There’s been a lot of questions lately about 5-lug conversions; What hubs to use? Can I use a standard -4 hub? Should I use the early -4 hub with the bosses? Should I get expensive 914-6 stub axles and use an early 911 hub? How about the 944 hub conversion? All great questions; the idea behind this post is to put it all together in one thread with a few pictures.

First, let’s take a look at the two basic styles of -4 hubs. The first series of hubs for a 914 were on the 1970 cars. They were a little different as the factory had bosses formed in the casting for not only 4-lug configuration but 5-lug as well. The 4-lug bosses were predominant as they sat at 11.75mm while the remaining 5-lug bosses sat at 7.5mm. These are very popular with people who are doing their own conversion to 5-lug because they simply had to take them to a machine shop and request a 5x130mm pattern.

Here’s a picture of an early 1970 -4 hub that has been drilled for the 5x130mm pattern (courtesy Mike Ginter). These hubs have been replated to make them shiny new

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The following is a picture of the standard -4 hub that you will find on most cars. From MY 1971 on, all 914 hubs looked like this.

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There are basically three things that can be done with these “914” hubs.

1. If you have the early hubs you can, as above, take them to a machine shop and have them drilled to a 5x130mm pattern.
2. If you have a later hub you can take it to a machine shop and have it spot faced (where they make the stud surface level) and drilled to the 5x130mm pattern, and
3. You can have them spot faced with the 5x130mm pattern, have ring bosses made up to bring the stud engagement back up to the 11mm depth. Press the studs in and weld the bosses on.

I think all are good choices. Regardless of what you hear out there, I’ve yet to see a -4 hub that’s been "properly" drilled fail. I’ve seen one picture posted here of someone who basically drilled out their hub with a hand drill and didn’t spot face it. The studs worked loose and buggered everything up but, I’ve never seen one done right fail.

I’ll add to that; I’ve never seen a stud fail. You can purchase inexpensive studs from EMPI at www.cip1.com. If they’re installed properly they will probably outlive you. I do like the factory Verbus studs because of full thread engagement and “consistency”. They are extremely consistent across all sizes and various studs in a batch. If you want custom length studs Porsche has probably tried them all on various vehicles so again, Verbus will be your only choice if you are using adapters etc. Be prepared… they are expensive. Some coming in at $10-15.00 EACH!

Here’s a standard -4 hub that’s been machined to the 5x130mm pattern. They all look a bit nicer when they get glass bead blasted. Note the ring bosses next to the hub. If you decide to go this route, discuss this with your machine shop first. Let them know what you’re attempting to do or, grab some of the pictures from this thread and show them. Basically they will be spot facing the hub and they will use one of the original 4x130mm bosses for your 5x130mm pattern. In the picture below it would be the boss in the 4:00 o-clock position. This one has simply been dressed and only a fraction of the metal has been removed. The ring bosses bring the remainder of the holes back up to that height.

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Here it is with the ring bosses inserted in the spot faced holes.

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Next you will (or your machine shop will) want to press in the studs. These are 45mm Verbus studs getting pressed into the prepped hub.

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Close up... looks like this -4 hub has had studs pressed in before

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In.

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Face of the hub.

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Ring Boss welded into place.

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All done and ready for paint.

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More work to do...

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Now, that’s a very strong 5-lug hub. It uses your existing stub axle and will slide right back into some new bearings on your control arms. This is by far the least expensive way to go 5-lug on your 914. What’s the down side? None that I can see but let me reach:

CV’s – If you’re planning an extreme horsepower application (V8, 3.6, like doing burnouts to impress the kids at the local high school) you may want to look into VW bus axles and or 944 conversions that use a larger CV.

