pieterinusa

Hi everybody.

i've searched high and low but cant get a straight answer. How much HP can I expect from changing an LM7 (5.3) pistons to flat top pistons. This will raise the compression up to 10.4:1 but how much HP does that equate to?

I'm on a budget and only have money left for a cam. I've ported the 706 heads myself.

Ls7colorado

iTrader: (3)

15hp?

RB04Av

Probably around a 3 - 5% bump.

00pooterSS

iTrader: (40)

10 ish

But that doesn't include the fun to drive factor too. More compression is more fun and usually get a little more mpg out of it too.

JKD

LMG 4th gen 5.3 has 10.1:1 compression with 799 heads and is 345hp

LLLosingit

iTrader: (4)

Probably not even half that. It's usually a 1.5% to 3% increase in HP for 1 full point of compression so if it made 300hp before the new number would be a 4.5 to 9hp increase.
Calculate New HP From Change In Compression Ratios

omc8

iTrader: (7)

Maybe you thinking of torque rating ! The highest LMG was in the Tahoe and Suburban and it was rated at 326 hp and 348 tq

AwesomeAuto

That calculator is so impossibly wrong. It claims a 3 HP loss going from 706 heads to 317s on a 5.3.

Despite the 317s flowing better, the difference is about 15 HP.

alowerlevel

iTrader: (1)

It also says youll only pick up 12hp going from 10:1 to 14:1 on a 500hp motor

LLLosingit

iTrader: (4)

It doesn't count difference in flow obviously but a point if compression is not worth as much as most people think. A better flowing head will obviously add more air/fuel and make more power.

LLLosingit

iTrader: (4)

Yeah, In that case it's not doing the math correctly and even if it didn't it probably would still read low because it would fail to account for the added power of going to the better fuel that would be needed at that ratio. I've never tested a compression increase myself where nothing else was changed but plenty others have so it not like it hasn't been proven. A 1%-3% increase for a point of compression is typical if that's the only change . I had someone tell me their sbc went from 275hp to 450hp because they went from 9:1 to 11:1 but to get from 9 to 11 he went from crappy cast iron small valve heads to Brodix Track 1's and new pistons.