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I'm quite sure your car has a far better performance than original base car with all these modifications.
For my LT-1, which is pretty stock for now, I think the situation is a bit different because I want to keep it as original as possible, but with some modifications in order to improve its handling.
I've checked all the possibilities and a lot of comments and posts. I've also read some issues with composite springs, apart the fact it's clearly not an original part on a quite original LT-1.
It seems that the F41 option was not mounted on 1972 cars (appart some ZR-1, perhaps...).
BUT it look like an original option for this time and it is the most important thing to me.
I would make a compromise and use a 474 lbs/in coil spring instead of 550.
I would also use a 15/16'' reproduction front sway bar and a 7-leaf rear spring from Eaton.
I wont add a rear bar for the moment and try the combo on our little roads without it.
FWIW-My car above apart from the 17 inch ZR1 style rims and ultra high performance rubber ^^^^^^^^looks fairly stock including the 355 L-82 with about 425+ Gross HP, rebuilt/upgraded in 2014 by me. Open the hood with the GM blue painted motor, L-82 aluminum intake, GM dual snorkel OEM cold air cleaner, the way the roller cam 10.2:1 motor idles and you would never know it was not an OEM L-82 unless you look carefully, and/or step on the gas even moderately. I understand your view point.
With that in mind, 550 springs instead of 474 springs would not be detectable. Same for Bilstein HD and Sport shocks with the 7 leaf steel gymkhana spring, no one would know. Poly upper and lower control arm bushings in black would like wise go mostly unnoticed in stock upper and lower control arms and are so much more effective in the suspension with minimal ride quality degradation.
Adding a 7/16 inch OEM GM style rear bar would also go largely unnoticed and easily removable in the future and will dial out the inherent understeer in any C3 without a factory rear bar, as delivered from the factory. One compromise might be the competition heim jointed struts in the rear which will dramatically improve the ride (less unwanted movement than rubber), improve steering feel and handling, AND again, can easily be removed,in the future, and put back to stock easily, if desired or required.
My 78 has many reconditioned L-82 forged engine parts still in the motor (engine numbers match the VIN and the 4 speed transmission, as well) like the L-82 forged crank, L-82 rods, L-82 aluminum intake,etc. The interior is almost 100% stock C3 except 80 style C3 seats. The suspension is 100% GM OEM design with updated with modern, and in some cases different material parts, BUT 100% GM concept. I wanted to keep the car as much as GM designed it BUT with improvements using that basic design.
Most importantly, as long as you save ALL OEM parts, you get the benefit of a much better C3 that can be returned to stock at any time.
Last edited by jb78L-82; Nov 11, 2020 at 12:51 PM.
Again, modern wheels and tires are certainly a BIG benefit on handling, but this is not what I want on my LT-1 !
Sure, it is difficult to find good 15'' tires these days... I've Pirellis P600 235/60 x 15 and I think they are quite good. But for future, I don't know what to use ? Maybe Michelins Classic, but they are very costly...
Interesting infos about engine. If I must rebuild mine, I'll be interested with a more modern but undetectable motor. The only thing I wont use are headers : to sad to see this in my engine bay...
For the suspension, it is interesting to read that some persons say you must not mount rear sway bar and other you must... I must try this for myself, I think !
And for the original parts, you're right : I've changed the steering wheel (the original one is definitively too large), but I keep it preciously apart.
It is, in my opinion, not the same with the wheels, because modern wheels simply don't fit the car...
I'm always waiting with steel rallye wheels with 17 or 18'', with original style chrome trim rings and compatible with original rallye center caps.
But apparently this type of wheels does not interest anyone: too bad :-(
Last edited by chris383; Nov 11, 2020 at 04:23 PM.
Last comment from me. The suspension changes were all completed before the 17 inch rims and ultra high performance tire change. The wheel/tire upgrade was done since the difference was so dramatic with the old 255/60/15’s I need better tires to maximize the effect. The suspension changes with the stock wheels were VERY dramatic and a BIG improvement, again, with the stock crap tires and 15 inch rims...
