I hear keeping the exhaust events in tact is one of the goals of a turbo exhaust. If that is the case, then some length to the equal length primary tubes might make for some benefit.

This is part of the reason a split scroll system works well. By matching up cylinders that exit the motor the events are more able to hit the turbine wheel in tact.


As copbait73 brought up, equal length also helps reduce the differences in residual pressure that will be present when the exhaust valve closes at each cylinder.

Seems even if we have some 20psi of pressure resident in the exhaust headers at full boost this dose not compare to the pressure and speed the gasses come out of each cylinder.

The pressure in the headers is going to appear in waves and with waves there are high pressure parts and low pressure parts.

If the exhaust valve closes during a high pressure part of the wave, less exhaust is going to exit. Low pressure, more will exit.

If this is the case, it dose not matter if each cylinder is getting exactly the same amount of fuel, there will be different levels of residual exhaust remaining in each cylinder and this will effect cylinder fill.

If so this could result in some cylinders running leaner than others and result will be seen with a variation in temperatures per cylinder.

Maybe we do not want to think of it as savaging like on a N/A motor but there seems to be something to this beyond letting the exhaust events just exit in a more orderly manner.

On a street motor where the duty level is modest this is probably not a bit deal. Under hight duty like in competition, it could become a very big deal.

The TT set up is very nice except the WG's coming back into the exhaust. That is not recommended and if has to be done should re-enter as far away from the turbo as possible. In this case just before the muffler.


For those that follow that are trying to decide between two or one I came across this from Garrett about single v double:



TurboByGarrett.com - FAQ's

FYI, I just measured a 930 J pipe. Thus:

1.5" primaries per Brian.
2" secondaries.
2.25" Y pipe to turbo.
K27/T3 flange 4 sq inch nominal, est. 3.5 sq inch actual.
T4 flange apx 6sq inch or est. 5.5 sq in actual.

These are nominal or OD sizes.

Here is how a stock system seems to play out:

The secondaries seem to have a ID cross section of about 1.8 times the primaries. As we have an exhaust event once every 240 deg per bank that is 1.5 exhaust events per revolution. An SC cam I believe keeps the exhaust valve open for about 220 deg. Thus, there is some reserve for exhaust expansion and collection at the secondary tube.

Then the two secondaries enter the Y or J pipe on a 930. The Y pipe is about 60% of the size of the two secondary tubes. Thus, gasses will have to be accelerated significantly as they enter the Y/J pipe.

The 2.5" Y pipe than supplies the K27/ T3 flange is mostly the same size at the turbo inlet so the velocity entering the turbo hot side dose not change.


On most after market 930 systems they seem to keep the primary to secondary ratio. However, the area of the two secondary tubes where they enter the turbo is much larger than the entry to the K27/T3 flange by close to 1.6 times. Thus, the gasses need to start accelerating before entering the turbo.


A couple of thoughts.

I wonder if we should be working from the turbo back and look at the changes in velocities?

On a stock 930 the Y/J pipe is going to see the highest velocities of any section of the headers and thus be the area that might be most likely to create back pressure. Doing something to retain the heat along that run might be something to consider as that would reduce back pressure to some degree. (wrap, coatings, larger tube?)

On most after market 930 systems the transition just before the turbo might be something to look at as gasses have to accelerate about 60% before they enter a K27 flange do to the cross section difference.

Putting a WG at that point is only going to add unnecessary turbulence and make the WG circuit unreliable. Moving the WG cricut away from the transition up into the turbo should make for an improvement.

A T4 turbine connected to two 2" secondaries moves most of any changes in velocity into the turbine housing as two 2" tubes have the cross section of about 1.1 times the hot inlet size. Seems like a good fit.

Running larger that stock 930 tubes to any turbo using a K27-7200 hot side (HF/K29 quick spool...) is probably not going make for much improvement as the turbine will probably not accept the increased flow potential anyway and WG sizing will probably become even more important. But that is just a guess.

Not an expert, just trying to figure this stuff out.

My 930 has very little Turbo lag. has special Muffler system and what turbo?

Can be seen here:

Cars For Sale - 1980 Porsche 930 EURO Turbo Coupe

Can't tell what 3K turbo is installed but probably a K27 7200 with a 964 support bracket, because that bracket doesn't look modified.

The exhaust headers with heat, and the intercooler are B&B with the single out muffler.

It looks like the crankshaft seal behind the flywheel is (still) leaking from all the oil all over the bottom of the bell housing.

On ebay:
Porsche : 911 : eBay Motors (item 280451069404 end time Jan-20-10 13:34:45 PST)

http://forums.pelicanparts.com/uploa...1264005418.jpg

How fun it that!

Fair comments re my headers. FWIW, I have tried dump-to-atmosphere vs plumbed-back WGs on a few cars and unless the exhaust system is undersized there isn't usually a large power difference. For my purposes I prefer the car to be a bit quieter @ WOT, hence the WGs dumping back into the exhaust stream.

Here is a photo of some iteration of 993 GT2 EVO race headers. They are large diameter, long tube and appear to be equal length. If I didn't mind driving around with ear plugs in I would do something similar on my car http://forums.pelicanparts.com/suppo...leys/devil.gif


http://forums.pelicanparts.com/uploa...1265257364.jpg

Yes, those are factory GT2 Evolution headers and they are gorgeous!

