| Author | Message | ||
| george bruton (Tazman632000)
Registered Member Username: Tazman632000 Post Number: 47 Registered: 2-2007 Posted From: 65.184.69.36 Rating: N/A |
just purchase a 8v71 with a v730 allision that both were rebuilt. the owner said that the engine was (A) timed for better performace. i suppose that means cam timming? and bigger injectors. how much will this affect fuel economy? should i change it back? how much trouble is that to do? thanks george | ||
| Luvrbus (Luvrbus)
Registered Member Username: Luvrbus Post Number: 193 Registered: 8-2006 Posted From: 74.33.62.149 Rating: N/A |
George, thats advanced timing for the larger injectors the fuel useage will depend on how you drive but its going to use more fuel because of the HP increase | ||
| Sammy (Sammy)
Registered Member Username: Sammy Post Number: 78 Registered: 8-2005 Posted From: 68.237.219.157 Rating: N/A |
Alot of work to change it back to standard timing. Gear train has to be re-configured - all gears. Trans has to come out, accessories - alt, air comp, etc to be removed, engine oil pan comes down and bellhousing has to come off. Easier to pull package and do it outside the bus. Hope this gives you a good picture. | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 766 Registered: 10-2003 Posted From: 71.58.48.5 Rating: N/A |
Hard to say how it will effect fuel economy. You could change it back and get worse mileage. Going to depend on what RPM that you keep the engine running at most of the time. Also it will depend on how big the injectors are. With a V730,you are going be cruising at higher that 1800 rpm. That engine will prefer advanced timing for that range. The reason for the timing settings, is that timing on these Detroits is fixed, not variable like on automotive or electronic diesels. Fuel is injected and ignited at almost top dead center of the compression stroke. Standard or Advanced timing is a compromise to best deal with the operating RPM characteristics of the engine in actual use. Standard timing would be nice with numerically low axle ratios and small injectors or low cruise speeds. Running a standard time engine at constant high RPM's is inefficient, as well as running an advanced timed engine at too low a constant speed. That is why the late electronic detroits will get better fuel mileage if in same setup; injection of fuel timing is optimum for all RPM's. BTW see what the injector size is- probably N65's. Bottom line.....leave it as is; you won't gain anything by changing it, except less power. If the injectors are larger than 65's, you could drop back to the 65's to eliminate some smoke if you see a lot with your foot in it at lower RPM's. | ||
| FAST FRED (Fast_fred)
Registered Member Username: Fast_fred Post Number: 113 Registered: 10-2006 Posted From: 66.90.229.143 Rating: N/A |
"as well as running an advanced timed engine at too low a constant speed." We have run our Grey marine with advanced timing and replacement injectors (Removed 90's and installed 60's) with great results. The difference is a prop load at low rpm will not create an instant overload at WOT , as flooring a throttle will. "A" timing is usually a help , bigger defulers will only help blow black smoke hill climbing . FF | ||
| Jerry Liebler (Jerry_liebler)
Registered Member Username: Jerry_liebler Post Number: 313 Registered: 3-2005 Posted From: 67.140.167.10 Rating: N/A |
'A' timing is a BAD idea in a bus!!! Because the torque peak is raised to,or above, 1400 RPM from 1200 RPM. Bus transmissions, including the V730, don't have enough gear choices and a shift to the next higher gear at max RPM puts you below the torque peak. With the same transmissions weight and climbing the same hill the bus with N60s and standard time will always beat the bus with N65s and 'A' timing. But the 'A' timed bus will burn much more fuel. 'A' timing is for trucks with 10 or more gear choices. not buses with 2,3, or 4 speeds. As said above though it isn't worth undoing this mistake by a P.O. Regards Jerry 4107 1120 | ||
