I have no problem twisting my cammed 6.0 to 5500, or even 6000 in first if accelerating, nor have I any issues with twisting my old 6.2 diesel to 4000 in second up long grades.
Whatever RPM the HP peak is at, you can safely hold that RPM until you run out of fuel, and you can safely accelerate 500 RPM past the HP peak. All engines are built to these standards, even from the mid 1960s on up to today. They all were built with adequate valve springs and rod bolts, the 2 limiters to RPM when there's no computer control.
Running at WOT, versus 80%, it'll run richer at WOT, which makes for a cooler burn. Good for pistons, good for keeping the platinum spark plugs from getting so hot that they cause pre-ignition, which will feel like a power loss.
Valve float shouldn't be a problem in any modern engine with less than 100,000 miles on it. But valve springs do lose tension over time / use, so in that way springs are a wear item.
enblethen wrote: To me 3500 is at the high end. I keep mine between 3000 and 3500 pulling over some of the higher steeper passes.
Bud what I do to find a safe RPM in each gear with an automatic is to do some WOT (wide open throttle) take offs and note the MPH and tack readout if so equipped. I also do this from time to time to see if I have any performance issues that need attention.
In the 454 TBI in the MH after I installed a tach that was 35 MPH/4000 RPM for 1st and 58 MPH/4000 RPM for 2nd. 3rd/4th WOT can not happen in a MH.
I think 4500 is the actual redline for the older 454 in stock truck use. Going down hill in 1st I let it push me up to that RPM and it shifted up to 2nd which is while I do not let it push me much beyond 4000 RPM anymore.
What scared me was when it shifted back down. When it upshifted to second I was nearing the bottom so I did not get concerned about it then all of a sudden it shifted back down into 1st again when the RPM's dropped enought. I should have manually shifted to 2nd after it upshifted due to high RPM.
I did it some in CA (Grapevine) but I do not like to run it at 4000 for miles at a time so on long climbs I try to limit it to 3800 which is about 50 MPH (45 MPH with new tires). I am go mile after mile at 3500.
wolfcat1 wrote: I keep reading a gas engine makes its max hp, and torque at high rpm's...So how do you know when you are in the "safe" zone, and not about to fry an engine?
thnks,
wolfie
Here is something to noodle and why said you need to know 'your' ICE's
torque/hp curve
For our truck engines...5K-6K is on the high end of the RPM scale, but
for a small displacement, motor cycle engine that red line is anywhere
from 12,000 to 16,000 RPMs
They are in the ONE liter range, where our truck engines are in the
5L to 8L range, which goes back to comments on why big blocks can't
spin that high...mass is the issue and reversing directions of a big
block piston vs one of these motor cycle engines has huge laws of physics issues
-Ben Picture of my rig
1996 GMC SLT Suburban 3/4 ton K3500/7.4L/4:1/+150Kmiles orig owner...
1980 Chevy Silverado C10/long bed/"BUILT" 5.7L/3:73/1 ton helper springs/+329Kmiles, bought it from dad...
1998 Mazda B2500 (1/2 ton) pickup, 2nd owner...
Praise Dyno Brake equiped and all have "nose bleed" braking!
Previous trucks/offroaders: 40's Jeep restored in mid 60's / 69 DuneBuggy (approx +1K lb: VW pan/200hpCorvair: eng, cam, dual carb'w velocity stacks'n 18" runners, 4spd transaxle) made myself from ground up / 1970 Toyota FJ40 / 1973 K5 Blazer (2dr Tahoe, 1 ton axles front/rear, +255K miles when sold it)...
Sold the boat (looking for another): Trophy with twin 150's...
51 cylinders in household, what's yours?...
Back in the '60's and '70's I was taught that working an engine below max torque rpm was harmful and called "lugging". John Deere on their diesel and gas engines had a green line starting at 1500 rpm with instructions to not load the engine below green line on the tractors. Red line was 2500 rpm and they would run at red line all day, day after day for thousands of hours.
