1jz lacking power since rebuild? please help

[ATMO_BT1]

hi guy's posting this up for a friend,

story goes engine/motor set up is a 1jz with a single gt3076 ".82",bc cams/springs/ti retainer's/ported head.

prior to blowing the engine it made 282rwkw on 15psi with just turbo and cam's NO springs NO ported head.
i then rebuilt the engine with a ported head and fitted bc springs and retainers aswell as arp bolts,new bearings/rings etc...
also chaned the diff gears to 4.3's..

went back on the very same dyno and made the exact same power except this time it took 20psi to do it... so 5psi more for a engine set up
with more compression,better springs and a better flowing head??? just doesnt add up
the tuner explained that the motor is at its peak for the current level of mods. im by no means just chasing the number i want to know why for a
engine with more mods and much better compression how it can take 5psi to make same power.

car has a 50mm gate with 1 straight through muffler and no cat.
the air filter was remooved on dyno = no difference
blocked bov = no difference

i have personaly checked engine timming 3 times and had a mate do it aswell just to be safe =) changed fuel and already had brand new filter
aswell as many many other things, zero boost leaks

personaly i wouldve expected at a minimum the same power for the same boost level and at the 20psi mark to push well into the low 300's


anyone have any suggestion's as im fed up with it,the car drives exactly the same pretty much.. im willing to try/test anyone's suggestions

[pandaah]

do you have adjustable cam gears?.. if you removed them have you rechecked if they are dialled in to there proper specs?

[ATMO_BT1]

do you have adjustable cam gears?.. if you removed them have you rechecked if they are dialled in to there proper specs?

no i dont have cam gear's however prior to the rebuild it didnt have gear's on it either... i had a friend suggest that the cam timming could be out because aftermarket cam's with stock gear's, i just assumed that this wouldnt be the case because it surely would've had the same issue prior to rebuilt.

[andrew_mx83]

how much meat was taken off the head and block in the rebuild? is this where you picked up compression? if so, cam timing will be altered very slightly but aftermarket cams really need to be dialled in properly to get the best out of them anyway

[e30-323ti]

Was it the same dyno?
Were all the variables / setup on the dyno the same?

Was there a big ambient temp difference to your pre-build dyno run?
You haven't mentioned what ECU you're using, ie. was the air temp correction 'tuned' properly originally, or just to get the best rwhp no. on that day...

[orangeute338]

does it feel quicker on the street?

[ATMO_BT1]

to be perfectly honest im not sure how much was skimmed off the head or the block but ill see what i can find out,
im running an apexi power fc "map sensor" with a gm 3bar map sensor that was also fitted and calibrated with the new engine went in. as for correction's im not entirly sure as i didnt tune it etc but again i could try find out..

the car feels pretty much identical on the street its actualy 500rpm laggier onto fullboost aswell
so as you can tell im not very impressed with the result's as clearly there is an issue.
any more suggestions im all ear's meanwhile ill try get more info on the engine spec/dyno setting's

[pandaah]

i think the difference is in the timing to be honest.. seeing as youve lost spool time, are you sure the tuner didnt just go easy on it since its a fresh motor?.. if he could dial more timing into it that could be your difference, or if your at your peak maybe thats because it has more compression now to make it detonate is easier..

any chance we could have dyno sheets with that sort of information pre build and post build?.. btw dialing your cams in should net quite a few extra ponies and will surely help spool times

[Shifty]

I have not read the thread but almost certainly be a cam or base ignition timing issue.

[ATMO_BT1]

the fact it takes more boost lead's me to believe that the comp ratio isnt the issue, more so that it could have a boost leak "highly unlikely ive checked everything" and or the cam timming is off "potential"

much to be gained with cam gear adjustment?
surely a 1jz with cams and good comp should be able to push over 300kw on 20psi and above?? surely

[Deeluded]

First guess is the same as everyone else. Cam timing.

But I'm Interested in what you changed diff gears from?
Was there a big difference in Torque? or was that the same too.

[Hurricane]

were you running the same fuel? and from the same servo?

could the port job have been done wrong?

i think cam timing could be a good one to look at. its amazing what the 1% ers like these can do sometimes.

was the tune changed at all? or just reran on the same dyno?

dan.

[Encyclopedia Ronnie]

the fact it takes more boost lead's me to believe that the comp ratio isnt the issue, more so that it could have a boost leak "highly unlikely ive checked everything" and or the cam timming is off "potential"

much to be gained with cam gear adjustment?
surely a 1jz with cams and good comp should be able to push over 300kw on 20psi and above?? surely

when my mate set his evo up we saw somewhere around a 30kw gain in dialling the cams in and made a huge difference to the cars feel on the street

[andrew_mx83]

member on here boxh34d bought a pair of my cam gears to put on his 7m-gte and picked up around 15rwkw on stock cams. definite gains to be had!

[MA61 Turbo A]

If your timing is correct, What port work was done to the head ?

500rpm slower to full boost = less air speed

Tuner said it's at its peak for mods, What hp can a gt3076 support ?

Cheers

Brad