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Posted by: Eric_Shea Mar 28 2010, 05:37 PM

This should be an important thread for those looking to get as much tire under the rear using vented rotors.

If you want to install vented rotors on a 914 you have a couple of options:

1. Pony up about $600.00 to have a pair of 914-6/GT rotors imported from Porsche DE. They're still available.

2. Put a 5mm rotor spacer under the hat of a 911 rotor. Our vented rear caliper kits come with a set of these spacers. If you want to cram as much meat under your rear fender (and a lot of us do) this will eat into 5mm of your tire space.

3. Put 5mm spacers underneath the caliper mounting ears. This will now have your calipers rubbing right up against the handbrake adjustment tube on most cars (some there is no issue).

4. Try a 944 rear rotor but, you would have to mill 2.5mm off the caliper and the mounting ears (spread the 5mm distance between the two) because the offset is too far out.

I finally dug into this today as I tried a set of 944 rotors for fit. No go. I wasn't about to mill my factory 914-6/GT calipers either. Next...

I could buy the 914-6/GT rotors. While $600.00 is a tad much for a pair of rotors, it's not that much in the grand scheme of things.

While I was under the car trying the 944 rotors I decided to see if my arms would work with the calipers spaced back. It fit but, it was rubbing on the arm where the handbrake adjustment tube is welded through the arm. I was only a few short steps away from solving this problem and then I could use a more affordable 911 rear rotor. I ended up getting out a bur grinder and finishing the edges of the handbrake arm tube. There was easily 5mm there to grind off and the bur grinder made short work of it.



Here's the area that needed to be ground down:



Here's the bur at work. If you do this on freshly powdercoated arms, make sure you put layers and layers of duct tape down first. I didn't have any and the bur "will" jump and nick the arms. Better yet, hopefully you'll see this thread "before" you powdercoat your arms and do this then:



Basically 1/2 way there on this side:



With the grinding work done, I needed to protect the metal:



I used a Testors paint marker and laid it on thick:



Done:



The calipers mounted up perfectly. I actually had two different spacer combinations on the car. about 4.8mm on the drivers side and a full 5mm on the passengers side:



Here you see the spacers under the mounting ear. Basically "washers" in various thicknesses. The Ferrari factory did the same thing to make up for manufacturing differences on their mounts... not a problem:



Wheels are mounted back on:



And I'm keeping my fingers crossed that this much meat will actually fit under the car now! LOL

Posted by: sixnotfour Mar 28 2010, 05:50 PM

Dang that tire and wheel combo looks Good.

Posted by: DNHunt Mar 28 2010, 05:56 PM

Cool Eric

So, 911 rear rotors and grind the trailing arms. What about the diameter? Does 8mm have to off the diameter of the rotors?

Dave

Posted by: Eric_Shea Mar 28 2010, 05:57 PM

No. That should be good with 914-6 calipers.

Posted by: Dr. Roger Mar 28 2010, 06:39 PM

is the inner rotor diameter clearance of 914/6 calipers different than 914/4?

Posted by: Eric_Shea Mar 28 2010, 08:47 PM

Yes. Six rotors are a little larger in diameter and six calipers are OK with that - four calipers are not and can rub on a six rotor or a 911 rotor.

Posted by: 396 Mar 28 2010, 09:23 PM

Thanks for the info... Those 'wide' wheels look like 15x8's correct?


Oh.. with 245's on them too or?

Posted by: RJMII Mar 28 2010, 09:52 PM

I thought you were in Brasil?

That's some nice looking progress!

Posted by: Eric_Shea Mar 28 2010, 10:02 PM

Those are Goodyear Bluestreaks on 8x15. They're 6.00's - so... whatever that works out to be. I seriously doubt it's a 245 as the stock 8x15 offset makes it difficult to get anything beyond a 215 in that profile on there.

Brazil is tomorrow. Ferg is going to suprise me by finishing my car while I'm gone.

