Now for something completely different Part 1
 

The long term goal..Holley carb on a '83 SC, type 2300 2 BBL. 350 CFM, manual choke.
Why? Simplicity, cost, performance.
1. I'm a good fab guy.
2. Very easy to adjust for A/F ratio. Lots of parts to customize the Holley.
3. Will prove out the system set up before going to Holley Sniper EFI system.
4. I have experience going this route on V8s but using larger CFM carbs.
The CFM numbers I have found here show the 3.0 have a max build out flow of 329 CFM so I am in the right size for the small 2300 carb.
The Problem, the long runners are good for torque but bad for fuel fall out. The heads have the injector well tear drop design to force fall out to cool the back side of the intake valve.. Ford used the same head design starting in '96 because cooling the valve was more important than atomizing the fuel, 6 pintle Bosche injectors be damned, just make funny shaped chambers and pistons to remix fuel in the cylinders. Ford used an intake valve seat of .080 wide to dump the heat. I have a set of SC big valve heads and Porsche uses a .040 seat width which is good for performance but bad for dumping heat so the tear drop injector dump design in the head runner on the long side radius.
Here is a solution I have used that I got from Chrysler big blocks, big cams ran poorly on the street so they made intake gasket sets the had window screen in-between 2 gaskets, the problem was that the screens worked great but cut down CFM because the screen created 25% blockage. When you got to the drag strip a quick change out to a regular open gasket and back to max flow.
The SC head needs a 3mm flare expansion at the end of the runner and at the beginning of the head to compensate for the 25% reduction from a screen to get the fuel back to a "fog" before entering the cylinder which has been the down fall of the central single carb set up. I have checked with 2 tier 1 builders one of which has done it back in the day and the result was high torque but rough drivability because of fuel drop out.
Flame on gents..

David Vizard shows use of fuel ramps in the region of the valve stem boss/ just upstream of the throat to control atomization. Given your >90 deg turn from intake plenum to valve, a ramp at the start of the turn may encourage fuel to jump from the bottom of the runner into the air stream, toward the opposite (long) wall.

Design of the plenum under the carb, specifically the blend from plenum floor to intake runner floor, should prevent fuel drop out and puddling.

I bet it works great. Intake runners are longer but not that much longer than in carbureted v8 hot rods.



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Is there a standard/known ratio as to how long intake manifold runners can be for use with a carb, maybe that also takes into account the I.D. of the runners? Also, what’s been done before when others installed American carbs on 911 engines?

Best, John

I do not know about a Known Ratio for runner length, but Mopar used the Cross Ram intake on the 413 CID V8 and had 34" long runners from the 2 carbs to the opposite bank of the engine in a large criss cross I will try to find a pic, it worked quite well but was too expensive to make and weighed a lot.
The old Pcar set up with the Holley were using 4 barrel 5600 types, and the smallest ones are still too big CFM wise. People over carb frequently and with a manual transmission carb CFM must be matched to engine flow closely. A 5000$ carb set up on a 911 is nice but do you really need 45mm bores for 8000RPM use when your there for mere milliseconds before shifting? What are you doing? Drag Racing? Driving around at 180MPH? Buy a Cup car it is cheaper.

[IMG]http:/https://photos.smugmug.com/Porsche/i-Q4gnrDM/0/f13f421b/D/iu-1-D.jpg[/IMG]http://forums.pelicanparts.com/uploa...1613341567.jpg

Mixed76, the cut in at the valve guide boss is call an "eyelash" cut and is a big deal in Ford custom heads by Trick Flow Heads. And I plan to use them too..that was going to be Part 2. I will dig through my Ford head pics and see...

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Pic 1 is the Trick Flow Head, notice the long taper "wineglass" guides and "eyelash" cuts
Pic 2 is the chamber side of the TFH.
3 is a stock Ford truck head I ported with the same injector well that the 911 has, this one has been cut out extensively.

Would be cool to see some dyno run comparisons of Webers vs a properly tuned Holley setup

The end point of the dyno runs should be close with the long runner Holley having more torque down low and the Webber better on the top end.

http://forums.pelicanparts.com/uploa...1613407754.JPG
This shows the "shiny spot"on the intake port in the injector well, this is where the fuel is actually hitting. All the Techron or Seafoam is not going to clean up the intake runners if the fuel doesn't contact it. Dirty Ford heads look just the same with a clean spot and the rear is filthy. I have had long battles about fuel atomization and the proof is in the shiny spots. You might as well jut squirt in the fuel in a stream because a 6 pintil injector "fog" is being aimed at the side wall to roll down the long side radius to drop onto the intake valve to cool it. The mixing takes place in the cylinder with "tumble port or "swirl port" designs which is why the pistons are funny shaped.