Strength? – I’d say that’s a “myth busters” episode. I believe Brant is running his 914-6 vintage car with spot faced hubs… no issues. You could spend more at the machine shop and get ring bosses made up to weld in…

Almost final option. If you want to simply “Do it the way they did it in Stuttgart” you could purchase the 914-6 stub axle and use a 911 hub. 911 and 914 hubs are identical in many aspects but the spline count is different (why oh why, I don’t know). The 914-6 stub axle has the same number of splines that the 911 hub has. 911 hubs can be around $150-200 per pair. 914-6 stub axles can be $450-$850 per pair (or higher).

As you can see, this is a very simple solution. Write some checks and bolt on the goodies. Keep in mind; you’ll be in it for $600-1,000 before you add bearings, 914-6 rotors and of course… those inexpensive Fuchs wheels!

Nice thread, I think I will go that route too.
Thanks for the post.

Thanks Doug

I'm looking for Andy's 944 conversion thread to link to this but... man, I'm on page 10 and can't seem to get the proper search criteria locked down. Anybody?

Thanks Eric,
Being a newbie to 914's I've been wondering what was necessary for the 5 lug conversion. Personally I'm considering your kits as a simple bolt on since I don't have a shop to work out of.

Great thread Eric. Thanks.

Faster

you didnt weld my boss rings on!

but i put a tack on them

Eric,

Just to clarify, since I have never torn my hubs apart....

My front and rear hubs have both been drilled for 5 lug.

In the rear then, can I change the brake disc if needed without redrilling?

In the front, I believe the disc andthe hub are piece so I have to redrill.

Does that make sense? Otherwise, great info. Hope mine were done that
well!

Let me add a few things for clarity. People have mentioned to me that they've seen the front side of the hub buldge outward when the stud is pressed in. I've heard of this as well. The holes were simply machined improperly. If you're shop undersizes the holes by .002" then this is not a problem so... poor exicution doesn't ride in my book. I've seen plenty of poor executions. It's not the fault of the hub.

Also, having thin material on the hub is exactly the problem resolved by having ring bosses... however, Brant and many others are running on "spot faced hubs" without ring bosses. The mounting face is only 3mm when a -4 hub is converted this way (the stud mounts through 3mm of hub material). Brant's told me that he's "never had a problem" with his. I tend to go by real world experience, but, I have seen them come loose.

Aa... yours was one of the first batches. You wouldn't have wanted me to weld them with the welder I had at the time.

JD,

You've got it. You can use a 914-6 rear rotor or use a drilled 914-4 rotor over top of your hub. It is starting to make sense to drill -4 rear rotors as the -6 rotors seem to be too expensive. Check with your local machine shop to see what they would charge to drill new -4 rotors to 5-lug.

Front... correct. Your front rotors on a 914 are actually the hub as well. So, every time you need new rotors you will have to have them redrilled to 5-lug. Some ideas there:

1. 911T front strut. This will give you an M-Caliper and most importantly a vented rotor with a stand alone hub. This is what was stock on a 914-6.

2. Drill them... how long does a rotor last for most people? 3-5 years? If they go quicker than that (racing etc.) look at option 3.

3. Drill them and cryo them. Some SCCA racing classes demand you retain the 914 stock rotor but, you can use whatever wheels you'd like. We've found cryo treatment ($100 extra) to be more than effective and give you 3x the life out of a rotor.

Thanks Eric!

Jeff

Thanks for the lesson; great pictures, good explanation.

Classic Thread.

Thanks Eric - will help me plan my conversion.

Nice thread!
FWIW, I've been racing with spot faced hubs without ring bosses for 7 years, 225 Kumhos and 245 Hoosiers without any failures. A couple of the studs have come loose a couple of times, once at the track, I pulled them back in with the lug nuts with some grease on them to protect things and decrease friction, but they've been tight for years now.

Hmm. I just took a pair of hubs from a 74 with the bosses for the 5-lug configuration. Does this mean that they have been changed at some time to an earlier version?

Spoke

That's exactly what it means.



Great topic Eric!

Eric,

Great write up..now how much for a set?

Eric,

Good stuff!

Thanks

Eric,
Gret post & pics.

