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

 

[patprimmer]

Could the belt be jumping because the rotors are nipping up as they expand due to the higher inlet air temperature.

A simple test would be to inject some water into the air duct just before the blower to cool the rotors.

If cooling the rotors fixes the problem, setting up the blower with slightly wider clearances should fix it. Harrop may also be able to advise on rotor clearances.

Can you get a better belt design or quality.



Regards
Pat
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[madmac666]

Pat, must admit i never really gave that much thought but i did speak to Harrop about heat when i prdered the blower. They advise 50c for 100k reliability but 80-90c would be ok as long as it wasn't all day long.

I've had a look inside the blower and can't see any evidence of the rotors touching anywhere. Also, the belt slips as soon as the inlet pressure reaches 1.5bar. if it was a clearance issue, would it not take a few seconds for the rotors to heat and expand?

I have a better belt drive in production now which should hopefully transmit the power without jumping. nce i have it finished i'll update with findings

Donald

 

[70btdc]

Hi,

Out of interest, do you have any sort of bypass around the SC at all currently? Or is this what you mean by the additional wastegate? What about during idle? Is the SC clutched?

Have you got any data with a measurement of the exhaust pressure?

 

[madmac666]

Yes, the blower has a built-in bypass operated by plenum vacuum so at idle or cruise the blower is pretty much freewheeling. The extra wastegate is now mounted on the manifold alongside the original one.

We tried the single wastegate without any spring in it to start with to see if it was physically big enough to bypass the turbo. It didn't take long to deduce another wastegate was needed....

No clutch on the blower - direct drive

Sorry, no exhaust pressure data

Back on the rollers on Tuesday eve

 

[70btdc]

Did you try using a wastegate pre-IC, i.e. on the pressure side as boost control? I realise this is a waste of energy; dumping compressed air, but I think this is what Warpspeed referred to when he mentions to use a 'wastegate' to control boost in the other thread.

If the main design objective is to reduce lag, have you considered only using the SC to bolster the bottom end and then bypass it with a diverter valve at higher rpm, allowing the turbo to provide the total boost?

 

[madmac666]

We see no need to use a wastegate as a bypass in the boost side as the blower has this built in. On cruise or lift-off, the valve opens and bypasses the air between the inlet and outlet of the blower. The wastegate is on the exhaust side to divert hot gasses past the turbine and allow control of the turbo boost - which determines the final boost after the blower.

We considered all options and did a lot of homework before starting this project. Using a diverter valve to bypass the blower would have meant we would only have seen the bottom end torque rise and the turbo producing top end power on its own. To me this wasn't an option as i want as much top end and low down torque as i can get. Economy isn't a consideration on this one... The turbo was running out of puff at the top end which limits the engine to around 650hp. The compound system seemed the best way to go - the turbo working at half it's designed pressure then have the blower multiply to have a much higher inlet pressure than the exhaust and therefore fill the cylinders more. I think it was covered in the previous thread about valve overlap and duration too. I could probably run more duration with this setup but cams for the 4G63 engine are designed to be used with a turbo only so i'm searching for cams with certain characteristics now. It may be that we have to design these and get a set ground to spec to get the best from the setup.

 

[70btdc]

Although the turbo may have been running out of puff, you are now substituting that loss of efficiency for another. The rootes SC at the top end will be a hell of a lot less efficient than any centrifugal compressor. I assume that with a 2:1 ratio, and a 7000rpm engine N, that you are pretty much maxing out the SC?

Would it be daft to suggest a larger compressor, and to transition between the efficient SC region into the efficient TC compressor region at a pre-set point? Of course this requires alot more complex control, and may not give the same throttle response, but the SC will see lot lower temps and the actual energy used to compress the intake air will be lower. Of course if fuel efficiency is not a problem then you can just burn more to get to the same air setpoint, but you will then have to deal with a hell of alot more heat.

Does the SC spec come with a rating for max intake pressure?

 

[madmac666]

The blower has a limit of 18K in everyday use but maxxed at 22k so we're not near the rpm limit. I've since fitted a larger pulley to the blower, mainly as we're still experimenting and the previous drive belt stretched too much and caused it to jump. I've also changed the belt drive with a much shorter belt so we hope the jumping issue will be sorted now.

