How to fit a blower in an R33

[Warpspeed]

Some excellent cam design info MegaGTS4 in the second link.

As far as blower size goes, it has more to do with required airflow than actual engine size. For instance a 5.0 litre engine with a 4,500 RPM redline might require about the same size blower as a 2.5 Litre engine that redlines closer to 9,000 RPM, at similar boost levels.

For both engines the maximum blower speed might be 13,500 RPM, but the 5.0 litre engine would turn the blower at 3 times crank speed, the 2.5 Litre engine at 1.5 times crank speed.

In my opinion an RB25/26 engine is not a typical production engine, it has far better top end breathing than a lot of similar capacity engines.

If you look at the power levels produced by the M90 on larger engines at typical roots blower boost, maybe 7 to 10 psi, you might expect 150 to 200 Kw. This would be a reasonable power goal for an RB25/26 at those same boost levels as well.

As a very rough guide, an RB26 will inhale 1300 cc worth of air each revolution. If you run 0.5 Bar boost (7.35psi), the blower must inhale 1950 cc worth of air per engine revolution.

With a theoretical blower capacity of 1400cc per revolution, it must be driven at 1950/1400, or 1.39 times crank speed.

There are going to be a lot of factors that influence the final boost you end up with, particularly exhaust back pressure.

My first guess with an M90 on an RB25/26 would be to try a blower drive ratio of about 1.5 as a starting point. This would be a pretty comfortable compromise between blower leakage and maximum blower RPM.

According to Eaton, the M62 is supposed to be a more appropriate size. It probably would be on an older 2.5 Litre two valve pushrod engine with lower redline.

[Steve]

Hey Mega and Warpspeed, thanks heaps for your replies its all good stuff. I realise that mounting the blower is not going to be easy, and I dont want to have to redo it once I have done it. I dont think that matching up the outlet of the eaton blower will be too difficult, isn't the 4.0L jag a straight 6? either way it shouldnt be rocket science to fabricate a collector for the outlet out of aluminium? What do you think?

Bottom line though is cost - I can get a new Eaton M90 from holden for about $1600 - buy one new from a supercharger dealer and it is around $1200 dearer, so it seems to me that perhaps the buying power of holden has kept the price down? 'Spose they can really buy in bulk.

It says alot that the eaton M90 is recommended for 3-5L as the SC14 (same size) is on a 2L and if anything wont pump the air required for an RB25 efficiently....

Warpspeed, could you explain why a 2.6L engine only inhales 1300cc per revolution? Also, how did you come up with the figure of 1950cc for a 1400cc blower at 0.5bar? Just curious - and it could help with calculations in the future. Is it in Corky Bells book?

Cheers Steve

[rev210]

First you need at about $100 and the location of your nearest redlight district.

[Warpspeed]

Hi Steve.

A four stroke engine only has an induction stroke every second revolution for each cylinder. So for each turn of the crank only three cylinders will be on an an induction stroke, or 1300cc of air per crankshaft revolution will be drawn into the engine, for an RB26 anyway.

If a positive displacement supercharger also had a displacement of 1300cc of air per rev, there would be no boost if it turned at the exact same speed as the engine. There would be atmosperic pressure upstream and downstream of the blower.

But if the blower pumps more air in, say 1.5 times as much, or 1950cc, then this air will be compressed so it fits into the volume of 1300cc that the engine will flow. The pressure will rise to 1.5 times atmospheric. This is 0.5 Bar boost, or 7.35 psi.

This is all very theoretical, perfect engine, perfect blower, no pressure drops, no rotor leakage, and so on. What you end up actually getting, might be more or less boost on a real engine.

But it is a good way to make a really quick rough guess as to how fast you might need to turn a certain blower on a certain engine to get somewhere near the boost you want.

Yes, the Jag is a 4.0 Litre straight six, DOHC four valves per cylinder.

I agree the new Holden M90 is a very good deal. I strongly suggest you make up a dummy blower first and see if it is going to fit before forking out $1600 though. I have never used one of these, and they look pretty bulky. Shorter drive snouts may be available from Eaton as a spare part, or it may be possible to fabricate something yourself if this is going to help to install it.

