Outer Limits 4x4 Board

hi all
i have 1990 nissan safari ute conversion,all the normal mods dnt wana bore u wiv that,
right here goes, done a turbo conversion using a ct26 from a gt4 celica,1st manifold was a log manifold work well but did not flow very well was happy wiv 8lb boost,made a new turbo manfold set of flows (headers) that go flow way better,but i have lost 4lb boost and have no idea why as new manifold flows way better so shud boost better and quicker??
any help would gr8 thanks vince,

youve changed something turbo wise putting it all back together. Check your waste gate actuator/linkage, intake or for exhaust leaks.

good luck with it.

Got pics of the manifold? Its good to see someone giving it a go and doing something different

In order to generate pressure, you have to have a restriction of flow to force against (ie your old "non flowing log"). You have now removed some of that restriction (higher flowing manifold), so for the same airflow volume it will be at a lower pressure.

that pressure is in the intake manifold not the exhaust manifold Damika

boost is a measurement of restriction not airflow. Reduce restriction = higher airflow but lower air pressure.

Damika is 100% correct.

hes made a new exhaust manifold.... what that got to do with a differing intake manifold pressure guys?

Z()LTAN is right.

GRPABT1 wrote:Z()LTAN is right.

Not necessarily..New exh man can help scavenging that reduces back pressure left in comb chamber so more air flows into chamber reducing pressure seen in inlet man.

Bazzle

but would less boost automatically equal less power? maybe it's just running more efficiently than before?

bazzle wrote:

GRPABT1 wrote:Z()LTAN is right.

Not necessarily..New exh man can help scavenging that reduces back pressure left in comb chamber so more air flows into chamber reducing pressure seen in inlet man.

Bazzle

You would still have the same restriction at the exhaust turbine .. The CT26 is not a great flowing turbo in stock form.

thanks for ur replies,truck still goes well but just missing get up and go it had before,its like the turbo is now lagging a bit,maybe i just space the waste gate or wack on a boost controller,just seems strange a better flowing exhaust manifold gasses out quicker more power?? turbo spools up faster??
thanks vince

love_mud wrote:

bazzle wrote:

GRPABT1 wrote:Z()LTAN is right.

Not necessarily..New exh man can help scavenging that reduces back pressure left in comb chamber so more air flows into chamber reducing pressure seen in inlet man.

Bazzle

You would still have the same restriction at the exhaust turbine .. The CT26 is not a great flowing turbo in stock form.

Spot on "love_mud", scavenging is what you will get in a NA engine, not a turbocharged engine. Scavenging requires a free flowing, low restriction exhaust system. Exhaust exiting into a turbo manifold on the other hand, is under high pressure (from the piston) to drive the exhaust turbine which drives the compressor when the engine is loaded and is therefore a restriction. A better flowing manifold will allow the piston to do this little easier and this benefit will be more noticeable at at higher RPMs. Not really what diesels like to do.

"pigfmr" Unless you've fitted an intercooler as well (this will reduce the PSI reading), I'd say you have either a boost leak or a faulty wastegate. So check ALL your hose clamps are tight and even try disconnecting the wastegate altogether. Another thing, be sure the pre-turbo intake hoses arent collapsing and the air cleaner is not clogged. Unfortunately the turbo you have is a little small for the job as well and is probably spooling at idle, generally a turbo off a petrol engine can supply a diesel engine of around 1 litre more capacity. Don't wind too much fuel into it and keep an eye on the pyro particularly when tuning.

Less restriction and longer runners causing lower EGT's? Lower EGT's = less air speed
also check your wastegate flap isnt jammed open.
Have you changed the orientation of the turbo ............... if the oil return isnt draining properly it can slow the turbo down heaps, ive seen it on a ct26 and a denco schwitser before

How is a ct26 too small the celica has the same trim spec as a 1hdt ct26

While I agree that it's restriction to the flow that creates boost pressure I would expect the engine itself to be the dominating restriction, not the design of the inlet manifold. Although I guess that a poorly placed boost pressure take-off could affect the boost reading, due to venturi effect? Possible, but unlikely, especially if it's got less "go".

There was mention of playing with wastegate springs? This will only help if the wastegate is opening at 4psi to limit boost. If the boost pressure is affected by some other fault then the wastegate may never be opening. Confirm that the wastegate is closed when the engine is off, and try to determine if it's opening during driving. If it's never opening, it's not the cause of the problem.

ffs fellas get on topic, hes built an EXHAUST manifold....

