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Discussion Starter #1
Before I had the 4.56 rear axle ratio installed this week, I had done some "baseline" timing runs with the 3,73 gears.

Since I don't have a G-Tech or other computerized accelerometer, and I don't want to abuse my vehicle anyway, I simply did a few straightforward 0 to 60 runs using a digital stopwatch.

Even that turned out to be pretty inconsistent, as I am unwilling to do stuff like "preload" the torque converter. I simply mashed the throttle and the stopwatch start buton at the same time, and when the speedometer touched 60, i hit the stop button the stopwatch.

I used the speedometer even though I knew it was damped (so that it won't appear "nervous as we drive). I figured the tachometer was not going to be trustworthy since even if I calculate he rpm versus speed relationship in 2nd gear, I KNOW that torque converters and auto transmission clutches slip under full throttle and shift conditions.

Turns out, that I may have made a big mistake using the damped speedometer. It may lag a lot more than I thought.

I learned this today when I finalyl got a chance to hit the throttle hard on a freeway entrance ramp from virtually a dead stop (just turned onto the ramp from a city street). With the new 4.56 gearing, the transmission hit the top of 1st REALLY fast - much, much faster than before the gear swap. But what was really revealing is that I caught the flash speedometer reading right at the shift point. With the new gearing and the raised 6200 rpm shift point, it ACTUALLY shifts at 39 mph. However, the speedometer had only gotten to an indicated 30!

This means I cannot "repeat" the timing runs with the 4,56 gearing with any degree of accuracy at all. In fact, it's pretty likely that the times I got with the 3.73 were also longer than reality, because while the speedo would lag LESS with the slower 3.73 acceleration, it would still lag appreciably.

I guess what I need to do is borrow a G-Tech and at least get accurate times for the 4.56 gearing. That won't give us any comparison base, as I'm sure my "protect-the-SSR" and "be safe at all times" approach to acceleration won't come anywhere near what the magazine test drivers and Chevrolet do when testing. Sigh . . .

Jim G
 

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sure wish you could have gotten better before and after data,
not very scientific at all , i guess ''seat of the pants'' is still
the best method......................
 

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JimGnitecki said:
Before I had the 4.56 rear axle ratio installed this week, I had done some "baseline" timing runs with the 3,73 gears.

Since I don't have a G-Tech or other computerized accelerometer, and I don't want to abuse my vehicle anyway, I simply did a few straightforward 0 to 60 runs using a digital stopwatch.

Even that turned out to be pretty inconsistent, as I am unwilling to do stuff like "preload" the torque converter. I simply mashed the throttle and the stopwatch start buton at the same time, and when the speedometer touched 60, i hit the stop button the stopwatch.

I used the speedometer even though I knew it was damped (so that it won't appear "nervous as we drive). I figured the tachometer was not going to be trustworthy since even if I calculate he rpm versus speed relationship in 2nd gear, I KNOW that torque converters and auto transmission clutches slip under full throttle and shift conditions.

Turns out, that I may have made a big mistake using the damped speedometer. It may lag a lot more than I thought.

I learned this today when I finalyl got a chance to hit the throttle hard on a freeway entrance ramp from virtually a dead stop (just turned onto the ramp from a city street). With the new 4.56 gearing, the transmission hit the top of 1st REALLY fast - much, much faster than before the gear swap. But what was really revealing is that I caught the flash speedometer reading right at the shift point. With the new gearing and the raised 6200 rpm shift point, it ACTUALLY shifts at 39 mph. However, the speedometer had only gotten to an indicated 30!

This means I cannot "repeat" the timing runs with the 4,56 gearing with any degree of accuracy at all. In fact, it's pretty likely that the times I got with the 3.73 were also longer than reality, because while the speedo would lag LESS with the slower 3.73 acceleration, it would still lag appreciably.

I guess what I need to do is borrow a G-Tech and at least get accurate times for the 4.56 gearing. That won't give us any comparison base, as I'm sure my "protect-the-SSR" and "be safe at all times" approach to acceleration won't come anywhere near what the magazine test drivers and Chevrolet do when testing. Sigh . . .

Jim G
Just a thought, was that with or without the Traction Control on? :confused
 

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Discussion Starter #4
That was WITH traction control on. You are right - that could have adversely affected the results too, but I ddin't want to deal with controlling wheelspin, as that's an even bigger variable, and also abusive to the vehicle.
 

