Twincharging - calling Warpspeed! 3

[madmac666]

thread71-174690

Hi guys, i subscribed to this forum because i found the thread (referenced above) on twincharging while doing a Google search for information on this subject.

I have to say, the thread and contributions from forum users was very good and informative, which gave me a direction to follow for my own twincharger build.

Some background on this: I have a 1997 Mitsubishi Lancer Evolution 5 which i've used for sprints and hillclimbs in Scotland for a few years now. The state of tune of the car is such that we were producing around 650hp, but with the big turbo at 2.6bar, lag was always an issue. Twincharging seemed the most sensible option for the car to eliminate the lag and hopefully produce a torque curve with spool much lower in the rev range.

I'm using a Harrop HTV 1320 blower and the existing turbo which is a hybrid T04Z with 0.82 housing. This is the turbo that gave us 650hp previously, but on a 0,63 housing. The system is compound compression with the turbo feeding the blower. The blower has a 75mm pulley and the crank 150mm pulley so a ratio of 2:1.

I have the blower mounted and all pipework finished and finally had her on the rolling road a few days ago. We saw some impressive torque figures but had to cut the session short due to belt slip on the blower pulley when the turbo reached 1.5bar. The system i have uses a 32mm toothed belt but the length of the belt seems to be an issue as it's stretching and allowing it to jump over the pulley when the turbo spools up. We also had issues with controlling the turbo boost and decided i need to install another wastegate to allow better control of the boost. I'll have that done by next week RR session so we have control of the turbo boost and can carry on mapping.

It seems the belt starts to jump when the turbo reaches 1.5bar and the drive simply cannot cope with the power needed to increase boost by a factor of 2. I have a larger pulley (100mm) which i'll be fitting over the weekend and hope the longer wrap around of the belt on the larger pulley and the reduction of the drive ratio should sort out the issue of the drive. If it doesn't then i have another modification i can do to run a shorter belt on the blower and split the ancilliaries onto 2 separate belts but i'd like to try this again with the reduction in drive frst before i go to the trouble of a re-design of the belt drive. Space is at a premium so 32mm is the widest i can go and still have a chassis leg...

We never went above 4000rpm. Despite this, we saw 460ft/lbs torque and 360hp at 4000 and 2.9bar which confirms there's definatley power to be made! Obvously slowing down the blower will mean the turbo will need to be producing more to reach our goal of 2.5bar total. The outlet temp of 80c from the turbo at 1.5bar was logged, which is about the limit of the blower seals. I hope to keep the turbo around 1.5 bar so the outlet temps don't fry the blower seals. The combined air then goes through a very good intercooler and reduces the final temps to 16c (this is Scotland remember....!) at the plenum.

I think we're almost there and hope to have it mapped on the larger pulley with the extra wastegate fitted for turbo control. Looking at the RR graphs and data we collected the other day, we monitored the pressure from the turbo and combined total and can clearly see a multiply of the turbo by the blower very close to 2:1 from 1800rpm to 4000rpm but we couldn't control the turbo and it looked like it would have carried on climbing which would have killed the engine or the blower.

Because the engine already had the big turbo and supporting mods to make good power, we hope to see some good figures once the issues are ironed out. The engine itself is built to produce 1000hp 'reliably'.

I would like to hear any views and comments on my findings so far. I had considered swapping the turbo and blower order to reduce the power needed to drive the turbo but i felt the extra restriction on the exhaust (because the turbo would be working harder than it used to) would likely end up making less power, as the exhaust back pressure would then be much higher. It would certainly reduce the power needed by the blower


Thanks for posting the useful information, it really was a huge help and if you have anything to add that could help us, i'm all ears!

Donald

 

[Warpspeed]

Oops, I meant to say Eaton M90, not Whipple M90.

 

[PorschaTwin]

Still looking into something like this for one (!) of my projects. Did Donald mention earlier that he had a spare broken Harrop blower? I would love to take him up on any offer to lend it out to size up a new installtion....... Any way of sending PM on here?

TIA

 

[HRHtex]

I read today that all the famous turbo aircraft engines (which means mainly the P-38 and P-47) were actually "twin-charged" - the engines kept their in-unit blowers. Presumably the idea here was better engine reponse as with car engines.

 

[Warpspeed]

I never knew that WW2 fighter piston engines were turbocharged, I thought it was mainly a high altitude bomber thing.

You can imagine how big a turbo would be involved, and turbo technology was not as sophisticated as today. The lag would have been considerable. Less than ideal for maneuvering in a serous close quarters life and death dog fight.

I am told by the fighter jocks, that acceleration is far more important than top speed in getting the jump on the other guy.

The Germans came up with a great idea, a twin prop bomber with THREE piston engines. The third engine sat in the fuselage and just drove an enormous roots blower to boost the other two engines. As I remember, the roots blower was almost as large as the engine driving it.

