930 EFI Conversion in process

[gtu935]

Jim,

Keep it coming. Great work

[TurboBert]

Hi Jim,
Great shots of the intercooler, but wow, that's pretty hard core.

I am taking your lead with milling the intake adapter out of bakelite (or phenolic black) - using my home-made Harbor Freight CNC. I am going the megasquirt route using the 3.2 intake.

Since I don't have my 930 intake removed, can you tell me what the height is from the cylinder head surface to the engine shroud? I need to know what the lip thickness should be on the adapter to seal the shroud. I'm guessing 0.2 inches.

[Jim2]

Hmmm CNC... That's an excellent approch to doing this, easy to reproduce too. Nice talent comes out of the woodwork.

0.2" is good. For what it's worth I recall 0.19". They sealed against the shroud as good as you could get without puting too much pressure on it. On cyl 3 and 4 (best as I recall) I had to sand a small radius on the perimeter of the isolator because the shroud is a little closer to the port. See the area at 2:00 and 7:00 in this picture. Wait until you are installing them to do this.

Your isolator is bringing back memories!

[dyerkes]

Steve,

If you're willing I may be interested in buying a set of those intake adapter spacers. What port size are you going with on your heads?

Thanks,
David
1986 911 Turbo

[89turbocabmike]

Turbobert, how about a pic of your home-brewed CNC?

[ZLP]

Is is possible to use the carrera manifold with the stock 930 ports?

[hobieboy]

Jim,
Did you have a chance to dyno the car? Just curious about how much hp you are putting out now.

And, have you tried the 72lb injectors? What dutycycle do you see now?

I just got mine up & running and it looks like I'm seeing 100% duty on my 52lb injectors

[CabMike]

Turbobert:

Would you be willing to share your drawing for the adapters? I would like to have a set made by emachineshop.com.

Thanks,
Mike

[TurboBert]

Hopefully this doesn't subvert Jim's thread, but here's the cheapo CNC using a Harborfreight micromill.

I say cheapo, but it's still a little over $1K when you add the stepper motors, power supply, and controller board. An old PC (>500MHz) works fine.

Mike, yes, I'd be happy to provide the CNC code but I wouldn't trust it until I've actually fitted it to my 930 to verify the work. I am not doing this with full force like Jim, so it could take me several months to get to that point.



This i snot exactly my setup but here's some background references:

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=44991

http://www.xylotex.com/3AxSysKit.htm

[Jim2]

Hobbieboy, I want my intercooler done before I put the car on a dyno. Also it's winter here (sort of). I have the 72lb injectors but I have not swapped them in yet.

I'm not surprised you maxed out the 52lb injectors. My calcs said they would be marginal with no reserve duty cycle, that's why I picked up 72s. So much for my conservative approach to this whole thing. It's good to hear your car is up and running! Post up some details!

ZLP: The stock 930 ports are 32mm and the Carrera intake is 38mm. If you look close at Turboberts cad drawing you can see the two diameter references. (Luckily my own engine was ported to 38mm) Also the Carrera injector cutout has no overlap on top of the 930 port which will result in a vacuum leak. This is also shown on the CAD drawing.

Looks good Tubobert! I know someone who wanted to do the exact same thing with a small Rusnok mill of mine. I'll refer him to this thread.

[hobieboy]

[QUOTE]Originally posted by Jim2
[B]Hobbieboy, I want my intercooler done before I put the car on a dyno. Also it's winter here (sort of). I have the 72lb injectors but I have not swapped them in yet.

I'm not surprised you maxed out the 52lb injectors. My calcs said they would be marginal with no reserve duty cycle, that's why I picked up 72s. So much for my conservative approach to this whole thing. It's good to hear your car is up and running! Post up some details!
[QUOTE]
Same here - the white stuff will be keeping me out till probably April. But I was surprised by the injectors as another friend who did his "934" was running fine with same injectors for 3 years and the car was producing ~500hp.

Yeah - your thread inspired me to post something Will gather some pictures and share some details in a separate thread though mine is definitely not as innovative.

[Rob 930]

Jim2,

I believe that stock Carrera intakes have an outlet diameter of 40.5 mm, not 38 mm. All the sets I've measured have been 40.5 or 41 mm. This is confirmed by the drawing above by TurboBert. That makes for a pretty big step from the stock 32 mm ports, but I know of one person who did run Carrera intakes on 930 heads with stock ports.

Rob

[adomakin]

still waiting for that thread on your build rob.......!!

[TurboBert]

Rob,
The step down from 41mm to 32mm isn't really too bad when you see the final product.

My drawing shows it best, there is only a 4.5mm width annulus.

[Jim2]

Unrelated to the EFI topic, I recall oberserving the opening diameter of my stock 1979 intake manifold where it mates up to the isolator was much smaller than the isolator diameter. I never measured my intake manifold before I sold it, but I would be curious to know what size it was. Anyone have a stock 930 intake handy?