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Discussion Starter #5
I did go out again this morning, and did some experimentation. I specifically checked to see at what point the transmission shifted from 2nd into 3rd.

With stock gearing, the shift point, at 5900, should have been 85 mph. As discussed above, I never thought to check this spcific thing BEFORE I had the rear axle changed,

With the 4.56 gears, and the new 6200 rev limit, that 2nd to 3rd shift should occur at about 73 mph.

The ACTUAL reading on the speedometer at that shift this morning, doing multiple attempts, was just over 60 mph indicated.

This unfortunately means that all my "before" measurements of 0 to 60 are fairly useless, as although I allowed for the full tank of gas and my own greater than average weight, it never occurred to me that the speedoemter might be lagging THAT much.

All the "after" measurements I took this morning are even more useless, as the lag with the new gearing is FAR greater than with the old gearing.

I can tell you all this much though, without grasping for more accuracy than is really there: the time from o to an indicated 60, which appears to be an actual 73, is AT LEAST 3/4 of a second quicker than the old time.

And remember, since I was shooting for the same "indicated 60" each time, and the "new" indicated 60 is definitely really a higher speed than the old indicated 60 was (because of the speedometer lag being greater with the new gearing), the actual "0 to same true speed" is MORE than 3.4 of a second quicker.

That agrees with what I predicted. My software predicted a 0.83 second reduction in 0 to 60 time with this gearing change.

Sorry I didn't understand everyhting BEFORE the gearing change that I knew now. If I had, and if I could have gotten access to a G-Tech, we might have actually gotten good data. As it is, all I can tell you is the SSR is now at least 3/4 second faster to 60 mph, and the feel under all driving conditions is remarkably different.

Jim G
 

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this is not accurate info what about converter slip ? I have a road race Sonoma that
I have drag raced also, it has 600rpm of slip going thru the traps there is no way to calulate
your speed by your tach. when there is slip involved. Any way the speedometer shouln't
have any problem keeping up , these trucks are fairly slow !
 

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Discussion Starter #7
Rick: A racing torque converter has a MUCH higher stall speed (speed where slip stops) than a street vehicle converter. Our SSRs converts probably stall under 2000 rpm.

A dragracer setup can have much more slip because it only needs to run under load for seconds at a time. If you run under slip conditoons very long, you are converting mechanical energy into heat - a LOT of heat, and the transmision will fail.

I agree that an SSR is too heavy to be "fast", but speedometer damping is a factor even on vehicles that are not "fast". Some tachometers are unfortunately not much better. Ask an automotive instrumentation enginerr.

Jim G
 

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The Sonoma I was refering to has a stock converter, and only locks up in over drive,
an automatic is coupled to the engine by fluid, there is always a speed difference between
the engine and the trans. gears unless lockup is happening in the converter which does not happen in 1st and 2nd in a 4L60E, its not actually ''slipping'' like a clutch would.
 

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Torque Converters

rick418cars said:
The Sonoma I was refering to has a stock converter, and only locks up in over drive,
an automatic is coupled to the engine by fluid, there is always a speed difference between
the engine and the trans. gears unless lockup is happening in the converter which does not happen in 1st and 2nd in a 4L60E, its not actually ''slipping'' like a clutch would.
:agree

I had mentioned this in another thread to Jim , but you have explained it better .
 

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Discussion Starter #10
Rick418cars and 41chevcoe: I think you guys MIGHT be right, but I'm not sure! I know that sounds stupid, but here's why.

Only one road test magazine, Road and Track actually gives you the individual actual shift points for each gear for each car tested (at least they did so in the 2005 road test annual I just examined), and that was interesting.

When I did the math using the actual gear internal automatic transmision gear ratios and final ratios, the tire dimensions, and the published actual shift points in mph, I found that they did NOT match up with the engine redlines. In all cases for automatic tranmissions, the shifts actually occurred at a road speed far short of the redline, averaging 90 to 93% of the redline. IF we can believe the published data.

Now, in some cases that's probably because the manufacturer set the transmissions to shift earlier than redline. But, the CLOSEST I found it ever got to redline (and that was a performance Cadillac model) was where the road speed was 97% of what the redline would be.

So far, you guys looked good on your statement that converter slip would always do this.

