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Old 12-11-2010, 01:53 PM   #1
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Default high boost @ low rpm torque monster setup

so i was thinking.. what would happen if you took a stock-port 13B and a small turbo and boosted the shit out of it at low RPM (~20+ psi), then bleed it off at high rpm so the turbo wouldnt destroy itself (~10psi), but give you a lot of low-end power? or would this be asking for trouble as far as engine reliability?

and what type of turbo would be better for this.. small compressor/small turbine (stock), small compressor/large turbine, or something different?






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Old 12-11-2010, 01:59 PM   #2
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why not look at variable geometry turbos?
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Old 12-12-2010, 12:00 AM   #3
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Unfortunately, the only advantage to this setup would be that you would have good street drivability. If you want to run 20 psi boost, you would need to build your engine for 20 psi boost, then it doesn't seem to make sense to limit yourself to about 300 WHp when you could have 450 WHp on the same build if you held the 20psi all the way to the redline. TitaniumTT has it figured out, he is using the stock twins sequentially to make good low end and high end.

The VGT is also a good option.
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Old 12-12-2010, 12:43 AM   #4
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Originally Posted by hades View Post
why not look at variable geometry turbos?
because the vgt can't handle the egts of a rotary. Get your egts down and you're good to go. I plan on ditching the panties and making it work though.

Twins are great, love 'em, but they suck to work aaround, work properly and they don't last long at all above 15psi.... but I hit boost cut <3k easily
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Old 12-12-2010, 01:20 AM   #5
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I still don't understand what the hangup is for more boost...

It's FLOW that's going to give you the torque / power.

So here's the dilemma...
BIG turbos obviously give you lots of flow, but they don't spin up well at lower RPM's - this isn't your answer, unless you get that big turbo to spin down low.
NOS?
You can try all the little tricks to get them to spin earlier, but I bet it's still not enough...
We're talking divided set-up's with high velocity runners for your turbo exhaust manifold trying to take advantage of pulse tuning, etc.
Pain in the ass and big headache to figure it out...

How about we run individual turbos per rotor?
This takes advantage of the strong exhaust gas pulse and keeps everything divided.
It's an extrapolation of the above, but it takes it one step further from (big) single turbo set-up's.
I can only remember only a handful of people who have tried individual twins, but I believe they have gotten very promising results...


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Old 12-12-2010, 03:58 AM   #6
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Old 12-12-2010, 06:40 AM   #7
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Rally cars (Imprezas, Lancers, etc.) do this all the time, making lots of torque at low RPMs, using high boost, etc.

I don't see why rotaries shouldn't try this, I think it can be done.
What ever kind of set up it takes.
Though I do recommend a built-up engine to handle the boost / stress at the low rpms.
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Old 12-12-2010, 04:56 PM   #8
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thats got me thinking.. rally cars retard the timing to spool the turbo at lower rpm. Has anybody tried that on a rotary and see how long the turbo lasts? That would be interesting.. i think you would have to convert to non-waste spark coils to avoid a spark event during compression on the next cycle. ive got a bunch of old stock turbo parts laying around to try it on
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Old 12-12-2010, 09:01 PM   #9
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What rally cars use is called a misfireing system or anti-lag system. They are very exspensive and the entire engine,turbo,turbo manifold,exhaust, and intake have to be made specifically for this system due to the extreme heat and pressure exposed to it all.

Just build you a fresh motor and put a relatively good sized turbo and you'll be more happy than you would be with a lesser setup. Also not to mention the extreme pre-turbine backpressure you'd experience with such a tiny turbo that would ultimetly destroy your new engine.

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I suppose you could orally BDC or even anally BDC someone? or be BDC'd in those two ways also

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Old 12-12-2010, 09:18 PM   #10
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Quote:
Originally Posted by TitaniumTT View Post
because the vgt can't handle the egts of a rotary. Get your egts down and you're good to go. I plan on ditching the panties and making it work though.