You will need a flat, very strong surface to bolt the blower onto, and the mounting/manifold can be either steel or aluminium.

Personally I prefer steel because it is easier to weld and work with, and I can do it all myself at home. Aluminium will need to be very thick, and probably will not end up any lighter in the end.

[Duncan]

4.0L jag is a v8. Just been stroked to 4.2L

[Warpspeed]

Hello Duncan.

Now this is mighty interesting. I know Jaguar make a 4.0 (4.2) Litre V8, but I have here a Magazine article that gives details of the supercharged six as also being 4.0 Litres ? ?

This article appears in Zoom April/May 1997 page 70, and briefly describes the following supercharged engines, Holden 3.8L V6, Mazda 2.3L 800M miller engine, Jaguar 4.0 six, and Mercedes SLK 2.3L supercharged.

What it says, and I quote from directly Zoom...........

The XJR uses a positive displacement Roots-type Eaton M90 blower - yes the same basic unit as the one on the Holdens ! The blower is driven at 2.5 times crankshaft speed (13,750rpm at the redline) and it boosts to a maximum of 0.7 Bar (10psi). A compression ratio of 8.5:1 is used and the valve timing is such that there is no overlap where both intake and exhaust valves are open at the same time. The 4 litre straight six has a mighty power output of 240kW (320bhp!) at 5,000 rpm and a peak torque of 512Nm at 3,050 rpm. If you buy the supercharger unit from Jaguar it will set you back by $2,970.

End of quote.................

I hear what you are saying Duncan, but now I am confused, anyone know more about this ?

[Duncan]

Fair nuff, there could be another engine. I just checked www.jaguar.co.uk, the engine in the XKR is definately 4.2 supercharged v8. Couldn't find details of the supercharger though....

Interesting, apart from this jag engine, are there any other supercharged straight sixes?

[Warpspeed]

Just did a netsearch myself. It seems Jaguar introduced a supercharged 4.0 straight six in 1994, then replaced it with a 4.0 supercharged V8 in 1998, hence all the confusion.

http://www.nsnews.com/issues98/w022398/testdriv.html

[Ender]

Hi,

I have looked into this a bit for an rb20det. Almost to the point of doing it.

The issues I thought were needing to be overcome are issues such as blower compressing air at low rpm and pushing it backwards out the turbo rather than through the engine. You may need some sort of a control valve to control this, also finding the correct rpm point to switch the blower off.

Does the engine management system have enough scope to provide enough fuel at low rpm given the huge increase in power you would get from idle?

I guess you can run two filters for intakes, and I gather that afms generally are just a cumulative voltage type arrangement therefore you could just wire the one from the blower and the one feeding the turbos together and feed that in to the management system.

I wonder if you might be better off removing the turbo and just put a blower on, you would smoke everyone in traffic because you have instant power from so low down.....

Cheers,

Russ

[Steve]

Hey Russ,

the problem of the air being compressed at low rpm is pretty easy to overcome by using a bypass valve, the air is allowed to pass back to the front of the blower when cruising and when at idle -

As for engine management, that shouldn't be too much of a problem, as the MAF sensor will fuel for whatever air is drawn into the system, so if you have boost at low rpm, the computer will know this and compensate appropriately.

there would be no need to use two AFMs, as this would confuse the computer - adding two voltage signals together will double the voltage, if you wired them in series this would also cause problems with the correct voltage being seen by the computer. If you did want to use two intakes you would probably have to run the car from MAP but then you will have troubles arranging a shut off for the blower outlet when the turbos come on boost.

[Warpspeed]

Hi russcb007.

Steve is right about engine management, the airflow meter just sees more air, so adds more fuel. In fact the engine management self learning will slowly adapt and fully remap the ECU over the whole part throttle fuel map.

