Hi All, where do you shift you Big Block for your best 1/4 mile times?

 

That is an enourmously open ended question. It depends on the motor, the power band, and any limits your valvetrain might have. Assuming you don't start getting into a valve float situation, you usually want to shift a few hundred rpm past peak power. But w/out seeing a dyno readout it's hard to know what your power curve looks like.

I shift anywhere from 7000 to 7500 in my 427, depending on how the race/run is going. But my motor is FAR from stock!

 

Depending on cam heads gear and tire size. 5500-6500 for most street strip applications. 7000 plus for race only deals. Now thats a general idea, you need to build a motor and get it on the dyno to know exactly what it wants. Typically you shift 200-300 rpm over peak Hp.

 

7500...or whenever it feels right!

JIM

 

Shift light set at 7000RPM's so by the time I shift it'll be in the 7500RPM range but so far haven't been able to make a good pass.

Jim glad your aboard, don't want to hijack this thread but last night I had a pretty good pass going, seemed to hook half decent, didn't power shift but shifted fairly hard into second and to my surprise I got some traction and was thinking finally I'm going to get a timeslip I don't throw in the garbage.

Anyway about 1/2 track or so at about 6000RPM my tires break loose and the back end starts to snake. Didn't scare me but I went home, I don't want to put it into the wall near 100mph.

Do you think I hit some oil or overpowered the street tires ?

 

That was just friggin awesome.... made my day !

 

Can't you just hear it ? Think I'll to the strip tonight !

 

When it starts to slow down.

 

My 1-2 shift is 5800-5900 and the 2-3 shift is 5900-6100 depending on the air. My engine peaks around 5750rpms on the dyno. Hyd roller.

 

You probably got into something on the track but the fact still remains, you NEED to get some real drag radials on that thing before it gets away from you....it's unsafe as hell trying to play with that car on regular radials....not to mention a waste of clutch/street tires trying to run it at the strip...

 

If you haven't already, watch a clip of Jim making an all-out pass.

 

You are correct, thought I might give it one more shot but you are dead on very dangerous, but I'm still thinking early 80's and 13 sec. was a fast car, now the power is just too much to be playing around with, last time for me on street tires

 

Finally after days of fishing I have a response I can use. Are you fairly stock?

 

At least that's what he tells everybody!!


I think you got a lot of good responses....considering the question had no parameters. Just where do we shift our bigblocks? They were all honest true numbers.

You never asked about a stocker. Heck...is it a fresh stocker..or a 100K one? Is it a solid lifter motor with rectangular port heads...or an LS-5?

Best answer is as mentioned...somewhere right before it noses over.


JIM

 

My old stock L36 wasn't happy revving past 4500 rpm so would be shifted at a lowish 3800/4000 rpm. My current 489 peaks on dyno at 5850 rpm - shift light is set for 6000 rpm and rev limiter is set for 6200 rpm

 

I checked ajrothm profile and he is nowhere near stock. Looks like a nice build though.
True I did not specify set up as I was hoping to maximize responses.
It is a stock 69 L68 (tri-power) set up except for large headers (3.5 inches at the collector connection.
The motor appears fresh, good oil pressure, better on gas than expected, no oil burn, no anything out the tail pipes at anytime.
I have not seen the cam but I am making 20 psi vacuum at idle (6 to 700 rpm) which is quiet and lump free so I assume its stock or close to.
I have pulled apart and rebuilt the carbs, metering plates, jets, power valve, accelerator pump, secondary springs all stock.
THM 400 transmission
Running 34 degrees all in timing, going up or down on either side of that by a couple of degrees makes no difference in the top end performance.
The car has a stunning low end but runs out by 4000rpm ish.
Fuel pump replaced, with the correct 40482 delco pump.
In carb filters replaced with a single in-line filter near the tank. Correct fuel lines installed pump to carbs. Snaked and blew out fuel line front to back, appears clean.
Sending unit good, I removed intake screen as it was falling apart
points replaced to petronix. (I beg forgiveness)
Coil replaced
plugs replaced
wires replaced
Played a bit with secondary carb diaphragm springs found, stock work best.
Have tried with and without air cleaner set up.
All of these things seemed to make no difference to the top end. In some cases above 4500 ish it will pop and fart out the back.
Should a stock BB not make good power at least until 5000 rpm?

Thanks, Rog.

 

On the old set up, what would happen after 4500 rpm. I am wondering if they were built to max out at 4000 rpm. would love to see a dyno on a stock BB

Thanks, Rog.

 

I shift at about 5000-5500 in my almost stock 454 LS5, using a 60202 mild Lunati flat hyd. camshaft and 9:1 CR pistons. I feel it revs happily to this range. You can see in this video where it shifted at about 5000 RPM in the 1-2 shift, the important thing is don't ever count on the stock mechanical tachometer! it will jump like crazy and will give you no clue! :

http://www.youtube.com/watch?v=FVIHIMw1re8

 

AvRog, I would guess either the valve springs are weak (since it's popping/nosing over real bad) or it's just got a stock or small replacement cam. But I agree even a stock cam in a good condition big block l68 should rev to 5000+.....it may not make any power up there but it should be able to rev up there.

My dad has a mild 461" with slightly ported 215 oval ports and an old Comp 270h cam which is tiny and it will still rev up to 5500+....although it stops making power at 5000. That is going through stock chevelle ex manifolds.

I would be checking into springs if it were mine.

 

I forgot to mention that I added headers, low restriction exhaust, MSD, bumped timing up get full avance at 2000 rpm, Torker 11 inlet, 750 DP - even though mid range was significantly enhanced there was little point hanging on past 3800 rpm in intermediate gears and again no improvement in rpm - no apparent valve bounce - I ended up wondering if the cam had been 'wiped' a little