EVIL ENGINE goes Twin Turbo - Your Chance to Design the 930tt Exhaust System - Page 3

WERK I · WERK I's Garage

Quote:

Originally posted by beepbeep
There is a slight downside to this as adding a X-pipe (which this merged wastegate pipe really is) will also lower the amplitude of exhaust gas pulses. With other words, pulses from left side will cross-talk to right side trough merged wastegate pipe annd vice versa.

As turbocharger is partly driven by pulses (as well as flow) you might expirience worse spool-up characteristics by X-ing headers in a TT-system. It does decrease the noise though.

........but, if you use equal length headers, problem solved! Yes?

TerryBPP · 09-19-2006, 08:05 AM

Quote:

Originally posted by WERK-I
........but, if you use equal length headers, problem solved! Yes?

Headers are before the turbo. What our swedish friend is talking about is the downpipe after the turbo. Basically, the pressure comming out of one turbo will produce back pressure in the other causing it to spins slower or erratically.

RarlyL8 · RarlyL8's Garage

The way I understand Goran's comment is that the common wastegate is connected (before the turbo) by a pipe frome each bank of cylinders. This common connection allows pulses from both banks to collide.

What type of unusual characteristics would such a cross-flow cause?
Amac has never mensioned this in his application; is the cross flow significant to cause a measurable disruption?

Terry - there is no picture on this puzzle box. We are drawing one.

RarlyL8 · RarlyL8's Garage

Here is an old (hijacked) picture of Stephen Kaspar's "Monster".
Very unusual placement of the turbos.
What are your thoughts on this configuration?

sand_man · 09-21-2006, 05:08 AM

Well that config looks like it would certainly fit your rear bumper as far es exhaust cut-outs go. Can't comment on the actual performance.

WERK I · WERK I's Garage

Too many bends on pressure side to intercooler, IMHO.

beepbeep · 09-21-2006, 06:25 AM

Quote:

Originally posted by TerryBPP
Headers are before the turbo. What our swedish friend is talking about is the downpipe after the turbo. Basically, the pressure comming out of one turbo will produce back pressure in the other causing it to spins slower or erratically.

Nono. I'm talking about X-pipe before the turbochargers. As this is a requirement for running a single wastegate on TT-setup, it effectivly short-circuits the headers allowing pulses from one to escape into another and vice versa.

As I said before, turbochargers live off the pulses as well as the flow and X-ing headers will mellow pulse amplitude at lower revs, effectivly pushing boost treshold upwards. You will get quieter exhaust note (at least as long as wastegate isn't venting to atmosphere) but you will also get boost later on. Equal length headers won't help in this case. Of course, X-ing the pipes after turbo with yield much less influence on spoolup and engine characteristics.

To further explain what I'm talking about. Here is dyno papers from identical engine configuration. One pull is made with trick equal length headers and other with complettly OEM cast-iron non-equal length exhaust manifold with narrow ports. As you can see, equal length headers give more power (some of extra power might be explained with boost runaway due to less backpressure) but they also spool the turbo 300-400 RPM later.

Regarding Caspers motor. Yeah, it probably works well but all those 90-degrees bend aren't helping. Exhaust-to-exhaust has been preffered route for most aft-mounted TT desings.

VZ935 · VZ935's Garage

RarlyL8 · RarlyL8's Garage

My rear bumper has no exhaust cutouts. The tailpipe exits below the bumper so I can do about anything EXCEPT center exit due to the issues addressed on page 2. I am not opposed to swapping out for another bumper if I have to.

Monster has a LOT of plumbing. My vision is simplicity. I believe this can be done with a lot less fuss.

Goran, did header version of your test have the X pipe or the stock H/E configuration? Do you recommend I use the 993 heat exchangers with rear mount or the shorty headers with side mount?

VZ, you are on a different planet than myself. HA! Thank you for the links - very nice stuff. What are the driving characteristics (if you can call it that) of the two?

VZ935 · VZ935's Garage

Quote:

Originally posted by RarlyL8
Z, you are on a different planet than myself. HA! Thank you for the links - very nice stuff. What are the driving characteristics (if you can call it that) of the two?

Well the GTR is newer tech , has Motec and two small turbo's.. (I think that engine/car still holds the GT1 PCA record at Road America..despite being geared 30 mph to tall and a bad push) has virtually no lag and great throttle response, better brakes and superior shocks, weighs 2100 lbs and has a ltd diff , 18 " wheels with radial slicks.. lots of fun to drive and would be considered an easier car to drive real fast... the 935 , really good brakes, 2300 lbs..two bigger turbo's with a Kugleficher MFI and a titanium spool on 16" Goodyear bias plys.. much more difficult to drive fast but still damn fast if all you want to do is point and shoot... both cars are a scream to drive.
One thing consistent between the two.. after a session or a race you get out of the car with either a big smile on your face or an immediate need to change your undies

Good luck with your project.. it's very interesting !

