Controlling turbo boost pressure
Discussion
Hi, im possibly looking to build a cossy YB turbo engine, im not after huge bhp figures probably only 350 max and tunable down to a 250max. what i do want though is to get that bhp spread out along as much of the rev range as i can. now i believe to do this i need to be able to vary the boost pressure with the rpm, so i can keep higher pressure lower down and bleed it off at teh higher rpm to stay under the max bhp limit...
any ideas how i'd do this. is there an ecu that i can map to do this or is there a separate programable boost controller that i can use
Ta
G
any ideas how i'd do this. is there an ecu that i can map to do this or is there a separate programable boost controller that i can use
Ta
G
Hi,
I looked into doing this with a supercharger, but it was too inefficient for me. It can be done by adjusting the waste gate on a turbo, but it would need some form of control. You would probably need a new ecu anyhow to provide a good fuel map so incorporating some control into that wouldnt be too difficult. Of course you could just stop pushing hard on the throttle and limit power that way,
Phil
I looked into doing this with a supercharger, but it was too inefficient for me. It can be done by adjusting the waste gate on a turbo, but it would need some form of control. You would probably need a new ecu anyhow to provide a good fuel map so incorporating some control into that wouldnt be too difficult. Of course you could just stop pushing hard on the throttle and limit power that way,
Phil
If you're handicapped by peak power then that's downright devious! On the other hand if it turns out the way they measure your power actually measures average power in some form, there would be no benefit. Other things being equal, I think you would normally design to produce constant torque since torque is normally the limiting factor.
My guess is, to get constant power you will need to reduce the boost with revs. It may be you can get this sort of effect just by under-speccing the turbo, which would I think also mean it spools up much quicker and crosses over at a lower RPM. If you want a more positive control, I think you would be looking at some form of electronic bleed control to bleed off some of the boost signal to the waste gate at lower RPM. Never heared of any standard widgets to do this, although you may be able to knock up a simple controller yourself it would add significantly to the overall complexity. You may be better off just going under size on the turbo and maybe bodging the ignition map to lose a bit more power at the top end.
My guess is, to get constant power you will need to reduce the boost with revs. It may be you can get this sort of effect just by under-speccing the turbo, which would I think also mean it spools up much quicker and crosses over at a lower RPM. If you want a more positive control, I think you would be looking at some form of electronic bleed control to bleed off some of the boost signal to the waste gate at lower RPM. Never heared of any standard widgets to do this, although you may be able to knock up a simple controller yourself it would add significantly to the overall complexity. You may be better off just going under size on the turbo and maybe bodging the ignition map to lose a bit more power at the top end.
I'm with peter .. a small turbo is self-limiting, plus if you go very small you might jusy be able to wind some advance off at high revs. Don't be fooled the turbo is the way to go though .. andy rouse always reckoned you needed 30% more power from a turbo motor to offset the lack of drivability .. admittedly that was big turbo 550 bhp cossie days, but the truth is there somewhere.
On the other hand seeing as I'm building a tassie for next year and might be competing against you (albeit as a constructor) I'd go for the turbo, big as you like, big is best and bigger is bestest etc etc
On the other hand seeing as I'm building a tassie for next year and might be competing against you (albeit as a constructor) I'd go for the turbo, big as you like, big is best and bigger is bestest etc etc
I think the GReddy PRofec e-01 ought to be able to do what you want. www.greddy.com/products/electronics_frame.htm There are probably some other electronic boost controllers that would do it as well. Haven't really studied up on which gizmos do what lately. Just using an undersized turbo will limit your high RPM power but it will also put additional heat into the intake charge as the compressor falls out of its efficiency zone. Better to use an electronic boost controller.
Smaller turbo will work harder produce more heat and not last as long....
I've suffered the Ultimate punishment for going this route on a 350bhp cossie engine....... the turbo boiled the brake fluid on track and I entered the corner at the end of the straight at Croft doing 150mph and no brakes (had brakes at the start of the straight).
End result a rolled car and lucky to be alive.
I wouldn't advise this route.
There are air to air boost control valves which control boost to a much more accurate degree, but if they are worthwhile or do what you want I don't know.
What I do know is that there are turbos out there that spool up at increadable rate almost removing turbo lag totally..... they are very very very expensive though.
Other options are NoS used to spool the turbo up at low revs or anti lag which carries on chucking fuel through when throttle shut, thus keeping the turbo spooled.
Realistically though my best advice is to go to a reputable company and buy a package.... when I had mine modified a mag did a group test on a load of cossie companies demo cars..... I picked the one who's car was the fastest, despite the fact that he was claiming the lowest power!
I've suffered the Ultimate punishment for going this route on a 350bhp cossie engine....... the turbo boiled the brake fluid on track and I entered the corner at the end of the straight at Croft doing 150mph and no brakes (had brakes at the start of the straight).
End result a rolled car and lucky to be alive.
I wouldn't advise this route.
There are air to air boost control valves which control boost to a much more accurate degree, but if they are worthwhile or do what you want I don't know.
