[oregon chevelle]

Here are a couple runs from the last time I went out.

DATE 8/25/2006
Time of Day 7:00 PM 7:43 PM
Reaction 0.1091 0.0749
60 ft 2.2149 2.2151
330 ft 5.9349 5.9570
1/8 ET 9.0199 9.0191
1/8 MPH 79.49 80.35
1000' ET 11.6748 11.6441
1/4 ET 13.9148 13.8720
1/4 MPH 100.65 100.68

My transmission gearing is 1st-2.64, 2nd-1.75, 3rd-1.34 & 4th 1-1.
Rear gears are 3.08.
Flywheel weight I do not know.
Tire size is 275/60/15 or 27.99.
Launch rpm is 4000-4500.

It does not fall flat during the run just on launch If I hook up. On the two runs I have posted I did not bog because I spun instead. It only falls on its face if it hooks up and does not spin. I believe the valves are adjusted correctly and the timing is at 16 initial and 36 all in by about 3200 rpm. this is to the best of my limited knowledge with trying to tune the thing myself.

 

[grandpaws 57]

bog at line

when I ran at Woodburn I had simular problem.I had a 55 4dr w/409 4sp. I went to a heavy fly wheel.I assume you have sb chev.Looking over your spec.I see your rear end ratio as the first thing I would change.A 3.70 would be a good pick if you drive a lot.Hope this helps

 

[xntrik]

Right now you are geared to 2200 rpm. To run effectively you will need to get to 2800 rpm @ 60 mph= 3.89 gear.

Certainly a heavier flywheel will help reduce the bog by holding inertia, but you just don't have enough launch gear. Remember you are moving a 3800 lb Chevelle. You aren't going to get 1.7 60 ft times easily.

We "old timers" talked gear ratio as "rpm @ 60 mph". So we know what it takes to make it work.

http://www.csgnetwork.com/multirpmcalc.html

Learning a clutch slipping launch technique will help too, but it is hard to be consistent and hard on the clutch. BTDT :thumbup:

 

[oregon chevelle]

Thanks to both of you. I figure it is probably the rear gears causing the problem but not positive. I am debating on either 3.55s or 3.73s as I do drive it on the street as well.

 

[red65mustang]

hey Oregon! congrats! all fixed!

3.55 or 3.73 gears will make your car ALOT more fun to drive on the street....."instant" throttle reponse with just a "tiny bit" of pedal.....more "push you back in the seat" cause your at the torque peak quicker and at lower mph

on the highway there is only a 3mph difference between 55's and 73's
3,000rpms/3.55=70mph
3,000rpms/3.73=67mph
at the track.....basically the same results with either but alot quicker than the 3.08's for launch

 

[farna]

I agree - rear axle ratio is to high for drag. 3.55 would be a good compromise, anything lower and you cut into the gas budget a lot -- unless you also go to an OD transmission.

What cam, carb, and stall converter do you have? If you've got to much carb that will cause a bog taking off. If it's to small, it woill take off great but become a restriction at higher rpm, choking the engine off. Gotta have it close to "just right" for the engine setup!

 

[xntrik]

I agree - rear axle ratio is to high for drag. 3.55 would be a good compromise, anything lower and you cut into the gas budget a lot -- unless you also go to an OD transmission.

What cam, carb, and stall converter do you have? If you've got to much carb that will cause a bog taking off. If it's to small, it woill take off great but become a restriction at higher rpm, choking the engine off. Gotta have it close to "just right" for the engine setup!

A bigger carb with properly adjusted vacuum secondary or air valve secondary will stop any carburetor induced bog, and give the engine the airflow it needs when it needs it.

 

[oregon chevelle]

the carb is a 1406 Edelbrock whic is a 600 and the cam is .454 lift with .216 duration.

Thanks Mustang! yes I got the heads back on last summer and made about 4 trips to the track. improved a little to 13.87 at 100.68. But the Bog is pretty bad if I hook up at all. 2.20s for 60ft still pretty ugly.

 

[red65mustang]

Oregon,
fair to good chance your car is twisting and/or squating to much at launch with the 3.08 gears....(usually alot worse on a unibody car)

just cause it is old and tired from use....you can only torque load a body/frame/springs/etc so many times before all weakens alot...
or very probable it got banged and bent atleast once in it's life....

just "messin around" trying out combinations of about $20 worth of twist in or rubber spring spring spacers, combos of rubber and/or urathane sway bar bushings, front and rear can make a huge difference how a old car behaves

"playing" with the rubber parts will tell you what (if any) permanent $$$ parts will help or hurt the most (stiffer springs, bigger/smaller sway bar, 90/10 shocks, helper springs on the rear)

not unusual to see a 1" difference between L and R front wheel openings measured from the floor just from the motor torquing over the years as an example

mess around long enough adjusting torque preload and weight transfer you can get a open rear gear car to behave like it is a "posi".... for launch

when you do get the 3.55 gears in it....you will need to "re-tune" the rubber parts.....

 

[mynuffinfutsitch]

try recurving ur distro for all advance is in at 2500 rpms

experiment

 

[oregon chevelle]

Yes I am going to look at recurving the distributor. Also I put all new polygraphite bushings in front and rear about 2 years ago, also new shocks and one inch lowering springs on the fornt.