Jim

[ZLP]

Originally posted by Rob 930
Jim2,

I believe that stock Carrera intakes have an outlet diameter of 40.5 mm, not 38 mm. All the sets I've measured have been 40.5 or 41 mm. This is confirmed by the drawing above by TurboBert. That makes for a pretty big step from the stock 32 mm ports, but I know of one person who did run Carrera intakes on 930 heads with stock ports.

Rob

Were there any problems?

[Rob 930]

ZLP and TurboBert,

There's been lots of debate over the years about this issue of how much of a step in the intake is too much. I'm not the expert in this, but frankly, I don't know anyone who is -- and I've talked to some top engine builders and head specialists around the country about this very question. I got answers that were contradictory -- some thought it would be a problem, others said it could be "programmed around."

The fellow who put Carrera manifolds onto stock heads ("Dean" on Pelican) does not think it caused problems, but he wasn't sure. He did a DTA EFI conversion on an otherwise stock motor. He experienced some tuning problems -- particularly a hesitation during throttle application. He eventually pulled the manifolds and match ported the heads. But if I recall correctly, the problem persisted, even after he match ported the heads. I think he's since gotten rid of the hesitation through tuning. So, the logical conclusion would be that the hesitation problem he experienced was unrelated to the step in the intake. Of course there may have been other negative consequences from that step that he never discovered or identified. But even if a step causes no apparent runability problem, it almost certainly will cost you some flow --and hence some horsepower. The question is, how much will it cost you and do you care about that loss?

I looked into this question myself when I did my EFI conversion because I didn't want to disassemble my engine and pull the heads, which had just been built with 36 mm ports for CIS. I eventually did pull it apart and match port it, just because I was uncomfortable with the prospect of a possible loss from leaving the step there (and I had 36 mm ports, which were already larger than the 32 mm stock ports). While I was at it, I had an extensive amount of additional head and port work done in addition to match porting, so I'm retrospectively glad to have gone back inside it.

One head specialist told me that you don't want transitions in the intake tract, near the ports, that have an included angle of greater than 7 degrees. Hence, to make insulater blocks that properly taper at a 7 degree angle requires some very tall blocks that might be expensive to make and would elevate the manifold too high to fit a decent-sized IC under the wing. The insulator blocks made by TurboBert look very nice, but they have a taper angle of 34 degrees if I'm reading it right. That's too large to be optimum, according to what little I know. But how great are the consequences for this? I don't know...

[TurboBert]

Rob,
Good points. If I did my math right, the angle of incidence is 19.5 degrees for an isolator thickness of 0.5 inches.

To get to a 7 degree angle, the thickness would need to be 1.45" (37mm)



Jim,
I agree with you, the 930 intake must be much smaller than the 930 intake gasket. Here are some superimposed images of the 930 and Carrerr 3.2 gaskets. [note these diagrams are different than from my previous thread, as I increased the isolator wiodth to 0.6 inches]

[Rob 930]

TurboBert,

Sorry. Your math above looks right -- at 19.5 degrees. I didn't do the trig; I just looked at your first diagram, which showed 56 degrees for the slope of the green line, from which I took the complement to get 34 degrees. But looking more closely at it, I now see that the green line is the angle of the cutout for the injector! The blue line is the line of interest. So your numbers look right.

Even with correct math, as you found, to maintain a 7 degree angle, the height of the insulator block would have to be about 1.5 inches. For my application, that's probably about an inch too high -- my IC clears the underside of my tail by about 1/4 inch. Things are really tight in there. After match porting, I used the factory Carrera insulator blocks, which were about 5/16 in thick, and custom matched them to each port, since there were minor variations. I also used the factory Carrera intake studs and barrel nuts, which was convenient. By the way, I did this with 930 heads -- not Carrera heads.

[dean]

Originally posted by Rob 930
ZLP and TurboBert,



The fellow who put Carrera manifolds onto stock heads ("Dean" on Pelican) does not think it caused problems, but he wasn't sure. He did a DTA EFI conversion on an otherwise stock motor. He experienced some tuning problems -- particularly a hesitation during throttle application. He eventually pulled the manifolds and match ported the heads. But if I recall correctly, the problem persisted, even after he match ported the heads. I think he's since gotten rid of the hesitation through tuning. So, the logical conclusion would be that the hesitation problem he experienced was unrelated to the step in the intake. Of course there may have been other negative consequences from that step that he never discovered or identified. But even if a step causes no apparent runability problem, it almost certainly will cost you some flow --and hence some horsepower. The question is, how much will it cost you and do you care about that loss?

Wow Rob, well written. I think you should do all my writing

I still have a hesitation even after port matching. I think it is a tuning problem that I haven't figured out yet.