However, I then checked the results in the same magazine for MANUAL transmission cars, and guess what: same thing, except that the actual shift points were running 95 to 97% of the redline. Where is the slip in a MANUAL?

Of course this COULD be because even road testers can be somewhat conservative in their shifting, but then again, my experience is that they are NOT!

So, in the absence of really good data, I am stymied.

I guess I have to revert to one of my original statements: we need to do runs using a G-Tech or similar onboard device, that has a 3-axis solid state accelerometer, engine rpm pickup signal, and a computer, and can give us REAL speed vs time vs engine rpm data.

Even then, you have to observe all the cautions: no wheelspin, no significant vehicle pitch changes, etc, so you don't fool the accelerometer with motion unrelated to actual straightline movement in the forward direction.

I have one of those types of devices, a "Veypor" actually, on one of my motorcycles, and it does it even better by adding a magnetic speed sensort to the rear wheel. That way, wheelspin and pitch changes are filtered out by the computer using a smart algorithm. The actual results the Veypor shows match my computer projections to a fraction of a percent. It's a little inconvenient as a PORTABLE test device, because it requires hard wire connections to both the rear wheel speed sensor and an rpm signal, and also needs 12 volts from the vehicle or other external source.

Jim G
 

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Even G techs are unreliable though much more accurate than stop watches and speedos. The right test would be a track, you get all those nice intervals and the only really poor number is the trap speed, which is averaged over the last 60'. Racing TCs aren't particularly slippy once they're getting rpm. I use a 10" 3500 stall in front of a TH350 and the slip at 4000rpm is very small.
 

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Discussion Starter #12
chuckbutcher: You are right about the terminal speed at the track. In an SSR, that has a quarter mile terminal speed of about 90 mph, it gains the last 1 mph during that last 60 feet (1260 to 1320 feet), so the terminal speed calculated by the track's equipment is going to understate the true speed at 1320 feet by about 1/2 mph.

HOWEVER. an even BIGGER error in terms of significance is the use of the staging area which creates a rollout error. It sounds small, but it is actually HUGE.

The difference between a shallow stage and a deep stage is say 12 inches. Basic physics tells you that:

distance = Vi x T + 0.5 A x TxT
where:
distance = 12 inches in this case = 1 foot
Vi = initial velocity = zero in this case
A = rate of acceleration, which for our SSRs is about 0.31g from a dead stop
T = Time used to get to distance specified

So, solving for T, we see that T = 0.45 second!

I tested this also by subbing a "zero" rollout into my software (I normally use 12 inches to calculate the "best" elapsed time posssible), and the actual difference turns out to be 0.43 seconds after internal incremental rounding, and the SSR is already doing 3 mph at that 12 inch point!

Experienced drag racers will verify what I am saying above. THAT contributes largely to where consistent or inconsistent 60 foot times AND 1/4 mile elapsed times come from! (consistency of launch techniques being the other factor of course)

Jim G
 

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Discussion Starter #13
Oh, and by the way, if you change the 160 lb "standard" driver to 230 lb, and the fuel in the gas tank from 2 gallons to 13 gallons (about half tank, which is far more realistic than 2 gallons for road use!), the 0 to 60 time changes by 0.23 second (!!) and the quarter mile time changes by 0.18 second!

So, those of you guys that have the heavy options (carpeted cargo lid, sidesaddles, running boards, etc), should expect significantly different acceleration times than tose who have no options.

Jim G
 

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My wife has pretty much committed to taking the SSR racing at the track where I race the 62. Since I find a 12.75 car a little tame, I have no interest whatever in going 15s in a 5K# truck, but it will be interesting to see how she does and the truck does.

As far as rollout is concerned, something is amiss. The SSR is not going to gain .43 in ET due to roll out. I have a 60' of 1.75 @ 2250' CA actual on 9.25 Hoosier Superpros DOTs. I've experimented with deep and shallow stage and the ET difference was smaller than you've postulated by quite a bit. I do shallow stage for the simple reason that it allows me to go on the flash of the last yellow and cut .009 - .020 lights vs having to wait which is extremely difficult to time and leads to huge variations in RT. As a testing proceedure it's simple enough to stage shallow consistently. BTW, space between the beams NHRA is 7", typically.

