Track times after 2.87 to 3.54 change (info)

[76 Sting]

76 Sting those tires if they are 255/70/15 are 29" tall. On a Vette those are mud boggers. Stock tire height is 27.4". At 29" it would be hard to spin those tires. One thing we don't know is whether or not the rear gears are the same ratio as the original and if not then did the speedo get calibrated to compensate. If it is correct then based on your numbers you have 3.73's. if that 76 is a stock or close to stock motor it will have a hard time spinning those tires off the line. Also if you have a big cam that doesn't turn on the power till it is up in rpm would also cause a lack of spinnage.Keep us posted.

Hey Moe-
I use an after market tach with a GPS system for dialing in the MPH. it was first done in a car that is brand new just to make sure it worked and it did up to 120MPH. A minute later we took a ride in my car and did the same.
We also did a car by car experience to triple check everything so I am 99% sure the the #'s are correct.
Here is what the motor looks like-350 rebuilt bored .30 over, trany rebuilt with shift kit, no emissions, true dual's w/ Borla and 2.25 exhaust, Shorty ceramic headers no cats, Edelbrock RPM intake, Edelbrock 1405 carb, Accel HEI disty, NOS PowerShot 125 hp, K&N Extreme filter, Stinger hood with direct type ram air injection.
Mudd bogers--- I like that one now you have me wondering if its the tires:confused . i just rechecked the tires and they are 225/70/15. With the set up I have above and take the NOS out of the picture for now because with that on I am all over the place. Do you think I should still have the problem? I do not know the cam spec's but it does pack a punch around 2500 to 3000 rpm's.

 

[76 Sting]

glensgages
I was going to check the way that "81 corvette" mentioned. Jack the car spin the drive shaft and count the revolutions of the tire. Is this fairly accurate measurement?

 

[dfw81shark]

Mudd bogers--- I like that one now you have me wondering if its the tires:confused . i just rechecked the tires and they are 225/70/15.

225/70s are a lot different than 255/70s..

 

[dfw81shark]

glensgages
I was going to check the way that "81 corvette" mentioned. Jack the car spin the drive shaft and count the revolutions of the tire. Is this fairly accurate measurement?

That's the way to do it for sure.

 

[76 Sting]

225/70s are a lot different than 255/70s..

You can count me in with another C3 to meet at the shows to bad their are not many of us. We'll just have to out shine the others.

Do you think my tire size represents a big problem concidering the engine mods?

 

[MoeJr]

I am now pretty sure you have 3.55 rear. The 225/70R15 tires are stock for that car. Looking at your set up the a couple things stick out. First is that the Edelbrock 1405 carb I believe is only 500 cfm where as the original QJet is 750. Next the Performer RPM is a high rise dual plane intake and is gonna cost u some low end torque. Those 2 thing shouldn't however cause u to not be able to spin them from a start. The only thing left is either tuning or the cam is way too big for the engine which is why the power seems to turn on at 2500-3000 rpm. U probably will never be able to hit the NO2 without those tires spinning. However I bet with some retooling of the combo you would be much more satisfied and not even need the nitrous. I will admit I am not a fan of nitrous cause it is a mishap away from total engine meltdown. Seen too many people hit the bottle only to lean out or have poor timing and blow the intake right off the car. Had a guy with a TPI iroc hit his nitrous and blow a hole in the fiberglass hood the size of the block. Keep us posted.

 

[Glensgages]

glensgages
I was going to check the way that "81 corvette" mentioned. Jack the car spin the drive shaft and count the revolutions of the tire.
Is this fairly accurate measurement?

76 Sting:
when done correctly, this method is't 'fairly accurate':
it's dead-nuts on the mark.


The only thing I'd do differently than spin the tires once and counting full-and-partial drive-shaft revolutions is spin the tires ten (10) times, and divide the drive-shaft revolutions by 10, and here's why.....

I'm an engineer/draftsman by genetics (my dad), and I've learned that some people aren't extremely accurate, or are intimidated by math and numbers:
I've also heard that some C3 guys say they've got 3.36 gears, others speak of 3.45 gears, and still others say they've got 3.54/3.55 gears.....

