Warden Posted October 20, 2015 Share Posted October 20, 2015 Hi , just picked up a mr688p with a E7 250 hp and auto , i love it , its a roll back 1995 with 30k orig miles Allison auto , my queston is , can this engine safely be turned up and not hurt itself or the trans ? If so how much ? Truck is heavy for a single axle 23,000. Tripple frame ! I know with my cummins and detroit series 60 , there was a critical parts list controling hp avail ! This single ax truck has a gvwr of 44,000 ,,,, i could use a bit more power and another 100- 200rpm. To cruise the thruway nicely , any advise ? Thank u warden. Quote Link to comment Share on other sites More sharing options...
kscarbel2 Posted October 20, 2015 Share Posted October 20, 2015 Hi , just picked up a mr688p with a E7 250 hp and auto , i love it , its a roll back 1995 with 30k orig milesAllison auto , my queston is , can this engine safely be turned up and not hurt itself or the trans ? If so how much ? Truck is heavy for a single axle 23,000. Tripple frame ! I know with my cummins and detroit series 60 , there was a critical parts list controling hp avail ! This single ax truck has a gvwr of 44,000 ,,,, i could use a bit more power and another 100- 200rpm. To cruise the thruway nicely , any advise ? Thank u warden.What's your rear axle ratio and tire size? Quote Link to comment Share on other sites More sharing options...
Warden Posted October 21, 2015 Author Share Posted October 21, 2015 Hi , 4.30 rear. And 1100Rx20 tires 482 revs per mile ! Quote Link to comment Share on other sites More sharing options...
kscarbel2 Posted October 21, 2015 Share Posted October 21, 2015 So your engine, E7-250, is governed at 1950 rpm. I wouldn't turn up the rpms.No Mack single axle has a 4.30 axle ratio. Maybe you misread the last digit.What's the axle model? If it's a Mack rear, it begins with "RA" Quote Link to comment Share on other sites More sharing options...
Warden Posted October 25, 2015 Author Share Posted October 25, 2015 Its a rockwell according to the line sheet and the tag , the build ticket says delete 4.10 rear & add 4.30 with inter axle connect /air/switchable ...im not quoting exact verbage , but its close ! What should it have ? I just put the gps on it tonite and 65 mph down hill or with a tail wind ! Delivered 2 small excavators 2 nites ago 220 miles round trip in hill country and power was not bad , Fuel MPG was outstanding @10mpg on the nose , top speed coming home empty was lacking , traffic on the tway was moving @74 mph. I was at 64 tapped out ! Truck is a keeper , this thing rides like a half ton chevy pic up. And turns as well or tighter ! I cant give up the air locking rear , not for my use (very important ) i did not study the trans blue print yet , many allison 5 speeds are realy 6 spd double overdrives but the valve body has to be modified to stop the 3rd planatary back instead of the second , that would be perfect. But not sure this unit has the correct layout , any help or ideas would be appreciated , i cant go larger on tires ... 1100x20s already , bed is 53" high already. Thats bout 5" more then perfect , thank u ,',, warden Quote Link to comment Share on other sites More sharing options...
TeamsterGrrrl Posted October 25, 2015 Share Posted October 25, 2015 Leave it stock... The CR654 is really a medium duty trans that Allison beefed up to be a low price option for big bore diesels. It was only rated for something like 950 or 1000 lbs/ft of torque, so Mack tuned a special derated engine for it... retune it for more power and you'll blow it. As for top speed, 65 is plenty and most of the fleet trucks are governed for about that speed, so you'll have plenty of company in the slow lane. Changing the differential ratio might help MPG, but you probably won't put on enough miles to pay back the costs. 1 Quote Link to comment Share on other sites More sharing options...
TeamsterGrrrl Posted October 25, 2015 Share Posted October 25, 2015 Forgot to mention, the 654 is an older mechanical trans and doesn't have the locked out 6th gear like the electronic big Allisons/ Quote Link to comment Share on other sites More sharing options...
TeamsterGrrrl Posted October 25, 2015 Share Posted October 25, 2015 On the other hand, if your truck has a 750 or the newer electronic Allison, ignore all of the above... Quote Link to comment Share on other sites More sharing options...
