Individual Runners
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From: Enumclaw WA
Individual Runners
Has anyone tried using individual throttle bodies, or carbs on a 928 V8? It seems that with the 16v motors anyway, that a lot of people complain about the stock intake manifold being restrictive. Individual runners don't seem like that complicated of a project. Just toss the old intake manifold. Make eight mounts for the carbs or TB's. Mount the TB's and injectors, or carbs, hook up a throttle cable, hope the car starts, and done! LOL, well not really, then there are the details, which is why I started the topic. I would think the main problem would be the stock computer, I mean what would the stock computer think about just not having any injectors, intake sensors, etc, there anymore? I have seen this mod done somewhere on the net on a 32V 928 track car. I think he used a MoTec Comp system with his TB set-up.
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From: Portland, Oregon
Well, you could go with 4 carbs(2per cyl), but you still have to tune them. I would think this would be too high a maintenace issue to perform on a regular basis. Mikuni or Weber are not street legal in some states as far as I know...definately not in Cali.
Do you really want to go out and tune 8 carbs frequently? Talk about high performance finicky needy engines...
THE EFI brain would be worthless at this point.
I know of one guy who had this idea for his track car. Not sure if he completed his project yet, but maybe he will speak up.
Do you really want to go out and tune 8 carbs frequently? Talk about high performance finicky needy engines...
THE EFI brain would be worthless at this point.
I know of one guy who had this idea for his track car. Not sure if he completed his project yet, but maybe he will speak up.
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From: Enumclaw WA
I don't mind the maintence issue. I have a street bike that has 4 carbs. 1 per cyclinder, not finicky at all. I would think that only the intial tunning of the carbs would be a hassle. As far as the street legal issues, in the part of the state I live in, we don't even have emissions, so the car could pollute away. As for the stock EFI brain, would it fire the ignition still? Or is it not even tied into the ignition on earlier cars?
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From: Ventura California, where the girls are so fine.
I believe on the 78 and 79 motors this could be do able. I dont know about taking my fuel injected motor and reverting back to a carb. There would definately be less parts to trouble shoot if you are having problems.
I would simply have a intake manifold made that would fit one holley 700 or 750cfm carburator. The hard part (and expensive) would be finding someone to build you a manifold. My car doesnt have a fuel computer so that is no problem. If someone had a manifold already fab'd I would be willing to give it a try. I believe a carburated 928 would make more horsepower. Let me back that up by saying the early cars 78 and 79. I wouldnt touch the later cars.
I would simply have a intake manifold made that would fit one holley 700 or 750cfm carburator. The hard part (and expensive) would be finding someone to build you a manifold. My car doesnt have a fuel computer so that is no problem. If someone had a manifold already fab'd I would be willing to give it a try. I believe a carburated 928 would make more horsepower. Let me back that up by saying the early cars 78 and 79. I wouldnt touch the later cars.
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How about machining a replacement for the plenum and single throttle body on the 16v cars, with individual butterflys/idle bypass port for each runner?
The rest of the FI system would be retained.
Could a big brain step in here and explain the large improvement in power with individual TB's?
The rest of the FI system would be retained.
Could a big brain step in here and explain the large improvement in power with individual TB's?
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From: Enumclaw WA
I know that Individual Carbs, or TB's are used on about 99.9% of the new bikes and 100% on high performance bikes. There has to be some reason for this. Unlike cars, they are not choked by emission laws. And nobody cares about mpg with them. Though most have single airbox/filter. Just adding that in there.
I know that individual runners are loud, more than likely MUCH too loud to be put on any car from the factory.
I know that individual runners are loud, more than likely MUCH too loud to be put on any car from the factory.
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From: Portland, Oregon
Since you are nixxing the injectors, I believe the whole fuel management thing needs to be nixxed. Nothing will make sense anymore.
Basically you have high fuel pressure lines running to each carb...you are back to mechanical.
You would have to figure out what to do with certain sensors though.
I guess there would be the possibility for more hp, but that was certainly not Porsches intention. Remember, the whole EFI thing is more for long term reliability and less F'ing with mixtures. Most carburated engines need tuning of sorts at least once a year...if your lucky. We're talking about the family car engines here.
