supercharger swap. its crazy...your thoughts?

[unclepaulie]

Why would you need to modify the OEM computer? I can't see how you would need to modify it any more than with the centrifugal unit.

You still have the same inputs and outputs. My main concern is that if you take out the turbos you then get different breathing characteristics due to the lower exhaust back pressure. Ideally you could benefit from exhaust tuning for bigger gains but that is another conversation.

i guess you are right, there would still be a maf and all related pressure sensors.

a whipple would make rear spark plug changes a breeze too if it was mount between the banks. it just seems that every whipple i hav seen comes with a kit for intake runners. this would make the entire conversion quite pricey. the centrifugal SC allows the stock intake manifold to be retained.

regarding the exhaust back pressure, proper equal length headers would be used, but i dont see a reason why the back pressure would changed significantly, i can understand it would change a bit as there is no turbine to spin now

 

[Kenneth]

The turbo turbine is a significant restriction to the exhaust flow. Though how much difference it makes, I wouldn't like to guess.

I was going to log onto the whipple forums and ask if it was ok to run the SC on its side... that would give you options for running it beside the engine with the discharge pointing either inward or outward depending on how your intercooler is configured.
Another thought is to make a very long snout and mount the SC back over the gearbox and run the discharge into a water to air cooler which sits on the gearbox and directly feeds the intake throttle body.

A new intake manifold would be best idea though, and compared to the setup cost of the SC, it probably isn't a considerable investment. In fact, it might be cheaper in the long run than all the mounting crap you have to deal with by trying to keep the standard manifold.

 

[unclepaulie]

yup i hear you. with no cash or time limit i would definitly consider what you said,

but, my hypothetical plan from the start was and still is a cheap alternative. if the cost was to blow out, then obviously the turbo upgrade would be beneficial. cost is the only thing that is keeping it afloat really.

However the back pressure differential is something i will look into, but both are boosted engines, just the load is placed on the engine via different methods, crank vs exhaust flow.

 

[Kenneth]

Some quick calculations on the smallest whipple SC (W100AX)
Displacement per Revolution = 1.6L
Max continuous RPM = 18,000

Max pully ratio = 18,000 / 7000 = roughly 2.5
Displacement per engine revolution at 2.5 pully ratio: 2.5 * 1.6 = 4
4L of air per engine revolution is going to give a pressure ratio of 4 / 1.25 (engine displacement / 2 ) = 3.2

3.2 * 14.7 = 47.04psi absolute

boost = 47.04 - 14.7 = 32psi of boost.

That is more than the SC is rated for, so you would need to alter the pully ratio. Needless to say, 30 PSI of boost almost instantly on tap is not to be sneezed at.

 

[unclepaulie]

just a note,

centrifugal superchargers build up boost like turbos, while the whipples (like the Kenne Bell unit in the videos) are instant.


thanks for that calc Kenneth, 30psi is certainly nothin to sneeze at.


on the mustang forums, a lot of the guys there are saying for outright power, the whipple is the winner, but its is expensive. the centri setups are good for powerful street applications though, but they come onto boost like a turbo does.

 

[Kenneth]

If you want cost effectiveness vs feeling of power, convert your transfer case to RWD. 1st and 2nd wheel spin GSD3s no trouble, 3rd lets go at 3k in the wet and I didn't have the nads to try it at highway speeds in 4th or 5th.

Failing that, if you want more response and a bit more torque, if you haven't already get some front pipes and a 3" exhaust. Then get a water to air cooler and run the standard turbo output directly into the intake without the large pipe areas. Along with that, custom make turbo feed pipes so you don't starve the turbos (should give you much better boost up high).

You should be able to get the exhaust work and the intake work done for the same amount as a pair of custom exhaust manifolds for a SC setup, not to mention you would need a new intake setup for the SC anyway.

 

[Kenneth]

No worries. I spent quite a bit of time in research, be good to not see it all wasted Just hope you found my ranting useful

 

[unclepaulie]

this kinda thing would be nice.

but once again, it would prove too expensive.

your insights are very helpful, but doing a whipple would be way to costly for the gains.

i will keep researching the centrifugal setup, just for kicks. i wont ever do it.

if it was to happen, there would be 3 criteria it would hav to meet.

1)no more expensive then a turbo uprgade
2)270kw atw min
3) retain as many factory parts as 'possible'


as far as response and all that, i already hav full exhaust/intercooler/tune etc, and if i wanted RWD, id probably just buy a rwd car lol. too much muckin round with the vr4, not to mention the loads placed on the t-case. the goal behind this wasnt based on my car's performance, just a "what if we could"

 

[king_panther]

Obligatory Mad Max pic inserted;

Pauli, you MUST make it look like this.

 

[TME_Steve]

Personal opinion, if you go to a supercharger you want to reap the benefits of it so a form of positive displacement to reduce lag would be my only choice.... Certainly could be a better proposition for a road car but as a track car the gains of less lag are outweighed by the losses on a supercharger so turbo's are the winner there....

And I suspect there is more gains to be had with cheap alternative turbos eg TD04's with some lateral thinking (not necessarily more than a supercharger just more cred than they get given) and from a cost point of view will be way cheaper than anything else.

That is all irrelevant if you want to be different for the sake of it or want the sound though.

As for tuning, in my opinion, the stock ecu can be retained for any application with enough time but you may need to upgrade the MAF and other anciliaries depending how far you go. Don't underestimate what the stock ECU can do, in a lot of ways it's better than aftermarket for a road car.

There's another option here but I'll let the person thinking about it chime in if they want to.

 

[Gary31]

I don't like positive displacement s/c, dont get me wrong i think they work really well on engines that are built for low rpm (ie engines with a long stroke), but they tend to run out of puff at the top end. I read an article on this a while ago, i just cant remeber where. i will post a referance when remeber where it was.

oh, someone mentioned the comodore s/c the design for the compressor was pattened in the 1800's.