Until we see some further data, i can't say how we'll end up setting up the relationship between the blower and the turbo. With the bigger blower pulley, the ratio is now 3:2 instead of 2:1 so we expect the turbo to be producing no more than 1.5bar and the blower then multiplying it to around 2.4 bar - pretty much where we want it to be. I suspect a pulley in between the 2 sizes would be ideal as we can then reduce the turbo pressure and therefore the charge temperature the blower is fed with.

Harrop say 50c is the design inlet temp Eaton specify for reliability but we could go to around 70-80c however that will reduce seal life. We saw 80c at the blower inlet when the turbo was producing 1.5 bar. Ideally i'd like to get this down to 1.2bar and have the blower supply the rest.

Fitting a larger blower isn't an option now. It took a while to get hold of this one from Australia then manifolds and brackets needed made. It sits behind the engine and only just fits in the space. A larger blower would mean a complete re-design of the whole system again. I think the pulley we're away to try is about right to keep the blower within a good range of efficiency to do the job we want it to do.

I guess it's a compromise, as most things like this are. Some minor changes to blower drive pulley may be needed but at the moment i think we're not too far off the mark to see some good results. Obviously with unlimited time and money we could perfect this, but at the moment we're going to keep going with this setup now that the drive has been modified.

Thanks for the input. None of this is set in stone and needs to be tried/played with to get the best from it.

 

[70btdc]

Sorry, I was suggesting a larger turbocharger compressor, not a larger SC, and an SC bypass.

Best of luck with the next test, it's a very interesting project and would be the first real 'current' account ` regarding compound charging on this site if you can post again afterwards. It would be great to see if the correct matching of drive ratios (TC and SC) will actually allow you to have a decent overall efficiency (i.e. temps are in check).

 

[madmac666]

Now the larger turbo is something i have deduced is probably not needed on this build. There's one tuner in the UK who is currently testing a compound charger on one of these engines for a customer. He's not giving anything away but he has posted his initial power/torque graphs on the forum. Someone deduced he had a GT42 turbo and on a later post he reckoned that was too big and he'd see the same results with a T04Z, which is the turbo i'm using. His first graph shows damn near 1000hp and he reckoned there was more to come.... He's doing his mapping on an engine dyno so he'll have the best IC and coolant system, exhaust etc and no doubt the figures will look better than they would be on a 4wd rolling road dyno.

I'll keep the thread updated as we progress and share the results as and when we have them. Next dyno session is Tuesday evening and i have a test day organised at a local kart track for the Thursday, so hopefully we'll have it mapped and safe to run, even if it's not quite finished.

My first Hillclimb is Doune on 17th April so i'm cutting it a bit fine!

 

[1gibson]

The blower's parasitic loss will increase based on the inlet air density. So 1.5 barg inlet pressure would require much more power to drive the blower than 0 barg. I doubt the manufacturer has a published chart for this. Fixing the belt slip would just allow the blower to draw more power. There will certainly be diminishing returns, and you're likely to find the next weakest length in that drive system.

You're sure you don't want to bypass the blower once the turbo has spooled? And just accept the increase in power under the curve, rather than try to use a blower to help keep your turbo on the charts at higher flows?

 

[madmac666]

Yes, i agree, the blower will be working hard so the belt drive would be the weakest link now. I've had her running tonight - took it out for a wee drive and all seems fine with the belt drive now. The map we did last week was only up to 4000rpm so i didn't take it above that. The turbo is producing 1.3 bar at 2800rpm so if i were to bypass the blower i'd have to do it less than 1.5bar to keep inlet temps to the blower down. Then there's the time taken to further spool the turbo to 2.6bar, which on it's own needed to see 5000RPM to be at full boost - that's a large area of the map wasted torque and right where i want max torque to be. I think it would be quite complicated to build a bypass at this stage. Packaging it all in the engine bay has been very tight just about everywhere, but if it turns out to need it then i'll have to make it fit (and work).

I'm also relying on the difference between cylinder inlet and exhaust pressures to make some real top end power as well - having the turbo do all the work at the top end loses that advantage as the exhaust pressure increases as the turbo takes over.

Definately food for thought tho. I really don't know if we'll finish the mapping next week but i'm confident that if it holds together, we'll see some interesting results! If the earlier power/torque figures are anything to go by, this engine will pull like a large capacity V8 from 1500rpm.

