| redmist |
Posted
Wednesday, Oct 19th 7:35pm [Edit] [Quote] [IMS] [View car] |
Member
Post nr. 627
NY USA
357i , 325i e30 turbo |
In order to maximize low end torque some engine systems use two turbos. One is a small turbo which feeds the sytem at low RPM and and another larger turbo which comes into play at higher RPM.
My question is that with a larger displacement engine that has good NA low end torque couldn't you just put a large turbo in? You would put in plumbing and RPM activated selenoids that would bleed off exhaust gases from a large diameter dual exhaust setup into a single pipe to feed the turbo when say you hit 3000 rpm.
Has this been done before? Is it practical/doable? |
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| JJG323 |
Posted
Wednesday, Oct 19th 8:20pm [Edit] [Quote] [IMS] [View car] |
Member
Post nr. 971
Reading MA USA
1979 BMW 323i |
Yes, for an engine like that you just run one turbo.
A garrett 28rs or even bigger garrett 35 series turbo is the more common setup. There are a lot of turbo cars, that just run one specific turbo, that matches the engine.
In fact eddie farcon's carbon fibered e36 car first engine ran two turbos and he blew up that engine.
The new engine is a e36 m3 3.0 with a larger that garret 28rs turbo on. He has over 500 HP.
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| M42powered |
Posted
Wednesday, Oct 19th 9:14pm [Edit] [Quote] [IMS] [View car] |
Staff
Post nr. 583
Arizona, USA
1981 BMW 320i |
| redmist wrote: | In order to maximize low end torque so engine systems use two turbos. One is a small turbo which feeds the sytem at low RPM and and another larger turbo which comes into play at higher RPM.
My question is that with a larger displacement engine that has good NA low end torque couldn't you just put a large turbo in? You would put in plumbing and RPM activated selenoids that would bleed off exhaust gases fromm a large diameter dual exhaust setup into a single pipe to feed the turbo.
Has this been done before? Is it practical/doable? |
You mean a N/A down low, turbo up high setup? Not really worth while. Because you WILL make more torque under boost than not. You will have to decrease the compression ratio to accomidate the added pressure at high RPM. That is what causes the loss in low end grunt. Or off the line power. The Mazda 20B has a solenoid actuated setup where exhaust gases are routed to a small or large turbocharger based on engine load, and RPM. The compression ratio is what kills low end power, because for a set period of time you are running naturally aspirated on lower cylinder pressures. |
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| Marquis_Rex |
Posted
Wednesday, Oct 19th 9:19pm [Edit] [Quote] [IMS] [View car] |
Member
Post nr. 375
UK
BMW 323i 2.7-as featured in Total BMW Nov 2002,Porsche 911/993TT |
| redmist wrote: | In order to maximize low end torque so engine systems use two turbos. One is a small turbo which feeds the sytem at low RPM and and another larger turbo which comes into play at higher RPM.
My question is that with a larger displacement engine that has good NA low end torque couldn't you just put a large turbo in? You would put in plumbing and RPM activated selenoids that would bleed off exhaust gases fromm a large diameter dual exhaust setup into a single pipe to feed the turbo.
Has this been done before? Is it practical/doable? |
I think it sounds do-able. However the issue of lag/poor low speed torque is often partly subective and partly "real".
Take my 993 Turbo for instance, 3.6 litre NON sequential turbos (unlike the legendary 959 which was sequential)-it makes around 230 Nm of torque at 1000 rpm (even though there's not much boost down there)- which is quite alot, even more than the stock naturally aspirated high compression 3.6 litre motor makes there. However the issues of lag are largely subjective, as a driver can't help but compare the 230 Nm at 1000 rpm with the 540 Nm PEAK at 4500 rpm and the accompanying STEEP rise in torque curve. In the naturally aspirated motor the peak torque is much lower and you don't get this feeling.
Also a comparable 2 valver naturally aspirated engine- that is needed to achieve the peak torque of 540 Nm and peak power of about 408 Bhp would be of around a 5.8 litre capacity. This NA set up would give around 405 Nm at 1000 rpm!
Assuming the same vehicle and gearing- the fuel economy, however of the Turbo charged set up should be better by virtue of the fact that you're gaining some kinetic work energy back from the hot exhaust gases. |
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| RDAvena |
Posted
Wednesday, Oct 19th 9:20pm [Edit] [Quote] [IMS] [View car] |
Staff
Post nr. 1508
SELECT * FROM users WHERE clue > 0
1981 323i, 1988 545is, 1997 528i |
| redmist wrote: | In order to maximize low end torque so engine systems use two turbos. One is a small turbo which feeds the sytem at low RPM and and another larger turbo which comes into play at higher RPM.
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You could but some of the dual turbo setups have been known to have their shortcomings once the owner decides to up the boost. Take into consideration the Toyota supra. Many of the owners of these cars go from a dual set up to a single set up. Ask Sweeny with his turboed e24 why he went from a twin turbo to a single turbo set up. Some of the new supposed to be brought into production turbo cars that are going to use or are using the twin turbo set up are using them for this reason as well. One turbo for low and the other for high but from what I have seen they are doing this because they have limited the capacity of the engine they will be running the set up with. They need the turbo to help it make enough torque to get it off the line plus another to help it when the engine has limited HP like passing a freight truck on the freeway.
| redmist wrote: |
My question is that with a larger displacement engine that has good NA low end torque couldn't you just put a large turbo in?
