 04 gto that I'm going to be swapping into my 70 c10. As far as I can see it has 241 heads and an ls6 intake. I'm looking to make around 450 hp hopefully n/a but probably expecting closer to 400. What would be the best way to go about it? Budgets probably around $4000.
Thanks for any help

 

Get some 243/799 heads, have them ported/valve springs, cam to match, long tubes, ported throttle body, tune and I think you are there and under budget. You could save a little and keep the 241s but would lose a little power. Maybe consider a little porting on the intake. Maybe injectors. Not sure what injectors came on LS1 GTO. Easy with what you have and your reasonable goal.

 

Looks like they came with 28 lb injectors. I have some 42 lb ones laying around somewhere that ill put in if i can find. Im looking at texas speed stage 2.5 5.3 heads and cam kit. Would it be worth it to spend the 2k over using stock ported/polished heads and just getting a cam?

 

All that porting gets expensive doesn't it? What really comes of and when?
By that I mean will you get 50 lbs or torque at 3k rpm, or 15 hp at 6,500? If the prior that's awesome and useful, if the latter then there isn't much point for 99.9% of people. I'm not trying to be a dick or hijack the thread, I'm asking because I don't know and am wondering about the cost/ benefit.

 

I have heard nothing but great things about the PRC 5.3 heads so if that's in your budget and you want something with a lot of supporting evidence and experience in the wild, you can't go wrong there.

I *think* you have 241 heads and LS6 intake if that motor is all stock. 241 heads aren't bad but not valuable. 243 heads are the "real" LS6 heads and have a smaller combustion chamber for more compression and flow a bit better even stock. Ported and milled, the 241s or 862s/706s(5.3 heads) would compare pretty well to a set of ported 243s. Maybe 5% or less difference from my research of a lot of opinions.

Normally I would say the 5.3 heads would have even smaller combustion chamber than 241 or 243 but it seems that the shops that move a lot of "5.3" heads are now using the later model 5.3 heads which don't have the small chamber of the early (like pre-2005-ish) heads(later 5.3s got their compression from pistons I think). They mill them to get them back down to early (862) volume if desired. The only reason this might concern me a bit is if you opt for the higher compression of what used to be a smaller chamber 862/5.3 head on your LS1, you may end up with a fairly milled head and that may limit you from using a *****-big cam at some point without cutting the pistons. Just don't know if that might be in your future. If you will stay under .600" lift don't worry about it too much though. Just likely expect to use your stock heads as decorations if you opt to buy another set of heads..not really desirable unported.

Little reference from other threads on this site:

241: 67-69cc chamber depending on year and who you ask
243: 64.45cc chamber
862: 61.15cc

BTW, I shifted gears a bit myself when I found a deal on an LS2 and will have a spare ~80K mile 5.3/LM7 with a nice set of 862s and also a different set of 60K mile 862s. Also a set of 853s(basically same as 241) that were 12K mile take-offs that are super clean. If you want any of these cheap to have something to send in for porting, we could work something out.

@Chuckd71 - a stock 241(typical LS1) head is reported to flow around 220CFM(intake) @ .550" lift. A properly ported version of the same head should be right around 300CFM. In theory, they support 36% more airflow and 36% on a 300HP motor is over a hundred horsepower. That's all theoretical but cut it in half and that's still a heck of a gain for under $2K.

 

Thanks for the info. I don't plan on running a lift over .600" as I don't want to be changing springs every 10k miles. Just want to make sure I don't really leave anything on the table while working on a budget. Coming from a 427 big block it's hard to "downgrade" to 400 horses lol. But it beats about 5 mpg.

 

There is always nitrous or a turbo setup with your stock engine. Nitrous will keep that gas mileage you are looking for with a stock engine.