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I am an acolyte of Colin Chapman, the man who said “Simplify, then add lightness” and “Adding power makes you faster on the straights; subtracting weight makes you faster everywhere”.
Porsche kept adding more and thicker sheet metal to the unibodies over the years so while your car is breathtakingly amazing, a true owner's build, it will never be a light car. Of all the cars I have owned and currently own, nothing touches my '73 with a 3.2 and headers weighing in at 2174 lb in terms of fun. You can drive it at 7/10s on public roads all day long with a huge smile on your face. But that's not a car for you. It's essentially a single fixed back Momo inside a chunk of steel with a hot 3.2 riding on 15s and a decent suspension. The absolutely most fun car I've ever owned and that includes a lightened M491, 69E, and lightened 84 Targa. If you want a truly fun car, get a 74 or 75, add as much lightness as possible stripping it, backdate it, figure out what you need to make 220hp with some torque, then start adding comfort, otherwise known as weight, back in, to make it livable and enjoyable. |
72 vs 75
my son has a 72T, i have a 75 S.
1. the mfi sound of the 72 is hard to beat. 2. the 72 is a bit lighter at speed and on the highway i prefer the 75.0 3. I actually prefer driving the 75. though the 72 is in near perfect condition. |
Thanks Bill I will try taking out the spare. I have hesitated in the past due to the number of things I’ve read about not getting the front end too light in comparison to the back for handling balance. But will see how this goes.
Interesting to hear you say that maybe I should stick with my 17s ... I assume the torque costs you refer to being low are due to the light weight of the wheels. And yes I love my brakes, have thought about going back to stock 3.2 brakes or even base Boxster calipers on 3.2 discs to fit 15s, but I would be down grading in capability. This is also where aesthetics crosses over with performance - if I backdate I wouldn’t want to keep the 17s, I just don’t think they look right on a longhood. I’ve already got euro bumper tubes and took out the fog lights, so if I keep the IBs next step would be FG and I don't know how in feel about those. |
Im in the middle of a g50 swap on my car so I though these 915 vs g50 weight difference might be interesting in this tread.
Mag case ‘75 8-31 915 with SC mainshaft, AL side cover and nose cone, Guard LSD and WEVO spray bar cooling setup, 100mm output flanges. 107lbs G50 with open diff. 142lbs 915 torque tube 11.8lbs G50 torque tube 19.6lbs The g50 aluminum trans mount might be a couple pounds lighter but the 108mm CV joints are a bit heavier then the 100mm ‘75-‘84 cars use. I think once I get a LSD in the g50, it probably is a going to be between 50 and 60lb weight gain irrespective of the clutch and flywheel for the swap. |
The bottom line to me, from years now of owning both longhood LWB cars (never owned a SWB driver or a G50 car) and G-bodies, is that the longhood cars come with the Miata feel right out of the box. Pre-Carrera G-series cars can get there with some focused lightweighting.
These chassis were mostly the same across time. Sure, they were beefed up in the name of structural improvement over time, but at the chassis level, it's not massive (said from having weighed a number of stripped chassis over the years). Key items that are somewhat bulky include the impact bumper mount plates - but these are easily removed with some tools, elbow grease and and afternoon. Otherwise, it's mainly the bolt-on stuff that makes the noticeable difference to anyone with sub-Rohrl senses. The later the car, the more they evolved into the yuppy '80s and safety era, when Porsche added more luxury, bling and features than die-hard enthusiasts necessarily wanted. The toughest call to me is the unsprung weight issue. I love wide wheels, I hate the weight. So, today, it just becomes a question of how silly you care to get with the G-bodies in the name of light weight to get that nimble feel. I am willing to get pretty silly, and I got tired of fixing rust over the course of owning a series of (much-loved!) longhoods, so I am in the G camp for now. |
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I've posted many comparisons of these effects, Ill try to do another for you later in 17 the most efficient yet effective tire sets will be 215/45//245/40, for a more powerful car like a 3.6 conversion 225/45//255/40 or if you could find them 225/40//265/35. The 215/45//245/40 is going to be more efficient than all 16 sets except for the 205/50//225/45 in 16 205/50//225/45 is the most efficient and effective setup, followed by 205/50//245/45, in 15 205/50//225/50 or 205/50// 225/45 or 225/45//245/40 In all cased tire radius and handling balance and grip and grip level desired and fit are the primary factors to consider. All take precedence over any individual weight metric. looks are a personal thing, you will have to make your own decision there as for brakes, if you go smaller the 3.2 Carrera front w/ pre '84 rear and no p/v is the way to go, 23.8 mm m/c can be used w/ them but expect to need a lot more leg, some guys even do this w/o boost. other than that only full 930s are an upgrade that work w/ 15s, Possibly some aftermarkets but none that I am familiar w/ |
some low hanging fruit
A couple of gignificant losses can be had by ditching the 50 gallon windshield washer tank and the enormous stock battery, all left side forward items.
