6 cylinder conversion

[pancake]

i have finally started my -6 conversion on my 74 914 2.0. i am going to put in a stock 2.7 and use the stock 914 tranny for the time being until i eventually upgrade to a 3.0 and a 915 tranny. i need to change the rear wheel bearings now so i want to upgrade the rear hubs to the early 911 stuff at this point so i dont have to do it again later. Can i change the cv joints out at the outer end and continue to run the stock axle shafts or ??? with the motor and tranny upgrade later, i will need better axles, what are the options there?
rear brakes: i would eventually like to seriously upgrade the brakes all the way around and currently have 911 front struts and brakes with both steel and aluminum calipers. i also have a set of the big black brembos that are realistically overkill but quite frankly, really cool!! any input from someone who has done good brake upgrades?
wiring: is any of the stock wiring/relay board useful or do i need to rewire the car? i understand that i have to change out the tach for the six cylinder. what about the rest of the harness and guages? i have a set of 911 guages as well.
another brake question: i removed the stock rear proportioning valve and have the 19mm master, do i need an adjustable proportioning valve for the rear or just put in a "T" in the back?

[Bob Ashlock]

Pardon the self-promotion, but you don't need to replace the tachometer... just use TACH-ADAPT .... Many happy users of my little product! check it out at: Home

[rfuerst911sc]

Pancake I converted my 75 to a 3.0 with 901 so have some experience, also converted to 911 brakes on all four corners. Not an expert but here's what I did. For brakes I'm running early 70's 911 front struts with the 3 inch ear spacing. Using early 70's calipers from a 911 with 20mm thick rotors. In the rear same era 911 rotors/calipers with the same 20mm thickness. When I purchased my rolling chassis it did not have the brake proportioning valve so I installed a tee. You will get a wide degree of opinions on if to do this or not, some will say it works fine others will say you have created a death trap . In the 3 years since I have completed the project I have yet to run into a situation where I felt like the rear was doing anything wrong due to the brakes. My thoughts were if I ever ran into that scenario I would install better grade front brake pads to shift more bite up front but have not had to do so. I am also running a 19mm master cylinder. My car is running carb's so the electrical wiring is pretty simple but yes I kept the original relay board. Good luck with your conversion.

[jeffs9146]

I have also converted a 75 1.8L to an 83sc 3.0L FI with a 901 and I love it!

I have 86 sc front suspension with 3.5" calipers and the car stops great! I didn't do anything to the rears except the 5-lug conversion.

The wireing is a bit of a challenge. I put a tach that matched the motor. I removed my relay board and reworked the pinout on the car harness to match the motor harness. I had to run a wire up front for the oil temp gauge or pressure gauge depending on which wire you used in the harness for what! The gas gauge will be gone so I took apart the 914 gauge and mounted it under the dash so I knew how much gas I had!

Here is a video of the motor running!
P1010064.MOV - YouTube

[Dave at Pelican Parts]

The prop valve is there to keep you from locking up the rears first. If you put better pads on the front, you will transfer more weight off the rear wheels, making that problem worse.

If you change to 911 front brakes and keep the stock 914 rear brakes, you will have more braking going on at the front so you are less likely to need the prop valve. But the only way to be sure is through testing, which is where an adjustable valve can be a handy thing.

--DD

[GeorgeRud]

You can use the 2.7 with the 901, but you will need to change out the flywheel. The factory 914-6s and -4s used basically the same axles, so that should be OK, just have to fine the correct 914-6 outer stub axle and 5 lug hats for the conversion.

[jeffs9146]

Stock stub axels will work fine you just need the 5-lug hubs and rotors!

[pcar916]

You may have discovered this already since it's been some time since the last post, but although the axles are the same length in both the 4's and 6's, they have different spline counts and so, use different CV's. Typically axles from SwayAway or machined (for the thicker CV's) 4 cylinder axles are used with 100mm 944 CV's, which have the same spline-count as the 914.

