Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

Register Log in

Twincharging - calling Warpspeed! 3

Status
Not open for further replies.
madmac666

madmac666

Automotive
Mar 19, 2010
59
0
0
GB
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
 
Replies continue below

Recommended for you

Sort by date Sort by votes
I hope to go to Harewood this year although it'll be around mid to late summer. We have Loton park planned in May. A few of us Scots heading down to give it a go.
 
Upvote 0 Downvote
Gordon, sounds great and I am sure it will be a bit of a monster to listen to also?!!

At what power was the max boost pressure achieved with the TC alone? How do you feel that the response time/lag has been improved? Have you noticed any greater oil loss from the TC compressor seal into the intake tract?

Sorry if this sounds like a repetition, but you would see alot lower intake temps and lose none of the anti-lag properties if you could bypass the SC at higher rpm, and use a slightly bigger TURBOcharger compressor. The control is simply a boost operated butterfly/flap valve. There are suitable valves used on most series connected twin turbo arrangements.

If you still intend to pass the whole boost through the SC when aiming for higher total Pr, then why not try fitting a valve next time its in the workshop when you are changing the pulley? Do a back-to-back run with it closed and with it opening just after max SC-only boost is reached to see the temp/efficiency differences. You will see higher power output due to recovering the SC drive power and lowering intake temps. Never mind exhaust pressure upstream of the turbine, if the turbine is correctly matched should have a positive drive ratio anyway at max boost, supplementing this with inefficiently produced SC boost will not win the war.

Although Warpspeeds very useful, insightful and obviously experienced posts are very positively written, the whole 'twincharging' story is not written there....

By the way, thanks for proving that a throttle ahead of a positive-displacement blower is not dangerous, even at those high Pr's. Also thanks to VW for proving that with their 2006/2009 engines of the year!!


 
Upvote 0 Downvote
The combined boost was showing higher than the turbo all the way up the revs but at 5000-6500 the blower was only 2 psi ahead of the TC. When we had the smaller pulley on, the blower pressure was showing almost double that of the TC. The idea now is to size the blower pulley so we can back off the TC boost. Hopefully have around 1.3bar at the TC and 2.5bar combined. This should keep TC temps low.

Interestingly, the intercooler i have is an awesome piece of kit. When the turbo was running alone, the IC took temps down from 212c to 21c so this is why we have the combined charge being cooled through the IC. Last time on the dyno the plenum temp was down to 6c with ambient air at 5c (cold night!)

No noticeable oil loss from the blower. looking inside it shows no oil leaking around the seals - so far so good.

Being honest, i've not really had many chances to drive it yet. The most i've done was a 6 mile 'stage' round the block. Throttle response is good, the turbo is at full spool at 3000rpm (ish) so she's very torquey to drive. I'm still wanting to try the new pulley ratios before i decide on any bypass. Going by the initial results, i don't think a bypass is required and we'll be keeping the compound effect throughout the rev range. It's most defiantely a development in progress so i'm not discounting a bypass in the future - i just want to try this before any decision is made.

I have my first event this weekend so i'll be back to post results at the start of the week

Donald
 
Upvote 0 Downvote
Sorry i haven't been in to update, it's been a busy week!

Had a good weekend, i got to within 0.6 of a second of my best ever time up the hill and set a new class record. Overall a successful 2 events as i beat the other competitors in the modifieds division to take maximum division points on each day along with 2 class wins and an extra point for breaking the record.

The car performed well, didn't break and had no issues over the weekend. I was taking it easy as the suspension geometry has changed so much to try and get rid of the understeer the car has always had. Took time to get to grips with this new setup on the Saturday. It rained all day sunday so i couldn't push hard and essentially just drove it smoothly up the hill! Looking back at the videos from last year and now this year the difference in low end torque is very noticeable. I think i had it over 8000rpm once but generally was short-shifting at 6000rpm and playing with the new torque while i learned the handling again.

Last years launches were around 2.3s to 64ft due to having to spin the wheels off the line to stop the turbo stalling. With the compound system i was regularly doing 2.09s with a 2.04s my best due to the torque.

While checking the car over the other night i discovered a crack in the bellhousing where the front stabiliser mount bolts on so it's in bits again! The box was stripped down to weld the crack and bracing added. I have it ready to go back together but waiting for my clutch plates to be re-lined since i was in there anyway as it was looking pretty worn. While it's apart i've decided to do the new pulleys to take the blower to 2:1 ratio so hoping these will be here by this weekend coming. I have the dyno booked for Tuesday evening to get it mapped with the higher boost level.

Hopefully we'll see some good gains and be ready for the next hillclimb on 8th/9th may at my local track- Fintray

I'll keep you posted
 
Upvote 0 Downvote
It certainly sounded like it was spooling very early in the video. I suppose the supercharger is slightly muted being after the turbocharger? Looked very quick!

