How do you keep the C3 from getting light above 120mph?
12-21-2012, 05:04 PM
#161
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Do excuse me for having apparently pi$$ed you off, as that certainly wasn't my intention. But, your suspension isn't exactly typical of C3's, and my post was as much as anything for the benefit of others who might mistake your comments about reducing front camber gain as something all C3'ers ought to consider. Obviously I should have made that point clear in my post. If you're satisfied with your current suspension setup without further experimentation, good for you.
That said, since you've invoked Herb Adams, IMCO it's worth pointing out that readers shouldn't mistake his advice to run the softest practical springs as meaning that they should necessarily run soft springs. Quite often more spring rate IS a good thing. Besides, higher spring rates (where higher spring frequencies are suitable) permit the use of smaller bars (read, "less crutch"); the former of which doesn't increase lateral weight transfer as does the latter.
...but, I digress. A healthy debate between schools of thought regarding springs and bars is best left to threads dedicated to such, suffice it to say that I'm admittedly a tad further away from the BBSS (big bars soft springs) line of thinking than most.
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That said, since you've invoked Herb Adams, IMCO it's worth pointing out that readers shouldn't mistake his advice to run the softest practical springs as meaning that they should necessarily run soft springs. Quite often more spring rate IS a good thing. Besides, higher spring rates (where higher spring frequencies are suitable) permit the use of smaller bars (read, "less crutch"); the former of which doesn't increase lateral weight transfer as does the latter.
...but, I digress. A healthy debate between schools of thought regarding springs and bars is best left to threads dedicated to such, suffice it to say that I'm admittedly a tad further away from the BBSS (big bars soft springs) line of thinking than most.
.
I'm an engineer. I love technical discussions. When done right there's generally an upgrade of knowledge on the part of both parties.
I don't subscribe to the "pure" SSBB philosophy. As noted in my previous post, my wheel rate is higher than probably 98% of the members here. My equivalent spring rate would be in the 700# range if duplicated on a C3 suspension. I have no desire to bump up the spring rates further on my car unless I have a compelling reason to do so.
I tried the SSBB combo a few decades ago with the original C3 suspension, using 460# springs and a 1 1/4" bar. The car was horrible with that. It seemed that under hard braking there was so much dive that I was darn near scraping the spoiler on the pavement, and the thick bar almost locked the two front wheels together, resembling an old straight axle in function when hitting uneven pavement. I then went with 550# springs and a 1 1/8" bar. Noticeably different and better car to drive after that.
I'm a design engineer by trade, so I have this wierd thing in my heard where I am rarely satisfied with the current configuration of any aspect of this car's design (I do like the bodywork styling however, and haven't changed much of that), so I expect that I'll keep making tweaks to the suspension geometry as reasons require, or ideas to experiment with pop into my head.
As I mentioned at the start, no hard feelings here.
12-21-2012, 06:14 PM
#162
Le Mans Master
No hard feelings here either, Mike. I'm OK with anything that ultimately serves to improve the breed or promotes a better understanding of it.
And, FWIW the 700'ish range (relative to standard C3 geometry) was pretty much what I had in mind, your having an all-aluminum BB. IIRC, the 700's I recommended to gkull some time ago worked out for him too.
I'm OK with anything that ultimately serves to improve the breed or promotes a better understanding of it.And, FWIW the 700'ish range (relative to standard C3 geometry) was pretty much what I had in mind, your having an all-aluminum BB. IIRC, the 700's I recommended to gkull some time ago worked out for him too.
12-22-2012, 08:52 PM
#164
Le Mans Master
Paul, it could be time to consider adding support to your air dam. I waited too long to catch mine before doing irreparable damage at high speed (actually folded the center back), but when it gets replaced (with another PC one) I'll almost certainly be adding a full-on splitter, similar to what Bee Jay has done. FWIW, I've already found that large body washers alone aren't really enough to properly support it, so if you decide to install struts without a splitter I'd suggest you fab up a backing panel for the underside of the dam to spread loads across a good area of the middle section.
