Rear gear, which one ? - Chevelle Tech
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post #1 of 18 (permalink) Old May 20th, 17, 5:11 PM Thread Starter
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Geoff Swanson
 
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Rear gear, which one ?

Last night I picked up .3 tenths in the quarter to run a 11.29 at 123.1MPH and this was with a "peddle the car" to avoid going into the other lane after just shifting into 4th. Since the car is hooking really good now I can bump the launch even more and get rid of some if not all of the bog. Right now I'm launching at 4400 RPM but still under peak torque. I ran out of time last night, but I was very pleased. Ultimately I'm convinced that I have to change the rear gear for the car to reach it's full potential. 60 foot time is 1.7 right now and in my eyes it is not very good and certainly does not match a car that goes 123 MPH through the traps. 1.55 60' is where we need to be. I'm shifting at 6700 but going through the traps at 6000 ish RPM's with my 4.11 rear gear . I have to also play with shifting at a higher RPM as the car is pulling like a locomotive even at 6600 where the shift light is set to come on. I'm going to hit my favorite back road and determine where she flattens out.
What rear gear should I be running ? Since I have a 9" it is easy to build another 3rd member. I have a gear in mind, but want to get some opinions before I choose.
The car weight with me in it and 7 gallons of fuel is 3853.
The goal is to run this car to the low 10'90's in Tucson which will equate to a 10.70 or 10.60 in Phoenix.

Last edited by tucson67ss; May 20th, 17 at 6:48 PM.
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post #2 of 18 (permalink) Old May 20th, 17, 6:05 PM
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jeff
 
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Re: Rear gear, which one ?

You need to tune some more to get rid of the bog.
You will not get the full potential of the build until you do that.

launching at higher R's may cover up some of it but the loss is still there.

I was getting 1.8 60 foot times with a 400-600 over stock rpm stall which put me at 1800rpm on the launch.. I did not leave at 1800 I left much lower as I had a TH350 in a 78 nova with a 350" and 3.70 gear and uniroyal tiger paw 275-60-15 tires. 270H comp hydraulic cam and ported double humps.
Yes 1.8 60 foot times.
Buddies Nova had ET streets 275-60-15 and 3000 stall B&M that stalls at 2200-2400 and his 60 foot times are 1.6
With 4.57 gear in a 9".

Tunnel-ram and 292 comp cam with 601 heads .
It got the same 1.6 60 foot with a 280H comp cam and 2 barrel 305 heads on the same engine with the tunnel-ram and 2 600 edelbrocks.

These are tuned and NO bog even when running 3.00 gears.

I would swap in my 3.00 gears into the 9" and tune my engine to run super excellent.
Then you get the full potential when running 4.11 or better.

I had 4.57 gears and built another set of heads and ran a single carb.. I thought it ran very well No issues at all.

I later swapped in my highway gears and found the tune was terrible at low speeds or lower RPM's.

I tuned it to run with the highway gears.
When I swapped the 4.57's back in i was amazed at how much better it ran than before with the same gear.

Do not cover up a tuning issue with R's.
Your gear is good at 4.11.
You could try some 4.56 4.57 gears and see if you are quicker but it better hook up.
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post #3 of 18 (permalink) Old May 20th, 17, 6:10 PM
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Chris
 
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Re: Rear gear, which one ?

I'm running MT ET Pro's that are 28" and Charlie at ATI told me for max ET and his treemaster to use 4.30's.
He was right for my combo.
1st pass ever with the 406 it went 1.55 60' and a 10.78 lifting
2nd pass is in my sig. Lil better burnout and it went 1.45
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73 nova,3515#(all steel)Pump gas!(91octane)406ci N/A, best 1/4,1.45 '60,[email protected],10.6 @ 122.38, short shifting,NO tuning!


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post #4 of 18 (permalink) Old May 20th, 17, 6:46 PM Thread Starter
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Re: Rear gear, which one ?

Quote:
Originally Posted by jeff swisher View Post
You need to tune some more to get rid of the bog.
You will not get the full potential of the build until you do that.

launching at higher R's may cover up some of it but the loss is still there.

