Launch RPM for a 4 Speed?

[Salvatore]

Put a little more air in the slicks and come out higher. 3000 rpm with slicks is a little low.

[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]

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... 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!...

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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.


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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...

[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.