If your car is a DD, as opposed to a track car, i would think twice about ditching the bumpers. In the last year, i had a couple of "Taps", one rear ended, no damage to the work truck, the other in a parking lot. Without the bumpers you could be in for some serious repairs. I heard of one 911, w/ FG bumper getting tapped and it broke his crankshaft. Glad they didn't hit the 74. |
Here's a generalized summary of what fits(or can be made to fit) an SC/Carrera body car
inertial and gearing costs go down the shorter the tire http://forums.pelicanparts.com/uploa...1609695003.jpg Here's a comparison of an efficient 15(not the most efficient though) to the most efficient 16" Fuchs setup http://forums.pelicanparts.com/uploa...1609695003.jpg Here's comparison of the most efficient Fuchs16 setup to the most efficient Fikse 17 http://forums.pelicanparts.com/uploa...1609695003.jpg It may be a little hard to read but the above 17 only has <6lb-ft cost wrt to an efficient, though not the most efficient 15 setup Lastly here's a comparison using the same tire lines, efficient 16 vs efficient 17 A052s, here the weight of the rear tires does make a big difference, all data comes from factory #s http://forums.pelicanparts.com/uploa...1609695662.jpg One more thing, backdating to early long hood isn' t the only way to lose weight in the ends There is the Ruf look, The RSR look w/ Carrera chassis and the SC/RS look w/ Carrera chassis |
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^ This x100. |
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did Porsche really use thicker sheet metal in the unibodies over the years?
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Thanks again Bill. I guess I have to decide the best combination of aesthetics and performance. If I stay with some form of Impact bumper I will stay with the 17s. If I go backdate I will probably go 15s.
There is a chance I could go in 16 205/50//225/45 ... 16” wheels radially clear my current 996 brakes, it’s just the taper of the standard Fuchs barrel that doesn’t work. If I can find some custom Fuchs replicas with less taper I could stay with 16s and keep my current brakes. Thanks Salazar, I have tracked but not autocross. I would like to try smaller tires, both for the effect Bill is describing and for the shorter gearing. |
BTW sorry to get mushy on you guys but I love this forum. I’ve been on many different forums over the years and to have to say this thread is an example of how helpful and encouraging the members are here. I’ve been on here since 2007 and the same great people come back to give in depth advice. I have now decided to keep my 87, and one of the reasons is so I can interact with the great people on this forum.
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Allegedly one of the main reasons pressuring the halt of VW Beetle production was the thicker sheet metal was getting rare (newer designs using thinner metal) and cost going up. The large curves with no supporting frame under them needed old fashion thick sheet metal that was out of vogue. At least that's what I recall of a rumor in the late 1970's and or early 1980's. More flexible higher carbon steel (crush zones) over the stiffer low carbon variety or something like that, the matrix blend changing. Then again, was it something to do with magnesium? 1950: The metal is magnesium, the car is the Beetle Porsche went back and forth with magnesium and aluminum for their blocks, how could cost not be a consideration? Before China flooded the market with cheap magnesium it was getting to be an expensive material. |
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The extra weight (that actually makes a difference) over the years comes from all of the items already discussed in this thread. If you are building a hotrod these days, you are better off with a later year car, take it down to the chassis and add in only what you want/need based on your preferences. It really doesn't matter if you start with a 73', 77', or 87'. |
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I believe reinforcements were added in the 80s to the chassis, doors etc and that galvanization added more mass as well which at the end of the day improves safety. |
If you want to keep the late bumpers you can replace the bumper shocks with Aluminum tubes and either replace rear bumper pads with Euro units or remove them for some weight reduction.
john |
FG bumper blades are available from getty as well. i'm fitting a set to my '74 as we speak. 1st year IB car, so i want to keep the bellows and narrow bumperettes, but i'm also trying to hit 2100 lbs. i fab'd up some aluminum to replace the crush tubes, they weigh almost nothing.
we shall see... |
I was surprised how light the impact bumper blades actually are. I wonder if the look of the FG units can be detected after paint? I considered using those when I did my "un-hot-rodding" of my car.
I used the RennLine struts and narrow rear guards (my car is ROW) so appropriate. I tried to think light on everything. I didn't notice any loss of fun or power with the slight added weight. I used to not run a spare at all, but now that it's in there, no big difference. As I get older, maybe I don't drive as fast? |
Can you share a pic Lawrence?
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