darknessxyz

iTrader: (22)

What's the combustion chamber volume and compression ratio of stock 5.3L head, without any milling or head work? According to the sticky, stock LS1 5.7L head is 66.67cc = 10.1 CR.

Another question, with the same combustion chamber volume (say mill to 62cc), will the CR be the same between 5.3L and LS1 5.7L head? According to the sticky, stock LS1 5.7L head mill to 61.63cc = 11.0 CR.

If mill a 5.3L head to the same 61.63cc = 11.0 CR, then what's the different between running 5.3L and 5.7L head?

To make the comparsion under same situation, let's assume:
1) both head install with stock LS1 intake and exhaust valve with proper valve seat cutting;
2) both head use the same GM 03+ MLS head gasket;
3) both head recevie NO porting at all.

Thanx

darknessxyz

iTrader: (22)

Can someone help?

Beaflag VonRathburg

iTrader: (176)

The intake and exhaust runners between the two heads are the same. The only difference is intake valve and combustion chamber size. People like the 5.3 heads because they start with a smaller chamber. You don't have to mill your heads as much to achieve a higher compression ratio. This helps with guys running larger cams where PtV clearance comes to be an issue.

darknessxyz

iTrader: (22)

So that means with the same combustion chamber size, both head will have the same CR right?

elias_799

iTrader: (8)

^^^ yes, as long as both heads have the same combustion chamber volume and use the same head gasket you will have the same cr.

regency

iTrader: (15)

stock 5.3 heads are 61.15 cc's
they also have a 1.89" intake valve compared to your 2.00"

darknessxyz

iTrader: (22)

If that number is true, is that means a 5.7L LS1 block with a stock 5.3L head will have 11:1 compression ratio?

One more question, a stock unmill 5.3L head install with LS1 2.00 intake valve, will the compression ratio change?

Beaflag VonRathburg

iTrader: (176)

^ Usually, in installing larger valves the chambers will be slightly opened up with a deshrouding cut. This helps the larger valves breath without the interferance from the chamber walls. The amount of material removed is very small. It's always a good idea to measure them with a buret once everything is done.

regency

iTrader: (15)

YEP its true!!

And no the compression wont change unless the chamber is modified, I dont think that unshrouding the valves would remove enough material to affect it much, it might bump it down .1 or something

novaflash2002

iTrader: (51)

you need to have the intake seats ground to put that 2.00 valve in those heads. also you can have your machinist de-shrowd the inside of the valve seat so that it breaths better. its hard to explain but easy to point out in person. also have him de-shrowd around the the valves, and have them milled .030. that will make up for the de-shrowding, and keep the compression ratio where you want it. the intake runner volume is about 10cc smaller than you ls1 heads. with minimal porting they make up for it though.

regency

iTrader: (15)

862/853/241 all have 200cc intake / 70cc exhasut runners
243 has 210cc / 75cc runners

darknessxyz

iTrader: (22)

I've stock 862 casting head and going to send out for the head work. I'm trying to run 11.5:1 SCR with a 224R cam. However the sh!tty gasoline in CA is a big problem here. Predator Z suggested keeping the combustion chamber @ 61cc (11:1) so I won't have KR issue from CA pump gas.

The another issue is the intake valve clearnace. If I mill the head for .030, I don't know if the intake valve will clear the piston with that 224R cam. That's why I wanna know the volume so I can tell my machinist exactly what to do.

Is it possible to port the intake runner to 205cc on a 862 casting head?

Uncle John

My 862s were done by West Coast Cylinder Heads. 2.02 and 1.57 valves. The chamber volume came out to 63cc after de-shrowding. The intake runners ended up at 233 cc.

regency

iTrader: (15)

My opinion, i would just call up Patriot and get some stock LS2 heads. I think they are about $475 shipped and have them milled .010 and use some .040 cometics for around 11.15:1 CR!!!!!!!!! and have about $650 in a better set of heads after milling and gaksets

darknessxyz

iTrader: (22)

I already have a set of 862 here. I got them for really cheap and they comes with LS1 valve. All I need is head work.