Twin Charging a Honda CRX 3

[patprimmer]

I having a moment of madness and considering twin charging a 1988 Aussie model CRX.

Aussie model has the DOHC D16A8 engine and factory A/C and P/S both of which I must retain.

The plan would involve a second hand Toyota SC14 roots type blower.

I already have a turbo being a brand new Garrett GT2859R-707160-9. M24 cast on compressor.
Ball bearing, water cooled bearings.
Compressor is 44.5 inducer, 59.4 exducer, 56 trim, 0.42 A/R
Turbine is 53.8 wheel dia, 62 trim, 0.64 A/R
It has an internal waste gate but I also have a 41mm Chinese external wastegate.

The turbo is correct size for my ambitions turbo only, but probably a bit small for twin charged.





Regards
Pat
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[patprimmer]

Plan would be to make a sheet metal very short runner manifold and mount the blower to it.

I hope there will be room for a sandwich plate water to air inter cooler. There should be enough room. This keeps the manifold inter cooler volume real small so throttle can be on the inlet to the blower.

Turbo would be on a mass produced after market cast iron manifold. Tried and true, reliable compact fits with A/C and P/S and stock radiator location.

Air to air inter cooler would be front mounted between grill/bumper and radiator to cool air from turbo before the SC-14

Just to prove I must be stark raving mad, I am also considering propane liquid injection as fuel.

I already have a Honda ECU with a fully programmable chip installed. These allow full remapping of fuel and ignition tables and retain all OEM features.

The engine will be bored to 78mm (from 75mm) and stroked to 94.5mm (from 90mm) with a raised deck via longer thicker iron sleeves and an aluminium closed deck plate about 12mm thick to holds it stable with longer 150mm rods (from 137mm) giving 1.59:1 (from 1.52).

The rods will be after market H beams, the pistons will be after market forged and the crank will be Honda D17 forged steel.

Head will be mildly ported with 1mm bigger 1 piece SS valves and stronger springs. Cams will be stock as these engines already make power to 7000 rpm stock. Lobe centres will be spread a few degrees as a starter


Regards
Pat
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[patprimmer]

Enough of the hype and BS.

The questions are:-

Has anyone had any real experience with a Toyota SC-14 with the clutch removed so it runs permanently coupled to the crank.

If so, how fast can you reliably turn the blower.

Do they perform better with the rotor coating or stripped off.

Do the bearings stand up. Can they be improved. Will I need to make new end housings to get reliability.

Will water injection before the blower help by lubrication, sealing and cooling the rotors.

Has anyone made better rotors, like 3 or 4 lobe high helix rotors like the Eatons. How much advantage will better rotors be on a twin charged system where high speed efficiency does not matter so much

Would the second inter cooler (the water to air one) be necessary or advantageous with water injection. Probably not.

With say 20# boost at 60 deg C charge temp, on propane at I think 105 octane and excellent exhaust scavenging and good quench and tumble in the chamber what CR can I run. 8:1 maybe.

How wide is the drive belt on the SC14 Is it toothed or multi grove V belt.

Can a chain drive work and be narrower to clear the chassis and eliminate slip.







Regards
Pat
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[TDIMeister]

Hi Pat.

No direct experience with that particular supercharger, but a couple of thoughts on your proposed setup. I would keep the supercharger's role light and use it to help the transient response while letting the turbo do most of the actual boosting work. This is especially true of you want to delete the clutch and run the charger full time.

In a serial arrangement, you don't need a high PR in each stage before you get far more boost than your engine can handle. Also, in this arrangement, the more boost generated on the first stage heats up the charge even more and costs more compressor work for the second stage.

Turbo sizing is only a concern in view of what your power output goals are. That compressor you've specified can flow up to 26 lb/min at PR=2.3 with 70% efficiency. Placing it as the second stage will push the operating points - with inlet correction factors - to the left, making the compressor an effectively bigger unit than it really is. Turbo alone, you're good for about 220 BHP at 6000 RPM, as I've calculated with your given numbers in the below link assuming a BSFC of 390 g/kWh at maximum power and a pretty rich AFR of 11:1

http://1l2.us/bd_

Done right with the additional supercharger and some form of water/methanol/fuel injection, you may be able to raise that to 270 BHP. That assumes you run a pressure ratio of about 1.3 across the supercharger. I don't estimate more because you are turbocharger mass flow constrained and not boost pressure constrained (here you'd already be running about 28 PSI gravimetric).

Lotus placed auxiliary fuel injectors in the Exige 275E (tri-fuel flexible) upstream of the supercharger to give a charge-cooling effect. Gasoline in the fuel can also provide some lubricating benefits as well, but if you try this, ensure that the turbo compressor seals are compatible with the fuel draw-through. My simulation have shown though, that pre-compressor injection of any fluid pushes operating points to the right of the map, making you closer to the mass flow limit. Water/methanol injection - preferably as close as possible to the inlet ports - could certainly help also help with charge-cooling and retarding knock.

HTH.

 

[TDIMeister]

I have no idea how big the SC14 is and, after all I have said above, it may turn out to be by far the greatest limiting factor. The Lotus Exige 275E uses a supercharged, Toyota-sourced engine. What charger does it use?

