Gaining torque

[pmolitor]

How much power to the ground would be gained from switching to 11r22.5s from11r24.5s. I'm still trying to get my ch to maintain 65mph when loaded at 55000 to 60000lbs. Would like to turn up motor but nobody can tell me how to do that exacly. Motor is an em6275L with eaton 9 speed and mack 4.17 gears.

[j hancock]

What rpm are you turning now at 65 mph loaded?

What style of wheels Daytons or Budds?

If you change to 22.5 from 24.5 you will have to change the hubs if you are running spokes.

[pmolitor]

I'm turning just over 1600 rpm's at 65 miles per hour. the truck is governed at 1725 rpm.

[pmolitor]

This is the truck.

[pmolitor]

Correction...1550rpms at 65mph. Just dropped skytrack at jobsite. Loaded with skytrack on 8000 lb trailer. Total weight 54000lbs. Running interstate I was passed on the hills by semis that were loaded. I would drop from 70mph to about 63.

[j hancock]

Doing a rough calculation (real rough) to maintain 65 mph with 22.5 would need to up the rpm about 100.

The tire size change would give a lower effective gear ratio which would help getting started.

If it was mine would probably leave it alone.

[oilburner]

That's not to bad of a speed drop, you would probley pull it at 60 with 80,000 lbs, you got to rember it is a small engine, not in horsepower but in cubic inces also, most road trucks have 14 and 15 liter engine in them and are geared for the highway. The mack i run is a ch 613 with a e7 454 and a maxi touqe 13 speed trans and 44 camelbacks with 4.17 gears. at 1900 it will do 77 mph with low pro 24.5 rubber. The hills around here are pretty good pulls and with a lowboy behind it grossing around 60 to 65 i can hit the hills at 75 and top them at 65, buy fliping the trans down in the underdrive postion, so i thank your truck is doing pretty good, they newer trucks just don't proform like the old mack engines did, mash on them and the smoke would roll and then things really started to happen! LOL. I have about had it with the electronic bull#?*!

[oilburner]

This is the truck.

Oh good looking truck buy the way!!

[41180]

there must be a way to turn it up. being a e6 it must be mechanical im assuming ? u should be able to get more power just by turning up the pump.

[pmolitor]

Thanks oilburner. It'll be even better when I get her all polished up.

Logtruckman... It is a mechanical engine. No computer at all. Specs say they made a 300hp and a 350hp version of this low rpm motor. But my mack dealer can't tell me what the difference is. I wouldn't mind if I were in the hills.... But I am in the middle of Iowa. No significant hills.

[dds92780]

Talk to Lmackattack. He is very knowledgeable and has experience with this. Maybe he will chime in. Also. OILBURNER how do you get your truck to run at 1900? doesnt it lose power after 1800?

[Lmackattack]

Difference will be in the pump and timing. 300 was a maxidyne and used less gears than a 350. At least that's how it was with the r models. gearing it slower will improve pulling power and it will be most noticed out of the hole. However I don't think you will see a huge gain in speed on the hills. The small displacement Mack just won't pull like a big cat. I have driven 400hp Mack's that pull good on hills but still will not keep up on the hill following a 400 cat.

Being that it's a dump truck the smaller tire is a better choice..

That's my .02

[pmolitor]

I just talked to my buddy whom I slip seated with running lowboy. ... We drove a cl700 with an e7 454 with a mack 18 speed. we can't remember ever dropping speed till we got the cat 330 on it. the truck and lowboy weighed 46000lbs empty! I think I might have been a little spoiled. I think it reved to 2100 rpm.

[Lmackattack]

Also just noticed that's it's a 275L.....yuck!

Under powered and low rpm... That is fleet spec for LTL in my opinion.

Check with a dealer on your options but im almost certain you can Have your pump converted to a 350 / 2100 rpm and reset timing and it will be a different truck. 350 and a 9 speed will pull much better and still gets good mpg with your overdrive. It will be about an 82mph truck, still have power and low end grunt. Drove one with that set up and loved it...

[pmolitor]

Would the cams be different? I just reread my old post in engines and trans. I think the L low rpm was what was being missed. I thought about swapping my gears to a set of 4.42s that I have, but that would raise my rpms and take me further out of the engines sweet spot.

[Lmackattack]

Not sure about the cam... Would have to ask a Mack mechanic to be sure. I have a friend that converted a 300L to a standard 300 has a 5 speed with overdrive in 5th. Think it had 4.42 or 502 gears? Truck had more go with the 2100rpm pump. and would do about 70 mph after RPM and fuel was turned up. She did drink fuel tho 5mpg maybe 5.2mpg....but it only had 5 gears so hi way speed was 1900rpm all day.

[rsb502]

You can turn that engine up and make plenty of power without changing anything other than the settings in the pump, as for the tires size and gearing, leave it alone you dont want to run an engine at max rpm all the way down the road, and if I remember right peak torque for that engine falls off around 1400 so Ill bet it slows down till it gets into the power band and then pulls on out. Just remember there is a lot more involved here than just rpm and road speed, if you run the rpm near max you are way past your peak torque so when you hit a hill it drops back to where the engine makes the torque needed to pull the hill out, if you had a 13 spd and a 3.86 gear you could drop to 9th low and get it into the power band to come on up a hill and by dropping from a .73 od or 9th high to a .86 or 9th low(eaton 13spd Mack is a little higher) you would actually get better torque multiplication thru the tranny and the higher gear(3.86 would be fine). I know I will get some crap for these comments but I wouldnt post it if I hadnt tried it, your truck will pull better near the peak torque rpm than it does at max rpm, just watch the tach on those hills and tell me Im wrong if my math is right you are maxed out at 70 and you are turning about 1400 at 63 which is the mph you said you hold a hill and that is dead in the peak torque for that engine. Get with a reputable pump shop or someone that knows that pump and you can turn up the governor and let the rack travel a little more to give you fuel faster that will help your boost get up quicker and if you can get the pump up about 10% and advance the timing about 10 degrees it will feel like a whole nother truck, but it will still pull best where it was designed to make torque not max rpm.

[Lmackattack]

I can't locate my performance chart but I recal the 250L and 275L made peak torque around 1050rpm. That's about 300rpm lower than a 2100 rpm pump. What I was trying to get at was if he wants more power for the hills. He shouldhave his pump re calibrated , set to 2100 rpm with 350 hp specs.... His turbo and injectors should be the same, cam may be different but that's all pretty easy stuff to check.

If its that simple he can go from a 275L to a 350HP 2100 rpm pump. Then with the 350 spec have the shop bump up flow + 10% to 15%. Not only will he have lots more power, more road speed and more rpm to work with . All for around $400. Not a bad price for all that gain...

I drove 2 diffrent 89 R models both with 350 and a 9 speed. Remember one trip to long island and back and the truck was getting 6.2 mpg with a van trailer. Pulled the hills great with a load of mail I was hauling. Went thru upstate ny and never dropped below 40mph on any of the long hills. That was a fun trip.

[pmolitor]

Thats what I'm looking for. All the 300s and 350s iv driven seemed to have plenty of power. All were in dumps and aged from 1989 to 2004 R models. Thats why I thought this 275 L might be ok when I bought it.