automotive twincharging applicaton 6

[stevefto]

I am currently researching twin charging, a lot of information on this subject matter appears to stem from this forum discussions and available through google.

My application is the possibility of installing a twin charge system on a mitsubishi fto 2litre gpx. I installed a custom supercharger system last year with reasonably succcessful results, 50 horse improvement with 65 ftlbs of torque over standard. The blower I am using is an Ogura TX12 from a corrolla compressor, the system is a mimic of the mini cooper, draw through with vacuum bypass, the sc clutch has been removed and is fixed drive, 127mm crank to 85mm sc pulley.

It is a low boost application (8psi)on stock internals, as with all roots type blowers the boost tails off the higher up the revs she goes, just as an engineering exercise what I want to do is maintain boost throughout to the 8.2krpm red line, will twin charging do this for me.

I am planning to lower the compression ratio as part of the project if twin charging is the way to go, but do not plan to change to forged internals.

As far as I know no fto has ever had this concept, there are planty of twin turbo, single turbo, eaton charged, VR4 engine transplants as well as evo lumps, but no twin charged fto exists.

Any advise would be welcome.

Regards

Steve

 

[MikeHalloran]

Start by reading _all_ of this:

http://www.eng-tips.com/viewthread.cfm?qid=267889

You can change to forged internals after you blow it up.


Mike Halloran
Pembroke Pines, FL, USA

 

[DigitalGT]

Steve,

Is maintaining boost pressure all the way to the 8200 RPM red line your only goal or do you have others as well? There are several good reasons to use compounded boost. I don't know if doing it just to be the first FTO on the block sporting compounded boost is the best reason though. If this is simply an engineering exercise then by all means do it, but it seems overly complex for a goal as low as 8 psi. Since you have no desire to upgrade to super duty internals and push the envelope, I see a twincharged setup as a waste of money in your case.

But to answer your question, yes the addition of a properly sized turbo placed upstream of the blower would allow you to carry 8 psi of boost all the way to the red line.

FWIW, I'm not trying to poo poo your idea, I'm just having trouble justifying it in my own head. I twincharged my car because I wanted large high RPM power with immediate low RPM torque. The turbo alone would not give me the low end, and the blower alone would not give me the top end.

 

[patprimmer]

I have to agree with all comments so far, but would like to add, a suitably sized roots blower set up with enough airflow on the suction side should have fairly steady boost through the rpm range.

Simply a much larger throttle body and air duct to the blower might get you some way toward your goal of 8psi to red line.

Regards
Pat
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[stevefto]

Thanks gents for the views, advise and guidance, much appreicated.

To answer a couple of points...

The 6A12 v6 is a revvy little engine, what it lacks in n/a guise is torque, the low boost blower solved that issue, now that it has torque low down, but when you power through the rev range you can feel the boost drop off quite a bit, which then lends to short shifting to get back into the sweet spot.

I am not looking for any super powerful, first of its kind fto, with bragging rights etc etc, but if the sc could holds its boost for a bit longer then it would be great.

Peak boost (0.53bar) comes at 3.5krpm, peak torque (235ftlbs) at 4.2krpm, at 8.5krpm boost is a miserly 0.25bar, with max power coming in at 8krpm (245ponies), just reading the rolling road graphs data.

Your views on the tb and inlet track are interesting, perhaps its not the charger thats the issue then, and system inefficiencies are my problem....

Justifying is something thats very personnal, the car does the odd Ring trip to germany twice a year, and occasional weekend run on the 1/4 mile, I could not justify a forged engine, but to play with mechanicals and diy and splash out a bit of the annual bonus...yes I can justify that, that is how I justified the supercharger conversion in the first place.

 

[DigitalGT]

Glad you replied back Steve.

What do most stock block turbocharged FTO engines make for power these days? This, minus lets say 10-15%, should be your goal if you choose to twincharge. Very rough appraisal here. I know nothing about the FTO motor except that a GPX has a 2.0 L V6 that makes about 200 HP NA.......which is saying quite a bit about an engine that came with a warranty.

I'd love to hear a bit more about your supercharger conversion. How is it routed......where is the throttle in relation to the blower.....what sort of charge cooling, if any, does it have? Do you have any efficiency charts of your blower? I've only seen an Ogura blower once before in my life and it was a twin lobed affair that looked and behaved pretty primitively.

 

[patprimmer]

Do you know what typically fails first as they turn the boost up on these, presuming a good tune so as to avoid detonation.

