Low vacuum - sr

[KoukiMonsta]

I've searched around and scratched my head a bit now I need some more input guys. Here's some background

Freshly built Redtop
8.5:1
.020 over
Bc 264
sard 850cc
Oem HG
Enthalpy
Blah...

Assembled this motor myself, mechanical timing is dead on. Boost leak tested it-good. Tps at .45 I dont have a bov. Recently fired it up for the first time with a boost gauge. Started it a couple times before that. Issue is I'm making 10mm hg! I understand I got cams but this is too low.~18 would be great from what I've read searching for people with similiar setups.

Ign timing is 15*
Now it does idle a bit low, and I've had trouble raising it. Tried an assortment of unplug tps/iacv adjust iacv up to 1200. Restart with them plugged in and it keeps going back to 750 or so. But even at higher idle 1200 vac is still low.

So what could be causing this? I figure I need a compression test too but it's not broken in so I know numbers wont be that great.

Input is appreciated people.

[KoukiMonsta]

Ok so I did a leak down test. About 20-25% except for #3 which was more like 35.

All cylinders had quite a bit going past the intake valves. It seemed none going past exhaust. At least I couldn't hear it.. Crank case and dipstick had mild leakage on all - expected from such a fresh motor.

So, if I get the valves ground should I see the vac numbers I'm shooting for? Is that gonna cause my low vac? Or would that only effect the motor In Compression?

[jr_ss]

You'll definitely see an increase in vac numbers if the valves seal correctly. Just because it's leaking past the valves doesn't necessarily mean its your valves. It could be a bad seat as well, which will be more expensive to fix. However, more than likely you have some slightly bent valves that need to be replaced. If you're in that far, you might as well have the whole head gone through.

[KoukiMonsta]

You'll definitely see an increase in vac numbers if the valves seal correctly. Just because it's leaking past the valves doesn't necessarily mean its your valves. It could be a bad seat as well, which will be more expensive to fix. However, more than likely you have some slightly bent valves that need to be replaced. If you're in that far, you might as well have the whole head gone through.

Ok great man some info!

I am not exactly familiar with a 'valve job' but I am under the impression I get the valves and head ground to match each other. Therefore seal better. That's what the 'seat' is right? I don't see any reason to believe valves are bent.


Would I need new valves for this or is what I speak of possible/common.

I'm with u on going through the whole head. As a said I recently rebuilt the motor. So freshly decked and got tanked along with valve seals. But nothing was done beside that (machine shop wise)

[jr_ss]

Ok great man some info!

I am not exactly familiar with a 'valve job' but I am under the impression I get the valves and head ground to match each other. Therefore seal better. That's what the 'seat' is right? I don't see any reason to believe valves are bent.


Would I need new valves for this or is what I speak of possible/common.

I'm with u on going through the whole head. As a said I recently rebuilt the motor. So freshly decked and got tanked along with valve seals. But nothing was done beside that (machine shop wise)

Typically valves are ground and seats are cut. Most of the time you dress both and they seal great. I say bent because valves can bend overtime. Over revving the motor, tossing a rocker, anything that stresses the valve can cause slight bending. When your machinist goes to grind the valves, he'll be able to tell you if they are bent. A straight valve should not wobble when put into a drill or grinding machine. If you can't see it with your eye, the machine grinding will show you where material has been removed and where it hasn't just by looking at the surface you are grinding if it's bent.

If you do indeed have bent valves, then yes you would have to replace what is damaged. Make sure you get the correct valves for the engine. If any exhaust need to be replaced, make sure they are sodium filled.