What I do know is that there are turbos out there that spool up at increadable rate almost removing turbo lag totally..... they are very very very expensive though.
Other options are NoS used to spool the turbo up at low revs or anti lag which carries on chucking fuel through when throttle shut, thus keeping the turbo spooled.
Realistically though my best advice is to go to a reputable company and buy a package.... when I had mine modified a mag did a group test on a load of cossie companies demo cars..... I picked the one who's car was the fastest, despite the fact that he was claiming the lowest power!
mmm nos i dont think id get away with that....
the idea is to do what jabba did with their luppo, that had a max bhp limit of 185 bhp they control the boost all through the range startinmg with 1.4 bar down to 0.4 going back to .5 bar to keep the turbo going.
that gives 265lbft at 3500 rpm
and a flat curve with 184 bhp from 3800 to 7100 !!!!
they also used a big dump valve to prevent lag ( and make noise!!)
they reconed they could get loads more torque but the box wouldnt take it..
with was all from a 1.8 turboed golf lump...
the idea is to do what jabba did with their luppo, that had a max bhp limit of 185 bhp they control the boost all through the range startinmg with 1.4 bar down to 0.4 going back to .5 bar to keep the turbo going.
that gives 265lbft at 3500 rpm
and a flat curve with 184 bhp from 3800 to 7100 !!!!
they also used a big dump valve to prevent lag ( and make noise!!)
they reconed they could get loads more torque but the box wouldnt take it..
with was all from a 1.8 turboed golf lump...
Hi,
wouldn't a Roots Supercharger give you a more constant boost? I beleive they tend to max out quite early in the rev range and lets face it they are a lot better than a turbo, no lag, not as hot and not the sort of thing you would associate with the boy racer brigade
. Worth looking into maybe,
Phil
wouldn't a Roots Supercharger give you a more constant boost? I beleive they tend to max out quite early in the rev range and lets face it they are a lot better than a turbo, no lag, not as hot and not the sort of thing you would associate with the boy racer brigade
. Worth looking into maybe, Phil
Graham said:
they reconed they could get loads more torque but the box wouldnt take it..
with was all from a 1.8 turboed golf lump...
This is probably why they played with the boost...
Can't see any other point in limiting the boost that way as your only dropping the torque back..... OK, nice flat torque curve, but not as good as a torque curve starting in the same place and then climbing!
Anyhow I P!$$ed with these bloody modded cossie's at the moment.... especially as mine is in disgrace after blowing a rad hose tonight (I hope it's not split!)...... got to go and rescue it in a while.
They're limiting the boost to stay under max bhp limits for the class whilst still getting more power lower down.
i.e ultimatley the engine could produce a lot more bhp if you didnt bleed down the boost at teh higher end but that would put tyou in a higher class. here your carrying the max power all through the rev range..
Any way im still undecided between the YB turbo route and the v6 24v angine arghhh.
i.e ultimatley the engine could produce a lot more bhp if you didnt bleed down the boost at teh higher end but that would put tyou in a higher class. here your carrying the max power all through the rev range..
Any way im still undecided between the YB turbo route and the v6 24v angine arghhh.
You can drop the torque off at the top end to stop the power going over your limit, but I guess the power will still drop off lower down the rev range because the torque required to maintain constant power will go through the roof. If you're looking for crazy solutions, CVT is a very good way to achieve this since you can set it for peak power and run at constant rpm. As well as giving the effect of a flat power curve across a massive speed range and avoiding coasting time during gear changes, this should liberate significantly more power since you don't have to spin up the engine as you accelerate the car. Probably not much fun to drive though!
GreenV8S said:
You can drop the torque off at the top end to stop the power going over your limit, but I guess the power will still drop off lower down the rev range because the torque required to maintain constant power will go through the roof. If you're looking for crazy solutions, CVT is a very good way to achieve this since you can set it for peak power and run at constant rpm. As well as giving the effect of a flat power curve across a massive speed range and avoiding coasting time during gear changes, this should liberate significantly more power since you don't have to spin up the engine as you accelerate the car. Probably not much fun to drive though!
Aren't CVT boxes limited to low torque outputs though?
I have a friend who knows all about this subject, email me & I'll pass his details on.
It's fairly easy to design a turbo set up with variable boost through the rev range you just need an ECU controlled boost control (normally solenoid actuated). Quite a few cars have a similar system as standard like Saab's. You could even retro fit the system.
But your are talking a small turbo by the sounds of it, to get a low down power. so long as its designed within it's limits there will be no problems with life.
You could use a VATN Turbo with variable pitch vanes, these have a HUGE operating range see Audi for them.
It's fairly easy to design a turbo set up with variable boost through the rev range you just need an ECU controlled boost control (normally solenoid actuated). Quite a few cars have a similar system as standard like Saab's. You could even retro fit the system.
But your are talking a small turbo by the sounds of it, to get a low down power. so long as its designed within it's limits there will be no problems with life.
You could use a VATN Turbo with variable pitch vanes, these have a HUGE operating range see Audi for them.
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff