Mrtsunami20

iTrader: (1)

Ok folks I have a 07 lq4 with ls6 heads and a ms4 cam..I currently only have a mail order tune.
The idle is set at 850rpm
But it only pulls 9lbs of vacuum or 62kpa
Is this normal.
The vacuum stays steady
And I check for vacuum leaks

Would a dyno tune help with the low vacuum

DietCoke

iTrader: (18)

I've seen them make 12 or 13 in an ls1. Are your pushrods the correct length?

sreve

iTrader: (3)

62kpa is 11.6 in hg vacuum

Tweaking the tune a bit could get you some more.

Mrtsunami20

iTrader: (1)

They are 7.4 comp pushrods. I called Texas speed and that's the length they suggested for my setup.

vmax211

62 kpa is just over 18 inches of mercury, which is a reasonable number for vacuum for your engine.

Mrtsunami20

iTrader: (1)

Ok awesome..I just need it alittle higher because the motor is in a 240z and the brakes don't work we'll till 68-70 kpa..I guess I need a dyno tune or a vacuum Reservoir

vmax211

Years ago I knew a guy running 240Zs in SCCA competition, and he used a vac reservoir to keep the power brakes happy.

If that is the only reason to run more vacuum, why not just convert to manual brakes? Much simpler, and no reliance on engine vac, which will be a greater problem if you start using a more aggressive cam, etc.

Or use a hydroboost setup.

Mrtsunami20

iTrader: (1)

Well I don't want to switch to a manual setup
Since I already have invested a good amount of money upgrade my brake setup
I guess I'll just look into a vacuum Reservoir

Thanks for the help guys

sreve

iTrader: (3)

You have that figured backwards 100kpa is atmospheric


Do the math the other way around and 38kpa = 18.7 in hg