The_Warden

Hello! I know it's been a while (I promise to try and be around more ;D), but I have a question just out of curiosity. I'm not sure if this sould go here or in the 12 valve engine forum, as I would assume that this would apply to all 12 valve engines, so if this is in the wrong spot, I apologize in advance.<br><br>What would you consider to be the &quot;ideal&quot; cruising RPM for a 12 valve 6BTA? Either from a fuel mileage or a power perspective (or, better yet, both ). In essence, at 65 or 70mph, in an ideal world, what RPM would you want to be at? If that number would be different if you're empty than if you're loaded, what would both of those numbers be?<br><br>I ask because I want to eventually put in an overdrive transmission in my F-250, and while the old 6.9l is still strong, I would like to do a swap to a 12 valve after the 6.9l goes (in the distant future, but I like to slowly get the ducks in a row). I'm also looking into getting the ideal RPM number for the 6.9l, and (hoping that they're close), I'll try and split the difference. <br><br>Thanks!

Jim Shulmister

I have a 6.9 and a 7.3 and both redline at about the same as the cummins (3k) but at 3k they are at about 70mph. The cummins ratios are different in the trans which will improve the cruise on the ford if you use the cummins trans also (i believe).<br> They both start hard and run like crap compared to the cummins and I only put up with them because they are paid for.So I think 70 or so woulod be ideal cruise.(the fuel mileage stinks as well as the power). <br> Good luck on blowing it up so you can enjoy the cummins!<br> -RATCHET-

The_Warden

Actually, part of this is that I want to put an NV5600 behind the 6.9l (either get one set up for a Cummins and get an adaptor plate to put on the 6.9l, or maybe do it and the Cummins at the same time ;D). Actually, my 6.9l runs beautifully right now and starts pretty quickly, even cold. My truck hits the governor at 75mph as is :'( and sounds like a 2-71 genset on the freeway I'm also trying to decide what the best rear end gear ratio (3.54, 3.73, or {unlikely} 4.10)...<br><br>Most of my driving is either on the freeway at 65 to 70mph empty, or on the freeway at 55mph loaded.

Jim Shulmister

My cummins has 3.54 and the fords 4.10-I like the 3.54 ,but the fords would die without the 4.10 cause they dont have the torque or power to push any less.They are really doggy even with the 4.10, but they are sliders (tow trucks) and are pretty heavy.<br>

Alec

I don't know the answer. However: It used to be a rule of thumb that an engine operated most efficiently at the speed at which it produced peak torque . . . On the flip side, truck engines used to be governed based on liner piston speed, which boils down to the engine stroke. The 6BT should be able to run at 2500 rpm all day long.<br><br>Given that and my seat of the pants experienc in my truck, I would look to cruise at 1700 rpm empty and 2200 rpm loaded. 2200 is just over 70 in my truck with the Getrag's .76 (?) overdrive and 3.54's. The NV4500 has a .74 overdrive, a little deeper than the getrag. A US Gear auxilliary would be pretty much perfect to make up the difference with either transmission for splitting and light load cruising.<br><br>That's my $.02. Good luck with the swap!

Lil Dog

In the TDR magazine they had the fuel consumption curves versus the power curves for all the pump types. The VE pump, the P7100 and the VP44. (89-93, 94-98, 98-2002).<br><br>The three years had different &quot;sweet spots&quot; for fuel economy and power. The VE pump, if I remember correctly, was best at about 1800 - 1900 RPM or about 60 MPH with a 5spd and 3.54 diffs. The P7100 was lower at about 16-1700 and the VP44 was in around 2100 I think... <br><br>So depending on the engine model, your sweet spot for speed and economy may be lower or higher than you want to drive.<br><br>I do notice with my truck that the MPG goes up about 2 points at speeds below 100 KPH (62 MPH) which is lower than my cruise speed of 125 KPH (78 MPH)... Don't tell the Mounties LOL... :<br><br>J-eh

The_Warden

Cool! Thanks for the responses thus far. <br><br>A couple of other quick questions...what RPM does the governor kick in (stock) at? Also, what temperature does the thermostat open? And last, but not least, if anyone's running a pure mechanical oil pressure gauge, what's the highest pressure they've seen (presumably at high RPM&quot;s with a cold engine)? And what's the average oil pressure at speed? For instance, on my 6.9l, I've seen the gauge go up to 60 psi when revving with a cold engine, but once the engine's warmed up and I'm on the freeway, the oil pressure's more in the 40 psi range...<br><br>I'm asking because I would be putting pure mechanical gauges in, and want to know what ranges I should be looking at (0 to 80 psi oil pressure gauge, 0-100, etc)<br><br>Thanks again! 8)

jleonard

I have a real gage on my 6Bta boat engine....oil pressure burries my 80 psi gage when cold...I need to install a 100 psi gage. Runs 60 psi when hot.<br>My governor at stock setting was set at about 2700.<br>I just turned the screw out one turn...now I get 2900.<br>Jay<br>

furious70

i get 75psi cold idle, 80psi cold run (i rarely get out on the road and start revving when it's truely cold tho, so i would expect closer to 100 if i did) i get about 40psi warm idle, 55psi warm @ speed