TeamsterGrrrl Posted October 25, 2015 Share Posted October 25, 2015 Looked at the title, you do indeed have an 754CR, here's a spec sheet: http://www.wanderlodgegurus.com/attachment.php?aid=74. Good fpr 950 lbs/ft NET torque. Quote Link to comment Share on other sites More sharing options...
theakerstwo Posted October 25, 2015 Share Posted October 25, 2015 654 Quote glenn akers Link to comment Share on other sites More sharing options...
Warden Posted October 26, 2015 Author Share Posted October 26, 2015 If i have to do a trans swap , its not an issue ! But my buddy that is 100% mack with over 35 trucks on the road , just told me about an E7 -250 hp. That he scrapped after trying 3 times to make it a 350 , and having many issues , like broken cams and other items ! So i guess my real question is , are all E7s capable of more hp reliably ? I would prefer 25-50 Hp more in the upper rpm range , this unit pulls hard from 1200 to 1700 assuming its tach is accurate , i can live with 65 mph if it will do it up hill ! Is there a "CPL" with mack ( critical parts list ) like cummins , or Detroit ? If this unit actually pulled to 1950rpm i would be pretty content with the gear ratios ! Im amazed at how much weight it will start and pull to 50mph , but it lacks top end power and falls like a stone to 1500rpm on hills ( even empty ) but i know there is more power in there , cause it pulls too good in a certian rpm range to be this weak on top ! I have people giving me info that is allover the place , some say tuned with a lap top , others say injectors , pump , & turbo ! I would love to hear accurate power boost info , if too involved , then i will just add a propane kit , done that to a couple of hundred diesels with great success , it dont really boost hp a ton on the dyno but it make them run perfect and smoother and pull way better ! I make my own kits ! Very mild , thank u ,,,warden Quote Link to comment Share on other sites More sharing options...
farmer52 Posted October 26, 2015 Share Posted October 26, 2015 Being a 1995...is it a V-MAC? Is it a Maxidyne EM7-250? If so, the EM7-250, EM7-275, and EM7-300 use the same turbo, fuel pump, and injectors. However you would need to reprogram the V-MAC data file. Max torque is 1190, 1305, 1425 at 1020rpm respectively. Operating range for all three is 1020-1750rpm. If you want to increase the operating range, you will likely need a new turbo and injectors (and reprogram). If you can get a copy of the 1995 Mack Engine Tune-Up Specifications manual #5-305, it will show you the various ratings available for the E7 engine and component part numbers. The info shown is from a 1993 manual which I bought off fleabay. Quote Ken PRR Country and Charter member of the "Mack Pack" Link to comment Share on other sites More sharing options...
Warden Posted October 27, 2015 Author Share Posted October 27, 2015 Hi , thank you , i dont know how to tell what E-7 it is ? Here is a pic of the engine tag attached , does that Tell what i need to know ? Warden Quote Link to comment Share on other sites More sharing options...
Warden Posted October 27, 2015 Author Share Posted October 27, 2015 Quote Link to comment Share on other sites More sharing options...
farmer52 Posted October 27, 2015 Share Posted October 27, 2015 Engine tag shows E7-250 (not Maxidyne EM7-250). According to the 1993 Engine Spec Manual, the E7-250 was only offered in mechanical (no V-MAC). Since I do not have a 1995 manual, I don't know if the E7-250 was offered with V-MAC. I can't tell from the engine tag if your engine is a V-MAC.E7-250 operating range is 1200-1950 and max torque is 975lbft. If you want to go to 300hp (1950rpm & 1083lbft), you will need different pump setting, injectors, and turbo. Again this is based on the 1993 manual information.Is there an electrical wiring harness on the back of the injection pump? That would indicate a V-MAC. Post pic if possible. Quote Ken PRR Country and Charter member of the "Mack Pack" Link to comment Share on other sites More sharing options...