I'm always waiting with steel rallye wheels with 17 or 18'', with original style chrome trim rings and compatible with original rallye center caps.
But apparently this type of wheels does not interest anyone: too bad :-(
You mean like these? They exist. Have been eyeing them myself on my frame off resto. 17 or 18 inch 7-10 inches wide, and custom offset. And factory centercaps fit! I just may bite the bullet and try them.
Up to 18 x 9.5 with a 4.75 backspace is what would fit as a bolt-on from my research. Fr & Rr. With 10" wide rubber.
BTW: I also have a barely used F41 style 7 leaf spring you are welcome to for chump change if you want it. Make me an offer. $100ish?
Shipping would be bad though, as they are heavy, like 35 lbs.
Last edited by leigh1322; Nov 11, 2020 at 06:09 PM.
You mean like these? They exist. Have been eyeing them myself on my frame off resto. 17 or 18 inch 7-10 inches wide, and custom offset. And factory centercaps fit! I just may bite the bullet and try them.
Up to 18 x 9.5 with a 4.75 backspace is what would fit as a bolt-on from my research. Fr & Rr. With 10" wide rubber.
BTW: I also have a barely used F41 style 7 leaf spring you are welcome to for chump change if you want it. Make me an offer. $100ish?
Shipping would be bad though, as they are heavy, like 35 lbs.
I do remember seeing these rally sport aluminum rims existing in 17/18 now that you reminded us^^^^^. They are perfect for the earlier 70’s C3 and would solve the OP’s dilemma. Unfortunately, for the later 70’s C3’s with the optional aluminum 15 rims, the same aluminum replica in a 17/18 rims does not exist but was considered at one time possible and never materialized. The good outcome for me was that I could live with the SLP rims on my car above (C4 ZR1 style aluminum rims) allowing me to use ultra high performance summer only rubber. I would jump on an OEM replica of the GM C3 15 inch aluminum rim in a 17/18. Even better, I got those 4 SLP rims specifically made for C3’s at close out 12+ years ago for $600 for all 4 with shipping included....no longer available for C3’s.
Anyone know if OEM C3 GM style 15 inch aluminum 17/18 inch rim replicas are out there?
Last edited by jb78L-82; Nov 12, 2020 at 07:23 AM.
The ET LT-IIIs may be your best bet. At least they have 8 slots, like the YJ8 and (Corvette) N90 wheels. But don't discount the period-appropriate Snowflakes.
Year One makes a one piece cast Chevy Ralley wheel for our cars (WP45) . 17x8 only size available. Zero offset. (Would prefer 1/2" may need spacers) but only $240. But tire selections in the 17" size are rapidly dwindling.
Bothe ET and American Racing make customizeable wheels. Up to 18x10 size and customizeable offset. Which is needed for a C3 vs other popular chevies which prefer zero offset and is what is commonly available in one piece aftermarket wheels. C3s came stock with -1/2" offset and that also works well with custom wheels. The problem is these are significantly more expensive at $550 & $650 each. I do like them both, especially the Ralleys. But I have not yet gotten over the sticker shock enough yet to be able to pull the trigger.
Several C3 guys run these at 18x9.5 inch and 4.75" backspacing for a 1/2" offset. There are around $550 each and are actually one piece, cut to order.
I love the "factory ralley" look of the American Racing YN3227s. Unfortunately they are asking $650 each for them. But you could order them in the exact same size and backspacing as the ETs above.
Cargotzman runs the LT 111s above. in a massive 18x9.5 inch size with a factory 1/2" offset and 4.75" backspacing. With massive 10" wide rubber. 275/40-18. I think it looks awesome! And would look even cooler with the ralley wheel look.
Last edited by leigh1322; Nov 12, 2020 at 09:55 AM.
The Rallye Wheels from Year One (WP45) looks good and are not (too) expensive...but always without correct chrome trim rings for 17-18''...
Again, I'm sure that 18'' rims with modern tires (like my '06 BMW Z4 with 18'' Goodyear Assymetric 3 have...) will improve a lot the handling... but not the classic look of that so sexy LT-1 ;-)
I hope they'll offer good tires in 15'' in the future (who knows...). Maybe Michelins, but they are quite expensive.
