1slowcar

iTrader: (5)

I've been reading about compression and milling the heads and so on. I've read that you shouldn't go below 55cc-56cc after that a lot of things can go wrong. I can't really find a answer to my question.

I have a 5.3 with the stock 7cc dish pistons and would use a .040 gasket, so that would make it like ~ 9.9:1 with 59 CC heads ?(PRC 5.3 stage 2.5) Would it be worth the trouble to mill the heads down to a 55cc-56cc (assume PTV is ok) to make it around 10.5:1 ? Will it make much more power ? Sound better ? (torquer V2 cam) Is there anything else I can do to gain more compression that I've missed?

I used http://www.rbracing-rsr.com/compstaticcalc.html

B 3.78
S 3.66
Gs .040
DH .008
PV +7cc
CC 59 / 56 / 55

PowerTalk

Interesting thread

Im thinking of doing similar with my 346ci with stock 853 heads.
Would it be worth milling the heads by XXX thou and fitting .040" cometics when I drop my baby cam (224ish ), LS6 intake and valve springs in.

Can't wait to hear some opinions so here's the free bump

1slowcar

iTrader: (5)

me too ...

1989GTA

Not being an LS1 man I can see one posible problem with milling to much. That would be the intake manifold would not line up correctly with the heads. On a regular SBC you could just mill the intake manifold to match the heads. I don't think you can do that with the LS1 style intake. So I think you would be limited in how much you can mill or you will get into trouble as you stated.

1slowcar

iTrader: (5)

I've read on here that with 55cc the FAST intake fit fine, but it was close

mchdg86

iTrader: (3)

Sorry for the hijack but I had a 224 on a 112 LSA and it loved 11-1 compression. Put down 400rwhp through a locked auto with TSP 2.5 5.3 heads. But to the OP yes it helps a good bit raising the compression expecially with a bigger cam.

Soul TKR

iTrader: (4)

with my 59cc AFR 205 heads and a 224 cam... my ratio is right around 11.2:1 and the car absolutely LOVES it... I wouldn't be afraid of it... but I'm sure there's a limit. I'm completely satisfied with it and have NO regrets...

th41427

I have the TSP stage 2.5 5.3l heads milled down to 59cc with a TSP233/239 on a 112LSA. Supposively my compression is about 11.1-11.2 but i am not quite sure. when my engine builder checked the heads he said they were actually 57cc. i dont know for sure and i am not taking them off toget checked it runs great. so far as milling the intake down i DID have to because the guide pins were hitting the outside edge of the line up holes on the heads. TSP said i shouldnt have had to but i DID. ohh well it wasnt that hard i just was a little skeptical about doing this to a brand new intake. so have fun with the higher compression still waiting on getting mine tuned as well. i am also doing the two foot drive. haha good luck

Jason 98 TA

iTrader: (4)

Compression is a huge helper in making big power. Our dyno testing showed most of the heads we compared that were out of the box were for the most part seperated by the compression differences. We had a small runner 66cc head make 522hp, while our 5.3l 2.5head with 62.5cc make 533hp & our new prototype casting made something like 539hp with 61.5cc chambers.

Milling 6cc of a head made nearly 20hp in our testing.

AINT SKEERED

iTrader: (2)

My 5.3's are milled to a 54 cc chamber. My intake bolted right up too.

I have 4cc mahle flat tops with reliefs and my compression still calculates to 11.73 with a .051 gasket. My stock lq4 would have been 11.63 if I had used these heads on that motor which is in my trans am.
my 347 is useing the 54 cc heads and going in my Nova.

My Trans am now has a lq4 with 241 casting heads milled to 63 cc chambers and my compression is 10.43/1 . This along with an f14 cam feels pretty strong but dont have new dyno numbers. I street tuned it but have not had time to take it to Thunder and see what is left with a little more timing yet.

1slowcar

iTrader: (5)

Well 54cc would give me 10.63 (so the calc says) I've read that going smaller than a .040 heads gasket is not a good idea because of the quench.

AINT SKEERED

iTrader: (2)

you are showing .008 for deck height, if it sticks outthe block like most ls1's it should be -.008 . that will change it to 10.95 with a 54 cc or 10.81 wtih a 55 cc.

also the stroke is 3.622 not 3.66

1slowcar

iTrader: (5)

I'm just going to go measure it here in a min while I'm thinking about it I forgot to put a -

I converted mm to inch is how I ended up with 3.622.


edit: I'll have to measure it later I forgot the motor is upside down I haven't put the main caps back on yet

PowerTalk

So if I fit 0.040" gaskets to my standard block and 853 heads what CR does that put me at?

What would taking an extra 0.020" off put me at as well?

or even more...

AINT SKEERED

iTrader: (2)

not sure on the 853 heads, are they 5.3 or 5.7 heads? What engine are you putting these on?

give me some specs

AINT SKEERED

iTrader: (2)

went back and found this post.

with stock unmilled heads you would see 10.68 with a .040 gasket. if you mill 2 cc's off which is about .012 , you would be at 10.95/1
and if your cam is 112lsa with a 108 cl you would have a dcr or 8.66/1

with that cam on a 110 icl it would be about 8.52 which would be better for pump gas. either way you would make good power.

PowerTalk

Thanks buddy. Thats some great info.

I appreciate it

AINT SKEERED

iTrader: (2)

no problem. good luck with your set up