I was getting 1.8 60 foot times with a 400-600 over stock rpm stall which put me at 1800rpm on the launch.. I did not leave at 1800 I left much lower as I had a TH350 in a 78 nova with a 350" and 3.70 gear and uniroyal tiger paw 275-60-15 tires. 270H comp hydraulic cam and ported double humps.
Yes 1.8 60 foot times.
Buddies Nova had ET streets 275-60-15 and 3000 stall B&M that stalls at 2200-2400 and his 60 foot times are 1.6
With 4.57 gear in a 9".

Tunnel-ram and 292 comp cam with 601 heads .
It got the same 1.6 60 foot with a 280H comp cam and 2 barrel 305 heads on the same engine with the tunnel-ram and 2 600 edelbrocks.

These are tuned and NO bog even when running 3.00 gears.

I would swap in my 3.00 gears into the 9" and tune my engine to run super excellent.
Then you get the full potential when running 4.11 or better.

I had 4.57 gears and built another set of heads and ran a single carb.. I thought it ran very well No issues at all.

I later swapped in my highway gears and found the tune was terrible at low speeds or lower RPM's.

I tuned it to run with the highway gears.
When I swapped the 4.57's back in i was amazed at how much better it ran than before with the same gear.

Do not cover up a tuning issue with R's.
Your gear is good at 4.11.
You could try some 4.56 4.57 gears and see if you are quicker but it better hook up.
Hi Jeff,
The bog is very slight and from the way the car is running I think changing the gear to a 4.56 would benefit with ridding the bog. There is some little things I could do like lean it out a little(currently low 12's AFR reading at WOT, cruising is high 12's and idle is mid 13's) and trying some other timing settings, but it is running really strong and does not miss a beat. The car is dead hooking now with a light burnout and 13.5 lbs of air pressure. Allowing the tires a little slip would also rid the slight bog. When I say bog it is not a fall on your face bog by no means and recovers very quickly.
My though process is a 4.56 gear would lower the 60 ' time and allow me to get up to my max RPM through the traps while maintaining the same MPH. This should equate to a faster ET. I currently cross the line at 6000 RPM's and the motor is very strong at 6700. I have not had it on the dyno yet, but the butt dyno I have is pretty darn accurate. I'm actually thinking the shift point should be 6900, but it for sure is not 6000.
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post #5 of 18 (permalink) Old May 20th, 17, 6:51 PM Thread Starter
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Re: Rear gear, which one ?

Quote:
Originally Posted by WHT/73 View Post
I'm running MT ET Pro's that are 28" and Charlie at ATI told me for max ET and his treemaster to use 4.30's.
He was right for my combo.
1st pass ever with the 406 it went 1.55 60' and a 10.78 lifting
2nd pass is in my sig. Lil better burnout and it went 1.45

Hi Chris,
I just added my car weight to the initial post. I'm weighing in at 3850 with me in the car and 7 gallons of fuel. Based on my current RPM (6000) MPH(123) through the traps I calculate I should be running a 4.56 gear. The motor is VERY strong and currently shifted at 6700 RPM's.
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post #6 of 18 (permalink) Old May 20th, 17, 7:24 PM
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Re: Rear gear, which one ?

How tall are your tires?
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post #7 of 18 (permalink) Old May 20th, 17, 7:27 PM
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Re: Rear gear, which one ?

What rear tire did you end up going with? Leaning my jetting to being my AFR from low 12's to 13 was worth 2.5 mph in my car.
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post #8 of 18 (permalink) Old May 20th, 17, 7:57 PM Thread Starter
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Geoff Swanson
 
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Re: Rear gear, which one ?

Quote:
Originally Posted by 72BBMonte View Post
How tall are your tires?
Hi Jon,
28 " Hoosier drag slicks I could go to a 26" tire and get closer to my peak RPM through the traps but would still be short a couple of hundred RPM's and would sacrifice a little in width of tread. Only .2 but every little bit helps especially with a manual car.
What are your thoughts ?

Last edited by tucson67ss; May 20th, 17 at 8:15 PM.
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post #9 of 18 (permalink) Old May 20th, 17, 8:13 PM Thread Starter
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Re: Rear gear, which one ?

