brent_strong

iTrader: (2)

I'm considering picking up a cheap set of 853 heads to clean up the ports and chambers a bit and to have decked for higher compression.

First off, would it even be worth my time and effort to do this? I understand gains would be a lot larger with a cam, but that isn't in the cards right now.

Secondly, what sort of static compression ratio would I be looking at as safe on a '99 LS1. I'll be running some dynamic compression calculations tomorrow, but if someone has experience using a stock cam and higher compression, I'd LOVE to hear about it.

This is going in my '93 RX-7. I have some supporting mods that should help things out - mostly just an LS6 intake, a decent set of 1 3/4" longtubes and a very good, freeflowing exhaust with an X pipe.

Would 11:1 be a reasonable goal? I'd imagine this shouldn't be a problem with a good tune and running 93 octane. If I do go to ~11:1, would it make a worthwhile increase in power?

Thanks for any help! I have searched for information on this, but everyone ends up talking about a larger cam or other setups.

fast01

iTrader: (16)

I wouldn't bother with 853's. 241's are a slightly better casting and about the same price, but if you're going to have them milled you're going to bring your cost factor up to where you could get a set of 243's. I would personally go with a set of the aforementioned 243's. They flow a lot better and already have smaller chambers which will raise your compression to about 10.5:1. Throw on a set of Cometic gaskets and you'll be up around your 11:1 goal which will be fine for your application...with a tune of course!

Do a search on the 243's and you should come up with the power difference between them and 853/241's.

brent_strong

iTrader: (2)

Hmm...interesting.

As for prices, I'm looking at 853s for $50 fully assembled and under 25k miles.
~$100 for machine work
Free porting
$30 GM headgaskets (same cost no matter the heads)
$45 headbolts (same cost no matter the heads)
Minus what I can sell my 853s for.

Mostly considering doing this just because of how cheap the 853s are that I found. I'll look up prices on 241s and 243s though. Do you have an idea of the "normal" going price for either?

fast01

iTrader: (16)

Ok, you got me! If you're looking at prices like that, you're right, the 853's will be cheaper. I'd definately swap the springs though. Even the newer 241's are 6 years old and the stock valvesprings are garbage to begin with. I'd still try to find a reasonable set of 243's (which have better springs to begin with). Just the bump in compression without more head flow I don't think will net you too much given the work involved...and don't forget pushrods. If you mill the deck surface, you'll need shorter pushrods. I'm not sure how much would need to be removed to obtain the compression you're looking for, but if you don't get a shorter pushrod on there you could hang a valve open (as the extreme). Ultimately, it's completely up to you. I just think the 243's will have some room to grow with your combo as you mod on.

Oh yeah, 241's seem to run about the same as the 853's and the 243's seem to be in the $300-$500 range. Check the classifieds on here. There's always reasonably priced heads on there that are often upgraded already.

brent_strong

iTrader: (2)

Thanks for the help! I hadn't thought about the pushrod issue...

Unfortunately, I won't be keeping this car past the summer, so I won't get to really grow into 243s, but man would it be fun! The car is at maybe 320-330whp right now, I can't imagine adding ~100 more with a decent cam and heads.

Oh well. I might pick up the 853s just to keep busy, but I'll be keeping an eye out for some 241s as well. I can always unload them later if I don't use them.

fast01

iTrader: (16)

Anytime! Do it and enjoy it while you still have the car!

Hi-Po

iTrader: (4)

Question? Are 853 heads 5.7 liter heads or 5.3?

BayAreaSS

iTrader: (10)

5.7

I have 853's