I do not think the primaries could be much shorter and accommodate a nice collector and waste-gate circuit.

Interesting how they carefully transition the WG's for efficient exiting.

I wonder--if we are expecting a substantial amount of exhaust gasses exiting the WG circut at WOT, if the same principles for reducing turbulence and promoting good flow should be extended to it to.

Usually the WG systems seems more like an after thought on most set up with us just sticking a 90 deg junction off the secondaries may or may not have an effect.

Could this offer some additional performance especially with the smaller turbine quick spool turbos that tax the WG even more.

Just a thought.

Any shorter and they wouldn't be equal length primaries. Equal length was considered important so here you have them.

The importance of flowing W/G has been recognized since the early 70s, mainly from work on Turbo Indy cars in the late 60s. I have a Crane Cams Turbo book from '75 showing it. This was made a science in the early to mid 80s with F1 Turbo motors. Also, running "spec" turbos CART champ car systems have beautiful header design with extra special attention to W/G flowing. You find very large piping off the secondary pipe going to equally large W/Gs.

As an aside, probably the best application of a W/G is 30degrees tangential on the turbine housing ported just upsteam of the volute throat. This was seen on many of the later F1 cars. Impossible to package on a 930 but interesting as best practice and you see the principle applied to the secondary pipes on the system above.

I learned something pretty cool today about WG's.

Thx!

Ok, back with some info from the first spring ride, track the car fairly often and I feel the 4-speed gearbox is the biggest setback with these cars on the track and a broader powerband was on the wishlist.. and I got it :)

(Euro exhaust figures above)


And with the stainless headers

0.5 bar at slightly under 2400 rpm
1.0 bar at 2700rpm

I was hoping for some improvement but this is almost unreal.. :eek: :)

Great info!

To be honest, I did not know changing from euros to shorties would make that much difference in boost response. Impressive.

That is about 400 to 500rpm sooner.

Puts .75 bar at about 2550rpm with a K27-7200 turbo.

What cams, intercooler, timing?

Any chance for a before and after dyno run?

My next set of headers, given the chance, will be Brian's new equal length headers for there quality, better efficiency and ability to make more HP. They are consistent with my goals and have several solid advantages over shorties that are important to me.

However, this thread is about equal v short headers and Zeb 930's info has given us a data point that can be used for comparison in place of a back to back.

Looking at the before and after Dyno for the equal length headers (ELH) over euro headers, it looks like the ELH made boost about 150rpm to 200rpm sooner compared to the shorties making boost about 400 to 500rpm sooner.

Equal Length dyno compassion before and after: http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/461519-latest-project-headers-14.html#post5195908

It also looks like peak (.75 bar) boost was reached at about 3100rpm with the ELH's compared to about 2600rpm. I do not think a comparison of boost points would be directly comparable or valid as they may be other factors that may create a variance (street v dyno; observation v dyno boost curve; and, possibly different cams). I just do not think there whould be 500rpm between ELH and shorties.

Thus, it looks like it might come down to the shorties making boost maybe 200 to 300 rpm sooner than the equal length but the equal length making more HP.

Me, I will take the quality and HP.

Standard cams, standard timing(29), powerhaus fullbay IC, no dyno figures unfortunately.

If I where to buy a set of new headers I would also go with brian's for sure, they are a work of art! (brian helped me with turbo tank, hose, connections and gaskets, thanks again)

Got these cheap from a friend about 2 years ago and thought i give them a try. And they worked way better than expected.. :)

(And not to forget it probably made the car 20-30 pounds lighter in the rear)

http://forums.pelicanparts.com/uploa...1270658788.jpg

http://forums.pelicanparts.com/uploa...1270658798.jpg

zeb930

Did you fabricate the fresh air box or buy it? If you bought it, where?

Thanks

Love the uncommon color of your car.

Keith,
The RPM graph was off on my dyno run by several hundred RPM. What I see from my car is a threshold reduction of ~500RPM over the Euro J-Pipe setup. This is with a K27-7200. Full boost is also ~500RPM sooner. I am getting a lot of client feedback now that supports what I am seeing. Beyond that you also see a very significant increase in off-boost torque that translates directly to driveability. You really need to drive it to fully appreciate the change. No dyno comparison will be necessary at that point.

100% homemade.. :) Found the ducts at the local hardware store, I knew the placing was good from the nato-Ruf BTR car.

Would have made a similar tube version as the Ruf if I had the room but my full-bay IC made me do a narrow version.

If you decide to do a fresh air intake remember to make a couple of small holes in the bottom of the airboxlid for water evac.. And a lid for the tube if you expect to park it in extremely heavy rain/ washing SmileWavy

http://forums.pelicanparts.com/uploa...1270690653.jpg

http://forums.pelicanparts.com/uploa...1270690683.jpg

Very similar to the one used on the Group B Turbo from the early 80s.

Check the "Group B info and picturs wanted" thread in this section.

Do you remember the original use for that duct? I can't recall seeing one before.

That would save me some upcoming work.

Thanks

zeb930,
Is that PVC ventilation ducting?