Quote:
Originally Posted by pockets View Post
What rear tire did you end up going with? Leaning my jetting to being my AFR from low 12's to 13 was worth 2.5 mph in my car.
Hi Kerry,
28"... Wow, that is quite the gain ! I will be working on that more later this week as I did not have the jets needed to get to where I wanted to be.
I was pretty happy when I added the AFR gage and saw I could lean it out 2 jet sizes on the primary and 5 on the secondary as that will improve MPG. However, I have 2 other cars with much better MPG and will stick to them to save fuel.
One thing I noticed was a big change in AFR at idle when I opened the cutouts for the track. It leaned out to high 15's however, the cruising and WOT were barely affected at all but were slightly leaner. I think 1 jet size smaller in the primaries and 2 in the secondary's will get me where I want to be. That reminds me, I need to write myself a note to stop at the speed shop. I have 11 sets of jets and go figure, I skip all around the ones I need
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post #10 of 18 (permalink) Old May 20th, 17, 8:20 PM
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Re: Rear gear, which one ?

Have you had someone video tape the car launching and examined how it leaves?
I would make sure that the suspension is reacting properly before the switch to rear gears.
If it's suspension tuning that you need and it improves your 60fts and accelerates faster and earlier, you may find your existing 4.11s will get you a better rpm in the traps.

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post #11 of 18 (permalink) Old May 20th, 17, 9:20 PM Thread Starter
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Re: Rear gear, which one ?

Quote:
Originally Posted by BlackoutSteve View Post
Have you had someone video tape the car launching and examined how it leaves?
I would make sure that the suspension is reacting properly before the switch to rear gears.
If it's suspension tuning that you need and it improves your 60fts and accelerates faster and earlier, you may find your existing 4.11s will get you a better rpm in the traps.

Hi Steve,
I have photo's of the launch and it has a real good bite now and could probably use some slippage added. I'm currently developing a 2 valve hydraulic clutch set up that will allow the clutch to slip slightly at launch that will allow me to maintain RPM.
I had it engaged last night and it did lighten the hit, but the proportioning valve needs to be able to restrict more than it's current state to slow down engagement even more. I found a different proportioning valve and ordered it.that It will allow me to have 100% restriction of release pressure if I wanted. The way the system works is you have a line lock and bypass y's to allow you to have flow only through the proportioning valve when the line lock is engaged, but when you release the line lock button mounted on the gear shift it will go back to normal operation for the following shift's. I made a slightly modified version that a person here on CT guided me through.


Correct me if I'm wrong but ideal rpms through the traps is the top of my power range, which is 6700 + RPM. I really don't think my current motor would push to that RPM with the current gearing in the quarter with out a significant boost of power. If it did I would go through the traps at 134 ish MPH. That would be nice, but without helping of N20 I don't see it happening.
Raising the rear gear would certainly improve the 60' if you hook and the motor certainly has the power to get to 6700 by the traps with a 4.56 gear.
What are your thoughts based on my theory ?
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post #12 of 18 (permalink) Old May 20th, 17, 10:01 PM
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Re: Rear gear, which one ?

I am far from an expert and have done similar to your intensions with the rear gears, (gone from 4.11s to 4.56s), but also know that my suspension needs sorting out in subtle or more drastic ways.
I am yet to return to the track to see what the changes are after the swap and now making more power with different heads.

From what I understand, your shift point and rpm through the traps should be +10% of your peak HP rpm. Your shifts depend on your transmission gear ratios and where your rpm will drop to in order to always have the maximum amount of power being transferred. As for through the lights, closer the redline I had read..
With my 4.11s (& 2 speed 'Glide) I was passing through the traps at a little under 6K @ 122mph. Way too low considering that my shifts were high 6Ks and my redline ~7200.
So yeah, I have switched to 4.56s purely to bring up the Rs in the traps (and have also gone from a 3500 to a 5500 converter for more available power off the line). I hope to be passing through much closer to 7K and mid-high 120s with this engine. (Moroso slide rule suggests low 130s but I'm not that optimistic.)
So yes, I agree with your theory, but just want to see that it's not a suspension issue and not gears before you go to the bother.