So how did the new mapping session go? Did you keep all temps in check with that HUGE intercooler? Did the belt manage to withstand the forces this time?

 
Upvote 0 Downvote
Here's last years best run on road tyres. You can compare how the engine delivers its power to the run i posted above:
The blower is actually very quiet and can't be heard when driving. Some spectators say they can hear it but others say they can't. There is a whine from the belt drive though. The new pulleys will be here today so over the weekend i'll build it back up with the 2:1 ratio in advance of the dyno session on Tuesday. Hopefully we'll be able to turn the turbo boost down a bit, reduce the temps into the blower and see the full compound charge effect of cylinder filling. If it stays together i'm predicting some good gains in spool, torque and power.

Intercooler is impressive! I haven't seen any other IC get close to this one in terms of flow and cooling. Every time we've had it on the dyno, it cools the inlet down to only a few degrees above ambient, even when the turbo was producing 212 degrees. The drive belt handled the bigger pulley (this was the one we were using at Doune last weekend). Whether the belt can handle the power needed with the 2:1 ratio remains to be seen!
 
Upvote 0 Downvote
The mapping session didn't get off to a good start - the blower has been damaged by what appears to be a small metal object going through it. We don't know what it was or where it came from. This happened while we were doing the warmup before mapping so never got a chance to see any results. The blower is away for rebuild so it'll be a few weeks before we're back on the dyno again.

We've come to the conclusion something had fallen into the turbo outlet during the latest pulley change and sat there until the turbo started producing boost - firing it into the blower. An expensive one! We first thought a turbo blade had broken off but the turbo looks in A1 condition on stripdown.

I've bought a water/air chargecooler, small radiator and a 12v pump to make up a small cooling system for the turbo outlet. Hoping this would also minimise any risk to the blower if the turbo ever came apart as i've always been aware this could happen. Having cooler charge entering the blower will also prolong its life and allow us to go slightly higher on the turbo boost.

I'll update once we're back on the rollers
 
Upvote 0 Downvote
Hello Donald, Just discovered this thread.

Sorry to hear about the demise of your blower, but these things happen to a great many of us sometimes.

A supercharger bypass is not required for performance, but if fuel economy, heat buildup in the blower, or noise and vibration is an issue in a civilized everyday road car, a supercharger bypass is well worth the effort.
If it is strictly for full throttle off road competition, you can do very nicely without a supercharger bypass.

Working up a trouble free supercharger drive is not as easy as it first appears. As the air density going into the blower increases, so does the required blower drive torque increase. There are several things to be on the alert for.

No doubt all the pulleys are dead in line, and parallel with the crank. Absolute rigidity of the blower mounting can be an issue.
It is not just absolute strength of the mounting points, but rigidity, and freedom from resonant vibrations. Belt stretch under load is sometimes another difficulty with a high mounted supercharger with wide pulley spacing. And lastly belt flap.
Where the belt feeds onto the crank pulley will always be under tension. But where the belt feeds back onto the blower pulley is the "slack" side.

The belt can start flapping and lead to it jumping or destroying itself. The solution is to fit an idler pulley on the outside of the belt a few inches ahead of where the belt feeds back onto the blower pulley. A flat slightly crowned pulley, or one with side cheeks will centre and damp the worst of the belt contortions, and feed the belt centrally onto the blower pulley with far fewer belt under tension dramas.

Looking forward to hearing much more about this exciting project.

 
Upvote 0 Downvote
Hi Warpspeed, thanks for the reply. You seem very knowledgeable on this subject so your input is appreciated. I think we have the belt drive sorted now, the blower is very rigidly mounted and i have a lockable tensioner on the loose side of the belt just before the blower pulley. It seems to cope for now. The main problem was our original belt system used a 1700mm belt which went around all the ancilliaries but it stretched under load and caused it to jump. The new drive uses a 960mm belt and we had no issues with it on the lower ratio drive. It remains to be seen if this will cope with the 2:1 ratio. New blower is here and am working on a large chargecooler before the blower so more 'development' going on.

Will keep you updated :)
 
Upvote 0 Downvote
UPDATE:

I have the chargecooler installed and went on to the dyno a couple of weeks back. The belt drive held up great - no issues we can see and the belt is reliably spinning the blower at a ratio of 2:1 now.

Turbo is putting out 1.2bar with the blower multiplying that to 2.2bar combined. Power: well we couldn't get grip on the rollers so the best figures i have are that it's making 591 wheel horsepower at 5000rpm, then the cams start working and we couldn't hold it back!

looking at coast-down losses from previous runs, we've deduced the engine to be making around 690-700hp at 5000rpm. The dyno couldn't give us coast down losses due to the wheelspin so we've had to interpret power approximately. On the road there's no lag that's noticeable at all and the torque and power delivery is very smooth. No 'whoosh-bang' from the turbo as it used to be like as all the power came in within 1000rpm with turbo only! We reckon it's somewhere between 750 and 850hp with torque not far behind.

