lilaaron233333

iTrader: (10)

Got a stock ls3 bottom end that’s possible getting a set of Trick Flow 255 heads. Question is... is a 67cc too small and will compression be to high or should I be fine? Cars going to be a daily and ran on ca shitty 91 oct gas.

Thanka

bortous

What will your compression be?

lilaaron233333

iTrader: (10)

dont know that’s why I was posting here hoping someone could tell me. It’s stock bottom end with TF255 heads that has 67cc chambers.

MechMan1

iTrader: (5)

Its all stock right now? The only thing you are changing is the heads? You didnt swap pistons or change the head gasket thickness?

lilaaron233333

iTrader: (10)

2 things have been changed in the motor cam, and heads. That’s it nothing else, running stock mls GM gaskets stock piston,rods,crank.

bortous

I just checked.
The ls3 head has 70cc chambers as standard.
Going down to a 67cc is not much different.
You will be fine.
If you are fitting a camshaft with some positive overlap they will bleed off some of your compression anyway.

MechMan1

iTrader: (5)

Stock compression is 10.7:1 on the LS3. With those heads you are looking at around 10.89:1, if it runs on the gas fine now I don't see any reason there would be an issue with the new heads.

KW Baraka

iTrader: (7)

1. What's your cam specs?

2. Are you gonna stay with OEM heads gaskets or are you gonna install a set of .040" compressed thickness head gaskets?

3. Why TF-255 heads.....why not TF-260 heads?

4. What vehicle is this engine going in to...and it's weight?

5. What transmission you gonna run?

KW

lilaaron233333

iTrader: (10)

1- can’t answer till wed.
2-OEM stock .051 gaskets
3- got good deal an 255s. Saved $$$
4-C5z stock weight
5-Tick built T56

6- my stupid self thought I had an ls3 when I really have a L99 short block. So with that said I have the valve reliefs in my pistons and not flat tops like a “true” LS3. So that’s gonna change it a little as well.

64post

iTrader: (5)

Go for it, there’s guys on here running 12:1 SCR on 93. As mentioned cam events set your dynamic.

KW Baraka

iTrader: (7)

Agreed.

Also, I'd go with .040" head gaskets. This will bump your compression a tiny bit, but it will bring your quench to .035" range which is EXACTLY where you want to be for a compression ratio that's higher than stock.

BTW.....the LS3 in my daily driver '95 Impala is 11.3:1 CR.....in my '14 SS, it's 12.2:1 CR.

If you don't have it yet, don't get your cam until AFTER you have everything else sorted out. THEN....call a reputable cam company with all your specs and tell them EXACTLY what you want out of the car. They should be able to spec you a cam specifically for your setup.

Best of luck!

KW

Tuskyz28

The TFS LS3 heads are not worth the money over the factory LS3 heads. Richard Holdener latest LS book showed a 21 hp difference on a stock bottom end LS3.
The GMPP CNC LS3 heads are worth 15 hp over the factory LS3 heads. Just some food for thought.

bortous

If anyone wants to upgrade the LS3 heads, your best best is using small bore LS7 heads.
These will cost less than high end cathedrals,
Produce around the same low and mid range torque as the cathedrals but make more torque an HP above 5000rpm and will rev higher

Smokey B

i wonder who you learned this from......lmao. You can say a ls3 with a 255 runner is smaller than a factory ls3 head yet a ls7 will generally have a smaller port than either for the same bore size. Port is taller as is no way around it even with a 255cc ls3 head.

bortous

Regardless, the LS7 head will make more power and torque.

Smokey B

Better line of sight and flow with the runner being raised.

chevyss2008

Im running TFS 255 on my WS6 with LS3 in it, and TFS cam...I daily drive it. You may as well helicoil all 16 of the rocker studs now, or you will be doing it later....trust me.