 

[patprimmer]

You don't need a bypass.

All those advising that do a site search using the google feature. You will find that topic has been covered in detail several times already.

The main thought process should involve mass air flow and density, not volume.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[madmac666]

Pat, my build has a bypass built-in to the blower for cruise and lift-off but not one to bypass the blower at high revs. All this talk of bypasses can confuse....

One thing i can't remember if i mentioned - the throttle butterfly is in its original place, on the plenum so the blower would compress against this it idle and cruise if there was no bypass. My previous supercharged engine build had the butterfly before the blower as the whole lot was mounted on the 'V' of the engine and the most sensible place to have this was right at the blower entry.

On this compound charged engine, the induction length is too long to have the butterfly before the blower as response would have been slow due to the mass of air to be moved through the pipework and intercooler.

 

[70btdc]

Yes pat, mass flow. 3.0 Bar or whatever is a great target, but not going to make any more power if it is all hot air. If you compound the two devices at higher rpm, you are also compounding efficiencies. This can be recovered through good intercooling and rich mixtures at the expense of overall fuel efficiency and extra heat to reject.

Thanks for the tip on the google search...

 

[1gibson]

My previous comment to bypass the blower was intended to mean "open the internal bypass to the blower."

It will still create some amount of boost as the small internal bypass then acts as an orifice from outlet to inlet. An M90 that usually creates 12 psig would still create 3-4 psig at full throttle with the internal bypass open, for example.

The bypass is a small butterfly valve, so that bore could be sleeved or partially filled to reduce the orifice size and increase the pressure developed when bypass is open at high RPM's. But still allow sufficient bypass at low RPM's.

This may allow you to use a higher drive ratio for better low end response, without excessive parasitic loss or pressure ratio of the blower, once the turbo is spooled.

I guess I am asking, have you tried opening the internal bypass once the blower sees a few psi of pressure on it's inlet (indicating that the turbo is ready to "take over"?)

 

[madmac666]

No unfortunately we never tried playing much with the bypass as we didn't get beyond 4000rpm on the dyno due to the belt slipping issue. We tried keeping it closed at idle and it just popped the BOV open due to pressure.

I like your idea to restrict the bypass if we need to allow bypass on boost. i hadn't really given that much thought before. The blower is a fair task to remove from the engine bay and the bypass is cast into the body so i think that would be quite tricky to do. I had thought the bypass was already too small for the amount of air we're pumping into the blower as it is!

Because the car is purely used for 30 - 70 second blasts up a tarmac hill, i'm prepared to live with minor gremlins in the search for massive torque and power over the widest range possible. As long as it's smooth between on/off power and the throttle response is sharp then i think i'll be happy. No doubt over the season i can iron out gremlins to continually improve the setup.

Just a few more adjustments to the belt drive and we're good to head for the rollers and see what it's capable of! All the info you guys have put forward has been really helpful. Thanks!

I'll keep the thread updated as we go.

 

[madmac666]

Well, we had her back on the dyno the other day and all i can do is grin from ear to ear now!

We had wheelspin problems so couldn't get any power readings but she's now mapped and safe to drive in anger. We're on the largest blower pulley i had, so i was aware that the blower could hardly be contributing to the overall pressure. Over 5000rpm there was only 2psi difference between the turbo and blower and turbo outlet temps went quite high during the runs so we tried an inertia run to keep the runs short. That halved the turbo temps and would mimic real world driving so i'm happy to leave to where is is for the moment. Total boost is 1.8bar although our target is 2.5bar. The pressures we logged show very similar trends to those seen when we had the 2:1 pulley on - just a lot less total boost so ultimately i want to get the blower back to 2:1 or even 2.1:1 as soon as i can get a break in the season

To change pulleys now will involve a re-make of the whole drive to accomodate available belts so i'll leave that for during the summer.

Driving it on the road, the low end torque is immense, turbo spools quickly and is at full spool by 2800rpm. At 4500rpm the cams come in and all hell breaks loose! Definately a lot quicker than last year (with 635hp), all i need to do now is learn to drive it again!

Thanks for all the help - we've got the basis of a good system to build on now so i'll post back again when changes are made

Donald

 

[PorschaTwin]

This sounds fantastic. I Need pictures!
Which hillclimbs will you be doing? Will you be at Harewood at all?