I expect that Porsche figured a doctor (or dentists wife) would not be wrenching under the hood anytime soon...they would prefer to get in the car, turn the key and go....part of that whole costly luxury thing....guess thats why someone invented the electric starter too! <img border="0" title="" alt="[Wink]" src="wink.gif" />
Most cars (if not all) now-a-days are EFI...figure it out.
Go for it! I am sure it will be a fun project. Just remember this also, you are going to need more than just carbs to breathe some more harumph into the engine.
Basically you have high fuel pressure lines running to each carb...you are back to mechanical.
You would have to figure out what to do with certain sensors though.
I guess there would be the possibility for more hp, but that was certainly not Porsches intention. Remember, the whole EFI thing is more for long term reliability and less F'ing with mixtures. Most carburated engines need tuning of sorts at least once a year...if your lucky. We're talking about the family car engines here.
I expect that Porsche figured a doctor (or dentists wife) would not be wrenching under the hood anytime soon...they would prefer to get in the car, turn the key and go....part of that whole costly luxury thing....guess thats why someone invented the electric starter too! <img border="0" title="" alt="[Wink]" src="wink.gif" />
Most cars (if not all) now-a-days are EFI...figure it out.
Go for it! I am sure it will be a fun project. Just remember this also, you are going to need more than just carbs to breathe some more harumph into the engine.
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From: South Texas
If you'd do so, your nixx the whole point behind the multi port fuel injection.
If Porsche just wanted reliability, they would have went to a TBI. One injector, traditional carb intake manafolds. Fewer parts, and the parts you do have are easier to build. What is there to lose?
Nearly all the new preformance engines out there have some sort of multi point fuel injection. Why? A realy wounderful example is Chevy's Vortec system.
To understand why you have to understand the limitations of carbs. To use a single carb, the plumbing between the cylinder intakes and the carb must be as short, and strait, as possible. This is because the fuel doesn't like to be mixed in the air. It trys to fall out, given a chance.
A multi point fuel injection system places the fuel injectos right infrount of the cylinder intake. This allows the plumbing to the cylinder to be any shape, lenght, or curve, the designers want. This allows them to resonance tune the intake, basicly the intake version of exaust headers. This is a good thing! It adds mid range torque, and might even help at the top end.
Unless Porsche was stupid, they tuned the US intake to SOMETHING. What I'm afraid is they tuned it to a US 79 4.5l engine, or almost as bad a 80 US motor.
If you want to improve on the stock design, I'd say try to build something like the S4's got. That would be sweet.
If Porsche just wanted reliability, they would have went to a TBI. One injector, traditional carb intake manafolds. Fewer parts, and the parts you do have are easier to build. What is there to lose?
Nearly all the new preformance engines out there have some sort of multi point fuel injection. Why? A realy wounderful example is Chevy's Vortec system.
To understand why you have to understand the limitations of carbs. To use a single carb, the plumbing between the cylinder intakes and the carb must be as short, and strait, as possible. This is because the fuel doesn't like to be mixed in the air. It trys to fall out, given a chance.
A multi point fuel injection system places the fuel injectos right infrount of the cylinder intake. This allows the plumbing to the cylinder to be any shape, lenght, or curve, the designers want. This allows them to resonance tune the intake, basicly the intake version of exaust headers. This is a good thing! It adds mid range torque, and might even help at the top end.
Unless Porsche was stupid, they tuned the US intake to SOMETHING. What I'm afraid is they tuned it to a US 79 4.5l engine, or almost as bad a 80 US motor.
If you want to improve on the stock design, I'd say try to build something like the S4's got. That would be sweet.
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From: Enumclaw WA
Whats with this carb vs. F.I. debate? lol.
I never said I wanted one giant 4 barrel sitting on top of the motor a la Chevy carb everyone. I was interested in sticking one single barrel carb OR TB right above the EACH intake port. I highly doubt that a OEM set-up can suck more air through it's ONE TB then could a Fuel Injection system with 8 TB's. Each TB resting right above the intake port. OR carbs for that matter. Though the intake manifolds on these engine are stunning to look at when polished, well made, etc., I still think that they are choking what could be a free breathing V8. I'm talking about the 16V's, not 32V motors.
As a end note,a much easier solution to getting more air in their might be just to get one massive single TB and still keep that 'spider' intake. Anyone know the diameter of the stock 16V TB? But then you still have the runners diameter being the same...
