hi am wanting to make a twin turbo set up on my oil burner vauxhall/opel/gm? 2.3td frontera, it currently has a kkk k14 turbo in it now running around 12psi the safe max is for the engine is 15psi. It boost fine around 2800 3000rpm and red lines at 4800 rpm, but it takes so long to get there its almost pointless having it so i was thinking of fitting a smaller turbo to kick in lower down the range say 1200rpm while the oem takes it own sweet time to spools up I was thinking of a rhf4 out of a 1.7td isuzu lump i think its off a x17dt lump.. will this work? as i have no clue on the maths side of it , i can build it ! but will it work

 

A vauxhall/opel/gm? 2.3td frontera. ? English please.

 

hi .. Am from the u.k its a 1995 Vauxhall Frontera 2.3turbo diesel 4x4, I don't know what make they come under in the u.s.a. I think they were badged up as G.M over your end

 

Isuzu Rodeo. Wasn't available with the diesel in the U.S.

 

well i never knew that!.... am presuming the theory behind it will still work ?

 

I have seen one here , a guy that used to come to the Fab shop i was working at and remember him saying what a dog it was but got almost 40mpg. Don't know where he got it but im sure he did not import it.

 

What you've invented is called 'compound boost', and while it can be done it's not simple or cheap. You'd come out ahead buying a new truck that drives the way you want. To make it work you have to have switching valves between both sides of the two turbos, so that whichever turbo is working doesn't lose all its exhaust drive pressure and boost out thru the other turbo.

Sure it was a Rodeo, and not a Trooper?

 

I think what you are describing is more like sequential twin turbo or some such thing where one or the other turbo is working depending on engine demand and gas flow etc...

Compound turbo is what I'm doing next with exhaust header into small turbo's turbine housing with dump pipe from that into turbine housing for big turbo with its dump then being the exhaust to atmo. Intake side goes air filter/intake into big turbo with its charge pipe going into intake of small turbo with its charge pipe going to throttle body/manifold. With this style the 15psi desired may be a little more complex to keep in check...

Playing with semantics a little but either setup will produce the desired results if the OP is bored/enthusiastic enough to give it a go!

If you have easy access to the proposed small turbo then I'd say give it a go.

Cheers,
Jason

 

OK, the goal is a quick spooling small turbo for low speed, and a big turbo for high speed, right? So how do you switch the small, restrictive turbine out of the loop when it's time for the big'un to take over, so that it doesn't choke to death and never make more power than it would with either just the little one alone or just the big one alone? And all the output from the big compressor has to go through the little compressor before it gets to the engine? I must be missing something here, cause that sounds like a horrible plan... unless you ARE going to use a few switching valves, in which case it almost sounds like an even worse plan.

 

Hehe it actually works on the principle of the turbocharger being quite dumb!
The small turbo is actually not a restriction at higher boost since it is simply taking the air it is given and compressing it as per its normal operation.

First up during acceleration at low engine speed the small turbo should start to kick in due to having first dibs at the exhaust gas plus just being small in general. At this point the small turbo compressor is breathing through the big turbo's for all intents and purposes inactive compressor. As the small turbo picks up activity and makes the engine produce more mass flow the dump feeding into the large turbo's turbine begins to bring it into action. When the large turbo starts making positive pressure from its compressor the air is then fed into the small turbo's compressor and compressed further again hence the small turbo does not in reality become a restriction. There is plenty of discussion and theory about just how much bigger the large turbo's turbine housing must exceed the small turbo's turbine housing by to ensure proper gas expansion for both units.

The biggest headache is the multiplication effect of the pressure ratios and controlling the target boost pressure... Say the large turbo is pumping 7psi (1.476 pressure ratio) and the small turbo is pumping 7psi (also 1.476 pressure ratio) then the total boost is now 17.3psi (2.178 pressure ratio). Small turbo can be wastegate controlled to the maximum desired psi from the intake manifold signal if the large turbo is 'small' enough to be on boost before the small turbo chokes. The large turbo in this scenario is then wastegate controlled to the signal from the charge pipe between the large turbo compressor output to the small turbo compressor intake. In that example the small turbo would be wastegated to 17psi and the large turbo would be wastegated to 7psi. The OP would want the small turbo wastegated to 15psi however!! That would give the large turbo 7psi (1.476 PR) blowing into the small turbo which in turn is only being allowed to compress to the output tune of 15psi (1.37PR from small turbo x 1.476PR from large turbo).

Cheers,
Jason

 

thank you lads i didn't know if i should fit 2x valves to cut the smaller one out at higher revs or do as Jason said and just bolt them though, smaller turbo first. If i was going to use a valve system id make it simple as possible use a spring loaded waste gate actuator, bigger bore of course and a by-pass to allow the larger turbo to spool up, so when say 7-11 psi was reached by the smaller turbo, the actuator would slam shut from the exhaust gas, allowing all off the gas to spool the larger turbo up. when the 7-11 psi dropped down it would open and spool the smaller turbo back up.

Saying that I'd need to leave some exhaust flow on the smaller one to help stop turbo lag or would the boost off the larger one keep it spooled up enough?

 

Be cheaper & easier to just buy a truck with a motor that has power.