We did find out why the first SC failed. We had been monitoring the turbo outlet temp ans pressure, and also the plenum temp/pressure. We never thought to measure these parameters within the pipe from the SC to the plenum. It would appear that at 'cruise' (exactly where we were setting up the dyno when the failure happened) the bypass valve can't flow enough at the 2:1 ratio and pressure starts building up against the throttle butterfly. This in turn allows the air to go past the partially open throttle and lowers the vacuum in the plenum. At this point the bypass valve closes - we think about halfway, and the air is bypassed between inlet and outlet thousands of times, heating up more each pass. This caused the blower to overheat very quickly and expanded the rotors until they contacted the rear face of the casing.

We measured the pressure in the pipe from the SC to the throttle butterfly and saw 2.5bar pressure in there at cruise throttle! 2% movement of the throttle is enough to stop this but it seems over time, cruising would kill another SC. For the moment i've fitted a BOV just before the throttle to stop pressure building up. It seems to work very well so far. I'd removed that BOV as we couldn't keep it closed on previous attempts.

If you've read all my posts, this now goes back to our first dyno session where i was seeing the BOV in that position opening at cruise. Now it all makes sense! We never thought to measure what was going on in that pipe as we were taking readings from the plenum and at full throttle, the pressures/temps would have been the same...

I'm just back from Shelsley Walsh hillclimb having never been there before. car performed 'almost' faultlessley! For some reason the idle when hot is very lumpy. Other than that, a successful weekend with me finishing just over a second away from the class record. Very much a power hill and the Evo drove every bit as well as i'd expected. The reliability was 100% and i took it home in one piece which is always a bonus!

It's blowing a bit of oil and we suspected the oil rings have been on their way out for a while. This engine is tired now but still producing the goods. I hope to build another engine to suit the charging system when coin allows.

Here's the car performing:
And in-car:
I touched the gearlever before i wanted to change into 2nd off the line and this kicked in the flatshift, so the first changes sound rough!

Enjoy!
 
Upvote 0 Downvote
Cruising down the motorway at speed, with an almost closed throttle,the supercharger will be recirculating a lot of air through the open air bypass.
The bypass does not need a very large flow area, as long as the up stream pressure from the supercharger does not rise all that high against the just open throttle.

But the same air will be flowing round and round in an endless loop heating up slightly on each pass.
A larger flow area bypass may help slightly, by unloading the blower more completely, but a much more effective solution is to bypass the air from the supercharger after the intercooler.

The supercharger heat input will not that high, because the pressure differential the blower is working against is low. But the total temperature rise can build up to become alarmingly high.
The intercooler will easily handle the low total heat input, especially at the high road speeds that always go with this condition.

It will result in a far cooler running blower casing, rotors, and all induction pipework. And then when you nail it.... that will initially absorb much heat too. So you will be a bit ahead there as well. Doing it that way can also reduce the acoustic rotor noise level coming from the open air bypass. It is all a step in the right direction.
 
Upvote 0 Downvote
Great idea about diverting the air after the IC. I did think about that but the blower has the bypass built in so it would be impossible to do unless i permanently closed the bypass and did the same job externally. I doubt there's enough room to do this now.

Having the BOV just before the butterfly works fine and although it doesn't stop the air circulating through the bypass valve, it does give it somewhere to leave the pipework stopping the heat building up & allowing cold air to feed the blower from the chargecooler

I'm having talks with the blower manufacturer about fitting the bypass from their larger model into the unit they have back for repair. They reckon this can be done easily enough so i might get that done before it's sent back to me.
 
Upvote 0 Downvote
Status
Not open for further replies.

Similar threads

johandelivera
  • Locked
  • Question
Compound twincharging with centrifugal supercharger
Replies
2
Views
4
EdStainless
EdStainless
Alfa33Phil
  • Locked
  • Question
Twin Charged Alfa 33 calling Madmac666
Replies
8
Views
13
Alfa33Phil
Alfa33Phil
drxlcarfreak
  • Locked
  • Question
Twincharging meets Compound Turbos - Calling the Experts! 3
Replies
14
Views
15
snoopnoon
snoopnoon
stevefto
  • Locked
  • Question
automotive twincharging applicaton 6
2
Replies
20
Views
21
stevefto
stevefto
StavFC
  • Locked
  • Question
Twincharging- Effects of turbine wheel/housing size- FAO Warspeed!
Replies
5
Views
6
TexasAceTA
TexasAceTA
Back
Top