# Boost Guru's i need help!



## Pingu (May 22, 2003)

Hey

Ive been trying to fix this problem for a while and cant seem to find the solution.

The problem has always been there since i got the car but i never really gave a shit because i usually ran stock boost and it keeps that roughly till the redline , well it fell off to 6psi by 6000.

The problem is the boost pressure falls from what ever i have set it to generally from 12 psi which will fall to lower than 7psi (stock) once higher rpms have been reached. The dropping off is proportional to rpms and this is very noticable. (various methods of boost control tried, problem endures)

The car is 88 Nissan Bluebird Attesa
ca18det
80mm afm , 3" intake relocated to foglight bay.
Rx7 s4/s5 & T3 hybrid turbo (who knows the a/r's maybe this is the problem)
on a pos modified flange manifold...
front mount VR4 intercooler with good piping (it is known the piping does not leak)
half decent 2.5" straight through exhaust system.
and eprom chip upgrade (this is knownnot to be the cause of the problem as on the old chip its just the same)

So i can be pretty sure that intake/exhaust restrcition is not the problem &as he boost falls lower than stock! 

Could it be a leaking actuator drum, or weak spring inside the actuator is failing me somehow? something wrong with the wastegate that would cause this? The actuator has a 7psi spring.

Since i have tried a variety of boost control systems that *should* hold the waste gate closed till the desired pressure is reached, since the pressure is less than this value the wastegate should be closed , but i cant imagine all the exhaust gasses serving the turbocharger at higher rpms and producing such low boost. I keep thinking it cannot be a leak in the intercooler because the fuel mixtures would be very off and this would be more obvious.

Could it be a failing fuel pump / fuel pump not up to the job?i would have thought the fuel mixture would go lean and i would pick up detonation on the monitoring system. 

I left standard gap of 1.1 or 1.2mm on heat range 7 champion spark plugs (standard plug but one colder)

My fear is that the turbocharger on it might not be suited for this motor? But it should boost higher than stock at higher rpms!!! 

I probably have left alot out of my description of the problem, but any ideas of wtf is going on would be great.

ANYTHING!!!!!


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## boost_boy (May 25, 2002)

Pingu said:


> Hey
> 
> Ive been trying to fix this problem for a while and cant seem to find the solution.
> 
> ...


Hey Man, the wastegate actuator is given you grief! Which actuator are you using and is it adjustable. I had this happen with my g/f's CA18 back in the days and i would get so frustrated, that I would pull the hose off the wastegate and let the turbo scream :dumbass: . But seriously, focus on the wastegate actuator and lower the gap to .85mm as this will definitely help with big boost response and ignition.


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## Pingu (May 22, 2003)

I has to be the actuator i think, i did two tests with a direct line from the turbo signal and also the manifold signal , no bleed , just a straight connection , so it shouldnt spike, it should creep the last little bit upto the regulated pressure. But in both tests it spikes to 9-10 psi and fell back to 5 psi by 5500 rpms. Does this sound like its the actuator/wastegate being an ass?

So the similarity also tells me at these boost levels/flow the restrcition across the intercooler is negligable.

The actuator is supposedly the standard rx7 s5 rotary one for the compressor , (rx7 s5 compressor, T3 skyline exh turbine) , connected to the skyline wastegate.

Can i sucessfully take the actuator off and put it back on while the turbo is still on the motor, how is it attached? Is it feasable for me to use one from a random car?

Maybe because of the greater exhaust gasses by rpm on the piston engine, it forces the wastegate flap open given the weaker rotary intended spring, or maybe the wastegate flap area is greater than the matched actuator is suited for , or something like that maybe. who knows, but its pissing me off , just like the damaged 80mm r32 afm i bought which has probably damaged my motor given on about 5 occassion's at sub 9 psi boost at 2800-3200 rpms it leans off and detonates (over 200 on the knocking level on the piggy computer). It seems to be "slow" to react to rapid changes in flow , and idles like shit. Hope it didnt ruin a bearing :|


Boost boy , i was also thinking of opening up the exit pipe on the intercooler to 2.5" from 2" and running that 2.5" all the way to the throttle body, is this a waste of time on this setup?

