Launch RPM for a 4 Speed?

[CopoFan]

So I finally got Ribbon COPO out to the strip this past weekend (first time I've ever drove a stick down the strip), and was disappointed with 4 passes all around 13.70. I was running slicks, and it has a pretty nasty bog when launching, even with the RPM's up in the mid 3000's. Tires didn't break loose at all.

I know we jetted the secondaries up at one point, and at that throttle position, the secondary accelerator pump is probably out of the picture. Timing is around 17, almost 40 at 3500 RPM. It runs fine on the street.

Its got a built 396 (11.5:1), 4 speed and 4.10 rear. My buddy did have a high 12 pass with it, and he didn't shift it too well.

I assume it just needs more RPM's at the line... but how high is safe? I'm not looking to break anything. I'd hate to damage its KQ rear.

Also, any chance of hurting anything since it has ladder bars, or do those actually help?

Thanks!

[PxTx]

I've got a 65 Malibu SS with a 327 and a 4 speed. It has been quite a while since I've had it at the track, but I was always of the opinion if you've got slicks- You leave at the smae RPM you shift at.

If the car is in good enough mechanical shape to race, you shouldn't break anything other than breaking into the 12's.

[markjohnson]

Hey, I just wanna say, is that a blast driving that 4-speed down the strip or what?! I've raced 9-second Drag Radial cars in competition but they always 'Glides or Turbo 400's. When I blasted down the strip in my 11-second '55 Chevy with the stick shift, I couldn't believe how much fun it was! It made me realize that this.......is what I've been missing from my life. A clutch pedal at the drags!

[Fast67VelleN2O]

My 67 Camaro, basically stock 350 with 3.42's on slicks with a 4 speed M20. I launch the car at 5,000-5,500 rpm. Dead hooks.

[Salvatore]

Put a little more air in the slicks and come out higher. 3000 rpm with slicks is a little low. http://www.yenko.net/ubbthreads/images/graemlins/dunno.gif http://www.yenko.net/ubbthreads/images/graemlins/3gears.gif

[sYc]

If worried about hurting the original rear, which is very possible leaving at 5000 or so, with slicks and a stick, I would put a set of street tires on it, which will spin when leaving, making it much easier on the RE, will allow your motor to rev (making power) and as you get used to it, you will still be able to turn some very respectable times.

[Chevy454]

What was your MPH? That will tell the tale of how good your engine is...also, you need your timing in a lot earlier...all in by 2k would be nice. Carb stuff...Eric would be the man to talk to, the bog could be from a number of things, wrong jetting, float level, fuel slosh, etc...

Also, if you value that KQ at all, get it the heck out of there...I've seen people twist rear ends on drag radials and even street tires...rare, but it happens...you have to realize, the track is prepped to hook, so you're gonna find the weak link in your drivetrain, I promise!

[YENKO DEUCE REGISTRY]

[ QUOTE ]
... but it happens...you have to realize, the track is prepped to hook, so you're gonna find the weak link in your drivetrain, I promise!...

[/ QUOTE ]

Very true, just ask COPO Pete when he was testing his COPO Camaro / Chevelle / Nova for MCR 10 years ago - the rear broke in the Chevelle! It didn't hurt the tube, but like Rob says - it happens!

[markjohnson]

I think I remember when COPO Pete broke that Chevelle 12-bolt. If I remember correctly, the axle tube actually ripped out of the cast center section. It was an ugly picture.

[CopoFan]

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.

I thought about going back to street tires, maybe next time out I'll give those a shot. Seems safer on the drivetrain at least. The slicks had about 13 psi in them, and i didn't bother burning out after the first time... to try and get them a little less sticky.

As for timing, I didn't realize you want the curve in that low... I always check it at 3000 - 3500 RPM. I'll have to check it at 2000... and figure out where to pick up some MSD weights and/or springs.

And thats quite frightening about COPO Pete... which is a big reason why I've been considering pulling the rear and storing it until (and if) I restore the car. I've also considered selling the KQ and using the $$$ to build a bigger motor... since the motor and trans are long gone... but I'm not ready to do that just yet.

[69L34M20]

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?

[goinforbroke]

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.

[Chevy454]

[ 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... http://www.yenko.net/ubbthreads/images/graemlins/beers.gif

[Salvatore]

Stop racing it before you break something. http://www.yenko.net/ubbthreads/images/graemlins/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! http://www.yenko.net/ubbthreads/images/graemlins/biggthumpup.gif http://www.yenko.net/ubbthreads/images/graemlins/3gears.gif

[YENKO DEUCE REGISTRY]

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 http://www.yenko.net/ubbthreads/images/graemlins/naughty.gif

[rockn69]

Just reading....you have to love this stuff! http://www.yenko.net/ubbthreads/images/graemlins/beers.gif

[mfchassisworks]

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.