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You could use the example of the M30 that everyone is currently turboing. It has decent torque that is helped a bunch with the addition of a turbo. Plus it ultimately depends on the a/r that you choose for the turbo. Some that have properly matched the ar ratio to their set up have been able to eliminate 95% of the lag inherent in a turbo engine. Some of us running outdated 1980s technology take a little while to reach grinning performance. It is not as simple as recommending the "run of the mill" or "most popular" turbo without considering these other important issues.
| redmist wrote: |
You would put in plumbing and RPM activated selenoids that would bleed off exhaust gases fromm a large diameter dual exhaust setup into a single pipe to feed the turbo.
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Wouldn't a two stage boost controller be better suited to control this instead of adding extra pipe? You have the boost made you can always bleed this off after instead of messing with the exhaust gases feeding the turbine.
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| redmist |
Posted
Wednesday, Oct 19th 9:37pm [Edit] [Quote] [IMS] [View car] |
Member
Post nr. 628
NY USA
357i , 325i e30 turbo |
Thanks for the replies from all you brainiacs. I understand a little better now.
I thought turbos "plugged up" the motor by restricting exhaust gases at low revs without a compensation intake boost from the turbo.
Big point I missed was from M42 which elightened me that the compression ratio would have to be dropped with a turbo setup at the cost of some low end torque.
So as Ray said a well matched turbo with a good AR is the answer to minimize the low end (possibly perceived/relative according to Marquis)torque reduction.
There is just a lot of guys putting a turbo on LS1 motors without dropping the compression much or at all, running about 10:1 with 4 to 8 pounds of boost. (this in of itself surprises me). They were complaining about a reduction in low end torque so I was trying to understand why and what a solution might be.
Really appreciate the help. |
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| bmw_m_320i |
Posted
Wednesday, Oct 19th 10:10pm [Edit] [Quote] [IMS] [View car] |
Member
Post nr. 472
Helena, Montana
none right now :( |
you're gonna turbo the 557?  |
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| M42powered |
Posted
Wednesday, Oct 19th 11:00pm [Edit] [Quote] [IMS] [View car] |
Staff
Post nr. 584
Arizona, USA
1981 BMW 320i |
Ray's point on AR ratio is extremely important. A good sequential setup can offer maximum efficienies throughout the entire RPM band. A Twin Turbo setup is simply splitting up the duty of 1 single larger turbo into the work of two. Sequential setups can offer great drivability with a big reduction in neck snapping / scary to drive in the rain / Dr. Jeckel and Mr. Hyde syndrome that so many people get from big single setups. Selecting turbos and controling variables of a sequential setup are difficult. |
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| greggearhead |
Posted
Thursday, Oct 20th 7:46am [Edit] [Quote] [IMS] [View car] |
Member
Post nr. 3
Colorado Springs, CO
1979 320i |
With today's modern turbos, a sequential setup is really not very cost effective. I have been pleasantly surprised with many setups that offer very good response down low, and insane top end. I have also driven crazy top-end powerbands that don't start until 4000rpm.
A well designed system with a single turbo (turbo, manifold, cam, porting, displacement, compression ratio, exhaust, ignition and fueling) will embarrass most sequential setups. Back in the 80s when turboing wasn't as developed, lag or boost threshold was more common to be pronounced.
The really, really cool setups use variable turbos - have ridden and driven vehicles with Aerodynes and holsett variable turbos that have really, really good response along with great top end. |
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| redmist |
Posted
Thursday, Oct 20th 7:04pm [Edit] [Quote] [IMS] [View car] |
Member
Post nr. 629
NY USA
357i , 325i e30 turbo |
Yeah, thinkin about (after the input I received thanks again) doing one of those rear mount turbo deals with junkyard/used parts. Need to do reasearch on turbos (especially AR!) that would work. What I like about these setups is not needing an intercooler, special exhaust manifolds, muffler. Less heat in the engine bay and the turbo runs cooler as well. The only tricky part is oil management of the turbo. Don't know if a want to do a dedicated "closed" lubrication system or feed off the motor.
Welcome any further thoughts on the subject. |
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| Jason_323i |
Posted
Sunday, Oct 23rd 10:03am [Edit] [Quote] [IMS] [View car] |
Member
Post nr. 298
UK, Scotland
323i 2.7 tripple webber track car. Maserati Biturbo |
Hi Pete
You could always try to copy the Group b rally cars and run a super charger and a turbo, or try using a NOZ system for antilag and early bost.
Jason |
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| ads 323 |
Posted
Thursday, Dec 21st 11:50am [Edit] [Quote] [IMS] [View car] |
Member
Post nr. 10
nsw australia
e21 323 turbo |
its easy to set up a anty lag sistem for a turb you just nead to retard the timing at idel and set up a air bipass to alow air into the exaust manifold this will alow boost at idel |
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