High Idle And Next To No Vacuum Built Rb25Det

[skygtsnt]

have just put my engine back into my r33 list of mods below. the problem i'm having it it has nearly no vacuum at idle when it idles at 1500rpm. then for no reason, the rpm will pick up and then idle at 2200rpm.

i have carried out a smoke test on the engine with no results. with the engine running, i have sprayed everywhere around anything that can potentially become a vacuum leak or cause one. e.g (injector seals, plumbing fittings under plenum, around the valve covers, the brake booster, the throttle body seal, the gasket faces) i have blocked of the hose to the brake booster to eliminate the booster, no change there. out of ideas, can anybody help me please. i have spent over $30k on this motor, i need to get it working, really getting frustrated. thanks

engine:

rb25det head full cnc with vg30 over sized valves 1.5mm

custom grind cams from surecams (297 in, 310 ex, 10.2mm lift)

hks adjustable cams gears

plazmaman plenum

plazmaman 75mm billet throttle body

40thou over JE customs pistons

perfect circle rings

brian crower rods

nitrided and heat treated crank

N1 oil pump

davies craig electric water pump and fan controller

hks 1000cc injectors on rb26 hks top feed rail

hks t04z 0.82 a/r rear housing

6boost high mount manifold

hks 50mm gt2 wastegate

plazmaman fmic

GZ motorsport vacuum pump with relief valve

fuel system:

bosch 040 intank

2L surge tank

2 x bosch 044 inline pumps

twin lines to fuel rail

aeromotive fuel reg.

[HR32GTS 4DOOR]

Cam timing is probably out, can cause it to pull hardly any vacuum. I put my money on that

[skygtsnt]

Yeah have checked that also, all spot on. The inlet cam is advanced 3degrees and the exhaust I'd retarded 2.5 degrees. Even with the vacuum pump relief valve done up all the way to hard, it still only pulls -2 inhg, and changing it does nothing. Should see about 5-6 inhg at least without the vacuum is this more or less correct?

[MBS206]

Huge cams, with huge overlap will cause a severe lack of vacuum.

[GTRPSI]

custom grind cams from surecams (297 in, 310 ex, 10.2mm lift)

This and did you degree them in or did you just bolt them in and think whatever the cam gears say is correct?

Big cam durations=little vacuum natuarally.

Degree wheels set on zero are rarely on true zero, skim the head, change the head gasket thickness and your degree wheels change position slightly, thats why people degree the cams in.

Even at its best, vacuum will be low with such massive duration cams.

Edited December 4, 2013 by GTRPSI

[SiR_RB]

Huge ass cams, need somfin more mild to be street friendly

[Ben C34]

Those cams are nuts! How did you decide on those, was it based on proven results?

[89CAL]

Those cams are nuts! How did you decide on those, was it based on proven results?

+1

seem super excessive for a 25T

[GTSBoy]

1500rpm idle seems optimistic with those cams.

[Simon-S14]

What ecu?

[Blackkers]

geez 297/310 thats huge how much power you chasing?

[Piggaz]

geez 297/310 thats huge how much power you chasing?

I'd say 700-750 HP going off turbo selection and injector selection.

[33GTRV]

Good cams for -7s yeah?

[skygtsnt]

hi guys, thanks for the replies,

i gave all the specs of the engine to sure cams and the purpose of the car. (80% strip and 20% street). so he went off that bassis. he has done a set of cams like this before, and to his knowledge, there have been no problems. the head has also had solid rb26 tomei lifters installed too.

i have base timing of 15 deg. is it worth trying a little more?

as for dialing in the cams with degree wheel, i will have to ask my engine builder about that. i have used him for years and so have my mates, but some times shit happens i suppose. he also tunes it.

the ecu is haltech e11v2 milspec.

i've been told to expect hp figures around the 750 to 840 atw.

it has a 18psi stall converter and 1300hp powerglide behind it from MV automatics ins SA. used to have built jatco 3 spd from keas, but smashed that to bits with the old setup. that was making around 720hp flywheel

[Guilt-Toy]

i would be checking for leaks again. but use an air compressor this time. i was chasing issues and found 2 leaks after pushing over 10psi pressure into the engine. works a treat.

[skygtsnt]

i would be checking for leaks again. but use an air compressor this time. i was chasing issues and found 2 leaks after pushing over 10psi pressure into the engine. works a treat.

thats a good idea, will try it tomorrow, i'll let you know how it goes either way

[skygtsnt]

ok, smoked tested again and found 2 leaks. had to block the exhaust off to find them though, and still wait about 5 minf for that to fill up. the leaks were at the adjsutment screw on the fuel reg, and at the fitting going into the plenum for the brake booster. now has about 5 inhg at idle, idle around 1800-1900 atm, will do some tuning next week or so. need looser converter though. will post figures pics after tuning.

thanks for all the help guys.

[GTRPSI]

We spoke to Camtech about our 26/30 also with a 80% strip/20% street setup and were recommended 280 duration 11.5mm lift cams for a easy walk in the park 600Kw at all 4 with a precision 7175.

RB30's also tend to absorb lumpy cams a lot better....

Will be interesting to see how user friendly you will find it on the street, post back with how it is to drive after you have tuned it.

[Lithium]

Refer to my avatar.

I don't know what angle the tuner/engine builder are coming from with this combination of parts but hope it works out well for you - do the same as everyone else and you get the same results, sometimes its for the better... good luck with the rest of this, update when you've got the bugs ironed out as I am sure a number of us would be very interested to see how this come out

[Simon-S14]

ecu is junk.... will not have any decent idle control with that cam spec either