one has the 914/6 suspension and brakes and one has the 914/4 suspension and brakes. Also assume both cars have anti-roll bars and 180hp engines. What’s the difference in how they perform on the track?

I take it you mean both have the same engine correct? Just the suspension is different??

as is, the /6 suspension should have slightly stiffer torsion bars and slightly stiffer rear springs if one used bone stock factory parts....

as for brakes, the /6 front rotors are vented, but that might not come into play depending on the driver or course...

I would almost have to say that as long as you have no issues with heating up of the front brakes, there will not be a measurable differance...

The torsion bars are the same diameter, just different splines. There were enough different rear springs used on the fours that you can probably find some that are about equal to the -6 springs.

The Six didn't come with sway bars, IIRC. The Four did; they were even standard on the 73 2.0 cars.



Well, the Six brakes are heavier...

Still and all; I'd say that any difference in on-track performance would be pretty small. Certainly much smaller than if, say, I were driving the one car and Bradholio were driving the other.

--DD

Good information, thanks. What were some more of the specific differences between the /4 and /6 suspension components? Where the front control arms longer on the /6? The upper mounting point for the struts is obviously the same, right?

With 5 lug you'll have more wheel choices.

main differences:
5lug vs 4 lug
splines on torsion bars are the same as a 911 on the 6 and different than the 4
larger calipers with vented front discs
other parameter are the same including length of a arms etc.
otherwise no one could do a 5 lug conversion by using 911 front ends.

Ok, I guess that's what I was trying to figure out. So the reasons people upgrade to the /6 suspension components are to get larger discs and five-lug hubs so they have more wheel choices? I like the four-lug Fuchs and I eventually want to buy the upgraded four-lug front hubs for vented discs so I don't need to do the 914/6 suspension swap.

For me it was mostly about getting bigger vented brakes and wheel choices for track driving. I have SC vented rotors on all 4 corners and a set of humungus BBS wheels.

I thought that the -6 used 19mm front bars and the -4's used 18mm

so I actually thought all of the 911 splined bars started 1mm larger minimum.

but here is an observation. A friend has a stock six and we used to run on the tracks frequently (for about 8 years)
The biggest difference was gearing and powerband. The stock -6 had another useable 1000rpm over a -4. On a track this gave him the ability to hold a gear often and avoid a shift.

We ran equal sway bars, equal tires, equal alot of stuff.
the -6 is faster because of its flexible powerband and ability to hold a gear.

brant

Like these magical mythical billet 4 bolt front hubs?

Use with M front calipers and early 911 vented rotors.

I have a real life example of what you want to know.

Gerard and I have nearly identical 2.0L '74 914s. This past labor day weekend we participated in a DE event called the Saint John's Grand Prix.

He is running MegaSquirt and I have stock D-Jet. His car has a stock four lug suspension, my car was upgraded to a 914-6 suspension in the early 80s. I have Bilsteines all around, 23mm front sway bar and 180lb rear springs. I also have stock brakes on the rear, 911 vented rotor front brakes.

The course was about 1.5 miles long. Gerard with the MegaSquirt has a little more top end speed and would gain a car link or two on the long straights, but in the twisty section, I could pull out about four to five car legnths. The only real difference in the cars is the suspension, so to answer your question, the upgraded suspension will make the car quicker. And a lot more fun to drive.

Thanks for the replies. I also plan on upgrading the torsion bars, springs and shocks to try to find a good balance.

M calipers use the same size pads as a /4 i think...

and i think piston size is only a few mm bigger

Nope, both used 17.9mm torsion bars. Different splines, same diameters. Check the factory manual or the little spec book for confirmation.

Not sure if the 911s ever had t-bars that small, but the Sixes did!

--DD

the reasoning for changing to M calipers is for the vented rotors, at least for me.
I wanted good venting (cooling) for my front brakes during 30+ min track sessions.
Also like the idea of being able to switch (change) rotors without having to change the hub and associated wheel bearings.
Now I just need to remove the hub/rotor combination and remove 5 bolts from the back and bolt on a new rotor, reinstall onto spindle and adjust bearings.

Same reason I placed my 914-4 front calipers on the rear...no more venting clearance...remove old pads, put in the new ones. Much easier for a 90% track car.

your results may vary

I switched to front calipers on the rear of my car too. for those exact same reasons.

Anyway I would like to run my 2.0L Type 4 against a 2.0L six. Either Autocross or track I would think the results would favor each car.
Mine in an Autocross and the six on the track.