Twins are great, love 'em, but they suck to work aaround, work properly and they don't last long at all above 15psi.... but I hit boost cut <3k easily
EGT's are going up to lower emissions. surely there is a factory turbo that can be tried out.
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Old 12-12-2010, 10:28 PM   #11
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I run a T04 turbo std stock Mazda porting and have 22psi at 4400rpm, but more to the point massive power at even these low revs, its so much that when the turbo comes on boost and power is there, it literally compresses the Ohlins race suspension and the nose lifts into the sky

It is stupid really, it is so violent coming onto power in 2nd gear that it will throw the car off the road and even F1 spec Race Logic traction control has trouble taming it (and that is in a FD Chassis with big rear tires of soft compound hot tires~!) and over 50% weight over the rear tires.

You can have too much low end mid range power. Having said all that I would not swap it for the world and that is someone who makes excellent street ports and loves the top end power they produce.

You have to be careful when you get into big power ranges (Ferrari F40 acceleration specs) cause if you use too small a turbo combination your EGT goes through the roof! and it is NOT reliable on the engine nor the turbine. I have all the details listed in my ride thread build up. I dont list EVERY specification but I give away more than anyone else when it comes to these topics

Water Injection is mandatory if you want reliability and power combined.
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Old 08-31-2011, 10:04 AM   #12
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i came across a tech article on subaru WRC engine tuning..

http://www.i-club.com/forums/subaru-...popcorn-69783/

basically the WRC engines are limited to about 300hp due to a 34mm restrictor placed in the intake. this makes it advantageous to maximize power throughout the rpm band, and the result is a very torquey 300hp at 3krpm from 2.0 liters. some of the notes:

2.0L engine, 9.1 cr (1995)
boost is 30-45psi! at low rpm, then it is tapered off to half that at redline
anti-lag is used to generate boost at low rpm. uses retarded timing, rich mixture, and a throttle bypass valve
water injection is used at low rpm to prevent knock, injected between IC and intake manifold, and results in almost ambient intake temps at max boost. water injection amount is controlled via an ecu map. uses an ERL aquamist 2C kit:

http://www.rotorsportsracing.com/per...njection2c.htm


I want to try something similar with a rotary, but not as extreme. I am thinking using antilag to generate the boost at low rpm, but only during wot low rpm conditions. at idle and normal throttle inputs, it would not be active. but if you go WOT, it would be activated briefly to generate the boost, then once a boost threshhold is obtained, it would be disabled and go back to the normal map. I have a haltech ps1000 waiting to install, so im going to try it with that, which has a better antilag function than my current e6k. the only other thing i need to upgrade is direct fire ignition, which i will probably just use a pair of trailing coils. should be interesting
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Old 08-31-2011, 12:00 PM   #13
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i've been thinking about this too. the race class i'm shooting for, TTC, limits HORSEPOWER (in the 250ish area) but not TQ. so building something that has a boost spike in the low end and tapers off might work really well.

i have seen a dyno of a stock S5 t2, with an exhaust, and it did like 230ft-lbs@like 2500rpm and only 210hp in the 6k area, its like a truck....

and actually on the extreme end, Mr Ko's FD has some boost control problem and it'll do like 17psi on the first turbo, its not as big a difference in acceleration as you'd think.

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Old 08-31-2011, 04:11 PM   #14
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Quote:
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and actually on the extreme end, Mr Ko's FD has some boost control problem and it'll do like 17psi on the first turbo, its not as big a difference in acceleration as you'd think.
Yeah, people need to get it out of their heads that's AIRFLOW - not boost - that makes power...

Boost heats up the intake charge.
Anti-lag / misfire stresses out the entire exhaust side from the engine to the turbo to the exhaust system and everything in between.


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Old 08-31-2011, 05:18 PM   #15
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Quote:
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Yeah, people need to get it out of their heads that's AIRFLOW - not boost - that makes power...
Boost is quite vague indication of flow against "certain" restriction. So one could say that when you measure certain pressure and temperature at plenum, as long as these two are same, you have same flow on given engine speed. Problem is that engine can pose quite different restriction due to very same device that drives compressor.

My point is that pressure canīt be ignored as there are situations where engine cares about inlet and exhaust pressures, especially their ratio

To the OP, there is something to consider, you canīt change fact that engines natural torque peak is above 5000 RPMs... you know, the feel when the engine really goes hard. If you would run high boost at low RPMs, you will be surge limited to small compressor and consequently choke limited on top end. Powerband wouldnīt be as good as you may think.

You should give yourself some realistic goals, concrete numbers. Maybe there is what you want with rather conventional approach
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