 

[vagman2]

Hi patprimmer,

are you familiar with VAG's 1.4 TFSI twincharging? I could find info for that setup for you. I believe TDIMeister could find it too.

 

[Warpspeed]

Hi Pat, I did something very similar to a Laser 4WD turbo a very very long time ago. It was one of my very first ventures into twincharging. Once many of the rather tricky mechanical installation problems were overcome, the results were spectacularly good for such a small capacity engine.

My experience with an SC14 was that they are designed for short term operation only. On the original engine, the clutch disconnects the blower drive except during short manic bursts of acceleration.

Hooked up to be driven constantly, my SC14 always ran hot, and the whole blower gradually become more and more loose and noisy, until mechanical sympathy forced me to retire it to the dumpster bin. I ended up wearing out three of these blowers one after the other.

As these SC14 blowers now only cost about $200 secondhand, twelve to eighteen months of service out of each one may actually not be such a bad deal.

These Toyota blowers are definitely not rebuildable. The bearings are a unique unobtainable size, and epoxied into the aluminium case. To get it apart requires pressing off both the helical timing gears together. Without the factory jig, you will never be able to press the same gears back on so they are both still a tight interference fit, and the rotors still correctly timed. So forget about any rebuilding. These are a throw away item.

An Eaton M90 is a far better designed and more robust piece of machinery, and only slightly larger. And if you could score an M65 "Kompressor" of a small Merc, that may be another option to think about, especially if space is at a premium.

All these modern blowers now run a multirib belt, which will be silent. Toothed 8mm pitch timing belts are going to whine, and some people really enjoy this characteristic sound, but not me.

An Eaton is robust enough to run continuously, and with a suitable air bypass system can be completely unloaded.

 

[patprimmer]

Thanks guys. Those responses where exactly what I was looking for.

Seems both components are correct size.

It seems an Eaton is a better option if I can find the space. I was thinking the SC14 was a lot smaller and lighter than the Eatons.

I have a budget for the turbo setup, but the twin charge would be extra budget and I expect an Eaton might blow that out of the water.

If the m90 is the onethat is std on the V6 Commodores, I think they are just to bulky and heavy and a reverse direction drive needs to be fabricated.

There is a kit from Jackson Superchargers (JSRC) for an M45, but they are for the single cam D series and are far from a bolt on and in my opinion expensive and poorly engineered and only make about 8# boost and have belt slip problems and manifold heat problems

270 hp is top limit for the drive train which is old enough for replacement parts to be a problem if I break them regularly.

Should I get a few SC14s and consider them consumables like brake pads or spark plugs.

Regards
Pat
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[Warpspeed]

I would suggest that a Toyota blower might make a good entry level blower for people working to a very limited budget. But the efficiency, flow, and the reliability simply is not there.

It is going to be just as much cost and hours of work fabricating mounts, plumbing, and fabricating up a reliable drive system, and debugging, as for something much better.
Why spend $1,000 on parts to install a $200 blower that is not going to be up to the mark?
And it will eventually cost that, by the time you have built everything twice, shredded four expensive drive belts, and purchased several new drive pulleys to get the drive ratio where you want it.

All this is based on personal experience over a few decades working on my own supercharger projects, and mentoring other people's projects.

About 90% of the effort will go into building and debugging the supercharging part. Hooking up the turbo is trivial.
So I might suggest you just plan on fitting the blower first. That will keep you entertained for a surprisingly long time, while you sort out the multiplicity of issues.

The results of just fitting a low boost roots blower will be fairly disappointing for all the work and cash sunk into the project. Be mentally prepared for that...
It will run well, but it won't be the ball of fire you may have been expecting.

If you go the other way and fit just the oversize turbo first, it will go like the clappers (if you really thrash it), but the high boost threshold, and a very narrow power band will soon become really annoying if you drive the car in traffic every day.

But with the whole twincharge setup installed, the results will be purely magical.
It will be absolutely nothing like it was with either just the turbo or blower fitted, but something unique and totally different.

 

[patprimmer]

I have installed roots blowers and turbos before. Just never on the same engine.

The blowers where GM type on American V8 for drag racing with MFI and methanol. Most things where available off the shelf as the first few where SBC. I am doing a 430 odd CI Ford Windsor right now. That has been a bit harder to buy off the shelf parts for.

I will ask around about an Eaton off a V6 Commodore and see what turns up.

I know what to expect (or not expect) from a low boost blower so I will not be disappoint at that stage.

I'm thinking it is all getting to hard

Regards
Pat
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[HRHtex]

It certainly does sound "too hard".
There has been so much written lately in these forums about the combination of a positive displacement blower and a turbo (and it does seem to be a good idea) maybe some manufacturer should think about making an aftermarket blower/turbo in the one unit?

 

[patprimmer]

Ideally a turbo should be close to the exhaust ports and the roots should be close to the inlet port.

Also ideally the air should be cool as it enters the roots.

The mounting of a roots is greatly limited by needing a stable strong mount to maintain belt alignment and tension while a turbo can be mounted pretty well anywhere you can run a pipe so long as the heat won't damage surroundings.