I can't state what the SSR will gain in the last 60' reasonably since I haven't tried it and the final gear ratio in the 1/4 and powerband position is outside my knowledge, but if it's making 99mph in the 1/4 with what has to be an abysmal 60' then it's making up a lot on the upper end. I run 12.75 @ 104.5 @ 0' (per NHRA alt correction tables) on 26" tires, 3.42 gears, TH350 w/10" 3500 stall at 3250# and my speed is climbing fast since I'm just into the gut of my powerband at the traps. (compromises must be made in a drag car that gets daily use @3500' in NE OR and wore studs for some of the year)

Well, as I said, it'll be interesting to see, if she goes along with the idea.
 

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Discussion Starter #15
Chuckbutcher: The terminal speed for the 03 and 04 SSR is 90, not 99!

As for rollout, do a google search on "rollout" and read the articles it pulls up!

Also read the decriotion of rollout on the G-Tech website.

My 0.43 is right on for the SSR! An actual driver that is experienced can change his own ET realistically by at least half of that. Getting it tighter than that is pretty tough without a lser to guide your staging!

Jim G
 

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There are 2 reasons I stage shallow, one is RT as I mentioned, the other is control of rollout. I can bump into the lights softly enough to make the stage light flicker on, that's my control point. If I mess it up, I'm probably going to redlight or try to wait and get some horrid RT. I race NHRA Div 6 Pro bracket, I'm at the slower end of the bracket. Since brackets are about dial and cutting a light, I don't worry too much about paring ET, I'm fast enough to stay in my Class and minute ET gains are meaningless. Yep, I have a faster car project, but it'll be a dedicated car with 9.0 as the goal. The 62 can have traction issues out the kazoo if track conditions get poor, it's a street car, gearing, full exhaust, steel wheels, 215R60-15 V rates/Cragar SS on front, IROC strut suspension, you ge the idea. Marginal gains just aren't in the picture. It's a very cool compromise car, going any further either direction would just wreck it.

I wasn't thinking about the poor HP/# of the SSR, that would surely make rollout a bigger factor than I experience. 1.75 60' is a heck of a hit for a 3250# car on 26" tires/3.42. Torque is your friend.
 

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Discussion Starter #17
chuckbuster: Yes, I also agree that torque is your friend. That's why I changed the SSR rear axle ratio from 3.73 to 4.56. That upped the torque to the rear wheels by 22%. Feels a LOT better with that gearing on the street (I'm not a street OR dragstrip racer). and believe it or not, it RAISES the top speed (if you actually get higher speed rated tires and disable the speed limiter) because the stock gearing is way tall in order to chase the last fractional MPG :)

Jim G
 

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If a little is good...

Jim,
With the typical "guy thought process" that if a little is good, a lot must be better, what would a 4.88 gear do the SSR's performance. What would the RPM be at 70 mph with a 4.88 gear?
 

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Discussion Starter #19
bass656: I am always willing to contribute to the delinquincy of a gearhead.

You asked, so here is the data, for a 160 lb driver, only 2 gallons of gas in the vehicle, and absolutely PERFECT technique (don't try this at home, and especially not on the street):

Ratio 0-60 1/4 mi RPM @ 70 Top speed (limiter disabled)

3.73 7.6 15.84 2097 139

4.56 6.7 15.24 2564 147

4.88 6.4 15.08 2744 146

Note that because of the "epa mileage" stock gearing, sitffening the gearing actually INCREASES top speed instead of reducing it.

CAUTION! CAUION! CAUTION!

With the 4.88, and no chnage in redline, top speed in 1st is only 34 mph
4.88/3.73 = 131%, so engine accessories and driveshaft will be spinning fast! This may not be acceptable (check with someone smarter than me).

With my 4.56 gearing, I LOVE the results, BUT (!) that darn new large diameter, ultra thin metal thickness, aluminum driveshaft rings like a bell at speeds above 30 mph and gets louder with increasing speed. What is happening as near as we can figure is that the aluminum driveshaft tube, which unlike many other high speed drievshafts does NOT have sound deadening material in it, is acting like an absolutely PERFECT "trumpet or horn", amplifying an acceptable gear whine a LOT, and delivering it right to the passenger compartment.

Before trying this, wait until next week, when I can report on my latest effort to stop the noise. On Monday, the driveshaft gets a foam sound deadener transplant! :)

Stand by . . . :)

Jim G
 
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