RarlyL8 · RarlyL8's Garage

That S.Car.Go 911 is gorgeous. I have lusted after that specific car for years, after first seeing it for sale in the back of either AutoWeek or Excellence, can't remember now.

Meanwhile, back at the farm ......................

I mounted the turbos as close together as I could (rear) with the exhaust sides facing one another. VERY IMPRESSED with the results. Much more room now and with the turbos closer together the plumbing will be easier.

Problem - 993 heat exchangers are out of the question with this configuration. They interfere badly.

How bad would it be to use a set of pre-73 heat exchangers with the rear mounted turbos?
I have a set of (purists - do NOT read the next words) '73 2.4T MFI heat exchangers I can hack up or use as is if need be.

Now for something really diferent .................
I mounted the turbos on the sides of the engine. WOW! The shorty header to turbo connection could not be a shorter run. This design looks killer from a performance standpoint but a much more difficult plumbing excersize.

Problem - no heat possible due to such a short run.

We do a DE event in January at the Talledega GP track. I MUST HAVE HEAT.

Take a look:

RarlyL8 · RarlyL8's Garage

Flanges are being machined by a very generous Pelicanhead for the turbo and shorty headers.
As soon as I receive them we will continue. I plan to bolt up the turbos side-mount first and then take a look at my rear mount options. We just may be designing a set of custom heat exchangers for the rear mount application, I have nothing stock that will work other than pre-73 heat exchangers. The runners in those units are probably too long for use with turbos.

Stay tuned ........

mb911 · mb911's Garage

Quote:

Originally posted by RarlyL8
Flanges are being machined by a very generous Pelicanhead for the turbo and shorty headers.
As soon as I receive them we will continue. I plan to bolt up the turbos side-mount first and then take a look at my rear mount options. We just may be designing a set of custom heat exchangers for the rear mount application, I have nothing stock that will work other than pre-73 heat exchangers. The runners in those units are probably too long for use with turbos.

Stay tuned ........

Go to www.autosportengineering.com he is one of our customers and uses a special heat exchanger very similar to the 73 and earlier exchangers for a turbo application//

RarlyL8 · RarlyL8's Garage

Thanks Ben!
How well do those exchangers work for a 930? Is there a lag problem?

beepbeep · 09-27-2006, 04:54 AM

You don't want that on turbocharged engine. You want your headers short and stubby. Minimal gains you might get from equal length headers are all eatenn up and then some by all heat loss trough lengthy pipes. Turbo lives of temperature difference before/after and pulse energy.

Long headers will:
1. lower the EGT, thus decreasing temp delta over the turbine and flow
2. Iron out the pulses, letting turbine live off the flow alone.

Check out the 935 headers (real ones, not kitted-out DIY stuff), they are extremly short, free-flowing and lead directly into turbo. No equal length mumbo jumbo.

It would be nice with equal length if you can keep the pipes short...if you cannnot (for packaging reasons), go for stubby headers.

RarlyL8 · RarlyL8's Garage

That's what I thought.
Please define "short".

mb911 · mb911's Garage

Quote:

Originally posted by RarlyL8
Thanks Ben!
How well do those exchangers work for a 930? Is there a lag problem?

I can let to much out of the bag here as it was given in confidence but those work very well with specific turbos. There are several of those header set ups sitting waitng for final setup. and to clarify It is not my company nor any affilation

mb911 · mb911's Garage

oh and food for thought those are all 321 and notice how short they really are. you can get them and not do all the fancy stuff behind. With them being all stainless they do not transfer heat like a mild steel header would. they keep the heat in. Now I must say I know very little as compared to beepbeep so Take his advise over mine. I just know my kits and and metals. beepbeep has done some amazing stuff.

RarlyL8 · RarlyL8's Garage

I can see the above "short SSIs" as a tremendous advantage over stock US or even Euro 930 heat exchangers due to the extremely long runs those stock systems have.
My engine has the luxury of a wide open design field. We can adapt an existing set of short headers to the application or if needed make something from scratch. I'm just looking for the best design that has heat ducting capability.

dozer · dozer's Garage

Here is something for those cold days.
You DON'T need heat exangers

http://www.eberspaecher.com/servlet/PB/menu/1013434_l2/index.html

http://www.webasto.us/am/en/am_auto_heaters.html