[Mr BB Chevy]

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

[PxTx]

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?

[CopoFan]

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!!! http://www.yenko.net/ubbthreads/images/graemlins/youguysrock.gif http://www.yenko.net/ubbthreads/images/graemlins/beers.gif

[mfchassisworks]

Awesome pic MR BB CHEVY!!

If you dont want to run a fuel pressure gauge make a temporary T-fitting install it as close to the carb as you can, get Autometer's copper oil pressure line, and get a small liquid filled gauage and install in on the end of the line. Run it up the cowl to the base of the windshield, under a wiper arm, or 200 mph tape it to the windshield where you can see it. Find a safe place to run through the gears, Then watch how low your fuel psi gets. You will be surprised. If you don't have always have 7psi then you aren't making hp. If you try to tune based off you plugs at the end of a run they will give you a false reading as the carb will seem lean but really there simply isn't enough fuel. No fuel means low hp = low mph.

For the launch don't worry about the other guy, when you are testing there is no prize for cutting a good light. Let the other guy leave first then watch your tach and go. Keep raising the RPM of the launch until the bog goes away. and...hold on!!

[Stitch]

This was my street car from the early 80's , small block , 4 speed , 5.13:1 rear . Launched around 5800 - 6000rpm

http://i203.photobucket.com/albums/aa157/rondeco30/camarobigger-1.jpg

[70 ls6 convert]

i pulled my 70 chevelle ls5 4speed out of 10 year storage to race at an abandend runway,been dumping the clutch at about 28oo,there aint nothen funner then racing a 4speed big block..http://www.youtube.com/watch?v=mKs4F9RDqrE

There is a chance your rims are spinning on the tires. I used to have that happen before I screwed the slicks to the rims.

[firstgenaddict]

After I trip the 2nd staging light I put my heel on the brake pedal and using my toes I begin to bring my rpms up to where I want to launch... then I pay attention to the tree...

[Verne_Frantz]

I've never tried the "heel-toe" method, but maybe I should have because I've rolled out of the lights many times..........ESPECIALLY at Broadway Bob's in Union Grove where the starting line is on a HILL. I know that track has a lot of history and people love it, but for me, it's the worst place I've ever run. I rolled back out of the staging lights THREE times before I finally kept my foot on the brake until the yellows came down, then had to HURRY back to the gas, set my launch rpm, then forget about timing the launch on the lights. By the time I was ready, the green was already on. They should have a sign in the pits saying, "line-lock required"!
I know I'll get flamed for my opinion and people will testify that they ran there with no problems, but my experience was terrible in '83.
Verne http://www.yenko.net/ubbthreads/images/graemlins/frown.gif

[PxTx]

My first vote would be to throw on a historically correct Hurst Link Lok, but the other option is set the e-brake just enough to prevent the roll and creep through the prestage lights to light the stagine ones.

[Verne_Frantz]

GREAT advice. http://www.yenko.net/ubbthreads/images/graemlins/confused.gif Your right hand is on the shifter; your left hand is on the e-brake release handle; your right foot is on the gas; your left foot is on the clutch. Who's steering the car? http://www.yenko.net/ubbthreads/images/graemlins/rolleyes.gif

[Dog427435]

You have a chin don't you? http://www.yenko.net/ubbthreads/images/graemlins/smile.gif

[firstgenaddict]

Verne I have had the same problem... way too much to do and way too little time to do it in!
To me the heel toe method is the easiest way... as soon as you roll to the gas you are naturally releasing the brake from your heel...

[firstgenaddict]

Whatever you do get a scattershield if you are going to be thrashing it! The best case scenario is destroying the bellhousing and back of the block or having the clutch disc come through the firewall/windshield... and gets worse from there!

[Motion Camaro]

<font color="blue">I used to do a half pump thru the line lock just before the pre stage, ease the clutch into pre-stage, then stage ...
at the light blink, right foot to the floor, side step the clutch (approx 8K) &amp; hold the f**k on!

Looked at the Moroso tell-tale when I was done.

Not the most consistent, but definatly a lot of fun. http://www.yenko.net/ubbthreads/images/graemlins/headbang.gif

331cu.in. - Super T-10 long 4200lb clutch - Verti-gate - 5.57 dana - 13/31 slicks
</font> http://www.yenko.net/attachments/422918-camarobuildup034%28Medium%29.jpg