Don't want to tell you how to do your job, but it would be better to bolt the bosses in, weld, re-spotface, and then press in the studs. Those expensive studs definitely aren't '10.9' strength anymore if they were in there when welded.

Thoughts?
SMD

Did you see his welding?? LOL There is nothing wrong with those studs..LOL

Seriously,

It would be best if those where welded without the stud in place.

We will have to wait to hear from him.

I also wonder if this brings up any balance issues?



B

I don't know if there is enough heat to affect the stud if its installed before the welding proceedure. He said he never had one fail and thats good enough for me. Crap I need this five lug perversion so bad.

Good job Enrike

I understand the concern but, to harden steel it is heated to a red glow (which the studs never were) and quenched in water or oil (which the studs never were). It this point they would be extremely brittle.

To anneal (temper or soften) it's heated to just over 1400°F and then slowly cooled for 20-40 hours at a very consistent and steady rate to soften. This would reduce the hardness “a very little” and the brittelness a lot.

I think it’s safe to say the hardness of these studs is hardly affected.

If the rings were welded prior to the studs being pressed in they would tend to warp.

Regarding balance: The relatively slow rotation of this centered mass will not be affected. Or so I’m told. After two year of making them, I’ve yet to be told otherwise by people who have them on their street and track cars

Tempering doesn't require a slow cool (its not quenched either). Its done after the original hardening w/ quench (sometimes the quench is air depending on the alloy - and Im sure you know all this, but others might not) Annealing is the only process that requires a very specific cooldown rate though the critical temp zones. Heating the steel will have SOME effect on temper. W/o knowing the alloy and actual temp reached, none of us know the extent of that effect. I was just staying it would be safer for the studs to not have them in there when welding (esp in todays litigious society!)



Agreed. Thats why I said to bolt, weld, and THEN re-spotface them;)

Just trying to offer suggestions/alternatives. No disrespect intended. I didn't say a THING about your welds like *cough* BRAD *cough* (BTW, Brad has no room to speak there. A monkey on crack could have made the welds on their spec boxster cage - I already gave them shit about that one;) I'll say no more.

Best,
SMD

Thread Hijack....

Eric,
If you are changing the -6 rear calipers (with a spacer already added to run vented rotors) to regular SC vented rotor calipers, is this a straight bolt-on mod with no other changes required?

Yes. You may need the 5mm spacer under the ears or under the rotor but yes... which would lead me to ask; Why?

Both have 38mm pistons and the same size pads.

It was a PITA messing with the vent clearance on a track car that was going through pads fairly often. The adjuster always leaked.

I installed the SC calipers two years ago and set the original -6s on the shelf. I read somewhere about possibly needing the spacers, but I couldn't tell just by looking. The calipers appear to be centered on the rotor. What should I be seeing as a result of not running the spacers all this time? Thanks.

P.S. I got your PM - I'm not sure what I'm going to do.

You should be seeing the rotor offset inward by 4-5mm... "I THINK"

The issue is a vented 914 rear rotor vs. a vented 911 rotor. I believe the offset is about 4-5mm off. DaveP is the only guy I know that is in possession of a vented 914 rear rotor (again, I think). It's called the 914-6/GT rotor and if I recall they were around $375.00 a piece.

The idea was then to throw a 911 vented rear rotor on there but, you would have to have a 4-5mm spacer under the rotor or under the ears (move the rotor out or move the caliper back to align the gap).

I will measure a 911 rear caliper gap to mount distance and compare it to some of the 914-6 calipers I have in the shop. It could be that the 914-6/GT rotor and the spacer issue only applies to 914-6/GT calipers.

Film at 11:00!

Damn it Andy... now ya got me hijacking my own thread!

Andy, the offset between the mount and the rotor gap is 15mm on both.

Puzzled now why it's working with a 911 rotor w/o the caliper spacers...

I really apologize about the hijack , but my @#$%^ car is in the shop or I would go take pictures and measurements. I may have it back by tomorrow night. I definately want to solve this mistery.