914-6 creation with 69 911S motor, Carburetor or 69S MFI? |
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914-6 creation with 69 911S motor, Carburetor or 69S MFI? |
Jett |
Jul 31 2022, 09:34 AM
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#1
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Senior Member Group: Members Posts: 1,665 Joined: 27-July 14 From: Seattle Member No.: 17,686 Region Association: Pacific Northwest |
We are building a 75 conversion with a freshly rebuilt stock 69S 2.0. I have a set of 914-6 webers that were just rebuilt (jewelry), and the fellow that sold the motor has offered up the injection for it.
I really wanted the sound and stock look of carbs, but my friend said that the injection provides close to 40hp for this motor, and sounds better than carbs?? Any thoughts? |
tygaboy |
Jul 31 2022, 09:36 AM
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#2
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914 Guru Group: Members Posts: 5,431 Joined: 6-October 15 From: Petaluma, CA Member No.: 19,241 Region Association: Northern California |
Seems to me it's down to your preference: originality vs convenience (post install/tuning) and drivability in varied conditions.
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Front yard mechanic |
Jul 31 2022, 10:05 AM
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#3
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Senior Member Group: Members Posts: 1,205 Joined: 23-July 15 From: New Mexico Member No.: 18,984 Region Association: None |
Cis or Mfi
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gereed75 |
Jul 31 2022, 10:22 AM
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#4
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Senior Member Group: Members Posts: 1,286 Joined: 19-March 13 From: Pittsburgh PA Member No.: 15,674 Region Association: North East States |
Assuming MFI I would try to go for it. That again assumes that it is in good working condition. If not in good condition then you have to be willing to work and or spend to get it right, which can be a project
The carbs are a more straightforward tune. All of the setup is a pretty well known formula for carbs. The MFI just adds a bit to the “cool” factor. Sound should be the same, maybe slightly better for MFI. I would be very skeptical of the 40hp claim. Well tuned carbs should not be very far behind MFI in the HP department, if at all. Either way I am a big fan of the small bore, narrow body hot rods. |
campbellcj |
Jul 31 2022, 10:36 AM
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#5
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I can't Re Member Group: Members Posts: 4,574 Joined: 26-December 02 From: Agoura, CA Member No.: 21 Region Association: Southern California |
I agree - would try to keep the MFI if at all possible/affordable. In addition to the extra coolness factor, its throttle response and drivability beats carbs. Someday I may actually try to convert my car over, and it already has MFI compatible cams as a start.
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brant |
Jul 31 2022, 10:45 AM
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#6
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914 Wizard Group: Members Posts: 11,739 Joined: 30-December 02 From: Colorado Member No.: 47 Region Association: Rocky Mountains |
MFI is expensive to buy and expensive to build
But oh so cool! |
gandalf_025 |
Jul 31 2022, 11:01 AM
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#7
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Senior Member Group: Members Posts: 1,471 Joined: 25-June 09 From: North Shore, Massachusetts Member No.: 10,509 Region Association: North East States |
MFI certainly does have a cool factor and will make the motor worth a lot more with that injection on it. It will have crisper throttle response and an interesting sound.
I don't see anywhere near 40 hp increase though. Costs a lot more to buy and set up and tougher to adjust unless you know someone very comfortable with it. As I remember it was not easy to get at the adjustments on the pump when in a 914 because it is backwards. I saw people cut through the firewall to get the adjustment tools through. Then again.. Dealerships in the 70's weren't pulling MFI off engines and replacing it with carbs for no reason.. My mechanic had a bunch of twin plug MFI engines running around the Boston Area back in the 80's and 90's... |
infraredcalvin |
Jul 31 2022, 11:38 AM
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#8
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Distracted Member Group: Members Posts: 1,552 Joined: 25-August 08 From: Ladera Ranch, CA Member No.: 9,463 Region Association: Southern California |
MFI for sure, carbs are a little loud right behind your head for any extended driving.
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targa72e |
Jul 31 2022, 12:01 PM
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#9
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Member Group: Members Posts: 269 Joined: 11-September 16 From: colorado Member No.: 20,392 Region Association: None |
I had MFI installed on one of the engines in my -6 conversion. Pretty straight forward to get working from fuel system standpoint. The pump just wants to see fuel pressure at a constant 14psi.
