Re: Launch RPM for a 4 Speed?
 

your mph seems low. You should be able to run a few mph more. The bigger picture is your 60 foot which is terrible for slicks... and killing your et.

As for breaking your diff, just think how you would feel if an axle broke it's .02 cent c-clip and you took out your rear 1/4 panel. Buy another diff and put a c clip elim kit on it and drive it like it ain't yours!!!!!

p.s. I'd think you should be able to get your mph up a few ticks too.....L78 cam?

Re: Launch RPM for a 4 Speed?
 

According to this calculator, (1320/mph=ET) which works out very close on my drag car 1320/114mph=11.48... I run 11.5 even, your car should be good for 12.7's or so. In regard to your rearend, I'm no expert but I know you either want to spin a little or have your clutch slip a little. Maybe the higher rpms would make you spin a little but then again, maybe they'd break something. I've heard arguments that lower rpm launches break more parts. Personally, I like to spin a little just to make sure I break nothing. Slicks are the fastest way to find the weak link in your driveline so, I'd agree on a good set of street tires as insurance.

Re: Launch RPM for a 4 Speed?
 

[ QUOTE ]
Hmmm, lots of good info to digest here.

To answer a few questions... MPH was 102 - 104 every time. 60 foot time was between 2.10 and 2.20.

My brother tried one pass, launched it at 4000... and the bog was almost gone... 60 foot time was 1.90, but unfortunately, the clutch linkage came apart after shifting to 2nd gear. (the cheapest weakest link I can think of), so no idea what 1/4 mile time would have been.


[/ QUOTE ]
I can tell ya, that woulda been a low-13, *maybe* high twelve at best, assuming you're out the back door @ 104...that's almost the exact same splits our Camaro ran when we first put it on track duty. Think it went 13.20s @ 104 with a 1.94 60' my first year @ Stanton. Anyway...

If you're 60' time with slicks is just 2.10-2.20, something is seriously wrong...that's manual trans-street tire range...and looking at your trap & weight I'm gonna say you're right around 300hp, which tells me you need to really look over that 396. Timing...you need to put a light on it and see when/where it stops advancing...it may be all in by 2,000, but if you've only checked it at 3,500 we won't know for sure. To get to your high-12s mark, you're gonna have to have a *really* efficient run (and car!) to get there on a regular basis at the current HP & weight...

But, it's all doable, and every car has to start somewhere... https://www.yenko.net/ubbthreads/imag...lins/beers.gif

Re: Launch RPM for a 4 Speed?
 

Stop racing it before you break something. https://www.yenko.net/ubbthreads/imag...emlins/eek.gif Just do a real nice Day-2 street set-up and run people from a roll if you need to race. At this point, from what you are telling us I think your whole set up needs to be looked over from soup to nuts just to see how you have things set up. If I were you, I would build a drag car like BBBenny has done. Pretty much bullet proof, safe, alot of fun and reasonably fast and economical! https://www.yenko.net/ubbthreads/imag...iggthumpup.gif https://www.yenko.net/ubbthreads/imag...ins/3gears.gif

Re: Launch RPM for a 4 Speed?
 

No, No, No Sammy, you got it all wrong - keep racing until you break something, then you've found your weak link. Just make sure it's not the rear!

This car just needs dialed in, it's running in my Deuce territory. I've run 2.1 60's, 13.5ET with 105+/- at the big end - on E70 whitewalls https://www.yenko.net/ubbthreads/imag...ns/naughty.gif

Re: Launch RPM for a 4 Speed?
 

Just reading....you have to love this stuff! https://www.yenko.net/ubbthreads/imag...lins/beers.gif

Re: Launch RPM for a 4 Speed?
 

What do you have for a fuel pump and fuel pressure on the top end? (not at idle)

For launch RPM , to simplify it, drive the car in 2nd or 3rd the speed isn't important, start just above an idle and accelerate hard, watch the tach, the rpm when it starts to pull hard is roughly where you combination starts to work, ( you can't go by the cam card) stick cars generally have a 1400/1800 drop in rpm from the launch rpm. For example if the rpm was 3200rpm then dump the clutch at no less than 4600 etc... Launching at 3200rpm would net a 1800 rpm conv. which is wrong. If it was an automatic you would choose a 32/3400 conv.
The bog isn't really a bog, it's the motor struggling to get in it's power band. You can tune it to make it better but it won't give you the et you are looking for.

Re: Launch RPM for a 4 Speed?
 

my street car

atco early 1980's

5800-6000RPM launch 11.22's 110-118mph
http://www.dragracers.org/my-toys/69-chevelle.jpg

Im re-doing my chevelle now keeping it as a day2 car.
M&W bars, tow tabs, mechanical tach etc.


newest add-on from ebay...
http://www.dragracers.org/my-toys/vgate2.jpg

Re: Launch RPM for a 4 Speed?
 

I've been running the same shifter on my 65 for a long time and LOVE it. It looks so good poking through the factory consol. Yours looks a lot more modern than mine. Do you know much about yours?

Re: Launch RPM for a 4 Speed?
 

69L34M20: I agree... I think the motor has a bit more... its never been properly tuned since it was built 10 years ago... its got about 1000 miles on it. Good point about the c-clips, that would totally suck to have one fail, and its happened to me already, at least it was an 81 Park Avenue and not a fun car like this.

The cam is a Comp Cam solid lifter 294 duration (248 @ .050) 0.595 lift solid lifter with roller rockers. Compression is a blueprinted 11.4 : 1, and it was bored .030 over. Intake is an Edelbrock Performer RPM, 750 Holley Double Pumper, and MSD ignition.

goinforbroke: I've never heard of that calc... but it sure seems pretty accurate... I tried it on a few buddies' car from Sunday and its pretty close for them all.

Rob: I'd be happy to run mid to high 12's consistantly, I know I don't have the cubes to hit the lower 12's with the weight. I'm hoping some tuning brings the MPH up a bit.

sc69sam: While I'm not going out every weekend, I love to take a car out a few times a year to have some fun. There is no street where I can open it up like the dragstrip.

mfchassisworks: Good question on the fuel pressure, its a holley mechanical pump and its pulling 6 psi at idle, but no idea under load. Awesome explanation on the "bog", my gut feeling was that I can't get big enough jets or enough timing to compensate for the "bog", it seemed like the only cure is RPM.

Mr BB Chevy: AWESOME picture!!! As much as that kind of launch would scare me... I'd brag about that picture for the rest of my life! What kind of motor were you running back then?

And one final kind of dumb question for all of you...

How do you watch your RPM's on the line, trying to keep them over 4000, while watching the tree? Its hard to go by sound when the car in the other lane is louder than yours. I think part of my problem was I was letting off a bit without realizing it as the lights ticked down.

And finally, you guys are all awesome, never expected this kind of response for a somewhat generic question!!! https://www.yenko.net/ubbthreads/imag...ouguysrock.gif https://www.yenko.net/ubbthreads/imag...lins/beers.gif