Your clutch set up sounds interesting and if it's an improvement, then it's an improvement.
I'm not sure how it compares to a clutch, but with a converter, talking 60fts, I found foot braking at the stall speed was much worse than say holding it near 2K where the main metering system was working (carb) and that seemed to allow the engine's acceleration/momentum to hit the converter better for a more aggressive launch (where my 60s still kinda sucked). The left very soft when foot braking at the stall speed.

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post #13 of 18 (permalink) Old May 20th, 17, 10:27 PM Thread Starter
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Re: Rear gear, which one ?

Quote:
Originally Posted by BlackoutSteve View Post
I am far from an expert and have done similar to your intensions with the rear gears, (gone from 4.11s to 4.56s), but also know that my suspension needs sorting out in subtle or more drastic ways.
I am yet to return to the track to see what the changes are after the swap and now making more power with different heads.

From what I understand, your shift point and rpm through the traps should be +10% of your peak HP rpm. Your shifts depend on your transmission gear ratios and where your rpm will drop to in order to always have the maximum amount of power being transferred. As for through the lights, closer the redline I had read..
With my 4.11s (& 2 speed 'Glide) I was passing through the traps at a little under 6K @ 122mph. Way too low considering that my shifts were high 6Ks and my redline ~7200.
So yeah, I have switched to 4.56s purely to bring up the Rs in the traps (and have also gone from a 3500 to a 5500 converter for more available power off the line). I hope to be passing through much closer to 7K and mid-high 120s with this engine. (Moroso slide rule suggests low 130s but I'm not that optimistic.)
So yes, I agree with your theory, but just want to see that it's not a suspension issue and not gears before you go to the bother.

Your clutch set up sounds interesting and if it's an improvement, then it's an improvement.
I'm not sure how it compares to a clutch, but with a converter, talking 60fts, I found foot braking at the stall speed was much worse than say holding it near 2K where the main metering system was working (carb) and that seemed to allow the engine's acceleration/momentum to hit the converter better for a more aggressive launch (where my 60s still kinda sucked). The left very soft when foot braking at the stall speed.
My current stats and you old ones are pretty much identical all the way down to the MPH.
I'm shifting at 6700 but am going to check out raising that to 6900 as it is pulling really strong at 6700. I'm running a Tremek TKO 600 and besides the launch the RPM dips very little with each shift.
I go through the traps at 6000ish and the car is just pulling like a locomotive. Straub and Wolfplace really did a great job and pairing up my top end. I could certainly run a bigger cam, but I want the car to be very street friendly. It did lose some of the street friendliness with the last change, but it was not severe and it was well worth the trade off.
The new rear gear would tell me very quickly if it was a good choice. The other issue is my current set up is 4.11 but is using a posi unit that I really would like to NOT destroy. It is just a matter of time before you smoke the clutches or blow the spider gears. A spool will be so much stronger for those hard launching.
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post #14 of 18 (permalink) Old May 20th, 17, 10:48 PM
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Re: Rear gear, which one ?

Quote:
Originally Posted by tucson67ss View Post
Hi Jon,
28 " Hoosier drag slicks I could go to a 26" tire and get closer to my peak RPM through the traps but would still be short a couple of hundred RPM's and would sacrifice a little in width of tread. Only .2 but every little bit helps especially with a manual car.
What are your thoughts ?

I wouldn't go to 4.56 or 4.57 with only 28" tires. Too much rpm and it would help create more traction problems.


4.29 might be better but it would only raise 400 rpm through the traps probably.

If you plan on anything but dedicated bracket car and putting around town I would keep the 4.11 at least until you break them. First gear gets real low with too much starting line ratio. if you go to much rear gear.
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post #15 of 18 (permalink) Old May 21st, 17, 12:11 AM
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Re: Rear gear, which one ?

Quote:
Originally Posted by tucson67ss View Post
A spool will be so much stronger for those hard launching.
A spool would be, but much nicer would be a TrueTrac or WaveTrac. I put a WaveTrac in mine..

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