[Ecotec] Factory L67 TwinCharged Plans

[VN_Luke]

Man i just read that whole thread, what a great find and an equally good read!

I'm glad so much of it made sense to me, kinda lessened the confusion about the topic! Anyone that hasnt read it, should!

I know it's been changed around a few times, but essentially it'd be agreeable to only have the one IC for numerous good reasons. Now which would be better: intake>turbo>cooler>supercharger inlet>intake manifold, or intake>turbo>supercharger inlet>cooler>intake manifold, eg on an m90 equipped car, the piping runs like this (not a commo i know but shows the piping well):

I'd be leaning towards the first option though, having the cooled air from the TC then IC entering the supercharger inlet to be boosted again, then into the engine.

Just thinking about this from a layout point of view also. I originally planned to go turbo only after running the M90 for a while. I've always liked the idea of having the turbo off to one side, preferably on the passenger side of the motor as opposed to right in front of it. This is for both looks and accessibility to parts of the front of the motor. I understand it may be better in terms of functionality to have the turbo right in front of the motor, as it's more likely the turbo would be receiving exhaust gases from both banks more simultaneously than if it were off to the side. The decision made here will obviously also determine the way pipes are run both to and from the turbo and cooler, then to the s/c inlet.

I'd like to hear people's thoughts/experiences with either or both setups and what they think would be better.

I know it might seem like the layout isnt what should be worried about so much at this stage, but i feel like if i've got the layout down pat then i've made a start!

As for turbo sizing, Commotion recommended me either a t04z or gt4094, but that was to run turbo-only. Thoughts? I'm not really up to speed on turbos at all to be honest, but would gladly be shown the way!

Cheers

I'd personally go with intake>turbo>supercharger inlet>cooler>intake manifold.

My reason is that the supercharger can deal with hotter air much better than an engine can ...

What intake temps are guys getting with intercoolers on just a M90 supercharged setup? (at whatever boost you want to run)

Turbo at the front of the motor just makes for easier piping, plumbing etc. Just lots of room, to work in/with. Notice the factory buick GNX setup

As for the turbo choice - I reckon the ONLY way to do it is to ask someone for a drive of their turbo car - or even to go for a spin in a turbo car, with a similar size engine and similar sized turbo and get a 'feel' for what they are like!

... And then remember that you can get (hopefully) the same top end power that you felt in that car, and have the turbo come on noise MUCH quicker!

 

[warrjon]

This is great thread. Discussion like this with theory's being viewed will foster creativity and you never know we might end up with a killer of twincharged V6

I agree with both points -
as for top end flow, I see how the gasses can flow either through the wastegate or the turbo - Although wouldn't it be more efficient to let them flow through the housing?

I read somewhere that the compressor needs a certain amount of energy to make it produce boost in the intake.

so now lets say you have two of the same sized compressors, and a huge and tiny rear for them both... they both need the same (or close enough) amount of energy extracted from the exhaust gasses to achieve the boost we want on the compressor side.

Now I read that smaller exhaust housing will require the exhaust gas to be under more pressure in order to extract the same amount of energy as a larger housing would, with less pressure.

I.e. larger housing allows more flow, so less pressure in the exhaust required to get the same amount of energy through, and vice-versa. - having said this, the more pre-turbo pressure the quicker the spool up, and the more mass flow through the turbo, the more potential energy can be extracted to drive the compressor.

Hopefully I'm making some kind of sense so far - ...

ok, since the wastegate is controlled by the *intake* side of the engine, it will set the exhaust pressure to whatever it needs to be in order to maintain the desired boost level on the intake, regardless of how big the gate is. (although of course if your gate is too small to vent all the 'waste' exhaust gas, boost creep will ensue)

Some pressure in the exhaust is fine - but in my opinion too much pressure will cost power and lead to a 'more dangerous/closer to detonation threshold' running engine.

So applying the above ^^ theory to the example you have given with the T76:

- The .5 AR rear would require more pressure in the exhaust manifold than a 1.0 AR rear in order to make the same amount of boost. - Regardless of how big the gate is.

- The 1.0 AR would spool later than the 0.5 AR, due to the lack of exhaust pressure excerting torque on the turbine wheel.

- The 1.0 AR can potentially harness more energy to drive the compressor.

This is correct the only thing I would add is that the exhaust back pressure is created by the restriction of the small turbine, so adding the large WG will keep the back pressure where it is needed to maintain TC compressor speed (boost).