03-12-2013, 05:07 PM
#165
Race Director
Thread Starter
Paul, it could be time to consider adding support to your air dam. I waited too long to catch mine before doing irreparable damage at high speed (actually folded the center back), but when it gets replaced (with another PC one) I'll almost certainly be adding a full-on splitter, similar to what Bee Jay has done. FWIW, I've already found that large body washers alone aren't really enough to properly support it, so if you decide to install struts without a splitter I'd suggest you fab up a backing panel for the underside of the dam to spread loads across a good area of the middle section.
I would like to add to this spoiler... I think I will order a new one, and then do some fiberglass mods on it and bring it down 1-2"...
03-12-2013, 06:14 PM
#166
Le Mans Master
Yeah, wouldn't it be nice if someone made a serious PC style dam that was a bit lower and already prepared for struts? ...and maybe throw in some brake ducts? Guess that's another one for the wishlist...
03-12-2013, 06:36 PM
#167
Race Director
Thread Starter
draw up one that you think would do this... i may make one.
I been thinking going lower, but I really can't.... i think im at like 3.5" at my lowest already... which is the exhaust near the rear end... and the headers are about 4" above ground...
wonder how 69427 under shielding turned out for the lift.... and drag
Last edited by pauldana; 03-12-2013 at 06:44 PM.
03-12-2013, 07:03 PM
#168
Le Mans Master
I would love to do just that, but I'd have to have a good one first to work from, and there's no money in my budget for that at the time. I haven't even been able to make much progress on my diffuser design concept I came up with a year or so ago, either. I'm afraid neither would help matters regarding ground clearance issues tho.
Haven't seen any recent reports from Mike, but I'd expect he'll check back in on that when there's any new info to share.
Haven't seen any recent reports from Mike, but I'd expect he'll check back in on that when there's any new info to share.
03-12-2013, 08:48 PM
#169
Get as much spoiler on the front as you can. C-2's are supposed to be even worse than C-3's, but this spoiler keeps me glued down when in the 140's. No drama at all...only need 3 digits at triple digits....
Last edited by FastEddy; 03-12-2013 at 08:52 PM.
03-13-2013, 10:41 AM
#170
Race Director
Thread Starter
I would love to do just that, but I'd have to have a good one first to work from, and there's no money in my budget for that at the time. I haven't even been able to make much progress on my diffuser design concept I came up with a year or so ago, either. I'm afraid neither would help matters regarding ground clearance issues tho.
Haven't seen any recent reports from Mike, but I'd expect he'll check back in on that when there's any new info to share.
Haven't seen any recent reports from Mike, but I'd expect he'll check back in on that when there's any new info to share.
I may be able to build one and make a mold like i did with the CAI's.... if interested lets talk design.
03-13-2013, 03:36 PM
#171
Team Owner
Paul, when I had my stock 79 L-82 front end. I extended the chin spoiler to within a couple inches of the gound. My 550# front coils kind of kept it from scraping. The fan shroud had a big bottom flap that would swing open if the air pressure on the motor side of the radiator was higher than behind the chin spoiler.
anyway extending the front spoiler is limited because of the distance ahead of the front wheels. The chin spoiler is back by the front wheels and it can be made lower and it keeps air from building under your car. I have another version of a chin spoiler today.
anyway extending the front spoiler is limited because of the distance ahead of the front wheels. The chin spoiler is back by the front wheels and it can be made lower and it keeps air from building under your car. I have another version of a chin spoiler today.
03-13-2013, 04:06 PM
#172
Race Director
Thread Starter
Paul, when I had my stock 79 L-82 front end. I extended the chin spoiler to within a couple inches of the gound. My 550# front coils kind of kept it from scraping. The fan shroud had a big bottom flap that would swing open if the air pressure on the motor side of the radiator was higher than behind the chin spoiler.
anyway extending the front spoiler is limited because of the distance ahead of the front wheels. The chin spoiler is back by the front wheels and it can be made lower and it keeps air from building under your car. I have another version of a chin spoiler today.
anyway extending the front spoiler is limited because of the distance ahead of the front wheels. The chin spoiler is back by the front wheels and it can be made lower and it keeps air from building under your car. I have another version of a chin spoiler today.