914-6 axles use the 911 spline count. You can use even the 108mm 911 Turbo CV's if you have 914-6 axles (machined for the thicker CV's) and stub axles to match. But unless you're running massive horsepower it might not be necessary to take on the BIG weight increase. In this case you can use the larger diameter 911 axles but since they're too short, you'll need a spacer also.

If you convert to larger cv's on the outside only, there are other requirements for the stub axles and hats. I don't know this forum (sorry) well enough to tell you where the threads are, but on the 914World there are several in-depth threads all about this topic.

The 5-lug hats fit both of these configurations.

I ran a 2.7L six in my conversion for five years until stuffing a 3.6L engine in it and even then, I ran stock 914-4 CV's until they wore out. Then I used 100mm 944 CV's (easy to find) and modified 914-4 axles so they would fit.

The trans flanges, stub axles, and rotors are 911SC bits while the brake calipers are from a Carrera. Lot's of ways to do this so...

Good luck

[TheCabinetmaker]

Originally Posted by Dave at Pelican Parts

The prop valve is there to keep you from locking up the rears first. If you put better pads on the front, you will transfer more weight off the rear wheels, making that problem worse.
If you change to 911 front brakes and keep the stock 914 rear brakes, you will have more braking going on at the front so you are less likely to need the prop valve. But the only way to be sure is through testing, which is where an adjustable valve can be a handy thing.

--DD

Dave...
Can you please explain this, seems like better front pads would have a simular result as the better 911 front brakes. Is this an error, or am I missing something here?

[infraredcalvin]

Putting larger 911 calipers on front (larger meaning larger pistons and pads) throws off the originally engineered brake bias (front vs rear balance). Larger fronts or in this specific case better pads up front will cause the front brakes to do more of the stopping than intended, causing less weight on the rear, contributing to earlier lockup of the rears, possibly leading to a spin.

It's the same issue.

[Dave at Pelican Parts]

Now I'm not sure what I was trying to say with that earlier note.

There are a few different things going on.

First, the more effective your brakes are, the more the car will pitch forward, and the less traction the rear tires will have--making rear lockup more likely.

Second, there is the proportion of pressure between the front and rear brakes. The brake pads grab the rotors with a force determined by the pressure on the caliper pistons and the area of those pistons. The 911 front calipers have larger pistons than the 914 front calipers. For an equal pressure, the 911 calipers will grab harder than the 914 ones.

Third, the proportioning valve reduces the amount of pressure that goes to the rear brakes. It initially lets the rears have the same pressure as the front, but as the pressure rises it starts to pass a smaller part of the increase to the rear brakes. This results in less grab by the rears.

Finally, you have pad choice. Presumably you would select pads that produce more drag on the rotor for the same amount of squeezing (grabbing) force by the caliper pistons.

Note that some of these things work against each other. If you have larger pistons in the front calipers, the fronts are doing more work and the rears less. But that can mean you can push the pedal harder and theoretically slow down more, which transfers weight off the rear tires and makes them more likely to lock up. And so on.

You have several degrees of freedom, and they can interact in ways that aren't necessarily completely straight-forward. Throw in things like how the pads react to heat, and how often you need to use the brakes hard, and it gets even more complex. Which is why testing is important to say what your car really does need.

I should note: The 914-6 used 911 M calipers up front, which have larger piston area than 914-4 calipers. The 914-6 rear calipers had slightly larger pistons (I think?) than the 914-4 versions, but much closer in size. The Six still had a proportioning valve--but the "curve" of inlet to outlet pressure was different from the 914-4 one.

--DD

[TheCabinetmaker]

Cool replies. I run stock calipers on my car, but have the really nice Porterfeld race pads up front. they grad like a vice, gret stopping, so much so i have to be careful i dont lock up the fronts. Of course there is no increase in pedel force required with teh new front pads, so the system pressure is likely not changed, if anything i use less pedel pressure than before, with regular pads.