Greg

Re the dry sump, i got this reply from pace

The question of venting is a much debated subject. It is usually down to engine builders discretion. However in tests we have found that running a vacuum does not have a positive effect until the RPM is above 9000. I do not have any details specific to this installation. It does depend on the engine and its characteristics.

I take from this the pace 928 system does not pull much vacum

 

Stuart don't want to take this thread too long off topic but on the site Hotrod and the forum Speedtalk there seems to be quite a lot of evidence to the contrary. Contrary at least in terms of big american iron, maybe it is different with smaller 4 cylinders? I have no idea except for the fact that I will go the high vacuum route with an auto verdi pump when funds permit. The pump I sold was in brilliant order like new and sold for a 1/4 of new price, it was state of the art about 5 to 7 years ago but a bit heavy when compared the Verdi. The better or optioned Verdi only weigh 4 kgs for a 6 stage pump.

Are you going to make headers yourself Stuart? You should have a go, as I found it really interesting and fun last time, just take it slowly and do what you need to do to get your skill levels to where they need to be. There is a guy in Oz that said he wanted to send my stainless headers to Taiwan to be duplicated, he wasn't sure of the market, they would only do polished stainless, I would guess going from his other Porsche header prices he would be in the $2000 to $2500 AUD range depending on the level of pre orders. I couldn't sell a set of flange plates for $50, had to throw them out, so I can understand his reluctance


In case you do go down the DIY route my tube was made by these guys

http://www.goodfabs.com/Default.aspx

and I don't know if they are close to you. I found them quite helpful. They have standard stainless too remember stainless is a better material for headers especially I feel in an engine bay as cramped as the 928. I don't buy it that it helps power.

I also coated my stainless headers and X pipe purely again to stop the engine bay heat, I think I am successful on that issue. I still have to ask a price about 3" inconel at least this time around I can order pre bent bends to exact degrees without have to put a weld on them. That should be very handy, the first time is always the hardest.

Greg

 

The inconel pipe makes a very distinct sound when welded, a groaning creaking noise. Anyway good penetration was achieved and the little blobs you see are just tacks. They are required as the pipe will distort when being welded. It has to be perfect otherwise you will blow a hole. The factory headers also have these tacks, maybe grind them down? The weld width is 2 to 3 mm.

Greg

 

That's good tig.

 

Just an observation - I don't really recognize that weld, the way I was taught you would always see the row of circles if no filler used and the row of nickles if filler was used. IOW always the circular motion to keep the pool constant and moving forward.

This looks very different almost machine like.

Grinding the spot welds could open up holes, depends on wall thickness I guess.

 

Don't forget with inconel you really need to bake the finished piece.
Iirc it is around 400C for 1.5 hours.

Interesting looking welds.

 

"Well looking at Phil's headers, the one thing I notice that is completely different to my design is the length of the primaries, mine are between 530 mm and 570 mm around 22" and normally these are around 20" for a Nascar engine but their revs are a bit higher in terms of peak revs but a lot higher on average rpms."

Well, yeah - 9800 RPM is just a bit higher than most 928 engines turn.

 

Wally you're on the money my primaries are around 530 to 570 except for one cylinder which had to be another 20 mm longer but it is very straight. Goodfabs who made the headers in my avatar and which is what I cut up. Their primaries tend to be longer than the 20" which btw is exactly where companies like Burns Stainless come out with their headers. There could be many ways to the same result btw.

Burns is of course highly respected and Goodfabs has been an F1 fabricator for many years and brought F1 technology to Nascar in the form of the material and the stepped design ala F1. The Goodfabs primaries were from 20" to 22" Mine are 21" to 23" but I will not operate at those high revs, or certainly not for long periods. Max revs 8,000 piston limited with the piston design I have.

I am also told that the tri-ys are tuned with the secondaries and are very sensitive to this.

Colin I suspect this baking may be stress relief? Because the noise this stuff make is quite odd. The F1 fabricators I have heard on Youtube and tv talk a lot about creep. That would make some sense however wouldn't putting it on the engine do the same?

Greg

 

TV I investigated this weld
Greg

 

Wow, those headers are a work of art / excellent welding too.

.02 about stepped headers: there is no dyno evidence that stepped headers increase horsepower... just sayin

also not that this pertains to 928s but here is a link to my recent header fabrication page:

http://ubercooper2000.blogspot.com/2...-horrible.html

 

I think I posted this suggestion somewhere else, but if you are having heat problems, or you are blowing holes in a piece, you can clamp copper plates right next to the welded area. The copper will eat a lot of the heat and prevent consecration (get it, making something holey? haha!)

 

Thomas, not blowing holes, just I think too hot, the weld is not fully burnt but it only has half that bluey purple color you should get. So that is the 20 to 25% too much power.
Greg

 

Copper is super soft. If you have a flat plate, just set it over a spare length of pipe and whack it with a hammer. It will deform to shape. I've never tried it, but what might also work is diamond thermal paste like they use for heat sinks in computers. There's some stuff called arctic silver, or if you don't want to pop for it, get some vaseline and some industrial grade diamond dust, mix the two, and apply. I think I found something online about the appropriate ratio. This would be a low-cost alternative that might be super-effective at contacting the copper plate to the workpiece. Just my $0.02

 

I'm amazed! nice work.

 

By Ubercooper
In regard to power, I will keep to the facts as I know them and I am conservative in my claims. Stepped headers came from F1, they are used to increase power over the engine's power range. That is tuned power range. That range is bigger with stepped headers. I will agree if this is your statement but I will also say I am not sure if it is correct. If you state that peak power is not increased that may be the case if the non stepped headers are tuned to run in say the last 500 rpm. Then they may get the same power.

However the stepped header will be better everywhere else. Also do you realize that every Nascar team uses stepped headers? There will be a reason for that. These particular headers came off a Gibbs Nascar engine and as you may well know they have some of the best resources available to them. A nascar engine will normally be in the $75,000 to 90,000 range these days and lots and lots of testing is done. To give you an example, ECR tried to DLC the crankshafts but only got an extra 1 to 2 hp. It was not worth the risk so it was abandoned. There is not normally anything on a Nascar engine that has not been proven to be worth its cost or risk.

Another example was Nicasil, again ECR tried using this but against the standard iron bore they could not find a power advantage. It did have a slight wear advantage but in a racing environment it didn't make enough difference to use it, they then allocate the money elsewhere. So to put this in perspective, these headers cost $8,000 each in job lots of 10. They IMHO are spending that cash for a reason, they are getting a return for it.

The headers are also tri-y in design which is a proven design in terms of power. That is again they have broader torque and the best ones like these will also beat out 4 into 1 in terms of top end power. The top teams switched from 4 to 1 at the turn of the century and if you think about they make a lot of sense.

I hope they really help broaden out the power and make the engine easy to drive. One thing I can tell you about 4 to 1 headers given you have experience in making them and well done BTW is that the better headers pulse in a rotating order. That is they fire like a gattling gun. That was a Nascar trick discovered just before they went to tri-ys I am told.

Greg