Thanks man.


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## boost_boy (May 25, 2002)

Pingu said:


> I has to be the actuator i think, i did two tests with a direct line from the turbo signal and also the manifold signal , no bleed , just a straight connection , so it shouldnt spike, it should creep the last little bit upto the regulated pressure. But in both tests it spikes to 9-10 psi and fell back to 5 psi by 5500 rpms. Does this sound like its the actuator/wastegate being an ass?
> 
> So the similarity also tells me at these boost levels/flow the restrcition across the intercooler is negligable.
> 
> ...


Leave the intercooler the way it is as it won't help much. Try this test, pull the wastegate and see how high your boost goes. If your boost goes above 14psi, then it's not your turbo combo. Why don't you just source an S14 or S15 Sr20DET turbo and use it. If you have to source another actuator, you have to make sure that it's feasible enough to bolt in the same location of the old one.


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## Pingu (May 22, 2003)

Can easily top 25 psi at lower rpms, i found that out by mistake not too long ago.

Ill jump on the next 2nd hand s15 bbt28 i see anyway, what sort of capacity does it have? would i be able to top 320 odd motor hp in that with reasonably high boost?

if they all bolt on in a similar fashion then it should be ok with that part of the mounting but how does the rod attach?

Ill just have a fiddle now.....


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## sersr20dk (Oct 15, 2003)

question...what are you using for a blow off valve? otherwise i think it must be wastegate related.


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## boost_boy (May 25, 2002)

Pingu said:


> Can easily top 25 psi at lower rpms, i found that out by mistake not too long ago.
> 
> Ill jump on the next 2nd hand s15 bbt28 i see anyway, what sort of capacity does it have? would i be able to top 320 odd motor hp in that with reasonably high boost?
> 
> ...


An S15 turbo will yield you very close to 300hp. One thing if the wastegate bolts up correctly and another thing is if the wategate arm is adjustable.


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## Pingu (May 22, 2003)

bov isnt leaking.....thanks, i wish it was 

the wastegate actuator has a puncture on the wastegate side (the empty supposed to be sealed cavity between the diaphragm and the actuator body where the spring is housed) Is this cavity supposed to be sealed to offer some force against the wastegate to the volume change when the diapragm moves?

I cant see a way to detach the actuator rod from the body of the actuator :|

Rod doesent look adjustable or detachable at the other end, i guess the actuator has to be rotated till the thread (guessing there is such a thing) on the rod is out while securly holding the rod so the little arm thing doesent get bent?

hmm...............


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## boost_boy (May 25, 2002)

Pingu said:


> bov isnt leaking.....thanks, i wish it was
> 
> the wastegate actuator has a puncture on the wastegate side (the empty supposed to be sealed cavity between the diaphragm and the actuator body where the spring is housed) Is this cavity supposed to be sealed to offer some force against the wastegate to the volume change when the diapragm moves?
> 
> ...


If you want to, bend the actuator arm to hopefully pull some of the slack out and shut the wastegate door.


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## Pingu (May 22, 2003)

boost_boy said:


> If you want to, bend the actuator arm to hopefully pull some of the slack out and shut the wastegate door.


Taking the turbo off and the manifold , might aswell get that jigged so i can make up some extractors.

There was no preload on the gate and was moveable by hand.


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## Joel (Jun 11, 2003)

Get a better sized exhaust - 3" complete with 3" dump and front pipes + cat. This will help stop boost fall. Also a good EBC will help.


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## Pingu (May 22, 2003)

That would help if i was making boost!!! , having a 3" exhaust over a 2.5" wont make any difference at the flows this car was producing...!

Thanks anyway, i do intend on making a 3" mandrel exhaust pretty soon. instead of EBC i made my own that has the same functions.

thansk


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