RPM Ranges in various gears

[SD5805]

Hi Guys,

I have a 351 W Ford Racing Crate Motor that is runing strong. I'm just wondering how far it can be pushed safely in each gear as far as the RPM.

I do have a limiter at 6000 RPM, but rarely go that high. What is a safe range? especially in 3rd and 4th gears

Thanks

[olddog]

I don't think which gear matters that much.

The G forces of changing direction with the piston tries to stretch the rod bolts on the down stroke. When the RPMs is high enough the bolts stretch and the rod cap seperates from the rod just enough to allow the bearing incerts to turn. Then the game is all over, except for the crying.

Of course there are other parts that can fail other ways, but it is power level and rpm that kills parts.

[wtm442]

The engine does not care what gear you're in ... just the RPM.

I try to keep mine at 5800 RPM or below. At 6000 RPM, the torque goes off the cliff into the dumpster, so any revs above that are actually slowing the car down. Amazing what you see from the graphs of a dyno pull. Well worth the $$.

[Clois Harlan]

A friend of mine (Scott C.) has a 351 W stroked to 392 and he turns close to 7800 RPM's at Road America. Saying that, he is running a solid lifter cam, some high dollar rods and pistons plus a few other upgrades.

What did your engine dyno at and what range did it reach peak torque and HP?

Clois

[Speedysnake]

I also have a 351 W / 385 hp. crate motor in my BDR #291.

I am running with a 6000 rpm chip & often hit the rev limiter at about 5800. I put it on a dyno and found that, as stated in comment above, the torque and HP are dropping way off at that point even though the engine "feels" like it wants to rev higher. I plan to try a 6400 rpm chip, just so I don't keep bumping the rev. limiter.

[Jerry Clayton]

If your looking for a rpm on acceleration----you must overwind above your max torque rpm to balance out with the drop below max torque rpm that the engine will be at after the shift---balance the area under the torque curve on your dyno graphs

Jerry

[SD5805]

it sounds like i should get it dynoed. I have not done that yet. I also thought of getting it dyno tuned, some say you can gain a bit of horse power with doing the tune.

I have a rev limiter set for about 6000. The car still feels like it can go more but i'm not sure how much more. It may be at its best at around 5500 rpm.

I just wondered how far you can push the rpms in ea gear for a performance stand point. I had the car in 3rd gear goinin about 95 with RPMs about 5700-5900. almost at its max.

At this point though the car had tremendous torque. In 3rd gear at 60-70 mph each press of the gas was pushing the front end up nicely.

[wtm442]

Originally Posted by SD5805

I just wondered how far you can push the rpms in ea gear for a performance stand point.

With any crate motor, I would not exceed 6K RPM. Too much chance of breaking something for just a little extra oomph. I used to drag race my 70 Olds 442. The engine would feel great all the way to 6100 RPM, but it posted its best times when I shifted at 5500 RPM.

[Rwillia4]

the torque and power of an engine are dependent on the cam profile and totally seperate from the safe RPM of the engine. So if you get a radical cam that comes into its powerband at 6K your engine will pull in that range but the engine may not be built/balanced to not fall apart in that range.

[snakebitekit]

the difference between red line and max hp are not the same. your red line maybe 6000 but max hp may be acheived at 5700. when racing in the 60's I would beat a lot of cars that should have beat me, but they shifted at red line. Generally you will loose hp at red line, not max it out.

[SD5805]

thanks for some of the feed back. Much of it is hyrgliphics to me though. I do not have the technical background in engines etc, hence this link. I'll try to figure it out, but if anyone could put all this rpm technical know how in laymens terms i would greatly appreciate it.

Thanks again

[wtm442]

Layman terms - shift at about 5800 and have fun. Don't sweat the small stuff. But get a dyno tune when you have a chance and then copy it to this forum.

Here is some info on a FORD 351W Crate motor ...

410 HP @ 5700 RPM (with headers and 650 CFM Holley HP carburetor, not included)

417 ft./lbs. of torque @ 4800 RPM

[Jerry Clayton]

using those numbers--417 ft 4800 rpm---shift at an rpm somewhere above 4800 that will give a rpm drop to a number under max t an equal amount as the rpm above max----5500-4800=700 rpm -----4800- 700= 4100rpm--- split the rpm drop on the gear change by an amount that centers the max t

If the gear change rpm drop is only 1000 rpm, split it by 500

Jerry

[SD5805]

Wow,
You guys are pretty good with the technical part. Thanks for all your help

just so you know, I smoked a 2004 or 2005 corvette the other day. Knowing he wanted to play, I dropped into third gear. RPM read about 4800 to 5200 going about 80-95 MPH. The torque in third gear is just awsome, I then shifted into 4th at this point and just pulled away nicely. I think the Corvette was an automatic because it was not around much longer after that.

I can't even imagine what a big block engine could do in these cars. My 351W with 385 horse is just amazing to me. Its such a nice mix as far as having performance or just a relaxing smooth ride.

Note: these numbers are approximate as I needed to pay attention to the road of course.