If you'd only spin the rear tires once, the margin between 3.36s and 3.45s is 1/10th of a drive-shaft revolution:
the difference between 3.45s and 3.54/3.55 is just another 1/10th drive-shaft revolution.
When you consider slack/slop in the drive-line and/or 'poor-judgement' in calculating partial drive-shaft revolutions, you can see how easy it may be to mis-read 3.36s and 3.45s, and 3.45s and 3.55s:
by using 10 axle revolutions, 3.36 gears would 33.6 drive-shaft revolutions, 3.45s would-be 34.5 drive-shaft revolutions, and 3.55s would be 35.5 drive-shaft revolutions.

It would be very easy to mis-judge 1/10th of a drive-shaft revolution, but anybody smart-enough to buy a C3 wouldn't mis-read 33.6 for 34.5, or 34.5 for 35.5, would they?
:confused

If you MUST rely on a single axle revolution method, try this helpful tip:
take a very flexible tape-measure (a cloth one, used by seamstresses work well), and measure the circumference (distance AROUND) the drive-shaft, and divide this circumference by 10.
Next, get a piece of 1'-wide first-aid tape (becuase it is White, and easy to read), and lay-out lines across the tape, spaced-out by the dimension you previously calculated, 1/10th the circumference of the drive-shaft.
Wipe the drive-shaft clean, and apply the "tape-measure" around the drive-shaft:
you will use the incremental-marks to figure partial-rotations.

A-fix a piece of 'anything' laying around the shop (an old coat-hanger works well) to 'someplace' on the bottom of the chassis, pointing towards the "tape-measure":
rotate the tires until the pointer is on a mark, and label this mark "0", and then begin rotating the tires, counting how many times the pointer passes "0", and how many marks past it.

(Basically, we've made a degree-wheel for the drive-shaft, similar to degreeing-in a cam-shaft)

Since each mark on the "tape-measure" is 1/10th of a revolution, it'll be easier to calculate gear-ratios:
3 times past "0", and slightly more the 3 partial marks would be 3.36,
3 times past "0", and slightly more the 4 partial marks would be 3.45,
and 3 times past "0", and slightly more the 5 partial marks would be 3.55:
3.70s would be 3 times past "0" and 7 partial marks, while 4.10s would be 4 passes of "0" and the first mark past "0".




Some of the math I supplied earlier have fallacies:
a torque converter that is extremely loose and doesn't approach 90% efficienciy would result in a error-prone calculation, and some drag-tires are designed to grow at-speed due to centrifical-forces.

Once, a buddy got a used rear-engine dragster that his wife "decided" that SHE wanted to drive it:
playing it safe, we dropped the motor/trans from her 13-second Camaro (10.0:1 pump-gas 355" SBC and THM400) into the frame-rails, where it ran effortless 6-fifties @ 105 MPH in the 1/8-mile, trapping at 5800 RPM.....

The first time we took it to a 1/4-mile strip, it ran 128 MPH, but trapped just 600 RPM higher (6400):
in other-words, it ran 22% faster (128 div/by 105 = 1.219), yet turned just 10% (6400 div/by 5800 = 1.103) more RPM.....

How can that be????? :crazy

After checking everything (tell-tale tach, ignition, converter, etc.) on the car, we decided we'd "try-something" at a future test-and-tune session by video-taping the car from the guard-rail at the finish-line (remote-control, of-course...), and what we saw was shocking:
even with a 'wimpy' (by dragster-terms) motor in the car, near half-track, the lower frame-rails and back of the car raised off the track-surface, as the slicks 'sucked-in' on-themselves, and grew incredibly, much like a Top Fuel slick you may've seen on TV.
:eek

after checking the 'code' on the side-walls of the slicks, we learned that the slicks that came with the dragster were specifically DESIGNED to grow at-speed, as the car was originally built for Competition Eliminator, where the racers use this tire-growth (quite-legal) as a poor-mans over-drive near the finish-line.
:duh

"..... and now, you know..... the REST..... of the story..... Good day!!!"