 

[Kenneth]

Super charger (positive displacement or centrifugal) or turbo, they do the same thing and all have limitations. The major one being that if you don't match them to your engine (or your expectations from the engine) then they will disappoint. To run out of puff top end means that it wasn't matched for top end performance, simple as that. It has no bearing on whether the technology is any better or worse than another.

The engine configuration has very little to do with it other than flow potential and, in the case of a turbo, being able to actually spool the turbo. Bottom end vs top end is all down to the engine setup (good luck getting any useful power out of a VR-4 engine above 6k without fiddling with the cams) and matching your turbo or supercharger for that.


My plan is compound turbo. Spin the standard turbos around 180 degrees and then feed a big lazy turbo sitting on top of the gearbox. Run a water to air directly up over the top of the engine into the intake via ITBs

 

[SLY-031]

Hardest part about that is matching a single to the twins, and seperating the compressor outlet air into the twins. You'd also probably want to weld up the internal gates and use externals units so that you know you can bypass enough gas past the twins.

I don't think the compressors of the twins would allow for enough flow of a very big single either.

Hey, I could be wrong on all accounts, care to try it, Kenneth?

Would be incredible to see work though.

 

[Kenneth]

Yes, it would most likely require external wastegates. I doubt that the standard setup would flow enough through the exhaust manifold flange to give the required exhaust flow. Could try boring it out and closely matching the TD03 wastegate flapper to the port. Would want to use a divorced turbine outlet flange though. I am still dubious to that being enough... Depends on the final goal I suppose.

The thing to get your head around with compound is that the final compression turbo (in this case the twins) seeing greater than atmospheric pressure, you are no longer talking about flow rates as seen in the compressor maps. Compressor maps use "corrected air flow" which is usually around atmospheric. If the final compression turbo was seeing 2 bar absolute then you would probably have to just about double those figures (air density has doubled). As such, air flow rate should not be a problem.
Heat will be though, but that can be dealt with.

It is in my long term plan to try

 

[Guest]

depends on 'how' you are talking about compounding them.
If you are using the flow of the small twins compressor outlet into the exhaust housing of the large one to spool it up, then you still run a relatively low boost pressure, just lots of flow.
The flow restriction through the head and combustion chambers causes the boost pressure to increase.
Choke the flow, and you loose any benefit. It can take some serious head and manifold work to realise the total potential.
Ideally you want to be able to flow the maximum amount of charge air without restriction.
If on the other hand you are running the outlet of the twins into the inlet of the big single (and have it sized according to expected flow) and the compressor outlets of the twins INTO the inlet of the single, the air is compressed even more. you dont see as high shaft speeds(airflow), but a larger multiplication of boost pressure.
As a benefit, you often see slighlty reduced inlet temps due to the lack of heated thermal mass in the exhaust section of the single turbo transferring into the compressor.
the end result is quite similar in that you need to work the head and manifolds but you have a higher pressure to 'force' the charge air into the cylinders.

 

[Kenneth]

I think you have it backwards Alan.

The setup is from intake side: Big lazy turbo -> split to small turbos -> engine
Exhaust side: Engine -> small Turbos -> big turbo -> Atmosphere.

This is how it needs to be setup to create compound boost. This setup sized correctly should have no trouble providing 3bar of boost.

As I said, you are getting caught up with flow rates at atmospheric pressure. Only the large turbo runs at atmospheric, by the time it gets to the small turbo inlets, the pressure will (at least when on boost) be greater than atmospheric. Because of this, the air density (ignoring the effect of heat for examples sake) will effectively be multiplied by the pressure ratio of the first (big) turbo.

For example, if the big turbo is set to produce a pressure ratio of 2.0:1, then with atmospheric pressure (sea level) on the inlet, the outlet pressure will be 14.7psi of boost (29.4psi absolute)
This being the case, in a perfect world the air temperature wouldn't have increased much and so you would effectively have 2x the air density on the compressor outlet.
So now you have the inlet for the small turbos. You have to ignore the flow rates on the standard maps now because you are at 2x atmospheric pressure, lifting the density of the air and therefore increasing the total volume of air that can pass through the smaller compressor housings.
Now if these turbos are set for a pressure ratio of 2.0 also, then the output pressure is inlet pressure x pressure ratio. If inlet is 29.4 psi absolute, then the outlet pressure is going to be 58.8psi absolute. Minus atmospheric at 14.7 you now have 44.1psi of boost.

The heads now see a shed load of pressure, so their flow rate is going to increase proportionally. Yes, the exhaust will cause some restriction and this is why it is likely that an external wastegate will be necessary.

None of this is new, it has been used in Diesel engines for some time. A lot of people will tell you that it is a waste of time and that you can get just as good results with a well matched turbo. Problem is, what if you want 30psi of boost at 3000RPM? This is what I would be aiming for.

 

[bradc]

The reason for needing large wastegates before the stock turbos is that there is now a lot more airflow through the engine, as you'd most likely be making 500-650hp and you only need a small amount of that air to flow through the stock turbos to keep them going, most of it needs to go out via a big wastegate.

Also rather importantly, once the TD03's make 0.5 bar of boost which happens at around 2250rpm to 2500rpm, you now have an effective 3.75 litre engine spooling the bigger turbo, which brings it on boost earlier than you'd otherwise expect from a large turbo on a 2.5L engine.

 

[TME_Steve]

compound turbo set ups can work very well. There's a good thread on a 4g63 (in an eclipse i think) with compound turbo's in the states. Really good results and for our cars could actually be quite cheap. Fitting it in is the hard part....