RPM - Where do you stop!!??

[JokersBel]

OKok, so the other day I ran the 348 for it's monthly checkup and I decided to do something different with her. ! I felt somewhat, ummm, brave, so up she wound! Now, you have to remember shes only on the frame with no exhaust system - now imagine the sound! Anyhow, for the past year since it was built, i've never give her more than around 2500 RPM's, just because. This time, I hit 6000+ a few times!

Was that wrong???

Jim

 

[JimKwiatkowski]

Rpm's

Jim,I don't see any problem with 6,000 rpm,when I built the 468 for the Camaro I had about 1 hour tune up time on the new engine and then took it to the dragstrip and shifted at 6,500 RPM'S with no harm

By the way hows your new garage going?I see you were vacuuming the coners in a thread so you must be all setup.

 

[Fathead Racing]

Free revving.

I never did like to free rev an engine, I do set timing with worn stock type distributors by revving the engine to a point that the mechanical advance is all in. I know it makes you feel all warm and fuzzy inside but besides that, what's the point?? . When I was a wee lad I can remember the old mechanics saying not to free rev an engine. I think it puts undue stress on the reciprocating parts! Things are too loose! :eek:

 

[CDNpontiac409guy]

I think most of the guys here know that I AM the guy who would much rather have excess RPM over torque anytime ... but I'm with Fat on this one. I don't like to free rev an engine without a load on it. If you must do it, be sure the engine is FULLY warmed up. Without a load, that could mean as much as a 1/2 hour running. I see MAYBE 4000 RPM as a "flash" point when setting total timing, just to make sure that the advance has peaked.

6000 RPM ? If that is the maximum expected usable RPM shift point of the engine ?.... NO... that's too much. If you have a 9000 RPM 287 inch small block with aluminum rods ?... Sure, that would be fine !

 

[SS425HP]

Free RPM

The 63 409 I was racing in 65, after the rear suspension work we did, Had to be launched at 6000 RPM to keep from bogging off the line. Did it many times. IT was a 4 speed. No torque converter to load. No MSD ignition box with RPM limiter. Did it with the foot. Bring it up to 6000 and watch the go sign. Off the clutch and full throttle the rest of the way. Shifted at 6500. Never seemed to hurt it.
Aubrey, what do you launch at? And Steven? Also, this was with a 2.20 low gear and I think a 4.56 rear gear. Might have been a 4.88, but don't think so. 4.88 has an 8 tooth pinion, and is very small, and not the strongest rear gear made. You wouldn't have to rev that high with the low gear you guys are using.
Any way, that's my story and I'm sticking to it!!!!!

Fred

 

[CDNpontiac409guy]

Fred, to me, that is a little different. The RPM is brought up as the clutch is engaged and engine is loaded. It's the free-wheeling that bothers me.

What do I launch at ?
I dunno .... With my 5.13's and a 2.43 1st gear... even with the aluminum flywheel & balancer, my brand new 28" X 9" M/T slicks smoke for 60 ft if I launch at 5000. I suspect that the track will be a little stickier though.

 

[SS425HP]

Launch RPM

No, it wasn't brought up against the clutch. Clutch was on the floor. Bring up 6000 waiting for green. Then drop the clutch and floor the throttle. This was 6000 RPM free. No load. What do you think the pro stockers are doing on the line. Only difference is they have rev limiter. They are way up there on RPMs on the wait for the green. It's still free wheeling RPM. Just against a rev limiter. I'll bet they are 6000 or better. They are turning those motors 9000 or better. You don't hear much change in RPM from the launch on out in 1st gear.
This is just my opinion. I don't know for sure where they are staging, but I do know we were at 6000 prior to launch, no load. We didn't have line lock yet. That came way later. Had to have a dual master cyl to hold front brakes on the line. That would be the only way to pre load the motor or drive train. We didn't have it.
Fred

 

[Fran Preve]

Fred: you must have had a horseshoe up your butt!. I'm shuddering just thinking of this. But then, with the tires back then, she probably slipped the tires, just a little.

Free revving, I shouldn't and I know better, but I'll zing it to mid 3's and 4's more than I should. Then I listen for expensive noises!.