Today when I read of people towing way below max torque I understand why so many trade at less then 150k miles. 2500 or less rpm on a gas motor with max torque speed of over 3000 rpm is too slow in my opinion for heavy towing and I wouldn't touch the vehicle at half it's book value. My experience has been a modern gas engine run properly in today's modern pickups will nearly keep up with the light duty diesels and last nearly as long so I've switched from diesel to gas. The diesel engines in pickups aren't even close to diesels found in class 8 trucks.
D. Steiner
The sooner I fall behind, the more time I have to catch up.
My 3500 Express van with 8.1 big block has the same 3.73 rear and LT265/75R16E combo as my 6.0 PSD Excursion that I sold and has the same seat of the pants feel when going up grades in OD on trips at fully loaded GVWR of 9,500 lbs vs 9,200 for the 6.0 PSD 4x4 Excursion.
If you want the ultimate gas engine for towing that runs on 89 octane gas get the SAR 762 cu in big block that has 1150 PEAK HP@ 6000 RPM and 11O5 FT LBS TORQUE @ 4900 RPM !
My 2005 Super Duty manual states that the optimal RPM for towing performance is between max torque RPM and max horsepower. On my V10 that's between 3250 and 4750. I'll use any RPM in there on a grade to deliver the speed I want.
I think many a gasser is traded off on a diesel by owners not willing to explore the actual powerband of the engine for fear of damaging it (acutely or chronically).
Redline means "do not exceed", not "do not approach". :-)
2005 F350 SRW V10 4.10 CC LB 4x4; BW Turnover ball; LineX
2011 Sequoia 5.7L 4.30; Tundra Towing Mirrors; LT 275/65R18 C Goodyear Wrangler MT/Rs on 2nd set of wheels
2005 Nash 22H TT
I think many a gasser is traded off on a diesel by owners not willing to explore the actual powerband of the engine for fear of damaging it (acutely or chronically).
Its not just gas engines. Just as many guys running diesels that are afraid of RPM as well.
I can't tell you how many miles my 5.9 Cummins ran at 2900+ RPM.
It was happier pulling long steep grades at those RPM than chugging along at 1500.
Same with my new Dmax. I paid for 397 HP,I'll gladly run the RPM needed to make use of that HP.
8.1 Van wrote: My 3500 Express van with 8.1 big block has the same 3.73 rear and LT265/75R16E combo as my 6.0 PSD Excursion that I sold and has the same seat of the pants feel when going up grades in OD on trips at fully loaded GVWR of 9,500 lbs vs 9,200 for the 6.0 PSD 4x4 Excursion.
If you want the ultimate gas engine for towing that runs on 89 octane gas get the SAR 762 cu in big block that has 1150 PEAK HP@ 6000 RPM and 11O5 FT LBS TORQUE @ 4900 RPM !
That is something I'd consider if won the lottery !
Big blocks vs small blocks...something lots of folks don't appreciate
I've had many 'built' small blocks and a few 'built' big blocks. Know
the difference.
My Silverado was given to me by dad after he sold the mom'n pop butcher
shop. Designed an engine that cost around $8K. Almost every thing ever
read in my hot rod magazines. Both daughters first ride and used to
catch the youngest beating up Mustangs on the local boulevard, but
even though it has similar torque to my 7.4L...there is no match
Buddies T-Bird (port hole that his mom gave him when she got a
new T-Bird) with that 427 we stuffed into it while in high school.
He first 'built' that small block V8 into a monster, but nothing
compared to the big block we stuffed in there. The front suspension
was not up to the task either.
Same thing with the Vette I owned. It came with a small block that we
built up for racing. When we couldn't touch the L88's out there, we
stuffed a 'built' L88. World of difference out there on the track and
on the street when we drove it there and back.
What is missed is that they all make their HP at higher RPMs and the
big block does so several hundred to over 1K RPMs lower. Most folks
today just look at the torque and HP numbers and think no difference.
So out of context.
With a big block it happens *NOW* where as the small blocks need to spool up.
Offline