I presume your approach, warrjon, is to drive the supercharger at a decent overdrive ratio, and as such, the turbo won't have to work very hard in order to achieve the total required boost once compounded? - If this is the case, a small rear housing would work nicely, as you won't need to extract much energy to drive the compressor, and hence the exhaust pressure won't need to be very high.

I would imagine this kind of setup will produce very quick full boost, and give a very flat torque curve throughout the rev range, however, at the sacrifice of sheer top end power... but regardless, this would make an awesome street car!

My approach is to drive the SC at standard boost thus not robbing the engine of power and use the TC to add the extra boost. These V6's have awesome lowend touque. What I am looking to do is have the TC spool as quickly as possible on full boost by 2000rpm TC boost will only be 3psi initially and then raise to 12-15.

WAy back in 1989 when I had my VL turbo we did some development on the TC. THe TC was replaced with a T3T4 hybrid, standard VL turbine with larger compressor. THis made awesome HP 400RWHP on the dyno but did not reach full boost until 3800rpm the car was a pig to drive in the wet being my daily driver.

So after some brain storming we decided to go smaller in the turbine using the T4 compressor, this worked to spool the TC much earlier full boost was now 2500rpm. BUT we used a TC with an internal wastegate and had trouble controlling the boost. We had boost spikes and boost would creep as the RPM rose. We did not do a dull RPM dyno run because boost crept way too high at the top end. Unfortunately we did not get to do any further R&D with an external WG as the car was stolen.

 

[eaton v8]

ok worrjon are you going to try the smaller zorst housing in your set up? if so then i might use the turbo i have and go the larger and see what happens for r&d sake.

 

[warrjon]

ok worrjon are you going to try the smaller zorst housing in your set up? if so then i might use the turbo i have and go the larger and see what happens for r&d sake.

Thats the plan, what I am looking for is a good streetable setup that will also make reasonable top end power.

I have used the small rear housing but that was a turbo only setup. In theory it should work so long as I can control the wastegate properly.

The larger rear in a twincharged setup will work very well, I wouldn't go out and buy another TC. If you run the SC continuously the TC will keep the boost up all the way from when it spools to redline. Connect the wastegate to the inlet manifold so the TC will vary boost to keep manifold boost constant. Sounds good in theory:thumbsup:

I works like varying Atmospheric pressure. A SC will vary boost pressure as the atmospheric changes, because it is running at a set speed in relation to engine RPM it will pump a known pressure ratio (set by SC RPM and engine volume) into the engine. The SC V6 at 6psi boost has a PR of 1.4, so the SC will compress its inlet pressure by a factor of 1.4.

A TC uses a WG so the compressor speed will vary so the TC will not be as susceptible to variations in inlet pressure.:wax: anyway enough rambling from me

SC's especially the M90 are notorious for dropping off at the top end, not to mention the power consumption at high SC RPM. At 12000RPM the M90 takes 28HP to drive at 5psi and 46Hp to drive at 10psi god knows what it would take to drive at 20psi.

SO my theory is keep the SC boost low enough to provide good lowend throttle response but not drain too much power at the topend. The reason I was going to use the small rear TC was just to carry on the R&D from where I left off 20years ago.

cheers
Warren

 

[eaton v8]

ok so what is the diffrence between normal rings and bearings in a l67 and a set of acl race series. i gess if i was to do this i may do it properly if it is worth it. i am lead to believe that the main problem with the l67 is the big end bearing is this correct? i have only ever played with 5l except for changing a sertain members engines due to not keeping its legs in bed, so a quick hone and rings and bearings may be a good idea, safety first i gess.

 

[Bluewildangel]

Wow cool thread lots of great info in here!
I have a twin charged vt l67 I just got it running a couple of days ago

 

[eaton v8]

so ho did it go??? and what turbo as needed

 

[VN_Luke]

Wow cool thread lots of great info in here!
I have a twin charged vt l67 I just got it running a couple of days ago

dyno sheets for boost and power/torque curves! STAT.

 

[HoldenManDan]

oh could the timing be any better? I dare say no!

Please give us some info on what you're using and how it's all set up!! Dont tease us!

Luke, looks like it goes intake>turbo>cooler>supercharger>inlet manifold, yes?

 

[VN_Luke]

oh could the timing be any better? I dare say no!

Please give us some info on what you're using and how it's all set up!! Dont tease us!

Luke, looks like it goes intake>turbo>cooler>supercharger>inlet manifold, yes?

yep it certainly does

curious to know how much boost the charger is running, and specs on the turbo... and results