I would not count on any high performance 15 inch tires in C3 sizes moving forward. In Fact, 15 inch 255/60/15 ultra high performance tires have been gone now for about 15 years and doubt will come back. BF Goodrich was one of the last in the early 2000's to offer a BFG Comp TA, Z rated, 255/60/15, but they are long gone.
You have mentioned a few times that modern tires are a big component of a great handling car (they are) but I think you may be overestimating, a bit here. As I stated earlier, almost all my suspension changes/upgrades done on my 78 occurred over many years with the 255/60/15, no performance tires, and the effect was VERY dramatic on the cars steering and handling with the 15 inch tires. The modern 17 inch ultra high performance rubber maximized the effects but it was not night and day, more incremental, from the modern tires.
I am currently in the midst of upgrading my wife's 2016 Audi Q3 that came with base suspension and tires (235/50/18 H rated). Just changing the tires (no other changes) to Ultra High Performance Rubber of 255/45/18 W rated (170 MPH speed rating) did NOT monumentally, upgrade the handling/steering, again, more incremental. What will more dramatically effect the overall handling and steering will be the Bilstein Sports I just purchased, guaranteed. Tires Yes but Suspension changes MORE!
Last edited by jb78L-82; Nov 12, 2020 at 02:09 PM.
Mhhh... On my Z4, I had changed the tires originaly mounted when I bought the car (Falken) to GoodYear : what a difference ! Don't forget : speed rating is not an indication of the quality of rubber. Here in Switzerland, there are a lot of people attracted with chinese tires (true, very cheap) : A good part of them return to the mecanic to change them after some good fears !
True, good tires in 15'' are gone (appart Michelin, very expensive). It's a real problem for people who want to really drive the car.
However, I've seen the brand Vitour Galaxy with V-rated tires in very reasonable price. I don't know if they are good,on the other side...
Last edited by chris383; Nov 13, 2020 at 01:15 PM.
A speed rating is indicative of the ability of the tire to stay together under tremendous centrifugal loads which is a leading indicator of the strength of the tires overall construction..meaning a W/Y speed rated tire is MUCH stronger than an H rated tire. This fact holds true for any tire in the world.
As for the rubber quality, the sidewalls of tires in the US have 3 additional ratings: Temperature, Traction, and Treadwear. You can ascertain much about the rubber's characteristics from these 3 ratings, in the USA, at least.
A high speed rated tire (W/Y) will almost always have a temperature of A, meaning it will stay very cool at high speeds and increased load.
A relatively high treadwear number indicates that tire will use harder rubber to last longer than a lower numerical treadwear rating
Traction of A or AA indicates a tire's traction, wet braking specifically. Obviously super hard rubber tire will not and could not have a AA traction rating,
in the wet.
So putting all this together, I just put a set of what I consider one of the best ultra high performance tires in the world on my Lexus IS 350 RWD F Sport, Michelin Pilot Sport 4S:
Speed Rated Y (Rated to 186 MPH)
Traction AA
Treadwear 300 (unbelievable for this class of tire, most ultra high performance tires are 100-200 treadwear rating)
Temperature A
These 4 factors can tell you MUCH about the tire's construction and rubber. quality...
Last edited by jb78L-82; Nov 13, 2020 at 06:39 PM.
Thank you for these information :-)
II just wanted to say that for the same speed index, two tires of different brands can behave ... very differently!
After that, I am not far from believing that a say Chinese tire of the V index will not be better (to say the least ...) than a good H index tire ... but that only involves me, it's only my personal experience.
Regarding Mechelin tires, they are know to be expensive, but they last also more than others. Nut I'm quite happy with GoodYear tires and they are less expensive than Michelin.
To sum up : I'll work now on my suspension (both front and rear) and change a few stategical parts (front and rear springs, front sway bar, trut rods) and see next summer, (always with my current Pirelli tires), what this combo will bring me in term of handling, but also comfort, which is also important.
Best regards from sunny (today) Switzerland :-)
Chris