Two problems with MFI in a 914 are that there are no provisions for getting heat to the thermostat and the standard -6 sheet metal will not fit. I used a wide band O2 system to tune the MFI and had it working very well. I had to eliminate the thermostat as it did not function properly without heat ducting. When everything was tuned well for hot running the car would not start when cold. I did not have the auxiliary cold start injection installed. I ended up making a mechanical adjuster in place of the thermostat to start the car when cold. There are other solutions to make this mechanical with a cable to the passenger compartment for cold start enrichment. For the sheet metal It needed to be modified to accommodate the pump drive. I had to use a 911 and 914 pieces spliced together to get it to work. The airbox was also a little tight on clearance so I removed the torsion bars for more clearance but this could of been do to engine mount positioning. john |
brant |
Jul 31 2022, 12:12 PM
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#10
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914 Wizard Group: Members Posts: 11,739 Joined: 30-December 02 From: Colorado Member No.: 47 Region Association: Rocky Mountains |
The factory hp rating was I believe 10hp between the 68s with carbs and the 69s with MFI
But the 69 heads also have bigger valves than the 68 So that could of been a part of the difference |
Al Meredith |
Jul 31 2022, 12:22 PM
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#11
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Senior Member Group: Members Posts: 967 Joined: 4-November 04 From: Atlanta, ga Member No.: 3,061 |
I believe the MFI had bigger cams and more compression ratio. You also drive the pump off the rear of the left hand cam.
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mlindner |
Jul 31 2022, 02:07 PM
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#12
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Senior Member Group: Members Posts: 1,557 Joined: 11-November 11 From: Merrimac, WI Member No.: 13,770 Region Association: Upper MidWest |
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rgalla9146 |
Jul 31 2022, 02:15 PM
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#13
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Advanced Member Group: Members Posts: 4,624 Joined: 23-November 05 From: Paramus NJ Member No.: 5,176 Region Association: None |
If nothing else secure the MFI It is expensive to rebuild but when done it is utterly dependable and magic. The sound is the same as carbs. I dream of MFI on a 3.2 short stroke in my GT replica I do have a 69 S that luckily still has its MFI but needs a restoration. |
mepstein |
Jul 31 2022, 02:30 PM
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#14
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914-6 GT in waiting Group: Members Posts: 19,518 Joined: 19-September 09 From: Landenberg, PA/Wilmington, DE Member No.: 10,825 Region Association: MidAtlantic Region |
If nothing else secure the MFI It is expensive to rebuild but when done it is utterly dependable and magic. The sound is the same as carbs. I dream of MFI on a 3.2 short stroke in my GT replica I do have a 69 S that luckily still has its MFI but needs a restoration. (IMG:style_emoticons/default/agree.gif) The engine is so much more valuable with the correct mfi. |
Superhawk996 |
Jul 31 2022, 04:23 PM
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#15
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914 Guru Group: Members Posts: 6,469 Joined: 25-August 18 From: Woods of N. Idaho Member No.: 22,428 Region Association: Galt's Gulch |
MFI -- if you've got the coin, and can find someone to set it up properly that is the way to go. (IMG:style_emoticons/default/drooley.gif)
I'm not sure if my numbers are right but I've heard that MFI rebuilds and modification can push $8k - 10k? Didn't @ClayPerrine used to have a 2.4 MFI? Would be great source of info. |
Jett |
Jul 31 2022, 07:11 PM
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#16
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Senior Member Group: Members Posts: 1,665 Joined: 27-July 14 From: Seattle Member No.: 17,686 Region Association: Pacific Northwest |
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Jett |
Jul 31 2022, 07:21 PM
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#17
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Senior Member Group: Members Posts: 1,665 Joined: 27-July 14 From: Seattle Member No.: 17,686 Region Association: Pacific Northwest |
Thanks everyone! Fortunately the MFI is not took expensive and we have folks to rebuild and tune. I’ll try to buy the unit (IMG:style_emoticons/default/smile.gif)
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Jett |
Jul 31 2022, 07:25 PM
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#18
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Senior Member Group: Members Posts: 1,665 Joined: 27-July 14 From: Seattle Member No.: 17,686 Region Association: Pacific Northwest |
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targa72e |
Jul 31 2022, 10:49 PM
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#19
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Member Group: Members Posts: 269 Joined: 11-September 16 From: colorado Member No.: 20,392 Region Association: None |
Sounds like you will get the MFI. The tools to tune a MFI (of carbs ) are so much better today than even 20 years ago. Using a wide band O2 system you can dial in the mixture very well. There is also a lot more documentation on how to go outside the factory tuning if displacement or cams do not exactly match factory.
john |
carr914 |
Aug 1 2022, 03:45 AM
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#20
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Racer from Birth Group: Members Posts: 121,084 Joined: 2-February 04 From: Tampa,FL Member No.: 1,623 Region Association: South East States |
MFI all day. My '69 911S was one of my favorite rides, that motor was incredible
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