Is it pistons, rods, rod bolts, bearings, crank, block/bores, head bolts/studs, gaskets.

If this blower is the little Toyota SC12, I believe there is an SC14 also.

The SC12 and 14 are not rebuildable, have low efficiency and are not designed to run constantly engaged and have a short life when they are run constantly engaged, however replacements are very cheap and in plentiful supply.

An Eaton M45 would do a lot better job if you can get hold of one. An M90 would be oversized but could be run slower. Anywhere American cars are popular, the M90s tend to be easy to find real cheap.

Regards
Pat
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[BrianGar]

Make sure you dont lose precious boost due to valve overlap, Im sure your oem n/a cams have some...

Brian,

 

[patprimmer]

Typically pent roof 4 valve heads don't run much overlap, but I guess that's because they scavenge so well they don't need it. Adjustable cam gears could help in that regard by opening up the lobe centres a few degree.

Also, not that it's relevant to boost numbers, but SC engines love real big exhausts.

Regards
Pat
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[stevefto]

Thanks again gents....lets get some answers going.

Q. What do most stock block turbocharged FTO engines make for power these days.
A. There are a couple on the FTO O / club with about 260 ish, they have been decompressed though.

If you go to utube and type in supercharged fto, you will see the set up, a lap of the ring etc etc, she is a white GPX Mivec, so has the cam switching arrangement, the system is pretty crude and my wedling is rubbish....the Ogura TX12 is primitive 2 lobe.

Q.Do you know what typically fails first as they turn the boost up on these, presuming a good tune so as to avoid detonation.
A. From what I have read its the rods that seem to be the weak link, rule of thumb on FTOOC is its safe stock up to 8/9psi.

Statement,,,An Eaton M45 would do a lot better job....there is an member who used to run a M45, it made 236 hp, but held the boost a lot better, he always thought it was undersized for the motor..the M62 is more than like the one that is better suited, but hey I got me a Ogura TX12....1140cc/rev..not ideal but its what came up at the right price...

Q. Make sure you dont lose precious boost due to valve overlap..
A. It does loose boost when the cams switch over at the mivec point which is 5.6krpm, but the torque line actually improves at switch over, I will get the RR graphs up loaded tomorrow and see what I mean if you dont mind..

Exhaust wise I have rpw extractor manifolds 3 - 2- 1, straight through system probably about 2 3/4 inch dia.

I have moved the TB from the plenum to direct mount to the sc inlet, the outlet of the sc goes to a air to air intercooler then up to the oem pleunum, inlectors were 166cc jobs, now got 275cc, running a greddy emanage blue piggyback ecu as standard ecu is not re-programable.

The pipe work is all 63mm od, tb I think is also 68mm body with a 60mm throat / butterfly.

Its not a great system I will admit, but its built on a budget, in a shed, with limited space and knowhow, the car is transformed with it, but for a project for next year I want to try to get the boost staying in a bit longer, and if you guys came guide me in eiter suggestions to improve whats there or look at the twin charge asan option it would be much appreciated.

Regards

Steve

 

[DigitalGT]

As much as I want to cheer on another twincharging project, I just don't think this is the right time or right car. Steve, I think for the cost of ditching the Ogura and moving up to an M62, that you can definitely have the boost pressures you want all the way out to red line along with a simpler and cheaper system than twincharging can provide you. My engine was a 2.0L before I stroked it, and I saw 12 psi all day long out to 7700 rpm with an M62 by itself. Peak power was at 7000 rpm.

If you're hell bent on twincharging and 8-9psi seems to be the limit for stock blocked GTO engines, I would, at the least, increase your blower pulley diameter, add a thicker head gasket and bolt on a small turbo with a very light wastegate spring and start playing with variables.

 

[BrianGar]

This is true Pat, but I thought it might be worth a mention as I got gains on different engines by dialing it down(as you mention)

Another point, make sure your bottom pulley is up to it, and doesn't slip on its key with the extra belt loads.

Brian,

 

[1gibson]

Does boost drop off evenly, or does it get the jitters up top? Consider belt slip, also how do your valvesprings hold up?

A small amount of water/methanol injection can improve the VE of a blower, a large amount can increase the parasitic loss.

I definitely second the suggestion by patprimmer to go as big as possible on the air intake. Moving the TB from plenum to inlet of SC effectively makes smaller since it is passing atmostperhic air instead of "compressed" air. Try a larger TB if possible, with exponential/cammed linkage; Cadillac Northstar 85mm are popular and readily available. A big TB with linear linkage (LS1)would affect driveability (lots of air when just cracking open the throttle.) Maybe the blower isn't giving up, instead you have more vacuum at the inlet than you think.