Warden Posted October 27, 2015 Author Share Posted October 27, 2015 I spoke to a mack dealer today and they seemed a bit confused at first , but they finally came up with the data that told them that i have a full mechanical injection pump with an electric shut down and an air throttle pedal with air slave on the inj pump , and that the engine is dressed to be 300hp but the pump is turned down to the 250hp setting ! So they say ! They still seemed confused with the truck specs . Triple frame ... Air throttle .... Disc brakes ... And various other options that the person i was speaking to claimed to not have seen similar specs in his 25 Mack years at the dealership ! Common for me to get the strange one ! Lol. Not always a bad thing! He said by my build date , i just missed the electronics and added that what i had for an E7 was "in his opinion the last of the real good and simple units" but he also said a triple frame single axle and some other items made no sense , but he pulled up svc records and verified the 35,000 miles as real and all components original ! I can try and tweak the pump a bit , (i have done hundreds of other diesels with great success ) this thing is touch 40psi of boost under High load . But it dont have the fuel to make proper use of it ! It burns cleaner then my 08 stock Duramax ! I need a jake pretty bad , i seem to use allot of brakes with this auto trans , the truck is nimble and quick , not fast tho !!Can anyone tell me if a jake install will be an issue with this eng and trans ? I have a switch on the dash to lock up the converter l Thank you. Warden Quote Link to comment Share on other sites More sharing options...
farmer52 Posted October 28, 2015 Share Posted October 28, 2015 40psi boost? What is your exhaust temperature? Spec for 250hp shows 25psi at rated load/speed (300hp - 28psi). Quote Ken PRR Country and Charter member of the "Mack Pack" Link to comment Share on other sites More sharing options...
theakerstwo Posted October 28, 2015 Share Posted October 28, 2015 If I were you I would check your boost with a known good gauge. Quote glenn akers Link to comment Share on other sites More sharing options...
Warden Posted October 30, 2015 Author Share Posted October 30, 2015 I put my 6" gage from my old engine analyzer in the cab with me and drove around loaded , it got as high as 34psi but most of the time 20 - 30 psi .... Its automatic so the boost varies allot according to what the converter does ... EGT stays real safe ! It runs strong down low , and weak on top ! Im getting 10.1 mpg avg ... Just checked again tonite and used my gps ! It could use a little more fuel on top .. Anyone know if these speedos can be calibrated ? My gps said the speedo reads 5 mph fast and the odometer reflects same ! Warden Quote Link to comment Share on other sites More sharing options...
Warden Posted November 4, 2015 Author Share Posted November 4, 2015 Ok , i have been using this truck daily , its near perfect for my use , it rides awesome . Handles great , it. Stops very well with its 4 wheel disc brakes. (Air ) the power is good mpg is an honest 10.1 avg ...great heat and ac , The auto trans and air throttle are flawless ! I need 2 things and it will be my daily driver , i woud appreciate all input and ideas , im hoping for an option i have not considered , my truck has an air diff lock rockwell btw ! Ok. I need to cruise @ 75 mph @ approx 1700rpm ( i have a 4:30 rear ) Without losing start from dead stop on a hill ! My trans is a 654cr allison 1:1 in 5th ( wish it was .70 :1 !Re2nd i need an exhaust brake , a nice loud and affective unit that is affordable hopefully used ,,, A clean used oil pan for the E7 250 would be good also. Any ideas are welcome , im an equipment mechanic and capabile of Making it happen once i have a plan ...im far from a mack expert ! Im shocked that i fell in love with this unit ! I want to make it as perfect as possible ! On the interstate 57 - 64 mph is tops verified by gps ! 2 slow ! Thank you for your help !! Quote Link to comment Share on other sites More sharing options...
TeamsterGrrrl Posted November 4, 2015 Share Posted November 4, 2015 You don't NEED to go 74 MPH, NY speed limit on rural interstates is only 65 MPH and you've got several miles of 55 MPH limit roads to even get to the interstate. So sounds like you WANT to be able to run with the fool "big dogs" and cats and Cummins and Detroits out there supporting the state of New York with their speeding fines. Besides the MR is a great truck, but an aerodynamic disaster area... You ain't gonna get no 10 MPG at 74 MPH! The exhaust brake may be doable though, and has safety and maintainence benefits too- I'd look into it,So you got a great Mack at hopefully a bargain price... It is what it is, work with it's limitations and assets, and you'll be more than happy with it. Quote Link to comment Share on other sites More sharing options...
HarleyD Posted May 16, 2020 Share Posted May 16, 2020 Triple frame, single axel, disc brakes, auto trans...I am guessing it was specced for a fire tank truck Quote Link to comment Share on other sites More sharing options...
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