Mongoose350

iTrader: (1)

Hi all, I've been reading this forum for a few weeks now in prep for my 5.3 build. I'm going for the budget build but am willing to drop a little extra cash. So that said in going to replace all bearing and rings with some new OE stuff. My question is this. Is it worth it to go with some 243's over stock. The higher comp will help spool faster I would I'm thinking, and would help make more power at lower boost. Is that right? I'll be using the stock ls1 intake that's on the car already and will upgrade later on.

Also, I'll be running the On3 non A/C kit with there 76mm turbo. 4l80e and 3'42's.

Forcefed86

iTrader: (4)

How much power do you want?

Mongoose350

iTrader: (1)

Well, to that I say around 600-700whp. However we all know that will change to 1000+ soon after lol. But for a start that's my goal.

JT86SS

from everything i read i would say no. you will run out of turbo with that 76mm before the stock heads start to restrict you. my first build i used 317 and they sucked. im sure they make more power uptop but down low i didnt like it. swaped back to stock and never looked back. i would say save your money. your going to be happy.

Mongoose350

iTrader: (1)

Also, this will be a street "race" car. So I want quick response at pretty much any rpm.

Forcefed86

iTrader: (4)

It's great to bench race and all but you can't have instant spooling stock cheap setup that makes 600-1000hp .

That being said any stock LS head will make 600-700hp with a decent turbo setup. 243's aren't going to give you 400 extra HP or cause you to build boost off idle. Save your money would be my input.

317 heads have larger runners and larger valves and can usually be found for around $100. Best bang for the buck IMO worked great with my setup.

Mongoose350

iTrader: (1)

The lm7 has low comp as it is. Around 9.5:1, not exact but that's close. 317's will take it even lower unless I mill them and to much of that will cancel out the flow advantage. I see people run the stock heads because they work great, but I was thinking if the motor can handle it, the 243's can get it done with less. I'll also be throwing in some K Tech or ARP rod bolts so I don't think the motor would have a problem. I know a simple swap from stock to 243's isn't going to get me 1000whp from 600. That's not even in my plans as of yet.

I guess the stock heads will go on first and I'll see how they do. I'm hoping to run about 12-14lbs at first and run gas only(93). Do you think that's enough to get me above 600whp? Future will be gas with meth and as much boost as she can hold.

JT86SS

didnt mean for you to think i was recommending the 317's to you. i was just making a point that the stock heads would work fine and that u should save or spend ur money elsewhere. ive havent been over 12psi. but i would assume from my research 14-16 would give you what ur looking for (600ish whp).

Mongoose350

iTrader: (1)

No it's cool. I've read about the 317's and agree with you.

Forcefed86

iTrader: (4)

I’d suggest you pick up a turbo book and stop listing to internet BS. This isn’t an NA motor. Throw all that crap out the window.

You don’t want high compression. Especially since your using pump gas. You only lose 4-5% power NA per point of compression dropped. So if your at 300hp NA at 9:1 dropping to 8:1 will cost you a massive 12 hp. It’s not a night and difference. It’s a very small price to pay for the additional 12-15% more power you will be able to make with the additional boost it will allow you to run.

243’s have the same valve size and intake/exh port volume size as a 317 head. The major difference I am aware of is the 64cc chamber VS the 317’s 72cc. I believe some had better valve material or castings, but that doesn’t make them worth 3.5 times the price of a 317 head IMO. Run 5 more lbs of boost and buy a 317 head would be my suggestion. If the hotside is sized correctly boost will build very quickly. If you have some money to spend on heads buy a nice set of aftermarket or OEM worked over heads that are CNC ported with larger valves.

I ran a dished piston LM7 as well with 317 heads. 8.6:1 compression ratio. Easily making over 800hp at around 24lbs with an OEM cam. It built boost very quickly and was useless on the street at anything above 13lbs of boost.

Also spending money on rod bolts isn't necessary IMO. I and many others have all ran OEM hardware on the bottom end at higher power levels than you are talking about with no issues.