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914World.com _ 914World Garage _ PMOs and altitude changes
Posted by: 914forme Jun 17 2018, 04:56 PM
I am working on getting the 2.7L redone for dad's 914-6 project. Plan is to drive it to Okteenerfest, and take dad for a beautiful run in the Georgia Mountains. I am not as good as I would like to be with carbs, more of an EFI guy. For some reason PMOs carbs are calling my name.
My one question comes into elevation changes. I really don't want to build the car and then hate the drive if they can't transition well with elevation changes.
Any one with experience and know they won't frustrate running up the mountain roads? Are the PMO carbs worth the price of admission?
Posted by: Mike Bellis Jun 17 2018, 05:50 PM
I don't know PMO. But no carbs adjust to elevation. It's a factor of oxygen density. Higher elevation is less oxygen. Less oxygen requires less fuel. Less fuel requires a jet change. Carbs should be tuned for your primary elevation. I'm sure some work better than others but if you travel through a bunch of elevations changes, EFI is a better choice.
Posted by: mb911 Jun 17 2018, 06:31 PM
Lots of jetting fun..
.
I will do efi some day just doing carbs now so I can get the car running and driving.
Posted by: rhodyguy Jun 17 2018, 06:53 PM
What kind of elevation changes do you expect to see?
Posted by: porschetub Jun 17 2018, 07:53 PM
Depends if you have rebuilt the Webers so they work great no need to go to PMO's if you have already spent the $$$ on them.
If you retain the Webers you could just fatten up the idles and mains a touch because they were jetting lean from day one so you won't have serious issues @ the higher altitude ,keep a close eye your oil temp you should be ok.
Posted by: JmuRiz Jun 17 2018, 08:51 PM
If planning on new PMO money, might as well spring a bit more on EFI.
Check with Al Imolska (sp?) for some ideas on any budget in that range and above.
Posted by: 914forme Jun 17 2018, 09:02 PM
Jim you talking about thesehttps://www.x-faktory.com/about.html
Posted by: SirAndy Jun 17 2018, 10:54 PM
I'm pretty sure higher altitude with *less* oxygen requires *less* fuel, not more fuel ...
Posted by: Edward Blume Jun 18 2018, 05:31 AM
I've done some research on EFI and can tell you that the pros outweigh the cons. The people who have done this conversion on the 911s seem to report back that its reliable amongst many other benefits.
The biggest issue is cost. Some of the kits are from hobbyists who deserve every penny for their efforts. Other company kits are higher than that.
For me, I have to solve oil cooling and the cost of other components to switch from a 2.4 to a 3.0 EFI, which is kind of frustrating because the 3.0 has a working CIS on it already, but given the leap in years and technology, the kits are the way to go.
Bitz Racing has a MS based system which uses the 3.0 intake which I would likely go with.
I would have to get a new Kennedy flywheel and clutch, $700. Oil lines, cooler and thermostat $1500, cut the front out $???, and install the kit, including dyno time.
The 2.4 when sold will pay for all of this, but I need to get it running and compression verified first.
Posted by: mb911 Jun 18 2018, 05:53 AM
I've done some research on EFI and can tell you that the pros outweigh the cons. The people who have done this conversion on the 911s seem to report back that its reliable amongst many other benefits.
The biggest issue is cost. Some of the kits are from hobbyists who deserve every penny for their efforts. Other company kits are higher than that.
For me, I have to solve oil cooling and the cost of other components to switch from a 2.4 to a 3.0 EFI, which is kind of frustrating because the 3.0 has a working CIS on it already, but given the leap in years and technology, the kits are the way to go.
Bitz Racing has a MS based system which uses the 3.0 intake which I would likely go with.
I would have to get a new Kennedy flywheel and clutch, $700. Oil lines, cooler and thermostat $1500, cut the front out $???, and install the kit, including dyno time.
The 2.4 when sold will pay for all of this, but I need to get it running and compression verified first.
You could always use the mfi ports in the heads for injectors and the carbs as throttle body's.. Thats my plan some day with my 2.4..
Posted by: JmuRiz Jun 18 2018, 07:30 AM
I've done some research on EFI and can tell you that the pros outweigh the cons. The people who have done this conversion on the 911s seem to report back that its reliable amongst many other benefits.
The biggest issue is cost. Some of the kits are from hobbyists who deserve every penny for their efforts. Other company kits are higher than that.
For me, I have to solve oil cooling and the cost of other components to switch from a 2.4 to a 3.0 EFI, which is kind of frustrating because the 3.0 has a working CIS on it already, but given the leap in years and technology, the kits are the way to go.
Bitz Racing has a MS based system which uses the 3.0 intake which I would likely go with.
I would have to get a new Kennedy flywheel and clutch, $700. Oil lines, cooler and thermostat $1500, cut the front out $???, and install the kit, including dyno time.
The 2.4 when sold will pay for all of this, but I need to get it running and compression verified first.
You could always use the mfi ports in the heads for injectors and the carbs as throttle body's.. Thats my plan some day with my 2.4..
jpnovak from the Pelican board did this and it looks good, just get a good controller (MS or something) and you're in the game!
If I didn't already have a good set of carbs I got a long time ago for cheap, I'd do EFI....maybe if/when I sell off all my old parts I'll have some $ to splurge
Posted by: Mark Henry Jun 18 2018, 10:17 AM
If you can DIY then you can build an FI system for around the price of the PMO's If it has to be bolt on and take it for tuning then it could cost double PMO's
PMO TB's are the same price as the carbs. If you can and have the time to DIY triumph TB's work. MFI stuff is getting spendy like all porsche goodies.
Dyno time isn't cheap, FI tuning has a learning curve.
Yes you can make a plenum FI system cheaper than ITB's, but that's comparing apples to oranges. PMO carbs will make more HP than a plenum system.
Posted by: mlindner Jun 18 2018, 12:31 PM
Give Richard at PMO a call. He'll have the answer for you. Having a extra set of jets to handle high elevation should not be a problem. Best, Mark
Posted by: Edward Blume Jun 18 2018, 04:51 PM
If you can DIY then you can build an FI system for around the price of the PMO's If it has to be bolt on and take it for tuning then it could cost double PMO's
PMO TB's are the same price as the carbs. If you can and have the time to DIY triumph TB's work. MFI stuff is getting spendy like all porsche goodies.
Dyno time isn't cheap, FI tuning has a learning curve.
Yes you can make a plenum FI system cheaper than ITB's, but that's comparing apples to oranges. PMO carbs will make more HP than a plenum system.
Good point.
With stock 3.0 cams I figured using the stock plenum would be safe.
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