04-03-2013, 09:50 PM
#173
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I would love to do just that, but I'd have to have a good one first to work from, and there's no money in my budget for that at the time. I haven't even been able to make much progress on my diffuser design concept I came up with a year or so ago, either. I'm afraid neither would help matters regarding ground clearance issues tho.
Haven't seen any recent reports from Mike, but I'd expect he'll check back in on that when there's any new info to share.
Haven't seen any recent reports from Mike, but I'd expect he'll check back in on that when there's any new info to share.
Working on the gauge mount. Test fit (bolts to the seat bracket):
The top gauge is the differential pressure gauge. First thing I want to check with that is the various pressure magnitudes/drops in the airbox, filter, and carb. Just trying to get a handle on if or where I might be losing some induction efficiency. I want to take a few measurements under the car also, but I'm still trying to decide what location I'm going to use as the reference pressure.
The lower gauge is for measuring the exhaust/termination box backpressure. I have a port in the box that I can install a WBO2 sensor or a pressure gauge line. (A pic while I was trying to fit new panels around the termination box.)
An old pic while I was modifying the trans crossmember to fit the under-cockpit bellypan material.
The termination box is supposed to be good for a few horsepower. I hope the theory is right.
I also put this H-pipe at the header outlets in last fall. This location is supposed to be the most efficient, and good for a few horsepower also. One thing definite, it does mellow out the exhaust note.
All I've got for data so far with the bellypan is just SOTP feel. The underside of a C3 is pretty rough aero-wise, and I'm just trying to smooth-over some of the rough spots where I can. The car feels damn nice at speed, but I don't know an easy way at the moment to quantify it.
04-04-2013, 12:49 AM
#174
Race Director
Thread Starter
Sorry, been distracted by a few things the last several months (carb airbox, exhaust size/H-pipe upgrade and termination box, and a few weight reduction items) so I haven't had a chance to do any pressure measurements yet. Trying to finish up a couple things before a track day in the next couple weeks.
Working on the gauge mount. Test fit (bolts to the seat bracket):
The top gauge is the differential pressure gauge. First thing I want to check with that is the various pressure magnitudes/drops in the airbox, filter, and carb. Just trying to get a handle on if or where I might be losing some induction efficiency. I want to take a few measurements under the car also, but I'm still trying to decide what location I'm going to use as the reference pressure.
The lower gauge is for measuring the exhaust/termination box backpressure. I have a port in the box that I can install a WBO2 sensor or a pressure gauge line. (A pic while I was trying to fit new panels around the termination box.)
An old pic while I was modifying the trans crossmember to fit the under-cockpit bellypan material.
The termination box is supposed to be good for a few horsepower. I hope the theory is right.
I also put this H-pipe at the header outlets in last fall. This location is supposed to be the most efficient, and good for a few horsepower also. One thing definite, it does mellow out the exhaust note.
All I've got for data so far with the bellypan is just SOTP feel. The underside of a C3 is pretty rough aero-wise, and I'm just trying to smooth-over some of the rough spots where I can. The car feels damn nice at speed, but I don't know an easy way at the moment to quantify it.
Working on the gauge mount. Test fit (bolts to the seat bracket):
The top gauge is the differential pressure gauge. First thing I want to check with that is the various pressure magnitudes/drops in the airbox, filter, and carb. Just trying to get a handle on if or where I might be losing some induction efficiency. I want to take a few measurements under the car also, but I'm still trying to decide what location I'm going to use as the reference pressure.
The lower gauge is for measuring the exhaust/termination box backpressure. I have a port in the box that I can install a WBO2 sensor or a pressure gauge line. (A pic while I was trying to fit new panels around the termination box.)
An old pic while I was modifying the trans crossmember to fit the under-cockpit bellypan material.
The termination box is supposed to be good for a few horsepower. I hope the theory is right.
I also put this H-pipe at the header outlets in last fall. This location is supposed to be the most efficient, and good for a few horsepower also. One thing definite, it does mellow out the exhaust note.