I never said I wanted one giant 4 barrel sitting on top of the motor a la Chevy carb everyone. I was interested in sticking one single barrel carb OR TB right above the EACH intake port. I highly doubt that a OEM set-up can suck more air through it's ONE TB then could a Fuel Injection system with 8 TB's. Each TB resting right above the intake port. OR carbs for that matter. Though the intake manifolds on these engine are stunning to look at when polished, well made, etc., I still think that they are choking what could be a free breathing V8. I'm talking about the 16V's, not 32V motors.
As a end note,a much easier solution to getting more air in their might be just to get one massive single TB and still keep that 'spider' intake. Anyone know the diameter of the stock 16V TB? But then you still have the runners diameter being the same...
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From: Florida
What's all this talk about running carbs. You can run six individual electronically injected throttle bodies with a good engine management system much like the Kelly Moss set-up. Check-out <a href="http://www.clewett.com" target="_blank">www.clewett.com</a> and click on catalog and then click throttle bodies.
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From: Enumclaw WA
That's one big TB that comes on their stock. I wonder if the US 16v's have the same size TB? For size comparison a 4 Cyclinder I use owned had a 55mm TB. I ended up switching to a 70mm with a sheet metal intake manifold, and that car did seem faster. This race shop that I use to frequent up here was building a Twin-Turbo V6 Drag car that used a 80mm. That car was prolly pushin at least 600 ponies to the rear wheels. So I doubt that the stock 80mm TB would be limiting for even a 300hp Euro. I'm pretty sure that 80mm is the biggest TB the aftermarket makes for any car. So I think that if there is a restriction in the intake system, it has to be the runners. Someone could go crazy trying to best Porsche in engineering though.
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From: Ft. Lauderdale FLORIDA
Incidently....
The very first M28 engine ever run ran with a four barrel Rochester Quadra-Jet. For about 5 minutes before the engine block cracked and coolant sprayed everywhere...
January 16, 1973 was indeed an ignominius day for Porsche's new program. While glycol was happily spraying around a room in Stuttgart, I was in Ms. McCarthy's first grade class at Park Lane Elementary School in Grosse Ile, Michigan, trying to learn to read.
Believe me; the engineers in Stuttgart were having more fun-
Well, I read fine now. And Porsche designed and fitted for production Bosch's K-Jetronic fuel injection system [which was the state of the art at the time, and since Porsche did not want to develop their own or use an injection system from another country...K was installed]. FI gives better fuel distribution, better response, higher power due to the "dry" manifold, and drastically better emmisions and fuel economy. It is simply better control-
-I actually saw a street rod [I think it was some sort of correct-me-if-I'm-wrong '29 Ford Model A coupe] with a two valve M28 with Weber carbs at a car show in Michigan in 1986. The guy who owned it found the engine in a junkyard and just wanted something different. He told me he had hell getting the thing to run right with the Weber carb setup that he installed- the jetting was way sensitive.
Stick with your K or L or LH Jetronic....
Normy!
'85 S2 5 Speed
The very first M28 engine ever run ran with a four barrel Rochester Quadra-Jet. For about 5 minutes before the engine block cracked and coolant sprayed everywhere...
January 16, 1973 was indeed an ignominius day for Porsche's new program. While glycol was happily spraying around a room in Stuttgart, I was in Ms. McCarthy's first grade class at Park Lane Elementary School in Grosse Ile, Michigan, trying to learn to read.
Believe me; the engineers in Stuttgart were having more fun-
Well, I read fine now. And Porsche designed and fitted for production Bosch's K-Jetronic fuel injection system [which was the state of the art at the time, and since Porsche did not want to develop their own or use an injection system from another country...K was installed]. FI gives better fuel distribution, better response, higher power due to the "dry" manifold, and drastically better emmisions and fuel economy. It is simply better control-
-I actually saw a street rod [I think it was some sort of correct-me-if-I'm-wrong '29 Ford Model A coupe] with a two valve M28 with Weber carbs at a car show in Michigan in 1986. The guy who owned it found the engine in a junkyard and just wanted something different. He told me he had hell getting the thing to run right with the Weber carb setup that he installed- the jetting was way sensitive.
Stick with your K or L or LH Jetronic....
Normy!
'85 S2 5 Speed