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Thread: 3.0 MFI Port Size Advice Needed

  1. #1
    Senior Member Neunelfer's Avatar
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    3.0 MFI Port Size Advice Needed

    Hi Gang,

    I'm currently building a 930/07 (80 SC 3.0) into an MFI engine for my RS clone project. I'm looking for advice on port sizes for a 3.0 engine. The 2.7 and the 3.0 used the same MFI space cam but I'm still unsure of the port size. 38mm? Larger? It will have S-cams, 9.5:1 compression and SSI's feeding a sport exhaust.

    I need to send the heads and throttle bodies (stacks too) off soon so any advice would be appreciated.

    Thanks!
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    Eric - Sandy, Utah
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  2. #2
    Goldmember ttweed's Avatar
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    Re: 3.0 MFI Port Size Advice Needed

    Originally posted by Neunelfer
    I'm still unsure of the port size. 38mm? Larger?
    According to B.A.'s book, the 3.0 MFI motor for the SC RS had 43mm ports. That was with 10.3:1 compression and open exhaust. You could probably go smaller.

    TT
    Tom Tweed
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  3. #3
    Senior Member Neunelfer's Avatar
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    Hmmmm Sounds Like a Type 930/18...

    Thanks for the reply TT,

    With both the port size and the compression it sounds like you're talking about a different motor then what I was after.

    I'm looking for info on a type 911/77 which was the 3.0 in the 74 RS. The SC RS motor used a different MFI system (Kugelfischer I believe). The 73-74 3.0 RS motor used the Bosch, it even had the same 2.7 space cam. Ironically, it's the only motor on Bruce's chart that doesn't give port dimensions.

    Your thoughts?
    Eric - Sandy, Utah
    71 911
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    914-6/ORV
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    Porsche Truck
    62 Beetle
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  4. #4
    I had the rare opportunity to veiw one of the 50 or so 911/77 engines when it was disassembled for a pulled head stud. The motor was just a continuation of all to the previous S motors. Just like the 2.7 is nothing more than a 90mm version of the 2,4 the 3.0 is just as the 2.7 just a larger bore. Thats right, 36mm intake and 35mm ports, with the exception of large valves, 36mm lower half throttle valve housings with 38mm butterflys, and standard plastic 2.4,2.7 S stacks. The camshafts were also S however they were small 4 journal without center lube. The pump was also a 019, however there is a difference interally with the pump, I have been working on building one of these engines for a while and did some research, and Gus at pacific did one of these pumps and said something was different on the inside, but could not remember what. Its just a giant S!

  5. #5
    Also it did share the same 3.0RSR engine case with the odd 83mm head stud spacing and finned bottom, additionally it had the same 2.7 distrubutor and a standard exhaust with heat exchanges of standard size.

  6. #6
    Senior Member Neunelfer's Avatar
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    Trouble Maker...

    Ohhhh thanks alot! Raising more questions!!

    Actually, excellent info. I'm now wondering about the pump. I chatted with Bruce Anderson and he mentioned the pumps were the same. I spoke with Gus about doing the rebuild and he didn't mention anything out of the normal. He "did not" think I should take it up to 3.2 (Bruce thought it might work as a 3.2... but it might be stretching it).

    I guess the displacement and the bump in compression would explain the only 20hp increase. I'm wondering if it might sneak up to 250 with the proper headwork? This is my first experiance with MFI so I'm a little cautious...

    Thanks for the great info. Any further thoughts on building this type motor on a 930/07 platform would be appreciated.
    Eric - Sandy, Utah
    71 911
    914-6/GT
    914-6/ORV
    87 944 Spec 1
    Porsche Truck
    62 Beetle
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  7. #7
    Bruce is a freind of mine, but he isnt a engine builder, the further you get from the original design the more the risk. That isnt to say that other combinations wont work. The discussion with the pump with Gus was many years ago when he had just done one and it was fresh in his mind, he mentioned that is was something that sounded significant to me, more than just a volumetric variation. Having said this it could be nothing that will affect performance it could be a variation in the pump to allow for some other application. In my opinion if it was that significant the pump would have a different part number from Bosch. I would go for it and leave it at a three liter. As for the power of 230 as quoted from Porsche it may be a little low. We know that as with the previous S type engines 300 cc is worth 20hp. This would account its 20 hp advantage to the 2.7 but the significant increase in compression is not factored. My estimate is a sound 240hp with the compression of 9.8 to one, the car hauled ASS. By the way the early SC heads have ports that are to big, the proper ones were later SC, they are a bit small and can be ported to the correct size.

  8. #8
    Senior Member Neunelfer's Avatar
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    SC Ports

    Thanks again...

    Checking the SC ports you described... looks like I'm safe. 930/07 was the first year with the 34, 35 setup. 930/03-06 all had the 39, 35 ports. Correct?

    You've got me wondering about the pump. I hope it will work out. I'll double check with Gus when I drop it off there. Maybe I can jog his memory.

    So... ports: 36, 35? I've had so many people recommend larger. Hence the original post... confusing.
    Eric - Sandy, Utah
    71 911
    914-6/GT
    914-6/ORV
    87 944 Spec 1
    Porsche Truck
    62 Beetle
    80 VW “Caddy” Pickup
    72 R75/5 Toaster Tank
    PMB Performance
    We'll Make Your Calipers New Again
    Love Us On Facebook

  9. #9
    The ports are that size for a reason, simply changing porting without changing camshaft characteristics, doesnt nessesarly gain you anything. Porsche used that size porting for a reason, it gave the best overall performance for the given cam, not just peak performance. Dont forget, if you are using plastic stacks and stock throttle valves, you are restricted upstream in the intake, and bigger ports wont solve that problem. Hey the motor rocks in its stock form, exellent low, mid and strong on top, as was my experience with the car, I would leave it.

  10. #10
    Buy the way I love the benz wagon in the background, obviously a pre 90 model, is it a 87 300td or just a gas?

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