Posted by: 396 Mar 28 2010, 11:20 PM

Thanks for the info.. I once had 245's on a set of 951 x8 on once.. the rears were pulled way out... my nephew has my wheels and tires on his 89 Car..now.

Posted by: Eric_Shea Mar 29 2010, 08:39 AM

Those would have been 8x16. Different offset. This is why people get confused when I say that 8's are very tight in GT flares... I usually refer to 8x15's (cause I'm stuck in another era)

Posted by: Kargeek Mar 29 2010, 04:13 PM

I did this many moons ago ago..911 rear rotors, 911 rear M calipers split with spacers and the 5mm spacer between the caliper mounting pad- no grinding needed- I guess I was lucky. See how I used the stock dust shields.

Posted by: J P Stein Mar 29 2010, 04:40 PM

If your tire is that close to the swing arm, be damn careful to keep your tire pressures high.......if you should drive that trailer queen aggressively.
I've eaten up 3/4 inches of clearance to the inner fender thru tire deflection.....got the pressures a couple pounds below the minimum apparently.


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Posted by: 396 Mar 29 2010, 11:21 PM

JP,

Thanks for sharing.. that must have been FUN.. I wish my car looked like that coming around a turn

Posted by: sean_v8_914 Mar 30 2010, 09:36 AM

that photo makes me want to say "gas, gas, gas, gas, gas!"
poor tire.

Posted by: Porcharu Mar 30 2010, 04:31 PM

I think a flap wheel on an angle grinder would be MUCH easier to control than a burr. I'm bookmarking this page for when I upgrade my rear brakes. Thanks
Steve

Posted by: J P Stein Apr 1 2010, 11:53 AM

Yes, well, that pic shows "a bridge to far" on pressure drops. IIRC, that was 18 psi in the rear....a guy's gotta go too far to find the edges of the envelope sometimes.....and hope nuthin' breaks. Normaly, all I adjust at an AX is tire pressures.

Till I saw that pic, I didn't realize just how much the tire was deflecting......I just saw a funny wear pattern and then later, the black marks on the fender wall. Now days, it's 19 in front & 21 rear...+/- 1. Bias plys ain't supposed to get lookin' like that.

Yeah, Sean, that was a kink at the end of a 50ish mph sweeper....pick a straight line in the turn for braking, bend in more lock with just a tad of trail braking, & gas it to get it to rotate......but not enuff to loop it. Many good course designers throw in decreasing radius corners just to make it interesting.

Same corner just a tad sooner....gotta gas it in 8-10 feet.....a prayer would be good. The man with the camera was a good shooter.


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Posted by: Loser_Cruiser Apr 12 2010, 12:43 PM

Of topic, but what is the color or color code for that car? It's beautiful

Posted by: Eric_Shea Apr 12 2010, 01:03 PM

Thanks,

That's Saturn Yellow/Chrome Yellow. Here's some links to the build:

http://www.facebook.com/album.php?aid=20575&id=1409883264&l=b421a958ac

http://www.facebook.com/album.php?aid=21130&id=1409883264&l=d147b32ef5

http://www.facebook.com/album.php?aid=25568&id=1409883264&l=3c26455147

http://www.facebook.com/album.php?aid=39249&id=1409883264&l=7c2510bef5

Posted by: Eric_Shea Mar 12 2011, 02:42 PM

for Jim Hoyland

Posted by: Eric_Shea Jun 11 2013, 12:09 PM

Update on my original reply to this question:

When installing my 914-6/GT calipers over top "Brembo" rear rotors we did not have any fitment issues.

We had a customer contact us about fitment issues with a 914-6/GT caliper over a Sebro rear rotor. We also had an issue here at the shop with a customer using our new alloy 914-6/GT rears on a Zimmermann rear rotor as well.

Bottom line is, check your fit with the rotor and the caliper. I recommend a total of 4mm to be turned off the edge of the rotor for proper fitment. Do not have the caliper/rotor clearance "tight" or "just fit" as it will heat up and interfere with your calipers.