 

[76 Sting]

Glensgages-

You scare me... you know too much about this stuff and I am extremely jealous. I am the type of person that sucks in info when it is given to me. Thank God I do not live near you because I would be throwing questions at you every day...over beers of course . The info that you provided me is just shy of superb!!!! I really appreciate it. I will try this method and let you know how I make out, it may take a few days (new born), but it will get done. I need to understand why I am not spinning the tires of the line especially if my gear ratio is pretty good, meaning not the stock 3.08, because to me anything in the mid 3.50 range is OK by me.

 

[Glensgages]

76 Sting:
I'm not smart:
just a lot of trial-and-error.....
and, BOY, have I made my fair-share of errors.....

.....I need to understand why I am not spinning the tires off the line especially if my gear ratio is pretty good, meaning not the stock 3.08, because to me anything in the mid 3.50 range is OK by me.

I agree:
"you can tell, from the smell, that all is not well....."
:ugh

If I understand this correctly, you can't smoke the hydes off the line in 1st Gear, but CAN get a chirp going into 2nd Gear?
:confused

I had a (fairly) similar motor in my Z28 many moons ago that barked the 225/70R15s going into 2nd Gear with a shift-kit, but it spun them off the line as far as I cared-to.......

Is it possible that the torque converter has been replaced with a much tighter (and fuel-efficient) model, that won't multiply the torque in Low Gear, but when the shift-kit slams into 2nd, it has enough pressure, and the motor is wound-up enough, to spin the tires?

I'd think that a smallish carb / dual-plane intake induction system wouldn't be the problem:
both usually make gobs of low-end torque, at the expense of top-end punch.....
unless you have a very big stick (camshaft), with 240*+ at .050" valve-lift, which makes it's smoke at the higher RPMs.

As MoeJr advises, make-sure everything is in tune (ignition, fuel-system, etc.), and, as stated earlier, over-sized (height/diameter) tires can kill gear ratio:
take 2 identical Corvettes, both with 4-speed standard transmissions, 3.70 gears and 27" tall tires.....

"Theoretically", they'd turn the exact same RPM at the exact same MPH:
now, put 30" slicks on one of the Corvettes.
This Corvette's tires are now 11% taller (30 div/by 27 = 1.111, or 11% bigger), and the exact same MPH, it 'should' turn 11% fewer RPM:
in-effect, we've taken 11% of the gear-ratio OUT-OF that Corvette, and, 11% of the power (as multiplied by the rear gear ratio).

In other-words, a stock Corvette, running that speed but turning 11% less RPM with the stock-sized tires isn't running 3.70 gears, but in-reality, has what is called an "effective gear-ratio" of 3.33:1 (3.70 div/by 1.11 = 3.33).

"Theoretically", the big-tired Corvette would be a stone-turd off the line, but be capable of turning 11% more speed (MPH) at the still-common red-line that BOTH cars still have from the factory.

You'll see the effect of gearing upon acceleration next month during SpeedWeeks from Daytona, where the cars are set-up for SPEED, not power.
When those cars are dropped off the jacks, they'll have a hard time spinning their tires away from their pit-stalls, partially because they'll be set-up to run near 200 MPH when turning just 6800 RPM by using gear-ratios of 2.9:1-3.1:1, which is about the limit when using restrictor-plates (the other reason for lower power) on the 2.5-mile tri-oval:
in April, when the Nextel Cup cars run at Martinsville's flat, hair-pin/paper-clip half-mile, they'll burn their rear tires ALL the way down pit-road after a stop, because they'll be geared for maximum POWER, not speed, with top-speeds on the very short 800'-long straight-away of (a guess?) 150 MPH when maxing-out near 9000+ RPM.

 

[76 Sting]

Glensgages-
Don't kid yourself you are smart!