 

[HRHtex]

Have a look at the turbo plumbing on a P-47 - you think you have problems.

http://www.aviation-history.com/republic/p47.html

I think only the P-38 and P-47 were the only turbo fighters made in any real numbers.

 

[madmac666]

I've been away from the forum for a wee while as i think i may have been a bit naughty and had some posts/login removed! I'm used to more open forums so i may have posted something that the moderators disagreed with.

Anyway, back on topic. I've made a few changes to my system and hope to go back to the dyno in the next few weeks. I will update the changes and link to a dyno graph as soon as i can. Suffice to say all these changes should release more of the systems potential and hope to see even more torque and power.

Interesting project and i feel my results are worthy of publishing for all to see so anyone wanting to have a go at compound charging can at least see the benefits of this on their car.

 

[madmac666]

We have the car on the dyno but despite my best efforts to keep the blower actuator together with a v-band, it has failed again. the ssumption is the diaphragm has burst so now i need to find another of similar proportions and operation, but stronger! I'm looking at a wastegate as suggested by Warpspeed but still keeping the internal SC bypass as the actual air bypass. There just isn't room to install an external pipe and wastegate unfortunately

So far we have seen more power at less boost but we are still a long way from having the mapping complete. The new ECU has had to be mapped from scratch so it's taking a while. Seems the old engine is still hardy and taking the punishment though!

The failure of the actuator won't stop us carrying on mapping as i fitted a BOV that opens at 11psi to bleed off the excess pressure which prevously caused the SC to overheat and fail.

Hopefully have a nice torque and power graph soon!

 

[Warpspeed]

The actuator from an aftermarket wastegate would be ideal, provided it has enough travel to do the job.
It will need to be fitted with a spring that exercises the actuator over its mechanical range with an applied differential pressure varying between about 2psi and 3psi.

HKS wastegates use dual springs, the stiffer outer spring providing most of the force. The much lighter inner spring can be changed to give much smaller force increments. If you just run one of the HKS inner springs by itself, it would be an off the shelf solution to finding a suitable spring for the actuator of your choice.

From memory, there are two springs that cover the range of pressures that are of interest for a supercharger bypass actuator.

 

[madmac666]

I thought i had found a ready built alloy actuator today but it turned out to be false hope!

The problem i have is the actuator is only 1mm away from the engine block and the space available is incredibly tight. I'm looking at machining my own one from alloy billet now so i can make it to my own spec. The operation of the internal Harrop bypass works great - it's just the actuator simply isn't strong enough to accept 38psi boost! In terms of driveability and how well it operates as a bypass it does seem to be perfectly setup with the right amount of spring pressure.

Warpspeed, i can't find a manufacturer that makes a wastegate body small enough to fit the space available, although Forge Motorsport had a good selection, only one was setup to pull the rod, and it wasn't designed to have pressure at the opposite side of the piston. Also, as you mention - the travel of these units usually isn't enough to open the bypass fully - it needs 25mm travel.

For the moment i can fit another Harrop actuator but only operate it with vacuum for the duration of the mapping session. Once the engine is out for rebuild next week i can look at the problem more closely and take more time over a solution.

I guess it's just another hurdle to overcome - hopefully the last one and the results should be worth the hours!

 

[Warpspeed]

The best bet might be to machine up your own housing, using the rolling type of long travel diaphragm that will come with a wastegate rebuilding kit.

As very high temperatures are not an issue, how about some sort of industrial rolling diapragm such as this:

http://img.directindustry.com/pdf/r...-rolling-diaphragm-design-manual-27709_5b.jpg

 

[MikeHalloran]

Do run through the lifetime calculations before designing in a rolling diaphragm. They are pretty accurate. ... and not very encouraging if the stroke is substantial relative to the diameter.



Mike Halloran
Pembroke Pines, FL, USA

 

[Warpspeed]

True, but wastegate rolling diaphragms are designed for the specific application, and rarely if ever fail in service.

 

[madmac666]

Thanks for the link, never really thought there was going to be a selection of diaphragms available.

I took apart the 3 actuators that have failed during the year and all have the diaphragm intact. These have the diaphragm held on the outer circle by the 2 casings that are glued together and this time it's come away internally.

I'm pretty confident i can make a new alloy casing that clamps together and holds the diaphragm in place reliably now. If i use the diaphragm that is designed for the stroke i need, ie the one from the old actuator, then as long as it's strong enough to handle the boost then i'm willing to give it a try.

Update to follow

 

[R34ztune]

Did you try to setup an extra butterfly that have connection to the atmosphere for the SC. So that in high rpms you can switch the charge lines of the turbo feed to by pass the SC, and let the SC and turbo to run in parallel setup? This will give you a parallel charge setup in top end, and compound/serial setup in low end.

