Rb26 Vacuum At Idle

[noone]

Hoping someone may be able to help us out

just got my new motor going forged internals big sump etc. etc.

Head was checked out and setup to run my Tomei poncams I had used previously

Now its running and all seems happyish

except only seeing -35 kpa vac at idle (factory spec -65 kpa)

this on the stock gauge appears as the mark half way to -700 mmHg (factory spec should be -480 mmHg)

would love to know what others with poncams are seeing

cams will obviously effect vacume at idle but this seems a bit excessive

have checked and cant seem to find any other vac leaks???????????????

any assistance apreciated

[horrace]

I'm sure you've thought of it but testing it with another gauge would be the easiest way to rule the factory gauge out, just about all factory gauges are useless.

[noone]

Mine actually reads almost identical to the Defi boost gauge

at least it does at vacuum

[noone]

anyone running poncams in a rb26dett able to help??????????????????

[Gareth87]

i think the cam timing will also determine how much vac you will have at idle.

[StealthX]

Yeh cams will affect vacuum, wats the duration and lift of these cams?

also double, triple, and quadruple check your intake side, for vacuum leaks. Im fighting a leak right now, and its a prick of a thing.

but id say its just the cams. does it rev and idle ok?

if it pops, farts and stumbles when you rev it, thatll be a vacuum leak, otherwise, its the cams.

[noone]

thanks for the replys

car runs well idle is a bit up'n down 900ish to maybe as high as 1000 rpm

but seems to be reasonably steady round 950ish once properly warm

car is not making much power though at really small throttle openings

eg trying to get up a steep driveway

new motor and new twin plate OS Giken so a new learning curve I spose as well

Have not done a real tuning run for power yet just checked afr's etc and loaded it up for a bit on the dyno

need rego next to put some km's on it

Am hoping once i get the cam timing done an a proper power tune it will be better

edit: poncams so 264 9.6 on both (if memory serves me right)

Edited January 20, 2010 by noone

[StealthX]

sorry man i dont have much experience with 26s... ill just say that in advance lol

stock duration is 240 deg IIRC so youve got an increase of 15deg there, should shift your powerband up a fair bit, but i cant see it having that much of a drastic affect of your idle, the overlap wouldnt be THAT major. compared to say, the 285s that some people use. in theory, if 265s cause you to loose that much idle vacuum, a car with 285s would barely idle sub 1000rpm!

but

idle is a bit up'n down

that is a classic symptom of a vacuum leak on a MAF sensored car. try spraying carb cleaner/aero start around the intake manifold, and if your idle changes or your misfire etc, youve found your vacuum leak.

i guess you're gonna have to hear from another 26 owner as to the vacuum they see...

do you still have the ITBs?

[noone]

Yeah ITB's am wondering if I still have a leak the cams are not that big

tried some carby cleaner but no real joy

After reading bout your drama with injector o-rings will try n blast some aerostart or somesuch

around there an see if that shows anything up

[StealthX]

yeh that fkn o-ring was my problem... prick of a thing to get to on my car, entire top half of the intake manifold needs to come off to get to the fuel rail (like half an hour job even though ive done it like 10 times now)

good luck bro, hope ya get it sorted. darwin needs more GTR love on the streets lol

[R31Nismoid]

car is not making much power though at really small throttle openings

eg trying to get up a steep driveway

Am hoping once i get the cam timing done an a proper power tune it will be better

Well you have a problem, and you know what's likely causing it...

The setup by your own admission isn't even done yet.

Its very hard to say what is wrong or right, if you've yet to sort it all out...

Side note - you may well find the driveway issue won't go away. Part and parcel of larger cams.

[noone]

These cams are not exactly new to me

Ran they in my last motor as stated in the first post

though had cam timing sorted on install so I spose without cam gears adjusted they might be that doughy down low

but I doubt it

Basic setup has been done, just not power tune

afrs etc looked fine tuner didnt really notice anything amiss till he did a lap of the block

to make sure no drivability issues, an there it was, along with an oil leak from the cam cover half moon seal

Appreciate the help though guys

Darwin definitely needs more GTR's

[StealthX]

Any luck with your vacuum problem bro?

[noone]

No definitive solution yet unfortunately

waiting on a mate to get back into town to try hooking his air compressor up

to the balance pipe an pressurize the intake side hoping that might make it more obvious

[DVS JEZ]

are you running cam gears?

have you adjusted the cam gears?

did you set the cam gears by dialling them in???

[DVS JEZ]

ment to say are you running adjustable cam gears?

[noone]

Yeah adjustable but still at this point set at zero ie. stock

[PM-R33]

Different engine and setup i know, but my car with poncams has a lot less idle vacuum than it did without the cams. Sits at about -40kpa to -45kpa on idle.

[noone]

Thanks PM-R33 good to hear an actual value and only post 18

LOL

Did get some good advise above though

[andy95'R33GTR]

hi, just want to ask if how did you pressurized the intake pipes?? did you block pipes?? or not? thnx