Yes..
No?
or Old Fart you are so full of ...

bad idea

poor cold weather starts & worse performance all the time

but have fun

I used to build Holley race carbs for a bunch of people. Pretty good results. Had a daily driven street Vega that was in the low 12s. Cold weather starting wasn't an issue. (manual choke and used the "below 0° give it a pump of gas and count to 10 before cranking to let the gas atomize" method) Obviously it worked really good to do 12s thru the mufflers. (even delivered pizzas for a while in that monster) ...

... That is, it worked good until I added real road racing springs, sway bars, brakes, and rubber. The Holley fuel bowls can't control the fuel under very high G cornering and braking forces. You can add plastic vent baffles which help a little. You can run a hose from one float vent to the other (slit in the middle to provide venting) to keep from sloshing directly into the venturies. You can solder extension tubes to the jets so they pick up in the middle of the float bowl and that will help a little. And they sell foam floats that are trimmed to help control fuel level during cornering. Quite a stack of bandaids but in the end nothing will totally solve the issues of truly high G forces.
If you look at any traditional "performance" intake manifold you will see they mount the carb tilted forward to help counteract acceleration Gs (which are the lowest ultimate G forces on a car). Under truly hard braking the front float bowl will tend to over fill and you will see slosh either into the venturies or from the rear bowl to the front bowl.

When real cornering is added the problems get worse. The car would stumble for a couple hundred yards coming out of a corner until it cleared the flooded cylinders. If you look at applications where Holleys are successfully used you'll see it is drag racing, muscle cars (that don't come near Porsche levels of lateral Gs), and circle track racing where you can compensate for lateral Gs that are only in left hand turns.

Feel free to try it instead of any number of much more successful solutions. (Even Holley figured out that a generic EFI solution works much better and when you add in the costs of "screwing with it to try and get it to work" the EFI is much cheaper.)

Now that is useful information..I am going to do it to prove out the set up and go to the Sniper EFI 2 BBL.

Ive threatened to try this with the modern 4bbl style efi setups... self learning, easy wiring..worth a try and cheap enough to do as an experiment.

Thank you for all the replays, I am not worried about high G forces anymore.. tore my left retina last July, doctors made me sell my Mustang race car, VW R32, dirt bikes, no more jet skies or any of the stupid stuff I do, plus I'm 65 now and recovery from road racing takes me 3 days. So that is how I got the 911, I started out at the local Porsche dealer-HBL Tysons Corner in VA. after the military in 1980 rebuilding burned up 911s, I was the in shop expert at the time on CIS systems and loved my job but the management was bad but I made a ton of money for a kid but wanted to kick the dog when I got home everyday. I do custom head work, mostly welding, fixing stuff the machine shops will not do but I have been out of work for 16 months now from Covid and my Miller Syncrowave 351 is on EBay. So I found a trashed 911 with no rust cheap and it is the latest restoration toy.
And for SpeedMetal they make the systems in 2 BBL also where the port velocity is going to be higher. and that makes for great starting.. sounds like a F1, they are good to 300HP.

It is your car, and your money. Go for it and have fun and good luck.

I have been around Porsches for 44 years. In all that time I have yet to see in person a 914 or a 911 that was fuel injected converted to carbs and run properly except at wide open throttle. Bad idle, rich low speed and fuel starvation in corners. I suspect someone out there has made the conversion work, but I have never seen it.

Well I agree..same for a big block Mopar. But EFI with all the adjustments the world still has a lot of problems otherwise there would not be so many tuners straighting out cars. To say a car is best from any factory is leaving 15% on the table from every maker. And if you go the NTSB web site you can look up what series tune your car is up to and it's not the one it came with. I am the guy that will try anything, I am very gullible and from that I have a ton of experience and dyno time, good and bad, and partly from I do not care about money. I know CIS and it works well in a very narrow range just like EFI works great in a +- 5% range, is all it can adjust to, out side of that and it is off to the
tuner. I know carbs and CIS, for EFI all I can do is data log and go to the tuner for a new tune and try again. After I get it right I look at how many tune adjustments $$ and dyno time $$$ and wow nothing is easy.
The price to keep a 40 year old CIS up to snuff is way out of line now. Switching to an '84 EFI is antique now. I have a good running CIS now but add a modern A/F meter to ether one and watch
what happens. Home adjustable types are the right way to max power and no more burned up parts.
I love your El Camino, what color is it?

Sacrilegious Blaspheme..http://forums.pelicanparts.com/uploa...1616432244.JPG
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Will be fun to see how this works out.