All I've got for data so far with the bellypan is just SOTP feel. The underside of a C3 is pretty rough aero-wise, and I'm just trying to smooth-over some of the rough spots where I can. The car feels damn nice at speed, but I don't know an easy way at the moment to quantify it.
FYI, when I did my pressure differential for my CAI I had a +.2 psi increases when measured differential from engine bay.
Where are you setting your low pressure side? And high side?
04-04-2013, 11:09 AM
#175
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FYI, when I did my pressure differential for my CAI I had a +.2 psi increases when measured differential from engine bay. I'm going to do a similar measurement. I've got the cowl air inlet on mine, so I don't expect the efficiency of this type induction to be as high as your radiator plenum intake. My main goal for the airbox is to feed the engine with 40-50* cooler air.
Where are you setting your low pressure side? And high side?
Where are you setting your low pressure side? And high side?
There's a hundred places to measure under the car, and a like number of places on top of the car too. I'm trying to decide if just using a sealed volume as the reference pressure would simplify things. This would let me make a small map of the pressure changes across the bodywork and undercar area.
04-04-2013, 03:22 PM
#176
Le Mans Master
Mike, I'm liking your expedient instrument mount (easily removable, I assume). I've been eyeing my glove box ('78) for permanently mounting my ∆ gauges, as I could just close the door and they're gone, but worried they'd be too difficult to read accurately without a co-pilot.
04-13-2013, 11:21 PM
#177
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I was all primed for a track day yesterday at a somewhat local facility that has open test and tune days on Fridays. Unfortunately the weather forecast was for 41* temps and possible rain. Perhaps I'm getting older, as I admit I've lately become a fair-weather track guy. I've run a few in the past on rainy unpleasant days, and the cost/fun ratio just isn't worth it anymore.
Regardless, I'll get around to doing the pressure measurements at the next track day. In the mean time, I just got some C6 rear toe links that I'm adapting onto my (C4) suspension. I'm trying to take out a bit of the rear (under)steer inherent to C4 suspensions. Hopefully that will reduce the workload that the front tires have to do to overcome this rear steer during cornering.
In addition to some differential pressure measurements I want to make some quasi-absolute pressure measurements. I'm not confident that the vehicle interior is always at (zero-speed) ambient pressure while going around the track, so I'm reluctant to use it as my reference pressure. I'm looking around for a modest volume sealed container to hook up to the differential pressure gauge to use as my reference pressure. I have considered making a sealed container out of PVC pipe and a couple of end caps, but I'm open to other option suggestions from the group if it saves me time and effort.
Thanks,
Mike
Regardless, I'll get around to doing the pressure measurements at the next track day. In the mean time, I just got some C6 rear toe links that I'm adapting onto my (C4) suspension. I'm trying to take out a bit of the rear (under)steer inherent to C4 suspensions. Hopefully that will reduce the workload that the front tires have to do to overcome this rear steer during cornering.
In addition to some differential pressure measurements I want to make some quasi-absolute pressure measurements. I'm not confident that the vehicle interior is always at (zero-speed) ambient pressure while going around the track, so I'm reluctant to use it as my reference pressure. I'm looking around for a modest volume sealed container to hook up to the differential pressure gauge to use as my reference pressure. I have considered making a sealed container out of PVC pipe and a couple of end caps, but I'm open to other option suggestions from the group if it saves me time and effort.
Thanks,
Mike
04-14-2013, 03:23 PM
#178
Le Mans Master
IMCO, some good thinking there.
I'm wondering if there's any reason a simple length of capped-off pipe (perhaps with a bleed valve so you could readily equalize it with ambient air) wouldn't have sufficent volume to function reliably as a fixed reference pressure. What you wouldn't want is anything which contracts or expands like a flexible bladder.
I'm wondering if there's any reason a simple length of capped-off pipe (perhaps with a bleed valve so you could readily equalize it with ambient air) wouldn't have sufficent volume to function reliably as a fixed reference pressure. What you wouldn't want is anything which contracts or expands like a flexible bladder.