| RJ Long (Rjlong)
Registered Member Username: Rjlong Post Number: 1340 Registered: 12-2000 Posted From: 67.181.166.160 Rating: N/A |
George - Take a few minutes and pull a valve cover. Take a look at the injectors - on the side you'll see a round tag with a letter/number combination on it. Let us know what you've got, it will help provide some more intelligence to our answers. FWIW & HTH. . .  | ||
| george bruton (Tazman632000)
Registered Member Username: Tazman632000 Post Number: 48 Registered: 2-2007 Posted From: 65.184.69.36 Rating: N/A |
the enigine is sitting on my shop floor is it worth the effort to change it back as far as the fuel economy it concered? thanks george | ||
| george bruton (Tazman632000)
Registered Member Username: Tazman632000 Post Number: 49 Registered: 2-2007 Posted From: 65.184.69.36 Rating: N/A |
my bus has the 24 inch tires on it now | ||
| george bruton (Tazman632000)
Registered Member Username: Tazman632000 Post Number: 50 Registered: 2-2007 Posted From: 65.184.69.36 Rating: N/A |
ok ill pull a cover and report back asap | ||
| george bruton (Tazman632000)
Registered Member Username: Tazman632000 Post Number: 51 Registered: 2-2007 Posted From: 65.184.254.216 Rating: N/A |
its got n65 injectors | ||
| Luvrbus (Luvrbus)
Registered Member Username: Luvrbus Post Number: 195 Registered: 8-2006 Posted From: 74.33.62.149 Rating: N/A |
George that engine is in the 300 hp range @ 2100rpm + or - but one thing that you will have is more heat to get rid of with this setup but i don't know if thats a problem on GM buses or not FWIW (Message edited by luvrbus on December 05, 2007) (Message edited by luvrbus on December 05, 2007) | ||
| Dan West (Utahclaimjumper)
Registered Member Username: Utahclaimjumper Post Number: 79 Registered: 1-2005 Posted From: 208.66.38.115 Rating: N/A |
It is a good horsepower increase and the torque curve moves up also, I would not return mine back to standard, not a chance. 8V71 "A" timed N65 brown tag injectors with VS2-8 trans, 26000Lbs. 4106 with 4100LBs towed,standard 06 radiator, no issues. I live at 5600 ft. and travel the west coast, so I loose 18% before turning the key. The propane mixing really makes the difference on grades.>>>Dan (1900 RPM=70MPH)& 6.5 to 8.5 MPG west coast travel. | ||
| Paso One (Paso_1)
Registered Member Username: Paso_1 Post Number: 100 Registered: 11-2004 Posted From: 142.165.246.239 Rating: N/A |
Hi Dan What rear end Ratio do you have in the bus?? | ||
| Dan West (Utahclaimjumper)
Registered Member Username: Utahclaimjumper Post Number: 80 Registered: 1-2005 Posted From: 208.66.38.60 Rating: N/A |
Paso, I found the VS2-8 to be too tall with the overdrive and stock 06 rear gears so I installed a 5:55-1 ring and pinion set and now have a slight overdrive.>>>Dan | ||
| RJ Long (Rjlong)
Registered Member Username: Rjlong Post Number: 1345 Registered: 12-2000 Posted From: 67.181.166.160 Rating: N/A |
George - It ain't broke - don't fix it! With the automatic V-730, the upward torque shift from the advanced timing is a moot point - it's more of an issue with the manual gearbox folk. The difference in fuel economy between an N65 and an N60 injector with the automatic is negligible. You're going to get mileage similar to Dan's with the automatic, depending on your right foot and how much is freeway vs city traffic. Because the 4106 is such a fun coach to drive, only those folk who have the tenacity to keep it between 55 - 60 mph on the freeway and still have their manual gearboxes, can get 9 - 10 mpg. Do watch for black smoke when hill-climbing, though. When you see it, back off the throttle to prevent overheating. These engines climb best in the 1700-1900 rpm range on a partial throttle - you should still be able to accelerate some. If not, it's time to downshift. Bottom line: Install it and go have fun!! FWIW & HTH. . . |