 

[walkerheaders]

What Fred said

good descripton fred,

yes, guys....... thats the way it was done. for me and my 63 09 car it was..... no line loc, 4.88 gears, 8x29 M&H's, 2.20 low, 40 lb flywheel, floor it on the first amber, at the time the 5th amber came on, it was just passing 6000. sidestep the clutch, shift at 7200, thru the traps at 7000. 12.20s @ 114 what fun, cant wait for my new car to be finished.
for those of you who are nervous to dead rev an engine, Dont try dragboat racing. i have an aluminum rodded BB that will turn 8600 across the finish line. 7 seconds seems like an eternity at those rpms, and the engine is so close you can touch it.
(this engine is in my new 63) i have a G-Force clutchless 4 speed with 3.08 low, inline long shifter, aluminum flywheel, 4.57 9inch, 35splinespool 10.5 x 28 M&H's and a chromemoly rollcage. the white paint and lettering will resemble Sox & Martins "friendly chevrolet" Z11
i'm on it everyday but it will still take me to next year to complete.
I'm also sad to say that Ronnies health isnt so good these days and he want"s to see this car done.
Also sad that i wont be able to bring my 09 car to kansas. i wish i had someone to take the car there in my place.

 

[Loafer409]

"Dont try dragboat racing. i have an aluminum rodded BB that will turn 8600 across the finish line. 7 seconds seems like an eternity at those rpms, and the engine is so close you can touch it."

====

Could you post up a picture of your NAD's, never seen a set as big as yours must be... :eek: ..

 

[dq409]

The 63 409 I was racing in 65, after the rear suspension work we did, Had to be launched at 6000 RPM to keep from bogging off the line. Did it many times. Fred

I think the difference here is that when you launch at a high rpm it isn`t the same as free reving up to 6K then free spinning back to idle.

I would think that when taking the rpm up and holding it there for a launch, the engine is spinning tight and is safer without the quick big drop in rpm you get free reving.
Seems the combo of the tight up rev and loose rpm backoff would be the problem. JMO ,,dq

 

[Dan Hunt]

If your motor is going to be hurt free reving it for sure is going to be hurt under load.The valve train doesn't know if the crank has a load so it doesn't care.
The pistons have less load under the power stroke and the same load on exhaust so they should be happy.
The crank has less twisting with no load so it's happy too.
Most motors blow up in high gear where they have the most load.
That's the way I see it.

 

[bobs409]

I don't know what's right or wrong, all I know is I won't do that with my 409. (I'm a good daddy)

The highest mine sees without moving is about 3,000 and thats only to check the total timing. Even driving, the most I hit was only in the 5's when I kicked that Mustangs butt a while ago. hee hee. (would be higher but mine unfortunately only has the 3.08 posi at the moment)

 

[unworthy]

I don't like to free rev 2 strokes because they can take off on you , and it can be difficult to bring it back down in time. 4 strokes...it may be bad to free rev them as well, but I'll free rev my bike, after the temp come up rev to 6,000 and hold it, then a few quick blasts to the 12-15,000 range. Bike's got lots of HARD miles on it and still going strong.

 

[MRHP]

Revs

I will free rev my 474 stroker 6000- 6500. I have heard this will hurt an engine but I have done this with all my race engines. Maybe I'm dumb or somthing but I have never once had any problems.

 

[fourspeed409]

I would think that deceleration would be hardest on an engine. A connecting rod can handle lots of pressure from combustion, trying to compress the rod and make it shorter. The killer is the intake stroke; this applies tension on the rod bolts. On deceleration the rods see tension on every revolution, not every 2nd revolution like when under load. Vacuum is higher under deceleration so this makes it harder for those rod bolts to keep things together trying to pull that heavy rod and piston down the hole with the resistance of vacuum added to the mix. I read somewhere that supercharged engines are easier on rods because under load there is no tension on the rods due to boost forcing the piston down the hole on the intake stroke.
I don’t like the idea of free revving an engine and I don’t make a habit of doing it. I am thinking free revving wouldn’t be as hard on the engine as going through the traps at max rpm and letting off the gas and using the engine to slow you down.
An engine is less likely to detonate free revving as with a load on it. I bet detonation is the #1 killer of a race engine.

 

[Southtowns27]

I hear a lot of people saying free revving on decell is bad... but what happens when you take off from a red light, wind it up to 6500 in 1st gear, then throw the clutch in to shift.... Doesn't it free rev decell until you hit second and get back on the gas again? My 283 sees a lot of free revving both up and down in offroad situations and it hasn't been hurt yet...maybe I'm just lucky!