Full throttle mapping at low RPM will not be that far out either, because it just adds more fuel automatically. It is not the same as say doubling the boost pressure with a stock turbo. Here the engine could go dangerously lean because either the injectors, airflow meter, or fuel pump may top out.

The only problem you might encounter is that the ignition may be over advanced at low RPM. But even here most mechanical (turbo) distributors and ECUs employ boost retard on the ignition curve, or alternatively, the detonation sensor will retard the ignition.

If your engine was originally n/a it will not have provision for boost retard of ignition timing, and you may have problems with overadvanced full throttle low RPM ignition.

Supercharging a previously turbo engine in my experience has worked o/k every time for me. For best results a full dyno retune is required of course, but you are not likely to blow your motor just because you now have a lot of new low end boost pressure than you originally had with the turbo.

Just removing a turbo and fitting a supercharger will radicaly change the engine characteristics, even with an identical boost level. A supercharger can never give that top end rush, but what you end up with is bulk low end and midrange grunt that slowly tapers off and dies right at the very top end.

How badly this tapering off is, depends on a lot of factors, but you can get most or all of it back with some further engine work.

Twincharging will give you absolutely everything you want, because you can set it up to behave as you desire. By changing pulley ratios, and turbine exhaust housing size you can make it act more like a supercharged engine, or more like a turbocharged engine. If cost and complexity does not frighten you, and you enjoy a challenge, go for it !

The easiest way to go about it is to first supercharge your engine, sort it all out and get it running right, then add a really large turbo in SERIES with the supercharger. Lancia and Nissan have both sold production twincharge systems.

Both of these are series flow, where the turbo compressor and supercharger flow the same air. I have built a system like this myself, and would have no reservations about doing it again.

[Ender]

hmmm..

Yes yes and...yes....

I have no A/Con so that should make life easier...I can easily fit the blower to the A/Con braket for belt tension etc....

All sounds too easy, just have to make the pipe..I have done the calculations for this already....

Just have to wait until I can have the car off the road for a week or so...

Will let you know how it goes...probably have many more queries etc....I am considerably less then competant with anything involving electrons providing current...many fires have been started due to my incompetance hehehe...

Cheers and thanks for the help,

Russ

[Warpspeed]

Hey russ, thats great.

What are you planning, come on now, make a full confession.

[Ender]

I was actually planning to use a toyota supercharger off 4agze..it has inbuilt clutch etc which I thought would be easy to switch on and off when needed. It almost bolts straight onto the A/Con bracket and it is smallish.

I am concerned about oil supply etc as maybe it has to be orientated a certain way. Also maybe it will be a bit small, after reading some of the previous posts ...maybe a bigger blower is warranted???

Ahhh it is also very cheap..already have one. May be the deciding factor

I thought it would be better run in parrallel with turbo not in series, but may change my mind, just wasn't sure how in series the blower wouldnt blow out the exhaust...I guess you would just have another valve...alot of valves though...

You said you have done in series and it worked well....could you give a brief description of how it was layed out etc...

Thanks,

Russ

[Warpspeed]

I have discussed this topic in a fair bit of detail on previous threads on both SAU and SDU Forums, it might be worth your while doing a search using SUPERCHARGER or TWINCHARGE as key words.

Another place to look is a thread I contributed to on the GT-R Register Bulletin Board (UK). Look under Technical/Turbos, in the archives there will be a thread titled "Supercharger as well?"

http:www.gtr.co.uk/forum/upload/showthread.php?s=c2f334bb7c5525911d87eaa6

I lost my password and have not bothered to re-register on that Forum. For some strange reason my WARPSPEED handle has defaulted to someone called "ellisnc" whoever he might be ? But in response to my posts I am referred to as Warpspeed, and it is really me not ellisnc !

So ellisnc must be as baffled as I am ?

For some reason the link does not come out as I typed it in, try

gtr.co.uk/forum/upload/showthread.php?s=c2f334b7c5525911d87eaa6

[Ender]

I have read the threads I could find and I have been enlightened somewhat...

Will check out the gtr one too

Thanks for the input.

Cheers,

Russ