Your are correct nothing off the line, but chirps second every time. MowJr mentioned the standard carb for the 76 vette is Quad 750 if I understood him correctly. So that got me wondering if the Edl 600 was maybe too small taking in the mods that were done already to the engine? I was thinking of putting in bigger jets and smaller springs...maybe to match the Edl 750 instead of buying a new one since my is brand new anyway? The fuel systems is brand new Edl with dual fuel regulators for the carb and NOS. Both pressure gauges are right on the money when in use. The tires are 225/70/15 and I measured them last night and they were 27" tall. So I am guessing they are OK, meaning not mud boggers (that is still funny as hell). I wish it was just the tires. I can only guess the stall is factory, which represents a problem in the first place. I believe the 76 came with a stall of approx 1400 or 1600 RPM. My car does OK but really does not seam to make serious power until 2500 RPM, but couldn't that be because of the gearing anyway?

 

[Glensgages]

I believe the 76 came with a stall of approx 1400 or 1600 RPM.

You're probably correct:
the OEM converter in my '79 Z28 was fairly tight, too.....

My car does OK but really does not seem to make serious power until 2500 RPM, but couldn't that be because of the gearing anyway?

I don't think so:
the motor makes power at certain RPM based-on a variety of items (heads, camshaft, induction, ignition, exhaust, etc.).....
but I don't think that gearing is one of them.


Put that motor on a dyno, with NO rear gearing, and it'd probably still begin making smoke at 2500 RPM, correct?
:confused

Gearing, and stall-speeds, allow you to GET to that RPM much quicker off the line:
in an 'ideal-world', at the strip, your motor would stay at peak torque-making RPM all the way down the track, while the slippage/gearing changes, to keep the car accelerating faster.....
This is why Top Fuel and Funny Cars 'slip' the clutch at a controlled rate of speed during a run:
if you listen close, you won't hear any gear-changes, but one, long continuous (altho LOUD) groan as the car moves down the track.....
only in the last 300'-400' do you hear the pitch of the motor change, as the fire-breathing Hemi begins to wind-up.....

An example of what a higher-stall torque converter can mean to a car:
my Z28 had a 10", fairly tight and mild converter in it, running 13.30s at 105 MPH on 26" x 8" stickie-street tires with 4.10 gears, but at various tracks, I wanted to change my launch RPM (to vary my Reaction Times due to variying roll-outs), so we got an 8", 4500 stall converter for the THM400.

(The stickie-streets wouldn't hook, so we had to get 28" x 10" slicks, which then threw the gearing out of whack.....once we installed 4.56 gears, to compensate for the 2" taller slicks [mud-boggers with the 4.10 gears], the gearing was back in the motor's RPM power-band)

The next time out (with slicks and 4.56s), it ran 12-eighties at 105, and has since ran a best of 12.774 @109+, with the same long-block, cam, intake, carb, and fuel system as it had running 13.30s.

The car went from 8-fifties to 8-teens in the 1/8-mile alone, showing that the converter really improved the car's off-the-line acceleration:
keep in-mind the 4.56 gearing wasn't a performance-enhancer, it just kept the gearing proportional.....
but I wouldn't advise running a 4500-stall converter on the street (been there/done that, TOO!!!), as my Z28 is now trailered to/from the strip...

 

[76 Sting]

Glensgages I tried your AOL address, but nothing.

To answer your questions-

The tires do come very close, sometimes you can feel it slightly, but not much. From a stand still and turning a corner, I will loose total control whipping from left to right. No clank at all...a little bump maybe, but that's it.

take care

 

[Glensgages]

Glensgages I tried your AOL address, but nothing.

To answer your questions-

The tires do come very close, sometimes you can feel it slightly, but not much. From a stand still and turning a corner, I will loose total control whipping from left to right. No clank at all...a little bump maybe, but that's it.

take care

I believe I received your E-mails, and replied.....
:confused

Glensgages@aol.com

sorry.....

 

[76 Sting]

I believe I received your E-mails, and replied.....
:confused

Glensgages@aol.com

sorry.....

It's the Corp address and sometimes it automatically blockes e-mail's.