Have a think about how much heat losses there are now from a thin manifold, remember heat is drive energy. If you have come from a thick cast iron manifold and fitted one made from thin wall steel you will be experiencing heat losses from the manifold. A turbo will spool quicker and stronger when all exhaust manifolding is lagged etc and there are minimal heat losses to atmosphere.

so by disconecting my waste gate, and i get the boost i want ,this means my wastegate is not working how it should be??? and not opening or closing as its only boost to 4lb but this could be factory setting on wastegate on a gt4 celica??,but my old log style boosted better,is safe to run without wastegate all the time,sorry for the questions
thanks vince

UGOTNUFN wrote:Have a think about how much heat losses there are now from a thin manifold, remember heat is drive energy. If you have come from a thick cast iron manifold and fitted one made from thin wall steel you will be experiencing heat losses from the manifold. A turbo will spool quicker and stronger when all exhaust manifolding is lagged etc and there are minimal heat losses to atmosphere.

hi
new manifold is made out of thick walled steam pipe and steam pipe bends
thanks vince

Stock GT4 CT26 wastegate should open around 8 or 9psi.

I think you either have a wastegate leak/opening too early or a boost leak on the intake side.

Manifold leaking at head or turbo flange and losing pressure - did you get the flanges machined flat after welding?
Leaking welds?

Pipe size - smaller tube = higher velocity of gas impinging on the turbine. Gone too big with the tube??

Collector pipes at turbo housing - angle of flow into turbine - same as before or changed?

Also pulsing of exhaust gas - interferance? Some designers use dividers to separate the flows into the turbo, some turbos have this built in

With your new manifold did you have it shot blast / cleaned inside to remove any slag, dags and debris? Maybe something has come adrift and damaged the turbine?

pigfmr wrote:thanks for ur replies,truck still goes well but just missing get up and go it had before,its like the turbo is now lagging a bit,maybe i just space the waste gate or wack on a boost controller,just seems strange a better flowing exhaust manifold gasses out quicker more power?? turbo spools up faster??
thanks vince

Not always. You can have higher air volume but lower air speed. Air speed = power. Has the intake tract changed at all? You can easily change something to increase size but if that then slows the airflow you go backwards. Wether the restriction is or was in the intake or exhaust is irrelevant. If the exh is now bigger the air speed may have slowed to a point the turbo isnt spinning as fast.

Gotta be the wastegate, just sticking open a fraction!

thanks for all your replys,waste gate actuator was not working right,put another one and it goes really well,so me is happy as,egt's are well down and this new manifold so all is good,thanks again ,will post sum pic's of my ute conversion and turbo install and spec's of my truck if anyone is keen,is there a forum i can post them on or just start a new post??
thanks vince....

If you've got a few pics and some info, go ahead and create a build thread in the members section, and post a link to it in your sig line. Maybe post up a link in this thread when you get a build thread up so we can have a look!

so it turns out it was something simple and a mechanical issue and not something black magic like those who were taking some rather astounding liberties with the laws of physics were talking about.

Of course every one of you will be thinking it was one of the other posters who was talking physics voodoo.

I thin what some poeple were trying to explain was something I have read about a couple of times, but cant find again.

Basicly, you dont get boost without restriction, if you remove restriction from your engine your boost level (psi) will be lower for the same horsepower. I think it applies more to superchargers where the superchargers speed is directly connected to the engine speed, if you put in a set of cams with large overlap, multiple throttle bodies, larger exhaust, or something else that allows the engine to breathe better, with a supercharger or a turbo that is "too small" your boost pressure will drop because the volume of air that can pass through the motor has increased (you have less restriction). If you turbo is "big enough" then it will just keep spinning faster (making more boost) until wastegate boost pressure is reached (unless the turbo is too small and it runs out of puff).

I hope that makes sense and I remembered it correctly.

True, pressure is a restriction to flow. In the same sense pumps do not create pressure, the restriction in the circuit does. yada yada yada

The main controlling restriction in the circuit (engine intake-combustion circuit) will always be the valves/head design.

Isn't pressure just a proxy measure for what you are really trying to achieve anyway, which is more air and fuel into the cylinders? If pressure drops because you have more air going through the motor then I don't understand why that is an issue.

(This is a question, I have never had anything to do with forced induction).

chimpboy wrote:Isn't pressure just a proxy measure for what you are really trying to achieve anyway, which is more air and fuel into the cylinders? If pressure drops because you have more air going through the motor then I don't understand why that is an issue.

(This is a question, I have never had anything to do with forced induction).

Pressure drop in itself isnt an issue at all. You want the highest air volume with the highest air speed to make the most power and torque.

I know first hand the complexities as i made this with a mate in his garage on a CNC machine for my car. We went through 3 manifolds, 3 blower cores and countless designs trying to maximise performance. (870hp atm)