By combining them, you need to compromise several of the above.

Regards
Pat
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[Warpspeed]

The American V8 guys have it too easy with readily available off the shelf manifolds and drive kits. An small inline engine in a very small car is a far more difficult proposition.

The mounting and driving of the supercharger will be by far the most difficult obstacle to overcome. As I said earlier, the blower part will be about 90% of the whole project.
It is almost certain that other major engine accessories may need to be moved to make space, and that is what rapidly complicates the whole thing.

The turbo is physically quite small in comparison, and the adjustable orientation of both housings on the core make it quite readily adaptable.

My own preference is to not mount the blower right over the inlet ports, but to use the original plenum and throttle body as is, and fit the intercooler between the blower and throttle body. But as we all know, Pat has some very strong objections to that idea, so I will not pursue it here.

 

[TDIMeister]

"My own preference is to not mount the blower right over the inlet ports, but to use the original plenum and throttle body as is, and fit the intercooler between the blower and throttle body. But as we all know, Pat has some very strong objections to that idea, so I will not pursue it here."

I guess I haven't been around here enough... what is the crux of Pat's objections to that idea?

 

[patprimmer]

I also was carefully avoiding that subject and looking for ways around it.

I have softened my view on that a little, but would still want more than just a bypass with either a burst panel or an emergency shut down throttle like those fitted to Detroit diesels to shut down runaways as well as the bypass.

An idler and the blower over the gear box certainly helps with packaging and direction of rotation.

Blower over the inlet port certainly helps response if the throttle is before the blower.

I will not remove A/C or P/S. It would be hard to move them much, but I have a few options from stock parts as I have the D16A8 and a D17Z1. Although both D series, they have different crank snouts and crank pulley stacks and ancillary mounts.

I really want to do this but I need a nice compact little blower. The engine will use about 7200 litres/min theoretical displacement so I guess the blower needs to have a maximum output of 1000 litres/min at reasonable efficiency to give enough boost to add a little power and keep inlet pressure higher than the exhaust during overlap.

What is the minimum pressure ratio I need for good scavenging. I guess that varies a lot with turbo housing and AR and exhaust system back pressure. Is 1.3 usually enough or do I need the 1.5 you have already mentioned.

Regards
Pat
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[Warpspeed]

The blown two stroke diesels usually reckoned on about 4psi differential for scavenging.
But a great deal depends on planned valve overlap.
That might end up as 8psi boost, with 4psi total exhaust back pressure in your typical big diesel two stoke truck.

A reasonable starting point might be a blower design pressure ratio of around 1.5 for this type of project.

Turbine back pressure is going to rob you of some of that, but it might be a reasonable starting point.

 

[1gibson]

M90 from a early 90's Ford Thunderbird SC (super coupe) is the smallest M90 you can get. 4 bolt outlet flange, bolt on inlet flange (unlike the cast inlet on most other M90's that are much longer). Most custom M90 projects I've seen tend to use this blower.

M62 from series 1 3800 (bonneville, other GM's, 91-95) might be getting harder to find. Same size or slightly larger outlat than the T-bird M90, longer case due to the cast inlet.

Mercedes or Toyota M45

Methanol injection before the blower will increase VE and raise boost 1-2 psi, but also increases friction and parasitic losses. It's a fine line, I've done this on a GTP (3800 series II, L67). Very temperamental, it eliminated the detonation but wasn't much faster. Ran into belt slip issues when I shouldn't have.

 

[70btdc]

Smallest Eaton (M24) is 24 CI/rev, or around 393cc. This would give you 10000 l/min at 25krpm. Next up M45 would need 14krpm. If your blower P1 is higer than 1BAR then you need rpms for same mass flow.

The M24 are the blowers fitted to the VW twincharger these days, if you can source one 2nd hand they are very expensive. If you are lucky you got one years ago from development of a certain Ethanol fuelled 1000cc RoCam engined Brazilian Ford ECOsport. You can still get them very cheap if you look from that source.

The Eaton website shows they are good to very high RPM's - due to small size.

M45 are fitted to BMW's mini and were very cheap 5 years ago but now not so. Still cheapest option.

One other thing to conider is the anti-lag effect of having the throttle downstream of the SC. Off-throttle the airflow is maintained through the turbo compressor (or Rp accross it).. You will LOSE this if you HAVE to have the throttle before the blower, and stall the TC each time you shut the throttle, change gear, tip out.

 

[Warpspeed]

Pat, is your Honda a manual, or the slush box version ?

That will make a significant difference to the importance of throttle response.

 

[patprimmer]

Manual.

A Blow off valve fixes the turbo blowing against a closed throttle just like in almost every turbo only application out there.

Response with throttle before blower is not an issue if the blower is mounted directly to a compact manifold with small plenum. Only last week I drove a T bucket Hot Rod with a 351 CI Ford Cleveland V8 with a 6:71, open plenum manifold and open plenum adaptor for the twin 4 barrel carbys. It smoked the tyres before the pedal even hit the floor when you slammed the throttle.

Regards
Pat
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