 

[stevefto]

Some good ideads to consider and try out, never considered the TB could be restricting the blower, might try to put it back onto the plenum and rework the system, instead of pull through with off boost vacuum bypass change to push through. That sort of makes sense, I will post up the Rolling road graphs, but I think you guys have cracked it.

Q. A small amount of water/methanol injection can improve the VE of a blower, a large amount can increase the parasitic loss.
Is this injected before the sc inlet, never really looked at this as an option, but perhaps I am better off looking at these small mods and trying to get a bit more efficiency out of what I have got.

Loads to think about, thanks gents, I will leave you in peace and pop in from time to time.

 

[patprimmer]

A suitable amount of fluid before the rotors helps cool, lubricate and seal the rotor to blower housing interface. To much displaces air and needs to be pumped out of the way.

Try a bigger TB or dual TBs.

The TB between the blower and the ports has some inherent dangers as a roots blower is positive displacement and if pumping against a closed throttle plate on overrun, it keeps pumping until something breaks, like maybe the throttle shaft. A bent or broken throttle shaft or plate causes a runaway engine.

Regards
Pat
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[1gibson]

Before blower if you want those specific benefits. Would suggest a very small amount of 100% ethanol or methanol, inject through a fine mist nozzle (one of the only good excuses for using a TB spacer - to fit the nozzle.) *In liquid form* both are corrosive to aluminum; you don't want pooling in the intercooler from too much fluid. Water will be more likely to pool (less likely to evaporate completely) compared to alcohol. Small amounts of alcohol vapor will not corrode the aluminum.

I've seen a 15% increase in boost on an M90 from injection of water/methanol (50/50) into the inlet. 10 lbs to 11.5 lbs with no other changes. It also didn't make me any faster, despite the increase in VE. Minimal injection would be best. Trigger it with RPM or with valvetrain change?

Use a diaphragm pump (shurflo) and a 30-ish PSI check valve directly before the nozzle. The check valve prevents siphoning due to vacuum, but also maintains pressure in the line so as soon as the pump kicks on, that first pulse causes fluid to spray. Without a check valve, the entire line would need to be pressurized. It eventually bleeds pressure back through the pump over 2-3 days but will hold pretty well.

For such minimal use, I wouldn't waste the money on a progressive injection controller. Just need on/off.

 

[patprimmer]

A roots type blower is positive displacement. Adding alcohol downstream of the blower does not improve VE as the air has already been metered by a positive displacement pump. Any leakage back past the pump would decrease VE and boost, but higher manifold pressure increases that leakage and adding fluid downstream from the blower does not influence seal. Effective charge cooling to increase VE reduces boost for the same mass air flow.

If it increases boost with the same mass air flow it increases parasytic losses.

As all as some methanol injected there can do is cool the charge, displace some air and make the mixture richer and maybe increase octane.

Adding water can only cool the charge and displace air.

As you cool the charge and simultaneously displace air you tend to increase boost reading.

While alcohols are corrosive and concentrated methanol is very corrosive, ethanol is not nearly so aggressive, especially when diluted greatly.

I agree, water and or alcohol collecting in an inter cooler is not a good thing.

Regards
Pat
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[stevefto]

Got the RR maps loaded now out of interest.

 

[DigitalGT]

Steve I'm guessing your torque curve is being measured in NM? The TQ and HP lines don't cross at 5250 RPM where they should over here in the colonies where we measure torque in ft/lbs. I only gave your second chart a cursory glance and the shapes make sense for a blown 2.0 L 6. The numbers just don't work in my head right now. Perhaps that last glass of Laphroaig 25 was one too many.

The first chart makes sense. Your blower is running out of steam at high RPMs. Not much to do about it. Positive displacement blowers like WIDE OPEN intakes. The shorter and bigger you can make it without disturbing any metering equipment due to turbulence, the better....in theory at least. Exhaust plays a big part too. Removing a catalyst and switching to a large diameter exhaust can have big impacts on measured boost pressures. E.g. when my engine was stock, I removed the catalyst and upgraded to a 3" diameter exhaust. My manifold boost pressure dropped from 12 psi to 9 psi but the car made quite a bit more power.

 

[patprimmer]

^^^^

Exactly, with a positive displacement blower boost can come from restriction downstream of the blower, even the exhaust as it leaves more pressure in the chamber at the start of the induction stroke.

Regards
Pat
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