What would you consider is a good safe MAX cruise rev limit for a slightlly modded 86 L98

I am looking to cover a couple of k this year in long stints.

Barry

 

I have an auto and 3.91 gears and when I had my stock L98 motor it didn't hurt it to cruise at 3000-3500 rpm. There will be slightly more bearing wear and less gas in your tank but it shouldn't destroy anything.

 

Even with a fairly low gear ratio installed in the differential, the OD in the tranny will keep the engine at reasonably low revs. Something like the 3.91 or even 4.11 gears will provide RPM's in the mid 2K to 3K range in OD at freeway posted speed limits.

You may lose 4-5MPG but if the proper machine work was done on the motor, it should be fine. Fresh oil and filter at the start of the trip would be a good thing to do.

 

Thats about what I figured, 3k is over a ton with my 3.07's so I would think that If I keep it below 120 it should be fine

Ta

Barry

 

With 3.07 gears? It would cruise all day at 120, IMHO, even faster if you wanted to pay the mpg penalty. At those speeds, the coolant, oil, and tranny fluid radiators have more than enough air rushing through them to keep things at regular operating temps. With a 4+3 and .60 OD 120 is 3000 rpm.

I have made several highway trips in the 500 mile range, and the 120mph cruise is a great thing, after a while it feels like 80 mph and you want to go faster. Obviously, this is tough to do in traffic. I plan my trips around traffic when possible. I'd rather leave at 3 am all amped up on coffee and cigarettes knowing there's no traffic and knowing that I can cut the ETA in half or more than trudge through brain-dead workaday losers in Toyota Camrys, schoolbuses full of band camp kids and 15 Chinese immigrants in the same Ford Econoline Van looking for a car accident that they can all collect insurance money on

Got between 25-32 mpg too on those trips, depending on the incline and if I was out of the gas for a while and had to get back up to speed.

on a side note, I've found that 100-110 is the fastest you can cruise at in top gear before your mileage per gallon starts to suffer. At 120 you have to have a little more "boot in it" compared to 100-110. At a 100 mph cruise on a flat surface I could get 37 mpg using just enough accelerator pedal to keep going at 100 mph. Also, having the windows up helps alot. The drag on the motor from the A/C compressor affects the mpg far less than the aerodynamic drag created by having the roof off or windows down....

 

Thanks for all of the help

I will let you all know how it goes

Ta

Barry

 

37 mpg? In your vette?!

 

Get some glasses if you're squinting, yes 37 mpg in the Vette!!!

Even at lower speeds (65 mph or so) you can still get low-mid 30's MPG out of a TPI Vette with a manual or an auto with "cruiser" gears. The vette slips so well through the air that the resistance doesn't rise AS QUICKLY as most other cars when you get the speeds going. I do 90 in my Jeep wrangler (Aerodynamics of an Amish Barn) and take my foot out of the gas (way out of the gas), it feels like you just opened the drag parachute, it slows down to 65-70 in like 4 seconds. Take your foot off the gas in a Vette doing 90, your mph is going to slowly creep down...

Try it and see for yourself. If your Vette is tuned properly, go on a smooth flat stretch of roadway, make sure your tires are properly inflated and your top is on, roll up the windows and get to 65 mph in top gear. Take your foot out of the gas until you just begin to slow down. Keep the throttle setting there and read your instant mpg.

I took a road trip with my mother a few years back (don't laugh, it was a family function) to North Carolina, maybe an 8 hour drive. I planned on taking the Vette, it was sunny and dry for the whole weekend. She said "let's take my car instead, yours is horrible on gas" When I told her that it gets better cruising mpg than her Z3, she bet me that if I got more than 20 mpg during the trip, she'd pay for my gas up and back.

We computed the mpg after driving down and if memory serves me correctly, the average was 28.2. That's with 3 stops at way-stations, and having to get into the gas to get around the f*&%ing stupid idiots on 95 that cruise in the left lane when they're not passing anyone... Anyway, I got free gas.

Her Z3 got 24 on the highway, same speed, top up, windows up, etc... it only had a 5 speed, 5th was 1:1 ratio, and it would be at 3500 rpm nearing 80 mph.

 

Well I'm not surprised as two weeks ago I was cruzin at 65-70mph on the GSP and registering 38mph...average.

Ummm, though that was with the new 25lb/hr injectors and stock EPROM. But it sure did look sweet. Too bad the ECM (or it's programmer) isn't smart enough to calculate real fuel flow based on O2 trim values, pulse width and air flow. Still that normalizes to 33mpg, not too shabby yet for a car that turns low 13s and pulls well over 1g on launch.

 

I've taken a couple of 1800 mile trips in my 93...it has 3:73 gears...rpm are about 3000 at 80-82 mph...oil temp got up to 240-250...

 

Hey trueBlue ChevyDude,
I am sure you did not mean anything by that statement, but I find it offencive. Further, I do not see how it adds anything to the thread.
JMO
Fred

 

One: it's a joke.

Two: Come down to I-95 in the morning around Penna., Maryland, Delaware and NJ Listen to the traffic report for accidents involving 15-passenger vans.

Three: Look at the statistics for these accidents, you'll find that the vans transport undocumented aliens, claim to be on their way to Atlantic City, and all get treated at the same 5-6 chiropractors or rehab therapists. Those chiropractors and rehab therapists also have immediate family members with interests in close corporations that are holding vessels for, *guess what* fleets of vans for AC bus trip operators. The injured parties also work under the table at restaurants and other similar ventures. Guess who owns those ventures? DING DING DING DING DING, you got it, the same family members that onw the fleet companies and the rehabs.....

Guess those fleet companies get really bad references for their drivers! They always smash up the vans and cause their passengers to complain of soft-tissue injuries! Silly drivers! Be careful out there!