I think a flap type valve can do the job, but not sure you have enough room under the bonnet of an Evo . This can directly solve the problems of bypassing and can be use to enhance fuel economy. But your EFI setup must use a map sensor.

 

[madmac666]

No, the bypass is internal to the blower so it unloads the blower at idle and cruise. Give it any throttle and the bypass closes to form a compound affect right to the redline. This gives the cylinders more intake pressure than exhaust manifold pressure to make considerably more power.

To make the turbo the only compressor at the top end increases exhaust backpressure dramatically and effectively strangles the engine - less power and torque than compounding.

 

[R34ztune]

What you are talking about is the volumetric efficiency (VE) of the engine due to effect of SC. Whether it is compounding or pure SC, if the intake pressure is always higher than the exhaust, then should follow the cam profiles setup using in an SC system. There is a lot of reference about it.

What camshaft does the engine has finally? It has mentioned a few in previous posts. If you are running compound compression which your intake pressure is always higher than exhaust pressure. Then you never need much overlap. One main reason is that you might have your fresh charged air/fuel mixture directly blowing out to the exhaust manifold. Have you ever notice this effect?

To correct this situation, only need is an adjustable cam spockets for intake side. Advance will make it more overlap, retard will make it less overlap. Retard too much will cause intake charge to flow back to the intake manifold. This is not harmful and will not cause much problem in fuel economy but hurt your VE therefore less power.

 

[gruntguru]

Madmac.
I don't have the pneumatic circuit for your actuator sorted in my head so this may be a stupid question. What is the highest differential pressure seen by the diaphragm - I assume 38 psi? If so - does it need that much, or does full actuation occur at a much lower pressure? If so - why not limit the pressure with a simple regulator? This should protect from the failures you are seeing.

Engineering is the art of creating things you need, from things you can get.

 

[madmac666]

Cams used are the S2 profile which are essentially a 272 cam. We will be looking at profiles during the engine rebuild as we felt the charge is going through the exhaust causing the black smoke on boost. So far on the dyno much of the black smoke is gone but it's still prominent enough to give reason to suspect the cams have too much overlap, and perhaps a bit too much duration - but the jury is still out on that.

I have the actuator beefed up and pressure tested now and the car is back at the dyno today for the final mapping session. I plan to make a completely new bespoke alloy actuator before the start of this season

To explain how the actuator is plumbed, it's a simple diaphragm with a port on each side. One port is connected to the plenum so the vacuum at idle and cruise opens the valve, and on boost it keeps the valve tightly closed. This end sees vacuum and boost up to 38psi. The other port is connected to the SC outlet, before the throttle body so that the bypass opens if pressure builds up in the pipe due to the throttle being partly closed. This was the reason we destroyed 2 blowers - at cruise the throttle was only part open but it appeared there wasn't enough vacuum in the plenum to open the bypass and the air still being compressed had nowhere to go. Result of that was superheated air in the blower and rotor growth. The extra port essentially opens the bypass should pressure start to build up before the throttle body, more of a fail-safe than anything. Only a fail-safe if the actuator works....! With the BOV in the pipework now this port only sees 11psi which is what the BOV spring is set at. Differential therefore would be no more than 25psi extreme case.

I had looked at a regulator for limiting the pressure to the actuator but long term i think making a stronger actuator is the best way to go.

Hopefully the mapping will be completed tonight then it's back to tear the engine apart for the rebuild.

The shonky old engine is doing well. Compression test indicates all 4 cylinders are still producing good compression - 13.5bar to be precise

 

[R34ztune]

It looks like if everything is done in electronics, it will be a much simpler setup. Some vacuum actuated system has a reservoir using a one way valve, it accumulates vacuum for future use in partial throttle conditions.

However, if you can go for electronics, its much more simple and can have a more flexible control strategy base on your parameters. If the control is a simple logic on/off signal, then it can be implemented using simple passive components rather than relying on vacuum which is a bit unreliable when you are driving almost full time partial/full throttle, the system have no chance to accumulate enough vacuum even you have a reservoir.

FYI, there are lots of electrical throttle bodies from wreckers as there are so many cars out there in the past decade moved to electronic throttle. They are very suitable in your application with good flow characteristics.

 

[Warpspeed]

What could be simpler and more reliable than a diaphragm and a spring ?

You are not seriously suggesting that a couple of pressure transducers, a microcontroller and a stepper motor would be simpler ?

On the other thread you asked if I knew anything about microcontrollers.
Well.......
Almost twenty years ago, I designed and built completely from scratch all the hardware, wrote all the software for my own EFI system and the GUI to go with it, completely by myself.
I am an electronic engineer by profession.
Does that answer your question.

I have been building twincharge systems with blower bypasses also for at least the last twenty years as well.
I just cannot see any need to use a microcontroller for this task.